Improvements in Code and Dynamic Analyses of Buildings: Vibration Periods and Modal Damping Ratios

这个项目的目标是“测量”大约40座建筑物在北岭地震和其他近期地震中记录的运动的两个重要特性——基本振动周期和模态阻尼比。这些建筑物受到地面运动的强烈震动，峰值加速度在0.15g到0.82g之间，与大多数现有的运动幅度较小的数据相比，它们将提供与建筑物抗震设计直接相关的信息。振动特性将通过系统识别程序从建筑物的记录运动中识别出来。这些来自北岭地震和其他近期地震的结果，结合1971年圣费尔南多地震的类似数据，将创建最全面的数据库，可以在每次大地震后轻松更新。该数据库将用于评估和改进：(1)用于计算设计基础剪力和侧向力的估计基本振动周期的代码公式；(2)当前动力分析中使用的阻尼值建议。1994年UBC和1990年SEAOC“蓝皮书”中的周期公式是1975年作为ATC-3项目的一部分开发的，主要基于1971年圣费尔南多地震期间记录的建筑物运动。同样，广泛使用的阻尼值最初是由Newmark和Hall在1978年推荐的。该项目最终将得出：(1)使用不同材料（钢、R/C、砌体等）和各种结构系统（抗矩框架、剪力墙等）估算建筑物基本振动周期的公式；(2)根据响应幅度和（如果合适的话）模态数，对不同类型建筑物的模态阻尼比提出建议。这是北岭地震项目。* * *

9416265 Chopra The objectives of this project are to "measure" two important properties--fundamental vibration period and modal damping ratios-of some forty buildings from their recorded motions during the Northridge earthquake and other recent earthquakes. These buildings, shaken strongly by ground motions with peak accelerations between 0.15g and 0.82g, would provide information directly relevant to earthquake resistant design of buildings in contrast to much of the existing data which are for smaller amplitudes of motion. The vibration properties will be identified from the recorded motions of the buildings using system identification procedures. These results from the Northridge earthquake and other recent earthquakes, combined with similar data available from the 1971 San Fernando earthquake, will create the most comprehensive database which can be easily updated after every major earthquake. This database will be used to evaluate and improve: (1) code formulas for estimating the fundamental vibration period used in calculating the design base shear and lateral forces; and (2) current recommendations for damping values used in dynamic analysis. The period formulas in the 1994 UBC and the 1990 SEAOC "blue book" were developed in 1975 as part of the ATC-3 project, based largely on motions of buildings recorded during the 1971 San Fernando earthquake. Similarly, the damping values used widely were originally recommended by Newmark and Hall in 1978. This project will culminate in: (1) formulas for estimating the fundamental vibration period of buildings using different materials--steel, R/C, masonry etc.--and various structural systems--moment resisting frames, shear walls etc.; and (2) recommendations for modal damping ratios for different categories of buildings, depending on response amplitude and, if appropriate, on mode number. This is a Northridge earthquake project. ***