International Concrete Abstracts Portal

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.

Several studies have indicated that the shear capacity of fiber-reinforced ultra-high-performance concrete (UHPC) girders outperforms that of conventionally reinforced high-strength concrete girders. However, the extremely high material and production cost of fiber-reinforced UHPC girders limits its applications. This paper presents the experimental and analytical investigations performed to evaluate the shear capacity and economics of using welded wire reinforcement (WWR) in place of random steel fibers in UHPC precast/prestressed I-girders. Two economical, practical, and nonproprietary UHPC mixtures that eliminate the use of steel fibers were developed and tested for their mechanical properties. Two full-scale precast/prestressed concrete girders were designed and fabricated using the developed mixtures and reinforced using orthogonal WWR. The shear testing of the two girders indicated that their average shear capacity exceeds that of comparable fiber-reinforced UHP girders while being 62% less in total material cost. In addition, the production of welded wire-reinforced UHPC girders complies with current industry practices, and eliminates handling, mixing, and consolidation challenges associated with the production of fiber-reinforced UHPC girders.

The effect of excessive debonding of prestressed strands can present a marked impact on the shear performance of prestressed concrete girders. This effect is taken into account by the AASHTO LRFD Specifications and the maximum percent of strand debonding is limited to 25% of the total number of strands. This paper presents field and experimental results demonstrating the effect of strand anchorage on the shear behavior of prestressed concrete girder. Two case studies presented and discussed in this paper show the effect of excessive strand debonding and proper strand anchorage on the shear performance of prestressed concrete girders. The shear behavior of the bridge girders under different load cases was predicted up to failure using nonlinear finite element analysis. The analysis accounts for the influence of strand debonding at the ends of the girders on the shear capacity. The applicability of the AASHTO bridge design specifications for the calculation of the nominal shear sectional capacity of prestressed girders with shielded strands is demonstrated. The interaction between shear and bond, and the favorable effects of strand anchorage on the shear capacity of the girders is highlighted.

Solid slabs supported directly on columns offer elegant solutions for short span bridges. For buildings, flat slabs are becoming more and more popular. Solid slabs are easy and economical to construct, and for buildings they offer ease of mechanical installations and maximum story height. The slab thickness is primarily governed by deflection/vibration limits or punching shear. The latter may lead to a very brittle and sudden type of failure that can be avoided by increasing the slab thickness, using high-strength concrete, or providing shear reinforcement. The most effective of these is shear reinforcement because it deals directly with the localized problem of punching and it also prevents brittle failure. The main challenges of shear reinforcement are the installation and the anchorage of the shear elements. These problems are most adequately solved by using headed studs mounted on rails. To investigate the effect of layout and the extent of the shear reinforcement on the punching shear resistance, six slab-column connections were tested at the University of Calgary. The tests showed that the strength of the connections and their ductility were significantly enhanced by shear stud reinforcement. They also demonstrated that the radial layout of the studrails as required by Eurocode 2 exhibited no advantage in performance over an orthogonal layout where the studrails were aligned with the orthogonal reinforcing mesh. This is the standard arrangement in North America. The latter is preferable because of the minimal interference with the non-prestressed or prestressed flexural reinforcement. In the present test series, maximum ductility was achieved by extending the shear reinforcement to 4d from the face of the column. Where the shear reinforcement was only extended to 2d from the face of the column, an increase in strength was recorded, but the mode of failure still had to be classified as brittle because the failure surface occurred outside the shear reinforced zone. Providing shear studs spaced at d/2 to a distance 2d from the column and spaced at d between 2d and 4d significantly increased the ductility of the connection. Ductile behavior is especially important for the performance of slab-column connections of bridges and buildings in seismically active zones.