Modeling of the seismic behavior of shear-critical reinforced concrete columns
ABSTRACT Inelastic failure of reinforced concrete (RC) structures under seismic loadings can be due either to loss of flexural, shear, or bond capacity. This paper describes the formulation of an inelastic nonlinear beam element with axial, bending, and shear force interaction. The element considers shear deformation and is based on the section discretization into fibers with hysteretic models for the constituent materials. The steel material constitutive law follows the Menegotto–Pinto model. The concrete model is based on a smeared approach of cracked continuous orthotropic concrete with the inclusion of Poisson effect. The concrete model accounts for the biaxial state of stress in the directions of orthotropy in accordance with the Softened Membrane Model, in addition to degradation under reversed cyclic loading. The shear mechanism along the beam is modeled using a Timoshenko beam approach. Transverse strains are internal variables determined by imposing equilibrium between concrete and transverse reinforcements. Element forces are obtained by performing equilibrium based numerical integration on section axial, flexural and shear behaviors along the length of the element. Dynamic behavior was accounted for by adopting the well-known Newmark approach. Rayleigh damping was assumed to simulate the damped behavior under seismic excitations. In order to establish the validity of the proposed model correlation studies were conducted between analytical results and experimental data of RC columns tested under the shake table.
[Show abstract] [Hide abstract]
ABSTRACT: This paper uses nonlinear truss models for the analysis of shear-dominated reinforced concrete (RC) columns subjected to cyclic loading. A previously established method, aimed to the analysis of RC walls, is enhanced to allow simulations of column members. The concrete constitutive equations are modified to account for the contribution of the aggregate interlock to the shear resistance. Additionally, an equation is proposed to determine the inclination angle of the diagonal members in the truss models. The modeling approach is validated using the results of quasi-static and dynamic tests on shear-dominated RC columns. The combination of predictive capabilities and conceptual simplicity establishes truss-based models as an attractive approach for the systematic analysis of shear-dominated RC frame construction.Earthquake Engineering & Structural Dynamics 04/2015; 44(5). DOI:10.1002/eqe.2480 · 1.95 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Purpose – A nonlinear finite element (FE) beam-column model for the analysis of reinforced concrete (RC) frames with due account of shear is presented in this paper. The model is an expansion of the traditional flexural fibre beam formulations to cases where multiaxial behaviour exists, being an alternative to plane and solid FE models for the nonlinear analysis of entire frame structures. The paper aims to discuss these issues. Design/methodology/approach – Shear is taken into account at different levels of the numerical model: at the material level RC is simulated through a smeared cracked approach with rotating cracks; at the fibre level, an iterative procedure guarantees equilibrium between concrete and transversal reinforcement, allowing to compute the biaxial stress-strain state of each fibre; at the section level, a uniform shear stress pattern is assumed in order to estimate the internal shear stress-strain distribution; and at the element level, the Timoshenko beam theory takes into account an average rotation due to shear. Findings – The proposed model is validated through experimental tests available in the literature, as well as through an experimental campaign carried out by the authors. The results on the response of RC elements critical to shear include displacements, strains and crack patterns and show the capabilities of the model to efficiently deal with shear effects in beam elements. Originality/value – A formulation for the nonlinear shear-bending interaction based on the fixed stress approach is implemented in a fibre beam model. Shear effects are accurately accounted during all the nonlinear path of the structure in a computationally efficient manner.Engineering Computations 10/2014; 31(7):1444 - 1483. DOI:10.1108/EC-04-2013-0114 · 1.21 Impact Factor
Conference Paper: Concrete and Carbon Nanofibers[Show abstract] [Hide abstract]
ABSTRACT: The use of nanotechnology is relatively new in civil engineering industry. Cement and concrete are weak in tension and self-monitoring capability. The modification of the cement matrix with nano particles improves the concrete properties and leads to build a better structure. Mixing of carbon-nanofiber (CNF) to concrete can improve the resistance of water penetration and also improves mechanical and electrical properties such as high Young’s modulus, improved fatigue resistance and self-monitoring behavior of concrete. In this paper, the advantages and need of nanotechnology in concrete is discusses.Proc. of the Intl. Conf. on Advances In Engineering And Technology - ICAET-2014; 01/2014