Investigation of Damaged 12-Year Old Prestressed Concrete Box Beams

Abstract

An investigation was conducted of unexpected damage to a pair of three-span continuous-spread prestressed box beam bridges after 12 years of service. Routine inspection had revealed cracks in the box beams near the piers and abutments. An investigation was conducted to assess the condition of the beams in the bridges as well as their as-built properties and remaining strength. The investigation showed that the beams were built in accordance with the design drawings and specifications. One beam was tested under a combination of flexure and shear. These tests showed that the effective prestress was lower than standard design estimates. Measurable slip of the strands initiated as shear or flexure-shear cracks developed; however, the bond strength was sufficient for the strands to fail by fracture. The measured ultimate strength exceeded the analytical estimates by 7 to 9%. The conclusion of the investigation is that the cracks in the beams developed from a combination of conditions created by the design, detailing, and production of the beams.