Research On Bending Performance And Improved Design Of Partially Prefabricated Castellated Steel Reinforced Concrete Beams

With the advantages of excellent seismic performance and good fire resistance,the traditional steel reinforced concrete beam has been widely used in large-span structures and super high-rise buildings.However,complicated construction process and low bond strength between solid steel and concrete limit its promotion and application.Partially prefabricated steel reinforced concrete beams apply prefabricated technology to the steel reinforced concrete structures with outstanding performance.It has a broad development prospect owing to the advantages of convenient construction,environmental protection,good seismic performance and high bearing capacity.In order to solve the problem of poor bonding between traditional solid web-steel and concrete,solid web-steel is replaced with castellated steel to form the partially prefabricated castellated steel reinforced concrete beam.The bending performance is thoroughly studied,and the results have important theoretical application value.The main research contents and conclusions of this paper are as follows:(1)The finite element software ABAQUS was used to establish the scale model of three partially prefabricated castellated steel reinforced concrete beams.Then the failure mode,stress distribution and load-deflection curve were analyzed,which were consistent with the test results and verified the correctness and reliability of the modeling analysis.(2)A full-scale refinement model of partially prefabricated castellated steel reinforced concrete beam was established,and numerical analysis was implemented to analyze the whole process from the aspects of crack development,failure morphology,stress distribution and load-deflection curve.The results show that the failure process of the beam is divided into three stages: uncracked,working with cracks,and steel yielding to section failure.Different from ordinary reinforced concrete beams,its stiffness does not decrease significantly at the cracking and yielding stages.Meanwhile,a similar-sized model of fully cast-in-place castellated steel reinforced concrete beam was established.The analysis and comparison results indicate that the ultimate bearing capacity of partially prefabricated castellated steel reinforced concrete beam was only about 5.1% lower than that of full cast-in-place beam.No obvious change was observed in load-deflection curve,ductility,crack development and failure modes,indicating the good performance of partially prefabricated castellated steel reinforced concrete beams.(3)Based on the parameters of material strength(concrete strength and castellated steel strength),span-to-height ratio,flange width,castellated steel opening form,castellated steel opening ratio,etc.,46 models of partially prefabricated castellated steel reinforced concrete beams were established to study the variation law of the bending performance.The results show that castellated steel strength,span-to-height ratio and castellated steel opening ratio are important factors influencing the bending performance of partially prefabricated castellated steel reinforced concrete beams.In addition,a reasonable matching scheme for the strength grades of different concretes and steels in the beams was given,and the span-to-height ratio of the beams was recommended to be 12-18.(4)In order to facilitate the construction,an improved design scheme was proposed for partially prefabricated castellated steel reinforced concrete beams combined with the composite beam-slab structure.Moreover,the structural design and installation process were discussed.The finite element analysis results of the improved partially prefabricated castellated steel reinforced concrete beams show that the bearing capacity of the beams was only decreased by 3.8%-6.5%,and the bending performance was still good.(5)Based on the theory of plasticity,the formula for calculating bending capacity of the improved partially prefabricated castellated steel reinforced concrete beams was deduced for numerical examples.The results show that the maximum error between calculated value and the simulated value is only 8.7%,which has reference significance for practical engineering.