Mechanical Behaviors Of T-shaped RC Beams With Large Circular Openings In The Shear Zone And Researches On The Ones Strengthened With Steel Plates

The openings of RC beams in existing buildings,which make equipment pipes and other facilities pass through,could avoid the occupation of the head room.As a result,economic benefits could be achieved.However,the influence of the openings on the shear capacity of RC beams and the working performance should not be ignored.Based on the problems encountered in the engineering practice,the experimental researches and analysis,as well as the researches of reinforcement method using steel plates were carried out on the mechanical behavior of the T-shaped RC beams with large circular openings in the shear zone under concentrated loads.First of all,based on the technical problems of the existing RC beams with openings in practical engineering,three T-shaped test beams have been designed.Such test beams were further divided into five test areas(one test area without any openings,two test areas with large circular openings in the shear zone,two strengthening test areas with large circular openings within their shear zones.).The main influence parameter in experimental study was the opening size(the ratios of opening diameter to beam height were 0.4 and 0.5 respectively).The test results revealed that,as a result of the openings,the shear strength decline of the T-shaped RC beams was about 40%.The failure of the T-shaped RC beams with large circular openings in the shear zone occurred in the upper and lower chords.The reinforcement method proposed in this paper could increases the shear strength of the specimens with large openings within their shear zones.by more than 36%,and the ductility of the strengthening specimens was also extended.The shear strength specimens with an opening in 160 mm diameter was greater than that with an opening in 200 mm diameter,whether it is a specimen with an opening or a strengthening one.Furthermore,a finite element model was established and the results of this were compared with the experimental results.The rationality of the finite element model was verified from the 2 aspects which were the shear-deflection curve and the shear-strain curve of the stirrup around the opening.Based on the finite element model,the opening size and the opening position of the T-shaped RC beams were analyzed.The analysis results showed that the shear strength of the specimens increased slightly when the opening position was close to the support or the loading point,but the ductility of the specimens was weakened.The size of the openings has great influence on the shear strength of the specimens,the larger the opening is,the weaker the shear strength of the specimens is.Finally,based on the experimental results above and combining with the theoretical analysis,the formulas for calculating the shear strength of the T-shaped RC beams and the strengthening ones with large circular openings in the shear zone were given respectively.The accuracy of the proposed formulas was verified respectively by comparing the experimental value with the theoretical value,and the formulas proposed in this paper could be used to guide the reinforcement design of this kind in engineering practice.