Crack Mechanism And Controlling Technique Of Cast-in-place Slab Wit Large-area

With the increase of the number of large-span large-area and large-space buildings in cities, temperature cracks of cast-in-place slab with large-area draw more and more public attentions. This problem has become a difficult nut in the engineering practice. The cast-in-place slab with large-area without special requirement can work with cracks, but the largest crack width must be less than that stipulated in the code of GB50010-2002. Hence, the control principle of cast-in-place slab with large-area is to limit the crack, that is, to control the width of crack in the allowable range as stipulated by the code.As a sub-topic of National Natural science foundation named "cracking mechanism and a whole set of control technique of modern concrete structure" (No: 50278031), this paper roundly study crack controlling technique of cast-in-place slab with large-area.The main work done in this paper is as follows: (1) The emergence mechanism and kinds of temperature crack have been probed. (2) The temperature field of cast-in-place slab with large-area during the construction has been simulated. (3) Stress field of cast-in-place slab with large-area has been calculated, the stress rule and the stress characteristics of cast-in-place slab with large-area subjected to all kinds of temperature effect have been summarized. (4) Sensibility of the influence of factors of temperature field and stress field has been analyzed. (5) The methods to control crack of cast-in-place slab with large-area in several aspects, such as frame design concrete material and construction techniques are summed up. (6) The validity of control methods of crack has been verified by using engineering instances.On the basis of the researches mentioned above, some crucial conclusions are acquired as follows: (1) During construction, the cracks in beams and girders were caused by the drop of temperature and by the difference in the inside and outside temperature. The crack in slab was caused by shrinkage due to the loss of water. (2) The stress caused by heat of hydration during construction is mainly distributed in the beams, and girders and stress in slab was smaller; during service process, the stress caused by difference in temperature in different seasons is mainly distributed in bottom components; the stress caused by difference of inside and outside temperature is mainly distributed in peripheral components of building; the stress caused by difference in temperature due to sunlight is mainly distributed in the components exposed to the sun. (3) The control methods brought forward such as setting the reasonable stripping time reducing cast temperature of concrete setting after-treatment joint inflicting prestress arranging steel for construction requirement and so on are effective and their application may be extended.