Quantification and Interregional Comparison of Structural Characteristics of Traditional Wooden Houses in Japan

Transcription

1 International Symposium on Earthquake Engineering, JAEE, Vol., Quantification and Interregional Comparison of Structural Characteristics of Traditional Wooden Houses in Japan Yasuhiro NAMBU, Jian JIAO, Noriko TAKIYAMA 3 and Yasuhiro HAYASHI Graduate Student, Dept. of Architecture and Architectural Eng., Univ.,, Japan, rp-nambu@archi.kyoto-u.ac.jp Graduate Student, Dept. of Architecture and Architectural Eng., Univ., M. Eng.,, Japan, rp-jiao@archi.kyoto-u.ac.jp 3 Member of JAEE, Research Associate, Dept. of Architecture and Architectural Eng., Univ.,, Japan, noriko@archi.kyoto-u.ac.jp Member of JAEE, Prof., Dept. of Architecture and Architectural Eng., Univ.,, Japan, hayashi@archi.kyoto-u.ac.jp ABSTRACT: The authors investigated structural details in eight regions. Our conclusions are as follows. (a) Structural characteristics and seismic hazards are various from different regions. (b) Directions of yield base shear coefficients can be confirmed for some regions. (c) The directionality of yield base shear coefficients can be clearly confirmed for some regions. (d) Weight can be roughly estimated from floor area because weight per the first floor area is approximately constant value if the region and number of stories is identified. Key Words: Traditional wooden houses, Regional characteristics, Structural characteristics, Seismic hazard INTRODUCTION Recently, most of fatalities came from the collapse of old wooden houses according to the recent earthquake damage statistics in Japan. Therefore, the seismic retrofit of old wooden houses is very important. However, it is not reasonable enough to perform seismic retrofit by the routine method in all cases because structural characteristics seem to vary from region to region. Thus, we have conducted the structural surveys of traditional wooden houses in historic districts and have accumulated their structural data. In this paper, as the first step towards the regional earthquake countermeasures, we have quantified the regional structural characteristics of traditional wooden houses. First, we described the current conditions of seismic hazard in the 9 districts designated as the Important Preservation District for Groups of Historic Buildings (IPDGHB) (Agency for Cultural Affairs). Next, we compared structural characteristics of traditional wooden houses in the eight regions, which have already been investigated by authors. The height, floor area, weight, the number of columns, and yield base shear coefficients are used as indices for describing the structural characteristics. Finally, we pointed out the necessity for implementing the earthquake countermeasures corresponding to the local structural characteristics of traditional wooden houses.

2 INVESTIGATION AREAS AND HOUSES We select eight regions which have already been investigated by authors. Figure shows Investigation areas. The following is investigation areas in order from the north. () Yamoto-cho (now, Higashimatsushima-shi), Kanan-cho (now, Ishinomaki-shi) in Mono County and Nango-cho (now, Misato-cho) in Toda County, Pref. (Shimizu H. 5). () Monzenmachikuroshima-cho, Wajima City, Ishikawa Pref. (Shimizu H. ). (3) Kisohirasawa, Shiojiri City, Nagano Pref. (Shiojiri City Board of Education 9). () -cho Kita, Nantan City, Pref. (Takiyama N. ). (5) City, Pref. (Ida S., Earthquake Research Committee Kyomachiya ). () Ominato-cho,, Mie Pref. (Kiso K. ). (7) -cho, Arida County, Wakayama Pref. (Watanabe C., Yokobe T. ). () -cho, Muroto City, Kochi Pref. (Tai T. ). For the sake of simplicity, in the order of the above, we call each region (), (), (3), (), (5), (), (7) and (). Table shows Investigation areas and the features of houses. In addition, Fig. shows the number of investigation houses. The following is the feature of the investigation houses in each region. In addition, Fig. 3 shows a typical house in the investigation areas. Fig. Investigation areas (a) (e) 5 5 Number of the investigation houses 5 Fig. Number of the investigation houses (b) (f) (c) (d) (g) (h) Fig. 3 Typical houses in the investigation areas

3 Table Investigation areas and the features of houses Areas Survey Year Designated Cultural Property - IPDGHB IPDGHB IPDGHB - - IPDGHB IPDGHB Main Roof (without paving mud) Metal sheet Thatch (covered by steel plate) (without paving mud) (with paving mud) Meral sheet Thatch (with paving mud) (with paving mud) (with paving mud) (with paving mud) Main Exterior Wall Mud wall Mud wall Mud wall Wooden wall Mud wall Mud wall Mud wall Mud wall Main Foundation Cut stone Ground sill Ground sill Conerstone Conerstone Conerstone Conerstone Conerstone Interval of Buildings Separate Approach Touch Separate Touch Approach Touch Approach In, houses (3 one-story houses, and 7 two-story houses) had been investigated in 3. Clay tile roofs without mud paving, metal sheet roofing and thatch roofs covered by steel plates are widely existed on houses in. There are also a large amount of houses with mud external walls and cut stone foundation. Many two-story houses, the floor area of the second floor are less than the floor area of the first floor. In, houses ( one-story houses and 7 two-story houses) had been investigated in 7. Roofs are often covered by clay tiles without paving mud. Houses with mud external walls and ground sills can often be seen in. In, houses (all are two-story houses) had been investigated in 9. Majority of the houses have gabled roofs (Kirizuma-zukuri) with the entrance at the side parallel with the ridge (Tsuma-iri). Roofs are often covered by clay tiles with paving mud or metal plates, and the foundation are ground sill. External walls are often made of mud, and for some houses, wooden walls exist on the lower side of the mud walls in the first floor. In addition, many houses share walls with houses besides. In, houses (all are one-story houses) had been investigated in. Roofs of houses in are covered by thatch, and wooden walls and cornerstone foundations widely exist. In, 9 houses ( one-story house and two-story houses) had been investigated in 7. Among the two-story houses, low-ceilings (Tsushinikai) exist in second floor in 7 houses. Many houses have gabled roofs with side entrance (Kirizuma-zukuri Tsuma-iri) and are often covered by clay tiles with paving mud, mud external wall and cornerstone foundations. Walls of adjusted houses often touch with each other, and many houses share side walls. In, houses ( one-story houses and two-story houses) had been investigated in 5. Many houses have gabled roofs with side entrance (Kirizuma-zukuri Tsuma-iri) and are often covered by clay tiles with paving mud, mud external walls and cornerstone foundations. In, 9 houses ( one-story houses and 7 two-story houses) had been investigated in. 5 of the 7 two-story houses have low-ceilings (Tsushinikai) in second floor. Many houses have gabled roofs with side entrance (Kirizuma-zukuri Tsuma-iri) and are often covered by clay tiles with paving mud, mud external walls and cornerstone foundations. Walls of adjusted houses often touch with each other, and some houses share side walls. In, houses (3 one-story houses and two-story houses) had been investigated in. of the two-story houses have low-ceilings (Tsushinikai) in second floor. Many houses have gabled roofs with side entrance (Kirizuma-zukuri Tsuma-iri). Majority of the external walls of houses are thick mud walls covered by many layers of Tosa plaster, while other thick walls are made of brick in. Many houses have clay tiles roofs with paving mud and cornerstone foundations.

4 REGIONAL CHARACTERISTICS OF SEISMIC HAZARDS There are two kinds of typical earthquakes threatening human lives, one is subduction zone earthquake and another one is inter plate earthquake. The epicenter, recurrence interval, scale and influence of earthquakes will be different by regions. Figure illustrates the hazard curve of earthquake in 9 IPDGHB included 5 investigation areas (relationship between the maximum velocity of the engineering base and probability of exceedance in 3 years), which means the higher of probability of exceeding of the maxim velocity, the higher the risk becomes (National Research Institute for Earth Science and Disaster Prevention). Probability of exceedance The maxim velocity of engineering base (cm/s) Fig. Hazard curve of earthquake in 9 IPDGHB included 5 investigation areas As the and which are near Nankai trough, seismic hazard has been greatly increased. This is due to the fact that massive earthquake in the Nankai trough (subduction zone earthquake) is imminent. On the other hand, as for, active faults with high probability of occurrence of the earthquake is close, in some areas the hazard curve is increased greatly in the lower range of the probability of exceedance. As described above, given that there is a difference in seismic hazard in different regions, the regional structural characteristics of traditional wooden houses will be analyzed in next chapter. REGIONAL CHARACTERISTICS OF TRADITIONAL WOODEN HOUSES Definition of structural characteristics In order to compare the difference between regions, the basic structural characteristics will be defined. a) Each storey's floor are is A,A is the area which is confined by walls or the center line of columns. The whole area A=A +A b) The height of the first story, H, refers to the distance from the surface of foundation ( from cornerstone while it is stone-based) to the upper beam edge of the second floor, while the height of the second storey, H, refers to the distance from the upper beam edge of the second floor to the upper beam of ceiling. And the total height is calculated as H=H +H. Whereas, H and H of and is particularly considered as the distance form surface of foundation to the underneath beam edge of the second floor and that from the second story floor to the underneath beam edge of ceiling (Shimizu H. 5, Shimizu H. ). c) The first floor weight W is measured from the half of first floor to the half of second floor, the second floor weight W is measured from the half of second floor to roof. The whole weight W is measured from the half of first floor and represented by W +W.

5 d) N c stands for the number of first storey's columns, and the modulus of first storey's columns, D c, is based on edge size of standard columns. Moreover, semi-column is not involved in principle. e) The residential direction is determined by the content below (Fig. 5). Regarding to other houses and the independent ones in and 's regions, the main house's ridge direction is defined by R direction, while the span direction is defined by S direction. And under the condition below which the arranged sequence of houses (Table ) in six areas included,,,, and, the parallel direction of the frontal road is called R direction, while the perpendicular direction of the road is called S direction. S (Span Dir.) R (Ridge Dir.) R (Ridge Dir.) Frontal Road (a), (b),,,,, Fig.5 Direction of houses in each region f) Limit strength calculation based yield shear force coefficient, C y, equals to housing shear capacity when storey drift is /3rad divided by weight, W, recorded as, according to the different directions (Editorial committee of seismic design of wooden houses ). S (Span Dir.) R (Ridge Dir.) S (Span Dir.) Analysis of structural characteristics In this section, a comparison of structural characteristics between districts will be represented by the scatter plots, the regression line and the average value of structural characteristics. Except the houses with significant large st floor area (A ) in each region and a few investigated houses for which the number of objects is too small to calculate regression line, all the two-story houses in all regions and one-story houses in and had been involved. Here, R is the correlation coefficient. Floor Area and Height Figure shows a comparison of A and H in each region. In addition, Fig. 7 shows a comparison of the average of A and ratio of nd floor area A to A between regions A (m ) A (m ) A (m ) A (m ) (a) (b) (c) (d) A (m ) A (m ) A (m ) A (m ) (e) (f) (g) (h) Fig. Relationship between A and H

6 Standard deviation Average A (m ) 5 A /A (a) A (b) A /A Fig. 7 Average of A and A /A As shown in Fig., A is diverse in different regions. Further, from Fig. 7 (a), A in,, and is greater than m. Thus, the significant difference for A between regions has been confirmed. According Fig. 7 (b), A /A is large for,,, and, and small for some two-story houses in. As shown in Fig., the height of the house H, is almost constant, while for other regions, the divergence of height up to around m which may due to the low-ceilings (Tsushinikai) in second story of some houses in,, and. In addition the comparison of average value of H between regions is shown in Fig Fig. Average of H From Fig., there is no significant difference between the height of one-story houses in and, while there is distinct difference between the heights of the two-story houses in different regions, and the value is higher in,, than that of in, and. Weight Figure 9 shows the relationship between W and A. Figure 9 indicates the comparison of the value of A divided by W between houses in all regions. From Fig. 9, the regression lines of the one-story houses and two-story houses are significantly different in. Figure shows the average value of W to the house divided by A and ratio of W to W in different regions. W, W of 3 houses in had been calculated. According the comparison between the two-story houses, as shown in Fig. (a), the value of W/A of, and is small. Also, as shown in Fig. (b)(c) and table, W/A and W/A is large in due to the thick mud walls and clay tile roofs, while this value is small in due to the wooden walls and thatch roofs. Comparing with other regions, W/A of two-story houses in is larger, and W/A is smaller. It may be one of the causes that A /A of is smaller than other regions. In addition, as shown in Fig. (c), W /W of, and is small, because of the light roofs which are covered by clay tiles or metal plates without mud as mentioned before (Table ). To summary, with respect of the weight of the houses, the regional structural characteristics have been confirmed. On the other hand, since the substantially constant value, by identifying the region or the floor area, the weight of the house may be able to estimate from the weight of floor area.

7 W = 3.A (R=.) W =.7A (R=.) A (m ) W = 3.3A (R=.5) A (m ) W =.5A (R=.75) W = 3.3A (R=.7) A (m ) A (m ) (a) (b) (c) (d) W =.A (R=.99) W =.5A (R=.7) W =.57A (R=.9) A (m ) A (m ) A (m ) A (m ) (e) (f) (g) (h) Fig. 9 Relationship between A and W 5 5. Standard deviation Average W/A (kn/m ) 3 (a) W/A W/A (kn/m ) 3 (b) W/A W /W (kn).... (c) W /W Fig. Average of W/A, W/A and W /W The number of columns Figure illustrates the relationship of A and N c of houses in different regions. N c =.35A (R=.5) N c N c N c =.55A (R=.3) N c =.A (R=.7) A (m ) N c N c =.5A (R=.55) A (m ) N c N =.55A (R=.79) c A (m ) (a) (b) (c) (d) N c =.9A (R=.79) A (m ) N c A (m ) N c (e) (f) (g) (h) N c =.57A (R=.) A (m ) Fig Relationship between A and N c N c N c A (m ) N c =.5A (R=.59) 3 A (m )

8 As shown in Fig. (a), the regression lines of one-story and two-story houses in deviate from each other. Figure shows a comparison of the average ratio of columns number to area of st floor N c /A between regions.. N c /A... Fig. Average of N c /A Figure illustrates the regional difference in terms of the value of N c /A which is the largest in houses in, yet small in one-story houses in and as well as two-story houses in. N c /A of may be large because the semi-columns which exist in the side walls were also counted. Yield base shear coefficients Figure 3 shows a comparison of the yield base shear coefficient and for both Ridge and Span directions of houses between regions (a) (b) (c) (d) (e) (f) (g) (h) Fig 3 Relationship between and C y is large in Span direction for the regions,,,, and, thus the directionality of yield base shear coefficients can be clearly confirmed. While as for houses in,, and, there is no significant directionality. A comparison of the average value of and between districts is shown in Fig. As shown in Fig. 3 and Fig., it has been confirmed that and is divergent from each other both between regions and among the houses in the same regions. As described above, there is a difference in structural characteristics of traditional wooden houses in different regions as well as the local seismic hazard.

9 (a) Fig. Average of and (b) CONCLUSIONS With the aim of demonstrating the regional structural characteristics of traditional wooden houses, and comparing the levels of seismic hazard of 9 designated as the Important Preservation District for Groups of Historic Buildings in Japan, the authors investigated structural details in eight regions, prefecture, town, town, town, city, city, town and town. And the mutual structural characteristics of wooden houses as for floor area, height, weight, the number of columns, and yield base shear coefficients have been compared between regions. Our conclusions are as follows. ) Structural characteristics and seismic hazards are various from different regions. ) The directionality of yield base shear coefficients can be clearly confirmed for some regions. 3) Seismic performance difference tends to be greater in the region than between regions. ) Weight can be roughly estimated from floor area because weight per the first floor area is approximately constant value if the region and number of stories is identified. ACKNOWLEDGMENT This research was supported by the Asahi Glass Foundation. And, a part of this research was supported by Grants-in-Aid for Scientific Research (A) (No.7), in Japan. REFERENCES Agency for Cultural Affairs: database of nationally designated cultural property, (accessed.9.) National Research Institute for Earth Science and Disaster Prevention. Japan Seismic. Hazard Information Station (J-SHIS), (accessed..5) Shimizu H., Hayashi Y., Suzuki Y., Saito Y., Goto M. (5). Evaluation of structural characteristics and seismic performance of damaged wooden houses by the Northern Earthquakes of July, 3, J.Struct. Constr. Eng., AIJ, No.59, 3-9. (in Japanese) Shimizu H., Arai H., Morii T., Yamada M., Hayashi Y. (). Seismic perfornmance and structural regionality of damaged wooden houses in the 7 Noto Hanto Earthquake, J.Struct. Constr. Eng., AIJ, No.3, (in Japanese) Shiojiri City Board of Education (9). Research report for disaster management plans in, Shiojiri City, Nagano Prefecture, designed as the Important Preservation District for Groups of Historic Buildings. Shiojiri City Board of Education. (in Japanese) Takiyama N., Miyamoto M., Mizutani Y., Matsumoto T., Watanabe C., Hayashi Y. (). Structural field survey and seismic performance evaluation for wooden houses of -Kitayama type in, J.Struct. Constr. Eng., AIJ, No.5, (in Japanese) Ida S., Morii T., Nii A., Hayashi Y. (), Simple method for seismic evaluation of traditional houses

10 in based on ambient measurements part : Proposal of seismic evaluation method, Summaries of technical papers of annual meeting architectural institute of Japan, Chugoku, 3-. (in Japanese) Earthquake Research Committee Kyomachiya (). Report for the establishment of repair methods to ensure earthquake resistance of Kyomachiya. Kiso K., Saratani A., Morii T., Sawada K., Aono F., Watanabe C., Hayashi Y. (). Study on reduction of seismic damage for traditional wooden house in Mie Prefecture local environment, AIJ J. Technol. Des., No., 7-7. (in Japanese) Watanabe C., Yokobe T., Jiao J., Takiyama N., Kanki K. Hayashi Y. (), The survey of wooden houses in the important district of groups of historic buildings in YUASA town, WAKAYAMA part : The feature of the district and main houses, Summaries of technical papers of annual meeting architectural institute of Japan, (in Japanese) Yokobe T., Mizutani Y. Jiao J., Takiyama N., Watanabe C., Hayashi Y. (), The survey of wooden houses in the important district of groups of historic buildings in YUASA town, WAKAYAMA part : Seismic Assessment, Summaries of technical papers of annual meeting architectural institute of Japan, (in Japanese) Tai T., Morii T., Watanabe C., Hayashi Y. (). Preparation to big earthquake of wooden houses in the important district of groups of historic buildings in Kochi, AIJ J. Technol. Des., No.3, (in Japanese) Editorial committee of seismic design of wooden houses: Seismic design method of traditional wooden building, Seismic design method with limit strength calculation. Publishers curator. (in Japanese) (Abstract Submitted: August 3, ) (Accepted: September 3, )