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1.
Motivated by the seismic damage observed to reinforced concrete (RC) frame structures during the Wenchuan earthquake, the effect of infill walls on the seismic performance of a RC frame is studied in this paper. Infill walls, especially those made of masonry, offer some amount of stiffness and strength. Therefore, the effect of infill walls should be considered during the design of RC frames. In this study, an analysis of the recorded ground motion in the Wenchuan earthquake is performed. Then, a numerical model is developed to simulate the infill walls. Finally, nonlinear dynamic analysis is carried out on a RC frame with and without infill walls, respectively, by using CANNY software. Through a comparative analysis, the following conclusions can be drawn. The failure mode of the frame with infill walls is in accordance with the seismic damage failure pattern, which is strong beam and weak column mode. This indicates that the infill walls change the failure pattern of the frame, and it is necessary to consider them in the seismic design of the RC frame. The numerical model presented in this paper can effectively simulate the effect of infill walls on the RC frame.  相似文献   

2.
The objective of the study presented in this paper is to investigate the effects of masonry infills on the shear demand and failure of columns for the case when reinforced concrete frames with such infills are modeled by means of simplified nonlinear models that are not capable of the direct simulation of these effects. It is shown that an approximate simulation of the shear failure of columns can be achieved through an iterative procedure that involves pushover analysis, post‐processing of the analysis results using limit‐state checks of the components, and model adaptation if shear failure of columns is detected. The fragility parameters and the mean annual frequency of limit‐state exceedance are computed on the basis of nonlinear dynamic analysis by using an equivalent SDOF model. The proposed methodology is demonstrated by means of two examples. It was shown that the strength of the four‐story and seven‐story buildings and their deformation capacity are significantly overestimated if column shear failure due to the effects of masonry infills is neglected, whereas the mean annual frequency of limit‐state exceedance for the analyzed limit states is significantly larger than that estimated for the case if the shear failure of columns is neglected. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

3.
This paper proposes a new analytical model for masonry‐infilled R/C frames to evaluate the seismic performance considering R/C frame–infill interactions. The proposed analytical model replaces masonry infill with a diagonal compression strut, which represents distributed compression transferred between frame and infill interfaces. The equivalent strut width is presented as a function of the frame–infill contact length, which can be evaluated by static equilibriums related to compression balance and lateral displacement compatibility at the frame–infill interfaces. The proposed analytical model was verified through comparisons with experimental results obtained for several brick masonry‐infilled R/C frames representing a typical R/C building with nonstructural masonry infill in Indonesia. As a result, good agreements were observed between the experimental and analytical values of the lateral strength and ductility of the infilled frames. The seismic performances of two earthquake‐damaged R/C buildings with different damage conditions were evaluated considering infill effects by applying the proposed analytical model. Consequently, the nonstructural brick masonry infill significantly affected the seismic resistances of the buildings, which seemed to lead to differing levels of damage for each building. These results indicate that the proposed analytical model can be an effective tool for more precisely screening earthquake‐vulnerable existing R/C buildings in Indonesia. Copyright © 2016 The Authors. Earthquake Engineering & Structural Dynamics Published by John Wiley & Sons Ltd.  相似文献   

4.
On 3 August 2014, the Ludian earthquake struck northwest Yunnan Province with a surface wave magnitude of 6.5. This moderate earthquake unexpectedly caused high fatalities and great economic loss. Four strong motion stations were located in the areas with intensity V, VI, VII and IX, near the epicentre. The characteristics of the ground motion are discussed herein, including 1) ground motion was strong at a period of less than 1.4 s, which covered the natural vibration period of a large number of structures; and 2) the release energy was concentrated geographically. Based on materials collected during emergency building inspections, the damage patterns of adobe, masonry, timber frame and reinforced concrete (RC) frame structures in areas with different intensities are summarised. Earthquake damage matrices of local buildings are also given for fragility evaluation and earthquake damage prediction. It is found that the collapse ratios of RC frame and confined masonry structures based on the new design code are significantly lower than non-seismic buildings. However, the RC frame structures still failed to achieve the ‘strong column, weak beam’ design target. Traditional timber frame structures with a light infill wall showed good aseismic performance.  相似文献   

5.
This paper presents pseudo‐dynamic test results on the in‐plane seismic behaviour of infilled frames. Thirteen single‐storey, single‐bay, half‐size‐scale, reinforced concrete‐frame specimens, most of which infilled with non‐structural masonry made of perforated bricks and cement mortar are tested. The infills are in contact with frames, without any connector; openings are not covered. The frames are different in their strength and details, reinforcement grade, and aspect ratio. Seismic input is the 1976 Tolmezzo (Friuli, Italy) ground acceleration, to which specimens are subjected two times: virgin and damaged by the previous test. The global seismic response of initially virgin infilled specimens considerably differs from that of bare specimens. This follows a dramatic change of properties: compared to a bare frame, the initial stiffness increases by one order of magnitude, and the peak strength more than doubles. The peak drift lessens; however, the displacement ductility demand does not. The energy demand is greater. Nevertheless, the influence of infill decreases as damage proceeds. Displacement time histories of damaged specimens are quite similar. At the local level, infill causes asymmetry and concentration of the frame deformation. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

6.
Operative seismic aftershock risk forecasting can be particularly useful for rapid decision‐making in the presence of an ongoing sequence. In such a context, limit state first‐excursion probabilities (risk) for the forecasting interval (a day) can represent the potential for progressive state of damage in a structure. This work lays out a performance‐based framework for adaptive aftershock risk assessment in the immediate post‐mainshock environment. A time‐dependent structural performance variable is adopted in order to measure the cumulative damage in a structure. A set of event‐dependent fragility curves as a function of the first‐mode spectral acceleration for a prescribed limit state is calculated by employing back‐to‐back nonlinear dynamic analyses. An epidemic‐type aftershock sequence model is employed for estimating the spatio‐temporal evolution of aftershocks. The event‐dependent fragility curves for a given limit state are then integrated together with the probability distribution of aftershock spectral acceleration based on the epidemic‐type aftershock sequence aftershock hazard. The daily probability of limit state first‐excursion is finally calculated as a weighted combination of the sequence of limit state probabilities conditioned on the number of aftershocks. As a numerical example, daily aftershock risk is calculated for the L'Aquila 2009 aftershock sequence (central Italy). A representative three‐story reinforced concrete frame with infill panels, which has cyclic strength and stiffness degradation, is used in order to evaluate the progressive damage. It is observed that the proposed framework leads to a sound forecasting of limit state first‐excursion in the structure for two limit states of significant damage and near collapse. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

7.
One of the main challenges in earthquake risk mitigation is the assessment of existing buildings not designed according to modern codes and the development of effective techniques to strengthen these structures. Particular attention should be given to RC frame structures with masonry infill panels, as demonstrated by their poor performance in recent earthquakes in Europe. Understanding the seismic behaviour of masonry‐infilled RC frames presents one of the most difficult problems in structural engineering. Analytical tools to evaluate infill–frame interaction and the failure mechanisms need to be further studied. This research intends to develop a simplified macro‐model that takes into account the out‐of‐plane behaviour of the infill panels and the corresponding in‐plane and out‐of‐plane interaction when subjected to seismic loadings. Finally, a vulnerability assessment of an RC building will be performed in order to evaluate the influence of the out‐of‐plane consideration in the building response. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

8.
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9.
Fragility curves are generally developed using a single parameter to relate the level of shaking to the expected structural damage. The main goal of this work is to use several parameters to characterize the earthquake ground motion. The fragility curves will, therefore, become surfaces when the ground motion is represented by two parameters. To this end, the roles of various strong‐motion parameters on the induced damage in the structure are compared through nonlinear time‐history numerical calculations. A robust structural model that can be used to perform numerous nonlinear dynamic calculations, with an acceptable cost, is adopted. The developed model is based on the use of structural elements with concentrated nonlinear damage mechanics and plasticity‐type behavior. The relations between numerous ground‐motion parameters, characterizing different aspects of the shaking, and the computed damage are analyzed and discussed. Natural and synthetic accelerograms were chosen/computed based on a consideration of the magnitude‐distance ranges of design earthquakes. A complete methodology for building fragility surfaces based on the damage calculation through nonlinear numerical analysis of multi‐degree‐of‐freedom systems is proposed. The fragility surfaces are built to represent the probability that a given damage level is reached (or exceeded) for any given level of ground motion characterized by the two chosen parameters. The results show that an increase from one to two ground‐motion parameters leads to a significant reduction in the scatter in the fragility analysis and allows the uncertainties related to the effect of the second ground‐motion parameter to be accounted for within risk assessments. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

10.
Recent earthquakes have confirmed the role played by infills in the seismic response of reinforced concrete buildings. The control and limitation of damage to such nonstructural elements is a key issue in performance‐based earthquake engineering. The present work is focused on modeling and analysis of damage to infill panels, and, in particular, it is aimed towards linear analysis procedures for assessing the damage limitation limit state of infilled reinforced concrete frames. First, code provisions on infill modeling and acceptance criteria at the damage limitation limit state are reviewed. Literature contributions on damage to unreinforced masonry infill panels and corresponding displacement capacity are reported and discussed. Two procedures are then proposed aiming at a twofold goal: (i) the determination of ‘equivalent’ interstory drift ratio limits for a bare frame model and (ii) the estimation of the stiffness of equivalent struts representing infill walls in a linear model. These two quantities are determined such that a linear model ensures a reliable estimation of seismic capacity at the damage limitation limit state, providing the same intensity level as that obtained from nonlinear analyses carried out on structural models with infills. Finally, the proposed procedures are applied to four‐story and eight‐story case study‐infilled frames, designed for seismic loads according to current technical codes. The results of these application examples are presented and discussed. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

11.
Effects of masonry infills on the seismic vulnerability of steel frames is studied through multi-scale numerical modelling. First, a micro-modelling approach is utilized to define a homogenized masonry material, calibrated on experimental tests, which is used for modelling the nonlinear response of a one-story, single span, masonry-infilled portal under horizontal loads. Based on results of the micro-model, the constitutive behavior of a diagonal strut macro-element equivalent to the infill panel is calibrated. Then, the diagonal strut is used to model infill panels in the macro-scale analysis of a multi-span multi-story infilled moment-resisting (MR) steel frame. The seismic vulnerability of the MR frame is evaluated through a nonlinear static procedure. Numerical analyses highlight that infills may radically modify the seismic response and the failure mechanism of the frame, hence the importance of the infill correct modelling.  相似文献   

12.
Post-earthquake surveys indicate that losses come from non-structural damage more than from structural damage. Current performance-based design would prevent excessive non-structural damage as well, but the effectiveness of relevant code provisions has not been assessed in depth. This study investigates the drift-sensitive non-structural damage to reinforced concrete frame buildings complying with the European seismic code. Damage to non-structural unreinforced masonry infill walls in contact with the frame is quantified in terms of numerical fragility curves with the same quantities considered in the design: the peak ground acceleration measures the seismic intensity; the peak value of the interstorey drift ratio is the damage index. The methodology for the fragility computation is described in detail. Peculiar is the use of probabilistic parameters of the drift capacity coupled to the fuzziness in the damage state. The drift demand is estimated by member-by-member modelling of typical frame structures and non-linear time–history analyses under spectrum-compatible artificial accelerograms. The kind of the infills and their modelling, the number of storeys, the ground type, and the ductility class are covered. Modelling the infills results to be essential. Any code-compliant verification is on the safe side, but the margin appears to be inconsistent among the frames under consideration. Furthermore, there is one case where occupancy appears to be not ensured despite the code verification is satisfied. The effect of the number of storeys may be misrepresented. The ductility class may be unimportant, however the damage seems to be correlated with the likely strength.  相似文献   

13.
Open Ground Storey(OGS) framed buildings where the ground storey is kept open without infill walls, mainly to facilitate parking, is increasing commonly in urban areas. However, vulnerability of this type of buildings has been exposed in past earthquakes. OGS buildings are conventionally designed by a bare frame analysis that ignores the stiffness of the infill walls present in the upper storeys, but doing so underestimates the inter-storey drift(ISD) and thereby the force demand in the ground storey columns. Therefore, a multiplication factor(MF) is introduced in various international codes to estimate the design forces(bending moments and shear forces) in the ground storey columns. This study focuses on the seismic performance of typical OGS buildings designed by means of MFs. The probabilistic seismic demand models, fragility curves, reliability and cost indices for various frame models including bare frames and fully infilled frames are developed. It is found that the MF scheme suggested by the Israel code is better than other international codes in terms of reliability and cost.  相似文献   

14.
为研究填充墙对底层框架多层砌体房屋地震反应的影响,以典型的填充墙-底层框架多层砌体房屋为基础,建立有限元计算模型并进行了弹塑性动力时程分析。根据不同模型的计算结果以及填充墙的刚度和强度,分析了填充墙对底层框架多层砌体房屋自振周期、地震作用下房屋整体变形、底层框架的损伤以及填充墙与底层框架相互作用的影响。计算结果表明：填充墙对房屋整体地震反应产生明显影响,其影响不能忽略。在上部砌体结构质量和刚度不变的情况下,结构自振周期随着填充墙刚度的增加而降低;随着填充墙与底层框架之间连接作用的增强,结构整体的变形减小,底层框架的损伤增大。当填充墙与底层框架之间采用弱连接时,采用强度较高的填充墙可以提高结构整体的变形能力,从而提高结构整体的抗震能力。  相似文献   

15.
The vulnerability of infilled frames represents a critical issue in many regions with high seismicity around the world where infills are typically made of heavy masonry as they are used for thermal control of the buildings because of their thermal inertia. In this context, the use of earthen masonry infills can give a superior performance because of their ability to regulate thermal‐hygrometric performance of the building and sustainability of its life‐cycle. This paper presents a numerical study on the seismic behaviour of infill walls made of earthen masonry and partitioned with horizontal wooden planks that allow the relative sliding of the partitions. The combination of the deformability of earthen masonry and the sliding mechanism occurring along the wooden planks gives a high ductility capacity to the in‐plane response of the infill and, at the same time, significantly reduces its stiffness and strength, as compared with traditional solid infills made of fired clay units. As a result, the detrimental interaction with the frame and the damage in the infill when subjected to in‐plane loading can be minimized. The numerical model is validated with results from an experimental study and is used to perform a parametric analysis to examine the influence of variations in the geometry and mechanical properties of the infill walls, as well as the configuration of the sliding joints. Based on the findings of this study, design guidelines for practical applications are provided, together with simple formulation for evaluating their performance. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

16.
This paper assesses the influence of cyclic and in‐cycle degradation on seismic drift demands in moment‐resisting steel frames (MRF) designed to Eurocode 8. The structural characteristics, ground motion frequency content, and level of inelasticity are the primary parameters considered. A set of single‐degree‐of‐freedom (SDOF) systems, subjected to varying levels of inelastic demands, is initially investigated followed by an extensive study on multi‐storey frames. The latter comprises a large number of incremental dynamic analyses (IDA) on 12 frames modelled with or without consideration of degradation effects. A suite of 56 far‐field ground motion records, appropriately scaled to simulate 4 levels of inelastic demand, is employed for the IDA. Characteristic results from a detailed parametric investigation show that maximum response in terms of global and inter‐storey drifts is notably affected by degradation phenomena, in addition to the earthquake frequency content and the scaled inelastic demands. Consistently, both SDOF and frame systems with fundamental periods shorter than the mean period of ground motion can experience higher lateral strength demands and seismic drifts than those of non‐degrading counterparts in the same period range. Also, degrading multi‐storey frames can exhibit distinctly different plastic mechanisms with concentration of drifts at lower levels. Importantly, degrading systems might reach a “near‐collapse” limit state at ductility demand levels comparable to or lower than the assumed design behaviour factor, a result with direct consequences on optimised design situations where over‐strength would be minimal. Finally, the implications of the findings with respect to design‐level limit states are discussed.  相似文献   

17.
The seismic response of non‐ductile reinforced concrete (RC) buildings can be affected by the behaviour of beam‐column joints involved in the failure mechanism, especially in typical existing buildings. Conventional modelling approaches consider only beam and column flexibility, although joints can provide a significant contribution also to the overall frame deformability. In this study, the attention is focused on exterior joints without transverse reinforcement, and a possible approach to their modelling in nonlinear seismic analysis of RC frames is proposed. First, experimental tests performed by the authors are briefly presented, and their results are discussed. Second, these tests, together with other tests with similar features from literature, are employed to calibrate the joint panel deformability contribution in order to reproduce numerically the experimental joint shear stress–strain behaviour under cyclic loading. After a validation phase of this proposal, a numerical investigation of the influence of joints on the seismic behaviour of a case study RC frame – designed for gravity loads only – is performed. The preliminary failure mode classification of the joints within the analysed frame is carried out. Structural models that (i) explicitly include nonlinear behaviour of beam‐column joints exhibiting shear or anchorage failure or (ii) model joints as elements with infinite strength and stiffness are built and their seismic performance are assessed and compared. A probabilistic assessment based on nonlinear dynamic simulations is performed by means of a scaling approach to evaluate the seismic response at different damage states accounting for uncertainties in ground‐motion records. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

18.
Assessment of the seismic performance of existing structures requires due consideration of both aleatory and epistemic sources of uncertainty; the former being typically associated with the randomness in ground motion records and the latter with the uncertainty in numerical modelling. Using a numerical modelling approach calibrated to available experimental test data collected from the literature, the uncertainty associated with different modelling parameters for existing reinforced concrete frames in Italy was quantified via an extensive numerical study. This was done to quantify the propagation of modelling parameter type uncertainty to the overall dispersion of the demand parameters typically used in seismic assessment, namely peak storey drift and peak floor accelerations. In addition, the impact of such modelling uncertainty on the median intensity and dispersion of the collapse fragility function was also examined. From the results of this study, empirical values of modelling parameter uncertainty were quantified with a view to being used in the assessment of existing reinforced concrete frames with masonry infill designed prior to the introduction of seismic design provisions in Italy during the 1970s. Comparing these empirical values to those available in the literature, it is seen how the fundamental behaviour of the frames differs from more modern frames with ductile detailing to the extent that values available in guidelines such as FEMA P58 cannot be reasonably adopted for these structural typologies.  相似文献   

19.
Reinforced concrete (RC) buildings in Nepal are constructed with RC frames and masonry infill panels. These structures exhibit a highly non-linear inelastic behavior resulting from the interaction between the panels and frames. This paper presents an extensive case study of existing RC buildings in Nepal. Non-linear analyses were performed on structural models of the buildings considered as a bare frame and with masonry infill, in order to evaluate the influence of infill walls on the failure mechanisms. Five three-storey buildings with different structural configurations and detailing were selected. The effect of masonry infill panels on structural response was delineated by comparing the bare-framed response with the infill response. Seismic performance is evaluated with regard to global strength, stiffness, energy dissipation, inter-storey drift, and total deflection of the structure. A parametric analysis of structures with masonry infill is also performed. For this, the influence of different material properties is studied, namely diagonal compressive stress, modulus of elasticity and tensile stress of masonry infill panels. Study results show that masonry infill increases the global strength and stiffness of the structures; it decreases the inter-storey drift and hence the total displacement of the structure. The results quantify the influence of the infill panels on structural response and, in particular, the effect of the diagonal compressive strength of the masonry wall.  相似文献   

20.
In this paper, a technique is presented which employs the results of pseudo‐dynamic tests for the development of a mathematical model. This technique, described by means of the mathematical modelling of a three‐storey reinforced concrete frame building with infill in the bottom two storeys, which was tested at ELSA in Ispra, proved to be effective and to lead to a fairly accurate structural model. The results of analyses suggest that the global non‐linear seismic response of reinforced concrete frames with masonry infill can be adequately simulated by a relatively simple mathematical model, which combines beam elements with concentrated plasticity, simple connection elements, and equivalent strut elements representing the infill walls (provided that the infill does not fail out of plane and that no shear sliding failure occurs). Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

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