共查询到20条相似文献，搜索用时 15 毫秒
1.
Analytical and empirical models for predicting the drift capacity of modern unreinforced masonry walls 
下载免费PDF全文
下载免费PDF全文 Displacement‐based seismic assessment of buildings containing unreinforced masonry (URM) walls requires as input, among others, estimates of the in‐plane drift capacity at the considered limit states. Current codes assess the drift capacity of URM walls by means of empirical models with most codes relating the drift capacity to the failure mode and wall slenderness. Comparisons with experimental results show that such relationships result in large scatter and usually do not provide satisfactory predictions. The objective of this paper is to determine trends in drift capacities of modern URM walls from 61 experimental tests and to investigate whether analytical models could lead to more reliable estimates of the displacement capacity than the currently used empirical models. A recently developed analytical model for the prediction of the ultimate drift capacity for both shear and flexure controlled URM walls is introduced and simplified into an equation that is suitable for code implementation. The approach follows the idea of plastic hinge models for reinforced concrete or steel structures. It explicitly considers the influence of crushing due to flexural or shear failure in URM walls and takes into account the effect of kinematic and static boundary conditions on the drift capacity. Finally, the performance of the analytical model is benchmarked against the test data and other empirical formulations. It shows that it yields significantly better estimates than empirical models in current codes. The paper concludes with an investigation of the sensitivity of the ultimate drift capacity to the wall geometry, static, and kinematic boundary conditions. 相似文献
2.
Kemal Hacıefendioğlu Emre Alpaslan 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(2):415-427
This paper presents the dynamic response analysis of industrial masonry chimney subjected to artificially generated surface blast induced ground shock by using a three-dimensional finite element model. The effects of surface blast-induced ground shocks on nearby structures depend on the distance between the explosion centre and the structure, and charge weight. Blast-induced ground motions can be represented by power spectral density function and applied to each support point of the 3D finite element model of the industrial masonry system. In this study, a parametric study is mainly conducted to estimate the effect of the blast-induced ground motions on the nonlinear response of a chimney type masonry structure. Therefore, the analysis was carried out for different values of the charge weights and distances from the charge center. The initial crack and propagation of the crack pattern at the base of the chimney were evaluated. Moreover, the maximum stresses and displacements through the height of the chimney were investigated. The results of the study underline that blast-induced ground motions effects should be considered to perform the non-linear dynamic analysis of masonry type chimney structures more accurately. 相似文献
3.
The in-plane capacity of unreinforced masonry (URM) elements may vary considerably depending on several factors, including boundary conditions, aspect ratio, vertical overburden, and masonry texture. Since the overall system resistance mainly relies on the in-plane lateral capacity of URM components when out-of-plane modes are adequately prevented, the structural assessment of URM structures could benefit from advanced numerical approaches able to account for these factors simultaneously. This paper aims at enhancing and optimising the employment of the distinct element method, currently confined to the analysis of local mechanisms of reduced-scale dry-joint blocky assemblies, with a view to simulate the experimentally observed responses of a series of URM full-scale specimens with mortared joints subjected to quasi-static in-plane cyclic loading. To this end, a mesoscale modelling approach is proposed that employs a simplified microscale modelling approach to effectively capture macroscale behaviour. Dynamic relaxation schemes are employed, in combination with time, size, and mass-scaling procedures, to decrease computational demand. A new methodology for numerically describing both unit, mortar and hybrid failure modes, also including masonry crushing due to high-compression stresses, is proposed. Empirical and homogenisation formulae for inferring the elastic properties of interface between elements are also verified, enabling the proposed approach to be applied more broadly. Using this modelling strategy, the interaction between stiffness degradation and energy dissipation rate was accounted for numerically. Although the models marginally underestimate the energy dissipation in the case of slender piers, a good agreement was obtained in terms of lateral strength, hysteretic response, and crack pattern. 相似文献
4.
Francesco Longo Lydell Wiebe Francesca da Porto Claudio Modena 《Bulletin of Earthquake Engineering》2018,16(12):6163-6190
Experimental tests have shown that unreinforced masonry (URM) infill walls are affected by simultaneous loading in their in-plane and out-of-plane directions, but there have been few attempts to represent this interaction in nonlinear time history analysis of reinforced concrete (RC) buildings with URM infill walls. In this paper, a recently proposed macro-model that accounts for this interaction is applied to the seismic analysis of RC framed structures with URM infill walls representative of Mediterranean building stock and practices. Two RC framed structures that are representative of low and mid-rise residential buildings are analysed with a suite of a bidirectional ground motions, scaled to three different intensities. During the analyses, the in-plane/out-of-plane interaction is monitored, showing that cracking of the infills occurs predominantly by in-plane actions, while failure occurs due to a combination of in-plane and out-of-plane displacements, with the out-of-plane component usually playing the dominant role. Along the frame height, the bottom storeys are generally the most damaged, especially where thin infill walls are used. These results are consistent with observations of damage to URM infill walls in similar buildings during recent earthquakes. 相似文献
5.
A hypothetical 5‐storey prototype structure with reinforced concrete (RC) frame and unreinforced masonry (URM) wall is considered. The paper focuses on a shake‐table experiment conducted on a substructure of this prototype consisting of the middle bays of its first storey. A test structure is constructed to represent the selected substructure and the relationship between demand parameters of the test structure and those of the prototype structure is established using computational modelling. The dynamic properties of the test structure are determined using a number of preliminary tests before performing the shake‐table experiments. Based on these tests and results obtained from computational modelling of the test structure, the test ground motions and the sequence of shakings are determined. The results of the shake‐table tests in terms of the global and local responses and the effects of the URM infill wall on the structural behaviour and the dynamic properties of the RC test structure are presented. Finally, the test results are compared to analytical ones obtained from further computational modelling of the test structure subjected to the measured shake‐table accelerations. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
6.
当前地震记录法检测中强震下砌体结构损伤时,基于已知砌体结构地震动记录实施损伤检测存在较高的局限性。提出新的中强震下砌体结构损伤检测方法,利用DASP动态测试分析仪和891型的压电式位移传感器,检测拟静力试验后的砌体结构模型,采用参数互补校正方法得到受损砌体结构的自振频率和振型检测,通过有限元分析获取砌体结构位移,依据频率和位移采用信号匹配方法检测砌体结构损伤情况,根据墙体刚度变化检测中强震下砌体结构的损伤程度。实验证明所提方法可对中强震下砌体结构损伤情况进行准确检测。 相似文献
7.
Many older unreinforced masonry (URM) buildings feature timber floors and solid brick masonry. Simple equivalent frame models can help predicting the expected failure mechanism and estimating the strength of a URM wall. When modelling a URM wall with an equivalent frame model rather than, for example, a more detailed simplified micro-model, the strengths of the piers and spandrels need to be estimated from mechanical or empirical models. Such models are readily available for URM piers, which have been tested in many different configurations. On the contrary, only few models for spandrel strength have been developed. This paper reviews these models, discusses their merits, faults and compares the predicted strength values to the results of recent experimental tests on masonry spandrels. Based on this assessment, the paper outlines recommendations for a new set of strength equations for masonry spandrels. 相似文献
8.
This article presents a new mechanical model for the non‐linear force–displacement response of unreinforced masonry (URM) walls developing a flexural rocking mode including their displacement capacity. The model is based on the plane‐section hypothesis and a constitutive law for the masonry with zero tensile strength and linear elastic behaviour in compression. It is assumed that only the compressed part of the wall contributes to the stiffness of the wall and therefore the model accounts for a softening of the response due the reduction of the effective area. Stress conditions for limit states are proposed that characterise the flexural failure. The new model allows therefore linking local performance levels to global displacement capacities. The limit states criteria describe the behaviour of modern URM walls with cement mortar of normal thickness and clay bricks. The model is validated through comparison of local and global engineering demand parameters with experimental results. It provides good prediction of the effective stiffness, the force capacity and the displacement capacity of URM walls at different limit states. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
9.
On 26 th October 2015, an Mw 7.5 earthquake struck northern Pakistan, with its epicenter located 45 km southwest of Jarm in the Hindu Kush region of Afghanistan. The earthquake resulted from reverse faulting at a depth of 210 km, resulting in 280 fatalities and substantial damage to some 109,123 buildings. Regional seismicity, characteristics of recorded strong motions, damage statistics, and building performance observations are presented. Earthquake damage was mostly constrained to seismic-deficient unreinforced masonry(URM) buildings. Typical failure modes included toppled minarets, partial or complete out of plane collapse of URM walls, diagonal shear cracking in piers, flexural cracking in spandrels, corner damage, pounding damage, and damage due to ground settlement. The majority of human loss resulted due to failure of URM walls and subsequent roof collapse. URM buildings located in rural hilly areas closer to the epicenter suffered more intense and frequent damage than urban URM buildings located farther away in larger cities. 相似文献
10.
Code design of unreinforced masonry (URM) buildings is based on elastic analysis, which requires as input parameter the effective stiffness of URM walls. Eurocode estimates the effective stiffness as 50% of the gross sectional elastic stiffness, but comparisons with experimental results have shown that this may not yield accurate predictions. In this paper, 79 shear‐compression tests of modern URM walls of different masonry typologies from the literature are investigated. It shows that both the initial and the effective stiffness increase with increasing axial load ratio and that the effective‐to‐initial stiffness ratios are approximately 75% rather than the stipulated 50%. An empirical relationship that estimates the E‐modulus as a function of the axial load and the masonry compressive strength is proposed, yielding better estimates of the elastic modulus than the provision in Eurocode 6, which calculates the E‐modulus as a multiple of the compressive strength. For computing the ratio of the effective to initial stiffness, a mechanics‐based formulation is built on a recently developed analytical model for the force‐displacement response of URM walls. The model attributes the loss in stiffness to diagonal cracking and brick crushing, both of which are taken into account using mechanical considerations. The obtained results of the effective‐to‐initial stiffness ratio agree well with the test data. A sensitivity analysis using the validated model shows that the ratio of effective‐to‐initial stiffness is for most axial load ratios and wall geometries around 75%. Therefore, a modification of the fixed ratio of effective‐to‐initial stiffness from 50% to 75% is suggested. 相似文献
11.
为探讨村镇建筑低层砌体结构在大震下的动力响应及损伤分布情况,基于农居结构性能实地调查与检测,在有限元软件ABAQUS中建立了不同抗震构造措施的砌体结构有限元模型,并进行结构动力特性及大震下弹塑性时程的分析,对比它们的自振特性参数、位移响应参数及损伤破坏形态。分析表明,低层砌体结构合理设置构造柱后结构自振周期略有减小,但振型不变;在弹性变形阶段构造柱能有效约束结构的动力位移响应,进入塑性变形后构造柱可提高砌体结构的耗能能力,但值得注意的是,结构刚度退化后构造柱会加剧纵横向抗侧刚度的不均衡性;低层砌体结构合理设置圈梁构造柱可有效抑制承重横墙的裂缝发展及楼屋盖发生支座失效破坏,且可以明显削弱结构的扭转效应。 相似文献
12.
对4榀相同特性的砖墙进行不同程度的酸雨腐蚀试验及低周反复荷载试验,得出其在不同腐蚀循环次数下的滞回曲线。基于陆新征-曲哲恢复力模型对砖墙试件进行模拟分析,并与试验结果进行对比,验证得出三弹簧单元模型能够较准确预测砌体构件的滞回性能。利用三弹簧单元模型对不同腐蚀次数下砌体结构进行IDA分析,得出不同腐蚀次数下砌体结构的易损性曲线,通过对"小震"、"中震"、"大震"下结构失效概率的分析得出,酸雨腐蚀能够严重影响结构的力学性能,使得结构的抗震性能显著下降。 相似文献
13.
The paper describes the earthquake performance assessment of two historical buildings located in Istanbul exposed to a Mw = 7+ earthquake expected to hit the city and proposes solutions for their structural rehabilitation and/or strengthening.
Both buildings are unreinforced clay brick masonry (URM) structures built in 1869 and 1885, respectively. The first building
is a rectangular-shaped structure rising on four floors. The second one is L-shaped with one basement and three normal floors
above ground. They survived the 1894, Ms = 7.0 Istanbul Earthquake, during which widespread damage to URM buildings took place in the city. Earthquake ground motion
to be used in performance assessment and retrofit design is determined through probabilistic and deterministic seismic hazard
assessment. Strength characteristics of the brick walls are assessed on the basis of Schmidt hammer test results and information
reported in the literature. Dynamic properties of the buildings (fundamental vibration periods) are measured via ambient vibration
tests. The buildings are modelled and analyzed as three-dimensional assembly of finite elements. Following the preliminary
assessment based on the equivalent earthquake loads method, the dynamic analysis procedure of FEMA 356 (Pre-standard and commentary
for the seismic rehabilitation of buildings, American Society of Civil Engineers, Reston, 2000) and ASCE/SEI 41-06 (Seismic rehabilitation of existing buildings, American Society of Civil Engineers, Reston, 2007) is followed to obtain dynamic structural response of the buildings and to evaluate their earthquake performance. In order
to improve earthquake resistance of the buildings, reinforced cement jacketing of the main load carrying walls and application
of fiber reinforced polymer bands to the secondary walls are proposed. 相似文献
14.
The Himalayan region is one of the major seismic areas in the world. However, similar to many other seismically active locations, there are substantial numbers of unreinforced masonry(URM) buildings; the majority of which have not been designed for seismic loads. Past seismic events have shown that such buildings are highly vulnerable to earthquakes. Retrofitting of these URM buildings is an important concern in earthquake mitigation programs. Most government school buildings in rural areas of northern India are constructed of unreinforced masonry. These school buildings are socially important structures and serve as a crucial resource for rehabilitation during any disaster. The effectiveness of ferrocement(FC) to create a URM-FC composite is described in this study by estimating the performance and fragility of a URM school building before and after a retrofit. Analytical models, based on the equivalent frame method, are developed and used for nonlinear static analysis to estimate the enhancement in capacity. The capacity enhancement due to retrofitting is presented in terms of the maximum PGA sustained and damage probabilities at the expected level of earthquake hazard. 相似文献
15.
The influence of interface geometry,stiffness, and crushing on the dynamic response of masonry collapse mechanisms 下载免费PDF全文
下载免费PDF全文 Failure of masonry structures generally occurs via specific collapse mechanisms which have been well documented. Using rocking dynamics, equations of motion have been derived for a number of different failure mechanisms ranging from the simple overturning of a single block to more complicated mechanisms. However, most of the equations of motion derived thus far assume that the structures can be modelled as rigid bodies rocking on rigid interfaces with an infinite compressive strength—which is not always the case. In fact, crushing of masonry—commonly observed in larger scale constructions and vertically restrained walls—can lead to a reduction in the dynamic capacity of these structures. This paper rederives the rocking equation of motion to account for the influence of flexible interfaces, characterized by a specific interface stiffness as well as finite compressive strength. The interface now includes a continually shifting rotation point, the location of which depends not only on the material properties of the interface but also on its geometry. Expressions have thus also been derived for interfaces of different geometries, and parametric studies conducted to gauge their influence on dynamic response. The new interface formulations are also implemented within a new analytical modelling tool that provides a novel approach to the dynamic analysis of masonry collapse mechanisms. Finally, this tool is exemplified, along with the importance of the interface formulation, by evaluating the collapse of the Dharahara Tower in Kathmandu, which was almost completely destroyed during the 2015 Gorkha earthquake. 相似文献
16.
以强震动台站结构类型作为控制因素,基于集中质量显式时域动力有限元方法,系统地分析了不同场地条件下观测室结构（砌体观测房、半地下观测室、玻璃钢罩观测室）对地震动的影响。通过对北京地球观象台院内并址观测实验台站捕获的地脉动和两次地震事件数据的处理并结合数值模拟结果,分析得到不同类型观测室对地震动的影响规律。结果表明：观测室结构对地震动的影响是客观存在的,由于观测室结构自振周期和体量不同,不同观测室对地震动的影响频带和影响程度亦存在差异,相较于其它结构对地震动的影响,玻璃钢罩观测室的影响频带较窄、影响程度最小。 相似文献
17.
Out‐of‐plane seismic response of vertically spanning URM walls connected to flexible diaphragms 下载免费PDF全文
下载免费PDF全文 A simplified numerical model was used to investigate the out‐of‐plane seismic response of vertically spanning unreinforced masonry (URM) wall strips. The URM wall strips were assumed to span between two flexible diaphragms and to develop a horizontal crack above the wall mid‐height. Three degrees of freedom were used to accommodate the wall displacement at the crack height and at the diaphragm connections, and the wall dynamic stability was studied. The equations of dynamic motion were obtained using principles of rocking mechanics of rigid bodies, and the formulae were modified to include semi‐rigid wall behaviour. Parametric studies were conducted that included calculation of the wall response for different values of diaphragm stiffness, wall properties, applied overburden, wall geometry and earthquake ground motions. The results of the study suggest that stiffening the horizontal diaphragms of typical low‐rise URM buildings will amplify the out‐of‐plane acceleration demand imposed on the wall and especially on the wall–diaphragm connections. It was found that upper‐storey walls connected to two flexible diaphragms had reduced stability for applied earthquake accelerograms having dominant frequency content that was comparable with the frequency of the diaphragms. It was also found that the applied overburden reduced wall stability by reducing the allowable wall rotations. The results of this study suggest that the existing American Society of Civil Engineers recommendations for assessment of vertically spanning walls overestimate the stability of top‐storey walls in multi‐storey buildings in high‐seismic regions or for walls connected to larger period (less stiff) diaphragms. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
18.
Umberto Tomassetti António A. Correia Francesco Graziotti Andrea Penna 《地震工程与结构动力学》2019,48(11):1297-1318
Typical low-rise masonry buildings consist of unreinforced masonry (URM) walls covered with various timber roof configurations generally supported or finished by masonry gables. Post-earthquake observations and experimental outcomes highlighted the large vulnerability of the URM gables to the development of overturning mechanisms, both because of the inertial out-of-plane excitation and the in-plane timber diaphragm deformability. This paper presents the static and dynamic experimental seismic performance of three full-scale roofs tested via quasi-static cyclic and shake table tests. Two of them were tested as part of a whole full scale one-storey and two-storey building. A single-degree-of-freedom (SDOF) numerical model is calibrated against experimental data and proposed for the analysis of this roof typology's dynamic behaviour. Several sets of analyses were conducted to assess the vulnerability of these structural components and to study the effect of the whole building's characteristics (eg, number of storeys and structural stiffness and strength) on the seismic performance of this roof typology. 相似文献
19.
在地下结构抗震设计简化分析方法中,强制反应位移法将土层变形施加在有限元模型侧边界模拟地震作用,反应加速度法将土层加速度施加到整个有限元模型上模拟地震作用,此外还有仅将土层加速度施加到土层模型上模拟地震作用的方法。上述方法均规避了反应位移法中关于弹簧刚度的取值问题,提高了计算效率。本文以1个双跨箱形结构为例,用动力时程分析的计算结果作为校核,分析了强制反应位移法、反应加速度法和仅将土层加速度施加到土体中的简化分析方法在不同侧边距条件下的计算精度,再结合常用的反应位移法,对比分析了4种简化分析方法的误差。分析结果表明:使用强制反应位移法时,侧边距取为1倍结构宽度导致的误差最小,反应加速度法和仅在土体施加加速度的简化方法对侧边距取值不敏感,反应位移法在角点造成的误差最大。 相似文献
20.
Assessment of the dynamic response of unreinforced masonry structures using a macroelement modeling approach 下载免费PDF全文
下载免费PDF全文 César Chácara Francesco Cannizzaro Bartolomeo Pantò Ivo Caliò Paulo B. Lourenço 《地震工程与结构动力学》2018,47(12):2426-2446
The seismic performance of unreinforced masonry structures is strongly associated with the interaction between in‐plane and out‐of‐plane mechanisms. The seismic response of these structures has been thoroughly investigated by means of experimental testing, analytical procedures, and computational approaches. Within the framework of the numerical simulations, models based on the finite element method provide a good prediction of the seismic performance of unreinforced masonry structures. However, they usually require a high computational cost and advanced user expertise to define appropriate mechanical properties and to interpret the numerical results. Because of these limitations, simplified models for practical applications have been developed during the last decades. Despite this, a great number of these models focus mostly on the evaluation of the in‐plane response, assuming box (or integral) behavior of the structure. In this paper, a simplified macroelement modeling approach is used to simulate the seismic response of 2 masonry prototypes taking into consideration the combined in‐plane and out‐of‐plane action. The numerical investigations were performed in the static and dynamic fields by using pushover analyses and nonlinear dynamic analyses respectively. The latter is a novel implementation of a model previously developed for static analysis. The results obtained from this study are in good agreement with those provided by a detailed nonlinear continuum FE approach, demonstrating the applicability of this macroelement model with a significant reduction of the computational cost. 相似文献