NONCONTACT LAP SPLICES IN BRIDGE COLUMN-SHAFT CONNECTIONS

Lap splices in reinforced concrete members typically consist of bars overlapped and placed in contact with each other. In the case of a large-diameter foundation shaft connecting to a smaller-diameter column, it is not possible to have the longitudinal bars be continuous, nor is it possible to provide a standard lap splice; instead an offset or noncontact lap splice of the longitudinal bars is required. With a noncontact lap splice, transfer of forces from one spliced bar to the other occurs through the surrounding concrete, and transverse reinforcement is typically required to provide satisfactory splice performance. Current code provisions on noncontact lap splices are very limited. This study experimentally investigated the behavior of noncontact lap splices in bridge column-shaft connections. Tests were performed on near full-scale panel specimens, representing a cross-section of a column-shaft connection, and on 1/4 scale column-shaft specimens under both monotonic and cyclic loading. Variables investigated included lap splice length, lapped bar spacing, and spacing of transverse reinforcement. Specimen performance was evaluated in terms of load capacity, failure mechanism, and strength degradation. Two-dimensional and three-dimensional truss models were developed to predict the behavior of noncontact lap splices. Experimental results supported the proposed behavioral models. Inclined cracks developed in the concrete which defined compression struts running between the offset lapped bars. Transverse reinforcement was required to provide equilibrium to the struts. Tests on specimens detailed based on the proposed models resulted in no strength degradation or slippage of the lapped reinforcing bars even when subjected to cyclic loading. Equations were proposed for the design of noncontact lap splices, including recommendations for required overall lap length and transverse reinforcement.