常见裂缝原因及预防混凝土结构

建筑工程最普遍的质量通病之一是建筑物楼面、墙体的开裂、缝隙统称裂缝。在众多混凝土裂缝中,有的超出设计与规范允许范围,影响到建筑结构的安全性、适用性,需要作整改处理。而大部分裂缝未超出其允许范围,对建筑结构不构成危害,可不作处理,但影响到建筑物的美学功能和使用功能。因此,有必要分析混凝土裂缝产生的原因,研究防止混凝土裂缝对策,防止此类质量通病的发生。一、房屋建筑工程混凝土裂缝主要出现在下列部     

浅谈砌体结构裂缝产生的原因与防治

砌体结构的房屋在中小城市建筑物中占的比例较大,分布较广,而砌体结构中的一般细小裂缝由于不危及使用,往往被人忽略.但这些裂缝在较长时间内很不稳定,降低了建筑物的抗震能力,在地震时容易引发墙体倒塌,必须重视解决.     

浅谈砌体结构裂缝产生的原因与防治

砌体结构的房屋在中小城市建筑物中占的比例较大,分布较广,而砌体结构中的一般细小裂缝由于不危及使用,往往被人忽略.但这些裂缝在较长时间内还不稳定,降低了建筑物的抗震能力,在地震时容易引发墙体破坏,甚至墙体倒塌,必须重视解决.本文根据本人几年的工作经验,提出自己对砌体结构裂缝产生的原因及其防治的浅显建议.     

浅谈砌体结构裂缝的控制

砌体是我国广泛采用的主要建筑形式,但是,由于涉及、施工、使用及建材等多方面的原因,常发生各种各样的裂缝,影响观感和使用功能,甚至缩短建筑物的使用寿命,文章对砌体结构裂缝的控制进行了详细的阐述。     

谈混凝土施工控制

随着超长、超大混凝土结构的发展，高强及各种外加剂、外掺料混凝土的广泛应用，使得混凝土裂缝控制变得更加复杂。而混凝土结构的破坏乃至建筑物的倒塌，是从混凝土结构的微裂缝发展而来的。现代混凝土科学的研究及大量工程实践证明，混凝土结构裂缝是难以避免的，裂缝也是人们可以接受的材料特性，只是如何将其有害的程度控制在一定范围内。影响混凝土施工开裂的因素较多，本文按照规范施工，分析混凝土施工过程中的每个环节，使混凝土浇筑这个动态的过程控制达到最佳效果，以供其他工程技术人员参考。     

砖砌体裂缝的分析与防治

通过对建筑物砖体产生裂缝的原因分析，提出了在严寒地区防治裂缝的措施；合理设置沉降缝；加强基础和结构的刚度，认真做了设计、施工和检验工作。     

民用建筑物的裂缝及其防治

本文对民用建筑物裂缝的产生及其发展进行了科学的分析，讨论了变形变化与荷载变化对建筑裂缝产生的影响，并着重讨论了变形变化对建筑物裂缝产生的影响，指出了各部位裂缝产生的原因及其特征，并从设计、施工及管理维修的不同角度提出了预防和处理裂缝的方法。     

简述大体积混凝土裂缝的产生原因及防治

随着国民经济和建筑技术的发展,大型现代化技术设施或构筑物不断增多,于是大体积混凝土逐渐成为构成大型设施或构筑物主体的重要组成部分。但是混凝土是抗压强度高、抗拉强度低的复合材料,因此混凝土极易被拉断,在混凝土表面产生裂缝。裂缝一旦形成,会降低结构的耐久性,削弱构件的承载力,同时会可能危害到建筑物的安全使用。因此如何采取有效措施防止大体积混凝土的开裂,是一个值得重视的问题。     

谈对混凝土裂缝的处理

工程结构出现裂缝是比较普遍的现象;而结构裂缝大部分是能够通过设计阶段、施工措施来避免的,本文对构件裂缝的成因、预防及处理进行了详细探讨。     

浅析林区建筑物墙体裂缝的产生及防止

本文阐述了林区建筑物墙体裂缝产生的重要原因有温度、地基、材料等;在设计施工中应采取具体措施。     

钢筋砼结构裂缝产生原因分析及预防

建筑结构产生裂缝是很普遍的现象，其中最常见的是钢筋砼构件以及砖墙裂缝。本文分析了钢筋砼结构裂缝产生的原因，并阐明了预防措施。     

Numerical analysis on tensile performance of bolted glulam joints with initial local cracks

Under varying climate conditions, cracks are commonly observed in bolted joints, owing to the shrinkage of wood and confinement from slotted-in steel plates and bolts. A three-dimensional finite element model was developed to investigate the mechanical behavior of bolted glulam joints with initial cracks. Wood foundation was prescribed in the model to simulate the local crushing behavior of wood surrounding the bolts. The behavior of wood in compression and the foundation were defined as transversely isotropic plastic in the software package ANSYS. Cohesive zone model was applied in the numerical analysis to consider the propagation of initial cracks and brittle failure of wood in the bolted joints under tension load. The numerical model was validated by the experiments conducted on full-scale specimens and it is indicated that the numerical model has good ability in predicting the failure modes and capacity of tension joints with local cracks. To further investigate the influence of crack number, length and locations, a parametric study was conducted with the verified model. Moreover, to study the effects of cracks on the behavior of bolted joints with different failure modes, another bolted joint including bolts with different strength grades and diameters was designed and analyzed in the parametric study, which was expected to have bolt yielding failure mode. It was found that the initial cracks can decrease the capacity and initial stiffness of tension joints by up to 16.5 and 34.8%, respectively.     

高场强微波处理对樟子松木材宏观裂纹的影响

探究高场强微波处理过程中，樟子松试材含水率、微波功率、处理时间对试材吸收微波能量和宏观裂纹的影响。结果表明，试材处理前的含水率、微波功率对试材吸收的微波能量有显著影响；当含水率为40%~60%、微波功率为140 kW、处理时间为120 s时，樟子松试材横截面的裂纹面积比和裂纹数量最大。建议根据功能化材料的应用领域，选择不同的微波处理工艺。     

建筑工程裂缝的防治措施

本文对建筑工程中,经常出现的温差及混凝土裂缝的原因及种类进行了分析,并提出了具体的防治措施。     

北方地区防止女儿墙开裂的措施

在北方地区由于冬夏温差过大,墙体开裂,尤其是女儿墙开裂是非常常见的现象,本文对怎样在设计施工方面采取一些措施来解决减少和避免这一通病(现象),进行了论述。     

谈砖砌体裂缝原因及其防治

分析了砖砌体裂缝的三种原因:即温差变形引发的、地基基础不均匀沉降引起的及特殊砌体材料产生的裂缝;并阐明了防治裂缝的对策.     

Effect of lamellas annual-ring orientation on cracking of glulam beams investigated with computer tomography and image processing

Abstract

Cracks in glulam beams can reduce their strength, depending on the crack's depth, length, and location and can also be a passage for the accumulation of water and dirt. To avoid cracks, the relationship between cracks (area of cracks, mm²) and annual-ring orientation in glulam beams of spruce (Picea abies), and pine (Pinus sylvestris) with different dimensions and surface treatments was investigated using RGB images of the surface and tomography images of the cross-sections. Image processing was used to measure characteristics visible in the photos such as crack area and lamella position in the beam. Combination of lamellas in lay up was measured from computer tomography images. Four types of combinations were defined; type 1 (pith side facing outward), types 2 and 3 (pith to the same side), and type 4 (pith sides meet pith side). It was found that the area close to the glue line in the lamellas in combination type 4 is the most subject to cracking, whereas combinations of type 1 show the highest resistance to cracking. This means that type 4 should not be used in glulam beams, because the lamellas shrink apart from each other causing stresses and resulting cracks.     

水泥混凝土路面早期裂缝形成机理研究

通过对混凝土化学收缩、干燥收缩、泌水收缩、自收缩、温度收缩机理进行分析,研究不同收缩机理对水泥混凝土路面早期裂缝形成的影响和裂缝特征以及影响水泥混凝土路面早期裂缝的因素。指出温度收缩是混凝土路面产生早期裂缝的主要原因。     

Microstructural study of sanded and polished wood by replication

Replicas of sanded and polished specimens of wood, mainly of pine and spruce, have been made to study microstructure and the development of drying cracks. Three surfaces, the radial surface, the tangential surface and the cross section, have been studied. Replication has also been carried out on knots, finger joints and complex surfaces where dimensional changes occur. It has been shown that sanding and polishing is a useful means of exposing microstructure of wood. The exposed microstructure can be successfully transferred to a replica to be investigated by light optical or environmental scanning electron microscopes. Microstructural characteristics, drying cracks, knots, finger joints and complex geometry have been observed and analysed. Problems associated with sanding and replication are discussed.This work was carried out in the Department of Wood Technology and Processing, Royal Institute of Technology (KTH). Financial support from KTH is gratefully acknowledged.     

Microstructure,strength and structural integrity of heat-treated beech and spruce wood

Abstract

Heat treatment of wood is an effective method by which to improve the dimensional stability and biological durability, but the mechanical strength is decreased at the same time. Besides chemical modification of cell-wall constituents, physical weakening of the microstructure owing to heat-induced defects may also contribute to strength loss. Therefore, anatomical properties of heat-treated beech (Fagus sylvatica L.) and spruce (Picea abies Karst.), studied by light microscopic and scanning electron microscopic analysis, and their interrelation with strength properties and structural integrity were investigated. For determination of structural integrity, the high-energy–multiple-impact (HEMI) test was applied. Microscopic analyses showed frequent formation of radial cracks in heat-treated beech close to the rays as well as tangential cracks in the latewood of spruce. In addition, the modulus of rupture was more affected by the heat treatments than the resistance to impact milling (RIM) determined by the HEMI test, because RIM is based on multiple fractures on the microlevel that are not affected by the formation of intercellular cracks or other defects due to the heat treatment. It was concluded that heat-induced defects in the wood microstructure contribute to the substantial strength loss of thermally modified timber.