Early-Age Deck Cracking from Asymmetric Thermal Behavior in Skewed Adjacent Box Beam Bridges

Abstract

This study investigates the causes of early-age deck cracking for skewed composite adjacent box beam bridges with integral abutments. It hypothesizes that cracking is attributed to (1) asymmetric thermal movements in a skewed deck and (2) thermal restraints from an integral abutment design, as well as box beams and post-tensioned tie rods. To verify this hypothesis, a bridge in Ohio was instrumented for measuring temperature and strain. The field investigation aimed at observing thermal movements of the deck for about five days immediately after placing the concrete deck. No visible cracks were found after completing the deck and abutments; however, 10 months later, visible cracks were observed. These cracks were mainly observed near the edges of the deck where it adjoins with an abutment, as well as at acute corners. Also, it was observed that a temperature gradient of 8°C developed through the deck depth. The rotation and expansion (or contraction) from the temperature gradient are partially restrained by the presence of box beams and post-tensioned tie rods, resulting in the effective tensile strain at the bottom surface. It is concluded that the skewed deck geometry causes an asymmetric thermal expansion, contraction, or both, leading to increased tensile strains. They exceeded the threshold cracking strain at the acute corner and at mid-width along the deck edges where they adjoin with asphalt roadways. It is also concluded that thermal restraints applied after completing the bridge is another factor for cracking. They are imposed by design features, including soil backfills and asphalt pavements, which are inherent to integral abutment bridges.