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4 for different types of composite steel bridge superstructures slab width criteria and maximum girder spacings used by the typical of those in use today. As a minimum, I-girder and tub- various states, documented in Appendix A (provided on the girder cross-sections should be considered. Both interior and accompanying CD-ROM). In addition, international prac- exterior girders should be considered. Composite floor sys- tice was surveyed and the various effective width provisions tems that participate structurally with tied arches, cable-stayed compared. The literature review is contained in Appendix B bridges, and deck or through trusses should also be consid- (provided on the accompanying CD-ROM). ered, along with variable- or constant-depth composite, pre- Task 4 involved an implementation of finite element mod- cast post-tensioned decks. Consider the effects of the larger eling techniques at an appropriate level of detail to predict elastic and shear moduli of high-strength deck concrete on both linear and nonlinear (post-cracking and post-yielding) the computed effective width. behavior of composite steel bridge member superstructures. Task 3. Prepare an interim report documenting the find- In order to determine what level of detail was appropriate, ings from Tasks 1 and 2. Provide practical recommenda- an extensive review of the shear lag phenomenon and effec- tions for promising methodologies to determine effective tive width definitions was conducted along with new defi- slab width that can be further developed and validated. Pre- nitions for effective width beff developed herein. The details pare an expanded work plan for the remainder of the project of this review and the new definitions are contained in describing the type of investigations needed to develop and Appendix C (provided on the accompanying CD-ROM), validate the recommended methodologies. while the finite element modeling and the verifications Task 4. Develop and validate the methodologies for deter- thereof are described in detail in Appendix D (provided on mining effective slab width using finite element analysis. the accompanying CD-ROM). Task 5. Verify the finite element analysis through a program Task 5, laboratory testing, was conducted of a two-span con- of laboratory testing of reduced scale structures as approved tinuous one-quarter-scale slab-on-girder bridge structure and is by the project panel. documented in Appendix E (provided on the accompanying Task 6. Perform parametric studies of different composite CD-ROM). Testing of two one-half-scale subassemblages of steel-bridge superstructure configurations using the current the negative moment region portion of such structures is doc- provisions of the AASHTO LRFD Bridge Design Specifica- umented in Appendix F (provided on the accompanying CD- tions and the proposed effective-width criteria. At least 100 ROM). These experiments were used to help establish the cred- cases shall be considered. In addition, a limited set of concrete ibility of the finite element modeling approaches developed in girders should be investigated to determine the applicability of Task 4 so that these approaches could be used for parametric the criteria and several cable-stayed bridges designed by oth- studies of various bridge configurations in Task 6. ers shall be investigated for axial and flexural effective width. Task 6 pursued a systematic set of analyses of finite element Task 7. Propose recommended revisions to the specifica- models representing bridges with various span lengths (15 m tions and provide design examples demonstrating their use. to 60 m), girder spacings (2.4 m to 4.8 m), skew angles (0 to For each case considered, develop suggested general guide- 60 deg), and (in the cases of continuous bridges) span length lines for designing the slab reinforcement and shear connec- ratios (from 1.0 to 1.5). Both single-span and three-span con- tors to transfer the calculated shear forces effectively between tinuous configurations were the focus of the systematic set. the girder and slab at each limit state. The design examples The set was assembled using "design of experiments" (DOE) shall conform to the provisions of the 2004 AASHTO LRFD concepts (Montgomery, 2001). Effective width according to Specifications. the new definitions developed in Task 4 was extracted from the Task 8. Perform impact testing to compare rating factors finite element analysis results considering both interior and resulting from the recommended revisions with those of the exterior girders, service and strength limit states, positive and LRFD Specifications. The method for impact testing devel- negative moment regions, and both right and skew alignments. oped in NCHRP Project 12-50 is recommended. Details of the "design of experiments" background, the finite Task 9. Submit a final report documenting the entire element modeling, and the suite of bridges analyzed in the research effort. The recommended specifications shall be parametric study along with the analysis results are presented provided in an appendix to the report and must be in a format in Appendix G (provided on the accompanying CD-ROM). suitable for consideration by the AASHTO Highway Sub- The bridges modeled in this parametric investigation committee on Bridges and Structures. needed to be designed first. Industry guidelines were carefully followed in the design of these bridges. These guidelines and 1.3 RESEARCH APPROACH the resulting bridge parameters (e.g., girder sizes) are described in further detail in Appendix H (provided on the Key specific aspects of the above research tasks are further accompanying CD-ROM). described below. Tasks 1 through 3 involved not only an In addition to the parametric study set of bridges, various extensive literature review of both analytical and experi- bridge configurations that go beyond the parametric limits were mental explorations of effective slab width and associated investigated. These included some of cable-stayed bridges, slab-on-girder bridge studies but also a survey of effective described in Appendix I (provided on the accompanying