seismic design

huangyhg

seismic design
recently, there are two major earthquakes, namely in turkey & taiwan.
under normal conditions of contract, earthquake is regarded as act of god. however in places like california & japan, earthquake is inevitable. based on the observation from the recent quakes, most buildings do not survive the disaster. how do we strike a balance between the value of a human live against the project cost?
what is the scale level ? (1 to 9 )
if so, is it safe to say the casualties in quakes at the renge of 7 to 8 are just unlucky & there isn't much can be done?
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we do place a dollar value on life in engineering design. most structures and many mechanical devices (cars, airplanes, etc.) can be made safer for the user, but only at higher cost.
we all accept a certain level or risk upon our birth. we compound this when we buy and use potentially unsafe products, ride on airplanes, bungy jump, skydive, move to california and live in an old concrete building, or ride in cars that have head-on closing speeds of well over 120 mph on 2 lane state highways separated only by a few feet.
we strike the balance by setting design and construction standards and enforcing those standards.
we could go to the extreme and permit only one story wood structures for all new buildings, but i think society desires a higher level of risk than that.
dear friend,
the focus of the modern seismic design of buildings is not to reach a zero-damage status during a major earthquake, the target is to control the damage in certain acceptable level. a good performance of the building gets manifested when you have damage but not colapse. it happens that in more the countries you have design codes but the designers doesn't understand really how to design with them, and the authorities has not an infraestructure to qualify the design. it is important to know that in more the cases that buildings colapsed in turkey, the materials were of very bad quality, and the real reason of the colapse is not a wrong design. if someone wants to upgrade the performance of buildings without investigate the details of the design it will be enough to use very simple rules:
1)use more reinforced concrete walls, from the foundation until the higher roof.
2)employ good quality of sands and cement, an a higher ratio of horizontal and vertical reinforcement.
3)don't be afraid of stiffness when your structure is not brittle. flexible structures are brittle when non structural elements don't let displacements to occure, and as a result of this the values of the response spectrum of the codes(for flexible structures) are not real.
4)be carefull with soft story effects, interhammering between buildings with floors in different levels and short columns effects when windows are beside (between) columns.
very simple, isn't it? but lots of people die when designers, contractors and authorities ignore it.