砖混结构墙顶温度裂缝控制

砌体结构由于气温变化,往往在墙体、屋面、挑檐等部位出现程度不同的温度裂缝,不仅破坏了结构的整体性,而且导致了房屋抗震能力的降低。本文主要通过对砌体结构墙顶温度裂缝的形状、特点和裂缝产生的原因进行分析,并结合砌体结构的型式、保温材料性能、砌体强度以及设计施工中一些问题,提出了温度裂缝预防措施。     

砌体结构房屋常见裂缝原因及控制

文章从温度收缩变形、干缩变形、地基不均匀沉降、荷载作用等方面分析了砌体结构房屋常见裂缝的原因,在剖析砌体裂缝根源的基础上,结合相关规范的防裂措施,总结裂缝控制的方法.     

浅谈混凝土的温度裂缝

经多年的施工监理实践,在查阅有关混凝土内部应力方面的专著后,对混凝土温度裂缝产生的原因、现场混凝土温度的控制和预防混凝土温度裂缝的措施进行阐述。     

浅析砖混结构住宅裂缝问题

砖砌体是脆性材料,其极限应变很小,它的抗拉强度只有混凝土的十分之一,且一般墙体为无筋砌体,抗裂性能极差,且砌体内部应力分布很不均匀,因此在拉应力区域易产生裂缝,这是主要原因之一.这类干缩变形引起的裂缝在建筑上分布广、数量多开裂的程度也较严重.     

浅谈混凝土的施工温度与裂缝

通过多年的现场观察和查阅有关混凝土内部应力方面的专著,对混凝土温度裂缝产生的原因、混凝土温度的控制和预防裂缝的措施等进行阐述。     

浅谈温度对混凝土裂缝的影响及预防措施

通过多年的现场观察并查阅有关混凝土内部应力方面的专著,对混凝土温度裂缝产生的原因、现场混凝土温度的控制和预防裂缝的措施等进行阐述。     

砖砌体结构变形裂缝的预防控制措施

根据多年的工程经验，对粘土砖砌体结构的变形裂缝，从砌体构造，温度影响，施工技术等几个方面，提出若干预防与控制措施。     

关于房屋砖砌体裂缝的原因及防治

分析了房屋砖砌体裂缝的性质、原因,并提出了砖砌体结构裂缝的控制措施和治理方法。     

简析混凝土裂缝原因及控制措施

通过多年的现场观察,通过查阅有关混凝土内部应力方面的专著,对混凝土温度裂缝产生的原因、现场混凝土温度的控制和预防裂缝的措施进行等进行阐述。     

砌体结构裂缝的预防及控制

总结分析了砌体裂缝的成因和裂缝控制原则,结合实际提出了控制及预防砌体结构裂缝的措施.     

砖混住宅顶层墙体裂缝的受力分析与防治

文章对砖混结构墙体裂缝向题进行了温度应力、地基不均匀沉降、砌体温度、变形等若干项分析,并针对墙体裂缝提出有效的防治措施。     

Radon penetration of concrete slab cracks, joints, pipe penetrations, and sealants

Radon movement through 12 test slabs with different cracks, pipe penetrations, cold joints, masonry blocks, sealants, and tensile stresses characterized the importance of these anomalous structural domains. Diffusive and advective radon transport were measured with steady-state air pressure differences controlled throughout the deltaP = 0 to 60 Pa range. Diffusion coefficients (deltaP = 0) initially averaged 6.5 x 10(-8) m2 s(-1) among nine slabs with only 8% standard deviation, but increased due to drying by 0.16% per day over a 2-y period to an average of 2.0 x 10(-7) m2 s(-1). An asphalt coating reduced diffusion sixfold but an acrylic surface sealant had no effect. Diffusion was 42 times higher in solid masonry blocks than in concrete and was not affected by small cracks. Advective transport (deltaP < or = 60 Pa) was negligible for the slabs (10(-16) m2 permeability), pipe penetrations, and caulked gaps, but was significant for cracks, disturbed pipe penetrations, cold joints, masonry blocks, and concrete under tensile stress. Crack areas calculated to be as small as 10(-7) m2 significantly increased radon advection. Algebraic expressions predict air velocity and effective crack width from enhanced radon transport and air pressures. Masonry blocks, open cracks, and slab cold joints enhance radon penetration but stressed slabs, undisturbed pipe penetrations, and sealed cracks may not.     

Failure Resistance of the Historic Stone Bridge Structure of Charles Bridge. I: Susceptibility to Nonstress Effects

The monitoring of deformations of the stone structure of Charles Bridge in Prague proved the gravity and relevance of nonstress effects (temperature, moisture content) on cyclic deformations and permanent strain accompanied by a gradual disintegration of its stone masonry, growing tilt of the breast walls, and development of cracks in the masonry of the stone bridge structure. Each deformation cycle is accompanied by a gradual growth in permanent deformations. The “unmanifested” primary deformation due to, e.g., a temperature change causes a mechanical state of tension, and it is mainly the tensile stresses thus arising that contribute to the development of tensile cracks in the stone masonry.     

Evaluation of Distress in Supports of Hyperbolic Paraboloid Shell

A church building structure, composed of a saddle-type hyperbolic paraboloid concrete shell roof supported by buttresses and brick masonry walls, was constructed in 1963. At one corner of the structure, the perimeter of the roof shell projects beyond the exterior building walls to form a canopy over the main entrance. This canopy is partially supported by two brick masonry fin walls that project outward from the main building walls. At the time of original design, closed-form methods (equations) were the only practical way of analyzing this shell structure. However, the configuration of the roof shell was not consistent with detailing requirements of the closed-form methods. After 36?years of service, the fin walls had bowed significantly, were exhibiting wide cracks, had slipped laterally with respect to the roof shell, and were in danger of collapse. The writer led an investigation team that developed a finite element model of the church structure, studied the behavior of the church structure when subjected to applied loads and temperature changes, and developed repairs to restore structural integrity and serviceability.     

Evaluation of Masonry Deep Beams Externally Strengthened with CFRP Sheets

In this study, carbon fiber-reinforced polymer (CFRP) sheets were examined as a means to strengthening existing masonry walls allowing for efficient creation of doors, windows, and passage openings. The research reported here deals with eight masonry walls made with concrete blocks, subjected to three-point quasistatic loading. The parameters examined include the reinforcement configuration and their amount. While CFRP sheets were used as external reinforcement, companion studies were carried out with conventional steel rebars. Test results indicate an increase of 180% in shear strength of the reinforced walls as compared to reference unreinforced walls. Load-deflection relationships indicate that the combined plain masonry and CFRP laminate system possessed some nonlinear deformability. The use of CFRP laminates on the walls was found to have an influence on the mode of failure. Anchoring the CFRP laminates at both support regions helped in using a larger portion of the strength of the laminates. The reinforced walls exhibited diagonal shear cracks that developed at a much slower rate and were ultimately accompanied by the peeling off of the CFRP laminates.     

Resistance of Membrane Retrofit Concrete Masonry Walls to Lateral Pressure

This paper first describes the current state of analysis for the response of unreinforced concrete masonry walls subjected to lateral uniform pressure. The formulation is based on the initial elastic response, the subsequent initiation of cracks and the nonlinear rocking response, and the eventual large displacement and potential collapse. The necessary equations are developed for these phases in the form of a resistance function. The paper then incorporates membrane retrofit materials to strengthen the wall’s resistance to lateral pressure, and develops the necessary resistance function equations. In blast tests, membrane retrofit unreinforced masonry walls have experienced severe cracking and large displacements without collapse. This is of high interest to the Department of Defense, the protection of diplomatic facilities, and the construction industry impacted by hurricanes and other high wind events. The paper concludes with examples that demonstrate application of membrane retrofits indeed increase the resistance of the wall to lateral pressure.     

Shrinkage in Concrete Masonry Walls: Case Study

In spite of our understanding and knowledge of the properties of concrete masonry as a material, shrinkage continues to be a problem affecting the performance of concrete masonry walls. A case study is presented which suggests that the behavior of concrete masonry walls subjected to the shrinkage of units is not completely understood. The paper discusses causes in material standards, design specifications, manufacture and construction practice which may contribute to shrinkage cracking of concrete masonry walls.     

Lateral Out-of-Plane Strengthening of Masonry Walls with Composite Materials

The structural behavior of masonry walls laterally strengthened with externally bonded composite materials to resist out-of-plane loads is theoretically and experimentally studied. Hollow concrete block masonry walls and solid autoclaved aerated concrete (AAC) block masonry walls are examined. A theoretical model that accounts for the cracking and the physical nonlinear behavior, the debonding of the composite layers, the arching effect, the interfacial stresses, and the unique modeling aspects of the laterally strengthened wall is presented. The experimental study includes loading to failure of 4 laterally strengthened masonry walls and 2 control walls. The experimental and analytical results point at the unique aspects of the lateral strengthening of masonry walls with composite materials. In particular, they reveal and explain the premature shear failure in laterally strengthened hollow concrete blocks walls and, on the other hand, demonstrate the potential of lateral fiber-reinforced polymer strengthening of AAC masonry walls. The laterally strengthened AAC masonry walls reveal improved strength, deformability, and integrity at failure characteristics.