多孔砖砌体抗剪强度原位检测的试验研究

多孔砖砌体因具有节约土地能源资源,砌筑效率高,保温隔热和透气性能好等特点,目前已逐步成为砌体结构房屋的主要墙体材料。本文通过多孔砖砌体与标准试件抗剪强度的对比试验研究及试验结果的有限元分析,提出了多孔砖砌体抗剪强度原位双砖双剪的检测方法及其抗剪强度的计算公式。该方法可为多孔砖砌体结构房屋的可靠性评定、房屋建设、事故分析以及抗震加固等提供最基本的技术数据,为多孔砖砌体的应用与推广奠定了基础,并为砌体现场检测技术标准的补充修订提供了依据。     

砌体结构破坏倒塌过程的离散单元模拟

基于传统颗粒离散单元模型（DEM）,开发了一种绑定式离散单元模型（BTDEM）用于砌体结构崩塌机制的研究,并对一个典型砌体结构的破坏倒塌过程进行数值模拟。结果证实BTDEM方法能够详细地模拟出砌体建筑结构的崩塌过程,同时还可以模拟出砌块的破碎,是一种普适性较强的模拟砌体结构建筑的高效数值方法。BTDEM方法具有计算速度...     

砌体复合剪压受力特性与数值分析方法

 从砌体细观结构出发，提出了用于砌体复合剪压受力过程模拟的细观力学 模型. 该模型假定砌体是由砂浆、块体及两者之间的粘结带组成的三相复合材料，以此为基 础对砌体三相组成的非均匀性予以表征. 提出了基于弹性损伤力学的本构关系，以最大拉应 力准则和摩尔库仑准则作为损伤发生的阈值，并借助复合材料破坏过程分析(MFPA)程序进 行受力分析. 结果表明，所采用的数值模型和模拟方法能够较好地模拟砌体复合剪压受力破 坏过程，为砌体开裂过程的机理分析提供了一种新的数值方法.     

砌体基础托换的钢梁——砖砌体Euler组合梁模型

针对砌体结构砖墙的基础托换问题,将钢夹梁和砖砌体视为弹性材料,基于经典Euler组合梁理论,建立了钢梁-砖砌体组合梁弯曲变形的控制方程,给出了砖砌体基础单段托换时,钢-砖砌体组合梁挠度和应力的表达式.在此基础上,考虑砖砌体的拱效应,得到了不同种类和型号钢夹梁的钢-砖砌体组合梁最大挠度和最大应力,以及基础单段托换的最大长度.结果表明:对于同类型形式的钢夹梁,其型号越大,钢-砖砌体组合梁的挠度和应力越小.同时,如钢夹梁高相同,工字钢-砖砌体组合梁单段托换最大长度将大于槽钢-砖砌体组合梁的单段托换最大长度,但钢-砖砌体组合梁紧箍压力变化很小.这些结果可为具体工程实践提供理论指导.     

底部两层框架-抗震墙砌体房屋的动力计算模型及侧向刚度控制

底部两层框架—抗震墙上部多层砌体房屋,属于混凝土—砌体混合结构的范畴。这种建筑适应城市建设发展的要求,且较纯框架结构经济,特别受到房屋开发商的青睐,在相对落后和不发达地区尤为适用。为了研究这类结构在地震区的适用性,作者在现有试验研究的基础上,分析了底部两层框架—抗震墙砌体房屋在水平地震作用下的力学性能,给出了这种结构的动力计算模型和特征点参数的取值方法,并编制了结构从受荷到破坏的全过程弹塑性分析程序。同时,结合工程实例,计算了六种不同侧向刚度比条件下结构的弹塑性动力反应。根据计算结果的分析,认为新颁布的《建筑抗震设计规范》(GB50011)对于砌体过渡层与第二层框剪层的侧向刚度比限值偏小,并提出了合宜的刚度比取值范围,可供设计人员在抗震设计时参考和借鉴。     

砌体结构长脉宽爆炸荷载损伤等级评估方法

随着百千吨级当量爆炸工业事故的频繁发生,建筑结构的损伤评估和抗爆安全性更受到关注。目前,构件级的评估方法相对成熟,而大当量冲击波作用下的建筑结构整体毁伤评估依旧是个开放性问题。本文中,面向结构级的毁伤评估,提出了一种新的评估方法?构件损伤加权。该方法以承重构件损伤程度为基础,通过基于应变能的构件权系数加权,进而评估结构级损伤破坏程度。为了验证评估方法的有效性,以典型砌体结构为例,利用自主研发的冲击波结构毁伤模拟有限元程序,开展了百毫秒脉宽爆炸冲击波荷载下结构动力学响应数值模拟。根据数值模拟结果,结合构件损伤加权的评估方法,获取砌体结构损伤等级与冲击波超压的关系。预测的超压值的相对误差为?16.9%～26.2%,验证了评估方法的有效性。该评估方法为获取砌体结构的超压-冲量曲线提供了可行的途径,可为结构的抗爆安全设计提供参考。     

一种满足多阶固有频率和节线位置等要求的结构动力学设计方法

在给定了多阶固有频率、振型节线位置、结构的质量与质心等要求条件下，运用优化方法进行结构动力学设计，文中还给出了一种振型节线的直接搜索法，且对一个实际的机翼颤振模型进行了设计。     

燃气爆炸作用下蒸压加气混凝土砌体墙的加固性能

为研究燃气爆炸作用下蒸压加气混凝土砌体墙的加固性能，基于有限元软件LS-DYNA，建立了砌体墙简化数值模型，分析了GB 50779-2012 石油化工控制室抗爆设计规范中建议的荷载作用下砌体墙高度和厚度的影响，对比了玄武岩纤维(basalt fiber reinforced plastic, BFRP)布与喷涂式聚脲对蒸压加气混凝土单向砌体墙的加固效果，并以防止砌体墙倒塌为设计目标，给出了加固建议。研究表明，本文中建立的简化数值模型能较好地模拟燃气爆炸作用下蒸压加气混凝土砌体墙的变形和破坏模式，计算结果与试验吻合良好；《规范》建议荷载作用下，未加固砌体墙以弯曲破坏为主，随着墙体高度增加，破坏模式由弯曲破坏向剪切破坏转变；BFRP布条加固可以有效提高墙体抗弯刚度和压拱效应，而聚脲涂层加固对抗弯刚度提高有限但墙体拉拱效应明显，二者均能显著提高墙体抗爆性能；加固墙体均发生弯曲破坏，BFRP布条材料的断裂一般发生在墙体位移最大处，而聚脲涂层材料的断裂发生在跨端边界处。     

一种结构振动系统移频方法

本文对修改结构局部刚度和质量参数，从而使其具有给在有频率的动力修改问题提出了一种求解方法。该方法将结构固有频率修改问题化为一个低阶实对称矩阵特征值问题求解。文中给出一个算例来说明方法的有效性。     

基于振动响应和HHT技术的机翼盒段结构损伤检测方法研究

提出一种利用结构振动响应和HILBERT-HUANG变换(HHT)技术检测结构小损伤的时域方法,研究了基于HHT的悬臂机翼盒段结构的损伤特征量的提取方法,给出了所提取特征量与结构损伤程度之间的关系。用HHT技术处理完好盒段与损伤盒段在信号激励下的结构动力响应信号,得到信号的希尔波特谱;然后求出希尔波特谱对应的瞬时能量,从中提取出结构损伤信息—瞬时能量变化量,作为损伤特征参数;并研究了将之作为损伤特征参数的抗噪声干扰能力。最后给出了瞬时能量变化量最大值与结构损伤程度之间的关系。     

Predictive model for the collapse load of masonry assemblage with two piers joined by a spandrel

The masonry assemblage composed of two piers connected by a spandrel can be considered a repetitive unit in large masonry walls with openings, occurring in masonry buildings. In this work, the collapse load of the above-mentioned masonry assemblage is predicted by solving a system of nonlinear equations, where the normal force in the spandrel is a root of an equilibrium equation of fourth degree. Piers and spandrel are assumed rigid and nonlinearity (crushing and no tensile strength) is concentrated at the pier-foundation and pier–spandrel interfaces. The model also takes into account the effect of a timber lintel supporting the spandrel and anchored into the two adjacent piers. This approach valid for assemblages with one spandrel can be extended for the evaluation of the collapse load of structures composed of N piers connected by N ? 1 spandrels. The system of nonlinear equations is easily solved with an iterative method and the collapse load provided by the solution agrees well with the experimental result.     

A preliminary approach of dynamic identification of slender buildings by neuronal networks

The study of the dynamic behavior of slender masonry structures is usually related to the preservation of the historic heritage. This study, for bell towers and industrial masonry chimneys, is particularly relevant in areas with an important seismic hazard. The analysis of the dynamic behavior of masonry structures is particularly complex due to the multiple effects that can affect the variation of its main frequencies along the seasons of the year: temperature and humidity. Moreover, these dynamic properties also vary considerably in structures built in areas where land subsidence due to the variation of the phreatic level along the year is particularly evident: the stiffness of the soil–structure interaction also varies. This paper presents a study to evaluate the possibility of detecting the variation of groundwater level based on the readings obtained using accelerometers in different positions on the structure. To do this a general case study was considered: a 3D numerical model of a bellower. The variation of the phreatic level was evaluated between 0 and −20 m, and 81 cases studies were developed modifying the rigidity of the soil–structure interaction associated to a position of the phreatic level. To simulate the dispositions of accelerometers on a real construction, 16 points of the numerical model were selected along the structure to obtain modal displacements in two orthogonal directions. Through an adjustment by using neural networks, a good correlation has been observed between the predicted position of the water table and acceleration readings obtained from the numerical model. It is possible to conclude that with a discrete register of accelerations on the tower it is possible to predict the water table depth.     

Stochastic representation of the mechanical properties of irregular masonry structures

A procedure for the stochastic characterization of the elastic moduli of plane irregular masonry structures is presented in this paper. It works in the field of the random composite materials by considering the masonry as a mixture of stones (or bricks) and mortars. Once that the elastic properties of each constituent are known (deterministically or stochastically), the definition of the overall masonry elastic properties requires the knowledge of the random field describing the irregular geometry distribution. This last one is obtained by a software, implemented ad hoc, that, starting from a colour digital photo of the masonry and using the instruments of the digital image processing techniques, gives the random features of this field in both the space and frequency domain. The definition of the stochastic properties of masonry structures may be very useful both for the application of the stochastic homogenization techniques and for the direct stochastic analysis of the structures.     

Dynamic response of rocking cracked masonry walls

The behaviour of masonry constructions results to be very far from the one characterizing ductile structures. In masonry constructions, the seismic action activates a rocking motion rather than a dissipating mechanism. A strength resource of masonry structures, properly reinforced in order to avoid early local failures, consists in exhibiting rocking behaviour, until a failure condition is attained. Aim of the paper is to investigate the dynamic behaviour of masonry single storey walls, according to Housner’s studies and innovatively introducing the effect of diagonal cracks developing from the toes of the piers and shown by typical post-earthquake cracking patterns. The proposed procedure can be easily applied to the case of multi-storey regular masonry walls with openings representing the main resistant structural components of a masonry building. Starting from the evaluation of the incipient rocking acceleration of the system, the free and forced motions of the wall are examined. In the paper, according to the classical Housner’s approach, the energy dissipation occurring during the impact is modelled. Finally, a numerical application, considering a simple constant horizontal acceleration impulse of given duration has been carried out.

     

In plane loaded masonry walls: DEM and FEM/DEM models. A critical review

This work is dedicated to the assessment of the nonlinear behaviour of masonry panels with regular texture and subject to in-plane loads, by means of numerical pushover analysis and an analytical homogenized model. Two numerical models are considered and adopted for performing a set of numerical tests: a discrete model developed by authors and a discrete/finite element model frequently adopted in rock mechanics field and effectively extended to masonry structures. In both models the hypotheses of rigid blocks and elastic–plastic joints following a Mohr–Coulomb yield criterion are adopted. The aim of this work is twofold: (1) a comparison and a calibration of the numerical models, evaluating their effectiveness in determining ultimate loads and collapse mechanisms of masonry panels, by assuming a nonlinear homogenized model for regular masonry as reference solution; (2) the evaluation of sensitivity of masonry behaviour and numerical models to panel dimension ratio and to varying masonry texture. In a first case study, sliding collapse mechanisms changing to overturning collapse mechanisms for increasing panel and block height-to-width ratio are obtained and the results given by the numerical models turn out to be in good agreement. Furthermore, a second case study, dedicated to square panels supported at base ends and vertically loaded, shows different ‘arch mechanisms’ depending on block height-to-width ratio.     

Identification of the representative crack length evolution in a multi-level interface model for quasi-brittle masonry

It is proposed here to identify the law of crack length evolution with a small number of parameters governing a recently presented model (Rekik and Lebon, submitted for publication) describing the interface behavior in damaged masonry. Studies on non-confined medium- and large-sized masonry structures have shown that it is necessary to obtain a linear increasing crack in the post-peak part of the “stress–strain or –displacement” diagram. In confined masonry structures showing softening and sliding parts, the results obtained with this crack evolution failed to match the experimental data. The crack lengths identified in the post-peak part at several points on the experimental “stress–displacement” diagram show that the representative crack length is a bilinear or trilinear function describing the increase in the crack length with respect to the decrease in the shear stress. Numerical studies on medium- and large-sized masonry structures consisting of the same materials subjected to various loads were performed to determine the ultimate crack length, and the results are relatively insensitive to the size of the masonry and the type of the load applied. The numerical local fields determined in the elementary and full-scale structures investigated were used to test the validity of the present model at the local scale, as well as to obtain an additional unilateral condition in the case of compressed masonry structures in order to prevent overlapping between the masonry components.