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 calibration of ACI 318-08 for concrete structures was focused on the flexural capacity. The objective of this paper is to develop the statistical parameters for shear capacity of reinforced concrete beams. The capacity of shear reinforcement is a function of steel cross section area, yield strength, and spacing of stirrups. In this paper, the capacity of concrete is considered using ACI formulas and other shear capacity models available in literature. The analysis is performed for various reinforcement ratios, longitudinal and transverse, including beams without web reinforcement. The statistical parameters of resistance are determined from the test results. The reliability analysis is performed, and it serves as a basis for the selection of resistance factors. The selection criterion is closeness to the target reliability index. Recommended values of resistance factors are provided for each of the considered shear capacity methods.

Revolutionary developments relating to novel materials of construction and improvements in the behavior of traditional materials have been taking place throughout the 20th century and into the 21st century. These developments have been considerably facilitated by increased knowledge of the atomic and nano structure of materials, studies of long-term failures, development of more powerful instrumentation and monitoring techniques, decrease in cost-effectiveness of traditional materials have necessitated stronger and better performing materials suitable for larger structures, longer spans, more ductility, and extended durability. The last few decades of the 20th century can be described as the decades of concrete admixtures and composite innovation. The 21st century will be the millenium of high-strength, high-performance concrete for the greening of structures. Population growth has magnified the infrastructure demands for new compatible materials and composites for sustainable green structural systems compatible with the needs of the environment. Increased industrialization has resulted in mineral byproduct wastes that are detrimental to the environment. For example, the world’s production of fly ash was over half a trillion tons in 1989. Currently, it exceeds one and a half trillion tons. Some of these environmentally unfriendly by-products, however, can particularly be used in new concrete to the benefit of the environment. The versatility of concrete and its high-performance derivatives will satisfy many future needs and impact on the structural performance of concrete systems in flexure, shear, torsion and their long-term behavior. The present century can become the golden age of environmentally friendly supplementary cementing materials for high-performance concrete. This paper gives a summary of some of the major developments in the art and science of concrete structures and materials technology through the 20th and into the present decade of the 21st century as the greening material for the environmental needs of the infrastructure.

Five full-scale prestressed concrete I-beams were tested to explore the effect of three variables: the shear-span-to-depth ratio (a/d), the transverse steel ratio ?t, and the presence of draped strands, on the web-shear and the flexural-shear capacity. The results from these five tests, together with 143 test beams found in literature, were used to develop an accurate, yet simple, equation for the shear strengths of prestressed concrete beams. This new equation is a function of the a/d ratio, the strength of concrete vfc', the web area bwd, and the ?t ratio. Although the ACI and AASHTO shear provisions include two other variables, namely, the prestress force and the angle of failure crack, this study showed that these two variables had no significant effect on the shear capacity. In addition, a new formula was derived to preclude the web crushing of concrete before the yielding of transverse steel, and the ACI minimum stirrup requirement was evaluated. The new shear design method hasbeen compared with the shear provisions of the ACI 318-08 and the AASHTO specifications. Finally, the simplicity and rationality of the new method has also been illustrated by a design example.