Splices in reinforced concrete columns in older buildings, or within the nonparticipating frames in some newer buildings, were typically designed as compression lap splices. Compression lap lengths are typically short (20 to 24db ), and only light transverse reinforcement is provided over the lap length. Observations of column damage following earthquakes have revealed that these splices perform poorly; however, relatively sparse information exists to assess the expected performance for typical conditions. To address these needs, a PEER Center research program was undertaken at UCLA to conduct testing of full-scale columns under a variety of conditions. The test specimens consisted of cantilever columns with a point load applied at the top. The 450 mm square column sections were tested under reversed cyclic lateral load with constant axial load. The primary variables include the level of axial load, the ratio of moment to shear, and the load history. Information on the test program, experimental observations, results, and conclusions are presented in this report.
Specimens with 20db lap-splice length and poorly confined cross section behaved unsatisfactorily under cyclic lateral loading. The lateral strength of specimens started degrading at lateral drift levels of 1.0%–1.5%. The lateral strength degradation was due to the deterioration of the bond between the reinforcement bars and the surrounding concrete. Although higher levels of the applied axial load slightly increased the lateral strength of the specimens, changes in shear demand did not appear to influence the lateral load at which bond deterioration initiated.
The degradation rate of the lateral strengt h was affected by the lateral displacement history and shear demand. The specimen subjected to a near-fault displacement history maintained more than half of its lateral strength up to a drift ratio of 5%, whereas the specimens with standard displacement history lost more than 75% of their lateral strength at that drift level. A comparison of specimens with moderate to high shear demand revealed that lateral strength degradation also increased with higher shear demand.
The rotational response of the sp ecimen was predominantly influenced by the slippage of reinforcement bars. At 1.5% late ral drift ratio, 80%–85% of the measured rotation was due to slip.
Full List of PEER Reports: click here.