住宅裂缝分析.doc

住宅工程现浇楼板裂缝的原因分析及防治近年来，我们发现，现浇钢筋混凝土楼板出现裂缝的情况较多，这已经成为影响住宅工程质量的一大通病，现对裂缝成因及防治措施简析如下：现浇钢筋混凝土出现裂缝的主要情况1、多层砖混结构2、小高层现浇钢筋混凝土短肢剪力墙结构3、高层现浇钢筋混凝土剪力墙结构4、多层现浇钢筋混凝土框架结构出现现浇钢筋混凝土楼板裂缝的工程，以住宅楼较为多见，商业楼、公建用房相对少些。若按层次分布情况，大部分裂缝与层次无关，只有极个别工程去，其裂缝在从上到下有递减趋势。结构楼板裂缝开始出现的时间一般多在结构封顶半年后陆续出现，如不及时采取补强措施，在1年至2年时间内，裂缝继续发展。三、裂缝所在部位及其特征1、现浇钢筋混凝土楼板裂缝，多分布在房屋转角所在的房间楼板上。裂缝一般呈45度斜向，有时一只角出现两条裂缝，裂缝基本上为上下贯通。2、部分裂缝产生在板内电线管道埋设位置。3、个别工程的楼板裂缝产垂直于板跨方向，或呈不规则状分布。裂缝原因分析经过各种分析因素的对比，认为1、现浇钢筋混凝土楼板裂缝，主要有混凝土的温度变形和收缩变形引起的。钢筋混凝土梁、板、墙、柱等构件处在一个共同的大气环境中，当环境的温度和湿度变化时，这些混凝土的构件多会产生相应的温度变形和湿度变形。由于体形上的差异，板的体积与表面积的比积较小，在水平方向上楼板的收缩变形一般均超过（或大于）梁、柱、墙使板内出现拉应力，梁内呈压应力。另一方面外纵墙和山墙在外界气温的影响下，经历热胀和冷缩的反复作用，它们的温差合力对房间对外墙角部楼板，将产生较大的主拉应力。以上两个力的叠加，对板形成最不利的状态，当板的拉应力超过混凝土的抗拉强度，并且楼板变形大于配筋后混凝土的极限拉伸的时候，楼板内就会产生裂缝。裂缝的位置取决于两个因素，一是约束，二是抗拉能力。对楼板来说，约束的位置在四个转角处，因为转角处梁或墙的刚度最大，它对楼板形成的约束也最大，同时沿外墙转角处因受外界气温影响，楼板属收缩变形最大的部位。一般来说，板内配筋多按平行于板的两条相邻边设置，也就是说，转角处评分线方向的抗拉能力最薄弱。故大多数板上上裂缝出现在沿外墙专角处，而呈45度斜向放射状。2、当前工程施工中，现浇钢筋混凝土楼板的混凝土普遍采用泵送混凝土，其水泥用量、水灰比、塌落度等比较大，石子半径比较小，混凝土收缩值比过去现象拌制的要大，为了抵抗板内受不均匀温差和收缩的影响而出现局部的应力集中，若外墙转角处楼板只按老规矩配筋，就不能适应变化的新情况。3、楼板内埋设电线套管，特别是近些年来普遍推广使用的PVC管代替金属管以后，使板内有效截面受到不同程度的消弱。又因该管与混凝土膨胀系数不一致，粘结效果较差，这时沿电线套管埋设方向就有可能因为应力集中而出现裂缝。4、由于施工安排不当，楼板近支座处的负弯矩筋常常被操作人员踩踏下沉，又没有得到及时纠正，使其不能有效发挥负弯矩的作用。控制钢筋混凝土楼板裂缝的对策;一、在采用商品混凝土泵送施工的条件下，处于外角转角处房间内的现浇钢筋混凝土楼板，应适当加大配筋后混凝土的极限抗拉伸能力，其技术措施条件如下。1、适当增加板厚。2、提高板的配筋。3、采用钢纤维混凝土，以提高混凝土的抗拉强度。4、采用“密筋密筋”的配筋方法。以上几种方法由于受到不同条件的限制，故应提高楼板含钢率的方主，还可以有效针对性地在外墙转角处增配放射性配筋。二、提高部分外墙保温隔热标准，特别是对外墙转角处的里墙面，要采用加贴保温隔热材料的办法，使温差对楼板裂缝带来影响，减少到最低限度。三、研究开发泵送混凝土的低收缩率的干硬混凝土，专门用在现浇钢筋混凝土楼板工程上。四、楼板内配备的PVC电线套管，只允许平行于楼板受力方向埋设,埋在PVC电线套管上下部,应加宽度不少于400mm的钢丝网，作为补强措施。五、有条件的不妨采用“放”特殊构造措施。例如：将端跨设计成简支板形式，即在楼板与梁之间设置施工缝隔离。六：严格施工管理，浇捣混凝土楼板时，必须铺设操作平台，防止施工操作人员直接踩踏上负弯矩筋。同时加强浇捣楼板混凝土整个过程钢筋的维护，随时将钢筋不正确的位置复位，确保其位置正确。七、设计楼板底摸及支架时，应充分考虑能够满足承受各种可能的施工荷载的需要，混凝土浇捣后，必须留有足够的养护时间。八、施工速度应建立在严密的科学组织的基础上，坚决抛弃违反科学的蛮干做法，只有这样才能使当前楼板结构裂缝多发性、普遍性这一质量顽症得到有效遏制。Residential construction of cast-in-situ floor cracks cause analysis and controlIn recent years, we found that cast-in-place reinforced concrete floor cracks is more, it has become a situation a housing project quality effect of crack endemic, now causes and prevention measures are as follows: introductionA, cast-in-situ reinforced concrete cracks main conditions1, multi-layer brick and concrete structure2, small high-rise cast-in-situ reinforced concrete short shear wall structureThree, high-rise cast-in-place reinforced concrete shear wall structure4, multilayer cast-in-place reinforced concrete frame structureAppear cast-in-place reinforced concrete floor cracks in the engineering, residential building more see more, businesses, public housing is relatively less. If press level distribution, most fractures and hierarchy is irrelevant, only the extremely individual projects in the cracks, from top to bottom has degressive tendency.Second, the floor cracks began to appear structure of timeMore commonly in succession in structure capped after half a year, such as not take timely appear reinforcing measures, in one year to two years time, crack continue development.Three, crack their positions and their characteristics1, cast-in-situ reinforced concrete floor cracks in housing, distribution in the room floor space Angle. Crack is 45 degrees of inclined to commonly, sometimes a horn, cracks appeared two cracks up basically is through.2, part of the cracks in the board inside wire embedded pipe position.3, individual project in the floor cracks across direction perpendicular to the board, or an irregular shape distribution.Four, crack causes analysisAfter various analyses factors that the contrast1, cast-in-situ reinforced concrete floor cracks, basically have concrete temperature deformation and contraction deformation cause. Reinforced concrete beam, plate, walls, column, etc component in a common atmospheric environment, when the environmental temperature and humidity changes, these concrete component will produce the corresponding temperature deformation and humidity deformation. Due to the differences and plate shape than the volume and surface area of deposition in a horizontal direction on smaller, floor systole generally exceeded (or more) beams and columns, the wall plate occurs within a tensile stress and beam stress. In On the other hand outside in vertical wall and outside temperature gable under the influence of heat and cold, and experience, they repeatedly role of room temperature of force foreign corner, will produce larger floor Lord tensile stress. Above the superposition of two forces on board, the most unfavorable condition, formed the tensile stress when board over concrete tensile strength, and floor deformation is greater than the limits of reinforcement concrete tensile, floor cracks within. Crack position depend on two factors: the first is the restraint, 2 it is tensile ability. On the floor for, constraints in four corner position, because the corner of the wall beam or biggest, it to floor stiffness of the constraints from the largest also, and outside temperature by exterior wall corner of influence, floor systoles largest area. Generally speaking, board inside reinforcement parallel to the board by more than two adjacent edge Settings, i.e., corner office score line direction the weakest tensile ability. So most board cracks appear along the wall up in a corner place, only 45 degrees of inclined to radial.2, the current engineering construction of cast-in-situ reinforced concrete floor, widely used the concrete pumping concrete, the dosage of cement, water cement ratio, such as collapsbillity is larger, gravel, radius smaller than in the past, concrete shrinkage mixing of the phenomenon, in order to resist the plate uneven temperature difference and contraction by the influence of the local stress concentration and appear only, if wall corner floor slab reinforcement ritual, cannot adapt to changing the new situation.3, floor buried wire casing, especially within the popularization in recent years as the use of PVC pipe replace metal tubes after, make board inside effective by different degrees of section weakened. And because the tube inconsistent with concrete expansion coefficient and bonding effect is poorer, then along the wire casing would likely because embedding direction stress concentration and crack.4, due to improper, floor construction arrangements in the negative moment nearly bearing steel are often operators trample sinking, and didnt get timely correcting, make its cannot effectively play in the negative moment role.Five, the control countermeasures of reinforced concrete floor cracks; One, in the ready-mixed concrete pumping construction by the conditions, the room is outside corner of cast-in-situ reinforced concrete floor, should be appropriately enlarging the limits of reinforcement concrete tensile ability, the technical measures conditions as follows.1, appropriately increase thickness.2, improve the reinforcement plate.3, steel fiber concrete, in order to improve the tensile strength of concrete.4, USES the secret reinforced steel reinforcement secret method.The above several methods due to different conditions of the restrictions, reason should improve floor of square steel ratio, still can effectively Lord pointedly ZengPei in exterior wall corner radioactive reinforcement.Second, improving exterior wall insulation standard part, especially the outward wall corner in metope, use the heat insulating materials to be stuck to floor slab temperature crack, impact, reduced to the minimum.Three, research and development of low pumping concrete shrinkage of concrete, the dry exclusively in in cast-in-situ reinforced concrete floor project.Four, floor of PVC wire inside casing, with parallel to the floor only allowed force direction, buried in PVC wire embedded casing, should add width top and bottom not less than 400mm of steel wire, as reinforcing measures.Five, the conditional might as well use put special tectonic measures. For example: will end cross designed to simply-supported plate forms, namely in floor and