Archive for December, 2012

Tall Buildings

Posted by cdj On December - 4 - 2012

In December 2011, the Council on Tall Buildings and Urban Habitat asserted “we can expect that in a mere two decades (2000–2020) the height of the ‘World’s Tallest Building’ will have more than doubled.” This assertion was illustrated with this graphic of the world’s skyline:

Tall Buildings Worldwide by Decade

Indeed, planned or under-construction buildings worldwide continue to grow taller each year. However, the recent Maule, Chile earthquake (Mw=8.8) resulted in the partial collapse of the new, 21 story Torre O’Higgins Building, the tallest structure in the city of Concepcion. This collapse jeopardized smaller, surrounding buildings. In Christchurch, New Zealand, the 2010 (Mw= 7.1) and 2011 (Mw=6.3) earthquakes severely damaged the 26 story Grand Chancellor Hotel which was subsequently demolished. The Great East Japan earthquake (Tohoku, Mw=9.0) caused the tallest towers in Tokyo, more than 250 km from the earthquake source, to sway in the long period motion of the ground causing discomfort and anxiety for residents but no significant damage to structures. Yet popular demand for taller, thinner buildings for urban living continues to grow in many places in the world, although not without dissent (See: NYTimes, January 9, 2013). Can taller buildings really be earthquake resistant?
Conventionally constructed, taller, fixed base buildings can experience large ductility demands and undergo some serious inelastic deformations of the structural system during the long duration shaking in very large earthquakes. Stiffer (normally shorter) buildings can experience large floor accelerations resulting in substantial, non-structural damage during earthquake shaking. The type and size of earthquake obviously determine the extent of ground shaking. The strength and intensity of earthquake shaking experienced by a tall structure are largely governed by distance from the earthquake source, the duration of shaking time, the types of soil present, and the type of structure and construction methods. The PEER Center developed “Guidelines for the performance based seismic design of tall buildings” to address earthquake resistance of taller buildings. Some of the effort supporting this PEER “Tall Building Initiative” is reported in a 15WCEE paper (Tuna,Z et al) comparing the seismic performance of two 42-story reinforced concrete, coupled core wall, (one a dual system with a perimeter moment-resisting frame) buildings located in Los Angeles, California. Some detailed seismic response comparisons and associated initial and lifetime maintenance costs of these buildings are presented in this paper. A PEER Annual Meeting presentation (Calugaru & Panagiotou) reported on the use of seismic isolation bearing layers, rocking walls and seismic dampers, used in a tall building, the Shiodome Sumitomo Building in Tokyo. A report, UCB/SEMM 2012-03 (Calugaru & Panagiotou), of this research was also recently published. The analytical assessment of similar rocking walls introduced to a 240-meter-high tall building to achieve earthquake resilience in a structural system of reinforced concrete (RC) core walls and peripheral steel reinforced concrete (SRC) frames (with and without dampers) was also reported by researchers (Y. Zhou, R. Li, X.L.Lu) from Tongji University in Shanghai, China at the 15WCEE in Lisbon. Other 15WCEE conference papers reflect the international discussion on the response of tall buildings to earthquakes including (Celebi et al) analysis of the strong shaking during the Tohoku earthquake of a 256 m tall building (55 stories plus 3-story basement) located on a reclaimed island near Osaka, Japan; approximately 770km from the earthquake epicenter. Another analytical research paper (Joonho Lee et al) examines the dynamic performance of different-shaped, irregular, tall buildings in Korea. Ongoing research (Coeto & Teran-Gilmore) on designing bracing systems to restrict lateral deformation during earthquake shaking for proposed slender, steel frame buildings in Mexico City was also reported in Lisbon. A building-specific seismic loss estimation study (Ramirez et al) that considered a tall, 24-story steel-framed building in Osaka, Japan provided a risk-focused view of taller buildings in earthquakes.

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