| This paper analyses the existing problems of present concrete structure design theory based on the failure characteristics of reinforced concrete beams of different reinforcement properties and crack development in view of the basic principles of fracture mechanics.And then,a hybrid reinforced concrete structure reinforced by both ordinary steel and high-strength steel is advanced based on structure design method of crack development stages.On the basis of consistent reinforcement ratio,this paper conducts the experiments design and research of ordinary beam,high-strength reinforced concrete beam and hybrid reinforced concrete beams.It focuses on crack developing law influenced by reinforcement properties.Based on the detailed analysis of crack distribution pattern in every loading stage,four crack developing stages of every beam are summarized by crack developing law of pure bending section.Main conclusions are as follows:①The RC beams with different reinforcement properties are in accordance with the ductile failure characteristics of typical reinforced beams.The ultimate load of ordinary beam is 21.5T,while the ultimate loads of other three beams whose reinforcement ratio is 30%,50%and 100%reach 36.2T,41.5T and 57.0T.The three rates are improved by 68.4%,93.0%and 165.1%comparing to that of ordinary beam.②The RC beams of different reinforcement ratio enter the crack-stable stage under average load of 13.5T.At this time,ordinary beam reaches 62.8%of its ultimate load,which is of low safety stock.While the reinforcement ratios of other three types of RC beams reinforced by different high strength steel bars are respectively 37.3%,32.5%and 23.7%.Their stable stage is obviously longer than that of ordinary beam,and that of the hybrid reinforced concrete beam is moderate.③After ordinary beam entering crack-stable stage,the number and height of its cracks no longer increases significantly except its width.When the load of ordinary beam reaches 20.5T when its maximum width of cracks is 0.32mm,the beam enters its instable stage.After going through longer crack width-increasing section,other three RC beams with high strength steel reinforcement ratio enter the crack-instable period.The loads of those beams reinforced by different high strength steel bars are respectively 32.5T,38.5T and 56.5T,and the corresponding crack widths are respectively 1.16mm,1.10mm and 1.42mm.The concrete structure reinforced by high strength steel makes it work normally in bigger crack width.④The maximum height of cracks stabilizes under load around 13.5T.Ordinary beam is stable when the maximum height of cracks is between 0.7 to 0.8 times the heights of the reinforced beams.It will surpass this height in the crack-instable stage.But the maximum height of cracks of the other three RC beams stops at 0.8 times the height of ordinary beam.All those indicate that the concrete beam reinforced by high strength steel makes the concrete structures work normally under bigger height of cracks and could make the crack-instable stage much longer to go through loading.⑤The crack numbers of ordinary beams and reinforced beams with the reinforcement ratio of 30%,50%and 100%are respectively 33,43,46 and 50.The average widths of the cracks are 11.4cm,9.5cm,8.8cm and 8.1cm.Ordinary beam presents "sparse and wide" crack distribution pattern,while the RC beams with different high strength reinforcement ratios are "dense and narrow" crack distribution pattern.⑥The finite element numerical simulation to the test beams verifies the crack-distributional pattern,the load-midspan deflection curve and the crack-retarding mechanism effectively.In this paper,the crack developing law of hybrid reinforced concrete structure based on the structure design method of crack development stages is studied in detail by theory analysis,experimental research and finite element analysis.It provides a new direction for the application of high strength steel in reinforced concrete structure,the design of concrete structure and the control of crack development. |
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