Reduction of the lateral thrust of masonry arches and vaults with FRP composites

Fiber-reinforced polymer (FRP) composites are being increasingly used for rehabilitation and strengthening of masonry structures and, in particular, to strengthen masonry arches and vaults against their most critical failure mechanisms. The FRP reinforcement, introducing tension resistance, allows the line of thrust to fall outside the thickness of the arch. This fact has two important consequences: the capacity of the arch itself is increased, and the lateral thrust transmitted to the piers is reduced, thereby increasing the capacity of the “arch + piers” system. While the first effect has been stressed by existing research, less attention has been paid to the second effect, which nevertheless is very important for practical applications. In this paper, the effect of bonding an FRP sheet to the intrados of a circular arch on the minimum value of the lateral thrust is evaluated analytically. The model is then applied in particular to the four lateral arches of an edge vault. Edge vaults are a valuable part of the architectural and cultural heritage of some regions of Italy, and are structurally similar to cross-vaults except for the presence of a double-curvature shell portion in the middle of four barrel webs. These vaults are usually subjected to symmetric loading, as a result of the large dead-to-live load ratio. Hence, collapse of a vault typically occurs when no tie-rods or tie-beams are adopted and the piers are unable to bear the thrust of the vault. The paper also illustrates results of an experimental investigation on masonry edge vaults strengthened with FRP composites and subjected to uniform loading with measurement of the lateral thrust. Test results and theoretical predictions are presented and discussed.     

带窗间墙扶壁柱砖混结构教学楼抗震性能的试验研究

为了解砖混结构教学楼在窗间墙扶壁柱增强配筋条件下的抗震性能和地震破坏机理,按照1/2的缩尺比例设计制作了1个2层砖混结构试验模型,在窗间墙中设置扶壁柱并增强柱截面的配筋,采用拟静力试验对模型的破坏特点、延性和耗能能力以及窗间墙的破坏模式和纵墙的宏观破坏机制等进行了研究。结果表明,窗间墙扶壁柱配筋率较高时,扶壁柱与两侧砖砌体的协调变形能力差,导致模型的破坏位置集中,模型表现为层间破坏模式,窗间墙发生剪切破坏并出现垮塌,纵墙的宏观破坏具有"强梁弱柱"特征,模型的延性和耗能能力均较差。因此,砖混结构教学楼的抗震设计应合理控制窗间墙中扶壁柱的配筋率。     

加固的历史风貌建筑墙体试验及结构抗震分析

针对天津现存的历史风貌建筑普遍存在砂浆强度低的情况,研究了原材料砖砌体及加固砖砌体试件的抗震性能。制作了2片原材料墙体试件、4片原材料墙体钢筋网水泥砂浆抹面加固试件,并对其进行了低周反复加载试验。应用等效体积单元(RVE)法对砖砌体进行模拟,对加固砖砌体则提出采用二次RVE法进行模拟,求得了其等效参数。用有限元模拟了加固墙体试件的低周反复荷载试验,并与试验进行了对比分析。最后对某一历史风貌建筑进行了加固前后的抗震性能有限元分析,验证了二次RVE法应用于加固砖砌体中的可行性。     

预应力砖墙在低周反复荷载下抗裂及承载力试验研究

通过１：２预应力与非预应力带圈梁，构造柱砖墙在低周反复水平荷载作用下的对比试验，研究了墙片的裂缝出现与开展过程、破坏机理、滞回特性、强度、刚度、延性及耗参能能力，本文仅就其抗裂及承载力进行了论述，说明在砖墙中施加预应力能明显提高其抗震性能，并提出了有关抗裂及级限承载力的计算方法，计算结果与试验相当吻合。     

Seismic safety evaluation methodology for masonry building and retrofitting using splint and bandage technique with wire mesh

The paper presents a seismic safety assessment of unreinforced masonry (URM) building using two approaches. The first approach uses the ‘Pier Analysis’ method, based on the concept of equivalent lateral stiffness, where in-plane and out-of-plane actions are considered independently. The second approach is developed with the program SAP2000, where the linear response is evaluated using continuum ‘finite element modelling’ (FEM). Both methods are compared to evaluate the safety of wall piers and the differences in the outcomes under combined gravitational and lateral seismic forces. The analysis results showed that few wall elements are unsafe in in-plane and out-of-plane tension. It is also observed that the pier analysis method is conservative compared to FEM, but can be used as a simplified and quick tool in design offices for safety assessment, with reasonable accuracy. To safeguard the URM wall piers under lateral loads, a retrofitting technique is adopted by providing vertical and horizontal belts called splints and bandages, respectively, using welded wire mesh (WWM) reinforcement. The study using the ‘Pier Analysis’ shows that the lateral load capacity of unsafe URM piers can be enhanced up to 3.67 times and made safe using the applied retrofitting technique. Further, the retrofitting design methodology and recommendations for application procedures to on-site URM buildings are discussed in detail.     

单层空旷房屋的抗震鉴定方法

对于由砖墙承重的单层空旷房屋的抗震鉴定,有时会被当作一般砌体房屋而按照多层砌体房屋抗震鉴定的方法来进行,从而走入鉴定误区.本文通过理论阐述和实例展示,明确了现有砖墙承重的单层空旷房屋的抗震鉴定程序和鉴定方法,指出了这类房屋抗震鉴定区别于普通多层砌体房屋抗震鉴定的特点,从而为这类房屋的抗震鉴定提供正确指导,即单层空旷房屋...     

Analytical modeling of rocking elements

The use of elements connected through compression at their contact surfaces, without tensile capacity, which allow rocking in their transverse direction, was attempted in the construction of bridge piers, masonry walls and frame structures. Columns or bridge piers can be designed to rock or overturn with minimal lateral resistance. However, as shown in this paper, due to the effects of stresses at the contact surfaces, including cracking, yielding and crushing, the lateral resistance varies substantially before rocking and before the columns overturn. Moreover, when the elements are confined between rigid surfaces, or when pre-stressing forces are applied to the connections, the lateral resistance varies substantially. Current models discretized using micro-models, or finite elements, are computationally inefficient for large structural systems, such as bridges or buildings. This paper attempts to model the strength and stiffness variation before rocking, using a macroscopic approach. The stiffness and flexibility formulations developed using virtual work concepts include flexural and shear effects, and can be implemented in many off-the-shelf analytical platforms. The analytical formulations are compared in this paper to the results of multi-purpose finite element models (FEM) for squat and slender columns.     

面内往复荷载作用下足尺砌体填充墙的易损性研究

为了研究钢筋混凝土(RC)框架结构中砌体填充墙的地震易损性，进行了6个足尺含填充墙RC框架试件的面内往复加载试验。各试件中RC框架的设计参数均相同，其中3个试件含普通黏土砖填充墙，另外3个试件含水泥空心砌块填充墙。试验过程中，记录了砌体填充墙的损伤发展过程，并以墙体裂缝宽度和破碎坠落现象作为损伤指标，定义了“明显破坏”、“严重破坏”和“危及安全”等3个损伤状态。在此基础上，以层间位移角作为工程需求参数，建立了普通黏土砖和水泥空心砌块填充墙的易损性曲线。易损性分析结果表明，当试件的面内侧向变形达到GB 50011—2010《建筑抗震设计规范》规定的框架结构弹性层间位移角限值时，黏土砖和空心砌块填充墙均极有可能达到或超越“明显破坏”状态，且空心砌块填充墙尚有22%的概率达到或超越“严重破坏”状态。与黏土砖填充墙相比，水泥空心砌块填充墙的易损性参数具有更大的离散性，且其整体性更差，当侧向变形较大时会出现破碎砌块坠落的现象。根据试验结果，给出了砌体墙最大残余裂缝宽度、最大裂缝宽度和层间位移角之间的近似相关关系。     

配筋砂浆带加固土坯墙体的抗震性能研究与实践

对于土坯墙承重结构,由于材料强度低、变形能力差,房屋抗震性能严重不足,目前是西部农村的主要危房改造对象。为提高土坯墙承重房屋的安全性,采用十形和X形两种配筋砂浆带加固方法对土坯墙体进行加固。通过对3片墙体的水平低周反复加载试验,分析配筋砂浆带用于抗震加固土坯墙片的受力特性与破坏形态,对两种加固效果进行了对比分析。研究结果表明：配筋砂浆带加固方法可以有效提高土坯墙片的抗震性能,采用十形配筋砂浆带加固的土坯墙具有良好的变形能力,采用X形配筋砂浆带加固的土坯墙水平受剪承载力得到大幅提高。配筋砂浆带加固方法在甘肃省农村危房改造工程中的应用实践证明,该方法操作方便,具有良好的经济效益。     

云南农村居民生土建筑土坯砌体的力学性能试验研究

介绍了云南农村居民土坯砌体试件的抗压、抗剪、抗折试验及试验结果,分析了影响土坯砌体强度的主要因素,提出了改善土坯砌体强度的建议和措施。     

水平配筋砖砌体抗震性能的试验研究

本文通过近百片墙体的反复荷载试验和四幢整体房屋模型的振动台试验,研究了水平配筋砖砌体的破坏机理、强度和变形性能,提出了强度计算的表达式。本文中提出的强度表达式已为我国的新建筑抗震设计规范(GBJ 11-89)采用。     

采用扁式液压顶试验方法确定砖墙中砌体抗压强度

本文对具有两个水平槽(内设扁式液压顶)的墙体,在其顶部和切槽内受均匀荷载作用时,按弹性理论作了分析。根据试验室14片墙体试伴和五幢5～8层房屋中的试验结果,考虑开槽之间砌体所受的约束影响,提出了使用扁式液压顶试验方法确定砌体投限抗压强度的计算公式。本文为该试验方法在砖结构中的推广应用提供了可靠依据。     

钢筋网水泥砂浆加固砖墙的抗侧承载力和刚度计算

北京市农村住宅抗震加固试验中采用了钢筋网水泥砂浆加固砖墙方案.为了解决农村住宅加固墙体的非线性计算力学模型,本文根据钢筋网水泥砂浆加固的单片墙的低周反复荷载试验的文献数据,探讨了针对农村住宅砖墙加固后的退化三线性恢复力特性曲线,提出了钢筋网水泥砂浆加固砖墙分别考虑剪切变形和弯剪变形影响下的抗侧力刚度计算方法.同时分别给...     

浅析建筑砖砌体裂缝原因及其防治

结合多年的工程质量监督实践,从温度变化、基础不均匀沉降、砌体材料等方面出发,分析了建筑砖砌体裂缝的产生原因,并提出了相应的预防措施,以达到提高建筑砖砌体结构工程质量的目的。     

西藏藏东南地区民居建筑热环境现状分析

随着社会经济的发展,西藏藏东南地区传统民居建筑的石木结构逐渐被钢筋混凝土及砌块所取代。现代建筑材料与传统建筑材料对西藏藏东南地区的民居建筑热环境到底有何影响?本文通过实际调查,在西藏林芝县八一镇觉木村选取两家代表性的民居建筑,一座是采用传统建筑材料(木材、块石、土坯砖、泥浆)建造的塔吉家,一座是采用现代建筑材料(砌块、钢筋混凝土、石灰)建造的江村家,分别对两家进行了温度、湿度、照度以及风速的测定。通过对试验数据的分析得出,在西藏藏东南地区,传统建筑材料在隔热保温性能方面优于现代建筑材料。     

7度区多层砖混结构的抗倒塌设计

介绍了在砖混结构的三水准抗震设计中,大震不倒是关键。就7度区砖混结构的大震不倒——抗倒塌设计从九个方面进行了论述,并列举了工程实例,以使多层砖混结构房屋设计合理。     

静压桩的静压力施加技术研究与应用

对承重墙下条形基础加固工程中的静压桩技术进行了讨论,通过工程实例指出了在砌体危房加固工程中,当由于软弱地基上墙下条形基础沉降过大时,可优先采用本文改进的静压桩静压力技术加固承重墙下基础.     

砖砌体建筑体外预应力抗震加固技术研究

针对城镇既有砖砌体建筑抗震性能较差的问题,提出了一种适合多层砖砌体房屋的抗震加固新技术,即采用竖向无粘结预应力筋对砌体墙体进行加固,从而改善墙体的抗震性能,提高房屋的整体抗震能力。为了解该技术的加固效果,完成了两批共17片墙体构件的拟静力试验研究和一栋2层足尺房屋模型的拟动力试验研究。墙体构件的试验研究结果表明,该项加固技术可以大幅度提高砖砌体墙体的抗裂能力、受剪承载力和延性。房屋模型的拟动力试验研究则进一步表明,采用该项技术加固后,抗震设防烈度不足8度的房屋,在模拟9度罕遇地震的拟动力作用下基本保持弹性,抗震能力显著提高。在试验研究的基础上,提出了预应力加固砌体墙体的受剪承载力的计算方法。该技术在北京市怀柔区某多层办公建筑的实际应用情况表明,其具有施工工艺简单、工期短、成本低等优势     

Methods of control for robotic brick masonry

The major use of brick masonry units in the U.S. is in facades for office buildings and single family homes. The traditional method for building masonry walls is on-site by bricklayers. An alternative method is panelization or prefabrication of brick panels in a plant environment. While many mechanical problems exist, the real-time control represents a challenging aspect of robotizing brick masonry work. This paper presents an effort to study the development of an experimental robotic masonry system and its relevant control modules. It also describes two control frameworks for different levels in a robotic brick masonry prototype: (a) local control, and (b) global control. The local control system includes three work cells: (a) gripping and handling, (b) quality control, and (c) brick placement. First, the components and equipment used in a work cell are listed, then the experimental work performed with them is discussed to show how sensors are used for dehacking, brick placement, brick color detection, and brick size measurements. The paper then continues to describe a global control system that will integrate the three local work cells utilizing a hierarchical structure.     

窗间墙锚固配筋砖混结构教学楼抗震性能试验研究

为改善砖混结构教学楼的抗震性能,通过对其纵向窗间墙局部配筋并在墙体两端采用竖向钢筋进行锚固配筋,按照1/2的缩尺比例设计了2个砖混子结构模型。采用拟静力试验分别对普通窗间墙和配筋窗间墙的子结构模型的破坏模式、承载能力、变形能力、刚度退化、延性、耗能性能以及窗间墙的破坏模式和纵墙的破坏机制等进行了分析。结果表明：普通窗间墙模型表现为层间破坏机制,窗间墙发生剪切破坏,纵墙发生“强梁弱柱”式破坏;窗间墙局部配筋并进行锚固的模型发生整体型破坏,窗间墙弯曲破坏,纵墙的破坏机制具有“强柱弱梁”特征,层间变形均匀,模型的破坏形态、耗能能力和延性等均得到改善。