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二、地震荷载地震是由于地壳破裂或者断裂的结果。在地表以下几万米乃至几十万米深处岩石的错动,这种突然的剪切破坏,使得积聚的应变能释放为震动能。地壳的破坏产生两种类型的波在地层中传播、一是压力波或纵波,一是剪切波或横波,分别称做P波和S波。P波的传播速度比S波快,因此它们按字母表顺序先后到达。于是,倘若已知两种波的传播速度,那么从观测点到震源的距离就可以计算出来。P波和S波一抵达地表,便接着产生地表波。图10表示了描述地震的主要的几何名词和P波与S波传播的途径。产生的地面运动用地震仪来测量,可以探测极小的振动,但对于强动却会失灵。当发生一定强度以上的加速度时,常采用强动地震仪。普通地震仪所测的结果主要用于地震力学的研究,强动地震仪测量的结果,尤其是当强动地震仪安装在建筑物上,测量的结构在地震期间的状态,对制定设计规范至关重要。图11是一个记录过程的例子。在震源的地震振扰用里氏(Richter)等级来标定,其划分
2. Seismic load The earthquake is the result of cracking or fracture of the earth’s crust. In the tens of thousands of meters below the earth’s surface and even hundreds of thousands of meters deep rock movements, this sudden shear damage, so that the accumulation of strain energy can be released as vibration energy. The destruction of the crust causes two types of waves to propagate in the formation, one is a pressure wave or a longitudinal wave, and the other is a shear wave or a transverse wave, which is called a P wave and an S wave, respectively. P waves travel faster than S waves, so they arrive in alphabetical order. Thus, if the propagation speeds of the two waves are known, the distance from the observation point to the source can be calculated. Once the P-wave and S-wave arrive at the surface, they then generate surface waves. Figure 10 shows the main geometric nouns describing the earthquake and the ways in which the P-wave and S-wave propagate. The resulting ground motion is measured with a seismograph and can detect extremely small vibrations, but it can fail with strong motion. When the acceleration above a certain intensity occurs, a strong motion seismograph is often used. The results measured by ordinary seismographs are mainly used in the research of seismic mechanics, and the results of measurements made by strong motion seismographs, especially when a strong motion seismograph is installed on a building, the state of the measured structure during the earthquake, and the development of design specifications to Important. Figure 11 is an example of a recording process. Seismic disturbances at the source are calibrated using the Richter scale.