Research On The Influence Of Reinforcement Properties On Loading Capacity Of Reinforced Concrete Beams

This paper,based on the structure design method of crack developing stages,proposes a hybrid reinforced concrete structure reinforced by both high strength and ordinary steel bars by replacing the ordinary steel bars in tension in traditional concrete beams with high strength steel bars of which the tensile strength is 2.76 times comparing with that of ordinary steel bars..The paper designs two different groups of hybrid reinforced concrete beams with different area ratio between the area of high strength steel bars and that of ordinary steel bars as well as comparison groups of reinforced concrete beams reinforced by high strength or ordinary steel bars separately.The paper conducts a comparative analysis on the developing laws of cracks through experiments and the influence of the steel bars' characteristics under different crack developing stages to the bearing capacity of the concrete beams,as well as the bearing capacity of those beams designed based on the structure design method of crack developing stages.The following conclusions have been obtained:? Based on the condition that the reinforced concrete bending components meets plane cross-section assumption,allowable strain method and the internal force equilibrium when failure are adopted to deduce the calculation formulas of the cracking load and ultimate load of concrete beam reinforced by steel bars with the similar or different characteristics with different arrangements under three-point loading.The theoretical calculated values of the cracking load and ultimate load agree with those obtained by experiments or finite elemental analysis.? With similar reinforcement ratio,the ultimate load of ordinary reinforced concrete beams(without high strength steel bars),type-1 hybrid reinforced concrete beams(reinforced by high strength steel bars with the area ratio of 29.00%),type-2 hybrid reinforced concrete beams(reinforced by high strength steel bars with the area ratio of 50.47%)and hybrid reinforced concrete beams(fully reinforced by high strength steel bars)are respectively 21.15t,36.2t,41.5t,and 57.Ot.Comparing to that of ordinary reinforced concrete beams,the ultimate load of the latter three are improved by 68.4%,93.0%and 165.1%respectively.It shows that high strength steel bars significantly improved the ultimate bearing capacity of the concrete beams.?The ratios between the loads at the stable crack developing stage and ultimate load of ordinary reinforced concrete beams,Type-1,Type-2 and hybrid reinforced concrete beams fully reinforced by high strength steel bars are respectively 58.14%,34.53%,34.93%and 25.44%,comparing with the former,the latter three are of longer cracking stable stage.? Comparing with ordinary reinforced concrete beams and reinforced concrete beams fully reinforced by high strength steel bars,the hybrid reinforcement concrete beams designed based on the structure design method of crack developing stages are of moderate cracking stable stage,which is much longer than that of ordinary reinforced concrete beams and much shorter than that of hybrid reinforced concrete beams fully reinforced by high strength steel bars.During the adjustable stable cracking stage,hybrid reinforced concrete beams experience four states from loading to its failure in sectional stiffness,namely elastic state,stiffness stable state,stiffness reducing state and stiffness failure state.? The strength of steel bars in ordinary reinforced concrete beams,when the beams arrive at the cracking stable stage,is mostly employed,with little residual strength.Those of steel bars in hybrid reinforced concrete beams and reinforced concrete beams fully reinforced by high strength steel bars are with huge residual strengths and strength reserve.When the ordinary steel bars in hybrid reinforced concrete beams yield,the high strength steel bars are still in its elastic stage.And the high strength steel bars can restrain the "unrestricted"deformation of ordinary steel bars and improve the ductility of the structure.? The sectional stiffness of all the test beams under cycling loading is lower than that of the beams before crack but higher than that of the beams under one-time loading,and the stiffness when loading and unloading within the same load range remains unchanged,which indicates that almost no new plastic deformation has emerged during the cycling loading process of the test beams.