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Coincident deformation between concrete and steel is of great importance in thereinforced concrete structure, however, lower ultimate strain of cement concrete make ithard to coincide the corporate deformation between concrete and steel, it is moreenergetic and innovative to replace concrete closing to reinforcement cover withpolymer-modified cement concrete with better ultimate strain and higher bendingstrength. The author suggests a polymer-modified cement concrete composite beambase on above judgments.In view of fundamental of coincident deformation, this paper combines knowledgeof fracture mechanics, summarizes mechanical properties of common beam, bringsforward mentality of composite beam. Basing on this mentality, the author derivativesthe calculation formula of polymer-modified cement concrete composite beam,experimentally study the mechanical properties of polymer-modified cement concreteand polymer-modified cement concrete composite beam, compares the test results withcommon cement concrete and common beam, founds models of common concrete beamand composite beam, calculates the model and makes the analysis at the last.Synthesized the relevant results, conclusions can be drawn as follows:①Prior to cracking, the rigidity of common beam is very large, the rigiditydepression of polymer-modified cement concrete composite beam is lower thancommon beam; After cracking, the rigidity of common beam has a sensible falling,however, the rigidity of polymer-modified cement concrete composite beam falls gently.The rigidity of common beam is markedly lower than composite beam. The ductility ofcomposite beam has a striking advantage over common beam.②Compared with common concrete beam, the crack load of polymer-modifiedcement concrete composite beam is increased by31.25%, the ultimate load ofpolymer-modified cement concrete composite beam is increased by9.5%.Polymer-modified cement concrete of composite beam possess excellent deformationperformance, which helps cutting the stress peak of steel at cracking sections,associating steel between the cracks to work together, making the axial stress of steelbecome more uniform, promoting the performance of composite beam.③Compared with common concrete beam, the yielding load of steel inpolymer-modified cement concrete composite beam is increased by12%to23%. Before the yielding of steel, the steel strain at the cross of composite beam is less thanthe steel strain at the cross of common beam under the same load level, in other words,the steel stress of composite beam is lower than the steel stress of common beam atcross section.④At the load of42kN, the tensile strain at0.5times height of common beambegin to grow, at the load of50kN, the tensile strain at0.6times height of commonbeam begin to grow; At the load of58-72kN, the tensile strain at0.5times height ofcomposite beam begin to grow, at the load of85-112kN, the tensile strain at0.6timesheight of composite beam begin to grow. This means that cracks of the composite beamare growing slower.⑤Compared with common beam, the numbers of cracks in the composite beamare growing more, and the height of cracks develops slower, the width of cracks aremore slender and the distribution of cracks are more compact and symmetrical under thesame condition. As same as the common beam, the height of cracks in the compositebeam is steadily interdictory at0.8times height of beam.
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