Load Rating of the Lahontan Arch Spillway Bridge at Fallon, NV

This study focuses on the load-rating analysis of a five-span, concrete arch bridge located at Fallon, NV. The Lahontan Dam Spillway Bridge was constructed in 1915 and, after approximately 94 years of service, the bridge has deteriorated. The U.S. Army Engineer District, Sacramento, inspected the bridge in 2009 and determined that the bridge is in poor condition. Advanced section loss, deterioration at different locations along the full length of the bridge, and severe spalling in the three main arch beams and in the piers were the main defects observed. These defects put in jeopardy the structural integrity of the bridge; thus, the bridge is currently closed to traffic. The purpose of the load rating was to identify the safe load capacity of the bridge under today’s design vehicle and legal loads. The load ratings were performed with two specifications, the American Association of State Highway and Transportation Officials’ (AASHTO) Manual for the Condition Evaluation of Bridges load factor rating and the AASHTO Manual for Condition Evaluation and Load and Resistance Factor Rating of Highway Bridges. The load ratings were performed for the following types of loading: notional HS20-44; the HL93; and the legal load for vehicles Type 3, Type 3S2, and Type 3-3. The rating factors’ results confirmed the poor condition of the bridge described in the 2009 inspection report. It was concluded that the bridge design does not follow current standards; thus, a weight limit sign is required to be posted on the bridge. The recommended weight limit based on the LFR at inventory level is 7 tons of the Type 3 loading, 11 tons of the Type 3S2 loading, and 14 tons of the Type 3-3 loading.