Flexural Behavior Of High-strength Concrete Beams Research Articles

Evaluation of post-heating flexural behavior of steel fiber-reinforced high-strength concrete beams reinforced with FRP bars: Experimental and analytical results

Despite many advantages provided by fiber-reinforced polymer (FRP) bars, their low resistance against fire has been an important barrier for their widespread application in reinforced concrete (RC) members. Studying the post-fire performance of concrete structures reinforced with FRP bars can be beneficial in understanding the structural safety and estimating the serviceability conditions after a fire incident. Since little information is available in the literature in this regard, especially for high-strength concrete (HSC) and fiber-reinforced concrete (FRC), this research attempted to investigate the flexural behavior of HSC beams reinforced with glass fiber-reinforced polymer (GFRP) bar and steel fibers after exposure to elevated temperatures. The variables under consideration consisted of the applied temperature (20, 250, 400, and 600 °C), volume ratio of steel fibers (0 and 1%), and reinforcement ratio (0.314 and 0.872%). Following the quasi-static four-point flexural test on the heated and non-heated beam specimens, various parameters involving the load-carrying capacity, load-deflection relationship, cracking pattern in terms of the number and width of cracks at service and ultimate loads, and ductility of the beams were examined. It was found that exposing the beams to 250 °C reduced their load-carrying capacity negligibly and exposing them to 400 °C increased their residual load-carrying capacity notably while exposing them to 600 °C led to severe degradation in their flexural capacity. Further, the effectiveness of steel fibers on the behavior of beams with the lower reinforcement ratio was not significant; however, as the reinforcement ratio of the beams and applied temperature increased, steel fibers properly demonstrated their ability in improving the load-carrying capacity and reducing deflection at service load. By evaluating prediction relationships provided by codes and other researchers against the experimental results observed in this research, ACI 440.1R-06 and ACI 440.1R-15 codes were found to be able to predict deflection under service conditions with proper accuracy. Ultimately, for capturing the load-deflection relationship of heated and non-heated beam specimens, an analytical model was developed using the sectional analysis method, which was able to predict the experimental results appropriately.

THE VALIDITY OF EXISTING INTERNATIONAL DESIGN CODES IN PREDICTION OF MOMENT CAPACITIES OF HIGH-STRENGTH CONCRETE MEMBERS

The availability and advancement of material technology and the acceptance has led to the production of higher grades of concrete. High strength concrete (HSC) offers superior engineering properties i.e. compressive strength, tensile strength, durability, modulus of elasticity and overall better performance when compared to the conventional concrete. Due to its enhanced strength and improved structural properties, high strength concrete has been increasingly used for the past two decades. In this research, many published studies on the behavior of HSC beams have been discussed and analyzed. High strength concrete used in this study is defined as concrete with compressive strength exceeding 50MPa. Although there are many publications proposing stress block models for HSC beams, a universally accepted stress block model is yet to be developed. In most design standards, the conventional rectangular stress block developed for normal strength concrete (NSC) is still being used for design of HSC beams. In this paper, published work has been analyzed to establish some understanding of flexural behavior of HSC beams. Models proposed in various design codes and standards have been analyzed to compare the experimental and theoretical moment capacities. A number of spread sheets in Excel were developed using available data and various graphs were plotted to determine the accuracy of the code provisions for calculating the ultimate moment capacity of beams. Based on this, conclusions are drawn for the design of high strength concrete beams in flexure utilizing different code provisions.

Flexural behavior of high-strength concrete beams reinforced with a strain hardening cement-based composite layer

High-strength concrete (HSC) is often used in construction. High-strength concrete exhibits high compressive strength, but the flexural strength and cracking are problems for this material. Strain-hardening cement-based composites were recently developed as a repair material for improving crack control and flexural strength. This paper details the behavior of high-strength concrete beams reinforced with a strain hardening cement-based composite (SHCC) and steel fibers. A new method for improving concrete beam flexural behavior was explored by laying a layer of SHCC in the concrete beam in situ. The flexural behavior of HSC beams containing steel fibers was also studied using a high fiber content. Three types of beams were cast, and a series of tests were conducted. The flexural results indicated that the added SHCC layer increased the load-bearing capacity of the beams. Adding steel fibers significantly increased the load-bearing capacity of the beam.