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 two-dimensional design and behavior of typical reinforced concrete (RC) structures has been extensively studied in the past several decades. Such design requires knowledge of the constitutive behavior of reinforced concrete elements subjected to a biaxial state of stress. These constitutive models were accurately derived from experimental test data on representative reinforced concrete panel elements. The true behavior of many large complex structures, however, requires knowledge of the constitutive laws of RC elements subjected to a triaxial state of stress. The goal of the proposed work is to develop new constitutive relations for RC elements subjected to a triaxial state of stress. To accomplish this task, largescale tests on representative concrete panels need to be conducted. The University of Houston is equipped with a unique universal panel testing machine that was used for this purpose. This universal panel tester is the only one of its kind in the United States, and the only one in the world that allows for both displacement and forcecontrolled load application through its newly upgraded servo-control system. The panel tester enhanced the understanding of the in-plane shear behavior of reinforced concrete elements. Recently, 20 additional hydraulic cylinders were mounted in the out-of-plane direction of the universal panel tester to facilitate testing of concrete elements subjected to tridirectional shear stresses. The addition of these cylinders makes the panel tester the only one of its kind in the world that is capable of applying such combinations of stresses on full-scale reinforced concrete elements. This paper presents the details of the mounting and installation of the additional hydraulic cylinders on the universal panel tester, and preliminary results of large-scale tests of a series of RC panels subjected to three-dimensional shear loads.

Reinforced concrete (RC) bridge columns are subjected to combined flexural, axial, shear, and torsional loading during earthquake excitations. This combination of loading can result in complex flexural and shear failure. The work presented herein included an experimental study conducted to understand the behavior of RC circular columns under combined loading. The main variables considered are the ratio of torsion to bending moment, and the level of detailing for high and moderate seismicity (low or high spiral reinforcement ratio). This paper presents the results of tests on eight reinforced concrete columns subjected to cyclic bending shear, cyclic pure torsion, and various levels of combined cyclic bending and torsional moments. It discusses the effects of combined loading on the hysteretic lateral load-deformation response, torsional moment-twist response, reinforcement strain variations, and plastic hinge characteristics. It also includes diagrams of interaction between bending and torsional moment. In addition, the results of this study highlight the significance of proper detailing of transverse reinforcement and its effect on torsional resistance under combined loading. Test results demonstrate that combined loading decreases both flexural and torsional capacity. Further, they show a significant improvement in the performance of columns with an increase in the spiral reinforcement ratio.

There are two basic assumptions for the shear force Vc in ACI 318-02: 1) Vc is the shear force at cracking; and 2) Vc is the same for members with and without shear reinforcement. By reviewing tests, it is shown that neither assumption is valid. Therefore, different terms have to be defined for the concrete contribution Vct of the shear capacity for members without shear reinforcement and Vc for members with stirrups. The size effect has to be considered for Vct for members without shear reinforcement, but plays a minor role for Vc for members with stirrups. Chapter 4, "Truss model versus Vc-term" shows that there is a clear relationship between the angle q of the inclined struts and a Vc-term. A more realistic model for the state of stress in the web, however, is described by the "truss model with crack friction," where the crack angle is different from the strut angle or angle of principal compression. There, the term Vc has a clear mechanical meaning as the vertical component Vf of friction forces along the inclined crack. In the web, an inclined biaxial tension-compression-field exists, so that the usual truss model is superimposed with a truss model with inclined concrete ties. Because the crack angles are considered, the shear design for prestressed concrete beams leads to a lower value for the angle q and less amount of stirrups than that for reinforced concrete beams.

Two-way flat slabs are extensively used in many structures, such as buildings, shopping centers, and parking garages, because their static efficiency allows to attain large span-depth ratios and to have more spaced columns. The reduction of the thickness, however, is limited by serviceability requirements (resulting from deflection criteria) and by the ultimate limit state of punching shear. This collapse mode has been widely studied in the past, with reference to ordinary conditions, but very limited attention has been devoted to the punching resistance of flat slabs in fire conditions, an issue which is of primary concern, especially in the case of parking garages. This paper deals with two key aspects of slab punching in fire conditions. The first is the sizable reduction of the punching resistance in a typical slab-column assembly, because of the thermally induced damage caused by the exposure to the fire, that is modeled by means of the temperature-time curve ISO-834 (that fits very well the points given by ASTM E119-08a. The second is the sizable load increase due to the redistribution of the internal forces ensuing from the fire that is modeled through a realistic fire scenario based on the available information coming from real car fires. Even if these two phenomena do not necessarily occur simultaneously in a real fire, they both testify to what extent punching shear can be critical for reinforced concrete slabs in fire.