Innovative Bridge Designs for Rapid Renewal Toolkit (2012)

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1Accelerated bridge construction (ABC) techniques have the potential to minimize traffi c disruptions during bridge renewals, promote traffi c and worker safety, and also improve the overall quality and durability of bridges. ABC entails prefabricating as much of the bridge components as feasible. Minimizing road closures and traffi c dis- ruptions is a key objective of ABC. The successful use of prefabricated elements to ac- celerate construction requires a careful evaluation of the requirements for the bridge, site constraints, and an unbiased review of the total costs and benefi ts. For ABC sys- tems to be viable and see greater acceptance, the savings in construction time should be clearly demonstrated. ABC applications in the United States have developed two different approaches: accelerated construction of bridges in place using prefabricated bridge elements and systems and the use of bridge movement technology and equipment to move com- pleted superstructures from an off-alignment location into the fi nal position. Rapid construction of bridges in place offers the promise of limited closures, maybe days or weeks at the most, to allow for the complete construction of a bridge. This type of construction traditionally relies on extensive prefabrication of bridge elements, includ- ing substructure and superstructure components, and the use of cranes to install these elements in their fi nal location. Despite the gradual lowering of costs, departments of transportation (DOTs) are hesitant about using ABC techniques because of their perceived risks and higher initial costs. Rather than custom engineering every solution, pre-engineered modular systems confi gured for traditional construction equipment could promote more widespread use of ABC through reduced costs and increased familiarity of these systems among owners, contractors, and designers. A key objective of the SHRP 2 Renewal Project R04 was to develop “standardized approaches to designing and constructing complete bridge systems for rapid renewals.” The aim therefore was to develop pre-engineered 1 INTRODUCTION

2INNOVATIVE BRIDGE DESIGNS FOR RAPID RENEWAL: ABC TOOLKIT standards for modular bridge substructure and superstructure systems that can be installed with minimal traffic disruptions in renewal applications. This project takes the approach that, for ABC to be successful, ABC designs should allow maximum opportunities for the general contractor to do its own prefabrication and erection. In this regard the R04 team has focused on specific strategies for ABC systems, as follows: 1. As light as possible: • Is sized in a manner to be manageable for transportation and installation, • Simplifies transportation and erection of bridge components, and • Could improve the load rating of existing piers/foundations; 2. As simple as possible: • Fewer girders, • Fewer field splices, • Fewer bracing systems, and • No temporary bracing to be removed; 3. As simple to erect as possible: • Fewer workers on-site, • Fewer cast-in-place operations, • No falsework structures required for prefabricated elements and systems, and • Simpler geometry. The ABC design concepts have been classified into five tiers based on implementa- tion duration as follows: • Tier 1: Traffic impacts within 1 to 24 hours; • Tier 2: Traffic impacts within 3 days; • Tier 3: Traffic impacts within 2 weeks; • Tier 4: Traffic impacts within 3 months; and • Tier 5: Overall project schedule is significantly reduced by months to years. Modular systems allow a more versatile option for ABC not limited by space avail- ability at the bridge site. Modular bridge systems are particularly suited to be used as Tier 2 concepts for weekend bridge replacements or as Tier 3 concepts where the entire bridge may be scheduled to be replaced within 1 to 2 weeks using a detour to maintain traffic. Tier 1 concepts include preassembled superstructures, completed at an off-alignment location and then moved via various methods into the final location using techniques such as lateral sliding, rolling, and skidding; incremental launch- ing; and movement and placement using self-propelled modular transporters (SPMTs). Tier 5 involves accelerating a statewide bridge renewal program by months or years by applying ABC technologies included in the other tiers.

3INNOVATIVE BRIDGE DESIGNS FOR RAPID RENEWAL: ABC TOOLKIT Project R04 was composed of three distinct phases over a time period of 4 years, beginning in 2008. Phase I was completed in November 2009. In this phase the team collected extensive data on ABC projects and identified current impediments and challenges to greater use of ABC by bridge owners. Phase II was completed between December 1, 2009, and December 31, 2010. The findings and ABC concepts from Phase I were subjected to critical evaluations in Phase II to identify concepts that can be advanced to ABC standard concepts in Phase III. Work on Phase III commenced on January 1, 2011, and was completed in March 2012. Phase III also included the con- struction of the first ABC demonstration project utilizing the modular ABC systems covered in the standard concepts. OVERVIEW OF THE ABC TOOLKIT Prefabricated bridge elements and systems (PBES) are structural components of a bridge that are built either off-site or adjacent to the site, in a manner to reduce the on-site construction and mobility impact times that can adversely affect the traveling public. Because of their versatility, PBES can be used to address many common site and constructability issues. Use of PBES has demonstrated proven benefits to agency owners, contractors, and the traveling public. Compared to conventional construction methods it is faster and safer, lowers mobility impacts, provides better quality, lowers cost, and is easily adaptable to many site conditions. Overcoming impediments to the greater use of PBES was a key focus of this research. The research team developed pre-engineered designs optimized for modular construction and ABC. Standardizing ABC systems will bring about greater familiarity with ABC technologies and concepts and also foster more widespread use of ABC. The ABC Toolkit (the Toolkit) developed for prefabricated elements and modular systems in the R04 project is composed of the following: 1. ABC standard concepts; 2. ABC sample design calculations; 3. Recommended ABC design specifications (load and resistance factor design [LRFD]); and 4. Recommended ABC construction specifications (LRFD). Standard concepts have been developed for the most useful technologies that can be deployed on a large scale in bridge replacement applications. They include complete prefabricated modular systems and construction technologies as outlined below: • Precast modular abutment systems: — Integral abutments, — Semi-integral abutments, and — Precast approach slabs; Use of PBES has demonstrated proven benefits to agency owners, contractors, and the traveling public.

4INNOVATIVE BRIDGE DESIGNS FOR RAPID RENEWAL: ABC TOOLKIT • Precast complete pier systems: — Conventional pier bents, and — Straddle pier bents; • Modular superstructure systems: — Decked steel stringer systems, — Concrete deck bulb tees, and — Concrete deck double tees; • ABC bridge erection systems: — Erection using cranes, — Above-deck driven carriers, and — Launched temporary truss bridges. The development of detailed sample design calculations for use by future designers provides a step-by-step guidance on the overall structural design of the prefabricated bridge elements and systems. The sample design calculations pertain to the same stan- dard bridge configurations for steel and concrete used in the ABC standard concepts. The intent was to provide sample design calculations that could be used in conjunc- tion with the ABC standard concepts so that the practitioner new to ABC would get a comprehensive look at how ABC designs are carried out and translated into design drawings and details. LRFD Bridge Design Specifications do not explicitly deal with the unique aspects of large-scale prefabrication such as element interconnection, system strength, and behavior of rapid deployment systems during construction. The work in this project also entailed the identification of any shortcomings in the current LRFD Bridge Design Specifications that may be limiting their use for ABC designs and making recommen- dations for addressing these limitations. Recommended LRFD specifications for ABC bridge design are also included in the Toolkit. The user should note that these are recommendations that have not been formally adopted by AASHTO. Recommended LRFD construction specifications for prefabricated elements and modular systems include best practices that were compiled by the research team with the intent that they would be used in conjunction with the standard concepts for steel and concrete modular systems. As such, these specifications for rapid replacement focus heavily on means and methods requirements for rapid construction using pre- fabricated modular systems. These tools have been included in the appendices to this report as follows: • Appendix A, ABC Standard Concepts; • Appendix B, ABC Sample Design Calculations; • Appendix C, Recommended ABC Design Specifications; and • Appendix D, Recommended ABC Construction Specifications.

5INNOVATIVE BRIDGE DESIGNS FOR RAPID RENEWAL: ABC TOOLKIT OBJECTIVES FOR THE ABC TOOLKIT An objective of this project was to identify impediments and obstacles to greater use of ABC and seek solutions to overcome them. Focus group meetings and owner surveys identified several factors that have contributed to the slow adoption of ABC in the United States. Despite the gradual lowering of costs and life-cycle cost savings, bridge owners are hesitant about using ABC techniques because of their higher initial costs and perceived risks. Another impediment to the rapid delivery of projects is the slow engi- neering process of custom engineering every solution. Rather than custom engineering every solution, pre-engineered modular systems configured for conventional construc- tion equipment could promote more widespread use of ABC through reduced costs and increased familiarity of these systems among owners, contractors, and designers. Use of pre-engineered standards in bridge engineering is commonplace. Many states have decided to make best use of their program dollars by greatly standardiz- ing design through development of pre-engineered systems, plans, etc., encompassing entire bridge systems including even the quantity takeoff for various standard con- figurations. These are guideline drawings that can reduce engineering calculations and details because the bulk of the calculations and details can be used for different site conditions. Use of pre-engineered bridge systems can lead to low in-place constructed costs and improved quality. A transition of the pre-engineered but stick-built systems to pre-engineered and prefabricated ABC systems is a worthy objective of this project. Standardized designs geared for erection using conventional crane-based erection will allow repetitive use of modular superstructure systems, which will make con- tractors more willing to invest in equipment based on certain methods of erection to speed assembly. Repetitive use will allow contractors to amortize equipment costs over several projects, which is an important component to bring overall costs in line with cast-in-place construction. Where site conditions make crane-based erection difficult, overhead erection using ABC construction technologies provides an attractive alterna- tive. Both these options are addressed in the ABC standards. Typical ABC details for superstructure and substructure systems for routine bridges that are suitable for a range of spans are included in the Toolkit. Bridge designers are well versed in sizing beams and designing reinforcing steel for conventional construc- tion for a specific site, and it would be appropriate for the engineer of record (EOR) to perform these functions for ABC projects as well. A single set of ABC designs for national use would also not be practical, as there are state-specific modifications to LRFD Bridge Design Specifications, including loads, design permit vehicle for Strength II, and performance criteria for service-limit states. The EOR, guided by the standard concepts and details and the accompanying set of ABC sample design calculations, will be able to easily complete an ABC design for a routine bridge replacement project. The standard concepts will need to be customized by the EOR to fit the specific site in terms of the bridge geometry, span configuration, member sizes, and foundations. The overall configurations of the modules, their assembly, connection details, tolerances, and finishing would remain unchanged from site to site. The ABC designs should also be reviewed for compliance with state-specific LRFD design criteria. Standardized designs geared for erection using conventional crane-based erection will allow repetitive use of modular superstructure systems.

6INNOVATIVE BRIDGE DESIGNS FOR RAPID RENEWAL: ABC TOOLKIT Repeated use of the same system will allow the continuous refinement of the ABC concept, thereby reducing risks and lowering costs. The standard concepts provide substantially complete details pertaining to the ABC aspects of the project. Much of the remaining work in preparing design plans is not particularly ABC related but more bridge- and site-specific customization. Specific instructions to designers are covered through general information sheets, plan notes, and instructions so that all the key design and construction issues in ABC projects are adequately addressed. The standard concepts, used in conjunction with the ABC sample design calculations and design specifications, will provide the “training wheels” that designers are looking for until they get comfortable with ABC. USE OF THE ABC TOOLKIT This Toolkit is not meant to be a comprehensive manual on all aspects of ABC. It is focused on the design and assembly of routine bridges using ABC techniques that would be of value to engineers, owners, and contractors new to ABC. It complements other publications on ABC, which should be consulted for more specific information on topics outside the scope of this Toolkit. The SHRP 2 R04 report is also a valuable reference for practical ABC technologies.