关于膨胀土地基工程设计问题初探

膨胀土地基上建筑物的开裂破坏是较为常见的现象,对建筑物的危害较大。如何在工程设计中防止这种现象的出现,则是工程设计人员所关注的重要问题之一。 膨胀土地基上建筑物因地基问题引起的开裂破坏与其他地基一样,主要是因地基不均匀变形所致。所不同的是,非膨胀土地基的不均匀变形主要是由于上部结构荷重和地     

加筋膨胀土挡墙蠕变试验研究

通过模拟试验研究了加筋膨胀土挡墙的蠕变特性,考虑了含水量对膨胀土的特殊作用.通过对试验结果进行分析后认为加筋膨胀土挡墙在含水量和温度升高时其蠕变变形会变大;膨胀土的湿胀干缩特性使加筋土中筋材并非一直处于受拉状态,可以减缓筋材的蠕变性质;在较低的极限荷载比例下,膨胀土体中含水量的变化对蠕变起主要作用,在较高的极限荷载比例下,加筋膨胀土的恒载对蠕变起主要作用.     

载体桩在元谋地区膨胀土地基中的应用

载体桩是一种新型桩基技术,具有承载力高、施工简便、经济性好、适用广泛等特点。结合元谋县易地扶贫搬迁安置甘塘片区建设项目,将载体桩应用在元谋地区膨胀土地基中,利用载体桩承载力高、桩身可穿越大气影响深度范围的优点,减少地基胀缩变形量,有效解决膨胀土对低层房屋的不良影响,证明载体桩在膨胀土地基中适用性较好,可为类似工程设计提供参考。     

基于信息熵-未确知测度理论的膨胀土胀缩分级评价

将未确知测度理论应用到膨胀土胀缩等级评价中,针对膨胀土中等级评价中许多不确定性影响因素,选用液限、胀缩总率、塑性指数、天然含水率、自由膨胀率等5个评价指标,建立了膨胀土胀缩等级分类评价和排序模型.根据15组膨胀土实测数据,建立各影响因素的未确知函数,对其进行定量分析;并利用熵计算各影响因素的指标权重,依照置信度识别准则进行等级判定,最后得出膨胀土胀缩分级的评价结果.该模型的评价结果与物元可拓评判法评价结果有较好的一致性.该评价方法能解决膨胀土胀缩等级评价中诸多因素不确定性问题,还可以按难易程度进行排序.     

膨胀土施工技术在高速公路工程中的应用

我国高速公路发展迅速,且行车荷载量也在不断地增加,一旦路基出现变形现象就会影响到整个公路正常运营的安全。膨胀土具有湿胀干缩性,路基常会出现各种难以处理的变形问题。文章根据膨胀土的判别以及分类,对膨胀土路基施工技术在高速公路工程中的应用进行了论述。     

黄土状地基土浸水后的沉降分析及补强加固

黄土状地基土受到水浸后,沉降变形由湿陷变形和压缩变形2部分组成,其中湿陷变形是产生不均匀沉降的主要原因,文中介绍了水浸后地基土的沉降计算,并对不均匀沉降地基进行补强加固处理。     

实木地板的干缩湿胀对其漆膜性能的影响

研究木材干缩湿胀对实木地板不同油漆漆膜性能的影响。结果表明:经普通紫外光固化漆(UV)涂饰的地板,表面漆膜因基材过度干缩产生皱缩,导致光泽度降低,过度湿胀导致漆膜开裂;采用柔韧性较好的弹性漆涂饰地板,基材干缩后漆膜表面光泽度仅小幅度降低,湿胀后漆膜不开裂。说明实木地板应选择具有一定柔韧性,可适应基材一定范围内尺寸变化的弹性油漆。     

长白落叶松木材构造性质与干缩关系的初步研究

木材是经常做为一种材料使用的,但由于其具有膨胀干缩性、不均匀性及其他缺点,故在使用时常给木材加工等部门带来很多困难。由于木材向异性干缩原因,如用一些干燥得不够好的木材锯成正方形柱材时,因弦缩大于径缩,结果使木材由方形变成菱形,有时形成开裂。落叶松属木材用途大,强度高,耐腐性也强,其中又以东北、内蒙地区的落叶松类木材强度更高,但其主要缺点是易于开裂,这也就是木材加工及处理等部门所经常遇到的困难问题之一。为此,作者特拟定是项研究,其主要目的在了解长白落叶松木材干缩及开裂与木材构造性质的关系,为木材干燥工业及进一步研究木材向异性干缩理论     

关于水泥混凝土的开裂问题

本文分析了温度裂缝、干缩裂缝、不均匀膨胀引起的裂缝等几种混凝土开裂形式。阐述了产生这几种开裂的原因 ,并提出了在混凝土拌合时用一部分冰块代替拌和水掺入混凝土中 ;适量掺加矿物混合材 (粉煤灰 ) ;谨慎选择水泥品种 ;控制水泥的总含碱量等方法。     

循环干湿处理对尾巨桉木材含水率影响的研究

在大气湿度循环变化的过程中,木材含水率随之改变,导致木材胀缩性发生变化,引起家具零部件松动,甚至脱落和开裂。采用人工模拟大气湿度变化规律,对尾巨桉木材进行循环干湿处理,探索尾巨桉木材含水率的变化规律,旨在探索降低尾巨桉木材胀缩性的新途径,为尾巨桉木材干燥和实木加工提供新理论。     

浅谈基础加固措施

结构补强技术在工程设计和施工技术中都是很重要的,尤其对古旧建筑维修和现有楼房增加层数等,如果基础承载力不足就不能实现。作者根据自己的实践经验对基础型式的几点加固措施作了较详细的介绍。     

大兴安岭地区防冻胀处理应注意的几个问题

本文从多层建筑基础防冻害处理办法、低层建筑基础的处理及建筑物的防冻害处理需加强 排水处理三方面论述了严寒地区地基基础防冻胀的处理办法。     

如何对待软弱地基

本文论述了软弱地基的性质及对建筑物的危害;并介绍了“轻基浅埋”是我国在软土地基上建造房屋的成功经验。     

河南林业生态省建设之环城林带的构建

构建环城林带的目的是追求城市外围生物多样性的生态型防护林地,缓解城市化进程给城市生态环境带来的压力。环城林带是有效抑制城市蔓延扩张的重要措施之一,是实现生态化城市的重要途径。本文阐述了构建环城林带的意义和原则,在此基础上论述了环城林带的构建模式。       

东北寒冷地区高等级公路软土地基沉降计算与分析

东北地区的软土地基沉降除了具有变形大、不均匀沉降大、沉降稳定历时较长的特点外。受地质和气候因素影响也较大，这极大地影响了道路的长期稳定和安全使用。这里结合塑料板排水法在东北寒区高等级公路软土地基处理中的应用研究课题，利用哈尔滨绕城高速公路软土地基沉降观测资料，分析了影响沉降的主要原因，利用二种计算方法对软土地基进行沉降计算井做了讨论分析，得出较为符合工程实际的结论。     

谈建筑工程管理之建筑工程合同管理

从建筑市场工程合同现状及形式、施工合同管理存在的问题及应对方案等方面论述了建筑工程合同管理。     

Shape stability of laminated veneer products – An experimental study of the influence on distortion of some material and process parameters

Abstract

A shortcoming of the laminated bending process is that the products may become distorted after moulding and during use. In this study, we have examined the influence of different UF-adhesive systems, adhesive distribution, and veneer properties such as species, moisture content, and fibre orientation. Two different species were studied: beech (Fagus silvatica L.) and birch (Betula pubescens Ehrh.). Distortion was determined directly after moulding and after storage in a changing relative humidity. The aim of the work was to study how the above-mentioned material and process parameters influence the distortion. The results show that the material and process parameters and the storage in a changing relative humidity had a clear impact on distortion. Fibre orientation, differences in moisture content between veneers, and the moisture gradient in the final product are identified in this study as being the most important parameters influencing the distortion and shape stability of laminated veneer products.     

Twist of wood studs: dependence on spiral grain gradient

Distortions due to moisture changes during drying or in service are a major problem for construction timber. Twist, caused mainly by the cylindrical geometry, the orthotropic nature of the wood material, and the tendency of the wood fibers to grow in a spiral around the stem, is often regarded as the most detrimental distortion of sawn timber. There is a need for a basic mechanical understanding of how the twist distortion arises and also a need for a simple formula to predict the amount of twist distortion. In this article such a formula is proposed, and theory and experimental data that indicate the validity of the formula are shown. The first term in the formula is a modification of a traditional expression which is proportional to the mean value of the spiral grain angle in the cross section in question. The second term in the formula is new and is proportional to the gradient of the spiral grain angle, and this term normally counteracts the first term so that a stud with a left-handed spiral grain might achieve a right-handed twist. Linear elastic finite element method (FEM) results and comparisons with experimental data show that the formula works well and that linear FEM calculations exaggerate the twist, which is probably partly due to nonlinear effects. The formula could be used to predict the twist of sawn timber from measured spiral grain angles on the log surface.     

The frequency dependence of hygro-expansive scaling of oak

ABSTRACT

Fluctuations in the ambient relative humidity are often cyclic of nature, composed of a wide variety of frequencies. Variations may be as fast as one minute or as slow as a complete season. A wooden object exposed to these fluctuations exchanges moisture with the air, resulting in a change in the local moisture content of the wood. Since moisture penetration is affected by the timescale of the changes in ambient conditions, so are processes caused by moisture content variations. Moisture content variations cause dimensional changes of a wooden object, which, if mechanically restrained, lead to a buildup of stresses and ultimately to damage. It is therefore important to predict the frequency behavior of moisture content and expansion in wood. In the presented study, experiments are conducted in which the moisture content and expansion of oak cubes with different sizes is measured during sinusoidal relative humidity fluctuations with different frequencies. The amplitude in moisture content and expansion is shown to be simply scalable based on sample size only. Derived diffusion coefficients are in agreement with literature values, although the experimental frequency behavior is shown to deviate qualitatively from diffusive frequency behavior.     

An efficient approach for tree digital image segmentation

This paper proposes an improved method to segment tree image based on color and texture feature and amends the segmented result by mathematical morphology. The crown and trunk of one tree have been successfully segmented and theexperimental result is deemed effective. The authors conclude that building a standard data base for a range of species, featuring color and texture is a necessary condition and constitutes the essential groundwork for tree image segmentation in order to insure its quality.