Low-rise structures in reinforced concrete: approximation of material nonlinearity for global stability analysis

In the analysis of the second-order global effects, the material nonlinearity (NLF) can be considered in an approximate way, defining for the set of each structural element a mean flexural stiffness. However, there is less research concerning low-rise buildings in the analysis of global stability in contrast to high buildings, because these have a greater sensitivity to this phenomenon and they are more studied. In this way, the paper objective is to determine the flexural stiffness values, of beams and columns, for buildings with less than four floors, to approximate consideration of the NLF in the global analysis. The idealized examples to buildings with 1, 2 and 3 floors, being simulated through the software CAD/TQS and an analysis model based in an iterative process. The simulations results defined the stiffness values of the set of beams and columns in each example, followed by a statistical analysis to define general values of application in the buildings. Finally, a proposal is suggested of stiffness reduction coefficients for beams and columns to be adopted in the approximation the NLF (EIsec = αv/p ∙ Eci Ic), as follows: buildings with 1 floor (αv = 0,17 and αp = 0,66), buildings with 2 floors (αv = 0,15 and αv = 0,71) and buildings with 3 floors (αv = 0,14 and αv = 0,72). The results obtained can be used for the analysis of low-rise structures to consider the second order global effects with more safely.