Zero-skew bridge deck behavior at expansion joints

The TxDOT IBTS detail is a standard design for the slab end of bridge decks, which is commonly used at expansion joints. The IBTS detail creates a four-foot wide edge beam by increasing the section depth and reducing the spacing of the reinforcing steel. This detail has performed satisfactorily in the field; however, its origin as well as ultimate capacity is unknown. In addition, there is little previous research testing the edge of bridge decks.

For this reason, a zero-skew, full-scale bridge deck test specimen was constructed and loaded with AASHTO design loadings. This rectangular deck will simplify data analysis as well as providing a baseline for comparison to future, skewed test specimens. An un-thickened slab end detail, named the Uniform Thickness Slab End (UTSE) detail, was also tested with the aim of increasing construction economy. The final specimen was a three-span, 18-foot by 32-foot composite bridge deck on steel girders. It contained four test areas and two variables, the deck span (eight and 10-foot) and the slab end detail (IBTS and UTSE). Influence lines were used to determine the critical loading locations to maximize positive and negative moment in the bridge deck. The tandem and truck loading configurations, given in the AASHTO LRFD Bridge Design Specification, were applied at the HS-20 and HS-25 design load levels. Then, typical design overloads of 20%, 75% and 200% were applied, and finally, the bridge deck was loaded to failure.

The failure mechanism for all tests was punching shear at the edge tire, although, after punching, significant reserve strength remained. The punching shear prediction given by AASHTO LRFD is unconservative for the edge tests performed on this test specimen. However, when the effect of unbalanced moment is included in the ACI 318-02 provisions, conservative and accurate predictions result.

At service load levels and overloads, when spanning eight-feet, the IBTS and UTSE details performed well as far as crack propagation, relative deflections, and strain magnitudes. The IBTS and UTSE details were un-cracked up to the 200% overload, when spanning eight-feet. However, when spanning 10-feet, both details cracked near the design load level. The UTSE detail was more flexible than the IBTS and had a lower punching capacity due to its smaller section depth. The reserve strength measured in the four test areas on this bridge deck test specimen ranged from 6.1 to 4.9 times the HS-25 design load.