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.
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ABSTRACT: An analytical model was developed to estimate the shear-strength degradation and the deformation capacity of slender reinforced concrete columns subjected to cyclic transverse loading. The shear capacity of the concrete compression zone was defined as a function of the inelastic flexural deformation of the column, based on the material failure criteria of concrete. The shear capacity is degraded as the inelastic flexural deformation increases. The deformation capacity of a column is determined when the degraded shear capacity reaches the shear force demanded by flexural yielding of the column. Other failure mechanisms including rebar-buckling and -fracture and flexural failure were also considered to estimate the deformation capacity. The proposed model was applied to test specimens possessing various design parameters. The result showed that the proposed model estimated the shear-strength degradation and deformation capacity of the test specimens with reasonable precision.Engineering Structures 01/2012; 34:187–197. · 1.77 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
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ABSTRACT: This study aimed to evaluate the changes of caries risk and oral microbial flora in the patients having an edgewise appliance by stimulated saliva test (caries risk kit: Bio Medical Laboratory: BML, Icn, Tokyo). Furthermore, commensal and transient bacteria in aerobic culture medium were examined in saliva. As a result, it was determined that caries risk and the oral microbial flora balance possibly change with placements of orthodontic appliances.International Congress Series 09/2005; 1284:189-190.