Numerical investigation of historic masonry walls under normal and shear load

The behaviour of masonry under seismic loads has recently become of great interest. New methods for design and analysis, as well as for resistance, have been developed. The main focus has been on experimental and analytical research for the development of new brick material and mortar. With the introduction of Eurocode 8, the behaviour of old masonry structures under seismic load became an interesting topic for engineers. In particular, the available resistance capacity of existing masonry structures is highly relevant to the restructuring of existing buildings. Laboratory tests on masonry walls were performed in order to determine the mechanical behavioural characteristics of old brick material.     

小开洞砌体墙抗震性能研究

为研究小开洞砌体墙的抗震性能,设计了3片小开洞砌体墙试件和1片无洞口砌体墙试件,并进行了低周往复加载试验;介绍了砌体墙试件的主要破坏过程及破坏机理,对比分析了各片砌体墙承载力、抗侧刚度及延性等抗震性能差异;基于试验建立有限元模型,研究了开洞率及洞口位置对砌体墙抗震性能的影响。结果表明：小开洞砌体墙破坏机理较实体墙发生了显著改变,无洞口墙表现为明显的转动破坏特征,小开洞墙主要表现为典型的脆性剪切破坏;开单个小洞口会削弱砌体墙的水平承载力和抗侧刚度,大幅降低墙体的延性;增加洞口数量或高度可适当提高小开洞砌体墙的抗震性能;随着开洞率的增大,墙体承载力和初始刚度逐渐下降,延性性能表现为先降低后提高的趋势;竖直方向上,洞口越往下,墙体抗震性能越差,水平方向上,洞口宜居中布置。     

Experimental testing of tall reinforced masonry walls under out-of-plane actions

This paper presents the results of experimental tests on tall reinforced masonry walls. Systems made with vertically perforated clay units for building mainly tall, load-bearing, reinforced masonry walls for commercial and industrial purposes were studied for applications in areas characterised by low to high seismic risk. Tests aimed at obtaining basic mechanical characterisation of the construction systems, and reproducing the behaviour of single-storey reinforced masonry buildings provided with deformable roofs. For this structural configuration, a special set-up for out-of-plane cyclic tests was designed and built. In particular, this paper presents: (a) systems used for tall reinforced masonry wall construction; (b) test set-up to reproduce the behaviour under out-of-plane loads and P–Δ effects; (c) experimental results obtained. The final aim is validating the effectiveness of the proposed construction systems and achieving complete mechanical characterisation for modelling and structural assessment purposes.     

Damaged masonry walls in two-way bending retrofitted with vertical FRP strips

Unreinforced masonry (hereafter termed ‘masonry’) structures comprise a significant proportion of the building stock in many countries worldwide, however their walls do not behave well under out-of-plane loading, such as that experienced during seismic events. Consequently, many existing masonry structures require some form of retrofit to comply with existing codes. As part of ongoing research at The University of Adelaide on the out-of-plane bending behaviour of masonry walls, eight full-scale walls (with window openings) were tested under reversed-cyclic loading. Four of the severely damaged walls were subsequently retrofitted using externally bonded (EB) (three walls) and near-surface mounted (NSM) (one wall) fibre-reinforced polymer (FRP) strips and tested again to quantify the increase in strength and ductility relative to the original capacities. A debonding mechanism not yet quantified for retrofitted masonry walls was observed and identified as displacement induced (DI) debonding. It is a result of a differential out-of-plane displacement at either side of a crack in the wall. NSM strips are more susceptible due to their orientation. This paper presents the results of the wall tests along with detailed accounts of the wall failure modes.     

高延性混凝土加固无筋砖砌体墙抗震性能试验研究

为提高砖砌体墙的抗震性能,采用高延性混凝土（HDC）对其进行加固,对4片HDC加固砖墙和2片作为对比试件的未加固砖墙进行低周水平往复加载试验,主要研究不同加固形式（构造带加固和面层加固）及墙体砂浆强度对加固砖砌体墙的滞回性能、破坏形态、水平承载力及刚度退化等抗震性能的影响。试验结果表明：采用HDC加固可显著提高墙体的承载力和位移延性,延缓墙体开裂和刚度退化,改善墙体的脆性破坏特征;HDC构造带可对砖墙形成有效约束作用,改变墙体的破坏模式。基于试件的破坏形态,提出加固墙体的承载力计算方法,并根据试验结果进行了验证。     

Shear behavior of unreinforced and reinforced masonry panels subjected to in situ diagonal compression tests

Approach to safety evaluations issued by modern codes is clearly based on quantitative assessment of performances. As a consequence, validated mechanical parameters and numerical models should be made available on large scale for practical applications. This is the background of the present paper that deals with a specific type of masonry largely used in Central Italy and particularly in Umbria and Abruzzo region, whose territory exhibits a relevant seismic risk. A research project focused on the shear behavior of masonry panels subjected to in situ diagonal compression tests has been issued. The project consists of two parts: tests were performed on unreinforced and reinforced panels. As to the unreinforced panels, focusing attention on the diagonal cracking failure mode, the experimental research allowed to provide representative values of the mechanical parameters adopted to define the limit strength domain of some typical masonry walls in old buildings of Umbria and Abruzzo. Conversely, reinforced panels were tested aimed at investigating the effectiveness of existing methods of repair. A comparison between traditional and innovative seismic-upgrading techniques has been made in order to characterize the behavior of historical masonry walls under different strengthening configurations.     

Practical modelling issues for masonry building retrofitted with squat shear wall

Damage observed following moderate to large earthquakes has shown masonry buildings are vulnerable to lateral shaking. The results of statistical analyses in Iran show that 90% of schools in the retrofitting list are unreinforced masonry buildings. A Practical Guideline for Seismic Rehabilitation of Masonry Schools has been published in Iran. This guideline proposed 2 retrofitting methods for retrofitting masonry schools: use of shear wall and shotcreting the perimeter of building. In the case of shear wall, their construction is usually expensive; there are less projects retrofitted by shear walls, and in most retrofitting masonry schools projects, perimeter shotcrete is used. The main aim of this study is offering recommendation to improve this guideline, resulting in more economical approaches. This study proposes including lateral resistance of masonry walls in resisting seismic loads and in the case of shear wall foundation proposes strip shallow foundation for concrete shear walls by including effect of rocking, sliding, and settlement response. It has been shown that with including masonry walls in lateral resistance of building, a considerable reduction in maximum drift occurred. Interaction of soil and structure by considered strip shallow foundation reduces the base shear and increases maximum drift of the building.     

In-plane retrofitting of masonry panels with fibre reinforced composite materials

Research activities carried out during the past years concerning the use of fibre reinforced polymers (FRP) as external reinforcement of masonry walls have shown that this system considerably improves structural stability and ductility with minimum increase in the load transmitted to foundations. However, different aspects of this retrofitting system should still be analyzed.The mechanical behaviour under in-plane compression and diagonal compression of clay masonry panels reinforced or repaired with carbon fibre reinforced polymer laminates is experimentally assessed in this paper. The results show that if correct retrofitting schemes are chosen, reinforcement and repairing with fibre reinforced polymers improves masonry behaviour, increasing ductility and, in some cases, ultimate strength and even stiffness. In this way, brittle behaviour and sudden failure of unreinforced masonry can be avoided.     

碳纤维布抗震加固开门窗洞口砌体墙片的试验研究与受剪承载力分析

通过对6片开门窗洞口砖砌体墙片在低周往复荷载作用下的抗震性能试验研究,探讨碳纤维布用于抗震加固无筋开洞口墙片的破坏形态、受力特性和加固效果,对比不同碳纤维布粘贴方式对无筋开洞口砌体墙片抗震加固效果的影响,据此建议对地震区开窗洞墙体采用沿洞口周围粘贴碳纤维布并在窗洞角部附加锚固碳纤维布条的有效加固方式,对开门洞墙体采用沿洞口周围粘贴碳纤维布并在宽墙肢上对角粘贴碳纤维布的有效加固方式。同时根据试验研究结果,建立以碳纤维布拉杆机制为基础的碳纤维布加固开洞口砌体墙片的受剪承载力计算模型,计算结果与试验结果吻合较好,说明该计算模型能较好地反映碳纤维布与无筋砌体墙体共同工作的受力机理,可供工程设计参考使用。     

墙体较少的砖混结构住宅楼抗震设计

提出了在砖混结构中设置一定数量的钢筋墙力墙的方法。以实例阐述了抗震验算和构造设计,指出这种做法造价虽比砖墙高4倍左右，但它满足了房屋开口大时的结构抗震设计要求。     

Local post-strengthening of masonry structures with fiber-reinforced polymers (FRPs)

In-plane loaded masonry structures can be post-strengthened effectively with fiber-reinforced polymers (FRP). This applies to shear walls under vertical and horizontal loading, as well as to walls with additional cut-outs or single loads. A mechanical model is required in all cases for the detailing and design of post-strengthening measures and to characterize load transfer within the wall and, from this, to calculate stresses of masonry and FRP materials. To establish a three-step model for local post-strengthened masonry walls, extensive testing on different scales has been carried out at the University of Kassel within the last few years. Firstly, the load transfer between single masonry units and FRP was addressed. Overall, 91 bonding tests were carried out with seven types of bricks and blocks to examine failure modes and the bonding strength for a broad variety of bricks and blocks. Two different types of adhesive were used in combination with four types of glass- and carbon–fibers. Based on the results of the bonding tests, 24 anchoring tests overall on two different types of masonry – clay brick and calcium–silicate – were carried out under different geometrical and loading conditions. The test results of all test series will be explained by a combination of fracture mechanics and strut-and-tie modeling. A mechanical model based on fracture energy provides the background for the theoretical explanation of the debonding phenomena. The model can be used to predict failure of bonding on single bricks as well as bonding geometries with more than one brick where the bonding area is separated by bed or head joints. Comparison of data from calculations and testing exhibited good correlation.     

Design models of reinforced masonry walls under monotonic and cyclic loading

Reinforced Masonry offers several advantages for low cost housing in seismic regions. Widely accepted design criteria, however, are not available — although several design rules are provided in several Codes. This paper is a contribution to the research needed towards a possible improvement of design recommendations, based on the following rational data: (a) Recognition of all failure modes, and (b) Specific contribution of force transfer mechanisms, such as tensile strength and compression strength of masonry, masonry to masonry friction, pullout force of steel bars and dowel action. Thus, using first principles and specific data from recent experimental results, several closed formulae are derived in this paper, predicting shear loads of (i) cracking (ii) tensile disintegration of the web and (iii) diagonal compression crushing of R.M. cantilever and double fixed walls. Ultimate loads proposed by this paper, as well as critical shear loads proposed by several Codes, are also calibrated through a data bank of 55 large scale experiments; conclusions are drawn regarding their validity.     

钢筋混凝土-砖砌体组合墙抗震性能

以往的研究表明,钢筋混凝土-砖砌体组合墙是一种抗震性能好、造价低的优良结构形式。本研究通过22片不同高宽比、不同竖向压应力、不同竖向配筋率和不同水平配筋率的钢筋混凝土-砖砌体组合墙的抗震性能研究,并通过国内其它65片类似墙体的分析,对这种墙体在竖向和水平荷载作用下的破坏特征、墙体的正截面承载力、斜截面承载力及抗震性能进行了分析研究,给出了墙体抗震承载力计算公式,可为该类房屋的设计提供参考。     

Cyclic behaviour of hinged steel frames enhanced by masonry columns and/or infill walls with/without CFRP

Abstract

This paper investigates the in-plane seismic behaviour of hinged steel frames that are enhanced with masonry columns and/or infilled walls. First, eight half-scaled hinged steel frame specimens were constructed according to the realistic structural system of Bund 18, which is a historical building in Shanghai, China. Then, cyclic loads were exerted on these frames. The test results indicated that the seismic behaviours of the hinged steel frames can be significantly improved with the use of masonry columns and/or infilled masonry walls as well as with proper strengthening due to carbon fibre-reinforced polymer (CFRP) sheets. A simplified model was developed to simulate the seismic behaviours of these frames. In this model, infilled walls and CFRP sheets were replaced by diagonal struts, and the steel members and their surrounding elements were treated as composite members. Finally, this model was verified by experimental results.     

两层预制板砖砌体结构房屋模型双向拟动力试验研究

对一栋缩尺为1∶2的两层单开间预制板砖砌体结构房屋模型进行不同强度地震作用下的双向拟动力试验和非线性地震响应分析,研究该结构在地震作用下的破坏机制、变形、滞回特性及耗能能力等。结果表明：构造柱与圈梁的存在,使得预制板砌体结构具有较好的延性,地震破坏主要集中在底层,即使墙体严重开裂,也不至于整体结构垮塌;双向地震作用下一个方向的承载力与刚度退化会加剧另一个方向承载力与刚度的退化,从而导致砌体结构整体抗震能力的下降;滞回曲线由弓形最后发展到反S形,具有明显的捏缩和滑移效应;建立的砌体结构非线性空间有限元模型,能够反映预制板砌体结构的弹塑性地震响应,计算结果与实测结果基本吻合;两层砌体结构房屋能够满足设计规范的抗震要求。     

In-plane cyclic behaviour of a new reinforced masonry system: Experimental results

This paper describes the behaviour under cyclic shear compression of an innovative reinforced masonry system, composed of horizontally perforated units, having common steel bars or prefabricated trusses as horizontal reinforcement. At the wall edges or crossings, confining columns for vertical reinforcement are built with vertically perforated units. Experimental tests to obtain information on the in-plane cyclic behaviour of the construction system were performed on masonry panels made of horizontally perforated units and on completed reinforced masonry walls. Tests on the entire system were repeated for two wall aspect ratios and two vertical stress levels, in order to force shear type and flexural behaviour. In particular, this paper presents: (a) results of shear compression tests in terms of strength, ductility parameters, energy dissipation, viscous damping and stiffness degradation, (b) strains and the effectiveness of reinforcement, (c) the influence of various parameters such as axial load, aspect ratio, and reinforcement type on the behaviour of the reinforced masonry walls, and (d) comparison of walls built with and without vertical reinforcement.     

预应力砌体抗震性能的试验研究

本文通过8片不同类型的预应力混凝土小型空心砌块砌体的水平低周反复荷载试验以及2片普通混凝土小型空心砌块砌体的对比试验,研究了预应力砌体破坏形态、滞回特性、延性、刚度退化曲线等抗震性能,明确了预应力、窗洞以及构造措施对混凝土小型空心砌块墙体的开裂荷载、极限荷载和变形性能的影响。研究结果表明,预应力延缓了混凝土小型空心砌块墙体的开裂,提高了结构的开裂荷载和极限荷载;预应力改变了墙体破坏时的裂缝分布形状,裂缝密而细,几乎布满墙体全部灰缝,主裂缝不明显;预应力提高了墙体的刚度、延性和耗能能力;在窗洞底部现浇水平配筋混凝土条带能有效地抑制裂缝的产生和发展,并能提高墙体的变形和耗能能力。     

FRP和TRC加固砌体墙受剪性能试验研究

砌体结构的抗震性能较差,且砌体墙作为主要承载构件易在地震中受到面内剪切作用。而加固是提高砌体墙面内受剪性能的有效方法。FRP (fiber-reinforced polymer)和TRC(textile-reinforced concrete)两种材料具有轻质、高强、耐腐蚀等优势,在应用于砌体结构加固时增强效果显著。为了比较这两种材料加固砌体墙的受剪性能,采用砂浆、FRP和TRC对砌体墙进行加固,进行了加固砌体墙试件的面内受剪试验,分析不同加固方式的破坏模式、承载力、延性和耗能能力。研究表明,未加固和砂浆加固的砌体墙在破坏时有不同程度的脆性特征,采用FRP和TRC加固均可改善这一现象。在本研究试验条件下,FRP和TRC在提升峰值剪应力方面增强效果相似,但TRC加固试件在延性和耗能方面效果更好。最后,结合现有规范中的相关计算方法,计算FRP和TRC加固层的受剪承载力,并且将计算值与试验值进行对比以评估相关计算方法的合理性,结果表明相关计算方法较为保守。     

混凝土空心砌块砌体抗震抗剪强度

针对现行《建筑抗震设计规范》(GB 50011-2010)和《砌体结构设计规范》(GB 50003-2001)中关于混凝土空心砌块砌体抗震抗剪设计强度取值上存在的问题,在砌体剪压破坏区理论的基础上,结合中国已有58片混凝土砌块砌体墙的剪压试验结果,提出了具有下降段的剪压复合作用下混凝土空心砌块砌体抗震抗剪强度平均值曲线公式,并推导出具有可靠度保证的混凝土砌块砌体抗震抗剪强度设计值公式。与现行规范相比,提出的抗震抗剪强度设计值公式不仅解决了现行规范间的不统一,而且较好的实现了剪压复合作用下混凝土空心砌块砌体剪摩、剪压和斜压3类破坏形态的模拟,避免了现行规范中混凝土砌块砌体抗震抗剪设计强度取值的不合理和不安全,可运用于高层配筋砌块砌体结构设计。