Difference between revisions of "708 - Prestressed Concrete"

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In general, MDOT utilizes consultants to provide fabrication inspection and project management; however, the Structural Fabrication Unit will randomly perform fabrication inspection and project management on select projects for various reasons. The consultant provides weekly updates for active fabrication projects to the SFU and other important information such as program changes, overall quality, communication with Fabricator, and key performance indicators (KPIs) are discussed.
 
In general, MDOT utilizes consultants to provide fabrication inspection and project management; however, the Structural Fabrication Unit will randomly perform fabrication inspection and project management on select projects for various reasons. The consultant provides weekly updates for active fabrication projects to the SFU and other important information such as program changes, overall quality, communication with Fabricator, and key performance indicators (KPIs) are discussed.
  
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The SFU adheres to MDOT’s Structural Fabrication Quality Manual (SFQM). The purpose of the SFQM is to provide the SFU and their consultants with information on implementing MDOT’s QA program for fabricated materials required to be accepted based on “Fabrication Inspection”.  
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The SFU adheres to [https://www.michigan.gov/mdot/programs/bridges-and-structures/structure-construction/structural-fabrication-unit/structural-fabrication-quality-manual MDOT’s Structural Fabrication Quality Manual (SFQM)]. The purpose of the SFQM is to provide the SFU and their consultants with information on implementing MDOT’s QA program for fabricated materials required to be accepted based on “Fabrication Inspection”.  
  
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The SFQM can be found on the SFU Website.
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The SFQM can be found on the [https://www.michigan.gov/mdot/programs/bridges-and-structures/structure-construction/structural-fabrication-unit SFU Website.]
  
 
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==[[#MATERIALS|'''MATERIALS''']]==
 
==[[#MATERIALS|'''MATERIALS''']]==
  
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===Description of Materials Used===
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==[[#EQUIPMENT|'''EQUIPMENT''']]==
 
==[[#EQUIPMENT|'''EQUIPMENT''']]==
  
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===Description of Equipment Used===
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===Equipment Specifications===
 
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===Pictures of Equipment===
 
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===Submittals and Shop Drawings===
 
===Submittals and Shop Drawings===
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===Permits===
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The Shop Drawing Review Process document summarizes the process for reviewing shop drawings for permanent structural elements, temporary bridges, and other temporary works. It is important for MDOT to respond quickly to shop drawing submittals in order to keep the project moving forward.
  
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[https://www.michigan.gov/mdot/-/media/Project/Websites/MDOT/Programs/Bridges-and-Structures/Structure-Construction/Structural-Fabrication-Unit/Shop-Drawing-Review-Process.pdf?rev=ebcd092327c4493295b254f8d3ea7a6c&hash=ACBDB51A5A9FF29CDAB435FF5B614C4D Shop Drawing Review Process can be found on the SFU website].
  
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===Qualified Products List (QPL)===
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Shop detail drawings, commonly called shop drawings, are a type of working drawing that the Contractor (Supplier/Fabricator) develops prior to fabrication. The Contractor is responsible for providing drawings that accurately show the appropriate details, dimensions, material requirements, fabrication procedures, and other requirements necessary to fabricate and erect structural members in accordance with the contract drawings.
  
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Note, some Contractor submittals may be labelled as a shop drawing in ProjectWise but don’t follow the shop detail drawing requirements listed above. These types of submittals are typically working drawings, construction submittals, manufacturing drawings, or product information sheets. These are not shop detail drawings and do not follow the Shop Drawing Review Process.
  
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===Plant Inspections===
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The Contractor must submit for review all shop drawings and calculations (when applicable) not furnished by MDOT for all parts of the work as required by the contract in Portable Document Format (PDF) into ProjectWise. The Contractor is responsible for the correctness of the shop drawings and calculations (when applicable) and ensuring their design (when applicable) complies with any permit and design requirements.
  
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If revisions are necessary after the shop drawing set is approved, the Contractor is required to submit a complete shop drawing set (proposed new sheets, revised sheets, and remaining sheets that are already stamped approved) for review to ensure each submittal is a standalone set.
  
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===Contractor Submitted Plans/Procedures===
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The MDOT Bridge Design PM (or their delegate) is responsible for coordinating the shop drawing review process for all shop drawings required for pay items on bridge plan sheets. The coordinator is responsible for distributing shop drawings to the appropriate MDOT technical review areas (structural fabrication, load rating, ancillary structures, etc.) for review and comment. Once all comments have been addressed, the Bridge Design PM (or their delegate) stamps the drawing according to the following three stamp designations:
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# '''Approved''' – This stamp is used when the shop drawings appear to be in general conformance with the contract plans. All sheets are required to be stamped.
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# '''Approved Subject to Correction''' – This stamp is used when the shop drawings appear to be in general conformance with the contract plans, but there are very minor corrections needed for historical records that will not affect fabrication of the elements. Only the first sheet is stamped.
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# '''Revise and Resubmit''' – This stamp is used when the shop drawings are not in general conformance with the contract plans and approval could result in elements being incorrectly fabricated. Only the first sheet is stamped.
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[[File:708.2.jpg|thumbnail|500px|center|'''Figure 708.2 MDOT Shop Drawing Stamps''']]
  
  
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==[[#CONSTRUCTION|'''CONSTRUCTION''']]==
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===Shop Inspections===
  
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===Construction Requirements/Procedures/Installation Methods===
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==== Fabrication Notification ====
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The Contractor (or the Fabricator/Supplier) must provide the Engineer with a fabrication start date at least 7 days before beginning fabrication per 708.03.B.1 of the MDOT Standard Specifications for Construction (MDOT SSC).
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===Safety===
 
  
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===Productivity information/charts===
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==== Prefabrication Meeting ====
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SFU (or the consultant PM on behalf of the SFU) will conduct a prefabrication meeting for all design-build and design-bid-build projects. Exceptions are listed below:
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*The frequency of prefabrication meetings can be reduced to an average of one meeting per month for Suppliers that perform continuous work for MDOT.
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*The SFU PM approves the deviation in writing.
  
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===Items of Note===
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Some prefabrication meetings may be combined with other projects provided both projects have the same suppler (Fabricator) and Contractor, each Engineer for the different projects is okay with the meetings being combined, and the projects will be fabricated back-to-back with no excessive downtime between production.
  
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Prefabrication meeting minutes are recorded to document topics that were discussed and to follow up on action items including who is responsible for the follow up. Draft meeting minutes are typically sent out 3-5 business days before production, but this can vary depending on when the fabrication unit was notified of the work or project schedules.
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Prefabrication meeting minutes are recorded to document topics that were discussed and to follow up on action items including who is responsible for the follow up. Draft meeting minutes are typically sent out 3-5 business days before production, but this can vary depending on when the fabrication unit was notified of work or expedited project schedules. Final meeting minutes are typically sent out within 1 business day of the comment due date established in the prefabrication meeting.
  
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===Layout / Survey===
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The following individuals are typically invited to the prefabrication meeting:
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* Contractor
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* Supplier (Fabricator)
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* Quality Control Inspector (QCI)
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* SFU:
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** Consultant PM
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** Consultant Quality Assurance Inspector (QAI)
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** MDOT Structural Fabrication Engineer
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** MDOT Transportation Engineer
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** MDOT Structural Precast Concrete Specialist
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* Engineer
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* Bridge Design PM
  
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The Contractor, Supplier (Fabricator), QCI, consultant PM, QAI, and MDOT Structural Precast Concrete Specialist must attend prefabrication meetings whereas the MDOT Structural Fabrication Engineer, Transportation Engineer, Engineer, and Bridge Design PM may choose to attend prefabrication meetings. MDOT encourages all individuals listed above to attend prefabrication meetings. Note that some unique projects may require the invitation of Supplier (Fabricator) specialty subcontractors (NDT, galvanizing, metalizing, etc.) to prefabrication meetings.
  
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==[[#INSPECTION & TESTING|'''INSPECTION & TESTING''']]==
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==== Inspection Facilities ====
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The SFU is responsible for implementing the Departments QA program for fabricated materials required to be accepted based on “Fabrication Inspection” (also known as shop or QA inspection) per the MQAP manual or project special provision. Most prestressed members require QA inspection, and this inspection is performed by a qualified Quality Assurance Inspector (QAI) representing the SFU. Prestressed concrete Suppliers (Fabricators) are located nationwide and the SFU coordinates inspection at these Suppliers when MDOT work is occurring. 
  
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===Inspection Procedures===
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Fabrication Inspection: SFU Website (see section 2.2 of SFQM)
  
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===Special Attention Areas===
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==== QAI Authority ====
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Throughout the fabrication process, the QAI will inspect the materials and fabricated elements for conformance to MDOT specifications and project special provisions (SPs) in accordance with the Structural Fabrication Quality Manual (SFQM) and supplemental Inspection Test Plans (ITPs). In addition, the QAI will collect all documentation regarding fabrication and verify Buy America (BA) provisions were met. If problems arise during the fabrication, the QAI will contact their PM for resolution and the PM may seek additional guidance from the SFU. Once fabrication is complete and the members inspected for conformance to project specifications, the members will be stored for shipping.
  
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===QA/QC Tests===
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QAI Requirements: SFU Website (see section 2.2.4 of SFQM)
  
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===Lab Testing / Field Testing===
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==== Acceptance ====
  
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===Rejection/Remedial Actions===
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Acceptance of prestressed members consists of the following two-part process per the SFQM:
  
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# QA (Fabrication) Inspection Acceptance: After the structural members are inspected to verify conformance to project specifications, the QAI will stamp each main member “Approved for Use”. The approval stamp indicates that the QAI has inspected the members and found that they appear to meet project requirements; however, it does not relieve the Contractor of their responsibility to meet contract requirements. Some secondary members and miscellaneous components will not be individually stamped.
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==[[#MEASUREMENT, DOCMENTATION & PAYMENT|'''MEASUREMENT, DOCMENTATION & PAYMENT''']]==
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# Visual Inspection (VI) Acceptance: the Engineer must collect one copy of the stamped Bill of Lading and use it to verify the delivered structural products. Additionally, the Engineer must verify that the products are stamped and VI them for signs of damage that may have occurred due to shipping and handling. This VI should be documented in the field inspector’s daily report.
  
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===Measurement===
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[[File:708-10.jpg|thumbnail|500px|center|'''Figure 708.10 “APPROVED FOR USE” Stamp''']]
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Figure 708.10 – “APPROVED FOR USE” Stamp
  
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===Documentation Requirements===
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Acceptance: [https://www.michigan.gov/mdot/programs/bridges-and-structures/structure-construction/structural-fabrication-unit/structural-fabrication-quality-manual SFU Website] (See section 2.2.7B of SFQM)
  
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===Basis of Payment===
 
  
 
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==[[#LOCAL AGENCY PROJECTS|'''LOCAL AGENCY PROJECTS''']]==
 
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==[[#RAIL PROJECTS|'''RAIL PROJECTS''']]==
 
  
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==== Furnishing and Fabricating ====
  
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=====Equipment=====
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[[Category:Construction Manual]]
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===== Void Boxes, Inserts and Attachments =====
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[[Category:Local Agency Projects]]
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[[Category:Rail Projects]]
 
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[[Category:New CM Format]]
 
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=[[#GENERAL|GENERAL]]=
 
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Structural precast concrete members are cast in forms at a facility certified by the Prestressed Concrete Institute (PCI) that is typically a location other than their final position in the structure. Precast concrete beams are also longitudinally prestressed (bonded pre-tensioned strands) and in the case of side-by-side box beams, are transversely prestressed (post-tensioned strands) as well. Prestressing and post-tensioning of precast concrete elements allows for longer, more efficient spans than traditionally reinforced concrete members by introducing pre-compression into the concrete members. The pre-compression force is typically designed to be larger than the effect of applied loads on the element, and therefore, stresses are well controlled.
 
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Other structural elements that are prestressed include concrete spun poles and in some cases, Prefabricated Bridge Elements and Systems (PBES) other than beams, and sound wall posts and/or panels.
 
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Structural precast concrete elements that are not prestressed include, but may not be limited to, sound wall posts and panels, culverts, and some PBES. Although structural precast concrete elements are typically fabricated off-site, they require on-site inspection to ensure successful forming, casting, transport, handling, and placement into their final position in the structure.
 
  
 
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==[[#Prestressed Concrete Elements|Prestressed Concrete Elements]]==
 
  
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Prestressing, refers to the process of pulling steel tendons in the concrete element into tension usually before the concrete is placed in the forms. After the concrete has hardened, the stressed tendons are released and transmit a compressive stress to the concrete. This offsets tension forces on the concrete and increases the load-carrying capacity of the beam. The result is similar to pressing on the ends of a set of books in order to pick up the whole set of books at once.
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===== Design and Proportioning of Concrete Mixtures =====
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===[[#Prestressing|Prestressing]]===
 
  
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Prestressing is generally defined as the preloading of a structure, before application of service loads, to improve its performance in specific ways. Precast concrete elements can be prestressed by pre-tensioning or post-tensioning. Pre-tensioning and post-tensioning are subcategories of prestressing and refer to whether the strands are tensioned before concrete placement or after concrete placement, respectively.
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===== Concrete Strength =====
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:'''2) Pre-tensioning:''' Is typically performed at the fabrication facility by using hydraulic jacks to tension seven-wire steel strands in the beam casting bed before the concrete is placed. After the concrete has reached its minimum required release strength, the tensioned strands are released by cutting at each end, which transmits a compressive force to the concrete via bond between the strands and concrete. This offsets tensile stresses in the concrete from dead load and live load and increases the load-carrying capacity of the beam.
 
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Pre-tensioning is typically used with beams and girders, although it can be used with other elements such as soundwall posts and panels, and other types of PBES such as precast pier caps, precast deck panels, etc. Concrete spun poles are also prestressed.
 
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:'''2) Post-Tensioning:''' Is performed similarly to pre-tensioning but the tensioning of the strands takes place after the concrete has been placed and cured, and the post-tensioning force is distributed to the concrete via mechanical anchorages. The most common application for post-tensioning in the Department is with side by side box beams. After side by side box beams are erected the grouted keyways between the beams are filled with non-shrink grout and cured. Typically the same seven wire strand used in pre-tensioning is grouped to make a tendon and then placed transverse to the beams centerline through ducts in the intermediate diaphragms. In some cases, more rigid steel rods are used for post-tensioning instead of seven wire strands. The quantity of ducts and the number of strands per duct are proportional to the beam length and depth. After hydraulic jacks are used to tension the tendons to the proper load, the force is locked in and the ducts are filled with non-shrink grout. Post-tensioning side by side box beams reduces differential deflection between adjacent beams and allows more effective live load distribution. Post-tensioning can also be used to transmit a compressive load in pier caps, decks, and PBES in order to offset tensile forces in the element.
 
  
 
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===[[#Beams|Beams]]===
 
  
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The Department uses four general kinds of prestressed concrete beams:  
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===== Steel Reinforcement and Prestressing Strand =====
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*Side by side box beams
 
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*Spread box beams
 
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*AASHTO I-beams (Types I-IV)
 
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*Bulb-tee beams (e.g. Michigan 1800 beam)
 
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Prestressed concrete beams vary in width, length, and depth. In general, deeper beams will span longer distances for the same loading conditions. Likewise, deeper beams used for the same span length may have wider beam spacing, and thus carry larger loads.
 
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The bulb-T beam shape can be a more effective section due to its larger bottom flange that allows more prestressing strands to be used. It also features a wider top flange that makes the shape more stable during handling, transport and erection.
 
  
 
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===[[#Concrete Spun Poles|Concrete Spun Poles]]===
 
  
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Prestressed concrete spun poles are used to mount cameras and other Intelligent Transportation System (ITS) equipment at high elevations in order to provide the proper vantage point. Similar to beams, strands are pre-tensioned and then the forms are rotated at a high speed to create a pole that is hollow in the middle.
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===== Miscellaneous Steel =====
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===[[#Prefabricated Bridge Elements and Systems (PBES)|Prefabricated Bridge Elements and Systems (PBES)]]===
 
  
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PBES can refer to either singular precast elements such as deck panels, footings, columns, pier caps, abutments, etc., or a system that contains multiple elements such as beams with a portion of the deck already attached. The connections between PBES elements or between PBES elements and cast in place elements are of utmost importance. One of the primary advantages of prefabricated elements is the speed at which they can be constructed which minimizes disruption to traffic. If the connections are not properly laid out or constructed, significant delays can result. Therefore, it is important for connection details to be checked by both the Contractor and the Inspector on-site prior to concrete placement or connection of elements, to ensure proper fit-up. All the necessary connection details should be in the design plans.
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===== Welding =====
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The use of templates by the Contractor and fabricator is encouraged. At the fabricator’s plant the dimensions should be checked by both the fabricator’s quality control (QC) personnel and the department’s (QA) quality assurance personnel. The Contractor and Inspector are also encouraged to work closely with the fabricator’s QC and the department’s QA to ensure construction goes as smooth as possible.
 
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Connection methods for PBES include, but are not limited to:
 
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*Grouted keyways or pockets
 
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*Grouted mechanical splice sleeves
 
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*Post-tensioning
 
  
 
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===[[#Soundwalls|Soundwalls]]===
 
  
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Sound walls, or noise abatement walls, can be detailed differently but typically are constructed of two types of elements, panels and posts. Both the panels and posts may be precast and prestressed or precast with conventional steel reinforcement.
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===== Strand Debonding =====
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<span style="color: red"> -Reserved- </span>
  
 
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=[[#FABRICATION OF STRUCTURAL PRECAST CONCRETE|FABRICATION OF STRUCTURAL PRECAST CONCRETE]]=
 
  
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===== Placing Concrete =====
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==[[#Request for Information Process|Request for Information Process]]==
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The Structural Fabrication Request for Information Process can be found [http://www.michigan.gov/documents/mdot/MDOT_Structural_Fabrication_RFI_Process_120415_510630_7.pdf here].
 
  
 
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==[[#Shop Drawing Review Process|Shop Drawing Review Process]]==
 
  
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See subsection 104.02, Plans and Working Drawings, of the MDOT Standard Specifications.  The Shop Drawing Review Process may be found [http://www.michigan.gov/documents/mdot/MDOT_Shop_Drawing_Review_Process_041513_471762_7.pdf here].
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===== Cold Weather Precautions =====
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==[[#Nonconformance Program|Nonconformance Program]]==
 
  
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The Structural Fabrication Nonconformance Program can be found [http://www.michigan.gov/documents/mdot/MDOT_Structural_Fabrication_Nonconformance_Policy_080414_464586_7.pdf here].
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===== Curing Elements =====
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==[[#Prefabrication Meeting|Prefabrication Meeting]]==
 
  
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The Structural Fabrication Unit will conduct a prefabrication meeting with the fabricator when deemed necessary. Prefabrication meetings are generally scheduled when the fabrication is more complex in nature or the fabricator is new to working with the Department but can be held for any project.
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===== Workmanship =====
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The QAI will inspect prestressed members after QC has performed their inspection and note any deficiencies or nonconformances (NCRs) caught by QC or observed by QA. The Supplier (Fabricator) is required to notify the MDOT QAI of all observed defects, damage, and potential NCRs and submit a proposed repair procedure to SFU for approval. The Supplier (Fabricator) must receive written approval from MDOT prior to performing any repairs.
  
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Approved repairs are typically completed at the Supplier’s (Fabricator’s) facility prior to the member shipping to the project site; however, there may be some circumstances where approved repairs are conducted at the project site due to project schedules. In both cases, the Supplier (Fabricator) typically performs the repairs. Repairs conducted at the Supplier’s (Fabricator’s) facility will be witnessed by the QAI and repairs conducted at the project site will be witnessed by the MDOT Construction Inspector.
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==[[#Shop Inspection|Shop Inspection]]==
 
  
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Quality assurance inspection is performed on most structural precast concrete elements such as prestressed beams, culverts 20 foot and greater, sound wall posts and panels, MSE wall panels, concrete spun poles, and other prefabricated bridge elements for accelerated bridge construction. The Department’s quality assurance program is implemented by Bridge Field Service’s Structural Fabrication Unit to perform shop inspection at structural precast concrete fabrication facilities nationwide.
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* NCR Process: [https://www.michigan.gov/mdot/programs/bridges-and-structures/structure-construction/structural-fabrication-unit SFU Website] (See section 8 of SFQM)
  
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Throughout the fabrication process the shop inspector will inspect the materials and fabricated elements for conformance to Department specifications, collect all documentation regarding the fabrication, and verify Buy America provisions were met. If problems arise during the fabrication, the shop inspector will contact the Structural Fabrication Unit for resolution. Once fabrication is complete and the elements are ready to be shipped to the project site, the shop inspector will stamp the elements as well as the shipping documents “Approved for Use”. See Figure 708.2. The inspector then submits all fabrication documentation to the Bridge Field Services Structural Fabrication engineer for placement into the corresponding ProjectWise folder. See Figure 708.3 for more information on the fabrication inspection process.  
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The SFU has developed standard repair procedures for common defects observed on fabricated prestressed members. These repair procedures have been reviewed by industry and should be used by the Supplier (Fabricator) when applicable to expedite the review process. The QAI or Construction Inspector should be familiar with these standard repair procedures for common deficiencies.
  
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[[File:Fig_708.2.png|600px|thumbnail|center|Figure 708.2 - Approved for Use stamp]]
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MDOT Standard Repair Procedures: [https://www.michigan.gov/mdot/programs/bridges-and-structures/structure-construction/structural-fabrication-unit SFU Website] (See Appendix A4 of SFQM)
  
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[[File:Fig_708.3.png|600px|thumbnail|center|Figure 708.3 – Structural Precast Concrete Fabrication Inspection Flowchart]]
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===== Tolerances =====
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==[[#Addressing Deficiencies|Addressing Deficiencies]]==
 
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As part of the shop inspection process, the MDOT shop inspector will note the condition of structural precast elements as they are removed from the forms, and note if corrective repairs are required prior to approving the element for use on MDOT projects. These repairs are typically done prior to being shipped to the project site, however, there are some circumstances where repairs will be required on site, so the construction inspector should be familiar with common deficiencies. The Structural Fabrication Unit has developed, with the assistance of the Materials Section, repair procedures to assist with evaluating fabricator proposed concrete repairs to fabricated structural precast concrete elements for MDOT projects.
 
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Fabricated structural precast concrete elements may contain defects from the fabrication process or can be damaged from the removal of formwork, handling, and shipping. The fabricator is required to notify the MDOT QA shop inspector of all defects and/or damages to fabricated elements and propose a repair procedure to MDOT for acceptance. MDOT will thoroughly evaluate the proposed procedure and provide a response. The repair procedure will be either be approved, rejected or approved as noted. The fabricator must receive MDOT approval before performing the repair. Structural precast concrete repairs can be generalized into the following categories:
 
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:*Minor Surface Defects (air holes, minor honeycombing, gouges etc.) See Figure 708.4 through Figure 708.06 for minor surface defects
 
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[[File:Fig_708.4.png|600px|thumbnail|center|Figure 708.4 – Minor surface defect – air holes greater than 1” in any direction]]
 
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[[File:Fig_708.5.png|600px|thumbnail|center|Figure 708.5 – Minor surface defect – rubber gasket crease]]
 
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[[File:Fig_708.6.png|600px|thumbnail|center|Figure 708.6 – Minor surface defect – honeycombing of PCI girder]]
 
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:*Major Surface Defects (moderate honeycombing, etc.)
 
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:*Minor Damages (spalls, cracks, broken corners, etc.) See Figure 708.7 through Figure 708.8 for examples of minor damages
 
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[[File:Fig_708.7.png|600px|thumbnail|center|Figure 708.7 – Minor damage – broken corner at end of PCI girder]]
 
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[[File:Fig_708.8.png|600px|thumbnail|center|Figure 708.8 – Minor damage – spalled bottom corner at the end of a box beam]]
 
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:*Other, which includes major damage and elements subject to rejection. See Figure 708.9 and Figure 708.10 for example of major deficiencies.
 
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[[File:Fig_708.9.png|600px|thumbnail|center|Figure 708.9 – Minor Damage – spalled bottom corner and exposed prestressing strands at the end of a box beam]]
 
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[[File:Fig_708.10.png|600px|thumbnail|center|Figure 708.10 – Major damage – improper consolidation of concrete and expose prestressing strands and steel reinforcement]]
 
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The repair of deficiencies to the satisfaction of the Structural Fabrication Unit, or rejection of elements for major deficiencies will occur at the fabrication facility prior to shipment to the site.  It is important to note the Approved for Use stamp on all structural precast elements prior to incorporation into the project.
 
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=[[#MATERIALS|MATERIALS]]=
 
  
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===== Stress Transfer =====
 
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=[[#CONSTRUCTION|CONSTRUCTION]]=
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==== Handling, Storage, and Transporting ====
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When loading and shipping occurs, the Supplier (Fabricator) will load the members on a truck and the QAI inspects all members again for conformance to specifications since handling damage can occur when members are transported and loaded for shipping.  
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==[[#Delivery of Structural Precast Concrete Elements|Delivery of Structural Precast Concrete Elements]]==
 
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Project personnel are required to use the following procedure for acceptance of fabricated structural prestressed concrete elements that are required to have “Fabrication Inspection” as the basis of acceptance in accordance with section [http://www.michigan.gov/documents/mdot/MDOT_MQAP_Manual_5_Section_D_307110_7.pdf 4.04.06.B of the Materials Quality Procedures Manual]. These structural prestressed concrete elements must not be shipped from the fabricator to the project or contractor’s yard without approval by the shop inspector at the time of loading.  If elements and the Bill of Lading arrive at the project site or the contractor’s yard without an approval stamp, the element must be rejected.
 
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Acceptance of fabricated structural prestressed concrete elements consist of satisfactory shop inspection by the MDOT shop inspector in accordance with section [http://www.michigan.gov/documents/mdot/MDOT_MQAP_Manual_5_Section_D_307110_7.pdf 4.04] of MDOT’s Materials Quality Assurance Procedures Manual (MQAP) and satisfactory visual inspection in the field by the engineer. The following two part process has been added to the MQAP to clarify the acceptance process:
 
  
−
<ol type="A">
+
The Supplier (Fabricator) is required to provide the QAI with a minimum of five (5) copies of the Bill of Lading for each proposed shipment per the SFQM. Each Bill of Lading will be stamped “Approved for Use” (see Acceptance process below). One copy of the Bill of Lading is retained by the QAI and the other four copies are distributed to the Contractor, Supplier (Fabricator), Engineer, and Trucking Company.  
−
<li>Fabrication Inspection Acceptance: Structural elements must be inspected by the shop inspector after they are loaded for shipping. The elements must be stamped “Approved for Use” prior to shipping if they meet contract requirements. Additionally, the shop inspector must stamp at least five copies of the Bill of Lading that is prepared by the fabricator. The approval stamp is for use by the Department and does not relieve the contractor of their responsibility to meet contract requirements.</li>
 
−
<li>Visual Inspection Acceptance: The engineer must collect one copy of the stamped Bill of Lading and use it to verify the delivered structural elements. Additionally, the engineer must verify that the elements are stamped and visually inspect them for signs of damage that may have occurred as a result of shipping and handling. This visual inspection should be documented in the Inspector’s Daily Report (IDR).</li>
 
−
</ol>
 
  
−
The Engineer must visually inspect the product for signs of damage that may occur as a result of shipping and handling. This visual information should be documented on the inspector’s daily report. Look for deficiencies in the beams in the form of cracks, honeycombing, spalls, or cold joints. Crack widths can be measured with a crack comparator as seen in Figure 708-11. Bring any damage to the attention of the Engineer and make a record of the damage in the daily report. Take measurements of crack width and length as well as spall measurements and photographs. Also note in the daily report when the beams arrive in good condition. If there is any concern regarding whether beams were approved for use or whether damage is acceptable, contact the [mailto:MDOT-StructuralFabrication@michigan.gov Structural Fabrication Unit].
+
Once the structural prestressed member has been visually inspected and accepted by the Engineer, the construction inspector should verify the products are stored properly prior to erection. The method of stockpiling and transporting members is covered in detail in subsection 708.03 of the Standard Specifications for Construction. Below is a list of items the inspector should check regarding the storage of structural prestressed members:
 +
* Support beams off the ground to prevent moisture and deleterious material intrusion.
 +
* Support beams across the full width on two battens, each greater than 4 inches wide.
 +
* Support beams on two battens, no more than 3 feet from the ends of the beams.  
 +
* Support stacked beams, one above the other along the same vertical plane at each end of the beams.
 +
* Support the beams on level, stable ground, avoid storing beams near side slopes, or areas near heavy construction traffic.
 +
* Do not support the beam at more than two points.
 +
* Prestressed I-beam shapes may need to be laterally braced on site.
 +
* Members are to be stored in an upright position and should be thoroughly braced to avoid overturning, which may damage the member itself, adjacent members or material, or injure personnel in the immediate vicinity.
 +
* Related items such as bearings and bridge railing should also be protected from damage, dirt, and corrosion.
  
−
The Structural Fabrication Unit will send a fabrication inspection memorandum via ProjectWise link to the project office at the end of each project. This memorandum is not the basis of acceptance, but rather a brief summary of the fabrication inspection for the project. The project office should use it as a reference when requesting fabrication information from the Structural Fabrication Unit. All fabrication records are stored in the project folder in ProjectWise.  See Figure 708.11 for a sample inspection memorandum.  
+
===== Loading and Shipping =====
 +
[https://www.michigan.gov/mdot/programs/bridges-and-structures/structure-construction/structural-fabrication-unit SFU Website] (See section 2.2.7A of SFQM)
  
−
[[File:Sample Structural Precast Concrete Memo.jpg|600px|thumbnail|center|Figure 708-11 Sample Structural Precast Concrete Memo]]
 
  
 
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==[[#Structural Precast Concrete Field Storage|Structural Precast Concrete Field Storage]]==
+
==[[#CONSTRUCTION|'''CONSTRUCTION''']]==
  
−
Once the structural precast concrete element has been accepted on the job site, the inspector should verify that the material is stored properly prior to installation. Below is a list of items the inspector should check regarding storage of structural precast concrete elements:
+
===Erection of Prestressed Beams===
  
−
:*Support beams off the ground to prevent moisture and deleterious material intrusion
+
Considerable care should be exercised when handling structural precast concrete elements. In many cases, there is no way to repair a damaged element short of re-fabrication. Below is a list of items the inspector should check regarding the erection of structural prestressed members.
−
:*Support beams across the full width on two battens, each greater than 4 inches wide. Support stacked beams, one above the other along the same vertical plane at each ends of the beams.  
+
* Prestressed beams should be always kept in an upright position, as the beam’s own dead weight counter acts the internal prestressing force to keep the beam stable.  
−
:*Support the beams on level, stable ground, avoid storing beams near side slopes, or areas near heavy construction traffic
+
* Verify lifting devices, usually loops of seven wire steel strand, are the only attachment used when moving a beam. The beam must not be lifted at the beams center in any way or undesirable stresses may develop and the beam may crack.
−
:*Do not support the beam at more than two points
+
* Ensure the lifting devices are removed once the beam has been placed in its final position on the substructure.
−
:*Taller, long span I-beam shapes may need to be laterally braced on site
+
* Per Section 105 of the Standard Specifications for Construction, the Engineer reserves the right to reject any shipped product that shows visual signs of damage or does not meet specification requirements.
−
:*Members are to be stored in an upright position and should be thoroughly braced to avoid overturning, which may damage the member itself, adjacent members or material, or injure personnel in the immediate vicinity.  
 
−
:*Related items such as bearings and bridge railing should also be protected from damage, dirt, and corrosion.  
 
  
−
Ensure the lifting devices are removed once the beam has been placed in its final position on the substructure.  
+
Check beam markings and compare to the beam layout sheet in the plans. Make sure the beams are placed in the right location and direction. They may fit in more than one place but there is only one correct location and direction for each beam.
  
−
Per Section 105 of the Standard Specifications for Construction, the Engineer reserves the right to reject any shipped product that shows visual signs of damage or does not meet specification requirements.  
+
==== Box Beams ====
 +
Below is a list of items the inspector should check regarding the erection of structural prestressed Box Beams:
 +
*Verify box beam widths will fit properly on the substructure units.
 +
*Verify box beam bearing pads are shimmed (when necessary) on each beam in an approved manner during erection to provide full bearing contact with the bottoms of the beams.
 +
*Box beams may camber more than anticipated or may experience transverse rotation such that they do not sit flush on the sole plates, which are typically beveled to accommodate camber and vertical alignment angles.
 +
*(Expansion Bearings Only) Verify the beams line up with the position dowel holes, and ensure the holes are filled with hot poured rubber sealant type filler at least 3 inches above the position dowels. Ensure the remainder of the hole is filled with Type H-1 grout.
 +
*(Fixed Bearings Only) Verify the holes are filled with Type H-1 grout.
 +
*(Side-by-Side Box Beams Only) Verify beams are set with spaces as specified on the contract plans or shop drawings and that seal washers are placed around the transverse post-tensioning conduit holes.
 +
*Note in the Daily Work Report (DWR) when erection has been completed.
  
−
Considerable care should be exercised when handling structural precast concrete elements. In many cases, there is no way to repair a damaged element short of re-fabrication. Prestressed beams should be kept in an upright position at all times, as the beam’s own dead weight counter acts the internal prestressing force to keep the beam stable. The method of stockpiling and transporting members is covered in detail in subsection 708.03 of the Standard Specifications for Construction. Beams shall be supported at two points no more than 3 feet (1 m) from the ends of the beams.  
+
Below is a list of items the inspector should check regarding the post-tensioning of side-by-side box beams after erection:
 +
*Verify the space between the box beams is completely filled, full depth, with R-2 grout mortar and cured for at least 48 hours.
 +
*Ensure the contractor does not grout when temperatures are below 40° F.
 +
*The deck width should be measured by the Contractor as soon as the beams are set to ensure the post tensioning rods or strand will be fabricated to the proper length.
 +
*All hardware dimensions must be as shown on the plans or shop drawings.
 +
*Tendons or rods for post-tensioning should be tensioned with calibrated jacks according to a Contractor-supplied calibration chart showing the corresponding jack pressures and elongations necessary to gradually build up to the required post-tensioning force.
 +
*After the post-tensioning is complete, ensure the conduit is flushed with water, then compressed air.
 +
*The tendon or rod holes will be grouted under pressure with Type E-1 grout for steel tendons or rods as specified in subsection 708.03B of the Standard Specifications for Construction.
  
−
Check beam markings and compare to the beam layout sheet in the plans. Make sure the beams are placed in the right location and direction. They may fit in more than one place but there is only one correct location and direction for each beam.  
+
'''Do not stand behind the jacking machine or rod holes during jacking procedures. If a tendon or rod snaps, it can cause serious injury'''
  
−
Lifting devices, usually loops of seven wire strand, are cast into the member and these should be the only attachment used when moving a beam. The lifting device must have adequate capacity to lift the beams and set them in place. Never lift the beam near the center. If the beam has to be set down before being placed, never allow it to be supported at the center. Crib it under the ends. The prestressing forces pulling in on the ends of the beam hold up the dead weight of the beam. If the beam is supported or lifted at the center, the prestressing forces will cause the beam to crack.  If cracks are noted to be greater than 0.006 inches, the Structural Fabrication Unit must be contacted.
+
==== I-Beams, 1800 Beams, and Bulb-Tee Beams ====
  
−
[[File:Fig_708-11.png|600px|thumbnail|center|Figure 708-12 Crack comparator for measuring crack width]]
+
Below is a list of items the inspector should check regarding the erection of structural prestressed beams and girders:
 +
*After the first and second member (beam or girder) are erected, the second member must be attached to first through the diaphragm connection(s). In addition, each subsequent member must be attached to the previously erected member through the diaphragm connection(s).
 +
*Prestressed beams and girders, especially taller and longer members, can be more prone to sweep, transverse deflection, or even rotation. For this reason, they should be rigidly blocked in place via diaphragm connections to ensure proper spacing between members and to avoid beam rotation during construction.
 +
*Verify member (beam or girder) bearing pads are shimmed (when necessary) on each member in an approved manner during erection to provide full bearing contact with the bottoms of the beam/girder.
 +
*(1800 Girder only) Verify use of beveled sole plates on each girder and note in the Daily Work Report (DWR).
 +
*Note in the Daily Work Report (DWR) when erection has been completed.
  
−
{{top}}
+
==== Spun Pole ====
−
==[[#Erection of Box Beams|Erection of Box Beams]]==
 
  
−
The beam widths should be checked to ensure that box beams will fit properly on the substructure units. Beam bearing pads must be shimmed in an approved manner during erection (when necessary) to provide full bearing contact with the bottoms of the beams. This needs to be checked on every box beam. Box beams may camber more than anticipated, or may experience transverse rotation such that they do not sit flush on the sole plates, which are typically beveled to accommodate camber and vertical alignment angles. Note in the daily report when the beam erection has been completed.
+
Below is a list of items the inspector should check regarding the erection of prestressed spun poles:
 +
*During installation, the poles must only be lifted and stored using the locations and methods shown on the approved shop drawings or manufacturer’s instructions.  
 +
*Visually inspect spun pole for any damage, cracks, or spalls and notify the Engineer if present.
 +
*Note, the concrete clear cover for spun poles is typically less than a prestressed beam so cracks or spalls may increase the members susceptibility to steel corrosion.  
 +
*Spun concrete poles must be safely secured after being placed in the drilled shaft installation before the concrete foundation is poured and cured
  
−
At expansion bearings, ensure the beams line up with the position dowel holes, and ensure the holes are filled with hot poured rubber sealant type filler at least 3 inches above the position dowels. Ensure the remainder of the hole is filled with Type H-1 grout. Ensure holes at fixed bearings are filled with Type H-1 grout.
+
==== Sound Wall ====
  
−
For side by side box beams, the beams should be set with spaces between them as specified on the plans or shop drawings and with the seal washers placed around the transverse post tensioning conduit holes. The space between the beams should be completely filled, full depth, with R-2 grout mortar and cured for at least 48 hours. Ensure the contractor does not grout when temperatures are below 40° F. The deck width should be measured by the Contractor as soon as the beams are set to assure that post tensioning rods or strand will be fabricated to the proper length.  
+
Below is a list of items the inspector should check regarding the erection of sound walls:
 +
*In most cases the sound wall panels are attached to the posts using tongue and groove joints. It is important during erection that the panels are lowered slowly into position and do not crack or spall the posts.
 +
*If the sound wall posts contain grout pockets (prestressed sound walls only), then the grout pockets at the ends of the posts must be filled with non-shrink grout and should be free of cracks.
 +
*Note, a ladder should be used to visually inspect the tops of soundwall posts.
 +
*Visually inspect sound wall posts for damage, shrinkage, cracks, or spalls and notify the Engineer if present.
 +
*Note, cracks and other deficiencies will be subject to moisture and chloride intrusion which can lead to rapid deterioration of the posts.
 +
  
−
All hardware dimensions must be as shown on the plans or shop drawings. Tendons or rods for post-tensioning should be tensioned with calibrated jacks according to a Contractor-supplied calibration chart showing the corresponding jack pressures and elongations necessary to gradually build up to the required post-tensioning force. After the post-tensioning is complete, ensure the conduit is flushed with water, then compressed air. The tendon or rod holes will be grouted under pressure with Type E-1 grout for steel tendons or rods as described in subsection 708.03B of the Standard Specifications for Construction.
 
−
 
−
'''Do not stand behind the jacking machine or rod holes during jacking procedures. If a tendon or rod snaps, it can cause serious injury.'''
 
  
 
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−
==[[#Erection of I-Girders and Michigan 1800 Girders|Erection of I-Girders and Michigan 1800 Girders]]==
 
  
−
Girder bearing pads must be shimmed (when necessary) in an approved manner during erection to provide full bearing contact with the bottoms of the girder. Beveled sole plates are also required for I-girders. This needs to be checked on every girder. Note in the daily report when the girder erection has been completed.
+
==[[#INSPECTION & TESTING|'''INSPECTION & TESTING''']]==
  
−
I-Girders and especially Michigan 1800 girders can be more prone to sweep or transverse deflection. For this reason they should be rigidly blocked in place to ensure proper spacing between girders before any deck or diaphragm forming.
+
<span style="color: red"> -Reserved- </span>
  
 
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−
==[[#Erection of Spun Concrete Poles|Erection of Spun Concrete Poles]]==
 
  
−
Spun concrete poles typically have less concrete clear cover from the outside of the element to the prestressing strands than prestressed beams. Pay particular attention to any cracking and bring it to the attention of the Engineer. During installation, the poles must only be lifted and stored using the locations and methods shown on the approved shop drawings or manufacturer’s instructions. Spun concrete poles must be safely secured after being placed in the drilled shaft installation before the concrete foundation is poured and cured.
+
==[[#MEASUREMENT, DOCMENTATION & PAYMENT|'''MEASUREMENT, DOCMENTATION & PAYMENT''']]==
  
−
{{top}}
 
−
==[[#Erection of Sound Walls|Erection of Sound Walls]]==
 
  
−
In most cases the sound wall panels are attached to the posts using tongue and groove joints. It is important during erection that the panels are lowered slowly into position and do not crack or spall the posts. If the posts are prestressed, and contain grout pockets, the grout pockets at the ends of the posts must be filled with non-shrink grout and should be free of cracks. In order to properly inspect prestressed posts a ladder should be used to visually inspect the tops of the posts. Any cracking whether from damage or shrinkage, or spalling, should be cause for concern as the horizontal surface will be subject to moisture and chloride intrusion leading to rapid deterioration of the posts.
+
===Basis of Payment===
−
 
 
−
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=[[#MEASUREMENT AND PAYMENT|MEASUREMENT AND PAYMENT]]=
 
−
 
 
−
There are three methods of payment for structural precast concrete elements as described below. All three methods are shown in Figure 708.03. No method of payment relieves the Fabricator or Contractor from damage due to transporting, storing on the project site, or erecting the elements. Additional information on payment can be found in Section 109 of the Standard Specifications for Construction.
 
  
−
{{top}}
+
There are three methods of payment for structural precast concrete members: Stockpile payment, partial shipment payment, and final shipment payment. No method of payment relieves the Contractor (or Fabricator) from damage due to transporting, storing on the project site, or erecting the elements. Additional information on payment can be found in Section 109 of the MDOT Standard Specifications for Construction.
−
==[[#Stockpile Payment|Stockpile Payment]]==
 
  
−
See subsection 109.04 of the Standard Specifications for Construction for stockpile payment requirements. Additionally, see subsection [http://www.michigan.gov/documents/mdot/MDOT_MQAP_Manual_5_Section_D_307110_7.pdf 4.04.06] of the MQAP manual for QAI’s responsibilities for verifying stockpile payment.
+
The Engineer will make stockpile payments for fabricated structural steel products in accordance with section 109 of the MDOT SSC. See subsection 2.2.6 of the SFQM for SFUs responsibilities with stockpile payment. These materials can be stored at the fabrication facility or at the construction site. If stored at the construction site, the materials must be inspected by the Engineer as stockpiling occurs since the approval stamp ink could wash away over time. If the approval stamp(s) appear to be fading away, the Engineer must mark the accepted structural steel products in a more permanent method.
  
−
{{top}}
+
After the Supplier (Fabricator) has shipped a portion of the structural concrete elements to the project site, visually inspect the members and verify they are stamped “Approved For Use” according to the sections above. If all the documentation is provided and there are no deficiencies, then partial shipment payment may be made. The Engineer must follow section 109.04 of the MDOT Standard Specifications for Construction.
−
==[[#Partial Shipment Payment|Partial Shipment Payment]]==
 
  
−
After the Fabricator has shipped a portion of the structural concrete elements to the project site verify that the shipping documentation and elements have been stamped approved for use, and inspect the product for signs of damage that may have occurred as a result of shipping and handling. If the shipping documentation and elements are stamped approved for use and there is no shipping and handling damage partial shipment payment may be made. The approved for use stamp indicates that all materials and processes during fabrication were according to specifications; a Fabrication Inspection memo will be sent to the TSC after final shipment.  
+
After the Supplier (Fabricator) has shipped all of the structural concrete elements to the project site, visually inspect the members and verify they are stamped “Approved For Use” according to the sections above. If all the documentation is provided and there are no deficiencies, then final shipment payment may be made. The Engineer must follow section 109.04 of the MDOT Standard Specifications for Construction.
  
 
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−
==[[#Final Shipment Payment|Final Shipment Payment]]==
 
  
−
As with partial shipments, after the Fabricator has sent the final shipment of the structural concrete elements to the project site verify that the shipping documentation and elements have been stamped approved for use, and inspect the product for signs of damage that may have occurred as a result of shipping and handling. If the shipping documentation and elements are stamped approved for use and there is no shipping and handling damage partial shipment payment may be made. The approved for use stamp indicates that all materials and processes during fabrication were according to specifications; a Fabrication Inspection memo will be sent to the TSC after final shipment.
 
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[[Category:Construction Manual]]
 
[[Category:Construction Manual]]
 
[[Category: Division 7]]
 
[[Category: Division 7]]
 
[[Category: Section 708]]
 
[[Category: Section 708]]
 +
[[Category:New CM Format]]

Latest revision as of 12:02, 23 October 2024

708
Prestressed Concrete


GENERAL DESCRIPTION

Structural prestressed concrete members (also known as elements) are cast in forms at a Fabricator certified by the Prestressed Concrete Institute (PCI). A Fabricator supplying prestressed concrete bridge beams for MDOT use must also be an approved Supplier per MDOT’s Supplier Qualification Standard (SQS). A list of approved prestressed concrete beam Suppliers for MDOT projects can be found on the Structural Fabrication Unit (SFU) Website

Prestressing (pre-tensioning and post-tensioning) of precast concrete members allow for longer, more efficient spans than traditionally reinforced concrete members by introducing compressive forces into the concrete members. These compressive forces are achieved by using a high grade of steel or carbon fiber strands that are pre or post-tensioned to a predetermined load based on design requirements, temperature of steel and concrete, Contractor/Fabricator equipment, and other factors. Most prestressed concrete beams are longitudinally prestressed and some may also be transversely prestressed, such as side-by-side box beams that are post-tensioned.

Structural members that are prestressed include, but not limited to:

  • Prestressed concrete beams
  • Spun Poles
  • Prefabricated Bridge Elements and Systems (PBES)
  • Sound Wall Panels and Posts

Structural members that are not prestressed include, but not limited to:

  • Culverts
  • PBES
  • Sound Wall Panels and Posts

MDOT requires on-site quality assurance (QA) shop inspection for the fabrication of prestressed concrete members. This inspection program is managed by MDOT’s Structural Fabrication Unit (SFU).

The SFU is responsible for implementing the Departments QA program for fabricated materials required to be accepted based on “Fabrication Inspection” per the Materials Quality Assurance Procedures (MQAP) manual or project special provision. The SFU also serves as the Departments structural fabrication expert and provides recommendation to design and construction staff regarding plan details, specifications, shop drawings, shop inspection, and field inspection.

In general, MDOT utilizes consultants to provide fabrication inspection and project management; however, the Structural Fabrication Unit will randomly perform fabrication inspection and project management on select projects for various reasons. The consultant provides weekly updates for active fabrication projects to the SFU and other important information such as program changes, overall quality, communication with Fabricator, and key performance indicators (KPIs) are discussed.

The SFU adheres to MDOT’s Structural Fabrication Quality Manual (SFQM). The purpose of the SFQM is to provide the SFU and their consultants with information on implementing MDOT’s QA program for fabricated materials required to be accepted based on “Fabrication Inspection”.

The SFQM can be found on the SFU Website.

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MATERIALS

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EQUIPMENT

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PRECONSTRUCTION

Submittals and Shop Drawings

The Shop Drawing Review Process document summarizes the process for reviewing shop drawings for permanent structural elements, temporary bridges, and other temporary works. It is important for MDOT to respond quickly to shop drawing submittals in order to keep the project moving forward.

Shop Drawing Review Process can be found on the SFU website.

Shop detail drawings, commonly called shop drawings, are a type of working drawing that the Contractor (Supplier/Fabricator) develops prior to fabrication. The Contractor is responsible for providing drawings that accurately show the appropriate details, dimensions, material requirements, fabrication procedures, and other requirements necessary to fabricate and erect structural members in accordance with the contract drawings.

Note, some Contractor submittals may be labelled as a shop drawing in ProjectWise but don’t follow the shop detail drawing requirements listed above. These types of submittals are typically working drawings, construction submittals, manufacturing drawings, or product information sheets. These are not shop detail drawings and do not follow the Shop Drawing Review Process.

The Contractor must submit for review all shop drawings and calculations (when applicable) not furnished by MDOT for all parts of the work as required by the contract in Portable Document Format (PDF) into ProjectWise. The Contractor is responsible for the correctness of the shop drawings and calculations (when applicable) and ensuring their design (when applicable) complies with any permit and design requirements.

If revisions are necessary after the shop drawing set is approved, the Contractor is required to submit a complete shop drawing set (proposed new sheets, revised sheets, and remaining sheets that are already stamped approved) for review to ensure each submittal is a standalone set.

The MDOT Bridge Design PM (or their delegate) is responsible for coordinating the shop drawing review process for all shop drawings required for pay items on bridge plan sheets. The coordinator is responsible for distributing shop drawings to the appropriate MDOT technical review areas (structural fabrication, load rating, ancillary structures, etc.) for review and comment. Once all comments have been addressed, the Bridge Design PM (or their delegate) stamps the drawing according to the following three stamp designations:

  1. Approved – This stamp is used when the shop drawings appear to be in general conformance with the contract plans. All sheets are required to be stamped.
  2. Approved Subject to Correction – This stamp is used when the shop drawings appear to be in general conformance with the contract plans, but there are very minor corrections needed for historical records that will not affect fabrication of the elements. Only the first sheet is stamped.
  3. Revise and Resubmit – This stamp is used when the shop drawings are not in general conformance with the contract plans and approval could result in elements being incorrectly fabricated. Only the first sheet is stamped.
Figure 708.2 MDOT Shop Drawing Stamps


Shop Inspections

Fabrication Notification

The Contractor (or the Fabricator/Supplier) must provide the Engineer with a fabrication start date at least 7 days before beginning fabrication per 708.03.B.1 of the MDOT Standard Specifications for Construction (MDOT SSC).


Prefabrication Meeting

SFU (or the consultant PM on behalf of the SFU) will conduct a prefabrication meeting for all design-build and design-bid-build projects. Exceptions are listed below:

  • The frequency of prefabrication meetings can be reduced to an average of one meeting per month for Suppliers that perform continuous work for MDOT.
  • The SFU PM approves the deviation in writing.

Some prefabrication meetings may be combined with other projects provided both projects have the same suppler (Fabricator) and Contractor, each Engineer for the different projects is okay with the meetings being combined, and the projects will be fabricated back-to-back with no excessive downtime between production.

Prefabrication meeting minutes are recorded to document topics that were discussed and to follow up on action items including who is responsible for the follow up. Draft meeting minutes are typically sent out 3-5 business days before production, but this can vary depending on when the fabrication unit was notified of the work or project schedules. Prefabrication meeting minutes are recorded to document topics that were discussed and to follow up on action items including who is responsible for the follow up. Draft meeting minutes are typically sent out 3-5 business days before production, but this can vary depending on when the fabrication unit was notified of work or expedited project schedules. Final meeting minutes are typically sent out within 1 business day of the comment due date established in the prefabrication meeting.

The following individuals are typically invited to the prefabrication meeting:

  • Contractor
  • Supplier (Fabricator)
  • Quality Control Inspector (QCI)
  • SFU:
    • Consultant PM
    • Consultant Quality Assurance Inspector (QAI)
    • MDOT Structural Fabrication Engineer
    • MDOT Transportation Engineer
    • MDOT Structural Precast Concrete Specialist
  • Engineer
  • Bridge Design PM

The Contractor, Supplier (Fabricator), QCI, consultant PM, QAI, and MDOT Structural Precast Concrete Specialist must attend prefabrication meetings whereas the MDOT Structural Fabrication Engineer, Transportation Engineer, Engineer, and Bridge Design PM may choose to attend prefabrication meetings. MDOT encourages all individuals listed above to attend prefabrication meetings. Note that some unique projects may require the invitation of Supplier (Fabricator) specialty subcontractors (NDT, galvanizing, metalizing, etc.) to prefabrication meetings.

Inspection Facilities

The SFU is responsible for implementing the Departments QA program for fabricated materials required to be accepted based on “Fabrication Inspection” (also known as shop or QA inspection) per the MQAP manual or project special provision. Most prestressed members require QA inspection, and this inspection is performed by a qualified Quality Assurance Inspector (QAI) representing the SFU. Prestressed concrete Suppliers (Fabricators) are located nationwide and the SFU coordinates inspection at these Suppliers when MDOT work is occurring.

Fabrication Inspection: SFU Website (see section 2.2 of SFQM)

QAI Authority

Throughout the fabrication process, the QAI will inspect the materials and fabricated elements for conformance to MDOT specifications and project special provisions (SPs) in accordance with the Structural Fabrication Quality Manual (SFQM) and supplemental Inspection Test Plans (ITPs). In addition, the QAI will collect all documentation regarding fabrication and verify Buy America (BA) provisions were met. If problems arise during the fabrication, the QAI will contact their PM for resolution and the PM may seek additional guidance from the SFU. Once fabrication is complete and the members inspected for conformance to project specifications, the members will be stored for shipping.

QAI Requirements: SFU Website (see section 2.2.4 of SFQM)

Acceptance

Acceptance of prestressed members consists of the following two-part process per the SFQM:

  1. QA (Fabrication) Inspection Acceptance: After the structural members are inspected to verify conformance to project specifications, the QAI will stamp each main member “Approved for Use”. The approval stamp indicates that the QAI has inspected the members and found that they appear to meet project requirements; however, it does not relieve the Contractor of their responsibility to meet contract requirements. Some secondary members and miscellaneous components will not be individually stamped.
  1. Visual Inspection (VI) Acceptance: the Engineer must collect one copy of the stamped Bill of Lading and use it to verify the delivered structural products. Additionally, the Engineer must verify that the products are stamped and VI them for signs of damage that may have occurred due to shipping and handling. This VI should be documented in the field inspector’s daily report.
Figure 708.10 “APPROVED FOR USE” Stamp

Figure 708.10 – “APPROVED FOR USE” Stamp

Acceptance: SFU Website (See section 2.2.7B of SFQM)


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Furnishing and Fabricating

Equipment

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Void Boxes, Inserts and Attachments

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Design and Proportioning of Concrete Mixtures

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Concrete Strength

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Steel Reinforcement and Prestressing Strand

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Miscellaneous Steel

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Welding

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Strand Debonding

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Placing Concrete

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Cold Weather Precautions

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Curing Elements

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Workmanship

The QAI will inspect prestressed members after QC has performed their inspection and note any deficiencies or nonconformances (NCRs) caught by QC or observed by QA. The Supplier (Fabricator) is required to notify the MDOT QAI of all observed defects, damage, and potential NCRs and submit a proposed repair procedure to SFU for approval. The Supplier (Fabricator) must receive written approval from MDOT prior to performing any repairs.

Approved repairs are typically completed at the Supplier’s (Fabricator’s) facility prior to the member shipping to the project site; however, there may be some circumstances where approved repairs are conducted at the project site due to project schedules. In both cases, the Supplier (Fabricator) typically performs the repairs. Repairs conducted at the Supplier’s (Fabricator’s) facility will be witnessed by the QAI and repairs conducted at the project site will be witnessed by the MDOT Construction Inspector.

The SFU has developed standard repair procedures for common defects observed on fabricated prestressed members. These repair procedures have been reviewed by industry and should be used by the Supplier (Fabricator) when applicable to expedite the review process. The QAI or Construction Inspector should be familiar with these standard repair procedures for common deficiencies.

MDOT Standard Repair Procedures: SFU Website (See Appendix A4 of SFQM)

Tolerances

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Stress Transfer

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Handling, Storage, and Transporting

When loading and shipping occurs, the Supplier (Fabricator) will load the members on a truck and the QAI inspects all members again for conformance to specifications since handling damage can occur when members are transported and loaded for shipping.

The Supplier (Fabricator) is required to provide the QAI with a minimum of five (5) copies of the Bill of Lading for each proposed shipment per the SFQM. Each Bill of Lading will be stamped “Approved for Use” (see Acceptance process below). One copy of the Bill of Lading is retained by the QAI and the other four copies are distributed to the Contractor, Supplier (Fabricator), Engineer, and Trucking Company.

Once the structural prestressed member has been visually inspected and accepted by the Engineer, the construction inspector should verify the products are stored properly prior to erection. The method of stockpiling and transporting members is covered in detail in subsection 708.03 of the Standard Specifications for Construction. Below is a list of items the inspector should check regarding the storage of structural prestressed members:

  • Support beams off the ground to prevent moisture and deleterious material intrusion.
  • Support beams across the full width on two battens, each greater than 4 inches wide.
  • Support beams on two battens, no more than 3 feet from the ends of the beams.
  • Support stacked beams, one above the other along the same vertical plane at each end of the beams.
  • Support the beams on level, stable ground, avoid storing beams near side slopes, or areas near heavy construction traffic.
  • Do not support the beam at more than two points.
  • Prestressed I-beam shapes may need to be laterally braced on site.
  • Members are to be stored in an upright position and should be thoroughly braced to avoid overturning, which may damage the member itself, adjacent members or material, or injure personnel in the immediate vicinity.
  • Related items such as bearings and bridge railing should also be protected from damage, dirt, and corrosion.
Loading and Shipping

SFU Website (See section 2.2.7A of SFQM)


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CONSTRUCTION

Erection of Prestressed Beams

Considerable care should be exercised when handling structural precast concrete elements. In many cases, there is no way to repair a damaged element short of re-fabrication. Below is a list of items the inspector should check regarding the erection of structural prestressed members.

  • Prestressed beams should be always kept in an upright position, as the beam’s own dead weight counter acts the internal prestressing force to keep the beam stable.
  • Verify lifting devices, usually loops of seven wire steel strand, are the only attachment used when moving a beam. The beam must not be lifted at the beams center in any way or undesirable stresses may develop and the beam may crack.
  • Ensure the lifting devices are removed once the beam has been placed in its final position on the substructure.
  • Per Section 105 of the Standard Specifications for Construction, the Engineer reserves the right to reject any shipped product that shows visual signs of damage or does not meet specification requirements.

Check beam markings and compare to the beam layout sheet in the plans. Make sure the beams are placed in the right location and direction. They may fit in more than one place but there is only one correct location and direction for each beam.

Box Beams

Below is a list of items the inspector should check regarding the erection of structural prestressed Box Beams:

  • Verify box beam widths will fit properly on the substructure units.
  • Verify box beam bearing pads are shimmed (when necessary) on each beam in an approved manner during erection to provide full bearing contact with the bottoms of the beams.
  • Box beams may camber more than anticipated or may experience transverse rotation such that they do not sit flush on the sole plates, which are typically beveled to accommodate camber and vertical alignment angles.
  • (Expansion Bearings Only) Verify the beams line up with the position dowel holes, and ensure the holes are filled with hot poured rubber sealant type filler at least 3 inches above the position dowels. Ensure the remainder of the hole is filled with Type H-1 grout.
  • (Fixed Bearings Only) Verify the holes are filled with Type H-1 grout.
  • (Side-by-Side Box Beams Only) Verify beams are set with spaces as specified on the contract plans or shop drawings and that seal washers are placed around the transverse post-tensioning conduit holes.
  • Note in the Daily Work Report (DWR) when erection has been completed.

Below is a list of items the inspector should check regarding the post-tensioning of side-by-side box beams after erection:

  • Verify the space between the box beams is completely filled, full depth, with R-2 grout mortar and cured for at least 48 hours.
  • Ensure the contractor does not grout when temperatures are below 40° F.
  • The deck width should be measured by the Contractor as soon as the beams are set to ensure the post tensioning rods or strand will be fabricated to the proper length.
  • All hardware dimensions must be as shown on the plans or shop drawings.
  • Tendons or rods for post-tensioning should be tensioned with calibrated jacks according to a Contractor-supplied calibration chart showing the corresponding jack pressures and elongations necessary to gradually build up to the required post-tensioning force.
  • After the post-tensioning is complete, ensure the conduit is flushed with water, then compressed air.
  • The tendon or rod holes will be grouted under pressure with Type E-1 grout for steel tendons or rods as specified in subsection 708.03B of the Standard Specifications for Construction.

Do not stand behind the jacking machine or rod holes during jacking procedures. If a tendon or rod snaps, it can cause serious injury

I-Beams, 1800 Beams, and Bulb-Tee Beams

Below is a list of items the inspector should check regarding the erection of structural prestressed beams and girders:

  • After the first and second member (beam or girder) are erected, the second member must be attached to first through the diaphragm connection(s). In addition, each subsequent member must be attached to the previously erected member through the diaphragm connection(s).
  • Prestressed beams and girders, especially taller and longer members, can be more prone to sweep, transverse deflection, or even rotation. For this reason, they should be rigidly blocked in place via diaphragm connections to ensure proper spacing between members and to avoid beam rotation during construction.
  • Verify member (beam or girder) bearing pads are shimmed (when necessary) on each member in an approved manner during erection to provide full bearing contact with the bottoms of the beam/girder.
  • (1800 Girder only) Verify use of beveled sole plates on each girder and note in the Daily Work Report (DWR).
  • Note in the Daily Work Report (DWR) when erection has been completed.

Spun Pole

Below is a list of items the inspector should check regarding the erection of prestressed spun poles:

  • During installation, the poles must only be lifted and stored using the locations and methods shown on the approved shop drawings or manufacturer’s instructions.
  • Visually inspect spun pole for any damage, cracks, or spalls and notify the Engineer if present.
  • Note, the concrete clear cover for spun poles is typically less than a prestressed beam so cracks or spalls may increase the members susceptibility to steel corrosion.
  • Spun concrete poles must be safely secured after being placed in the drilled shaft installation before the concrete foundation is poured and cured

Sound Wall

Below is a list of items the inspector should check regarding the erection of sound walls:

  • In most cases the sound wall panels are attached to the posts using tongue and groove joints. It is important during erection that the panels are lowered slowly into position and do not crack or spall the posts.
  • If the sound wall posts contain grout pockets (prestressed sound walls only), then the grout pockets at the ends of the posts must be filled with non-shrink grout and should be free of cracks.
  • Note, a ladder should be used to visually inspect the tops of soundwall posts.
  • Visually inspect sound wall posts for damage, shrinkage, cracks, or spalls and notify the Engineer if present.
  • Note, cracks and other deficiencies will be subject to moisture and chloride intrusion which can lead to rapid deterioration of the posts.


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INSPECTION & TESTING

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MEASUREMENT, DOCMENTATION & PAYMENT

Basis of Payment

There are three methods of payment for structural precast concrete members: Stockpile payment, partial shipment payment, and final shipment payment. No method of payment relieves the Contractor (or Fabricator) from damage due to transporting, storing on the project site, or erecting the elements. Additional information on payment can be found in Section 109 of the MDOT Standard Specifications for Construction.

The Engineer will make stockpile payments for fabricated structural steel products in accordance with section 109 of the MDOT SSC. See subsection 2.2.6 of the SFQM for SFUs responsibilities with stockpile payment. These materials can be stored at the fabrication facility or at the construction site. If stored at the construction site, the materials must be inspected by the Engineer as stockpiling occurs since the approval stamp ink could wash away over time. If the approval stamp(s) appear to be fading away, the Engineer must mark the accepted structural steel products in a more permanent method.

After the Supplier (Fabricator) has shipped a portion of the structural concrete elements to the project site, visually inspect the members and verify they are stamped “Approved For Use” according to the sections above. If all the documentation is provided and there are no deficiencies, then partial shipment payment may be made. The Engineer must follow section 109.04 of the MDOT Standard Specifications for Construction.

After the Supplier (Fabricator) has shipped all of the structural concrete elements to the project site, visually inspect the members and verify they are stamped “Approved For Use” according to the sections above. If all the documentation is provided and there are no deficiencies, then final shipment payment may be made. The Engineer must follow section 109.04 of the MDOT Standard Specifications for Construction.

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