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: a b s t r a c t Reinforced concrete (RC) shear-dominant walls can fail suddenly at lower ductility levels, which can lead to catastrophic damage. Accurate modeling of shear-dominant RC walls is therefore essential. In this paper, fiber beam elements, which are proven to be computationally very efficient, were developed to model the behavior of thin-walled RC shear walls. Concrete and steel were considered as separate materials, and are combined at the section level to describe the behavior of the reinforced concrete member. Concrete was modeled as an orthotropic material in which the principal directions of total stresses were assumed to coincide with the principal directions of total strains, thus changing the directions continuously during the loading. The constitutive model follows the Softened Membrane Model (SMM) in which the compressive strength of concrete is reduced as a function of the lateral strain. The model was subsequently used to conduct a series of numerical studies to evaluate the effect of several parameters affecting the nonlinear behavior of the shear dominated wall. These parameters include the aspect ratio, the transverse reinforcement ratio, the axial force, and the concrete compressive strength. These studies resulted in several important conclusions regarding the global and local behavior of wall systems.
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ABSTRACT: Severe infections at the forearm level are difficult to treat not only in terms of sterilization but also in terms of functional restitution. Traditional radical debridement is very important, however, reconstruction of the excised tissues sometimes meets with difficulty when there is used of such conventional techniques. At the forearm level, local flaps generally are not sufficient in covering big defects. Conventional bone grafts may be resorbed or they cannot help healing when placed in infected and hypovascular tissue bed. Therefore, bone reconstruction is a real challenge. Development of microsurgical techniques has increased the possibilities of treatment when those severe infections occur. Reconstruction of large soft tissue defects can be achieved by choosing the appropriate free flap. Vascularized fibular grafts allow the use of a segment of diaphyseal bone which is structurally similar to the radius and the ulna, and of length that would suffice to reconstruct most skeletal defects. In the upper limbs the vascularized fibular graft is indicated for patients in whom conventional bone grafting has failed or large bone defects are present (extending beyond 5 cm). When contemporary soft tissue reconstruction is needed, the fibula may give osteocutaneous and osteomyocutaneous grafts to be transferred. We report the results of a series of 22 cases of severe chronic osteomyelitis of the radius and/or the ulna treated with free vascularized fibula bone grafts. All patients were reviewed at a mean follow-up of 3 years (10–93 months); in all cases the infection never recurred. We report only one bone resorption, in the case of a double-barrel fibular transfer, which probably occurred due to vascularization failure. Even in this case, the patient was able to resume previous occupation.Engineering Structures - ENG STRUCT.
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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 01/2005; 1284:189-190.