水平层状场地自振频率的剪切质点系法研究
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摘要
场地土层的自振频率是场地土的重要动力特性之一。为避免结构物与场地地基的共振效应,工程设施的固有频率应尽量避开地基的固有频率。在传统的基于集中质量矩阵的剪切质点系法(集中质量法)的基础上,发展了基于一致质量矩阵的剪切质点系法。在此基础上,对利用剪切质点系法求解水平层状场地自振频率的精度的影响因素进行了分析,主要考虑了土层分层特性、质量矩阵形式以及材料阻尼3个影响因素,分析表明:分层数越多,计算结果越接近真实解,从实际工程角度出发,分层数超过三层时可不再细分;在层数相等的情况下,层厚对计算结果精度的影响甚微;一致质量法的计算结果要优于集中质量法,且表现出上限解性质;在通常小阻尼情况下,阻尼对自振频率的影响很小。
Natural frequency is one of the most important dynamic characteristics of field soil layers. In order to avoid the resonance between structure and ground,the natural frequency of engineering establishments should be different from that of ground. On the basis of traditional shear particle system method based on lumped mass matrix(lumped mass method) ,a new shear particle system method based on consistent mass matrix(consistent mass method) is developed. Then,influencing factors on computing precision of shear particle system method are analyzed. The three aspects of soil delamination,mass matrix form and material damping are mainly considered. The analysis indicates:the more layer numbers we divide,the more precise the results will be and from the standpoint of practice engineering,when layer number is more than three,a subdivision is needless;layer thickness has very small effect on computing results;the result of consistent mass method is superior to that of lumped mass method and has the property of upper bound solution;in small damping circumstance,the material damping has small influence on natural frequency.
Natural frequency is one of the most important dynamic characteristics of field soil layers. In order to avoid the resonance between structure and ground,the natural frequency of engineering establishments should be different from that of ground. On the basis of traditional shear particle system method based on lumped mass matrix(lumped mass method) ,a new shear particle system method based on consistent mass matrix(consistent mass method) is developed. Then,influencing factors on computing precision of shear particle system method are analyzed. The three aspects of soil delamination,mass matrix form and material damping are mainly considered. The analysis indicates:the more layer numbers we divide,the more precise the results will be and from the standpoint of practice engineering,when layer number is more than three,a subdivision is needless;layer thickness has very small effect on computing results;the result of consistent mass method is superior to that of lumped mass method and has the property of upper bound solution;in small damping circumstance,the material damping has small influence on natural frequency.
引文
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[2]王钟琦,谢君斐,石兆吉.地震工程地质导论[M].北京:地震出版社,1983.
[3]熊建国,许贻燕.分层土自振特性分析[J].地震工程与工程振动,1986,6(4):23-37
[4]陈龙珠,吴世明,魏玉伦.用机械阻抗法求成层地基的固有频率[J].岩土工程学报,1989,11(2):82-87.
[5]葛双成.场地卓越周期计算浅议[J].浙江建筑,1999,(1):32-33.
[6]IDRISS I M,SEED H B.Seismic response of horizontal soil layers[J].Journal of Soil Mechanics and Foundation Engineering Division,ASCE,1968,94(SM4):1003-1031.
[7]刘增武.场地土层的周期特性[C].中科院工程力学研究所地震工程研究报告集(4).北京:科学出版社,1981.
[8]吴世明.土动力学[M].北京:中国建筑工业出版社,2000:210-211.
[9]胡聿贤.地震工程学[M].北京:地震出版社,1988:262-264.
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