International Concrete Abstracts Portal

Several studies showed that the eccentricity between beam and column connections has a detrimental effect on the joint shear strength. With regard to this issue, ACI 318-08 restricts the average shear stress on a horizontal plane within the joint, which equals to the effective joint width times column depth. The formula of effective joint width given in ACI 318-08 may be too conservative for eccentric beam-column joints. This paper suggested a more rational formula of effective joint width associated with the softened strut-and-tie (SST) model for eccentric beam-column joints. Using the proposed effective joint width, the shear strength predictions of SST model agreed well with the results of 18 eccentric joint specimens failed in shear. Furthermore, together with the proposed effective joint width, several available definitions for effective joint width are also used as comparisons to estimate joint shear strength of collected database for eccentric and concentric joints using ACI 318-08 code design equation. The proposed effective joint width was successfully verified with available database of beam-column joints with or without eccentricity in literature.

Results from the test of a large-scale coupled-wall specimen consisting of two T-shaped reinforced concrete structural walls joined at four levels by precast coupling beams are presented. Each coupling beam had a span length-depth ratio (ln/h) of 1.7, and was designed to carry a shear stress of 7vfc' [psi], (0.59vfc' [MPa]). One reinforced concrete coupling beam was included along with three strain-hardening, high-performance fiber-reinforced concrete (HPFRC) coupling beams to allow a comparison of their behavior. When subjected to reversing lateral displacements, the system behaved in a highly ductile manner characterized by excellent strength retention to drifts of 3% without appreciable pinching of the lateral load versus drift hysteresis loops. The reinforced concrete structural walls showed an excellent damage tolerance in response to peak average base shear stresses of 4.4vfc' [psi], (0.34vfc' [MPa]). This paper presents the observed damage patterns in the coupling beams and the structural walls. The restraining effect provided by the structural walls to damage-induced lengthening of the coupling beams is discussed and compared with that observed in component tests. Finally, the end rotations measured in the coupling beams relative to the drift of the coupled-wall system are also presented.

Reinforced concrete shear walls are typically modeled with two-dimensional continuum elements. Such models can accurately describe the local behavior of the wall element. Continuum models are computationally very expensive, which limits their applicability to conduct parameter studies. Fiber beam elements, on the other hand, have proven to be able to model the behavior of slender walls rather well, and are computationally very efficient. With the inclusion of shear deformations and concrete constitutive models under a biaxial state of stress, fiber models can also accurately simulate the behavior of walls for which shear plays an important role. This paper presents a model for wall-type reinforced concrete structures based on fiber beam analysis under cyclic loading conditions. The concrete constitutive law is based on the recently developed softened membrane model. The finite element model was validated through a correlation study with two experimentally tested reinforced concrete walls. 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 wall. These parameters include the slenderness ratio, the transverse reinforcement ratio, and the axial force. These studies resulted in several conclusions regarding the global and local behavior of the wall system.

Past reinforced concrete panel tests performed at the University of Houston have shown that reinforced concrete membrane elements under reversed cyclic loading have much greater ductility and energy dissipation when steel bars are provided in the direction of the principal tensile stress. This paper presents the experimental results of two low-rise and two mid-rise shear walls under reversed cyclic loading. The low-rise shear walls have a height-width ratio of 0.5, and the two mid-rise shear walls have a height-width ratio of 1.5. In critical regions, the wall reinforcements were designed in the orientation close to the principal stress direction. Furthermore, nonlinear finite element analyses of the tested walls were performed using the finite element analysis program Simulation of Reinforced Concrete Structures (SRCS), which was recently developed at the University of Houston. SRCS was developed by implementing the cyclic softened membrane model (CSMM) to the finite element framework OpenSees. The comparison showed good correlation between the predicted and experimental results of the four shear walls in terms of initial stiffness, ultimate strength, hysteretic loops, and energy dissipation, and the capability of SRCS to assess the cyclic behavior of shear walls with diagonal steel grids was validated.

The causes of the nonlinear behavior of concrete until failure are numerous and complex, particularly for nonmonotonic and rapid loadings. A model is presented coupling damage and plasticity including several effects: development and closure of cracks, damping, compaction, and strain rate effects. The idea is to describe, with the same tools, a wide variety of problems, the model is of explicit form, and what makes possible its implementation into explicit numerical scheme well adapted to the treatment of fast dynamic problems. In this context, the finite element "Abaqus explicit" code is used, and the model has been successfully applied during the past few years to model a large range of complex reinforced concrete structures subjected to severe loadings. In this paper, the main model concepts are presented, and some examples of numerical simulations are given and compared with experimental data. The applications proposed are related to quasi-static loading as well as to rapid loading (impact); in particular, one of them is within the framework of an experiment linked to the design of a reinforced concrete rock-shed gallery located in the French Alps. The results show the relevance of the modelling used, which makes some real numerical experiments very useful for complex structures and/or extreme loadings.