The Numerical Study of Base-Isolated Buildings Under Near-Field and Far-Field Earthquakes

The behavior of base-isolated building frame is investigated with the help of a numerical study for far-field and near-field earthquakes with directivity and fling-step effects. Both design-level and extreme-level earthquakes are considered. Selected response parameters are peak floor displacement, acceleration, base shear, and isolator displacement. Inelastic behavior of base-isolated structure during the earthquake is investigated performing nonlinear time history analysis of a ten-story building frame. This study shows that base isolation is not effective for near-field earthquakes. Even for design-level earthquake, the frame gets significantly into inelastic range for earthquakes with fling-step effect.     

故宫灵沼轩的动力特性及抗震性能研究

故宫灵沼轩是我国最早建造的钢铁-砌体组合结构之一,具有重要的历史、艺术和科学价值。为了评估灵沼轩在地震作用下的结构安全状况,建立了灵沼轩结构的三维有限元模型,并对其进行了动力特性和地震时程分析,得出了其固有频率、模态振型、地震位移响应和地震应力响应。结果表明:灵沼轩整体结构布置对称性较高,扭转刚度较大,对抗震较为有利;在8度多遇地震、设防地震和罕遇地震作用下,灵沼轩的金属结构部分及砌体结构部分的顶点位移和层间位移角均符合现行规范要求,砌体结构部分的第三主应力响应均小于材料的抗压强度,不存在压溃风险。在8度多遇地震和设防地震作用下,砌体结构部分的第一主应力响应均小于材料的抗拉强度,结构不会发生拉裂。但在8度罕遇地震作用下,砌体结构的部分位置拉应力超过材料的抗拉强度,这些位置存在开裂危险。最后,综合动力特性和抗震性能分析的结果,提出了灵沼轩的抗震加固建议。     

Physics-based Simulation and High-fidelity Visualization of Fire Following Earthquake Considering Building Seismic Damage

This work proposes a framework for the physics-based simulation and high-fidelity visualization of fire following earthquake (FFE) considering building seismic damage. The seismic damage of regional buildings is simulated using multiple degree-of-freedom building models in conjunction with nonlinear time-history analysis. In parallel, a high-fidelity visualization is presented to simulate fire spread and smoke effects. A case study of downtown Taiyuan with 44,152 buildings is performed. The results show that the influence of different ground motions and building seismic resistances on fire ignition and fire spread can be taken into account and that the FFE scene can be displayed realistically.     

Seismic Vulnerability Assessment of Hybrid Steel-Timber Structure: Steel Moment-Resisting Frames with CLT Infill

In this article, seismic vulnerability assessment is carried-out on a novel hybrid structure (steel moment resisting frame (SMRF) and cross laminated timber (CLT) infill panels). For the seismicity of Vancouver, Canada, a three-bay, 3-, 6-, and 9-story height SMRFs are designed for two ductility levels (ductile and limited ductility). To study the seismic vulnerability CLT infilled building, parametric analysis was performed by varying infill configuration (bare frame, one-bay infilled, two-bay infilled, and fully infilled). The structure is modeled in OpenSees and nonlinear dynamic analysis is performed. Peak inter-story drift demand and corresponding FEMA performance limits (capacity) values are used to compute the corresponding fragility curves. From the analyses, it can be seen that as more bays are infilled, the fundamental period and seismic vulnerability is reduced significantly. The results highlight that, within the performance-based earthquake engineering, different objectives can be met with varying the CLT configuration.     

Hysteretic Model for Flexure-shear Critical Reinforced Concrete Columns

A model for predicting the cyclic lateral load-deformation response of flexure-shear critical reinforced concrete (RC) columns subjected to combined axial load and cyclic shear is proposed. Strength deterioration in the primary curve due to the effect of shear after yielding is considered by a modification coefficient. Rules for unloading and reloading branches of the hysteretic curve are obtained from regression analysis of test results. Unloading stiffness is fitted as a function of displacement ductility and secant stiffness of the point with maximum displacement in the primary curve. Pinching is simulated by changing the slope of reloading branch. Path-based cyclic strength deterioration is incorporated in the proposed model. In the expression of cyclic strength deterioration, the effects of aspect ratio and axial-load ratio are considered. Comparison between the predicted cyclic response and experimental results indicates that the proposed model can predict the observed hysteretic response of flexure-shear critical RC columns well.     

Elastic Displacement Spectrum-Based Design Approach for Buckling-Restrained Braced Frames

The design focus for a buckling-restrained braced frame (BRBF) is that the buckling-restrained braces (BRBs) dissipate most of the seismic energy while the main frame retains a degree of elastic stiffness under a major earthquake. An elastic displacement spectrum based design method is presented in this article, which can directly determine the sectional area of the BRBs. The yield displacement in the roof of the main frame is taken as the target displacement under a major earthquake. An elastic displacement design spectrum is used to solve the target period of the BRBF. To validate this method, a six-story buckling-restrained braced steel frame is designed using the proposed method, and a series of nonlinear response history analyses (RHAs) are performed to verify the design result. The example shows that the required BRB area can be simply and accurately determined by the proposed method. The error between the given target displacement and the RHA results is 4.0% and 21.3% for BRBFs designed with BRB yield strength of 235 Mpa and 100 Mpa, respectively.     

西藏坚塞颇章宫的结构计算分析

本研究以全国重点文物保护单位西藏罗布林卡三大宫殿之一的坚塞颇章宫为实例,分析藏式古建筑的结构特点,探讨计算分析方法,并针对静力荷载工况和地震组合工况下的结构性能进行了讨论。本研究区别于以往藏式结构的研究方法,主要在于:在计算分析中将墙体建入整体结构模型,考虑墙体对结构的影响;考虑墙体和木柱的“收分”造型的影响;将楼板和屋面的密布木檩等刚度转化为单向板考虑;同时考虑构件已存的变形缺陷影响。计算结果表明:西藏坚塞颇章宫在静力荷载工况作用下,整体状态良好,梁柱墙及节点均满足承载力要求;在地震组合工况作用下,部分柱和墙不满足抗震承载力要求。在地震作用下,该建筑刚度较小的木结构构件首先发生振动。结构薄弱部位是中部四根二层通高木柱。这四根通高木柱长细比较大,刚度较小,一旦发生较大的变形,将直接影响整体结构安全。木柱与墙体之间的变形差异较大,两者变形协调性较差。此外,存在变形缺陷的中部通高木柱所在梁柱节点的抗震承载力不满足要求,应注意加强防护。研究涉及的计算分析方法及相关计算结论对藏式建筑结构的深入研究具有重要的参考价值。     

Predicting the Seismic Response of Capacity-Designed Structures by Equivalent Linearization

An equivalent linearization procedure is developed for predicting the inelastic deformations and internal forces of capacity-designed structures under earthquake excitations. The procedure employs response spectrum analysis, and mainly consists of the construction of an equivalent linear system by reducing the stiffness of structural members that are expected to respond in the inelastic range. These members are well defined in structures designed with capacity principles. Maximum modal displacement demands of the equivalent linear system are determined either from the equal displacement rule, or from independent nonlinear response history analysis of SDOF systems representing inelastic modes.

Predictions obtained from the proposed equivalent linearization procedure are evaluated comparatively by using the results of nonlinear response history analysis as benchmark, linear elastic response spectrum analysis and conventional pushover analysis. The deformations and capacity controlled actions of a 12-story symmetrical plan concrete frame and a 6-story unsymmetrical plan concrete frame are obtained by each method under 96 strong ground motions. It is observed that the proposed procedure results in better accuracy in estimating the inelastic seismic displacement response parameters and capacity controlled forces than the other two approximate methods.     

Analytical Collapse Study of Lightly Confined Reinforced Concrete Frames Subjected to Northridge Earthquake Ground Motions

Review of older non seismically detailed reinforced concrete building collapses shows that most collapses are triggered by failures in columns, beam-column joints, and slab-column connections. Using data from laboratory studies, failure models have previously been developed to estimate loading conditions that correspond to failure of column components. These failure models have been incorporated in nonlinear dynamic analysis software, enabling complete dynamic simulations of building response including component failure and the progression of collapse. A reinforced concrete frame analytical model incorporating column shear and axial failure elements was subjected to a suite of near-fault ground motions recorded during the 1994 Northridge earthquake. The results of this study show sensitivity of the frame response to ground motions recorded from the same earthquake, at sites of close proximity, and with similar soil conditions. This suggests that the variability of ground motion from site to site (so-called intra-event variability) plays an important role in determining which buildings will collapse in a given earthquake.     

南京长江大桥桥头堡抗震加固受力性能研究

为研究南京长江大桥桥头堡填充墙加固对结构抗震性能的影响,提出考虑较高填充墙开裂的双斜撑模型,用于罕遇地震工况下桥头堡的抗震性能计算,同时提出考虑填充墙加固后刚度增强效应的建模方法。利用SAP2000建立了加固前后用于多遇地震工况、设防地震工况及罕遇地震工况的分析模型,并选取了桥头堡在1974年经历的实际地震激励时程及El-Centro地震激励时程作为激励进行了加固前后结构的抗震性能分析比较。研究发现,填充墙加固后桥头堡的抗震性能有了明显提升,其位移响应峰值约下降8%~23%,层间位移角响应峰值约下降12%~22%,而且桥头堡结构在设防地震情况下2个方向的层间位移角均满足了规范要求。另外,在罕遇地震工况下,未加固的填充墙开裂会使结构的扭转刚度下降,而填充墙加固可有效提升结构的扭转刚度,降低桥头堡在地震时发生扭转振动的概率。这2种地震荷载激励的分析结果差异约在3%~21%不等,且响应峰值出现的位置也有一些不同,故对桥头堡进行抗震时程分析时建议选取多条地震波输入综合分析。研究成果可为同类型的钢筋混凝土建筑遗产的抗震加固提供借鉴和参考。     

Survey and Experimental Investigation of Movable Fire Loads in Japanese-Style Wooden Historical Buildings

ABSTRACT

This study investigated the movable fire loads and the characteristics of combustible materials in Japanese-style wooden historical buildings via field surveys and cone calorimeter experiments. Twenty-one historical buildings with 102 rooms and a total floor area of 2235.06 m² were surveyed to determine the movable fire load. Strong correlations among fire load density, compartment floor area, and spatial use are found in this survey. The mean values of the movable fire load density in decreasing order in terms of room use are storeroom (431.38 MJ/m²), study room (298 MJ/m²), bedroom (294.88 MJ/m²), reception room (287.20 MJ/m²), and dining room (217.11 MJ/m²), providing fire engineering design with a reliable fire load setting in various types of rooms in historical buildings.     

A Nonlinear Frame Test Structure with Repeatable Behavior for Experimental Dynamic Response History Investigation

This article describes a novel, small-scale nonlinear beam-column connection and an associated six-story frame test structure for the experimental dynamic response investigation of multi-story buildings subjected to earthquake loading. The objective is to create a re-configurable, reusable experimental platform on which several aspects of nonlinear dynamic response can be investigated through successive, exhaustive testing under suites of earthquake records. Static and dynamic calibration tests demonstrate excellent test-to-test repeatability of four structure configurations. These results confirm that the properties of each configuration (period, strength, energy dissipation) remain invariant, thus allowing future experimental investigations (e.g., of peak engineering demands) under earthquake loading.     

汶川地震导致的壁画文物震害研究——以广元市觉苑寺大雄宝殿壁画为例

为保护壁画文物,以四川省广元市剑阁县大雄宝殿为例,对汶川地震作用下殿内壁画的震害进行了研究.根据震后勘查结果,讨论了大雄宝殿壁画的典型震害症状,分析了古建筑侧脚构造对壁画抗震的有利影响.根据大雄宝殿壁画加固工艺作法及古建筑榫卯连接特点,建立了大雄宗殿的震前有限元模型.为研究汶川地震作用下壁画的震害特征,首先对其进行了模态分析,然后将模拟汶川地震波进行调幅,然后作用于大雄宝殿进行地震反应分析.通过采用时程分析法,获得了地震作用下不同时刻壁画整体的内力与变形响应峰值,并获得了典型节点的地震响应曲线.结果表明:大雄宝殿壁画开裂与空鼓的主要原因是面层与墙体粘结不牢导致的受拉破坏;地震作用下壁画保持稳定的振动状态;为提高壁画的抗震性能,壁画木框与外墙板间应加强连接,并在空隙处填塞隔震材料,同时应加强壁画本身保养工作.     

MODELLING OF RC BEAM-COLUMN JOINTS AND STRUCTURAL WALLS

The deformation of beam-column joints may contribute significantly to drift of reinforced concrete (RC) frames. In addition, failure may occur in the joints due to cumulative concrete crushing from applied beam and column moments, bond slip of embedded bars or shear failure as in the case of existing frames with nonductile detailing. When subjected to earthquake loading, failure in RC structural wall is similar to failure of frame joints as it may occur due to cumulative crushing from high flexural stresses, bond slip failure of lap splice, shear failure or a combination of various mechanisms of failure. It is important to include these behavioural characteristics in a simple model that can be used in the analysis of RC frames and RC walls to predict their response under earthquake loading and determine their failure modes.

Global macro models for the beam-column joint and for RC structural walls are developed. The proposed models represent shear and bond slip deformations as well as flexural deformations in the plastic hinge regions. The models are capable of idealising the potential failure mechanism due to crushing of concrete, bond slip or shear with allowance for the simultaneous progress in each mode. The model predictions are compared with available experimental data and good correlation is observed between analytical results and the test measurements.     

Experimental Studies and Vulnerability Assessment of Timber-Arched Lounge Bridges

ABSTRACT

There are many preserved timber-arched lounge bridges in China and some of these bridges are hundreds of years old. The woven arch is the main bearing structure of a timber-arched lounge bridge. Few studies still exist about woven arch mechanical performance, a fact that contributes to the improper repair. This article concerns the structural performance of the woven arch. The results of experimental studies on deformation, stress distribution, force-transferring mechanism, and failure modes were presented. Two woven arch models with and without П-shape braces under symmetrical load and asymmetrical load were investigated. The results indicated that the woven arch had high bearing capacity, especially under symmetrical load. The comparison of experimental results obtained for models with and without brace showed that braces modified the failure mechanism and increased the load carrying capacity and integrity. Based on the failure conditions observed experimentally, limit criteria were defined in order to facilitate vulnerability assessment of timber lounge bridges.     

Performance-based Seismic Design of a Pendulum Tuned Mass Damper System

The study implements the performance-based analysis and design methodology to assess the seismic vulnerability of a coal-fired power plant and to optimally design its equivalent pendulum-type tuned mass damper system such that the direct losses are minimized. A building-specific total loss ratio is developed to link the component level losses with the total repair cost of the original structure. The optimal system configuration is finally derived for cases with the minimum loss. The study demonstrates a systematic way of achieving the optimal pendulum-type tuned mass damper design with considerations of uncertainties in earthquake inputs and the combined component level damages.     

Numerical Investigation of Variable Length of Seismic Damage Region for Reinforced Concrete Columns

ABSTRACT

The seldom investigation of variable length of damage region prevents the estimation of probabilistic drift limits of reinforced concrete columns at different performance levels for the performance-based seismic design. However, if using the numerical approach to predict the variability of damage region within the framework of force-based beam-column element, the current force-based beam-column element is unable to model the spreading of damage region. Therefore, a new numerical simulation method is proposed to compute the emergence, propagation and termination of damage region of reinforced concrete columns. Then, based on the developed numerical simulation method, the measured response of experimental testing is calibrated. From the calibration, it can be observed that there is a rapid increase on the variable length of damage region with the increasing of lateral displacement and then followed by a stable stage. The propagation of the longitudinal reinforcement yielding and concrete tensile cracking mainly occurs in the ascending branch of the load–displacement response. Then, based on the growth characteristic of the damage region from the numerical simulation, an empirical equation is proposed to describe the variable length of damage region by using the least-square regression analysis to fit the computed responses for its simplicity to use in engineering practices. Finally, the stable length of damage region is reinvestigated by carrying out a parametric study with the developed numerical simulation method, indicating that two critical design parameters, specifically the axial load ratio and the shear span ratio, have considerable influences on this quantity of interest.     

EVALUATION OF THE SEISMIC PERFORMANCE OF EXISTING RC BUILDINGS: II. A CASE STUDY FOR REGULAR AND IRREGULAR BUILDINGS

The results of a parametric study are presented, concerned with the evaluation of the structural overstrength, the global ductility and the available behaviour factor of existing reinforced concrete (RC) buildings designed and constructed according to past generations of earthquake resistant design codes in Greece. For the estimation of these parameters, various failure criteria are incorporated in a methodology established to predict the failure mode of such buildings under planar response, as described in detail in a companion publication. A collection of 85 typical building forms is considered. The influence of various parameters is examined, such as the geometry of the structure (number of storeys, bay width etc.), the vertical irregularity, the contribution of the perimeter frame masonry infill walls, the period of construction, the design code and the seismic zone coefficient. The results from inelastic pushover analyses indicate that existing RC buildings exhibit higher overstrength than their contemporary counterparts, but with much reduced ductility capacity. The presence of perimeter infill walls increases considerably their stiffness and lateral resistance, while further reducing their ductility. Fully infilled frames exhibit generally good behaviour, while structures with an open floor exhibit the worst performance by creating a soft storey. Shear failure becomes critical in the buildings with partial height infills. It is also critical for buildings with isolated shear wall cores at the elevator shaft. Out of five different forms of irregularity considered in this study, buildings with column discontinuities in the ground storey exhibit the worst performance. Furthermore, buildings located in the higher seismicity zone are more vulnerable, since the increase of their lateral resistance and ductility capacity is disproportional to the increase in seismic demand.     

Evaluation of Strength Hierarchy of Beam-Column Joints of Existing RC Structures under Seismic Type Loading

To evaluate the strength hierarchy, three different types of exterior beam-column joint, i.e., gravity load designed, non ductile and ductile, following two different codes are considered. Strength of different components of beam-column joint, i.e., column, beam, and joint core, is individually calculated from different failure criteria. Shear strength of the joint is evaluated from softened strut and tie model. Strength hierarchy, ultimate strength, and critical failure modes of the specimens are analytically estimated and found to be well corroborated with the experimental results. The study will help in designing the earthquake resistant RC structures in a more rational way.     

Empirical Fragility Curves for Non-Residential Buildings from the 2010–2011 Canterbury Earthquake Sequence

This study develops a motion-damage database (the Canterbury Earthquake Building Assessment, CEBA database) using surveyed information obtained from the Canterbury earthquake sequence. The database is then applied to derive fragility curves for non-residential buildings in New Zealand. The results indicate that unreinforced masonry buildings are the most vulnerable to damage, while the concrete shear wall buildings were found to be the most resilient. Discrepancies were found when comparing equivalent structures in New Zealand and the United States. Inherent difference of building characteristics between the two countries, significant ground failure, and accumulated damage from multiple events might explain the difference.