BACKGROUND
For composite steel girder bridges, stud shear connectors are provided along the length of a bridge at the interface between the concrete deck and the steel girder to resist the interface shear and prevent slip of the concrete deck on the top flange of the girder. Currently, bridge engineers use the AASHTO LRFD Bridge Design Specifications (BDS) to determine the size and spacing of the stud shear connectors to satisfy the fatigue and strength limit states. Section 6 of the AASHTO LRFD BDS only allows the horizontal shear force between a concrete deck and steel girder to be transferred through the shear connectors. However, field studies on steel girder bridges designed as noncomposite have indicated that some level of unintended composite action is present despite having no stud shear connectors. Quantifying a reliable contribution of friction and cohesion in transferring the horizontal shear force between a concrete deck and the top flange of a steel member could result in a dramatic improvement on the calculation of the demand and resistance of stud shear connectors at the strength and fatigue limit states. Reducing the number of required stud shear connectors without compromising the performance of composite steel girder bridges will also increase the efficiency of fabrication and erection as well as decrease the number of tripping hazards during construction. Bridge engineers need guidance on updating the current AASHTO LRFD BDS design of stud shear connectors in composite steel girder bridges.
OBJECTIVES
The objectives of this research are to provide (1) guidance on calculating the demand and resistance on stud shear connectors for steel girder bridges (including straight, skewed, and horizontally curved) at the fatigue and strength limit states and (2) design examples.
At the minimum, the research shall investigate:
- The contribution of friction and cohesion in transferring the horizontal shear force between a concrete deck and the top flange of a steel member (include I-girder, tub girder, stringers, and floor beams) and
- The validity of the shear flow equation.
Accomplishment of the project objective will require at least the following tasks.
TASKS
Task descriptions are intended to provide a framework for conducting the research. The NCHRP is seeking the insights of proposers on how best to achieve the research objectives. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers' current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meeting the research objectives.
PHASE I—Planning
Task 1. Conduct a literature review of relevant research related to the design of stud shear connectors for composite steel girder bridges. The review shall include published and unpublished research conducted through the NCHRP; FHWA; and other national, international, state, and pooled-fund sponsored research.
Task 2. Synthesize the results of the literature review to identify the knowledge gaps related to the research objectives. These gaps should be addressed in the final product or the recommended future research as budget permits.
Task 3. Propose an analytical program to be executed in two parts as follows.
- Part 1, to be executed in Phase I, includes analytical studies to develop the testing program described in Task 4.
- Part 2, to be executed in Phase III, includes parametric studies and modeling (finite element analysis) utilizing the results of the testing program to finalize the design requirements for the stud shear connectors in composite steel girder bridges.
Task 4. Propose testing experiment, to be executed in Phase II, to achieve the project objectives. At a minimum, the testing program shall include:
- Lab testing to investigate the contribution of friction and cohesion on stud shear connectors demands for different concrete deck and steel girder top flange combinations. The concrete contact surfaces to be tested include cast-in-place concrete and precast concrete with grout. The steel girder surfaces to be tested include mill scale, blast cleaned, and coated. The work plan shall include a matrix of testing parameters and detail;
- Field testing includes (1) instrumentation of a number of bridges, as budget permits, to be built (to capture the stresses at the interface surface between concrete and steel members) and (2) controlled load tests after the construction is completed to determine the measured demands on stud shear connectors accounting for friction and cohesion shear force transfer between the deck and steel members; and
- Full-scale lab testing to supplement the field testing and to achieve the research objectives.
Task 5. Identify existing articles of the AASHTO LRFD BDS that the research results may influence or may be impacted by the research results and propose at least four design examples, including a horizontally curved girder, to illustrate the research results. The design examples should include a comparison between the current design and a new design based on the research findings.
Task 6. Prepare Interim Report No. 1 that documents Tasks 1 through 5, includes the data archiving and sharing plan, and provides an updated and refined work plan for the remainder of the research no later than 6 months after contract award. The updated plan must describe the process and rationale for the work proposed for Phases II through IV.
PHASE II—Testing Program
Task 7. Execute the testing program according to the approved Interim Report No.1.
Task 8. Finalize the analytical program, Part 2, and include a matrix of proposed studies. Describe how the parametric studies and modeling results will be utilized to achieve the research objectives.
Task 9. Prepare Interim Report No. 2 that documents the results of Tasks 7 and 8 and provides an updated work plan for the remainder of the project. This report is due no later than 24 months after approval of Phase I. The updated plan must describe the work proposed for Phases III through IV.
PHASE III— Parametric Studies and Research Findings
Task 10. Execute the parametric studies according to the approved Interim Report No.1.
Task 11. Based on the analytical and testing programs, prepare draft language for consideration by AASHTO to incorporate the research results in the next update of the AASHTO LRFD BDS (herein called AASHTO Deliverable), supported with design examples.
Task 12. Prepare Interim Report No. 3 that documents and summarize the results of Tasks 10 and 11 no later than 9 months after approval of Phase II.
PHASE IV—Final Products
Task 13. Present AASHTO Deliverable to the AASHTO Committee on Bridges and Structures for comments and propose any revisions to NCHRP. Revise the AASHTO Deliverable considering the NCHRP’s review comments and prepare the draft final deliverables listed in Task 14 no later than 3 months after approval of Phase III.
Task 14. Prepare final deliverables including (1) a final report that documents the entire research effort, (2) the design examples, (3) the AASHTO Deliverable, and (4) a stand-alone technical memorandum titled “Implementation of Research Findings and Products.”
STATUS: Research in Progress
