摘要
随着建筑经济和建筑技术的迅速发展,地下商场、地下交通、地下车库等地下工程屡见不鲜。随之而来的是地下工程的外墙、底板和顶板等地下结构的不同时期的开裂问题凸显了出来,尤其是施工阶段模板拆除后墙体开裂的问题。
本文研究的主要内容就是在施工阶段钢筋混凝土地下构件的外墙裂缝的控制,其目的在于利用有限元分析软件SAP2000计算并分析短期内的温降和约束对施工阶段的墙体的影响,最终确定控制墙体开裂的有效措施。
本文介绍了地下室外墙裂缝控制的国内外研究现状,墙体裂缝的分布状态,并从施工和设计两方面分析了墙体裂缝形成的原因；阐述了墙体裂缝控制和处理的一般方法和措施；研究了混凝土结构温度场和温度应力的概念和计算方法；说明了施工阶段地下室外墙产生温度应力除了考虑水泥水化热以外还应考虑的因素包括：混凝土的环境温度,混凝土的收缩和徐变。通过对各种因素的分析和实例计算得出本工程的温度荷载值,同时计算出龄期的抗拉强度和弹性模量,再将温度荷载值施加到墙体模型中,最后将得出的最大拉应力乘以应力松弛系数与龄期抗拉强度进行比较。此外,本文通过分析比较地下室外墙在不同温度,不同长度,不同浇筑方式,不同约束强度等条件下的应力状况,得出如下结论：1、温度荷载是影响墙体开裂的最主要因素之一,温降越大,墙体温度应力就越大,开裂的可能性就越高。因此采取必要的措施以减小温降是合理的。如初期升温阶段的降温和降温阶段的保温。2、约束也是影响墙体开裂的最主要因素之一。局部刚性约束如顶板、柱子等将增大墙体的应力。并且如果约束太强还会使墙体在约束附近产生应力集中现象,结构更容易开裂。整体柔性约束如横向的分布筋则会使应力减少,降低墙体开裂的可能性。因此可以通过合理控制约束的范围、性质和强度以达到控制裂缝的目的。
本文的研究结果为钢筋混凝土地下室外墙的裂缝控制提供了有效参考。
The underground markets, communications and garages have been everywhere with the fast development of building economics and building technologies. However, the problem of cracks in large concrete components like walls, bottom slabs etc. takes people much attention, especially the wall's cracks during the construction.
My research is mainly on the controlling cracks of reinforcement concrete underground external wall during construction period. The purpose is to confirm effective measures for controlling cracks through analyzing and computing the influence which is caused by short-term temperature loads and restraints acting on the structure. This is achieved by finite element analysis software SAP2000.
The author introduces present research states at home and abroad and the distribution of wall cracks in dissertation. Besides, he analyzes the reason why the cracks occur from both construction and design aspects. General methods and measures about preventing and curing the cracks are simply stated. The author also represents temperature field and stress's conception and computing methods, illustrates the wall's temperature stress is affected by temperature changes of environment, concrete shrinkage and creep besides cement's hydration heat. Get the project's temperature loads through analyzing and computing kinds of factors above in the example, get age tensile strength and age elastic modulus, then apply temperature loads to wall model, at last compare the age tensile strength with the largest tensile stress which multiplies stress coefficient of relaxation. In addition, the author compares the wall's stress situation in different cases, such as different temperature, different length, different casting pattern and different restraint strength. Finally, reaches a conclusion bellow:1. Temperature load is one of the most important factors affecting the wall's crack. More temperature reduction will make bigger temperature stress, and the wall will be much easier to crack. So it is reasonable to reduce temperature fall by any methods, such like the reduction of temperature in the increasing state and keeping of temperature in dropping state. 2. Restraint is another one of the most important factors. Partial rigid restraint like top slab and column will increase the wall's stress. If the restraint is too strong, the stress will grow suddenly and concentrate nearby, and the wall is easy to split. Entire flexible restraint like horizontal distribution bar will reduce the wall's stress, and the wall is not so easy to split. Therefore, we can control the wall's cracks by controlling the restraint's range, properties and strength.
The research results of this article provide a useful reference to prevent concrete underground external wall splitting.
引文
[1]. Control of Cracking in Concrete Structures reported by ACI Committee 224,1980.12
[2].王铁梦.工程结构裂缝控制[M].中国建筑工业出版社,1997
[3].王铁梦.工程结构裂缝控制“抗与放”的设计原则及其在“跳仓法”施工中的应用[M].建筑工业出版社,2007
[4].朱伯芳.大体积混凝土温度应力与温度控制[M].中国电力出版社,1999
[5].叶琳昌等：《大体积混凝土》[M],北京,中国建筑工业出版社,1987.40
[6].中华人民共和国国家标准.混凝土结构设计规范(GB50010-2002)[s].北京：中国建筑工业出版社
[7].富文权,韩素芳.混凝土工程裂缝分析与控制[M].北京：北京中国铁路出版社,2000：93-108
[8].孙剑云,防止超长建筑物因温度收缩裂缝的设计方法[C].中国科技信息,2005.12
[9].王杰.浅谈混凝土温度裂缝的原因分析及防止措施[J].山西建筑,31(21)
[10].Control of Cracking in Concrete Structures reported by ACI Committee 224,1980.12
[11].A.W.Bee.Creaking,Cover and Cormsion of Reinforcement of Concrete. Imitational FEB,1983,5(2)
[12].A.M.内维尔.李国洋、马贞勇译.混凝土的性能[M].中国建筑工业出版社,1983
[13].冯健,吕志涛,吴志彬等.超长混凝土结构的研究和应用[J].建筑结构学报,2001,Vol.22(6)：14-19
[14].杨小欧.超长地下室外墙裂缝的控制[J].建筑施工,2003,vol.25(4)：296-297
[15].时旭东,过镇海.钢筋混凝土结构的温度场[J].工程力学,19%,Vol.13(1)：35-43
[16].赵海东,赵鸣,沈水明.超长钢筋混凝土结构的温度响应[J].四川建筑科学研究,2000(12)：7-10
[17].吴显.超长现浇钢筋混凝土结构无缝施工[J].山西建筑,2003,Vol.29(9)：38-39
[18].陆少连,过寿先.杭州铁路新客站超长地下室的设计与施工[J].建筑技术开发,2000,Vol.27(1)：34-36
[19].杨小哑.超长地下室外墙裂缝的控制[J].建筑施工,2003,vol.25(4)：296-297
[20].刘宁,刘光廷.大体积混凝土结构随机温度徐变应力计算方法研究[J].力学学报,1997(2)：189-201
[21].中华人民共和国国家标准.民用建筑热工设计规范(GB50176-93)[s].北京：中国计划出版社
[22].梁志广,李建中,王军文.几种常用混凝土收缩徐变模式中徐变系数计算的比较分析[J].工程力学增刊,1999：175-179
[23].惠荣炎,黄国兴,易冰若.混凝土的徐变[J].北京：中国铁道出版社,1988
[24].Y.Yuna.Z.L.Wan. Prediction of cracking within early-age concrete due to thermal, drying and creep behavior. Cement and Concrete Reserch,(2002):1053-1059
[25].J.H.Hettle, J.Torborg. A numerical model for predicting the thermomechanical condition, during hydration of early-age concrete. Applied mechanical modeling.2003(27):1-26.
[26].李骁春.高层建筑地下室侧墙温度裂缝机理及控制技术[D].南京：河海大学,2004
[27].Robert Springenschmid. Avoidance of Thermal Cracking in Concrete at Early Ages[C]. RIL EM Technical Committee1119 TCE.1998.
[28].康庆,吴胜兴.超长钢筋混凝土框架结构季节温差作用分析[A].中国水利水电出版社,2003(11)
[29].顾渭建.纤维混凝土在高层建筑超长结构无缝设计中的应用[C].首届全国纤维增强塑料混凝土结构学术交流会论文集,北京,2000
[30].李潘武.大体积混凝土非荷载应力的施工系统控制[D].西安：西安建筑科技大学博士学位论文,2004：1-3
[31].郭惠琴.超长混凝土结构裂缝控制措施[A].山西建筑,2005.1,31(6)
[32].范青.防止和减轻超长混凝土结构温度裂缝的建议[A].施工技术研究和应用
[33].徐强.大掺量粉煤灰混凝土温度应力及抗裂能力的分析[C].上海市科技启明星计划项目,2003
[34].Wilson E L. The determination of temperatures within mass concrete structures (SESM Report No.68-17). Structures and Materials Research [J]. Department of Civil Engineering, University of California, Berkeley,1968,(12):56-58
[35].AB.雷柯夫著,裘烈钧,丁履德译.热传导理论[M].北京：高等教育出版社,1956：41-5
[36].王铁梦.大体积混凝土的瞬态温度场和温度收缩应力的计算机仿真[M].工业建筑,1990(1)：37-42
[37].柳爱群,高翔,张来芝.计算混凝土水化热问题的有限元解[N].山东科技大学学报,2000，19(4)：88-90
[38].李潘武,李慧民.通过配筋控制大体积混凝土的温度裂缝[J].四川建筑科学研究,2005(31)
[39].Effect of Restrain, Volume Changes, and Reinforcement on Cracking of Mass Concrete[R]. ACI MATERIALS JOURNAL COMMfl-lEE REPORT No.87-M31 ACI-207.2R.reported by ACI committee 207
[40].杜锋,肖建庄,高向玲.钢筋与混凝土间粘结试验方法研究[J].结构工程师,2006.4(22)
[41].惠荣炎,黄国兴,易冰若.混凝土的徐变[J].北京：中国铁道出版社,1988
[42].金成棣.混凝土徐变对超静定结构变形及内力的影响[N].土木工程学报.1981(9)：24-30
[43].刘忠.混凝土徐变收缩的递推AME法[N].重庆交通学院学报.1994(12)：18-26
[44].周红军.温度对混凝土徐变影响的数值模型[D](硕士学位论文).南京：河海大学,2004
[45].朱晓东.高层建筑与钢管混凝土结构徐变收缩理论研究[D](硕士学位论文].南京：东南 大学,2001
[46].I,Soroka, Concrete in Hot Environment,London:E&FN,Spon.1993.
[47].陈晓东.超长混凝土半地下室外墙环境温度效应研究[D](硕士学位论文).上海：同济大学,2006
[48].江见鲸,陆新征等.混凝土结构有限元分析[M],北京：清华大学出版社,2005