Field Vibration Testing & Analyses of an Existing RC Building

在动态载荷条件下，缺乏足够高的空间分辨率数据集，这大大限制了地震工程师提高他们对结构和岩土系统抗震性能的理解的能力。例如，主要地震事件后高度非线性结构响应的现场观测得到了定性观测的很大支持。在过去的几十年里，建筑物的仪器记录一直是一种宝贵的资源；然而，仪器的密度(每个结构平均分配~12个仪器)太低，无法对系统或部件的响应进行详细的评估。为了解决这一缺点，加州大学洛杉矶分校的土木工程系正在开发设备，作为NSF地震工程模拟网络(NEES)计划的一部分，显著增强强迫振动测试的现场测试能力。该项目题为“现场测试和监测结构性能”，于2000年1月启动，将持续到2004年9月。正在采购的现场测试设备包括最先进的振动源(线性惯性质量振动器和偏心质量振动器)、传感器和无线数据采集系统(加速计、LVDT、光纤测量读数单元、数字化仪、路由器、工作站)、CPT卡车和现场土壤振动传感器，以及联网设备(数据集中器、卫星上行链路站)，以实现实验结果的实时数据采集、处理和万维网广播。该项目仅涉及设备的采购和集成；通过与加州大学洛杉矶分校/NEES项目以实践者为基础的实施咨询委员会(IAB)的合作，洛杉矶的一座四层写字楼被确定为强迫振动测试的候选建筑。这座建筑之所以受到普遍关注，是因为(1)它有一个非常常见的结构体系，由周边弯矩框架和内部后张法板柱框架组成，(2)它在北岭地震中遭到严重破坏，导致它被废弃。以前以分析为基础的震后研究通常无法解释观察到的破坏。业主计划拆卸该建筑物；但由于种种原因，他们在大约两年内不会这样做，并已批准私人投资者进行测试。拟议的研究包括使用NEES设备对建筑物进行强迫振动测试，以及详细的系统识别和数值模拟研究。地震类型和简谐力历史都将应用于屋顶水平的建筑，并将记录波形，以便能够评估完整的结构系统响应、结构组件的行为(例如，板柱连接和桩帽)、非结构组件(例如，隔断、管道系统)的响应以及这些组件对系统响应的影响。将使用密度仪器阵列，包括加速计、位移传感器和应变计。将安装无线局域网，以采集和记录波形数据。测试产生的详细数据集将为了解这种常见类型的结构系统的性能以及北岭地震期间主题建筑性能不佳的原因提供宝贵的见解。测试还将在设备使用协议和数据归档模型方面为NEES计划提供宝贵的经验。在本供资期间内就这些问题积累经验特别有用，因为国家环境教育系统的设备开发工作正在进行中，所吸取的经验教训可在2004年国家环境教育系统上线之前实施。与这项提议的及时性有关的还有一个事实，即这座重要的建筑将在两年内被夷为平地。

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.