engleski

Nonlinear analysis of space r/c frames with non-uniform torsion

This paper presents a numerical model of stability and load-bearing capacity of space reinforced concrete (R/C) frame structures taking into account the material and geometric nonlinearity. The developed model describes behavior of space frames with composite cross sections under a monotonically increasing load, from zero up to the ultimate load (i.e. collapse of the structure). The collapse of the structure occurs due to exceeded limit of the load and/or loss of the stability of space beams or whole structure. The fiber decomposition procedure is developed to solve material and geometrical nonlinear behavior of composite cross-section in three-dimensional frames. The filaments in the fiber decomposition model of the cross-section, which describe uniaxial behavior of materials are extended over corresponding finite element and create a separate prismatic body discretized by the brick finite elements. After mapping of the boundary forces on prismatic body (i.e. ‘ comparative body’ ), the capture of non-uniform torsion is applied. Focus of this approach is concentrated on the evaluation of the torsional stiffness, which are strongly nonlinear. Three integration levels exist: the first one along the beam-column finite element, the second one over the fiber decomposed cross-section, and the third one over a prismatic comparative body. Behavior of the space frames shall be more realistically described in this way, espe-cially flexural, lateral and torsional stability effects. The global procedure includes an incremental-direct iteration step approach. The incre-mental step model of gravitational load level is applied. Geometrical nonlinearity is assumed by Total Lagrange small displacement formulation. The perfect bond-slip effect between con-crete and bars as well as smeared crack model is assumed. Two examples are studied to verify the accuracy of the program and demonstrate its applica-tion in practical engineering.

R/C space frame; comparative body; fiber decomposition; non-uniform torsion

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