International Concrete Abstracts Portal

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.

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.

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.

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.