Experimental Behavior of Pretensioned Bent Caps with Internal Voids for Weight Reduction

Precast bent caps offer the opportunity to reduce onsite labor and materials and to accelerate the speed of construction. For many bridges, the weight is manageable for shipping and placement without the need for large cranes. For large bent caps, the weight can become a significant challenge for construction. Internal voids can be effective in reducing the weight but introduce the potential for the formation of shear cracks at service loads, because the shear width is smaller than in a solid bent cap. Internal voids are an attractive option when bent caps are pretensioned, because pretensioning delays the formation of cracks. This paper presents the results of a full-scale experimental test program that investigated the progression of damage and the failure mechanisms of pretensioned bent caps with internal voids. Test specimens were subassemblies of a portion of a multicolumn bent that included an overhang, a negative bending region at the connection to a column, and a positive bending region. The variables investigated were the presence of a void, the amount of prestressing, and the void termination location. Results indicated that voided caps had similar flexural behavior to solid caps, but were more prone to shear cracking and had more brittle failures. The use of a higher prestressing force was found to significantly delay flexural cracking but to have a minor effect on delaying the formation of shear cracks. The location of void termination adjacent to the connection region influenced the extent of the damage at failure.