Economic Impact of AASHTO, LRFD Specifications and its Optimization for the Prestressed I-Girder Bridges Using High Strength Concrete in Arizona Department of Transportation

Arizona Department of Transportation (ADOT) will adopt the AASHTO LRFD Bridge Design Specifications in 2007. The task preparation of such enormous undertaking has initiated a number of research investigations in ADOT’s Bridge Group. Apart from the new specification, HPC/HSC is going to be widely used by most DOTs. This paper represents the investigation on girder slab bridges designed by both LRFD and Standard Specification using conventional or High Strength Concert (HSC). Major changes in LRFD design methodologies were discussed and a general comparison was made. A dual purposed (LRFD and LFD) program was developed for the analysis, design and cost evaluation of these superstructures. Research results revealed that LRFD gives slightly (less than 10%) heavier (more costly) superstructure design. The cost evaluation of superstructures with different configuration (girder type and spacing) led to practical design charts for the optimum girder type or girder spacing. The use of High Strength Concrete was shown to be a great structural advantage for the design of prestressed concrete girders. It was observed that the use of High Strength Concrete enables the achievement of significantly longer span lengths and/or girder spacing which is not possible when using normal strength concrete.