Design and construction of UHPC-filled duct connections for precast bridge columns in high seismic zones

Abstract

One of the column connection types that has been recently emphasised for accelerated bridge construction (ABC) in high seismic zones is grout-filled duct connections. Experimental results have shown that the seismic behaviour of reinforced concrete columns connected to precast cap beams using this connection type is emulative of conventional columns. However, an alternative ABC connection is required to connect precast columns to shallow cap beams and footings due to insufficient anchorage length in those elements. Ultra-high-performance concrete (UHPC) was proposed in this study to be used instead of conventional grout in the connection to reduce the anchorage length. First, fourteen large-scale pullout tests were performed to investigate the bond strength of UHPC-filled duct connections. The test results showed that the incorporation of UHPC instead of normal grout as duct filler can reduce the bar embedment length by 50% or more. Second, design equations were developed based on the pullout test data to compute the bar development length in these connections. Subsequently, two half-scale precast bridge columns utilising this connection type at the column base were tested to verify the design equations. Full column plastic moment was developed in both specimens under cyclic loading with no UHPC-filled duct connection failure such as bar pullout even under 12% drift ratio cycles. Finally, a guideline was proposed based on the pullout and column test data for the design and construction of the UHPC-filled duct connections to facilitate field deployment.