外文翻譯tallbuildingstructure外文翻譯(編輯修改稿)
2025-01-11 05:18 本頁面
【文章內(nèi)容簡介】 s surface directly above this point is called the epicenter. The main or greatest shock is usually followed by numerous smaller aftershocks. These aftershocks are produced by slippage at other points on the fault or in the fault zone. Types of earthquake faults Faults are classified in accordance with the direction and nature of the relative displacement of the earth at the fault plane. Probably the most mon type is the strikeslip fault in which the relative fault displacement is mainly horizontal across an essentially vertical fault plane. The great San Andreas fault in California is of the type. Another type is termed a normal fault — when the relative movement is in an upward an downward direction on a nearly vertical fault plane. The great Alaskan earthquake of 1964 was apparently of this type. A less mon type is the thrust fault — when the earth is under pressive stress across the fault and the slippage is in an upward and downward direction along an inclined fault plane. The San Fernando earthquake was generated on what has usually been classified as a thrust fault, although there was about as much lateral slippage as up and down slippage due to thrust across the inclined fault plane. Some authorities refer to this bined action as lateral thrust faulting. The pressive strain in the earth of the San Fernando Valley floor just south of the thrust fault was evidenced in many places by buckled sidewalks and asphalt paving. Forces exerted by an earthquake Slippage along the fault occurs suddenly. It is a release of stress that has gradually builtup in the rocks of the earth39。s crust. Although the vibrational movement of the earth during an earthquake is in all directions, the horizontal ponents are of chief importance to the structural engineer. These movements exert forces on a structure because they accelerate. This acceleration is simply a change in the velocity of the earth movement. Since the ground motion in an earthquake is vibratory, the acceleration and force that it exerts on a structure reverses in direction periodically, at short intervals of time. The structural engineer is interested in the force exerted on a body by the movement of the earth. This may be determined from Newton39。s second law of motion 39。 which may be stated in the following form: F=Ma In which F is a force that produces an acceleration a when acting on a body of mass M. This equation is nondimensional. For calculations M is set equal to W/g, then: F=W/g*a (1) In which F is in pounds, a is in feet per second per second, W is the weight of the body also in pounds and g is the acceleration of gravity, which is feet per second per second. Equation (1) is empirical. It simply states the experimental fact that for a free falling body the acceleration a is equal to g and the acceleration force F is then equal to the weight W. For convenience, the acceleration of an earthquake is generally expressed as a ratio to the acceleration of gravity. This ratio is called a seismic coefficient. The advant
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