Triaxial elastoplastic damage constitutive model of unreinforced clay brick masonry wall

Due to differences in the properties of composition materials and construction techniques,unreinforced masonry is characterized by low strength,anisotropy,nonuniformity,and low ductility.In order to accurately simulate the mechanical behavior of unreinforced brick masonry walls under static and dynamic loads,a new elastoplastic damage constitutive model was proposed and the corresponding subroutine was developed based on the concrete material constitutive model.In the proposed constitutive model,the Rankine strength theory and the Drucker-Prager strength theory were used to define the tensile and compressive yield surface function of materials,respectively.Moreover,the stress updating algorithm was modified to consider the tensile plastic permanent deformation of masonry materials.To verify the accuracy of the proposed constitutive model,numerical simulations of the brick masonry under monotonic and cyclic uniaxial tension and compression loads were carried out.Comparisons among the numerical and theoretical and experimental results show that the proposed model can properly reflect the masonry material mechanical properties.Furthermore,the numerical models of four pieces of masonry walls with different mortar strengths were established.Low cyclic loadings were applied and the results show that the proposed constitutive model can properly simulate the wall shear failure characteristics,and the force-displacement hysteretic curves obtained by numerical simulation are in good agreement with the tests.Overall,the proposed elastic-plastic damage constitutive model can simulate the nonlinear behavior of unreinforced brick masonry walls very well,and can be used to predict the structural response of masonry walls.

Twin lintel belt in steel for seismic strengthening of brick masonry buildings

A single-room,single-storey full-scale brick masonry building with precast RC roofing system was tested thrice under displacement controlled lateral cyclic loading,to assess the effectiveness of the basic repair and seismic strengthening techniques.Initially,the virgin building specimen was loaded laterally to f^tilure.In the second stage,the damaged building was repaired by stitching across the cracks,and tested under the same lateral loading.In the third stage,the twice-damaged structure was repaired once more by stitching and strengthened by twin lintel belt in steel and vertical comer reinforcement, and re-tested.The building strengthened by twin lintel belt in steel showed about 28% higher strength under lateral loading than the virgin building.

Blast response of clay brick masonry unit walls unreinforced and reinforced with polyurea elastomer

Clay brick masonry unit(CBMU) walls are widely used in building structures,and its damage and protection under explosion loads have been a matter of concern in the field of engineering protection.In this paper,a series of full-scale experiments of the response characteristics of 24 cm CMBU walls unreinforced and reinforced with polyurea elastomer subjected to blast loading were carried out.Through setting 5.0 kg TNT charges at different stand-off distances,the damage characteristics of masonry walls at different scaled distances were obtained.The reinforcement effect of different polyurea coating thicknesses and methods on the blast resistance performance of masonry walls under single and repeated loads were also explored.Five failure grades were summarized according to the dynamic response features of masonry walls.Based on the stress wave propagation pattern in multi-media composite structures,the internal stress distribution of masonry walls were analyzed,and the division basis of the masonry walls’ failure grades was then quantified.Combined with Scanning Electron Microscope(SEM)images,the deformation characteristics of soft and hard segments of polyurea and effects of detonation products on microstructures were revealed respectively,which provides an important reference for the design and application of polyurea in the blast resistance of clay brick masonry walls.

A 3-D DDA damage analysis of brick masonry buildings under the impact of boulders in mountainous areas

In mountainous areas, geological disasters carrying large boulders can cause severe damage to the widely used masonry buildings due to the high impact forces. To better understand the damage of brick masonry buildings under the impact of boulders, a "block-joint" model is developed using threedimensional discontinuous deformation analysis(3-D DDA) to simulate the behaviour of the "brick-mortar" structure. The "block-joint" model is used to capture not only the large displacement and deformation of individual bricks but also the large-scale sliding and opening along the mortar between the bricks. The linear elastic constitutive model is applied to account for the non-plastic deformation behaviour of brick materials. Furthermore, the mechanical characteristics of the mortar are represented using the Mohr-Coulomb and Drucker-Prager criteria. To propose safe structural design schemes and effective reinforcement for brick masonry buildings, seven construction techniques are considered, includingdifferent grades of brick and mortar, effective shear areas and reinforced members. The proposed 3-D DDA model is used to analyse the velocity distribution and the key point displacements of the brick masonry building under the impact of boulders. The results show that upgrading the brick and mortar, increasing the wall thickness, making full use of the wall thickness, and adding a circular beam and structural column are very effective approaches for improving the impact resistance of brick masonry buildings.

Investigations of Physical and Chemical Characteristics of Masonry Stones and Bricks during Building Cleaning： Part 1. Physical Testing

This series of study focused on analysing and assessing the changes of the physical and chemical characteristics of the surfaces of the masonrystones and bricks during the sandblasting cleaning process by conducting various physical and chemical tests. Seven masonry stones and bricks were adopted, including yellow sandstone, red sandstone, limestone, marble, granite, white clay brick and yellow clay brick. The physical testing included evaluating the cleaning degree, determining the Vickers hardness, and detecting the water absorption. Using a digital imaging analysis method, the greyscale and cleanness were introduced to quantitatively assess the effectiveness of masonry building cleaning and confirmed to be useful and appropriate. The cleanness analysis, together with the hardness and water absorption tests showed that a masonry stone or a brick with a higher cleaning degree corresponded to a brighter and harder stone surface. In general, the physical properties were found to vary largely during the building cleaning.

Experiment and Numerical Simulation on Axial Compressive Performance of Autoclaved Fly Ash Solid Brick Masonry Columns

To study the influence of slenderness on the axial compressive performance of autoclaved fly ash solid brick masonry columns, compression experiments were conducted on 12 samples of autoclaved fly ash solid brick masonry column and 4 samples of fired clay brick masonry column. The damage patterns and compressive performance were compared and analyzed. The experimental results indicate that the compressive bearing capacity decreases as slenderness increases from 3 to 18, and the compressive bearing capacity of the autoclaved fly ash solid brick masonry columns is lower than that of the fired clay brick masonry columns. The formulae for the axial compressive bearing capacity of autoclaved fly ash solid brick masonry columns were derived based on the experiments. The nonlinear FEA program ANSYS was adopted to simulate the behaviors of masonry columns. By comparing the simulation results and experimental results, it is shown that the simulation results agree well with the experimental ones. The rationality and applicability of the simulation results were verified.

Applications of Compliance to Cost Ratio (C-CR) Analysis in the Determination of Optimum Mix of Insulating Bricks in Masonry

The scarcity of housing increases as population continues to rise all over the world. Despite government efforts at providing houses, yearly demand keeps on exceeding available houses and hence the hike in rent, the cost of erecting houses and the cost of building materials. This ultimately calls for a decisive solution. This study therefore applied compliance to cost ratio (C-CR) analysis in evaluating the optimum properties of fired ceramic bricks. The optimum mix proportions of waste glass (WG) and wood saw dust (WSD) in fired bricks, that will be suitable for housing constructions were hence determined. Fired clay brick samples which contained varied proportions of WG and WSD were examined for physical, mechanical and thermal properties in line with standard procedures. The results were compared with existing standards and property evaluation index, compliance level and C-CR were applied in analyzing the results obtained. It was observed that with increasing WG content, compliance level increased. Also, cost ratio and experimental cost of each brick sample trended upward. Sample with mix proportion;20 wt% WG, 5 wt% WSD and 75 wt% clay had compliance level of 94% and C-CR index of 7.81, hence chosen as optimum mix proportion for masonry bricks.

Dynamic Analysis of Historical Brick Masonry House

Brick masonry constructions are very common in many areas in the world and their failure in earthquakes has been the cause of many deaths. Since human safety is main issue of disaster management, people are more concerned about the structural assessment and strengthening of those constructions. One historical brick masonry house located in Kathmandu world heritage site is modeled by FEM （finite element method） and analyzed in E1 Centro earthquake ground motions. Bricks are modeled as solid elements and the interfaces between the brick units are modeled as zero thickness joint elements. Then, non-linear analyses of the house are applied satisfying the famous Mohr-Coulomb failure criterion. The result shows that the house is very weak and sustains large deformation in El Centro 1940 Earthquake. A strengthening solution modifying the connections of existing elements and adding wooden frame inside the house can reduce the deformations significantly.

Investigations of Physical and Chemical Characteristics of Masonry Stones and Bricks during Building Cleaning： Part 2. Chemical Testing

This series of study focused on analysing and assessing the Changes of the physical and chemical characteristics of the stone surfaces during the sandblasting cleaning process by conducting various physical and chemical tests. Seven masonry stones and bricks were adopted, including yellow sandstone, red sandstone, limestone, marble, granite, white clay brick and yellow clay brick. The chemical investigations included the micrographing of the stone facade and the analysis of the chemical elements and compounds on four of the seven stones and bricks before and after the cleaning using the Scanning Electron Microscope （SEM） and Energy-Dispersive X-ray Spectroscopy （EDX） techniques. In general, the chemical properties were found to vary largely during the building cleaning. The chemical tests showed that the chemical elements and compounds on the stone facade significantly varied after long term exposures to the atmosphere, mainly due to the soiling on the building fagade caused by environmental erosion and weathering.

注浆加固砖砌体的受压性能试验研究

我国许多20世纪所修建的砖石砌体结构排水管渠面临年久失修、功能丧失等问题,影响城市的正常运作,亟需对其进行加固修缮。针对砌体结构排水管渠长期遭地下水冲刷、灰缝砂浆不饱满、性能劣化的特点,可采用注浆法填充原结构灰缝,在充分修复原结构的基础上再进行整体结构加固修复。为了验证注浆加固受损砌体的可行性,通过砌筑灰缝饱满度为50%~60%的砌体试件来模拟砌体灰缝砂浆长期受水流冲刷的状态,并完成6个注浆砖砌体、3个未注浆砖砌体的受压试验来对比分析注浆前后砖砌体的受力性能,根据试验结果,拟合砖砌体应力-应变曲线。结果表明,注浆后砖砌体的抗压强度为未注浆砌体的280%,注浆加固砌体的弹性模量和泊松比为未注浆砌体的281%、60%。证明注浆法能够改善受损砌体结构的力学性能,在砖石砌体结构排水管渠的加固工程中可起到修复原砌体结构的作用。

CFRP-聚合物砂浆加固震损构造柱约束砖砌体墙试验研究

为研究斜向碳纤维布条带或斜向聚合物砂浆条带与外覆角钢组合的加固方式对震后砌体结构的加固效果,对模拟经过地震作用的三面带构造柱约束砌体墙片进行抗震加固,并进行拟静力试验。三面砌体墙均采用角钢外覆加固,面层采用不同方式处理。研究结果表明:采用碳纤维布-聚合物砂浆条带的加固方式能很好地恢复震损墙体的承载能力和变形能力;碳纤维布条带在限制裂缝开展以及提高震损结构延性方面有一定贡献;面层采用斜向聚合物砂浆条带加固的震损墙体延性和承载力均较低。工程实际应用中,建议考虑两种材料的复合加固形式。

砌体轴心和局部受压离散元仿真在教学中的应用

砌体是块体和砂浆的黏结组合材料,为了让学生更好地理解砖块体和砂浆对外力的分担作用,运用离散元方法建立了砖块体团簇模型、砂浆团簇模型,进而“砌筑”了普通砖砌体数值试件,对砖砌体分别开展轴心受压和局部受压仿真。仿真复现了砌体受压时的应力-应变关系和破坏模式,应力峰值处伴随大量砖颗粒-砖颗粒胶结接触破坏。砌体应力主要由胶结接触承担,其中砖-砖胶结接触>砖-砂浆胶结接触>砂浆-砂浆胶结接触,砂浆主要起到连接块体的作用;法向接触力承力大于切向接触力。通过仿真教学,有助于学生建立砌体宏观力学表现受控于微观结构和微观力学的认知,加深了学生对砌体受力机理和强度的理解。

改进关系阈值比的砖混结构建筑抗压强度检测

针对因砖混生土砌体建筑结构影响因素多、压力强度特征难以捕捉,导致检测精准度低的问题,提出一种超声波回弹拟合分析的抗压强度检测方法。忽略建筑试件自然抗压变化,设定修正系数,以计算出的标准砖混生土试件抗压强度作为检测质量优劣的判定阈值。采用最小二乘积算法,建立抗压强度与其它参数间的拟合函数,分析强度值与碳化深度、回弹强度以及硬度等参数间线性关系。将超声波检测仪器作为算法实现载体,计算回弹势能与抗压强度、抗压强度与声波信号的正向变化关系,通过关系阈值比,判定反馈信号的抗压强度数值,完成抗压强度检测。仿真结果证明,所提方法的检测精准度高,在多种环境下均能完成有效检测。

面向数值模拟的砖砌体单轴受压本构关系模型研究

在现有的砖砌体单轴受压本构关系模型中,弹性模量和峰值应变预测精度较差,导致砖砌体的数值模拟分析难度较大。基于收集到的145个试件数据,对砖砌体的弹性模量、轴心抗压强度以及峰值应变取值进行分析。结果表明:现有的弹性模量计算公式不适用于过低或高弹性模量的砖砌体,弹性模量与峰值点割线模量呈倍数关系,应按照砌体的材料强度和种类进行取值;轴心抗压强度计算公式适用性较好;砖砌体的峰值应变应按照混凝土砖和非混凝土砖进行分类,非混凝土砖砌体峰值应变与砂浆强度呈非线性关系,应按照砂浆强度大小进行取值;然而混凝土砖砌体峰值应变受砂浆强度影响较小,取值在0.001和0.002之间。最后,提出了适用性更好的面向数值模拟的砖砌体单轴受压本构关系模型。

水热固化淤泥质渣土砖砌体抗压性能试验研究

通过模拟地下成岩机理的水热固化技术,将淤泥质渣土脱水处理并添加石灰、再生骨料等搅拌均匀后压制成砖坯,在蒸压釜中进行高温高压养护,使其内部发生水热固化反应,制成绿色环保的水热固化渣土砖。设计制作了水热固化渣土砖砌体并进行轴心抗压试验,研究砖的类型和砂浆类型及强度对水热固化渣土砖砌体破坏过程、荷载-变形特性、抗压强度和弹性模量的影响。结果表明:水热固化渣土砖的抗压强度设计值和弹性模量平均值分别较GB 50003—2011规范值高38%和44%,该产品可用于替代传统墙体材料在实际工程中应用。

铁尾矿砂浮石混凝土多孔砖砌体力学性能试验研究

为寻求铁尾矿堆积问题解决方案,以材料再利用为基础,结合实际,提出用铁尾矿砂、浮石分别代替部分细、粗骨料制备砌块,并对该砌块砌筑成的砌体进行力学性能试验研究,主要进行抗压、抗剪及沿通缝和齿缝抗弯试验,分析其破坏过程及破坏形态。试验结果表明,铁尾矿砂浮石混凝土多孔砖砌体表现出更大的脆性,抗压、剪、弯强度试验值均比现行规范计算值大,尤其是抗剪及抗弯强度,主要原因是出现了类似结构加固中销键的构件。最后,对试验数据采用最小二乘法进行回归分析,建立了该砌体对应的强度平均值计算公式。

RC顶升托梁与砖砌体受力性能试验研究

为研究RC顶升托梁与砖砌体接触界面的复合受力性能,设计了3种类型共10个双梁夹墙托换构件,对其进行静力加载试验,从而研究不同接触面积、连接方式对托换结构受力性能的影响。试验结果表明,托换构件共有3种破坏形式:一是沿RC顶升托梁与砖砌体界面发生剪切滑移破坏,二是上部砖砌体受压破坏,三是RC顶升托梁与砖砌体界面开裂且砖砌体受压破坏。根据试验结果,销键、穿墙筋与托梁协同作用,钢筋应变变化趋势具有一致性;销键连接与穿墙筋连接均对界面抗剪能力有所增强,使构件极限荷载有所提升;无连接措施的托换构件存在脆性破坏的风险,实际工程中不建议采用,而销键和穿墙筋连接的构件具有延性破坏特征,能够满足实际工程需求。

新型预制自保温墙体力学性能影响因素研究

采用烧结淤泥多孔砖复合保温材料,通过拉接浇筑形成结构保温一体化预制自保温墙体。研究了砌筑砂浆种类、砌筑方式、灌孔和插筋数量对烧结淤泥多孔砖砌体力学性能的影响。结果表明:对于烧结淤泥多孔砖砌体,薄层砌筑砂浆通缝抗剪强度标准值为0.52 MPa,比普通砂浆砌筑提高了34%;标准砌筑方式比非标准砌筑方式的通缝抗剪强度提高了15%;烧结多孔砖孔内铺设2根或者3根增强钢筋并灌浆后,砌体平均抗剪强度由0.53 MPa分别提高至1.39、2.25 MPa,分别提高了162.26%和324.53%。3孔铺筋注浆试样的抗剪强度比2孔铺筋注浆试样的抗剪强度提高了61.8%。

泸定县6.8级地震村镇建筑震害调查与分析

为分析泸定县6.8级地震中村镇建筑的震害,对震中附近的磨西镇、得妥镇、燕子沟镇的村镇建筑开展了震害调查,总结村镇结构中砖木结构、砖混结构和框架结构的典型震害特征,对震中附近评估烈度为Ⅸ度区域的村镇建筑进行地震破坏等级评估、统计与分析。调查结果显示:整体上,砖木结构及砖混结构是此次地震中震害现象较为明显和严重的结构形式;框架结构震害整体较轻,基本未破坏数量占调研框架结构的72.5%。砖木结构及砖混结构震害特征主要表现为地基的不均匀沉降、墙体开裂、楼(屋)面破坏、非结构构件破坏及整体倒塌;框架结构震害特征主要表现为梁、柱及节点破坏、非结构构件的破坏。此次地震中,砖木结构、砖混结构严重破坏及倒塌的房屋占该两类房屋整体震害的比例较高,严重破坏砖木及砖混结构约为框架结构的6倍,且框架结构未出现倒塌,基本未破坏的框架结构占比较高。3种结构抗震能力由强到弱依次为:框架结构、砖混结构、砖木结构。针对不同结构形式的震害特征,应通过抗震加固全面提升可修复震害房屋及既有农房抗震防灾能力,以提高村镇建筑整体力学性能,减少地震伤亡及损失。

清水砖外墙修缮技术在优秀历史建筑群保护中的实践与应用

清水砖墙作为上海优秀历史建筑外立面的典型特征,其保护修缮质量直接决定了建筑的历史风貌和耐久性。由于工期、成本、修缮工艺及工人的技术水平等问题,现有清水墙的修缮方式相对机械、单一,对材质、肌理及耐久性等方面的考虑比较欠缺。依托清水墙修缮工程,给出了清水砖墙劣化类型及成因,制定了各劣化情况下的针对性修缮方法,并对修缮流程及关键修缮技术要点进行了剖析,最后在杨树浦路670项目中开展了工程实践应用研究,以期为历史建筑群清水砖外墙修缮提供实践指导及经验参考。