International Concrete Abstracts Portal

This CD-ROM consists of 29 papers that were presented at technical sessions sponsored by Joint ACI Committees 343, 445, and 447, at the ACI Fall 2009 Convention in New Orleans, LA, in November 2009. The papers represent state-of-the-art advances in knowledge on shear and torsion. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-265

This paper describes the structural behavior of precast, prestressed concrete sandwich wall panels reinforced with carbon fiber-reinforced polymer (CFRP) shear grid to achieve composite action. The study included testing of six full-scale sandwich wall panels, each measuring 20 x 12 ft (6.1 x 3.7 m). The panels consisted of two outer prestressed concrete wythes and an inner foam core. The study included two types of foams and several shear transfer mechanisms with different CFRP reinforcement ratios to examine the degree of composite action developed between the two concrete wythes. All wall panels were simultaneously subjected to applied gravity and lateral loads. The paper also presents a general methodology to determine the behavior of fully and partially composite wall panels. The effects of imperfect connection between the two concrete wythes are considered by varying the total shear force transmitted through the shear connectors at the interface. The shear flow capacity of the insulating materials as well as the CFRP shear grid is determined using the proposed approach. The influence of the degree of the composite interaction on the induced curvature and slip-strain behavior is presented. A simple design chart for estimating the flexural capacity of the wall panels with different shear reinforcement ratios is proposed.

Recent advances in computational capabilities, both hardware and software, have made nonlinear analysis a viable tool for seismic structural engineering. To fully realize the potential of this tool, however, engineers require nonlinear models and modeling recommendations that have been validated using extensive experimental data sets. For reinforced concrete beams and columns that exhibit primarily flexural response, beam-column elements with fiber-type cross section models have been shown to simulate well observed response. While these types of models are used commonly in practice for design of concrete wall buildings, a comprehensive evaluation of these models for simulating wall response has not been accomplished. Thus, as part of an ongoing study funded by NSF through the NEES program, an investigation of the accuracy of these models for simulating concrete wall response was undertaken. A data set comprising 60 planar wall tests was assembled and used to evaluate the accuracy with which critical response parameters could be predicted. The force-based beam-column element formulations available in the OpenSees platform were used with a standard fiber-type cross section model that simulates flexureaxial load interaction. A MATLAB code was created to facilitate the evaluation process. Results of the evaluation showed that the basic model over-predicted stiffness and under-predicted critical displacements, and an enhanced model was developed that includes a bar-slip model at the base of the wall and an effective, elastic shear stiffness. The enhanced model was calibrated using the data set, and the MATLAB-based code and MATLAB optimization toolbox were used to find an optimal shear stiffness. For three representative walls, the response history simulated using the enhanced beamcolumn element was compared with that simulated using the Response 2000 and VecTor2 analysis programs. The results of this study show that the enhanced beamcolumn element is appropriate for use in simulating the response of concrete walls with a range of design parameters.

Eight full-scale panels were tested to study the constitutive relationships of elements (panels) made of reinforced concrete with steel fibers (RCSF). The RCSF panels were subjected to biaxial tensile-compressive loadings. The principal variables of the testing program were: (a) percent of steel fibers by volume, Vf, (b) length-to-diameter ratio of steel fibers, Lf/Df, (c) reinforcing bar ratio in the tensile direction, ?, and (d) the tensile strain, eT, in the direction of the principal applied tensile stress. Based on the test results, analytical expressions are proposed for the smeared stress-strain curves of cracked steel fiber concrete (SFC) in tension and compression, as well as the smeared tensile stress-strain curves of mild steel embedded in SFC. The proposed analytical expressions take into account the effect of the steel fiber index, Wf (Wf = Vf Lf /Df).

This paper provides a theoretical overview on the most influential theories for compression field models for shear and torsion. Special attention is given to the steel behavior because this is the point where the rotating-angle softened-truss model (RA-STM) and modified compression field theory (MCFT) depart. A new proposal for the steel model is presented. This proposal has the advantage of an embedded bar system, but it does not introduce additional complexity in the formulation. The steel model is based on tension stiffening behaviour. Several examples are presented, including a prestressed girder and a wall-type structure.