Forensic Collapse Investigation of a Concrete Bridge with Timber Piers

摘要

This report outlines the forensic investigation of the collapse of Bridge No. SN 019-5010 in DeKalb County,Illinois on August 19, 2008. The bridge consisted of three 42 feet precast prestressed concrete deck beamssimply-supported by concrete pile caps with a timber pile foundation. Assessment based on site investigation, insitu readings, and analysis indicated that a geotechnical or superstructure failure may be ruled out. Samples ofthe oak timber piles were retrieved and tested under pure compression as well as combined compression andflexure. Laboratory testing results of these specimens were used to calibrate an analytical model of a full-scalesingle timber pile. The analytical model considered both symmetrical and unsymmetrical loading of the bridge.The results of the analytical model were used to determine the required live load to initiate collapse. The resultsof the investigation indicate that structural overload, leading to fracturing of the timber piles in combinedcompression and flexure, is the likely reason for the bridge failure.