Research On The Indirect Internal Force And Control Of Cracks For Over-long Concrete Structures

As the development of construction, more and more over-long concrete structures appeared recently. To avoid the disadvantages of lying moving joint, these structure always select set _ting no moving joint. Then, how to control the cracks causing by temperature variation and shrinkage of concrete become a urgent problem. The rules in the code for over-long structure is not detailed enough, and the cracks are often controlled through techniques in construction and material, etc, few rules could be referred to for designing. The research of this paper is based on these phenomenons.Firstly, basic material test of concrete was undertook, as the large flat in the Olympic Centre of Nanjing the background. These following items are reviewed:â‘ The strength and elastic modulus of concrete in different age.â‘¡The shrinkage of shrinkage-compensated concrete with different steel ratio.â‘¢The creep of concrete with different load ages. Many researches have been carried out about the indirect stress of concrete. The study of precision about two approximate methods for calculation stress is carried out in this paper, one is about the temperature-equated shrinkage, another is about the thermal stress when creep is taken into account.There are many chances that crack appears in over-long concrete structure, and the main topic of this paper is about the behavior of member after cracking. The cracks caused by indirect action is quite different from those caused by direct load. The axial stiffness of the member will decrease after cracking, and the internal force will drop accordingly. The development of indirect stress and the process of crack were simulated through a computer program, in which the development of indirect action with time was taken into account, and the iterative method was introduced to solve the reduction of axial stiffness after cracking.Based on prior researches, some advices about the design of over-long concrete structure were given, including the layout of structure and the combination of indirect action, the combination of indirect action for structures in which cracks are allowed and not allowed should be different. The effect of prestress on the final formation of crack were given based on an example, and then, the amount of steel which is necessary to control the crack to a certain level was calculated using the formula of the code.In addition, some researches about the mechanism of cracking and crack-resist design for over-long wall are listed.