Long Term Investigation of Live Load on Illinois Bridges

摘要

The Federal Highway Administration (FHWA) is requesting that all states implement the American Association of State Highway and Transportation Officials (AASHTO) Load Resistance Factor Design (LRFD) specifications for bridge design beginning in 2007. The LRFD specifications is considered to be state-of-the-art and was developed to improve the reliability of bridges and increase safety of highway structures rn[FHWA 2004]. In the design of bridges, the LRFD specifications require an increase in bearing forces. As a result, the required shear and reaction forces in bridge girders may increase to over twice the Load Factor Design (LFD) specifications. This is caused by the HL-93 truck loading requirement along with the lane loadings to be considered together in the LRFD code, as well as an increase in the shear distribution factor for some girder spacings. rnThe purpose of this study was to examine the live loads on Illinois Bridges. Shear forces were measured and recorded in several bridges for a duration from six to eleven months. This required the instrumentation of several strain gage rosettes on two girders for each bridge. Twelve bridges were selected to be tested; six were located along the I- 55 corridor and the other six were located along the I-70 / I-270 corridor in Illinois. These bridges were chosen such that the sample of bridges included a variety of characteristics, which included number of spans, span lengths, skew angles and girder materials, steel and concrete.