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Earthquake Resistant Design of Reinforced Concrete Buildings Past and Future Shunsuke Otani1

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Earthquake Resistant Design of Reinforced Concrete Buildings Past and Future Shunsuke Otani1 Journal of Advanced Concrete Technology Vol. 2, No. 1, 3-24, February 2004 / Copyright © 2004 Japan Concrete Institute 3 Invited Paper Earthquake Resistant Design of Reinforced Concrete Buildings Past and Future Shunsuke Otani1 Received 9 September 2003, revised 26 November 2003 Abstract This paper briefly reviews the development of earthquake resistant design of buildings. Measurement of ground accel- eration started in the 1930s, and response calculation was made possible in the 1940s. Design response spectra were formulated in the late 1950s to 1960s. Non-linear response was introduced in seismic design in the 1960s and the capac- ity design concept was generally introduced in the 1970s for collapse safety. The damage statistics of reinforced con- crete buildings in the 1995 Kobe disaster demonstrated the improvement of building performance with the development of design methodology. Buildings designed and constructed using out-dated methodology should be upgraded. Per- formance-based engineering should be emphasized, especially for the protection of building functions following fre- quent earthquakes. 1. Introduction damage have been identified through the investigation of damages. Each damage case has provided important An earthquake, caused by a fault movement on the earth information regarding the improvement of design and surface, results in severe ground shaking leading to the construction practices and attention has been directed to damage and collapse of buildings and civil- the prevention of structural collapse to protect the oc- infra-structures, landslides in the case of loose slopes, cupants of building in the last century. and liquefaction of sandy soil. If an earthquake occurs Thank to the efforts of many pioneering researchers under the sea, the associated water movement causes and engineers, the state of the art in earthquake resistant high tidal waves called tsunamis. design and construction can reduce the life threat in Earthquake disasters are not limited to structural reinforced concrete buildings. Attention should be di- damage and injury/death of people under collapsed rected to the protection of existing structures con- structures. Fire is known to increase the extent of the structed using old technology. The vulnerability of these disaster immediately after an earthquake. The breakage existing structures should be examined and seismically of water lines reduces fire fighting capability in urban deficient structures should be retrofitted. One of the areas. The affected people need support, such as medi- important research targets in present earthquake engi- cal treatment, food, clean water, accommodations and neering is the development of design methodology to clothing. Continued service of lifeline systems, such as maintain building functions after infrequent earthquakes, electricity, city gas, city water, communication lines and for example, through the application of structural con- transportation, is essential for the life of affected people. trol technology. Damage to highway viaducts or railway, as seen in the This paper reviews the development of earthquake en- 1995 Kobe earthquake disaster, can delay evacuation gineering in relation to earthquake resistance of build- and rescue operations. It is the responsibility of civil and ings and discusses the current problems in earthquake building engineers to provide society with the technol- engineering related to reinforced concrete construction. ogy to build safe environments. Reinforced concrete has been used for building con- 2. Development of seismology and struction since the middle of the 19th century, first for geophysics some parts of buildings, and then for the entire building structure. Reinforced concrete is a major construction Earthquake phenomena must have attracted the curiosity material for civil infrastructure in current society. Con- of scientists in the past. Ancient Greek sophists hy- struction has always preceded the development of pothesized different causes for earthquakes. Aristotle structural design methodology. Dramatic collapse of (383-322 B.C.), for example, related atmospheric events buildings has been observed after each disastrous such as wind, thunder and lightning, and subterranean earthquake, resulting in loss of life. Various types of events, and explained that dry and smoky vapors caused earthquakes under the earth, and wind, thunder, light- ning in the atmosphere. Aristotle’s theory was believed through the Middle Ages in Europe. The 1755 Lisbon 1Professor, Department of Design and Architecture, Earthquake (M8.7), which killed 70,000, partially due to Faculty of Engineering, Chiba University, Japan. a tsunami tidal wave, and a series of earthquakes in E-mail: [email protected] 4 S. Otani / Journal of Advanced Concrete Technology Vol. 2, No. 1, 3-24, 2004 London in 1749 and 1750 attracted the interest of scien- the fault-line, and the stresses thus induced were the tists. forces which caused the sudden displacements, or elas- The first scientific investigation about earthquake tic rebounds, when the rupture occurred....” Reid did not phenomena is believed to have been carried out by explain what causes the external forces acting along Robert Mallet, who initiated the physico-mechanical fault lines. investigation of earthquake wave propagation. He in- Recent developments in geophysics are fascinating; vestigated the earthquake phenomena of the 1857 especially research on the relationship between plate Naples Earthquake, and used such technical terms as tectonics and earthquakes. Alfred Wegener presented the “seismology,” “hypocenter,” “isoseismal,” and “wave theory of continental drift (Wegener, 1915). He pro- path” in his report (Mallet, 1862). vided extensive supporting evidence for his theory such The measurement of earthquake ground vibrations as geological formations, fossils, animals and climatol- must have been a challenge for scientists. Chan Heng, in ogy. He claimed that a single mass, called Pangaea, 132 A.D. in China, developed an instrument to detect drifted and split to form the current continents. Wegener, earthquakes and point out the direction of the epicenter. however, had no convincing mechanism to explain the Mallet also invented an instrument to record the inten- continental drift. Exploration data regarding the earth's sity of ground motion by measuring the direction and crust, notably the ocean floor, increased in the 1950s; distance of a particle moved by the motion. Many at- e.g., American physicists M. Ewing and B. Heezen dis- tempts were made to develop seismometers (seismo- covered the great global rift (the Mid-Ocean Ridge in graphs) that could record ground movement during the Atlantic Ocean). On the basis of such exploration earthquakes. Luigi Palmieri developed an electromag- data, H. Hess, professor of Geology at Princeton Uni- netic seismograph in 1855. One was installed near versity, proposed the theory of sea-floor spreading in Mount Vesuvius, and another one at the University of 1960, which provided a mechanism to support Naples. The Ministry of the Interior of Japan adopted Wegener’s continental drift. Plate tectonics can describe Palmieri-type seismometers in 1875. the accumulation of strains at the boundaries of adjacent The first seismological society in the world, the Seis- plates or within a plate due to plate movements at the mological Society of Japan, was founded in 1880 when earth's surface, which cause earthquakes. European and U.S. engineering professors, invited to the Major earthquakes occur along the boundary of mov- College of Engineering in Tokyo, were interested in the ing tectonic plates when the strain energy, accumulated 1880 Yokohama earthquake (M5.5), which caused mi- by the resistance against inter-plate movement, is sud- nor damage to buildings, but collapsed a chimney. John denly released. This type of inter-plate earthquakes oc- Milne, professor of Geology and Mining at the Engi- curs repeatedly at a relatively short interval of 50 to 200 neering College, was the leader in scientific and engi- years. Seismically blank regions, where seismic activity neering research. Milne, together with J. A. Ewing and T. is quiet for some time along the tectonic plate boundary, Gray, developed a modern three-directional seismome- are identified as the location of future earthquake oc- ter in 1881. Important research findings were published currences. However, it is not possible at this stage to in the transactions. For example, Milne introduced Mal- accurately predict the time, location and magnitude of let’s work on seismology and Ewing noted the differ- earthquake occurrences. ence between primary and secondary waves in the re- Another type of earthquakes occurs within a tectonic corded ground motion. plate when the stress accumulated within a plate by the The University of Tokyo was renamed as the Imperial pressure of peripheral plate movements, exceeds the University in 1886. Kiyokage Sekiya, who worked resisting capacity of the rock layers at the fault. The closely with Ewing and Milne, became the first profes- epicenter is relatively shallow within 30 km from the sor of seismology chair at the Faculty of Science. earth surface. The fault in a plate remains as a weak spot Fusakichi Omori who succeeded him in 1897, was ac- after an earthquake, and earthquakes occur repeatedly at tive in experimental as well as theoretical research for the same location if stress accumulates up to the failure earthquake disaster mitigation. level. The location
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