Accelerated bridge construction chapter 5 modular bridge construction issues Accelerated bridge construction chapter 5 modular bridge construction issues Accelerated bridge construction chapter 5 modular bridge construction issues Accelerated bridge construction chapter 5 modular bridge construction issues Accelerated bridge construction chapter 5 modular bridge construction issues Accelerated bridge construction chapter 5 modular bridge construction issues Accelerated bridge construction chapter 5 modular bridge construction issues
CHAPTER Modular Bridge Construction Issues 5.1 Prefabricated bridge elements and systems 5.1.1 Introduction In earlier chapters and 4, the concepts of PBES were introduced The prefabrication of bridge elements appears to have revolutionized the transportation industry, increasing efficiency through faster delivery Prefabrication is an essential part of unlocking the benefits of ABC Modern technology in construction techniques has provided new avenues of production In this chapter the latest trends and the many advantages of purchasing ready-made bridges by using prefabrication methods are addressed A glossary of ABC terminology applicable to all the chapters is listed for ready reference in Appendix 2: ABC Examples of development of a wide range and variety of successful projects completed in the United States in recent years are presented in Tables 5.1–5.7 Full prefabrication for both superstructure and substructure components is shown Superstructure applications adopted by various states include steel girders, trusses, and precast concrete I shape and box girders according to design requirements and availability for speedy construction In the past few years, a number of states have jumped on the ABC bandwagon and have been at the forefront of promoting and implementing innovative technologies Like many other industries such as car manufacture, “the supply should always meet timely demand.” Further details of interesting projects completed in selected states are provided in Chapter The following bridge construction methods can incorporate ABC and related prefabrication methods: • A new bridge on a new highway • A replacement bridge on an existing footprint: this involves demolition and staged construction, and a temporary bridge or detour is required • A replacement bridge on a new footprint: deck widening and additional lanes may be required • Deck replacement only • Repairs to deck only • Deck and girder replacement only • Bearings retrofit and upgrades • Repairs to substructure only Details of repairs required for steel beams and connections are described Ongoing research is focused on identifying and developing new bridge elements and systems for all materials that would help accelerate bridge construction Prefabricated bridge elements and systems (PBES) are manufactured off-site, ready for installation when they are brought to the construction site Bridge elements are the basic building blocks of bridge construction, such as deck panels, girders, pier caps, columns, pile cap footings, and foundations Accelerated Bridge Construction http://dx.doi.org/10.1016/B978-0-12-407224-4.00005-8 Copyright © 2015 Elsevier Inc All rights reserved 215 216 CHAPTER 5 Modular Bridge Construction Issues PBES offer costs savings in both small and large projects Construction can be completed during limited-duration off-peak lane closings Prefabricated systems allow bridges to be built in days or weeks rather than months or years, and the manufacture can be accomplished in a controlled environment without concern for job-site limitations; this increases quality and can lower costs Shipment of precast components to the job site reduces the impact on the environment Finally, prefabricating takes elements and systems out of the critical path of a project schedule Precast fabricators can produce quality components or systems in a controlled plant environment in much less time than is required on-site Improved quality translates to lower life-cycle costs and longer service life The quicker installation of prefabricated bridges will minimize the huge daily delay-related user indirect costs Also, daily traffic control costs from installing and maintaining traffic control devices, flagging, lighting, and detours will be a drain on DOT budget Minimize life-cycle costs: No bridge is designed to last forever Bridges need repairs, rehabilitation, or replacement to deal with increased live load and widening Maintenance expenses are recurring and the extent of work is based on yearly inspection reports They may apply to over 50% of the inventory of bridges in a given state Substructure construction duration: Bridge construction and rehabilitation extending over several months has become a primary source of congestion In cast-in-place construction, foundations for piers and abutments must be built first Then pier columns and caps must be built before beams and decks are placed However, off-site prefabrication technologies and processes help solve this problem 5.1.2 Practical considerations for prefabrication Prefabrication is a specialized subject for analysis and design Connection details between components need to be safe The contractor needs guidance on many issues of long-term performance The consultant needs to perform research to come up with the right solutions The conventional contracting system lacks focus on the new fabrication technology issues and feedback can only come from research results obtained during construction Achieving accelerated construction requires an experienced consultant, as well as experienced engineers and field staff Other requirements and benefits of ABC and PBES include: Training: Technicians need training in specialized manufacturing processes Equipment: Availability of high-capacity construction equipment Lighter material: Availability of stronger and lighter materials also contributes to the uniform quality of bridge components Bridges installed using PBES have a life of 75–100 years Transportation of modular bridges: Availability of self-propelled modular transporters (SPMTs) Leadership in the application of ABC: Updates and technical guidance to be provided by the federal agencies such as FHWA, AASHTO, TRB, etc Design-build: Simplified contract management procedures will lead to improved modern day communications between the contractor, the consultant, and the owner due to video conferencing and use of e-mails and cell phones, etc helping to expedite construction Priority of bridges for accelerated repair: The buildup of inventory to fix, repair, and replace an increasing number of bridges as they get older and the capability of highway agencies to meet the challenges Provision of much-needed social benefits to the public can be achieved through early completion and rehabilitation of highways and bridges 5.1 Prefabricated bridge elements and systems 217 Time and cost savings: The role of ABC in the multibillion dollar transportation industry is significant Building upon the progress in prefabrication made in multistory building construction and car parks, stadiums, etc will be helpful Labor availability: Relocation of large workforces to the construction sites for cast-in-place construction is no longer necessary with factory production Improved connection details and construction specifications: These are now available due to research in seismic design and flood-control measures at bridges The construction of most bridge elements and systems can be done with controlled fabrication 5.1.3 Types of modular prefabricated deck slabs Innovative bridge designers and builders are finding ways to prefabricate entire segments of the superstructure This may involve prefabricated truss spans and preconstructed composite units that are fabricated or assembled at or away from the project site and then lifted into place in one operation The maximum dead load in a bridge comes from the deck slab that gravitates to girders, bearings, substructure, and the foundations If this weight can be reduced, there will be savings throughout as the supporting components will be lighter New materials being used for decks are high-performance concrete (HPC) and corrosion inhibitor aggregate concrete Common precast deck shapes are rectangular, skew, or curved Precast construction has improved tolerances during manufacture and it helps control minimum sight distance in curved bridges and superelevation of concrete decks, thereby reducing accidents Precasting integrates quality control and avof silica fume and high-early-strength LMC will open the deck to traffic, within 3 h of curing Silica fume, pozzolans, fly ash, and slag may be used to reduce concrete permeability and the heat of hydration Fly ash and cenospheres are preferred for HPC in bridge decks, piers, and footings Self-consolidating concrete (SCC): Since vibration time is saved, SCC helps ABC; it is a more workable concrete with lower permeability than conventional concretes Byproducts of coal fuel such as fly ash, flue gas desulfurization materials, and boiler slag provide extraordinary technical, commercial, and sustainable advantages 5.13 Proprietary manufacturing companies In the United States there is a market economy that encourages both small and big entrepreneurs The income tax system provides subsidies for genuine losses This environment has helped large manufacturing companies to grow The following represents a list of some of the manufacturing companies for prefabricated products and components The list of new companies is growing, both in the United States and abroad Major factories are being supported by smaller manufacturing factories, resulting in a consortium There are many bridge companies, such as CONSPAN and Mabey-type temporary bridges Since construction time is reduced with design-build applications, traffic jams are fewer and detours are avoided, and there are additional benefits to commerce and industry Most industry observers predict a period of continued recovery, with new design innovations that will help bring about more diverse construction methods (see http://www.constructiondigital.com/innovations/where-is-the-constructionindustry-headed-in-2013) Modular design and prefabrication have a number of benefits with shorter production cycles and enhanced sustainability This results in lower production costs, with savings to be passed on to the client The use of eco-friendly materials and the prefabricated design also make these modular structures ideally suited to the changing demands of the transportation industry CONSPAN Modular Concrete Bridges: Clear spans range from 12 to 60 ft The arch-box units can accommodate a wide range of fill heights together with AASHTO or AREMA loading Headwalls are precast with the unit or separately Footings may be precast or cast in place Units may also be set on a slab bottom, pedestal walls, or pile caps 252 CHAPTER 5 Modular Bridge Construction Issues Acrow Modular Steel Bridges (located in Parsippany, New Jersey): Acrow’s bridges can be assembled in less than half the time of conventional bridges They are compliant with AASHTO, ASQC (American Society of Quality Control), AWS (American Welding Society), AISC (American Institute of Steel Construction for small bridges), and ASTM (American Society of Testing Materials) guidelines Acrow’s bridges have been full-scale tested in the laboratory at Lehigh University, Pennsylvania for load-carrying capability and by military organizations Ready-made truss bridges are being manufactured by Acrow USAID sponsored a project in Pakistan to replace flood-damaged bridges Assembly was done near the sites The ABC technique can be successfully utilized in the aftermath of flood and earthquake damage to restore highway links to cities Examples are given below from Pakistan, where recurring floods and earthquakes have been a regular feature The more modern approach is to use modular or prefabricated bridges manufactured under improved quality control in supervised factory conditions These may then be delivered to the site as preassembled bridges on special tractors Acrow also has provided assembled prefabricated movable bridges on rivers that allow passage of vessels such as Bascule, vertical lift, and sliding bridge spans After the Pakistan earthquake of October 2005, when bridges got damaged and paralyzed important highways, Acrow truss-type bridges provided immediate relief During manufacture, robots are extensively used to guarantee quality workmanship All Acrow bridges are certified to be manufactured under the quality assurance standards of ISO9001 and American Institute of Steel Construction (AISC), thus assuring the highest level of quality Acrow bridges have similar characteristics to a type of bridge known as the Bailey bridge Bridges have been used on roadways of all types They have been used on interstate highways, motorways, state highways, provincial highways, primary and secondary roadways, rural feeder roads, and many more applications 5.14 Further case studies of prefabricated bridges Some case studies from the United States and Canada offer new ideas on techniques and construction details to achieve the goal of “Get in Get out Stay out.” Prefabricated elements for the substructure and superstructure and complete bridge systems for rapid replacement are available and have been used for several years Prefabricated systems allow bridges to be built in days or weeks rather than months or years • In 1995, the George P Coleman Bridge in Virginia, the largest double-swing bridge in the United States, was dismantled and replaced in only 9 days using barges • In 2006, the Florida Department of Transportation used self-propelled modular transporters (SPMTs) to remove and replace a bridge superstructure in northeast Orlando • In March 2013, a new bridge in the Everglades was designed to heal environmental damage using the CONSPAN system (see Curtis Morgan, “A Bridge to Help Heal the Everglades,” Miami Herald, March 19, 2013, http://www.miamiherald.com/2013/03/19/3294968/a-bridge-to-helpheal-the-everglades.html) The completion of a new one-mile-long bridge was described earlier The bridge is the last major piece in the Modified Water Deliveries project, a series of projects originally approved by Congress in 1989 as part of plan to restore water flows to a newly acquired 107,000-acre section of Everglades National Park 5.14 Further case studies of prefabricated bridges 253 5.14.1 Accelerated girder/deck production One girder/deck unit cast per day was precast at Pre-Con’s Woodstock, Ontario precast plant using a reusable wood form • Units were prestressed and conventionally reinforced, but with a monolithically cast deck slab above The girder deck was formed with a parabolic shape in elevation and cross-slope in section to account for girder camber and cross-fall • The deckside form was notched for projecting reinforcing steel to ensure proper alignment with steel in adjacent units Focus was placed on the edge detail, girder-to-girder • High-performance concrete was required for production of these units, together with similar curing and temperature restrictions/monitoring procedures for the abutment and wingwall units Center and surface thermocouples were cast into the unit: three wires/deck, two wires/girder, and three locations per deck and girder (15 thermocouples/unit total) A seven-day wet cure with burlap was maintained, including a layer of plastic vapor barrier • Temporary steel stands were required for stability after the girder/deck units were removed from the wood form Preventing shrinkage and micro-cracking: The concrete temperature was maintained between 100 and 700 °C and the temperature difference between any one set of the center and the surface thermocouples could not exceed 200 °C All units were wet cured with burlap or filter cloth for a seven-day period Soaker hoses were used to keep units continuously wet during the seven-day curing period A moisture vapor barrier was used to prevent air flow between layers during the curing period The I-85 Bridge located in North Carolina was planned as a four-span concrete structure with eight columns per bent Prefabricated elements were used for the substructure’s columns, pier caps, and deck beams The bridge components were cast off-site and shipped to the site on conventional semitrailers Each component was carefully cast to within a 0.25-in tolerance so connections made in the field would fit precisely Using precast, prestressed columns and caps on the bridge expedited the work ABC heavy lift techniques have been used on the following projects in Massachusetts: • Phillipston Bridge • Craigie Bridge • Wellesley • I-93, Medford • Morton St., Boston • River St., Boston Boone IBRC Bridge project (120th Street Bridge over Squaw Creek in Boone County, Iowa) (see Bowers et al., 2007): Through the FHWA Innovative Bridge Research and Construction program, a bridge in Boone County, Iowa was constructed using several different precast, high-performance concrete elements Researchers from Iowa State University performed laboratory testing on the precast components that were used in the Boone County Bridge Field instrumentation and testing were used to verify the post-tensioning operation and to verify several of the construction methods Also, a comparison of the actual construction schedule with a theoretical schedule was completed 254 CHAPTER 5 Modular Bridge Construction Issues Three deck panels could be cast in one casting operation Panels could be fabricated every other day with a maximum of nine panels cast per week The beams used were Iowa Standard “B” beams modified for wider spacing than the typical standard beam spacing Superstructure: The superstructure for the bridge utilized traditional PPC beams Beams were modified from the standard design in order to eliminate a beam line To modify the beams, additional prestressing strands were added and the concrete release and 28-day strengths were increased Transverse joints were cast in place with a high early strength concrete mix Due to the tight deck panel spacing, a small aggregate size was used with a maximum top size of 3/8 in The maximum water cement ratio was 0.38 and the slump was increased using a high-range water reducer (HRWR) that allowed the slump to go to a maximum of 8 in A retarding admixture was used as well that seemed to extend the life of the HRWR for workability The HRWR was very effective in aiding in the placement of the concrete A cast-in-place concrete diaphragm and deck end-section was constructed to complete the integral abutment Superstructure testing: Laboratory tests were conducted to determine the flexural and punching shear capacity of the deck panels Panels were designed for HS-20 loading 5.14.2 Conclusions The following conclusions were reached for this project: • Placement of a single precast pier cap or abutment cap could be done in less than 30 min because piles were driven within tolerances • Deck panels for half the bridge could be erected in half a day A theoretical work schedule predicted that the Boone IBRC Bridge could be assembled in 12 working days • The abutment connection capacity is at least 4.5 times greater than the unfactored service load. 5.15 Conclusions for prefabricated bridges Initiatives taken by FHWA have led to considerable progress in implementing ABC concepts ABCrelated design needs to be made part of AASHTO and state bridge design codes and specifications To gain confidence in structural behavior, full-scale testing of joints in precast curved deck is required Analytical methods applicable to discontinuities of components need to be developed Application of the latest techniques in concrete manufacture, composites, HPS, and hybrid materials is feasible Integrated software covering all aspects of ABC design and drawings should be developed Deterrents and bottlenecks such as MPT, construction easement, right-of-way, permit approvals, and utilities relocation need to be resolved and administrative procedures simplified to facilitate ABC Certification and training of construction personnel, continuing education of engineers in rapid construction techniques, and construction management for ABC courses at universities are recommended Details of repairs required for steel beams and connections are described 5.15.1 Improvements in the manufacture of ready-made bridges There are many bridge companies such as CONSPAN and MABEY-type temporary bridges Since construction time is reduced with design-build applications, traffic jams are fewer and detours are 5.15 Conclusions for prefabricated bridges 255 avoided in addition to benefits to commerce and industry The use of eco-friendly materials and the prefabricated design also make these modular structures ideally suited to the changing demands of the transportation industry Prefabrication is a specialized subject for analysis and design Connection details between components need to be made safe enough The contractor needs guidance on many issues of long-term performance The consultant needs to perform research to come up with the right solutions The conventional contracting system lacks focus on the new fabrication technology issues and feedback can only come from research results obtained during construction Achieving accelerated construction would also require training of both the consultant and the contractor’s engineers Consider sample projects using the following bridge elements for guidance, in the absence of an ABC code of practice: • Precast foundation elements • Precast pile and pier caps • Precast columns • Precast full-depth deck slabs • Cored slabs and box beams • Next beams and deck girders • Full-span bridge replacement units with precast deck • Bridges installed with SPMTs • Cost evaluations are important and should be accurate: • Estimation of time and materials • Roadway user costs • Maintenance of traffic costs • Safety costs • Agency costs • Life-cycle costs If ABC cost