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4 CHAPTER 1 INTRODUCTION AND RESEARCH APPROACH 1.1 INTRODUCTION efits from the reduced weight of the steel. Integral construc- tion reduces this mass and, with close attention to detailing, Conventional girder bridge superstructures usually are provides improved aesthetics. supported on bearings placed on the bridge substructure. The This report presents the details and results of the work on bearings are designed to support the vertical reaction of the the use of integral connections between steel I-girder bridge bridge girders and may also be designed to restrain the hori- superstructures and concrete substructures. This work was zontal movements of the bridge. The bearings are usually conducted under NCHRP Project 12-54. detailed to allow the superstructure to rotate at pier locations. Past use of integral pier connections for steel bridge struc- The superstructures and substructures of conventional bridges tures was reviewed to determine the best approach to this are essentially designed as separate systems. investigation. The reasons that led to using integral connec- Unlike conventional bridges, an integral connection between tions in the past (type of construction, pier configurations, and the superstructure and substructure provides some degree of the performance of integral pier bridges) were documented. continuity between the two systems. The elevation of the bot- In addition, research on integral connections for concrete tom of the integral pier cap may be the same as that of the structures was reviewed and summarized. bottom of girders. Moments, in addition to vertical and hori- Several integral pier cap connections were developed and zontal forces, are transferred from the superstructure to the reviewed by bridge designers and steel bridge fabricators. substructure. Concepts for the connections between the girders and the In past applications, integral connections of steel bridge integral pier caps were also developed. The review of the structures were typically used on bridges crossing over other expected performance of different concepts resulted in rec- highways or railway tracks at sharp skew angles. The use of ommending five connection concepts for further develop- integral connections allowed the pier cap bottom elevation to ment and detailing. One concept representing I-girder super- be the same as the elevation of the bottom of the girders. This structure supported on a box-beam integral pier cap and a allowed orienting the pier cap in the direction perpendicular to reinforced-concrete single-column pier was recommended the girders without causing the pier cap to reduce the overhead for detailed analytical and experimental validation. clearance of the lower highway or railroad. This orientation of the pier cap eliminated the problems associated with orienting 1.2 PROBLEM STATEMENT the pier cap at a sharp skew, which would be required if a con- AND RESEARCH OBJECTIVE ventional pier cap were used. The use of the integral pier cap also eliminated the need to raise the elevation of the bridge The objective of was to develop recommended details, and bridge approaches to maintain underclearance while ori- design methodologies, and specifications for integral con- enting conventional pier caps perpendicular to the girders. nections of steel superstructures to concrete substructures. Integral connections were also used to enhance seismic per- The recommended specifications were to be in a form suit- formance of bridge structures. Figure 1 depicts a concrete able for consideration by the AASHTO Highway Subcommit- bridge pier connected integrally to a steel superstructure. tee on Bridges and Structures (HSCOBS). The stated objective Past research on integral connections was essentially con- was further narrowed to exclude integral abutments and only ducted on concrete structures. The use of integral connec- include integral connections between steel superstructures tions on concrete bridges helped in reducing the mass of con- and concrete intermediate piers or bents. crete bridges and, thus, improved their seismic performance. A composite steel girder bridge superstructure weighs sub- 1.3 SCOPE OF THE STUDY stantially less than a concrete superstructure. This reduction of mass in the superstructure reduces the seismic susceptibil- The scope of the study was generally determined by the ity of bridge structures. Nevertheless, steel superstructures tasks identified in the RFP as the tasks anticipated to be placed on top of large concrete drop bent caps or hammer- encompassed by the research. The task description, copied head piers can result in unnecessary mass, offsetting the ben- from the RFP, is provided below.