Experimental Investigation of Crushing Capacity of I-Girder Webs Containing Post-Tensioning Ducts

The shear capacity of a post-tensioned, concrete I-girder may be influenced if the crushing capacity of the web is reduced by ducts for the tendons. An experimental investigation was conducted on compressively-loaded, high-strength concrete panels with embedded post-tensioning ducts to better understand the parameters influencing girder web crushing behavior. The panels were intended to represent portions of a girder web subjected to shear-induced, principal compressive stresses. Material properties and construction procedures utilized in the fabrication and erection of bridge members in the field were considered.

The primary goal of this study was to assess the impacts of various parameters on web crushing capacity. The results were needed to determine which variables should be considered for shear testing of full-scale girders. The parameters considered in the panel test program were duct type, grouting, member thickness, and the inclusion of confining reinforcement near the ducts.

Notable findings from this study indicate that 1) elements with plastic ducts exhibit lower capacities than those with steel ducts, 2) a significant size effect exists when determining crushing capacity, and 3) the presence of a small amount of reinforcement placed near a duct through a member’s thickness can greatly improve its capacity.

Results indicated that American design codes may be severely unconservative in their handling of ducts when designing for shear. Recommendations to refine and expand the standard approach for reducing web crushing capacity were developed. Additionally, a new means of estimating web crushing capacity was introduced.