Seismic Test Research On Knee Joints Lapped Splice Joint Located At Outer Side Of Column Top In Frame Structures With HRB335 Bars

Five specimens of knee joints in reinforced concrete frames under cyclic reversed loading with HRB335 longitudinal steel designed basing on"Code for Design of Concrete Structures"(GB50010-2002) are tested, which verifies the efficiency of seismic measures in knee joints with the negative moment reinforcement and linear lapped splice joint located at outer side of column top. Meanwhile, relevant issues the application of Wakabajashi lapped method on knee joints are discussed. By disposing the horizontal stirrups in upside of knee joint, the bending resistance of oblique section in knee joint has been improved, and the Wakabajashi lapped method has been developed. The main points and conclusions are summarized as following:①Construction measures of knee joints in reinforced concrete frames in which the steel bears beam and column negative moment: The first specimen is tested through the method of locating the negative moment reinforcement linear lapped splice joint at outer side of column top according to"Code for Design of Concrete Structures"(GB50010-2002), in which the column flank longitudinal reinforcement horizontally bends to knee joint after its extending to the top of column, the bend length is 12 times of longitudinal steel diameters, the overlapping length in the knee joints is 1.7laE and the inner diameter is equal to 6d. The results of the test illustrate that the weak surface through the ratius of main bar and the apex of the negative moment reinforcement has not appeared. It also proves the efficiency of seismic measures in knee joints which designed basing on"Code for Design of Concrete Structures"(GB50010-2002). Other four specimens adopt Wakabajashi lapped method. And by disposing the horizontal stirrups in upside of knee joint, the bending resistance of oblique section in knee joint has been improved, and the Wakabajashi lapped method has been developed. Moreover, the located position and quantity of the additional horizontal stirrups has been analyzed.②The anchorage of bottom beam bars of knee joints in reinforced concrete frames: according to"Code for Design of Concrete Structures"(GB50010-2002), the anchorage measures of bottom beam bars in exterior joints is the same with that of knee joints in reinforced concrete frames. Meanwhile, the horizontal length of 90°hooked anchorage should be no less than 0.4laE and the length of end piece should be no less than 15 times of longitudinal steel diameters. The current test shows that the anchorage measure is not effective enough. But the anchorage measure has been improved when the bottom beam bars of the fifth specimen anchored with anchor plate.