JMEC has been structural consultant to evaluate rehabilitation options for the Kings Mountain Road Bridge over West Union Creek (Caltrans Br. No. 35C0123). The bridge was built in 1905. It is a single span earth filled concrete spandrel arch on reinforced concrete abutments with monolithic wingwalls supported on unknown foundations (assumed to be on spread footings for evaluation purposes). It has a clear span of 15'. The total length of the bridge is 22' and the overall width is 22.1' and a clear width of 19.5' between concrete railings. The bridge has scouring problem and it is functionally obsolete with a sufficient rating of 55.6 according to Caltrans. Due to its historical significance and neighborhood's objection, replacement of this bridge is not preferred.

As part of this project, load rating was performed for the concrete arch bridge and the adjacent 2-span timber pedestrian bridge (with 36'-8' span and 44' total length) that was built in early 70's.

Bridge load rating for the arch bridge was evaluated by Load and Resistance Factor Rating (LRFR) per AASHTO Manual for Bridge Evaluation to determine rating factor for AASHTO legal vehicles. CSiBridge computer program was used to model the arch with foundation springs to model the foundations.

Load rating for the pedestrian timber bridge  was evaluated for Strength I load combination per AASHTO LRFD Guide Specifications for the Design of Pedestrian Bridges; 2nd edition and with 2015 Interim Revisions. Due to lack of as-built record, timber material properties were based on values shown in Table "Reference Design Values for Visually Graded Sawn Lumber" of AASHTO LRFD Bridge Design Specifications, 8th Edition, 2017.

The inventory R.F. for the timber bridge was 0.73 and the operating R.F. was 0.96. The timber log stringers that made up this bridge were later damaged by rainstorm in 2023 and the bridge was repaired and strengthened.

The inventory and operating R.F. were found to be lower than the HL-93 load for the arch bridge. The recommendation was to construct scour mitigation measures, maintain the appearance of the arch bridge and strengthen the bridge by installing steel arch lining underneath the bridge with new foundations.

Project Role:  Prime Design Consultant

Clients:  Town of Woodside - Department of Public Works

Schedule:  Completed in 2021
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Kings Mountain Road Bridge
Looking Upstream
Timber Pedestrian Bridge