Earthquake-Induced Damage Detection in a Monumental Masonry Bell-Tower Using Long-Term Dynamic Monitoring Data

ABSTRACT

This work investigates the use of an advanced long-term vibration-based structural health monitoring tool to automatically detect earthquake-induced damages in heritage structures. Damage produced in a monumental bell-tower at increasing values of the Peak Ground Acceleration (PGA) of the seismic input is predicted by incremental nonlinear dynamic analysis, using a Finite Element model calibrated on the basis of experimentally identified natural modes. Then, predicted damage effects are artificially introduced in the monitoring data to check for their detectability. The results demonstrate that a very small damage, associated to a low intensity and low return period earthquake, is clearly detected by the monitoring system.     

Transient and Long-Term Changes in Seismic Response of the Natural Resources Building,Olympia, Washington,due to Earthquake Shaking

The Natural Resources Building (NRB) in Olympia, Washington, was shaken by three earthquakes (Mw = 5.8, 6.8, and 5.0) between 1999 and 2001. Building motions were recorded on digital accelerographs, providing important digital recordings of repeated strong shaking in a building. The NRB has 5-stories above grade with 3 sub-grade levels and a ductile steel-frame elongated in the E-W direction. The upper two floors extend significantly beyond the lower 3 on the southern and eastern sides. N-S motions dominate the fundamental modal vibrations of the building system. In the 1999 Satsop M5.8 earthquake, the frequency of this fundamental system mode was 1.3 Hz during motions of 10% g. The frequency dropped to 0.7 Hz during the 2001 M6.8 Nisqually strong motions. Moreover, the Nisqually recordings reveal both numerous high-frequency transients of up to 0.18 g, several of which are visible on widely spaced sensors, and long-term tilts of some of the sensors. The weaker 2001 M5.0 Satsop earthquake motions showed the frequency remained depressed at less than 1 Hz for the eastern side of the structure, although the western side had recovered to 1.3 Hz. An ambient noise survey in 2008 showed the fundamental frequency of N/S vibrations remains about 1.0 Hz for the eastern side of the building and 1.3 Hz for the western side. These results suggest that in the Nisqually earthquake, the east side of the NRB suffered a permanent reduction in fundamental mode frequency of 37% due to loss of system stiffness by undetermined mechanism.     

三维激光扫描技术在岩土文物保护中的应用

三维激光扫描是近年来飞跃发展的一项高新测绘与信息技术,在文物保护中发挥了重要作用介绍了三维激光扫描技术的主要特点,从岩土文物保护需求出发,结合实际文物保护工程,重点介绍了三维激光扫描技术在文物信息留存、虚拟修复、监测等方面的应用,最后指出三维扫描技术在岩土文物保护中的心用与发展须与保护需求紧密结合,而硬软件的改进完善及相关技术的集成心用亦是重要研究方向。     

开放参观对莫高窟洞窟微环境的影响

洞窟微环境相对湿度是影响壁画保存的关键因素,为了解开放参观对莫高窟洞窟相对湿度的影响,本研究选择莫高窟南区四个相似洞窟进行长达10年(2004~2013年)的定期监测,对比分析了开放洞窟和关闭洞窟其相对湿度的变化情况。结果表明:开放洞窟相对湿度在开放时段波动频率与游客参观频次正相关,发生降雨时开放洞窟相对湿度迅速上升,关闭洞窟可有效阻隔窟外相对湿度波动的影响。开放洞窟在参观量大的旅游旺季,其相对湿度月极大值、日较差月均值以及日极大值超过60%的频次均明显高于关闭洞窟。将开放洞窟关闭,关闭洞窟开放后,其相对湿度呈相反规律变化。开放参观会导致洞窟相对湿度水平显著升高,日波动幅度明显增大,从而增加壁画劣化风险。这些结论可为洞窟的预防性管理和风险评估提供科学依据。     

基于环境监测的三星堆遗址祭祀坑考古现场预防性保护

目前考古现场保护主要以应急保护技术与临时加固材料的研究和应用为主,而关于考古现场预防性保护少有报道。本次三星堆遗址祭祀坑发掘保护构建了由考古舱、考古舱环境调控系统、空气质量监测系统、土遗址监测系统、区域气象站、预防性保护措施、监测信息智能管理平台组成的预防性保护体系。发掘前,通过土遗址监测系统和区域气象站获取文物埋藏环境信息和区域气象信息,为考古舱内环境设置提供了依据。发掘过程中,采取舱内温湿度调控、保湿、空气杀菌净化、控制舱内人数与新风换气等预防性保护措施,达到控制考古舱温湿度、减少细菌和真菌总数、降低舱内CO_(2)浓度,减缓象牙等文物失水速度的目的,有效控制了出土文物开裂、酥粉、霉菌暴发等病害发生,为考古发掘与保护赢得了时间。三星堆祭祀坑考古现场预防性保护的创新探索与实践为以后重要遗址的现场保护指引了方向、提供了可借鉴经验。