Yoon-Keun Kwak

Prediction of Flexural Capacities of Steel-Fiber Reinforced Concrete Beams

The results of previous tests by many researchers have been compiled to evaluate the flexural strength of steel-fiber reinforced concrete beams. Existing prediction equations for flexural strength of such beams were examined, and a new equation based on mechanical and empirical observations, was proposed. In other words, the constitutive models for steel fiber reinforced concrete(SFRC) were proposed, which incorporate compressive and tensile strength. A steel model might also exhibit stain-hardening characteristics. Predictions based on the model are compared with the experimental data. For the collection of tests, a variation of the Henager equations, modified to apply to fiber-reinforced concrete beams, provided reliable estimates of flexural strength. The proposed equations accounted for the influence of fiber-volume fraction, fiber aspect ratio, concrete compressive strength and flexural steel reinforcement ratio. The proposed equations gave a good estimation for 129 flexural specimens evaluated.

Evaluation of flexural strength prediction of reinforced concrete beams with steel fibres

Abstract This paper presents experimental programme to investigate the effects of steel fibres on flexural strength of steel fibre-reinforced concrete (SFRC) beams and proposes a prediction model to evaluate flexural strength of beams which is their main contribution to literature. Four point bending test was carried out on the 11 SFRC beams which are 6 normal-strength SFRC beams and 5 high-strength SFRC beams. The variables studied in the investigation were steel fibre volume fractions (0, 0.75 and 1.50%), flexural reinforcement ratios (1.0 and 2.0%), and concrete compressive strengths (28 and 56 MPa). The test results confirmed that ultimate flexural strength increased with increasing fibre volume contents. The constitutive model for SFRC was proposed, which incorporated strength of fibre-reinforced concrete and strain-hardening of tensile reinforcement. Predictions of moment–curvature relationship based on the model matched well with the experimental data. The results of previously reported tests were combined with the results of new tests to document observed flexural failures of 129 SFRC beams. A simplified, empirical design equation to determine the flexural strength of SFRC beam was proposed and compared with existing equations. The analysis indicated that the proposed equation provided the most accurate estimates of flexural strength.

A Study on the Shear Behavior of Recycled Aggregate Reinforced Concrete Beams without Stirrups

Dept. of Architecture and Architectural Engineering, Seoul National University, Seoul 151-744, KoreaABSTRACT Little investigations have been carried out to study the shear behaviors of RC beams with recycled aggregates. So, this experiment investigates the shear performance and suggests the possible application of Recycled Concrete Aggregate (RCA) for building structures. In general, shear strength of reinforced concrete beam without stirrups is dependent on the compressive st rength of concrete, the longitudinal steel ratio, and the shear span-to-depth ratio. In this study, total 28 recycled aggregate concrete beams without shear reinforcement were tested by two-point load and all beams were singly reinforced. The variables studied in this investigation are shear span-to-depth ratios ( a/d=2, 3 and 4), RCA replacement ratios (0, 15, 30 and 50%) and longitudinal steel ratios (0.80, 1.27 and 1.84%). The designed concrete compressive strength with a 30 MPa is used. This research will play an important r ole toward the establishment of the structural design standard for RCA concrete.Keywords : recycled concrete aggregate (RCA), construction waste, recycling, shear strength

Behavior of Steel Fiber-Reinforced Concrete Exterior Connections under Cyclic Loads

Beam-column gravity or Intermediate Moment frames subjected to unexpected large displacements are vulnerable when no seismic details are provided, which is typical. Conversely, economic efficiency of those frames is decreased if unnecessary special detailing is applied as the beam and column size becomes quite large and steel congestion is caused by joint transverse reinforcement in beam-column connections. Moderate seismic design is used in Korea for beam-column connections of buildings with structural walls, which are to be destroyed when the unexpected large earthquake occurs. Nonetheless, performance of such beamcolumn connections may be substantially improved by the addition of steel fibers. This study was conducted to investigate the effect of steel fibers in reinforced concrete exterior beam-column connections and possibility for the replacement of some joint transverse reinforcement. Ten half-scale beam-column connections with non-seismic details were tested under cyclic loads with two cycles at each drift up to 19 cycles. Main test parameters used were the volume ratio of steel fibers (0%, 1%, 1.5%) and joint transverse reinforcement amount. The test results show that maximum capacity, energy dissipation capacity, shear strength and bond condition are improved with the application of steel fibers to substitute transverse reinforcement of beam-column connections. Furthermore, several shear strength equations for exterior connections were examined, including the proposed equation for steel fiber-reinforced concrete exterior connections with non-seismic details.

An Experimental Study on the Size Effect of Reinforced Concrete Beams without Stirrups Using Recycled Coarse Aggregates

The authors examined the size effect of reinforced concrete(RC) beams using natural coarse aggregates and recycled coarse aggregates. The specimens were made of concrete with a maximum coarse aggregate size of 20 mm. In this study, depth-to-width ratio, shear span-to-depth ratio, tension steel ratio and RCA replacement ratio were fixed 1.5(i.e., h/b=1.5), 3(i.e., a/d=3), 1.2%(i.e., ) and 30%(i.e., ) respectively. The test variables only include the RC beam size and aggregate type. A total of 10 simple RC beams were tested under four points loading. It has been shown that shear strength decreases as member size increases. This is associated with a phenomenon called size effect. However, the size of the RC beams does not seem to affect the shear strength proportionally. Besides, test results were analyzed and then compared with the findings and various shear design equations. To conclude, the shear equations reflect relatively well with most of experimental data.