Seismic Vulnerability of Post-Islamic Monumental Structures in Iran: Review of Historical Sources

This paper reports on a study undertaken to investigate the earthquake performance and assess the seismic vulnerability of post-Islamic monumental structures in Iran. These structures are primarily of brick masonry construction, though some notable stone and mud-brick structures also exist. The structures are first classified according to their structural forms. A review of the available historical and recent sources on the earthquake behavior of different structural forms is then conducted. A second classification of the structures is subsequently made according to their seismic vulnerability. By estimating the location intensity for a large number of past and present structures, subjected to earthquakes in the last millennium, “damage” and “survival” intensity levels are calculated for different structural groups. Based on the estimated damage and survival intensity levels, an intensity scale is proposed for the post-Islamic historical structures in Iran.     

Evaluation of Strengthening Techniques of Traditional Masonry Buildings: Case Study of a Four-Building Aggregate

Increasing appraisal of the durability, conservation state, and changeable use and function of old buildings in urban centers relies a great deal on the structural safety evaluation of vertical load capacity and the ability to resist horizontal forces. The need to assess seismic vulnerability, particularly of traditional masonry buildings, is a key issue. Evaluation of the seismic vulnerability of old buildings is essential in the definition of strengthening needs and minimization of damage from seismic actions in the safeguarding of built heritage. A three-dimensional model was developed for an aggregate of four traditional masonry buildings located in the old city center of Coimbra, in Portugal. The finite element modeling of these buildings has aimed to identify structural fragility, understand the damages detected, and evaluate the global structural safety of these types of buildings. The primary results obtained in this case study helped to interpret the structural damage and stress distribution, and verified global stability and its consequences. Different strengthening techniques to improve the global behavior of these buildings were modeled and analyzed. A comparison of the efficiencies of strengthening strategies is also discussed.     

Lessons Learned from the Damaged Chi-Lu Cable-Stayed Bridge

A disastrous earthquake struck central Taiwan at 01:47 a.m. September 21, 1999 (Taiwan local time). The Seismology Center of the Central Weather Bureau (CWB) determined the magnitude of this earthquake to be ML 7.3 (CWB) and MW 7.7 (Harvard CMT). The earthquake caused heavy casualties and structural damage to bridges and buildings. In the damaged areas, the only cable-stayed bridge, the Chi-Lu, was in the final stages of completion at the time of the earthquake. This bridge connected Chi-Chi to the small town of Lu-Ku across the Juoshuei River. Viaducts ran from both banks of the river to the ends of the cable-stayed bridge. The bridge, designed by T. Y. Lin International, was supported on a single pylon, which was connected to the center of the roadway by two rows of cables. In this paper, the damage suffered by the Chi-Lu bridge is reported. Severe damage occurred in the deck on the southern side of the bridge. Additional damage occurred in the pylon. Below the roadway, the pylon showed evidence of only minor cracking. However, above the roadway there was severe spalling of the cover and a crack extended upward nearly to the level of the lowest cables. The seismic performance of the bridge was evaluated by computer modeling. The damage predicted by the computational results was compared to that sustained by the bridge. The lessons learned from this study are described.     

高层建筑的扭转破坏机理与抗扭措施

国内外历次震害表明,建筑物因扭转破坏占地震破坏的比例非常大,随着高层建筑结构平面,立面的多样化和复杂化,不规则结构的扭转破坏问题日益凸显。为了减轻地震时的扭转破坏,本文运用satwe软件,分别采用四种方案对周边构件进行刚度调整,得出加大离刚心最远处构件的刚度,最能有效地减轻扭转效应,并根据扭转机理提出了一系列的抗扭措施为工程设计提供依据。     

Introspection on improper seismic retrofit of Basilica Santa Maria di Collemaggio after 2009 Italian earthquake

The 2009 L'Aquila, Italy earthquake highlighted the seismic vulnerability of historic masonry building structures due to improper "strengthening" retrofit work that has been done in the last 50 years. Italian seismic standards recommend the use of traditional reinforcement techniques such as replacing the original wooden roof structure with new reinforced concrete (RC) or steel elements, inserting RC tie-beams in the masonry and new RC floors, and using RC jacketing on the shear walls. The L'Aquila earthquake revealed the numerous limitations of these interventions, because they led to increased seismic forces (due to greater additional weight) and to deformation incompatibilities of the incorporated elements with the existing masonry walls. This paper provides a discussion of technical issues pertaining to the seismic retrofit of the Santa Maria di Collemaggio Basilica and in particular, the limitations of the last (2000) retrofit intervention. Considerable damage was caused to the church because of questionable actions and incorrect and improper technical choices.     

Causes of Collapse and Damage to Low-Rise RC Buildings in Recent Turkish Earthquakes

This study assesses performance objectives defined in the Turkish Earthquake Code (TEC) in order to make a realistic evaluation related to heavy damage and collapse reasons of reinforced concrete (RC) buildings that experienced severe earthquakes in Turkey. A series of three-dimensional RC buildings with different characteristics and representing low-rise structures damaged and collapsed in the earthquake areas is designed according to Turkish codes (Turkish Design Standards and Turkish Earthquake Code). Pushover analyses are carried out to determine nonlinear behavior of the buildings under earthquake loads. Building performances are determined by using the displacement coefficients method, which is a commonly used nonlinear static evaluation procedure for different seismic hazard levels defined in the TEC. The stipulated performance objectives in the TEC are checked in terms of plastic rotations and maximum story drift. From the results of this research, it can be concluded that low-rise RC buildings designed according to Turkish codes sufficiently provide for the performance objectives stipulated in the TEC. Reasons for the heavy damages and collapses of RC buildings during severe earthquakes are explained by commonly occurring themes (i.e., project errors, poor quality of construction, modifications of buildings, etc.).     

Formulation of Seismic Fragilities for a Wood-Frame Building Based on Visually Determined Damage Indexes

The study of earthquake engineering has made significant strides over the last one-half century with scientists developing methods to better understand the basis and mechanisms of earthquakes and engineers working to mitigate economic loss and fatalities. A paradigm known as performance-based seismic design (PBSD) not only provides life safety to building occupants, but seeks to control structural and nonstructural damage in buildings and other structures. The development of fragility curves based on the well-known Park-Ang damage index is examined herein. This type of formulation can provide the information needed to assess the seismic vulnerability of a structure. Existing shake table test data from the NEESWood Project’s test of a 223?m2 (1,800 sq ft) two-story house was combined with a participant survey to calibrate a damage model. The result was the development of damage fragilities based exclusively on nonlinear time history analysis. Then, the proposed numerical damage model was applied and fragility curves were developed for a six-story light-frame wood condominium building. The results appear logical based on observations of system-level shake table tests over the last decade, and thus the method shows promise provided significant torsion is not present in the system.     

Inelastic Damage Analysis of Reinforced Concrete Bridge Columns Based on Degraded Monotonic Energy

This paper summarizes the prediction of seismic damage of two existing bridges. The objective is to apply a damage index definition for reinforced concrete bridge columns under cyclic loading to existing bridge columns that might experience real seismic loading in the future, and to evaluate the ability of the damage index in describing the damage progression of the bridge columns during real seismic loading. Two existing bridges were selected from the Greater Vancouver Area in Canada. The first bridge, the Garneau Flyover, was designed in 1985 to ATC-6-1981 and is expected to have sufficient resistance to lateral earthquake loading. The second bridge, the Clydesdale Street Underpass, was designed long before ATC-6-1981 and is expected to show little or no lateral earthquake resistance. The damage index is applied to each of these structures, with columns modeled using the CANNY nonlinear structural analysis program. Shear and bond slip deformations were considered by making a simple modification to the column flexural properties. A series of nonlinear dynamic analyses were performed using records from the 1971 San Fernando, 1978 Miyaki-Oki (Japan), 1989 Loma Prieta, and 1999 Taiwan earthquakes fitted to the Vancouver firm ground spectrum. The calculated damage index provides a simple numerical indicator of the damage during an earthquake, easily computed from the results of a nonlinear dynamic analysis.     

National Program to Improve Seismic Performance of Steel Frame Buildings

This paper reviews the performance of welded steel moment frame buildings during the Northridge earthquake. Some of the studies being undertaken in the United States as part of the FEMA-funded SAC Steel Project are described. The intent of these studies is to devise improved methods for designing new steel frame structures; for inspecting, evaluating, and repairing seismic damage to these types of structures following a major earthquake; and for inspecting, evaluating, and retrofitting existing at-risk steel frame buildings. General observations resulting from these studies are highlighted and the overall format for the new design provisions is presented.     

Assessment of Mortar and Brick Strength in Earthquake-Affected Structures in Peru Using a Schmidt Hammer

This study describes results of surveys with Schmidt hammer conducted after the earthquake of August 15, 2007 in coastal cities of Ica, Pisco, and Chincha, Peru. Statistical analysis included comparison of data on compressive strength collected from various types of buildings in damaged and intact walls and bricks. Results of statistical analysis suggest that architecture and nonstructural building design considerations in masonry structures may be more important determinants of seismic resistance than construction material strength. Comparison of mortar samples with respect to structure ownership revealed that strength of mortar at test locations in privately owned buildings was significantly greater than in public buildings.     

轻质混凝土拼装墙板填充钢框架协同抗震性能试验研究

为了研究墙板与钢框架结构之间的协同抗震性能,对采用不同墙框连接节点的轻质混凝土拼装墙板填充钢框架进行了低周往复荷载试验。通过对比试件的承载力、滞回性能、刚度、耗能以及延性性能,探讨了轻质混凝土拼装墙板及其整体性对结构抗震性能的影响。结果表明:填充墙板钢框架结构的最终破坏形态以墙板挤压开裂,框架梁柱端部翼缘屈曲为主;轻质混凝土拼装墙板与钢框架协同工作,有利于提高结构整体的承载力和变形能力,减轻钢框架在平面内的屈曲破坏;与刚性节点相比,采用柔性节点连接墙板与钢框架对结构的承载力、层间刚度和耗能能力更为有利;增强拼装墙板的整体性,有助于提高结构整体刚度、变形和耗能能力。研究结果可为轻质混凝土拼装墙板填充钢框架结构的抗震设计提供参考。      

浅谈抗震构造在结构设计中的重要性

本文根据唐山地震、汶川地震及玉树地震的震害分析,结合《建筑抗震设计规范》（GB50011—2010）,提出抗震设计时应注意的几点看法。希望引起设计、施工、监理及开发商等建筑界同仁对抗震构造的高度重视,把抗震构造实实在在地运用到工程建设的各个环节。     

设防烈度对框架—核心筒结构受力性能和材料用量的影响

为了考察设防烈度对钢筋混凝土框筒结构受力性能、材料用量的影响,在充分调研了目前我国100 m以上已建或在建超高层建筑的基础上,选择150~300 m范围内钢筋混凝土框架-核心筒办公类超高层作为代表性研究对象,建立了12个不同烈度、不同高度下的计算模型,详细分析了其结构的周期比、剪重比、刚重比、地震作用和风荷载影响等结构受力性能以及结构的用钢量、混凝土用量随设防烈度的变化情况.研究结果表明,对于济南恒大国际金融中心工程,随着设防烈度的提高,结构自振周期减小,扭转周期滞后于平动周期,扭转效应减小,而结构剪重比明显增加;低烈度地区结构受重力二阶效应的影响较大,整体稳定性成主要安全控制因素;地震作用的影响随设防烈度的增加而增大;6度区建筑超过200 m后,用钢量明显增加,而8度区用钢量随建筑高度呈线性增长;6度和7度区单位面积混凝土用量接近,而8度区混凝土用量增幅约为19%左右,所以设防烈度对结构工程材料用量影响显著.      

Seismic Performance of RC Bridge Column under Repeated Ground Motions

Seismic performance of reinforced concrete bridge column under repeated earthquake ground motions is investigated through shake-table experimentation on a scale model. The specimen is subjected to a series of simulated ground motions at different levels of shaking intensity. The deformation and damage evolution of the test column is addressed in terms of selected mechanical quantities including the effective stiffness, hysteretic energy dissipation, residual displacement, and dominant vibration frequency. The test column, designed according to the AASHTO seismic design specifications, survived successive ground motions by virtue of its outstanding energy-absorption and ductility capacity. Analysis of the experimental data indicates that structural degradation of the column closely correlates with its decreasing effective stiffness and increasing hysteretic energy dissipation. The residual displacement measured at the column top after each shaking event increases with the growth of damage in the column. A frequency-domain analysis of the vibration response of the column during successive ground motions indicates that increase in the structural degradation of the column results in a decrease in the dominant vibration frequency of the column.     

Seismic Effect on Highway Bridges in Chi Chi Earthquake

This paper reports the bridge damage in the Chi Chi earthquake. Damage to bridge structures may occur in the superstructure, the substructure, or the approaches. Typical types of damage are discussed and illustrated in this paper. A review of the design specifications in Taiwan is also presented to give the background on the seismic design of highway bridges in Taiwan.     

Earthquake Simulator Testing and Seismic Evaluation of Suspended Ceilings

Past seismic events have demonstrated the vulnerability of suspended ceilings, classified as nonstructural components, to earthquake damage. Engineers, architects, and manufacturers all participate to help ensure that the units perform satisfactorily during earthquakes. To address the seismic susceptibility, the U.S. national codes and federal and regulatory guidelines recommend two distinct approaches. The first mandates capacity and installation requirements and the second addresses damage states, introducing performance based. Application of these methods entails either accurate structural analysis or seismic qualification by experimentation. Until recently, scant data were available to evaluate the adequacy of the required installations or the damage states. To address this issue, full-scale earthquake laboratory tests of suspended ceiling systems have been undertaken by researchers and manufacturers. Experimentation showed that ceilings meeting the code requirements performed well. The only mode of failure observed during the tests was the loss of panels. Laboratory data were also used to construct fragility curves for the specimen. Large vertical accelerations, typically not observed in the field, dislodged panels close to the center of the test frame. This type of response differs from that presented in past earthquake reconnaissance reports and thus necessitates further examination.     

加强抗震观念 减轻地震灾害

本文根据唐山地震及汶川地震的震害分析,结合《建筑抗震设计规范》(GB 50011-2001 2008年版)提出抗震设计时应注意的几点看法。呼吁全社会加强抗震观念,从而减轻地震灾害。     

Evaluation of Seismic Damage to Memphis Bridges and Highway Systems

This paper presents a procedure for the evaluation of the expected seismic damage to bridges and highway systems in Memphis and Shelby County, Tenn. Data pertinent to 452 bridges and major arterial routes were collected and implemented as a geographic information system database. The bridges were classified into several bridge types using a bridge classification system modified from the NBIS∕Federal Highway Administration coding guidelines. The bridge damage states considered are no∕minor damage, repairable damage, and significant damage. The fragility curves corresponding to these damage states were established for various bridge types. Given an earthquake with a moment magnitude of 7.0 occurring at Marked Tree, Ark., the intensity of ground shaking and liquefaction-induced permanent ground deformation in Memphis and Shelby County were estimated, and then the expected damage to bridges and highway systems was determined. The results can be used to prioritize bridges for retrofitting, to prepare a pre-earthquake preparedness plan, to develop a postearthquake emergency response plan, and to assess the regional economic impact from the damage to highway transportation systems.     

A comparison of IBC with 1997 UBC for modal response spectrum analysis in standard-occupancy buildings

This paper presents a comparison of the seismic forces generated from a Modal Response Spectrum Analysis (MRSA) by applying the provisions of two building codes, the 1997 Uniform Building Code (UBC) and the 2000-2009 International Building Code (IBC), to the most common ordinary residential buildings of standard occupancy. Considering IBC as the state of the art benchmark code, the primary concern is the safety of buildings designed using the UBC as compared to those designed using the IBC. A sample of four buildings with different layouts and heights was used for this comparison. Each of these buildings was assumed to be located at four different geographical sample locations arbitrarily selected to represent various earthquake zones on a seismic map of the USA, and was subjected to code-compliant response spectrum analyses for all sample locations and for five different soil types at each location. Response spectrum analysis was performed using the ETABS software package. For all the cases investigated, the UBC was found to be significantly more conservative than the IBC. The UBC design response spectra have higher spectral accelerations, and as a result, the response spectrum analysis provided a much higher base shear and moment in the structural members as compared to the IBC. The conclusion is that ordinary office and residential buildings designed using UBC 1997 are considered to be overdesigned, and therefore they are quite safe even according to the IBC provisions.