Abstract
The important structural elements of traditional timber structures in Japan are rotational resistances of column-beam joints. The restoring forces characteristics of their structures depend on the rotational resistances of the joints. Therefore, the elasto-plastic restoring force characteristics of embedment of joints are the most significant in order to evaluate the seismic performances of traditional timber structures.
The authors have already made clear the embedment mechanism of crosspiece joint which is the most basic and their rotational center is easily understood, and formulated the elasto-plastic restoring force characteristics of embedment of joints by using Elasto-plastic Pasternak Model (abbreviated to EPM).
However, there are many types of joints and their resisting mechanisms may be different. The crosspiece joint is the most simple and basic because of the symmetry in rotational mechanism. The formulation of restoring force characteristics of T-type joint including Sashikamoi has not been made because it is difficult to find the rotational center. Of course, it is possible basically to find the rotational center based on the geometrical and force conditions. However, the solution is complicate and it is difficult to express the position in a closed form.
Therefore, the authors assume the rotational center by T-type joint loading test results, focusing on the movement of the center of joint and rotational center. They assume the rotational center on the surface of Nuki (Fig. 11) and under the edge of Sashikamoi (Fig. 12). Then, the restoring forces characteristics are formulated based on the EPM, and parameters are determined in order to trace the restoring forces characteristics of the test results.
The loading tests are carried out as follows; The test setup is shown in Fig. 2. The column is made of steel and test specimens of Nuki and Sashikamoi are made of Japanese Cypress. Nuki consist of A, B, C, D, E, F and G types and Sashikamoi are S and K as shown in Fig. 3 and Table1.
The test results of joints are shown in Photo1～Photo4. The movement of the center of joint A-2 and S-2 are shown in Fig. 6 and Fig. 7. Then, the rotational center C is searched from the geometrical relation between the center of joint and rotational center. Distribution of the rotational center C is plotted in Fig. 9 and Fig. 10. As a result, the rotational center C mostly situates on the surface for Nuki, and under the point V for Sashikamoi.
Thus, the authors assumed the position of the rotational center and rotational embedment models are shown in Fig. 11 and Fig. 12. The EPM formulation of the Nuki and Sashikamoi are proposed in equations from (4) to (36). The restoring force characteristics of test results are simulated based on the EPM formulation and obtained the EPM parameters as shown in Table2 and some examples of simulated results are drawn in Fig. 13～Fig. 16.
As a conclusion, the simulated results of M-θ relations are fairly well comparing with the test results and the proposed formulations are confirmed to be adequate.
