INFLUENCE OF THE SEISMIC EXCITATION FREQUENCIES CONTENT ON THE BEHAVIOR OF A TUNED MASS DAMPER IN LOW-RISE BUILDING CONSIDERING SOIL-STRUCTURE INTERACTION

Abstract The influence of the frecuency content of seismic excitations on the behavior of an optimal tuned mass damper (TMD) is studied in the context of a system with explicit consideration of soil-structure interaction. A stochastic analysis is made in the time domain for two random processes, one considering a broad bandwidth process (BBP) and other considering a narrow bandwidth process (NBP). A structure built over three different types of soil (soft, medium and hard) is considered. For the optimization of the TMD, the minimization of the ratio between the standard deviation of the displacement of the main structure with TMD with respect to a structure without TMD, is used as the target function. It is found that for seismic excitations with high frecuency content, the ratio of the TMD frequencies compared to the fixed base frequency of the structure approaches to 1 as the soil becomes more rigid. It is also observed that the TMD become tuned with the flexible base frequency for all soil types, producing perfect tuning for small mass ratios and detuning gradually for higher mass ratios. On the other hand, the TMD optimal damping ratio increases as the TMD mass ratio is higher, independently of the soil type. The TMD is more efficient for higher values of the TMD mass ratios, especially on soft soil. In structures built over flexible base, that are subjected to low frequency content excitations, the optimal TMD is tuned with the flexible base, independently of the type of soil and the fixed base period of the main structure. The TMD optimal damping is not sensitive to the flexible period for small mass ratios, and reaches its minimum value when it matches with the predominant period of the seismic event. On the other hand, the TMD reaches its maximum efficiency when it is tuned with the flexible period of the soil-structure system, and coincides with the predominant period of the seismic exitation and is higher on soft soil. A deterministic analysis is made using two seismic records, an artificial earthquake compatible with the Chilean code NCh2745 characterized by high frequencies content and other similar to the event in 1985 in Mexico, characterized by low frequencies content. It is seen that the optimal TMD is efficient controlling the response of the structure in all types of soil analyzed.

摘要 本文在明确考虑土-结构相互作用（soil-structure interaction）的系统框架下，探讨了地震动频率成分对最优调谐质量阻尼器（Tuned Mass Damper, TMD）力学性能的影响。针对两类随机过程开展时域随机分析：一类为宽频带过程（BBP），另一类为窄频带过程（NBP）。研究对象涵盖建造于软、中、硬三类不同场地土上的结构。在TMD优化环节，以安装TMD的主体结构位移标准差与未安装TMD的主体结构位移标准差的比值最小化作为目标函数。研究表明，当地基土刚度越高，针对含高频成分的地震动，TMD最优频率与结构固定基底频率的比值越趋近于1。同时可观测到，对于所有类型的场地土，TMD均会与柔性基底频率实现调谐：在较小质量比下可达成完美调谐，而随着质量比增大则逐渐失谐。另一方面，不受场地土类型影响，TMD最优阻尼比均随TMD质量比的提升而增大。TMD在较高质量比下的减振效能更优，尤其在软土地基上表现更为显著。对于建造于柔性基底、受低频成分地震动作用的结构，最优TMD会与柔性基底频率调谐，且该特性不受场地土类型以及主体结构固定基底周期的制约。当质量比较小时，TMD最优阻尼比对柔性周期不敏感，而当最优阻尼比与地震动的卓越周期匹配时，其数值达到最小。另一方面，当TMD与土-结构系统的柔性周期调谐，且该周期与地震动的卓越周期一致时，TMD可达到最大减振效率，且该效率在软土地基上更高。本文采用两条地震动记录开展确定性分析：一条为符合智利规范NCh2745的人工地震波，其特征为高频成分丰富；另一条为类似1985年墨西哥地震的地震动，以低频成分为典型特征。分析结果显示，在本文分析的所有类型场地土上，最优TMD均可有效调控结构的响应。