An instrumentation and load-testing analysis of the 536-ft, two-span, open spandrel arch-rib hennepin avenue bridge over the mississippi river in minneapolis, minnesota, was conducted to measure the transverse load distribution among the six arches of the bridge and to determine whether the buckled webs of the arch ribs carry any load. When the structure was rated for hennepin county in 1983, the loaddistribution and the ability of the buckled web plates to carry axial stress were questioned. Thus, an instrumentation analysis under static load was performed. The bridge was instrumented with 18 straingauges and was loaded with three 27.5-ton tandem dump trucks positioned in nine different loading arrangements. strain readings were averaged for each loading to determine the magnitude of load carried by each arch rib and then compared with a computer-modeled (linear) transverse distribution. It was found that the arch ribs carried not only axial stress, but also stress due to bending moments. It was concluded from the study that the floor beams and diaphragms do not transfer loads from one side of the bridge to the other. The results of the web testing demonstrated that a nominal axial load was being carried by the web, and that, although buckled, it was working effectively through a tension-field mechanism similar to that of a simple truss. This paper appears in transportation research record no. 1180, bridge design and testing.
Abstract