The Council on Tall Buildings and Urban Habitat announced in Dubai that current codes of practice around the world are inadequate for the seismic design of tall buildings and has called for a more rigorous design approach.
While cities in Middle Eastern countries like Iran are known for high levels of earthquakes, U.S. cities like New York have moderate levels of seismic activity similar to Dubai, says Dr. Sissy Nikolaou, director of the geoseismic department at Mueser Rutledge Consulting Engineers, New York.
The use of inappropriate building codes for tall structures in those and other cities could lead to inefficient and potentially unsafe construction, according to the CTBUH. That leads some architects, engineers, government officials, and building code experts to be concerned about the ability of tall buildings that are designed to meet traditional code procedures to survive major earthquakes.
“Nobody [has] argued that the current codes are adequate for the analysis and design of tall and very tall buildings,” says Michael Willford, co-chair of the CTBUH and director of the engineering firm Arup, London. “This shows a growing awareness that current building codes are unsuitable for high-rise buildings … the evidence is now incontestable.”
Willford says current codes around the world, many of them based on U.S. codes, were developed to address the seismic design requirements of low- to moderate- rise buildings. As such, they may fall short in conveying specific modeling, analysis, and acceptance criteria for tall buildings. He adds that the structural characteristics that control the seismic behavior of tall buildings are different from those of shorter buildings, especially the limited degree of ductility in a taller structure.
“Building code procedures were not written for the design of the very tall buildings that are now being built around the world,” Willford says. “This is not necessarily a problem for wind, strength, or material performance, but it is an issue for earthquake design.”
Willford, along with Professor Andrew Whittaker of the University of Buffalo and Ron Klemencic of Seattle-based Magnusson Klemencic Associates, developed the first set of recommendations for seismic design of high-rise buildings for CTBUH.
They recommend a modern, performance-based approach to the seismic design, similar to that practiced for tall buildings in Japan and China. This requires the design of a proposed building to be evaluated through computer analysis with a series of simulated earthquake events that are consistent with the seismic hazard at the site.
“We are now in an era where modern sophisticated computer analysis can predict with reasonable confidence how a building will behave in extreme earthquakes,” says David Scott, CTBUH Chairman. “We need to use this knowledge to change our codes without waiting for the next disaster.”
