Revision of seismic design codes corresponding to building damagesin the “5.12” Wenchuan earthquake

A large number of buildings were seriously damaged or collapsed in the "5.12" Wenchuan earthquake. Based on field surveys and studies of damage to different types of buildings, seismic design codes have been updated. This paper briefly summarizes some of the major revisions that have been incorporated into the "Standard for classification of seismic protection of building constructions GB50223-2008" and "Code for Seismic Design of Buildings GB50011-2001." The definition of seismic fortification class for buildings has been revisited, and as a result, the seismic classifications for schools, hospitals and other buildings that hold large populations such as evacuation shelters and information centers have been upgraded in the GB50223-2008 Code. The main aspects of the revised GB50011-2001 code include: (a) modification of the seismic intensity specified for the Provinces of Sichuan, Shanxi and Gansu; (b) basic conceptual design for retaining walls and building foundations in mountainous areas; (c) regularity of building configuration; (d) integration of masonry structures and precast RC floors; (e) requirements for calculating and detailing stair shafts; and (f) limiting the use of single-bay RC frame structures. Some significant examples of damage in the epicenter areas are provided as a reference in the discussion on the consequences of collapse, the importance of duplicate structural systems, and the integration of RC and masonry structures.     

我国7度设防等跨RC框架抗地震倒塌能力研究

我国建筑结构抗震设计主要采用基于小震下的构件承载力计算保证结构的抗震承载能力,配合抗震构造措施保证结构的变形能力,缺乏大震抗倒塌定量计算.而实际地震震害表明,即使是同类结构,其结构体系参数对其抗地震倒塌能力也有很大影响.为此,本文依据《建筑抗震设计规范》GB50011 - 2001,按照7度抗震设防设计了24个不同跨度...     

Towards a direct collapse–load method of design for concrete frames subjected to severe ground motions

Most current methods of design for concrete structures under earthquake loads rely on highly idealized ‘equivalent’ static representations of the seismic loads and linear‐elastic methods of structural analysis. With the continuing development of non‐linear methods of dynamic analysis for the overload behaviour and collapse of complete concrete structures, a more direct and more accurate design procedure becomes possible which considers conditions at system collapse. This paper describes an evaluation procedure that uses non‐linear dynamic collapse–load analysis together with global safety coefficients. A back‐calibration procedure for evaluating the global safety coefficients is also described. The aim of this paper is to open up discussion of alternative methods of design with improved accuracy which are necessary to move towards a direct collapse–load method of design. Copyright © 2002 John Wiley & Sons, Ltd.     

Application of consequence-based design criteria in regions of moderate seismicity

Current design criteria and principles of earthquake engineering design are reviewed, including safety factors, probabilistic approach, and two-level and multi-level functional design ideas. The modern multi-functional idea is discussed in greater details. When designing a structure, its resistance to and the intensity of the earthquake action are considered. The consequence of failure of the structure is considered only through a rough and empirical factor of importance, ranging usually from 1.0 to 1.5. This paper suggests a method of “consequence-based design,” which considers the consequences of malfunctioning instead of simply an importance factor. The main argument for this method is that damage to a structure located in different types of societies may have very different consequences, which are dependant on its value and usefulness to the society and the seismicity in the region.     

Seismic performance and probabilistic collapse resistance assessment of steel moment resisting frames with fluid viscous dampers

This paper evaluates the seismic resistance of steel moment resisting frames (MRFs) with supplemental fluid viscous dampers against collapse. A simplified design procedure is used to design four different steel MRFs with fluid viscous dampers where the strength of the steel MRF and supplemental damping are varied. The combined systems are designed to achieve performance that is similar to or higher than that of conventional steel MRFs designed according to current seismic design codes. Based on the results of nonlinear time history analyses and incremental dynamic analyses, statistics of structural and non‐structural response as well as probabilities of collapse of the steel MRFs with dampers are determined and compared with those of conventional steel MRFs. The analytical frame models used in this study are reliably capable to simulate global frame collapse by considering full geometric nonlinearities as well as the cyclic strength and stiffness deterioration in the plastic hinge regions of structural steel members. The results show that, with the aid of supplemental damping, the performance of a steel MRF with reduced design base shear can be improved and become similar to that of a conventional steel MRF with full design base shear. Incremental dynamic analyses show that supplemental damping reduces the probability of collapse of a steel MRF with a given strength. However, the paper highlights that a design base shear equal to 75% of the minimum design base shear along with supplemental damping to control story drift at 2% (i.e., design drift of a conventional steel MRF) would not guarantee a higher collapse resistance than that of a conventional MRF. At 75% design base shear, a tighter design drift (e.g., 1.5% as shown in this study) is needed to guarantee a higher collapse resistance than that of a conventional MRF. Copyright © 2014 John Wiley & Sons, Ltd.     

Seismic collapse capacity of basic inelastic structures vulnerable to the P‐delta effect

The collapse capacity of earthquake‐excited inelastic nondeteriorating SDOF systems, which are vulnerable to the destabilizing effect of gravity loads (P‐delta effect), is evaluated. In this paper, the collapse capacity of the system subjected to a ground motion is defined as spectral acceleration at its initial structural period, at which the structure becomes unstable. Characteristic structural parameters, which affect the collapse capacity, are identified. Ground motion records of the ATC 63 far‐field set characterize severe earthquake excitation. In extensive incremental dynamic analyses studies, the impact of these parameters and of aleatory uncertainties on the collapse capacity is assessed and quantified. Median and percentile collapse capacities are plotted against the initial structural period leading to collapse capacity spectra. Nonlinear regression analyses are applied to derive analytical expressions of the design collapse capacity spectra and collapse fragility curves. The ultimate objective is to provide collapse capacity spectra for easy application and yet sufficient accurate assessment of the dynamic stability of flexible multistory buildings. Copyright © 2011 John Wiley & Sons, Ltd.     

INELASTIC SEISMIC RESISTANCE OF REINFORCED CONCRETE STACK-LIKE STRUCTURES

A method is presented to quantify the inelastic seismic resistance of reinforced concrete stack-like structures by non-linear earthquake analysis. The deformed configuration of stack is idealized as an assemblage of beam elements and actual stress–strain relationships of concrete and reinforcing steel are used to evaluate element matrices. Repeated non-linear analyses are performed by gradually increasing the intensity of acceleration time histories to a level where collapse of the stack is observed in primary stresses. The set of time histories thus obtained are then used to define the ultimate intensity of ground motion that the stack can sustain if inelastic deformations are permitted. A procedure is presented to quantify the difference between inelastic seismic resistance and elastic seismic resistance in terms of displacement ductility capacity factors. For seismic design using available inelastic resistance, values of curvature ductility factor demand for the cross-sections of stacks are also presented. © 1997 by John Wiley & Sons, Ltd.     

框架结构在汶川5.12大地震中的震害分析及抗震启示

列举了框架结构在汶川5.12大地震中的典型震害现象,重点调查了框架柱、梁柱节点,强梁弱柱及填充墙的震害特点,分析了框架结构未能实现强柱弱梁机制的原因,指出了提高框架柱抗震能力的措施及减轻填充墙地震破坏的对策.     

The GIS and analysis of earthquake damage distribution of the 1303 Hongtong M=8 earthquake

The geography information system of the 1303 Hongton M=8 earthquake has been established. Using the spatial analysis function of GIS, the spatial distribution characteristics of damage and isoseismal of the earthquake are studies. By comparing with the standard earthquake intensity attenuation relationship, the abnormal damage distribution of the earthquake is found, so the relationship of the abnormal distribution with tectonics, site condition and basin are analyzed. In this paper, the influence on the ground motion generated by earthquake source and the underground structures near source also are studied. The influence on seismic zonation, anti-earthquake design, earthquake prediction and earthquake emergency responding produced by the abnormal density distribution are discussed. Foundation item: National important fundamental research “The Basic Research of Important Project in Damage Environment” and The important project “The Seismic Hazard Assessment Research and Anti-earthquake Structure Research” from China Earthquake Administration during the 10th Five-year Plan. Contribution No. 04FE1008, Institute of Geophysics, China Earthquake Administration.     

基于IDA的方钢管混凝土框架-SPSW核心筒结构地震易损性研究

为研究方钢管混凝土框架-钢板剪力墙（SPSW）核心筒结构在不同强度地震下破坏概率,使用拉杆模型作为钢板剪力墙等效模型,与已有试验对比验证各参数有效性。以地震动峰值加速度（PGA）作为地震动强度参数,按照场地条件等要求选择11条地震动记录。以结构最大层间位移角作为损伤指标,对一典型方钢管混凝土框架-钢板剪力墙核心筒结构进行增量动力分析（IDA）,得到IDA曲线簇。基于增量动力分析进行易损性分析,得到易损性曲线,并计算结构的抗倒塌储备系数。结果表明:8度多遇地震作用下,此结构处于正常使用状态。8度设防地震作用下,处于修复后可使用状态。8度罕遇地震作用下,处于生命安全状态。表明该结构具有良好的抗震性能,满足规范中“小震不坏”、“中震可修”和“大震不倒”的抗震设防目标。该结构抗倒塌储备系数大于规范建议值,具有较好的抗倒塌能力。     

双防线可恢复性能斜交网格结构耗能机制和抗震性能研究

为提高斜交网格结构的抗震性能,提出一种双防线可恢复性能斜交网格结构。双防线可恢复性能斜交网格结构采用剪切耗能段和特定梁端塑形铰进行集中耗能,使主体结构构件保持弹性。剪切耗能段不承受和传递重力荷载,易在震后修复或更换,使建筑可迅速恢复功能。为实现目标耗能机制,对等效能量塑形设计法进行改进以适用于可恢复性能斜交网格结构,并进行结构设计举例。采用OpenSees软件对所设计结构建立详细的有限元计算模型,进行非线性动力时程分析,以验证双防线耗能机制并评估抗震性能。分析结果表明:（1）小震、中震和大震下的结构顶部位移角分别为0.28%、0.8%和1.7%,与性能设计目标基本相同;（2）中震时剪切耗能段屈服,特定梁端未出现塑性铰;（3）大震时,特定梁端出现塑性铰以增加结构耗能能力,剪切耗能段屈服且处于延性范围内。因此新型可恢复性能斜交网格结构具有有效的双防线耗能机制,在中震后可迅速修复,在大震中可保持延性,实现"中震可修,大震不倒"的性能目标。     

七层钢筋混凝土异型柱支撑框架结构模型振动台试验研究

七层钢筋混凝土异型柱支撑框架结构体系的模型，缩尺比为１：３，在振动台上进行了模拟地震动试验，结果表明：该体系的抗震性能较好，可使斜杆在预估地震强度的作用下先开裂并继续工作，从而减轻主体结构的地震破坏。并指出，该体系应进一步实现抗裂抗倒双重设防准则与其设计方法，研究发挥支撑的消能减震作用。这种抗震结构体系，已在天津市的轻质节能建筑中采用。     

Collapse of a nonductile concrete frame: Shaking table tests

Post‐earthquake reconnaissance has reported the vulnerability of older reinforced concrete (RC) columns lacking details for ductile response. Research was undertaken to investigate the full‐range structural hysteretic behavior of older RC columns. A two‐dimensional specimen frame, composed of nonductile and ductile columns to allow for load redistribution, was subjected to a unidirectional base motion on a shaking table until global collapse was observed. The test demonstrates two types of column failure, including flexure‐shear and pure flexural failure. Test data are compared with various simplified assessment models commonly used by practicing engineers and researchers to identify older buildings that are at high risk of structural collapse during severe earthquake events. Comparison suggests that ASCE/SEI 41‐06 produces very conservative estimates on load–deformation relations of flexure‐shear columns, while the recently proposed ASCE/SEI 41‐06 update imposes significant modifications on the predictive curve, so that improved accuracy has been achieved. Copyright © 2008 John Wiley & Sons, Ltd.     

工程抗震设计思考

抗震设计规范主要是理论研究与地震工程实践经验的概括和总结。而且它还将随着地震认识的深化和科学的进步,与时俱进,不断地修改、完善。因此,文中就一些理论概念、设防要求、结构分析、抗震措施等问题阐释我们的体会和看法。明确指出,地震烈度的意义应依据应用的不同状况给出合理解释;将地震烈度附上概率的概念,不易于应用;抗震设防的目的在于减轻建筑物地震破坏、避免人员伤亡、减少经济损失;地区抗震设防应以设防烈度为防范对象;工程抗震设计的设防烈度应考虑场地条件的影响;基于弹性反应谱理论,在考虑抗震设防要求的计算分析中,引入重要性系数及结构系数是合理的;重要性系数及结构系数都与地震发生概率无关;没有必要取多条地震时程曲线按所谓多遇地震下进行补充计算;地震作用的准确性有限,除结构计算分析外,采用适当抗震构造措施是必要的;超越设防烈度的地震是抗震设计的风险问题。     

ASEISMIC CONSTRUCTION AND DESIGN METHOD FOR MULTI-STOREY COMPOSITE STRUCTURES

Using a newly introduced ductile low-rise shear wall with vertical keyways, a seismic resistance design approach for a practical type of composite structure, which consists of a reinforced concrete frame in the bottom floors and masonry structures in the upper floors, has been presented. The purpose of the new design approach is to improve the earthquake resistance of the whole structure by increasing the energy dissipation capacity in the bottom part of the structure. Non-linear analysis shows that, by adopting the newly proposed ductile low-rise shear wall in the bottom of the structure, the lateral deflection of the structure is not much more than that of a structure using conventional solid low-rise shear walls under a small or moderate earthquake excitation, and that even under the attack of a severe earthquake, a stable structural response can be expected for the proposed structure. Thus it is easy for such a structure to achieve the design objective of ‘minor damage in a small earthquake and prevention of collapse in a severe earthquake’ and the design method is of practical value for similar types of composite structures.     

Post‐earthquake functionality of highway overpass bridges

Bridges are crucial to the transportation network in a region struck by an earthquake. Collapse of a bridge determines if a road is passable. Ability of a bridge to carry traffic load after an earthquake determines the weight and speed of vehicles that can cross it. Extent of system and component structural damage in bridges determines the cost and time required for repair. Today, post‐earthquake bridge evaluation is qualitative rather than quantitative. The research presented in this paper aims to provide a quantitative engineering basis for quick and reliable evaluation of the ability of a typical highway overpass bridge to function after an earthquake. The Pacific Earthquake Engineering Research (PEER) Center's probabilistic performance‐based evaluation approach provides the framework for post‐earthquake bridge evaluation. An analytical study was performed that linked engineering demand parameters to earthquake intensity measures. The PEER structural performance database and reliability analysis tools were then used to link demand parameters to damage measures. Finally, decision variables were developed to describe three limit states, repair cost, traffic function, and collapse, in terms of induced damage. This paper presents the analytical models used to evaluate post‐earthquake bridge function, decision variables and their correlation to the considered limit states, and fragility curves that represent the probability of exceeding a bridge function limit state given an earthquake intensity. Copyright © 2005 John Wiley & Sons, Ltd.     

套建增层预应力钢骨混凝土框架弹塑性地震反应分析

从套建增层改造实践中存在的问题出发,提出了一种新型外套增层结构型式,即以内置H型钢预应力混凝土组合梁为框架梁、以配置4个或8个角钢的角钢混凝土柱为框架柱的套建增层用框架结构,并给出了节点构造。根据不同的场地条件和地震设计分组,对基于现行设计标准设计的跨度为16m的新型套建增层框架进行了罕遇地震作用下的时程分析。分析结果表明,在满足常遇地震作用下的设计要求时,在7度和8度罕遇地震作用下,建造在I、II、III类场地上的部分套建增层框架将会倒塌。根据弹塑性反应分析结果,提出了在罕遇地震作用下避免这种套建增层框架发生倒塌的设计建议。     

Characteristics of Seismic Damage of Buildings: Constraints from Tilt Photography Technology

In this paper, the tilt photography data acquisition and three-dimensional modeling of the Tashkurgan M_S5.5 earthquake in Xinjiang are conducted using the tilt photography system of the Rotor UAV. The three-dimensional model is used to interpret the earthquake damage on buildings in the mega-earthquake area in order to acquire different-level house damage in the Kuzirun village disaster area. In addition, the characteristics of seismic damage on typical buildings are analyzed. The results show that the main collapsed houses in the mega-earthquake area are sand-stone buildings, of which about 39% are sand-stone buildings. Several brick-wood buildings and brick-concrete buildings are seriously damaged, while the buildings with frame structures are mainly slightly damaged, and the houses near the macro-epicenter of the earthquake are all in good conditions. Three-dimensional tilt photography technology can vividly display the scene of earthquake disaster, and can provide significant demonstration in building damage degree together with detailed analysis of disaster situation.