The Effect of Steel Fibers and Compressive Reinforcement on the Plastic Rotation Capacity and Properties of Reinforced Concrete Continuous Beams

A reinforced concrete structure must satisfy adequate strength at ultimate load stage and serviceability at service load, and it must meet the ductility requirements. Unfortunately reinforced concrete, unlike steel, tends to fail in a relatively brittle manner due to its limited ductility, which has led to a limitation in steel quantities to be used by the ACI Code. An over-reinforced concrete section will fail by crushing of concrete before the yielding of steel, whereas in under-reinforced section the steel will yield before the crushing of concrete. Ductility plays a significant role in structures, especially those built in seismic zones or those subjected to blast or suddenly applied loads. Numerous investigations have dealt with. ductility in reinforced concrete structures, thus leading to improved economy, and sometimes to simplified design procedures. New design concepts have been developed, especially the use of the limit state design concept, which relies heavily on the inelastic behavior of reinforced concrete. For the limit state design concept to be valid, a concrete structure must have adequate rotation capacity that exceeds what is required by the plastic hinges. Plastic hinge rotation depends primarily on concrete compression failure. A low compressive strain in concrete will reduce the degree of moment redistribution; therefore, a collapse mechanism will develop without reaching the ultimate load capacity, unless the ultimate strain can be increased in some way, as adding fibers to the concrete mix