Load Distribution Factors in Straight and Skew Concrete I-Girder Bridges

Abstract

<p>Skew bridges in modern highways have become increasingly popular for economic and aesthetic considerations. The current Canadian Highway Bridge Design Code (CHBDC) specifies skew factor equation for shear at the obtuse corner for braced steel I-girder bridges. However, skew factors for concrete I-girder bridges for girder moment and shear at obtuse and acute corners as well as middle supports due to CHBDC truck loading are yet unavailable. Also, CHBDC load distribution factor equations for moment and shear in straight bridges do not include the presence of concrete traffic barriers and intermediate diaphragms as integral parts of highway bridges. Moreover, literature review revealed that CHBDC overestimates the moment and shear at fatigue limit state design of slab-on-girder bridges. Despite the availability of computer software for bridge analysis, designers prefer simplified analysis methods to reduce the time and cost spent in the design. A practical-design-oriented parametric study was conducted, using the finite element modelling to address the shortcomings and gaps found in CHBDC. The first study included the analysis of straight and skew concrete I-girder bridges under dead load, while the second study included the analysis of such bridges under CHBDC truck loading conditions. The third study included the effect of concrete barrier stiffness and concrete intermediate diaphragms on the moment and shear distribution factors for this type of bridge. Different bridge configurations were considered to cover key parameters such as span length, skew angle, number of girders and girder spacing. The obtained results were compared with those available in CHDBC, AASHTO LRFD Bridge Design Specifications and previous research related to slab-on-girder bridges. Using the data generated from the parametric study, sets of empirical equations for moment and shear distribution factors for the studied bridge configurations under dead and live load were deduced to design such bridge types more reliably and economically. Results show that inclusion of intermediate diaphragms and concrete barriers built integrally with the deck slab generally affect bridge performance. This conclusion can be used to evaluate existing bridges since any additional girder strength would decide on keeping the bridge in service or address its structural deficiency.</p>