Analysis Of Nonlinear And Second-order Effect Of Reinforced Concrete Structures

The analysis of second-order effect is the most important issue for reinforced concrete members in structural design. So far, lots of researches have been made progress, and even many achievements have been adopted in the standards, but because of the complexity of the issue, there remains a series of important problem needed to be studied.In this paper, a further research about the nonlinear stability of axial compression member, the second-order effect of eccentric compression member and frame is made based on the material and geometrical nonlinear characteristic. The detailed works listed as follows:(1) Based on numerical analysis, the formulas for effective length of member subjected to different constraint and bearing are established.(2) The bearing capacity of uniaxial compressive reinforced concrete members is studied from nonlinear theory’s viewpoint, and longitudinal bending coefficient in concrete critical state is obtained. It is indicated that the concrete creep has a significant effect on the bearing capacity of uniaxial compressed members.(3) Based on the material and geometrical nonlinear analysis, and by considering the tension stiffening of concrete, the load-deflection characteristic of non-sway reinforced concrete columns is studied, and the expressions for the additional deflection of columns with symmetric eccentricity at ends and equivalent uniform moment diagram factor of columns with asymmetric eccentricities at ends are provided. Comparison with the test data from different source shows that it is better than that in the Code for design of concrete structures.(4) By taking second-order effects into account, the axial force and moment interaction diagrams are calculated according to Chinese code GB50010—2010, American code ACI318-08and European code EN1992-1-1:2004. Comparison shows that, without considering the second-order effect, the result for bearing capacity of member calculated from Chinese code is close to that of European code, but greater than that of American code, because in American code, the strength reduction factor is considered. While the second-order effect is considered in the analysis, the specification of Chinese code for bearing capacity is much simpler than that of American code and European code. (5) By considering the material and geometrical nonlinear characteristic, the reinforced concrete frames are analyzed. While in the geometrical analysis, the P-△effect and P-δ effect are taken into account. Comparison with test data shows that the calculated method derived from the paper has good precision and accuracy.