James K. Wight

Shear Behavior of Steel Fiber Reinforced Concrete Beams without Stirrup Reinforcement.

This paper investigates the behavior of steel fiber-reinforced concrete (SFRC) beams in shear, as well as the possibility of using steel fibers as minimum shear reinforcement. In the study, 28 simply supported beams with a shear span-to-effective depth ratio of approximately 3.5 were subjected to a monotonically increased, concentrated load. The target concrete compressive strength for all of the beams was 41 MPa (6000 psi). The studied parameters included beam depth, fiber length, fiber aspect ratio, fiber strength, and fiber volume fraction. Three types of steel fibers were considered, all with hooks at their ends. The behavior of beams failing in shear prior to or after flexural yielding was also investigated by varying the longitudinal reinforcement ratio. Compared to reinforced concrete (RC) beams without stirrup reinforcement, the use of hooked steel fibers in a volume fraction greater than or equal to 0.75% led to an enhanced inclined cracking pattern and a substantial increase in shear strength.

Experimental study on seismic behavior of high-performance fiber-reinforced cement composite coupling beams

Current design provisions in the ACI Building Code for reinforced concrete (RC) coupling beams in earthquake-resistant structures require substantial reinforcement detailing to ensure a stable seismic behavior, leading toreinforcement congestion and construction difficulties. As a design alternative, the use of high-performance fiber-reinforced cementitious composites (HPFRCCs) in coupling beams with a simplified reinforcement detailing was experimentally investigated. To validate this alternative, four coupling beam specimens were tested, including an RC control specimen detailed as per the 1999 ACI Building Code. A precast construction process was proposed for the HPFRCC coupling beams in this study. This construction alternative would lead to significant savings in time and workmanship at the job site, and provide good material quality control. Results from large-scale tests demonstrated the superior damage tolerance and stiffness retention capacity of HPFRCC coupling beams. It was also observed that diagonal reinforcement is necessary to achieve large displacement capacity. However, the transverse reinforcement around the diagonal bars was successfully eliminated due to the confinement provided by the HPFRCC material.

Unified Shear Strength Model for Reinforced Concrete Beams—Part I: Development

This paper describes the development of a theoretical model to predict the shear strength of reinforced concrete beams with and without shear reinforcement. It was assumed that the shear strength of concrete beams can be determined from the failure of the compression zone of a beam cross section. The shear strength of the compression zone was evaluated, considering the interaction between the shear strength and normal stresses developed by the flexural moment. The failure mechanism of the compression zone changes from a tension failure to a compression failure as the shear span-to-depth ratio decreases. The transition of the failure mechanism was properly addressed by considering the geometry of the beam and using material failure criteria of concrete. The proposed strength model can describe the failure mechanisms of both slender beams and deep beams with and without shear reinforcement. This model is verified and further discussed in a companion paper.

Strain-based shear strength model for slender beams without web reinforcement

In this paper, a theoretical model is developed that addresses the effect of flexural deformation on a beam. The model is used to predict the shear strength of slender reinforced concrete beams without shear reinforcement. The shear force applied to a cross section of the beam was assumed to be resisted primarily by the compression zone of intact concrete rather than by the tension zone. The shear capacity of the cross section was defined based on the material failure criteria of concrete: failure controlled by compression and failure controlled by tension. Interaction with the normal stresses developed by the flexural moment in the cross section was considered in the evaluation of the shear capacity. The shear capacity of the beam was defined as a function of the flexural deformation because the magnitude and distribution of the normal stresses vary due to the flexural deformation of the beam. The shear strength of the beam and the location of the critical section were determined at the intersection between the shear capacity and the shear demand curves. Results from this model were compared to previous test results on simply supported beams to verify the proposed model.

Shear Strength of Steel Fiber-Reinforced Concrete Beams without Web Reinforcement

This work was supported by the Post-Doctoral Fellowship Program of the Korea Research Foundation (KRF).

Strength of Struts in Deep Concrete Members Designed Using Strut-and-Tie Method

Results from an experimental investigation aimed at evaluating the adequacy of the strength factors for concrete struts in strut-and-tie models given in Appendix A of the 2002 ACI Building Code are presented. The main design variables considered were: the angle between primary strut-and-tie axes, amount of reinforcement crossing the strut, and concrete strength. A total of 12 deep beams were tested, eight with normal strength concrete and four with high-strength concrete. The ratio between experimentally obtained failure loads and the strengths predicted using the strut strength factors given in Appendix A of the ACI Code ranged between 1.00 and 1.22, and between 0.91 and 1.02 for normal and high-strength concrete beams, respectively. Inconsistencies were found in the provisions for minimum reinforcement crossing a strut in Sections A.3.3 and A.3.3.1 when applied to the test specimens, with the former leading to substantially larger reinforcement ratios. The use of a strut strength factor β s = 0.60 in high-strength concrete bottle-shaped struts without web reinforcement led to strength predictions approximately 10% higher than the experimental failure loads. The limited test results suggest that, as a minimum, an effective reinforcement ratio of 0.01, calculated according to ACI Code, Section A.3.3.1, should be provided in high-strength concrete members when a strength factor β S = 0.60 is used. Additional test data, however, are required before a definite recommendation can be made in this regard.

Wide Beam‐Column Connections under Earthquake‐Type Loading

Wide beam-column connections, whose beams are wider than their supporting columns, are often found in one-way concrete joist systems and in other buildings where floor-to-ceiling heights are restricted. Research into the seismic behavior of these connections stems from the recommendation by ACI-ASCE Committee 352 (Monolithic Connections in R/C Framed Structures) that these connections be evaluated for use in high seismic zones. Four exterior 3/4-scale specimens, including transverse beam with reinforcement, were tested at the University of Michigan Structural Engineering Laboratory. The effects of joint shear stress level, fraction of beam longitudinal reinforcement anchored in the column core, and beam-width to column-width ratios (b w /b c ) were explored as part of this research. The experiments show that wide beam-column connections can be used in high seismic zones if they are detailed correctly. If they are not detailed correctly, the exterior connections will be incapable of transferring the plastic hinge bending moments to the column because the transverse beam cracks in torsion. To prevent this cracking of the transverse beam, limits on the torque applied to the transverse beam are proposed.

Shear Strength Model for Steel Fiber Reinforced Concrete Beams without Stirrup Reinforcement

A simple model is presented to estimate the shear strength of steel fiber reinforced concrete (FRC) beams without stirrup reinforcement. The model was developed on the basis of observations from tests of 27 large-scale beams under monotonically increased concentrated loading. Three types of hooked steel fibers were evaluated in volume fractions ranging between 0.75% (59  kg/m3 or 100  lb/yd3) and 1.5% (118  kg/m3 or 200  lb/yd3). All but one beam failed in shear either prior to or after flexural yielding. In the proposed model, shear in steel FRC beams is assumed to be resisted by shear stress carried in the compression zone and tension transferred across diagonal cracks by steel fibers. Shear carried in the compression zone is estimated by using the failure criterion for concrete subjected to combined compression and shear proposed by Bresler and Pister. The contribution from fiber reinforcement to shear strength, on the other hand, is tied to material performance obtained through standard ASTM 1609 four...

Reinforced concrete wide-beam construction vs. conventional construction: Resistance to lateral earthquake loads

Experiments and analyses were conducted to address concerns about performance of reinforced concrete connections with shallow, wide beams subjected to lateral earthquake loading and to compare behavior of wide beam connections to that of conventional connections. Two wide beam-column-slab connections and one conventional beam-column-slab connection were subjected to cycles of reversing lateral displacements up to 5% drift. The conventional beam and wide beam connections exhibited similar overall load-displacement behavior, with similar beam plastic hinge development. The wide beam connections dissipated almost as much energy as the conventional beam connection and had greater slab participation and less joint and beam shear cracking than the conventional beam connection. Experimentally determined wide beam connection stiffness was closer to the conventional beam connection stiffness than had been predicted. Refined models were developed, with features such as rigid end offsets for wide beam connections, to better represent observed behavior. Nonlinear models were also developed that accurately captured differences in energy dissipation as well as stiffness.

Experimental Investigation on Seismic Behavior of Eccentric Reinforced Concrete Beam-Column-Slab Connections

This paper seeks to supplement existing information on the seismic behavior of eccentric connections by presenting an experimental study that focused on the effect of eccentricity of spandrel beams with respect to the column. Specimens included a floor slab and transverse beams to evaluate the effect of slab participation. Test results indicated that including the floor system significantly reduced the negative influence of eccentricity. Damage was reduced, specimens had fuller load-versus-drift hysteresis loops with high energy dissipation capacities, and deterioration of joint shear stiffness and strength were delayed. The joint shear stresses resisted by the connections, without major damage, also were higher than current design values due to the participation of a larger area of the joint region in resisting shear. These findings indicate that current ACI-ASCE recommendations for effective joint width of beam-column connections in monolithic reinforced concrete structures are conservative. Since joint shear distortions contributed significantly to the total story drift for all subassemblies, accurately predicting drift demands requires a joint model that accounts for the inelastic deformations in the beam-column connections.