Thermal behaviour of masonry walls: Mathematical modelling and field monitoring

This Canadian study shows that the potential use of their procedure is very broad since the data computed can be used to investigate deterioration problems, to check risks associated with any proposed thermal upgrading and to perform stress analysis. The variation between the computed data and recorded data is small, except at peaks where the maximum differences occur.     

Finite element modelling of deformation characteristics of historical stone masonry shear walls

Two dimensional nonlinear finite element analysis based on experimental test data has been carried out to model deformation characteristics, such as load–displacement envelope diagrams and failure modes of historical stone masonry shear walls subjected to combined axial compression and lateral shear loading. An experimental research work was carried out on three different types of historical stone masonry shear walls that can be considered representative of ancient stone masonry constructions. Those three types of masonry are: (i) sawn dry-stack or dry-stone masonry without bonding mortar, (ii) irregular stone masonry with bonding mortar, and (iii) rubble masonry with irregular bonding mortar thickness. Plasticity theory based micro modelling techniques has been used to carry out the analysis. The stone units were modelled using eight node continuum plane stress elements with full Gauss integration. The joints and unit-joint interfaces were modelled using a six node zero thickness line interface elements with Lobatto integration. This paper outlines the experimental research work, details of numerical modelling carried out and report the numerical lateral load–displacement diagrams and failure modes. The numerical analysis results were compared with the experimental test results and good agreement was found.     

Parametrical study of masonry walls subjected to in-plane loading through numerical modeling

This paper deals with the numerical assessment of the influence of parameters such as pre-compression level, aspect ratio, vertical and horizontal reinforcement ratios and boundary conditions on the lateral strength of masonry walls under in-plane loading. The numerical study is performed through the software DIANA^® based on the Finite Element Method. The validation of the numerical model is carried out from a database of available experimental results on masonry walls tested under cyclic lateral loading. Numerical results revealed that boundary conditions play a central role on the lateral behavior of masonry walls under in-plane loading and determine the influence of level of pre-compression as well as the reinforcement ratio on the wall strength. The lateral capacity of walls decreases with the increase of aspect ratio and with the decrease of pre-compression. Vertical steel bars appear to have almost no influence in the shear strength of masonry walls and horizontal reinforcement only increases the lateral strength of masonry walls if the shear response of the walls is determinant for failure, which is directly related to the boundary conditions.     

多层砌体结构窗下墙的破坏研究

通过汶川地震震害调查,探讨多层砌体结构窗下墙体的破坏,分析破坏规律、墙体的窗下墙设计,对多层砌体结构窗下墙的破坏模式进行分析。通过分析发现窗下墙在地震作用下同样处于危险状态,窗下墙的破坏模式是一种延性破坏模式,应对砌体窗下墙破坏进行深入研究。     

含嵌固墙体古建筑木结构震害数值模拟研究

以四川广元市某古建筑木结构为例,在考虑墙体嵌固作用的基础上,研究了汶川地震下古建筑的震害症状与地震响应状况。采用ANSYS软件对该古建筑榫卯节点的半刚性特征及砖砌体与木构架的嵌固作用进行了模拟,并建立了结构的有限元模型。通过模态分析,获得了结构的基频和主振型;通过将汶川波进行调幅作用于该结构,获得了结构在不同时刻的内力及变形峰值,并获得了典型节点的地震响应曲线。结果表明:考虑墙体的嵌固作用后,该古建筑的基频为1.59Hz,振动形式以第一振型为主,地震作用下木构架产生的位移很小,内力均在容许范围内,且保持稳定的振动状态;墙体由于强度不足,在某些部位将产生破坏,与震害现状基本吻合。     

Robustness of hollow clay masonry units and seismic behaviour of masonry walls

As the recent experimental investigations indicated, the robustness of masonry units is one among the most decisive parameters which define the behaviour of masonry walls when subjected to seismic loads. If local brittle failure of units occurs, the mechanism of behaviour and known relationships between the strength and ductility properties of masonry walls change. In such a case, the design values of load bearing and energy dissipation capacity of masonry walls are overestimated, although the equations and requirements specified in the codes have been taken into consideration. If brittle units are used for the construction of structural walls, the actual structure will be exposed to an increased level of seismic risk although it has been designed for earthquake loads according to codes. This is especially the case of reinforced masonry, where brittle local failure prevents the transfer of predicted forces from reinforcing steel to masonry units. In order to provide limitations for the use of hollow units with large hole volume ratio and thin shells and webs in seismic areas, a measure to define the qualitative term “sufficient robustness”, specified in Eurocode 8, should be found.     

Out-of-plane behavior of surface-reinforced masonry walls

This paper presents the results of an experimental program designed to evaluate the out-of-plane shear strength of masonry wall system; and to evaluate of the influence of the area of externally bonded FRP composites on the shear strength of the system. Eighteen compact masonry wall panels (3′×2′×8″, 900×600×200 mm) were tested for static out-of-plane loads. Nine panels were reinforced by one layer of WEB ‘S-Glass’ fiber-reinforcing system attached to the tension side of the wall, while the remaining nine were reinforced with two layers of composite overlay on the tension side. The influence of the overlay's embedded length (the distance between the support and the overlay's end) on the shear strength was also investigated. The variables evaluated included three layout configurations and two reinforcement ratios. Three different distances between the overlay end and the adjacent support were tested, 0, d/4 (d is the block unit thickness) and d/2. Both one and two layers of WEB fibers were used and three specimens were evaluated for each variable. An MTS machine was used to test each panel under four-point load conditions. The failure loads, mid-span deflection, fiber-end slippage and failure modes were recorded. Based on the results of the experimental program, it appears that the out-of-plane shear strength of the concrete masonry wall systems is constant over the range of variables tested. The measured shear strength of the masonry wall specimens evaluated in this program indicates that the code defined shear strengths may not be as conservative as assumed.     

Fire resistance of load-bearing masonry walls

A comprehensive theory is being developed to predict the behavior of load-bearing masonry walls subjected to fire on one side.     

Out-of-plane behaviour of confined masonry walls

This paper presents the results of a study on the behaviour of confined masonry walls subjected to out-of-plane uniform pressures. Six full scale confined masonry walls were tested in the laboratory. The variable studied was the wall support conditions; four-sided and three-sided simple supported walls were considered. Simplified analytical models were developed for predicting cracking and maximum pressure for the walls. The former was predicted using the finite element method and the latter using the yield line method, the failure line method, and the compressive strut method. This last method was modified to account for the stiffness of the confining elements and the observed failure mechanism. The observed maximum pressures and failure cracking pattern for the walls with three-side supports were similar to those with four-side supports. This was related to the strength and stiffness provided by the non-supported confining element, which acted as a fourth support. Based on the comparison of experimental and analytical results, it is concluded that both cracking and maximum pressure can be predicted with the analytical models developed in this work.     

砖砌墙体裂缝浅析

结合工程实例，对裂缝产生的各种原因进行了分析，介绍了相应的防治措施，指出加强施工现场的管理力度、严格执行设计图纸内容、严格规范施工对于防治裂缝的重要意义。     

Cyclic behavior of combined and confined masonry walls

Results of tests conducted for combined and confined masonry walls are reported in this paper. The cyclic testing followed the protocol established by Mexican guidelines for masonry structures (NTCM-2004), which is similar to that used worldwide for the cyclic testing of wall structures. Resisting mechanisms and deformation characteristics of such walls were evaluated. Indicative values of useful parameters for analysis and design were also defined. In addition, it was verified if such a system is earthquake-resistant according to NTCM-2004 guidelines.     

砖砌体室外独立墙壁及围墙结构设计

通过对砖砌体独立墙壁及围墙的受力分析,根据国家相关规范要求,对净高较高的砖砌体独立墙壁及围墙进行极限承载力验算,并确定合理构造柱和圈梁间距。     

Testing and numerical modelling of lean duplex stainless steel hollow section columns

Stainless steels are employed in a wide range of structural applications. The austenitic grades, particularly EN 1.4301 and EN 1.4401, and their low-carbon variants EN 1.4307 and EN 1.4404, are the most commonly used within construction, and these typically contain around 8%–11% nickel. The nickel represents a large portion of the total material cost and thus high nickel prices and price volatility have a strong bearing on both the cost and price stability of stainless steel. While austenitic stainless steel remains the most favourable material choice in many applications, greater emphasis is now being placed on the development of alternative grades with lower nickel content. In this study, the material behaviour and compressive structural response of a lean duplex stainless steel (EN 1.4162), which contains approximately 1.5% nickel, are examined. A total of eight stub column tests and twelve long column tests on lean duplex stainless steel square (SHS) and rectangular hollow sections (RHS) are reported. Precise measurements of material and geometric properties of the test specimens were also made, including the assessment of local and global geometric imperfections. The experimental studies were supplemented by finite element analysis, and parametric studies were performed to generate results over a wider range of cross-sectional and member slenderness. Both the experimental and numerical results were used to assess the applicability of the Eurocode 3: Part 1-4 provisions regarding the Class 3 slenderness limit and effective width formula for internal elements in compression and the column buckling curve for hollow sections to lean duplex structural components. Comparisons between the structural performance of lean duplex stainless steel and that of other more commonly used stainless steel grades are also presented, showing lean duplex stainless steel to be an attractive choice for structural applications.     

小型混凝土空心砌块墙体质量控制

从施工准备、材料选择、门窗安装、水电安装、防裂防渗等几个方面对小型混凝土空心砌体质量的控制措施作了阐述 ,以使其达到不裂不渗的质量要求 ,并最终能够推广使用。     

Out-of-plane behavior of dry-stack brick masonry walls

As a result of the combination of the complex behavior of masonry buildings with insufficient material quality and lack in engineering calculations, a large number of damages has been observed in the earthquakes that occurred in recent years. Therefore, a realistic understanding of the behavior of masonry walls and buildings is necessary to construct seismic-resistant structures. Since masonry walls have many variables, performing experiments in which each variable is present at the same time will make it difficult to understand the behavior. For these reasons, considering the out-of-plane failures that are frequently mentioned in recent earthquakes, in this study, variables in dry-stack brick masonry buildings such as the aspect ratio of the wall (2, 1.33, and 1), the presence of the transverse walls (2, 1, and 0), and the openings in the walls (door and/or window) were taken into account separately. Eighteen different wall configurations were designed, and a total of 48 dry-stack walls having U-shape, L-shape, and I-shape in plan were tested by a specially constructed tilting table setup to determine their out-of-plane behavior. From the test results, it was found that lateral load capacity of the U-shaped walls without openings increased as the aspect ratio (L/H) decreased. No change in capacity was observed in L- and I-shaped walls when the aspect ratio was reduced from 2 to 1. Door and/or window openings were found to affect only the L-shaped walls. In addition, it was determined that failure patterns were affected from the aspect ratio and the presence of the openings.     

Uncertainty modelling in plate buckling

A brief account is given of the basic principles of uncertainty modelling with first-order second-moment methods. The main features of the behaviour of plates subjected to compressive loads are considered and various prediction methods are compared. The governing parameters of plate behaviour are used to construct probabilistic models for the laboratory test situation, for the analysis and for the design of plates. The uncertainty of the strength predictions is quantified in the different cases. Special attention is given to the implications of problem formulation and to the methodology of uncertainty modelling.     

Thermal performance of concrete masonry walls in fire

Under consideration here are the effects of cement paste, autoclaving, aggregates, geometry, and moisture on the fire endurance of concrete masonry walls. Note: This paper was originally published as Canadian Building Digest CBD 140 by the Division of Building Research, National Research Council of Canada, and is reproduced here by permission.     

浅析砖混结构墙体裂缝的形成原因及防治措施

从地基不均匀沉降、温度变化、干缩变形三方面分析了砖混结构墙体裂缝的形成原因，介绍了设计及施工中应采取的防治措施，以保证房屋结构的安全性。     

砖混结构墙体裂缝的防治

从建筑设计方案、地基的检测检验、施工工序的安排三方面分析了砖混结构墙体裂缝的产生原因，并提出了相应解决措施，以减少裂缝的发生，保证住宅用户的安全。