INFLUENCE BY SASHIGAMOI JOINT SHAPE AND STRESS STATE AROUND JOINT ON RESTORING FORCE CHARACTERISTICS OF TRADITIONAL WOODEN FRAME

Abstract

 In traditional wooden buildings, damage often occurs near the joints with cross-section defects during an earthquake. Also, in a wooden frame with large cross-section beam (called Sashigamoi), axial force generated in the beam when the columns inclined. Because the distance between columns geometrically shortened. Due to this axial force, the stress state generated in the column and the frame restoration force were changed, and there is a concern that damage might occur near the joint. Furthermore, in the calculation of critical strength, which is one of the calculation methods currently used to evaluate the seismic performance of traditional wooden houses, the restoring force characteristics are given to each seismic element without considering the different joint shapes or material property, and the restoring force characteristics of entire building is estimated by simply adding those shear forces. Seismic performance of the building may be overestimated or underestimated.

 Based on the above, the purpose of this paper is to quantify the variation of axial force and restoring force of the Sashigamoi, which were caused by the different joint shape of the column-Sashigamoi joint and the proportion of the frame. According to the data analysis of the full-scale frame experiment and the elemental experiment of joint, we conducted a series of studies such as the construction of the analysis model, and the proposal of the M-θ relation estimation formula considering the axial force of the Sashigamoi.

 The findings obtained are summarized below.

 (a) Based on the experiment and analysis results of the full-scale frame in the previous research, we compared the M-θ relationship occurred in joints with the same joint shape. It was confirmed that the proportion of the entire frame caused a big variation in the restoring force characteristics of the joint. It was shown that the existing method might not estimate the restoring force characteristics accurately. In addition, the relation between the inter-story deformation angle of the frame and the axial force fluctuation that occurs in the Sashigamoi is shown by an approximate expression.

 (b) Static bending experiment was carried out on eight elemental specimens with different proportions and grades as parameters, the axial force fluctuation of the Sashigamoi and variations in the M-θ relationship were confirmed. Even if the joint shape were same, the factors that affect the restoring force characteristics could change when the parameters of the specimen changed.

 (c) Based on past research, we proposed a formula for estimating the restoring force with consideration of the axial force of each Sashigamoi joint in this paper. We also constructed a simple model using the beam-column elements to simulate the experiment.

 (d) The relationship between the axial force of the Sashigamoi and the bending moment at both ends of the Sashigamoi was derived from each of the experimental results, estimation formulas, and analysis results. According to the comparation with the design value, it was shown that the experimental value was about 50% of the design value when the interlayer deformation angle was 1 / 30rad in some joint.