Appendix A Outline of Earthquake Provisions in the Japanese Building Codes Masaomi Teshigawara Abstract The outline of seismic provisions in the building code of Japan is intro- duced. They feature a two-phase design for earthquakes. The fi rst phase design is for medium earthquake motions, and this is basically working stress design. The second phase design is intended to give protection to buildings in case of severe ground shaking. It requires the checking of several aspects of the building. These include story drift, vertical stiffness distribution, horizontal eccentricity and ulti- mate lateral load carrying capacity. Both phases of the design are reviewed in detail. Some provisions are discussed in the light of recent earthquake damage in Japan. This paper is revised one written by Aoyama [1]. That is to say, this appendix is heavily quoted from the paper by Aoyama [1], and revised to include several amend- ments in the building code of Japan after 2000. A.1 Introduction The seismic design of Japanese buildings is featured by a two-phase design for earthquakes. The fi rst phase design for earthquakes aims at the safety and reparabil- ity of buildings during medium earthquake motions. The second phase design for earthquakes is added to give safety against severe ground shaking. The history of seismic design in Japanese building code started in 1924 when the Urban Building Law was revised, as a consequence of the disaster of great Kanto earthquake of 1923. This adopted a set of structural provisions including a seismic coef fi cient of 0.1. After the World War 2 the Building Standard Law replaced the Urban Building Law with much more elaborate provisions for various aspects of M. Teshigawara (*) Nagoya University , Nagoya , Japan e-mail: [email protected] Architectural Institute of Japan (ed.), Preliminary Reconnaissance Report of the 2011 421 Tohoku-Chiho Taiheiyo-Oki Earthquake, Geotechnical, Geological and Earthquake Engineering 23, DOI 10.1007/978-4-431-54097-7, © Springer Japan 2012 422 M. Teshigawara structural design. The standard value of seismic coef fi cient was raised to 0.2. The essential feature of seismic design was, however, unchanged as this increase in seis- mic loading was accompanied by comparable increase in the allowable stresses for various materials. Both the Urban Buildings Law and the Building Standard Law speci fi ed only loadings and allowable stresses, and certain minimum requirements for the detailing of members. Details of structural design, such as methods of structural analysis and the proportioning of members, are speci fi ed in the Structural Standards issued by the Architectural Institute of Japan (AIJ), and “Commentary on the Structural Calculation based on the Revised Enforcement Order, Building Standard Law (in Japanese)”, supervised by Housing Bureau and National Institute of Land Infrastructure Management in Ministry of Land, Infrastructure, Transport, and Tourism (MLIT), and Japan Conference of Building Administration, 2007. These Standards, prepared separately for each structural material, have served as the sup- plements to the Law. They have been revised more frequently to adapt new knowl- edge and to provide for new materials as they developed. A particularly important event regarding seismic design was the 1968 Tokachi Oki earthquake which caused signi fi cant damage to modern buildings designed in accordance with building regulations. Various actions were undertaken as a conse- quence of this event. A partial revision of the Building Standard Law incorporating ultimate strength design in shear of reinforced concrete, the establishment of review procedure of existing buildings for seismic safety, were some of the changes. The following year, another important event took place, the 1978 Miyagi-ken Oki earthquake. Damage was as severe as in the 1968 Tokachi Oki earthquake. It also demonstrated the more complicated characteristics of urban disaster in the city of Sendai with more than 600,000 populations. In July, 1980 a revision of the Enforcement Order of the Building Standard Law was released. It was also announced that this order, together with supplementary documents, would be enforced from the fi rst of June, 1981. The second phase design for earthquakes is added in this time to give safety against severe ground shaking. After the 1995 Hyogo-ken Nanbu earthquake, another seismic design method, “Response and Limit Deformation”, is introduced in 2000. This utilizes the linear response spectrum, in which earthquake motion is de fi ned on the engineering bed- rock whose shear wave velocity is not less than 400 m/s, and ampli fi cation of sub- soil in construction site is considered. In this chapter a simple review of the revised seismic design method in 1981 is attempted. A.2 Types of Construction in Japan Figure A.1 shows types of building construction and the commonly employed num- ber of story for each type of construction. Traditionally, Japanese houses have been built in timber, and they are one or two story high. They are still very common. Appendix A Outline of Earthquake Provisions in the Japanese Building Codes 423 60 50 40 30 OFFICES 25 20 18 OFFICES 16 HOTELS 14 APART- 12 HWF MENTS 10 9 8 Number of Stories 7 HOSP- 6 ITALS 5 APART- SCHOOLS 4 MENTS OFFICES 3 SHOPS 2 HOUSES 1 0 Timber R.C.Wall R.C.Frame S.R.C. Steel Fig. A.1 Types of construction in Japan Recently, three story timber houses can be built. Masonry houses are scarce. Although provisions exist in Japan for the construction of reinforced concrete block masonry apartment houses up to three stories high, this construction is not shown in Fig. A.1 . The more common type of construction for apartment houses uses reinforced concrete “wall” structures. For these structures the building code allows a much sim- pler method of design than for ordinary reinforced concrete frame construction. This wall construction is in the majority of low-rise apartment houses, ranging from three to fi ve stories. High rise framed wall construction (HFW) which consists of wall-column and wall-beam in the longitudinal direction is also used for higher buildings up to 15 stories. Ordinary reinforced concrete (RC) frame structures, with or without shear walls, represent the most common type of construction for various types of buildings, such as shops, of fi ces, schools, and hospitals, ranging from three to seven stories. It may also be used for lower or higher buildings. At present the tallest RC frame structure is a 56 storied apartment building in Tokyo. 424 M. Teshigawara However, in ordinary cases Building Of fi cials recommend the use of SRC construction for buildings taller than seven stories until 1990. SRC, an abbreviation for steel-reinforced-concrete, is a composite construction method consisting of a structural steel frame encased in reinforced concrete. It has a long history in Japan, probably evolving from as early as 1920, when buildings were constructed with exterior steel frames encased in brick masonry and interior steel frames encased in concrete. SRC was generally believed to be more ductile and hence more earth- quake-resistant than ordinary reinforced concrete. A steel structure is used for most high-rise construction in Japan ranging from about 15 stories up to the tallest building in Japan, at present the 70 storied Yokohama Land Mark Tower. Recently steel structures became more popular in all ranges of buildings, mainly due to the rapid erection on the site. Some of these are frame structures but for lateral load resistance many of them rely, at least partly, on bracing. A.3 General Flow Chart of Seismic Design Figure A.2 shows the general fl ow of structural design stipulated by the current Enforcement Order of the Building Standard Law. All buildings are fi rst divided into four groups, mainly based on their heights. They are shown in the boxes marked as (1)–(4). For buildings taller than 60 m, in box (4), provisions of the Building Standard Law do not apply directly. These high-rise buildings are to be designed by the “spe- cial study”, usually incorporating time-history, non-linear response analyses. The design is then subjected to the technical review by the High-rise Building Structure Review Committee in examination organization entrusted the Minister of Land, Infrastructure, Transport, and Tourism, such as the Building Center of Japan. Upon its recommendation, a special approval of the structural design is issued by the MLIT. For buildings, not exceeding 60 m in height, the basic intent of the general fl ow in Fig. A.2 is to make a two-phase design. This means that an additional design phase, hereafter called the second phase design for earthquakes, follows the work- ing stress design, including the seismic design, hereafter called the fi rst phase design for strong earthquakes which can occur several times during the life time of the building. The second phase design is intended mainly for severe or extraordinary earthquakes which could occur once in the life time of the building. The application of the two-phase design is shown in Fig. A.2 for three different groups of buildings up to 60 m in height, in boxes (1)–(3). For all of these buildings, working stress design is carried out fi rst, box (5), including the fi rst phase seismic design. As explained later, this is an allowable stress design for permanent and temporary loadings, also taking ultimate strength into account. Major changes of the code in 1981 relevant to this phase of the design is the method of seismic force evaluation. Appendix A Outline of Earthquake Provisions in the Japanese Building Codes 425 (1) Timber construction. (2) (3) (4) Others, specified by 31m<h<60m h>60m Ministry of Construction (1) (5) Conventional structural design including first phase design for earthquakes (6) Check for story drift Second phase Note:- design for h=height earthquakes (7) Check for rigidity factor and eccentricity (8) Use of (9) Check specifications ultimate of Ministry of capacity for Construction lateral load (10) Approval by building officials of local (11) Special government body approval required Fig.