Crack Mechanism And Controlling Technique Of Reinforced Concrete Super-long Frames

Quality questions evoked by cracks in reinforced concrete super-long frames draw more and more public attentions. This problem has become a difficult nut in the engineering practice and needs urgent solutions to meet engineering demands. As a sub-topic of "cracking mechanism and a whole set of control technique of modern concrete structure" (No. 50278031) supported by national natural science foundation, this paper studies all roundly crack mechanism and controlling technique of reinforced concrete super-long frames.The main work done in this paper is as follows: (1) Based on finite element method of beam and shell structures and generalized stress-strain relation of member section, a simplified numerical method, grid-equivalent section method, is put forward to perform nonlinear analysis of reinforced concrete space frame structures. (2) According to the theory of concrete creep and stress relaxation, and based on T-B method, a method of improved equivalence elastic modulus which can consider the behavior of concrete creep is derived. (3) HHUSFNA, nonlinear analysis program of space frames, is coded by hybrid programming method. (4) Distribution regularity of thermal internal forces when super-long frames are subjected to environmental temperature is studied. The susceptibility of kinds of possible influencing factors and the mechanism and the regularity of thermal cracks are analyzed. (5) According to combined action theory of super structure-foundation-ground solid, additional forces of super-long frames due to foundation differential settlement and influencing factors are studied. The mechanism and the regularity of settling cracks are found out. (6) A design flow chart of reinforced concrete super-long frames is put forward, which takes temperature and differential settlement as two actions into structural design, and limits the width of cracks to modify reinforcement arrangement of beam-column members.On the basis of the work mentioned above, some crucial conclusions are acquired as follows: (1) HHUSFNA is reasonable and correct. (2) Thermal cracks of super-long frames induced by environmental temperature change are mainly on the bottom and peripheral members of the structure. (3) When super-long frames are calculated by routine method that doesn't consider the effect of differential settlement, internal forces may be less than factual values and settlement cracks may occur. (4) The design flow chart of reinforced concrete super-long frames is worth spreading and applying.It is doubltless that the work done in this paper is beneficial to the application of nonlinear analysis in reinforced concrete frames, and that it has theoretic value to crack control of reinforced concrete super-long frames, and has benefit to enhance controlling level of cracks.