Field Vibration Testing & Analyses of an Existing RC Building

在动力荷载条件下，全尺寸结构的现场测试缺乏足够的高空间分辨率数据集，这极大地限制了地震工程师提高他们对结构和岩土系统地震性能理解的能力。例如，主要地震事件后高度非线性结构响应的现场观测在很大程度上得到了定性观测的支持。在过去的几十年里，来自建筑物的仪器录音一直是一种宝贵的资源；然而，仪器的密度（每个结构通常配置约12个）太低，无法对系统或组件的响应进行详细评估。为了解决这一缺陷，加州大学洛杉矶分校土木工程系正在开发设备，以大幅提高强制振动测试的现场测试能力，这是nsf地震工程模拟网络（NEES）计划的一部分。该项目名为“结构性能的现场测试和监测”，于2000年1月启动，一直持续到2004年9月。购买的现场测试设备包括最先进的振动源（线性惯性和偏心质量振动器）、传感器和无线数据采集系统（加速度计、lvdt、光纤计读数单元、数字化仪、路由器、工作站）、CPT卡车和原位土壤振动传感器，以及网络设备（数据集中器、卫星上行站），以实现实时数据采集、处理和实验结果的全球广播。本项目仅涉及设备的采购和集成；项目资金并未用于具体的研究活动。通过与加州大学洛杉矶分校/NEES项目的实施咨询委员会（IAB）合作，洛杉矶的一栋四层办公楼已被确定为强制振动测试的候选者。该建筑引起普遍的兴趣，因为(1)它有一个非常常见的结构系统，包括一个外围弯矩框架和一个内部后张板柱框架，(2)它在北岭地震期间严重受损，导致它被遗弃。以前对该建筑的震后分析研究通常无法解释所观察到的破坏。业主计划拆除该建筑物；然而，由于各种原因，大约两年内不会这样做，并已授予pi进行测试的许可。拟议的研究包括使用NEES设备对建筑物进行强制振动测试，以及详细的系统识别和数值模拟研究。地震类型和谐波力历史将应用于屋顶水平的建筑物，波形将被记录下来，以便评估完整的结构系统响应，结构组件行为（例如，板柱连接和桩帽），非结构组件（例如，隔板，管道系统）的响应以及这些组件对系统响应的影响。将使用密集的仪器阵列，包括加速度计、位移传感器和应变计。将安装一个无线局域网来获取和记录波形数据。从测试中产生的详细数据集将为这种常见类型的结构体系的性能以及在北岭地震期间主题建筑性能不佳的原因提供有价值的见解。该测试还将为NEES项目在设备使用协议和数据存档模型方面提供宝贵的经验。由于NEES设备开发工作正在进行中，在目前的资助期内获得这些问题的经验特别有用，并且可以在NEES系统于2004年上线之前实施所吸取的经验教训。这一建议的及时性也与这个重要的建筑将在两年内被夷为平地的事实有关。

The lack of adequately high spatial resolution data sets from field testing of full-scale structures underdynamic loading conditions significantly limits the ability of earthquake engineers to improve theirunderstanding of the seismic performance of structural and geotechnical systems. For example, fieldobservations of highly nonlinear structural response following major seismic events have been largelysupported with qualitative observations. Instrument recordings from buildings have been an invaluableresource over the past few decades; however, the density of instruments (with ~12 per structure being acommon allocation) is too low to enable detailed evaluations of system or component responses.To address this shortcoming, the Civil Engineering Department at UCLA is in the process of developingequipment to substantially enhance field testing capabilities for forced-vibration testing as part of the NSFNetwork for Earthquake Engineering Simulation (NEES) program. The project, entitled Field Testingand Monitoring of Structural Performancece, was initiated in January 2000 and continues throughSeptember 2004. Field testing equipment being purchased consists of state-of-the-art vibration sources(linear inertial and eccentric mass shakers), sensors and a wireless data acquisition system(accelerometers, LVDTs, fiber optic gage readout unit, digitizers, routers, workstations), a CPT truck andin situ soil vibration sensors, and networking equipment (data concentrator, satellite uplink station) toallow for real-time data acquisition, processing, and world wide web broadcasting of experimental results.The project involves only purchase and integration of the equipment; no specific research activities arebeing conducted with the project funds.Through collaboration with a practitioner-based Implementation Advisory Board (IAB) for theUCLA/NEES project, a four-story office building in Los Angeles has been identified as a candidate forforced vibration testing. The building is of general interest because (1) it has a very common structuralsystem consisting of a perimeter moment frame and an interior post-tensioned slab-column frame, and (2)it was significantly damaged during the Northridge earthquake, causing it to be abandoned. Previousanalysis-based post-earthquake studies of the building have generally been unable to explain the observeddamage. The owners plan to demolish the structure; however, for a variety of reasons, will not do so forapproximately two years and have granted the PIs permission to conduct testing.The proposed research involves forced vibration testing of the building using the NEES equipment aswell as detailed system identification and numerical modeling studies. Both earthquake-type andharmonic force histories will be applied to the building at the roof level, and waveforms will be recordedto enable evaluations of the complete structural system response, structural component behavior (e.g.,slab-column connections and pile caps), and the response of non-structural components (e.g., partitions,piping systems) as well as the influence of these components on the system response. A denseinstrumentation array will be utilized that will include accelerometers, displacement transducers, andstrain gauges. A wireless local area network will be installed to acquire and record waveform data,. Thedetailed data set generated from the tests will provide valuable insight into the performance of thiscommon type of structural system and the reasons for the poor performance of the subject building duringthe Northridge earthquake. The testing will also provide invaluable experience to the NEES program withrespect to equipment use protocols and data archiving models. Gaining experience on these issues withinthe present funding period is particularly useful as the NEES equipment development work is ongoing,and lessons learned can be implemented prior to the NEES system going online in 2004. Also relevant tothe timeliness of this proposal is the fact that this important building will be razed in two years.