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Title: Live Load Distribution Factors for a Partially Composite I-Girder Bridge

Author(s): Ikram Efaz, Nur Yazdani, Eyosias Beneberu

Publication: Symposium Paper

Volume: 352


Appears on pages(s): 51-67

Keywords: Live load distribution factors, composite I-girder bridges, partially composite action, vibration of highway bridges, bridge evaluation

DOI: 10.14359/51734856

Date: 5/31/2022


The current AASHTO LRFD provisions for live load distribution factors (LLDF) for composite prestressed concrete I-girder bridges depend on various factors, such as span length, spacing and stiffness of girders. The approach assumes 100% composite action between the deck and the supporting girders and does not consider the effect of any possible loss of composite action due to construction issues or time-dependent deterioration. The current study evaluated the actual bending moment LLDFs in a recently constructed partially composite prestressed concrete I-girder bridge on SH-75 in Dallas, TX that has excessive vibration issues. In-situ load testing with loaded trucks and instrumentation (strain gages and rotational tiltmeters) showed only 15% remaining deck-girder composite action. Two load tests at an interval of about one year were employed to determine any time-dependent loss of composite action. The interior girder LLDF values obtained from load tests varied between 0.26 to 0.43, while the AASHTO LRFD approach yielded a constant value of 0.52 for all girders. A calibrated numerical model showed good agreement with load test results and may be used for evaluation of any retrofitting methods to increase the composite action.