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采用反应谱原理计算结构物地震荷载时,首先必须求得结构的自振周期,振型及阻尼。十分明显,结构的前几个自振型对地震荷载的影响是主要的,尤其是基本振型作用是决定性的。我国工业与民用建筑抗震设计规范TJ11—78规定对于高度超过150米的高柔构筑物,当计算地震荷载产生的结构内力(弯距、剪力或轴向力)时,一般只须考虑前1～3个振型。但是,高振型的影响应如何考虑,计算高耸结构物地震荷载时仅计算前三个振型是否足够准确,这些问题都值得深入探讨。现今土建设计日益广泛使用电子计算机,通过大量的计算分析是可以把上述问题弄清楚的。
When calculating the seismic load using the principle of response spectrum, the natural period, vibration mode and damping of the structure must first be calculated. Obviously, the influence of the first few natural modes of the structure on the seismic load is dominant, especially the role of the fundamental mode is decisive. The seismic design code TJ11-78 of China’s industrial and civil buildings stipulates that when calculating the structural internal force (bending moment, shear force or axial force) caused by earthquake load, generally only 1 ~ 3 modes. However, how to consider the effect of high-vibration mode and how to calculate the first three modes only when calculating the seismic load of high-rise structure is worthy of further discussion. Nowadays, civil engineering design is widely used in electronic computers. Through a lot of calculation and analysis, it is possible to make clear the above problems.