最後，本研究提供建議，對於結構物的耐震設計若有鋼筋截斷的需求，應考慮拉力外移的效應，一般建議增加一斷面有效深度，避免因鋼筋截斷長度不足，而導致鋼筋產生滑移，造成鋼筋握裹破壞。 ;The purpose of this study is to understand the seismic behavior of rebar cut-off RC beams subjected to seismic loading, and to investigate if current building codes for rebar cut-off designs are adequate during seismic activities.
In this study, four RC beams are tested. The properties of the four beams are described as follows: the concrete compression strength of the concrete is 28 MPa and the yield strength for longitudinal reinforcement is 420 MPa. One beam is used as a control beam where no rebars are curtailed. The other three beams have longitudinal curtailed rebar according to code ACI 318-11 (American Concrete Institute). The curtailed beams have three #8 rebars placed on both upper and lower sides of the beam, and the center bar is curtailed. The curtailment of the two sets of rebar has two different designs. Both designs follow the code described in ACI 318-11, but the second design includes consideration of tension shift which is adopted from NZS 3101:2006. The second design is adopted to overcome the lack of detail in ACI 318-11 with regard to rebar cut-off in seismic performance design. Thus, the conventional design of rebar cut-off may lead to bond slipping due to insufficient cut-off distance when the beam is subjected to seismic loadings.
Excess transverse reinforcements are required in the region of the cut-off section by ACI 318-11. Two different types of transverse reinforcements are added and compared in the test. The first type is a #3 tie hooked on the center bar; the second type is a #2 closed hoop. This design allows the contribution of the transverse reinforcement to be observed with regard to prevention of bond slipping, and the results from both types are compared.
Finally, this study provides some recommendations for rebar cut-off design. The consideration of tension shift for rebar cut-off design of RC beams is necessary. Conventional cut-off design according to ACI 318-11 is inadequate because the general structure has to consider shear effect during an earthquake. Therefore, an additional length of effective sectional depth should be taken into account when the rebar cut-off is designed.
