The Evaluation for the Structural Performance of Traditional Townhouses with Timber Through Columns in Japan

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1 The Evaluation for the Structural Performance of Traditional Townhouses with Timber Through Columns in Japan Hiromi SATO 1, Mikio KOSHIHARA 2, Tatsuya MIYAKE 3 and Izuru KAWAJIRI 4 1 Research Associate, Department of Human and Social Systems, Institute of Industrial Science, the University of Tokyo, Japan sato31@iis.u-tokyo.ac.jp 2 Professor, Institute of Industrial Science, the University of Tokyo, Japan 3 President, Nihon System Sekkei Architects & Engineers Co., Japan 4 Nihon System Sekkei Architects & Engineers Co., Japan ABSTRACT This paper presents a study of the structural performance of traditional timber townhouses in a historical town in Japan. The aim of this study was to clarify the structural performance of traditional townhouse with timber through columns in Japan. The target area Sawara has many traditional timber townhouses built in from the late of 18th century to the early 2th century and these townhouses have few structural walls in the frontage direction at the first floor. In the previous study, the structural evaluation of the frame with through columns was perfoermed. Moreover the earthquake response analyses of the townhouses were performed to clarify the seismic behavior. In this study, the earthquake response analyses were performed on the five townhouses in Sawara with through column or jointed column as parameter. As results, it was clarified that the structural performance of the through columns was greatly influenced by the wall quantity at each floor. Keywords: traditional timber construction, seismic diagnosis, earthquake response analysis 1. INTRODUCTION 1.1 Background of research Japan has a long history of earthquakes and timber structures in Japan have suffered great damage caused by strong earthquakes. Old traditional timber structures suffered especially heavy damage. Besides, many of historical towns in japan have many traditional timber buildings that they have uniform construction system or structural elements in each area. If the structural performance of their system and elements is clarified, the technique of earthquake-proofing suitable for those buildings can be examined. Therefor it is important to clarify the structural performance of their characteristic elements in each historical area.

2 October 215, Kathmandu, Nepal 1.2 Characteristics of timber through column In the previous study, the static tests and the seismic analysis of the frame with through columns were performed. The static tests were conducted on the three type specimens that have the overall wall at the second floor. As results of the test, the structural performance of the frame with through columns was verified (Sato, 21 and 212). The seismic analysis was performed on the mass system model with parameter study. In the case the townhouse has not the wall at the first floor, it was verified the relationship of the wall quantity at the 2nd floor (Sato, 212). 2. OBJECT TOWNHOUSES 2.1 Sawara district and the target townhouses The research area of the present study is the Sawara district of Chiba Prefecture, which is located near Tokyo. The Sawara district is a historical town arranged on the riverside and contains traditional timber townhouse and storehouse with thick walls. They are built in from the late of 18th century to the early 2th century (The Sawara City, 24). In townhouses in this area, the frontage direction of the first floor has few walls and the frames which consist of through columns. In this study, five townhouses faced on the main street were targeted (Figure 1 and 2). Figure 1: Facade of the target townhouses Excluded the survey N Through column Y+ X+ FKS KBR SNTK KBK SBD Figure 2: Plan on the first floor of objects New Technologies for Urban Safety of Mega Cities in Asia

3 2.2 Seismic diagnosis Seismic diagnosis was performed on the target townhouses based on the investigation (The Japan Building Disaster Prevention Association, 24). The marks of the seismic diagnoses at the first floor varied from.3 to.2 in the X direction (Table 1). The mark calculated horizontal load-carrying capacity by necessary horizontal load-carrying capacity and if it was less than 1., the building has possibility of collapse by large earthquake in Japan Cord. The seismic diagnosis on five townhouses indicated high possibility of collapse because these townhouses on the X direction of the first floor have few bearing walls. Table 1: Characteristics of the object townhouses name FKS KBR SNTK KBK SBD Construction year unknown unknown 188 Building area (m 2 ) [Total floor area (m 2 ) ] 47.5 [87.1] 28.7 [51.8] 41.4 [79.7] 49.1 [91.7] 35.5 [63.3] Number of through columns Size of through columns (cm) Mark of seismic X diagnosis *1,2 Y *1: at the first floor *2: based on reference [5]; -1.5: Safe, : Temporarily Safe,.7-1.: Possibility of Collapse, -.7: Dangerous (High Possibility of Collapse) 3. EARTHQUAKE RESPONSE ANALYSIS 3.1 Model of analysis To evaluate the structural performance, the five townhouses were modelled two type as three-dimensional frame model, as shown in figure 3. To clarify the influence of the through column on whole performance, the models of have through columns with the actual situation and the models of consist without through columns as replacing through column with jointed column. The horizontal load-resisting elements are mud walls and frames which consist of the through column and beam. The skeleton curves of the structural elements were shown in figure 4. The models of hysteresis characteristics were referenced (Architectural Institute of Japan, 21). The roof truss was not modeled but just considered to the weight. Figure 3: Analysis models (FKS) The Evaluation for the Structural Performance of Traditional Townhouses with Timber Through Columns in Japan

4 October 215, Kathmandu, Nepal Load (kn/p) Deformation angle (mrad.) (1) mud wall and floor (2) beam-column joint (3) joint 3.2 Input wave Mud wall Boading horizontal diaphragm Moment (knm) Sashikamoi Tenon joint (+) Tenon joint (- ) Deformation angle (mrad.) Figure 4: Skelton curves of structural elements The input waves of the analysis were three simulated earthquake motions equivalent to design earthquake ground motion based on the Japanese Code, as shown in figure 5. The simulated waves were modulated to the standard level using coefficient.85 and the input scale was changed to determine the seismic clearance of them. Moreover, to understand the limit of collapse, the input scale of the simulated waves were controlled Tenon and Cotter pin Cramp iron acceleration (gal) acceleration (gal) acceleration (gal) 6 4 No time (sec) 6 4 No time (sec) 6 4 No time (sec) (1) Time history waveform (2) acceleration response spectrum 3.3 Results of analysis Acceleration (gal) Figure 5: Characteristics of the input waves Period(s) The earthquake response analysis was performed on the five townhouses (Table 2 and Figure 6). In the results of the model, KBR and SNTK were collapsed by the large earthquake scale on equal with the Japanese Code, therefore they were not satisfied the structural requirement of the Japanese Code. The seismic shear coefficient (C ) varied from.6 to.42. In the results of the model, it was found that in the case of almost half, they were collapsed by the same input scale of model. The seismic shear coefficient varied from.4 to.41. It was that the structural performance of FKS and SBD became lower and that of KBK was almost the same No.1 No.2 No.3 New Technologies for Urban Safety of Mega Cities in Asia

5 Table 2: Results of the analyses (X) Type Wave Value of FKS KBR SNTK KBK SBD Input scale No No.2 Maximum load * No.3 (kn) Ave *2 C Input scale No No.2 Maximum load * No.3 (kn) Ave *2 C *1: at the first floor, the scale of the input wave is on the safety clearance *2: the seismic shear coefficient, the maximum load divides by the weight of the building *3: in the shaded parts, the maximum load were adopted before collapse 12 8 FKS KBR SNTK (1) FKS (input scale: 1.) (2) KBR (input scale:.6) (3) SNTK (input scale:.5) 12 8 KBK SBD (4) KBK (input scale: 1.7) (5) SBD (input scale: 1.5) Figure 6: Load - displacement relationship (1F-X) The Evaluation for the Structural Performance of Traditional Townhouses with Timber Through Columns in Japan

6 October 215, Kathmandu, Nepal 3.4 Comparison with through column and jointed column The results of the model with through column ( model) are compared with that of the model without through column ( model), as shown in table 3. As the result of the model, FKS, KBK and SBD have enough structural performance. On the other hands, as the result of the model, Only KBK has high structural performance. Moreover, the bearing load per one through column and the bearing load ratio were calculated from difference of the two models. In the case of FKS and SBD, they have high seismic coefficient in the model and the bearing load, because they have many or large size of through columns. In the case of KBR and SNTK, they have few structural performance for lack of through columns and other structural elements. However, in the case of KBK, though there were through columns of the fairly large size the bearing load of the through column was very small. It was indicated that there are also other factors that determines the structural performance of through column in addition to the number and the size of column and the wall quantity at the second floor. Table 3: Seismic Performances on the frontage direction (X) FKS KBR SNTK KBK SBD Through Number column Size (cm) Total weight (kn) Seismic diagnosis * Px-1F (kn) Px-2F (kn) Structural Px-2F/1F Performance * C Bearing load *3 (kn) Load ratio *4 (%) *1: Px is bearing capacity, *2: the seismic shear coefficient, refer to the Table 2 *3: the bearing load is the value per one through column. it was calculated from difference of two models *4:bearing load ratio of the through column, ( - ) / 1, refer to the Table 2 4. VERIFICATION OF THROGH COLUMN Furthermore, to verify the other factor that determines the structural performance of through column, the structural analyses were performed on the new models changing the wall quantity. It was focused on the wall quantity at each floor and the relationship between them. 4.1 Model of analysis In the results cited above, it was focused on the difference between KBK and FKS or SBD. The difference between KBK and other two townhouses were few number of through columns and high performance at the first floor. Therefor the new models were made as changing the wall quantities at the first floor or the second floor, as shown in table 4. New Technologies for Urban Safety of Mega Cities in Asia

7 4.2 Results of verification Table 4: Parameter of the new models name FKS KBK +1F +2F -1F Seismic diagnosis * Px-1F (kn) Px-2F (kn) Px-2F/1F *: Px is bearing capacity As the results of new models, the bearing load per one through column was indicated from.8 to 1.5 (Table 5 and Figure 7). In the result of FKS, the structural performance of the whole townhouse, as the maximum load and the seismic coefficient, became larger but the performance of the through column, as bearing load, became decrease. In the result of KBK, when the wall quantities at the second floor was increased, the structural performance of the whole townhouse was the almost same and that of the through column improved slightly. Moreover, in the case of KBK decreasing the walls at the first floor, though the structural performance of the whole townhouse decreased too that of the through column improved. Table 5: Result of the new models FKS KBK name +1F +2F -1F Maximum load (kn) *1 C Bearing load *2 (kn) Load ratio *3 (%) *1: the seismic shear coefficient *2: the bearing load is the value per one through column. it was calculated from difference of two models *3:bearing load ratio of the through column, ( - ) / FKS +1F 15 1 KBK +2F, - 1F F F F F - 1-1F - 1F (1) FKS (2) KBK Figure 7: Load - displacement relationship of new models (1F-X) The Evaluation for the Structural Performance of Traditional Townhouses with Timber Through Columns in Japan

8 October 215, Kathmandu, Nepal 4.3 Factor on the structural performance of through column The new models of FKS and KBK increasing the walls at the second floor and the original model of KBK have the fairy enough wall quantity about the first floor. However their through columns were bearing small load. Meanwhile, in the new model of KBK decreasing the walls at the first floor, there were few structural performance, however the through columns were bearing much load. Thereby, it was indicated that the factors that determines the structural performance of through column are the excess of the walls at the first floor and the relationship the wall quantity between the each floor. 5. CONCLUSIONS In this study, the earthquake response analyses were performed on the five traditional townhouses. It was presented the following conclusions: 1. As results of the earthquake response analysis with actual situation ( model), the seismic shear coefficient (C ) varied from.6 to The bearing load ratio of the through column varied from 2.3 to 49.9 %. The bearing load per one through column varied from.3 to 3.2 kn. 3. In the seismic diagnosis based on the current building code in Japan, all of the five townhouses have high possibility of collapse. However, in the earthquake response analysis, three townhouses (FKS, KBK and SBD) have the structural performance which is needed in Japanese Code. 4. The factors that determined the structural performance of through column are the excess of the walls at the first floor and the relationship the wall quantity between the each floor. REFERENCES Architectural Institute of Japan, 21, Fundamental Theory of Timber Engineering, Sato, H., and Koshihara, M., 21, Horizontal load capacity of sashikamoi frame with through column, Summaries of Technical Papers of Annual Meeting Architectural Institute of Japan, C-1, Sato, H., Koshihara, M., and Miyake, T., 212, Horizontal load capacity of sashikamoi frame with through column Part 2 Effects of seismic performance of second floor on through column, Summaries of Technical Papers of Annual Meeting Architectural Institute of Japan, C-1, Sato, H., Koshihara, M., and Miyake, T., 214, Seismic behavior of traditional timber frames with through columns of townhouses in Japan, Summaries of 13th International Symposium on New Technologies for Urban Safety of Mega Cities in Asia, Myanmar, The Japan Building Disaster Prevention Association, 24, Seismic diagnosis and reinforcement of timber house The Sawara City, 24, Townscape of the Sawara district New Technologies for Urban Safety of Mega Cities in Asia