Research On The Loading Capacity And Strengthening Properties Of Hybrid Reinforced Concrete Beams

Hybrid reinforced concrete beam is a new type of reinforced concrete structure,whose principal tensile steel bars are composed of both high strength and ordinary steel bars. In the hybrid reinforced concrete beam tested in the paper, the yield strength of the high strength steel bars is 2.76 times of that of ordinary bars, and by using the method of reinforcement by crack filling under a sustained load, the bearing capacities of the hybrid beam before and after the reinforcement were studied, with the contents and conclusions being as follows:① Compared with that of ordinary reinforced concrete beams with same reinforcement ratio, the ultimate bearing capacity of hybrid beams was substantially improved. Experiment showed that the ultimate bearing capacity of an ordinary reinforced concrete beam was only 21.00 T, while that of a hybrid beam was 35.50 T.However, the defect of large plastic deformation exists in hybrid beams. If unloading on the beams after loading to the ultimate load, the mid-span plastic displacements of the hybrid beam and ordinary beam were 26.15 mm and 5.78 mm respectively.② After reinforcement by crack filling under different sustained loads, and then reloading on the beams until the sustained loads, the hybrid beam did not crack, and structural stiffness was substantially improved.1) The hybrid beam was reinforced by filling under the sustained loads when the moments of the beam at its pure bending section were 50%, 70% and 100% of Mu respectively, and the corresponding loads are 15.62 T, 25.72 T and 38.13 T. After reinforcement, the cracking load of the beam when reloading were 16.00 T, 27.00 T and40.50 T respectively. Compared with those before reinforcement, the cracking loads of the beam after reinforcement were improved by 2.43%, 4.98% and 6.22% respectively.2) The hybrid beam was reinforced by filling under the sustained loads when the moments of the beam at its pure bending section were 50%, 70% and 100% of Mu respectively, and the gradients of the load within the elastic loading section versus mid-span displacement curves of the beam before reinforcement were 2.33T/mm,2.54T/mm and 2.18T/mm respectively; those of the beam after reinforcement were6.35T/mm, 5.22T/mm and 5.49T/mm; and the structural stiffnesses of the hybrid beam was improved by 172.53%, 105.51% and 151.83% respectively after the reinforcement.③ Another hybrid beam was loaded until its ultimate state by one time and thenreinforced by filling under sustained load. In this case, the ultimate bearing capacity of the hybrid beam can be retained and the beam did not crack under the sustain load with no plastic displacement, and the structural stiffness of the hybrid beam was substantially improved. The ultimate loads of the beam before and after the reinforcement were35.50 T and 36.50 T respectively. The cracking load is 35.00 T after the reinforcement under the sustained load(33.84T) of about the ultimate load. The gradients of the load within the elastic loading section versus mid-span displacement curves of the beam before and after the reinforcement were 2.16T/mm and 7.17T/mm respectively. After the reinforcement by filling under a sustained load, the ultimate load of the hybrid beam was improved by 2.82%, its cracking load improved by 3.43% and its structural stiffness improved by 231.94%.④ After reinforcement of the hybrid beam by filling under the sustained loads when the moment of the beam at its pure bending section was 50% of Mu, by changing the loading points to achieve worse load bearing situation at an oblique section, the oblique section of the hybrid beam did not crack under the load which is below the sustained load, proving that the reinforcement by crack filling under a sustained load can enhance not only the normal section performances, but also the oblique section performances of the beam.