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Title: Load Testing: Not Just for the Big Bad Bridges

Author(s): Andrew J. Foden and Zachary James Van Brunt

Publication: Web Session



Appears on pages(s):



Date: 11/19/2018

In 2016, Rhode Island DOT identified a group of small reinforced concrete structures that had been built circa 1930 and that were rating poorly using default AASHTO LRFR assumptions. The structures were semi-rigid concrete frames, with two sloping reinforced concrete abutments supporting a separately-cast variable-depth concrete slab, tied together with reinforcement and a series of river rock “bonding stones”. The clear span for the slabs was merely 10ft, but the poor ratings led to potential load postings on rural roads throughout the state. Three of the slabs were chosen for diagnostic load testing. Strain sensors and LVDTs were installed on the slab soffits, and testing was conducted using 65-kip trucks. To provide an economical load test for the small structures, instrumentation and testing was completed in as little as 48 hours from sensor installation to removal, using a crew of 2-4 people. Results from the load testing allowed for calibration of finite element models of the top slab. Notably, a level of fixity was observed in some slabs due to the location of the reinforcement and the bonding stones. Distribution of wheel loads through the fill above the structures was also found to be much greater than that assumed by AASHTO. State legal loads were then applied to the calibrated finite element models to provide general distribution factors that could be used for current and future load ratings. These distribution factors were typically 30-70% of the original factors.