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NCHRP Project 12-102 4 C H A P T E R 1 Background 1.1 Problem Statement and Research Objectives ABC is not new to the United States Bridge market; however the use of ABC technologies in the United States has expanded dramatically over the last decade. Prior to this period, the use of ABC was limited to special projects that necessitated the use of ABC because no other reasonable alternative existed. At this time, agencies have discovered that ABC produces other benefits, some of which include: ⢠Reduced On-Site Construction Time (Prefabrication Off-site) ⢠Reduced Mobility Impacts ⢠Reduced Environmental Impact Time ⢠Reduced Road User Costs ⢠Improved Safety (Construction Crews and Road Users) ⢠Improved Quality (Plant Produced Prefabricated Products) Numerous agencies, universities, and research institutions (including NCHRP) have stepped up and completed significant amounts of research that is relevant to ABC relating to design, performance and construction of prefabricated bridge elements and systems. Most research projects of this nature conclude with recommendations for implementation of the technologies by including new provisions in the AASHTO LRFD Bridge Design Specifications, the AASHTO LRFD Bridge Construction Specifications, and the AASHTO Guide Specifications for LRFD Seismic Bridge Design. Various Technical Committees of the AASHTO Subcommittee on Bridges and Structures (SCOBS) have investigated these recommendations; however there has not been a concerted effort to incorporate ABC specifications into these documents. The proliferation of ABC projects and research has resulted in a variety of reports, manuals and documents that are used to aid designers in ABC projects. This has resulted in inconsistent design and construction practices relating to ABC. Many agencies have also expressed a resistance to the widespread use of ABC citing the lack of AASHTO specifications that should be used for the design and construction of these bridges. The lack of consistent specifications and scattering of technologies is hampering the more widespread use of ABC. Increased use of ABC through better specifications will not only benefit the bridge design and construction community but the greater transportation community as a whole. 1.1.1 Research Objectives The objective of this research is to consolidate and synthesize all past specifications, design guides and construction recommendations research and practices into one Recommended AASHTO Guide Specification for ABC Design and Construction. This document will lead to more consistent application of ABC technologies in both design and construction, which will lead to projects that are more constructible and durable. An added benefit is that costs for ABC projects (both design and construction) will be reduced as designers and contractors are given clear and consistent guidance for successful ABC technologies.
NCHRP Project 12-102 5 This project will accumulate all existing and proven ABC technologies, but does not look to break new ground or develop new technologies. The goal will be to establish a framework document, where future research and technologies can be accommodated and housed in one place, as they mature to the stage of meriting specification language as opposed to inserting the technologies piecemeal into existing documents. This document, if adopted by the AASHTO SCOBS, will resolve some of the resistance to use of ABC technologies by providing a national consensus document that is critically reviewed and accepted by the same organization that maintains the current LRFD design and construction specifications. An ABC Guide Specification will provide practical, implementable and timely solutions to common issues that are described above. The overall goal of the project is to facilitate the use of ABC by removing barriers, such as lack of specifications, to its adoption in projects. That goal, and the fact that the finite project resources should be concentrated in the most cost-effective manner, implies that some guiding principles are needed to steer the work. The following will be used here: ⢠The information sought from available literature will concentrate on previous work that has resulted in proposed specification language, design and construction guidance, lessons learned, etc. Reports that simply describe a process or project without developing such guidance will be recorded, but will be afforded a lower level of attention. The team membersâ current familiarity with the discipline of ABC means that this restriction should not be severe, because they are already aware of much of the literature. ⢠The specification provisions resulting from this research must enable, and not hinder, ABC. Thus, in those cases where the technology in question has not yet been well developed, the specification language should outline concepts and principles, rather than expressing detailed requirements. The level of detail in the specification provisions should be consistent with the level of technology readiness. 1.1.2 Terminology and Definitions The AASHTO Technical Committee T-4 of the Subcommittee on Bridges and Structures has established standard terminology and definitions for ABC. These terms have been used throughout the development of the proposed guide specifications. The terms and definitions are included in the proposed guide specifications. The following is a re-print of these terms and definitions: 1.1.2.1 General ABC Definitions Accelerated Bridge Construction Bridge construction that uses innovative planning, design, materials, and construction methods in a safe and cost- effective manner to reduce the on-site construction time that occurs when building new bridges or replacing and rehabilitating existing bridges. Conventional Bridge Construction Bridge construction that does not significantly reduce the on- site construction time that is needed to build, replace or rehabilitate a bridge. Prefabrication is typically limited to beams and girders in this form of construction. Lateral Slide A method of moving a bridge system built adjacent to the final bridge location using hydraulic jacks or cable winches while supported on sliding materials or rollers. The bridge is typically built parallel to its final alignment, facilitating the installation.
NCHRP Project 12-102 6 Prefabricated Bridge Elements and Structural components of a bridge that are built off site or near Systems (PBES) site that include features that reduce the on-site construction time that occurs with conventional bridge construction. Prefabricated Element A category of PBES which comprise a single structural component of a bridge. Prefabricated element can be made of any approved structural material. SPMT Self-Propelled Modular Transporter. A high capacity transport device that can lift and move prefabricated elements and systems with a high degree of precision and maneuverability in all three directional axes without the aid of a tractor for propulsion. Self-Propelled Modular Transporters A line on an SPMT refers to the transverse grouping of two (SPMT) Line wheel sets that are akin to an axle in a conventional transport trailer. SPMT Power Pack A module that is attached to the SPMT that provides hydraulic power for adjustments and movement. SPMT Unit An SPMT machine that contains a grouping of axles that are interconnected with a hydraulic system. Multiple units can be joined together longitudinally and transversely in a modular fashion to create larger SPMT configurations. SPMT Wheel Set A grouping of wheels that are controlled by hydraulic systems. Each wheel set has the ability to raise and lower to adjust the height of the SPMT, and pivot to provide steering of the SPMT. 1.1.2.2 Systems Prefabricated System A category of PBES that consists of an entire superstructure, an entire superstructure and substructure, or a total bridge that is procured in a modular manner such that traffic operations can be allowed to resume after placement. A Prefabricated system is rolled, launched, slid, lifted, or otherwise transported into place, having the deck and preferably the railing in place such that no separate construction phase is required after placement. Superstructure System A system that includes both the deck and primary supporting members integrated in a modular unit. Superstructure/Substructure System A system that includes either the interior piers or abutments which are integrated in a modular manner with the superstructure as described for the superstructure system. Total Bridge System A system that includes the entire superstructure and substructures (both abutments and piers) that are integral with the superstructure that are built off-line and installed as a unit. SPMT System A system installation that uses Self-Propelled Modular Transporters to move the structure. Lateral Slide System A system installation that uses Lateral Sliding equipment to move the structure.
NCHRP Project 12-102 7 1.1.2.3 Deck Elements Aluminum Deck A full thickness deck made with extruded aluminum elements that are connected to form an orthotropic deck system. Exodermic Deck A steel grid deck system made with a partially filled concrete composite topping that is placed above the top of the grid. Full-Depth Precast Deck Panel w/PT A full thickness deck panel that makes up the entire structural deck. Connected in the distribution direction with post-tensioning. Full-Depth Precast Deck Panel w/o PT A full thickness deck panels that makes up the entire structural deck. Connected in the distribution direction without post-tensioning (typically with a reinforced concrete closure joint). Orthotropic Deck A steel deck system made with a steel plate deck combined with welded transverse and longitudinal ribs. Partial-Depth Precast Deck Panel A reinforced or prestressed concrete deck panel that makes up the lower portion of the bridge deck that is combined with a reinforced cast-in-place concrete topping to form the completed structural deck. Steel Grid (open) A steel grid deck system made without concrete fill. Steel Grid (concrete filled) A steel grid deck system made with a partially filled concrete placed within the grid. 1.1.2.4 Beam Elements Adjacent Deck Beam Element Beams fabricated with an integral deck that is separated by a small grouted joint, or a small closure joint. Also referred to as butted beams. Adjacent beams come in several shapes including deck bulb T, Inverted T, Double Tee, Box, Slabs, Voided Slabs, etc. Full Width Beam Element An element that eliminates conventional on-site beam placement activities. It is typically rolled, slid, or lifted into place to allow deck placement operations to begin immediately after placement. Given the size and weight of the element, the entire deck is not included. Modular Decked Beam (MDB) An element that is fabricated with beams combined with an integral composite reinforced concrete deck to form a modular unit. MDBs can be made with steel or prestressed concrete beams. A MDB is typically made with two or three beam elements. 1.1.2.5 Pier Elements Precast Caisson Cap A reinforced concrete element that is placed on top of piles or drilled shafts that are designed to support reinforcing and cast-in-place concrete that is placed after the cap is erected.
NCHRP Project 12-102 8 Precast Cap Shell A reinforced concrete element that is fabricated without the core concrete. The core concrete is placed after the shell has been erected. Precast Cap and Column A reinforced concrete pier element comprised of a precast column cap combined with precast column(s). Precast Column A vertical reinforced concrete element that supports a beam or cap. Precast Column Cap A reinforced concrete element placed on top of column elements. Precast Integral Cap A reinforced concrete element that is integrally connected to the superstructure and the lower pier elements to form a rigid connection. Precast Footing A reinforced concrete element that makes up the structural footing of a substructure or wall. Precast Footing Shell A reinforced concrete shell that is used as a stay-in-place form for a cast-in-place reinforced concrete footing. Precast Pile Cap A reinforced concrete element that is placed directly on top of piles. Precast Semi-Integral Cap A reinforced concrete element that is integrally connected to the superstructure and pinned to the lower pier elements to form a pinned connection. Steel Cap and Column A structural steel element comprised of a steel column cap combined with integral steel column(s). Steel Column A vertical structural steel element that supports a beam or cap. Steel Column Cap A structural steel element placed on top of column elements. Steel Pile Cap A structural steel element that is placed directly on top of piles. 1.1.2.6 Abutment Elements Precast Abutment Cap A beam type element that is placed directly on top of and connected to the abutment wall elements to form the bridge seat. Precast Abutment Stem A wall element that is located above the abutment footing that retains embankment fill. Precast Backwall A wall panel element that is behind the end of the superstructure that retains the upper portion of the embankment fill. Precast Cheek Wall A wall element that is placed at the corner of the abutment seat to hide or retain the beam ends. Precast Footing A footing element that is placed on soil that supports a substructure element. Precast Integral Abutment Stem A reinforced concrete wall element that is integrally connected to the superstructure and the abutment piles to form a rigid connection. Precast Lagging Panel Panel element placed between vertical structural elements to form the face of an earth retaining wall system.
NCHRP Project 12-102 9 Precast Sheet Pile A vertical precast element that is driven or jetted into the soil to create a cantilever wall (abutment or retaining wall). Precast Wing Wall A wall element that retains embankment fill behind or alongside the abutment. Precast 3-Sided Culvert A precast culvert element that has a top and sides, but no bottom, placed on footings or pile caps to form a bottomless culvert structure. Modular Block Wall A precast wall system made up of stacked precast block elements that form a gravity retaining wall. The elements can be solid or voided. Soil or crushed stone are typically placed within the voids to enhance the resistance of the system. MSE Wall A mechanically stabilized earth retaining wall system made up of precast wall face elements connected to horizontal soil reinforcing elements. Steel Sheet Piling Interlocking vertical steel elements that are vibrated or driven into soil to create a cantilever wall (abutment or retaining wall). 1.1.2.7 Geosynthetic Reinforced Soil Integrated Bridge System (GRS/IBS) GRS/IBS A bridge that has an abutment that blends the roadway into the superstructure to create a jointless interface between the superstructure and the approach embankment. GRS Abutment Alternating layers of compacted fill and closely spaced geosynthetic reinforcement combined with facing blocks to provide support for the bridge and retain the embankment soils. Integrated Approach Alternating layers of compacted fill and closely spaced geosynthetic reinforcement placed behind the superstructure ends and between the top of the GRS abutment and the pavement structure. The integrated approach eliminates the need for approach slabs. Reinforced Soil Foundation (RSF) Granular fill material below the GRS abutment that is compacted and encapsulated with a geotextile fabric. It provides embedment and increases the bearing width and capacity of the GRS abutment. It also prevents water from infiltrating underneath and into the GRS mass from a river or stream crossing. 1.1.2.8 Miscellaneous Elements and Definitions Assembly Plan A package of plans, specifications and calculations developed by the contractor that describes the process for the assembly of prefabricated elements. The assembly plan may include handling and erection plans, materials specifications, details and calculations for bridge temporary works, and construction scheduling.
NCHRP Project 12-102 10 Bars in Splice Coupler A connection that provides tension, shear and/or moment force transfer between two precast concrete elements via a mechanical connection that uses a projecting bar from one element grouted into a reinforcing bar splice device cast into the adjacent element. Closure Joint A gap between two elements or systems that is filled with materials to form a connection. The joint may or may not include reinforcing. The width of the closure joint can vary based on the type of material used to fill the joint and the reinforcing within the joint. This feature is also referred to as a âclosure pourâ by some agencies. Closure Joint: CIP Reinforced A connection that provides tension, shear and/or moment force transfer between two precast concrete elements via lapped reinforcing bars combined with cast-in-place (CIP) concrete, ultra-high performance concrete (UHPC), or grout. Closure Joint: Grouted Key A connection that provides compression or shear force transfer between two precast concrete elements via a keyed joint filled with a cast-in-place concrete or grout. Grouted key closure joints can be combined with post-tensioning to form a moment connection. Closure Joint: Match Cast A connection between two adjacent elements with a very small width epoxy grouted joint that is fabricated by casting one element against the adjacent element in the fabrication shop to form identical matching surfaces. Match cast joints may be used to provide a shear connection or combined with post-tensioning to form a moment connection. Connection A means of transferring force between two or more elements. Connection: Grouted Duct A connection that provides tension, shear, and/or or moment force transfer between two precast concrete elements via a mechanical connection that uses a projecting reinforcing bar from one element grouted into a metal duct cast into the adjacent element. Connection: Pocket A connection between two prefabricated elements thru the projection of multiple bars or connectors of one element into a single void that is cast internal to the receiving element. The void is then filled with either concrete, grout, or other suitable material. Connection: Socket A connection between two prefabricated elements thru the projection of a single portion of one element into a single void of the receiving element. The gap between the two elements is then filled with either concrete, grout, or other suitable material. Contractor The company responsible for the construction of the bridge or structure. Designer The engineer responsible for the design of the bridge. Also known as the engineer of record. Fabricator The company responsible for the fabrication of the prefabricated element.
NCHRP Project 12-102 11 Falsework Temporary construction used to support portions of the entire permanent structure until it becomes self-supporting. Falsework could include steel or timber beams, girder column piles and foundations, and any proprietary equipment including modular shoring frames, posts shores, SPMT, and horizontal shoring. Grouted Blockout w/Shear Connectors A means of creating a composite connection between a full- depth precast deck and a supporting beam or girder via shear connectors in a grouted pocket. Link Slab Links slabs are a transverse deck level connection at piers between the decks of two adjacent spans, providing a jointless bridge without continuity. The deck is made continuous across the pier, but the supporting beams or girders are not connected. Load Path A continuous path along which a load travels through structural elements and connections. Precast Approach Slab A reinforced concrete slab element that spans between the end of a bridge deck or abutment and the approach pavement. Prefabricated Railing An element used at the edge of a bridge deck to contain vehicles, bicycles and pedestrians. PT Ducts, Bonded A pre-stressing system used in concrete comprised of a duct and a pre-stressing tendon that is grouted after stressing to form a bonded reinforcing system. PT Ducts, Unbonded A pre-stressing system used in concrete comprised of a duct and a pre-stressing tendon that is stressed to form an unbonded reinforcing system. Seismic System A series of connected elements that transfer seismic loads through the structure to the foundations. Seismic Subsystem A localized group of elements and connections within a seismic system that serves a specific design function, such as a knee-joint, plastic hinge region, etc. Shop Drawing A drawing that depicts the fabrication of elements based on the requirements of the project plans and specifications. Special Material A material used in construction that is proprietary or non- conventional. A special material often requires the use of a performance specification. Temporary Works Structures and other construction that are used to facilitate the construction in progress, but removed in the final structure. In some cases, temporary works can be left in place; however they are not part of the completed structure. Working Drawings Details and calculations developed for bridge temporary works that involve the design of elements and processes. Specifications for working drawings often require a seal by a professional engineer.
NCHRP Project 12-102 12 1.1.3 Related Research Projects 1.1.3.1 NCHRP Project 12-98 A second NCHRP ABC related research project entitled âRecommended Guidelines for Prefabricated Bridge Elements and Systems Tolerances and Dynamic Effects of Bridge Movesâ was underway during the development of this project. The objective of this project was to develop AASHTO format guidelines for the two subjects stated in the project title. Fortunately, the same principal investigator was selected for both projects, which facilitated the development of the all of the documents in the two projects. The team carefully separated the two project specifications in an attempt to not duplicate provisions, which could lead to inconsistencies. There are many cases where cross referencing is used to make all of the documents work together. At some point in the future, the AASHTO Technical Committee (T-4) for Construction may choose to merge the documents created in the two projects. The potential merging of these documents is beyond the scope of this project. In the interim, the cross referencing should suffice for application of these technologies in ABC projects. 1.1.3.2 On-going and Recently Completed ABC Research The project team is aware of a number of other ABC related research. The intent is to develop a framework guide specification that can be modified in future as research is put into practice. Each technology was evaluated by the project team. An important part of this evaluation is the practical application of the research in an actual project. Therefore, research projects that have been recently completed may not be included in the guide specifications developed under this project, since they may not have been applied to an actual construction project.
