This paper presents an analysis of reinforced concrete deep beams tested to failure. A nonlinear strut-tie model approach implemented with an interactive computer graphics program was utilized to evaluate the behavior and strength of the beams. Different types of strut-tie models for the beams were developed based on the compressive principal stress trajectories, actual specimen detailing, and loading and support conditions. It was shown that the proposed nonlinear strut-tie model approach in the present study could provide simple and effective solutions for a large number of analysis situations by describing the essential aspects of structural behavior and predicting the strength of structural concrete. It also allows for the conceptual representation of the complex interactions of concrete and reinforcing steel, and permits the study of localized effects through the nodal zone concept. The framework provided by this nonlinear strut-tie model approach for handling combined actions across the entire range of structural concrete is a strong endorsement for its use with structural concrete deep beams.

Experimental results of the bond behavior of 10, 13, 19, and 25-mm diameter bars corroded to various levels are presented. A total of forty specimens were tested to obtain the bond - slip behavior. The corrosion level ranged from 0 to 4.79 percent diameter loss. Externally applied current was used to induce controlled amount of corrosion. The results were analyzed to study the influence of bar diameter and corrosion level on bond strength, slip at peak load, and overall bond - slip behavior. The results indicate that exponential reduction in bond strength occurs once the diameter loss exceeds a fraction of a millimeter. At a diameter loss of O.l-mm, the strength reductions are substantial. The reduction in slip at maximum load is even more significant with corrosion. The actual magnitude of corrosion can be predicted using the applied current input with reasonable accuracy.

The objective of this research was’ to investigate the strength and serviceability, viz cracking behaviour and flexural stiffnesses, of structurally damaged reinforced concrete beams strengthened in flexure by incorporating thin ferrocement laminates reinforced with additional longitudinal bars onto the soffits (tension face) tested under quasi-static and cyclic loadings. Results from seven test beams are discussed. The beams were fabricated and precracked under quasi-static mid-span loading to three levels of damage: 1) flexural failure with crushing of concrete and yielding of tension reinforcements viz 115%, 2) 100% and 3) 90% of their respective theoretical flexural capacities. They were then repaired and strengthened after unloading. Four of the strengthened beams were tested to failure under quasi-static loading while the remaining three were subjected to cyclic sinusoidal loads up to 150,000 cycles. It was found that, under quasi-static loading, the structurally damaged and then repaired and strengthened beams exhibited improved performance compared to their behaviour during the precracking stage. Their performance was comparable to a control beam strengthened in its virgin state showing only marginally larger reopened crack widths. Under cyclic loading however, the presence of a distinct ferrocement/concrete interface at the soffit of the beams resulted in cracking at the interface under repeated loading of high load levels.

This paper presents results of an investigation into the tension stiffening effects of steel fiber reinforced concrete members in direct tension. Tension stiffening effects and losses of strain energy were analyzed from the load-defl .ection curves with the main experimental variables such as concrete strength, steel fiber content, and concrete cover depth. Tension stiffening effect of RC members increases linearly until first crack, decreases inversely with number of cracks, and then decrease rapidly when splitting cracks occur. The higher the content of steel fiber the higher tension the stiffening due to its bridging effect after cracking inside of member. Therefore, it is necessary to consider the tension stiffening effects with a nonlinear analysis. From the comparison between the results of experiment and existing models, it is found that the existing models could not incorporate the effects of concrete strength, cover depth and fiber reinforcement. Thus, it is required to develope a new model which could include these factors. This study proposes a new model which is defined by tension stiffening factor by considering concrete strength. and the ratio of cover depth with al and a2, respectively. The tension stiffening model for steel fiber reinforced concrete is, also, proposed as a shape of u-i-bilinear, considering concrete cover. depth. The analysis using the proposed model shows good agreement with that of experiment on direct tension and flexural members at all concrete strength levels.

This paper describes a nondestructive method to evaluate two-dimensional size and depth of interfacial flaws between concrete members and the enclosing steel plate by the infrared thermographic technique. In this procedure, in order to investigate the influence of a defect in a thermography, liquid nitrogen was used to cool the surface of the steel plate. Its thermal distribution was measured. From these measurements, it was possible to estimate the diameter of circular defects from the calculated inflection points in the thermal distribution curve. The process to evaluate the depth of the flaws by using the relation betweenthe volume tof the flaws and proposed thermal parameters is also presented.