|主題||Tensile Capacity of Main Bar Splice at a Reduced Precast Shear WaIT Thickness|
|筆頭著者||Jose Caringal Adajar（University of Tsukuba）|
|連名者1||Teruaki Yamaguchi（Kabuki Construction）|
|連名者2||Hiroshi Imai（University of Tsukuba）|
This study focuses on the development of an earthquake resistant connection for precast concrete shear wall using an innovative, simple and economical technique of connecting vertical bars. As shown in Fig. 1, the design of this connection incorporates the idea of confining the four lap splices around the tubular steel sheath by a spiral steel. The ends of two main bars are inserted inside the steel sheath and grouted with high strength mortar. The proposed location of the joint is at mid-height of the precast shear wall which is less stressed during earthquake excitations.
This is the second in the series of experimental tests. The pioneering test was done in 1992 where its tensile capacity was investigated at 200mm wall thickness. The proposed connection was concluded to be structurally adequate as it provided tensile resistance more than main bar yield strength when the wall thickness was 200mm and the splice length was 20 times the lapped bar diameter. This conclusion led to the idea of further testing the tensile capacity of the connection at a reduced wall thickness of 150mm and 180mm. The main bar was changed from D25(SD390) to D22(SD490) and the steel sheath diameter from 42mm to 38mm. The variation of strength was done because in the first series, all connection failures happened after yielding of main bar. In this series, collapse before main bar yielding was expected.
The conclusions and recommendations drawn are the following:
1. The tensile capacity of main bar splice is reduced when the thickness of the wall is reduced from 200mm to 180-mm and 150-mm.
2. Within the elastic stage of main bar, the failure of the connection is by bond on the sheath.
3. A main bar spacing of 300mm in 180mm-thick wall, pitch of spiral of 30mm and splice length of 25d will provide direct pullout of main bar.
4. At 150mm and 180mm-thickness, the yield of the connection is at approximately 18.0-tonf load and a displacement of 1.5mm to 2.0mm which is almost equal to half of sheath lug width.
5. From 15d to 25d splice length, the maximum load increases as the splice length increases. The maximum bond stress on the sheath is approximately 70kgf/cm2.
6. The diameter of steel sheath has a negligible effect when the wall thickness is 150mm. At 180-mm thickness, 42-mm sheath gives slightly lower resistance compared to 38mm.
7. Spiral steel with greater pitch is more stressed compared to that with smaller pitch although smaller pitch has greater confinement capacity.
8. Increasing the spacing of main bar from 200mm to 300mm will provide slight increase on the capacity.
It is recommended to conduct additional tests in order to obtain quantitative information on the failure mechanics of the connection.