| The “thin” steel bars refers to steel bar is drawn and straightened manually,leading to increased yield strength,brittle mechanical property and its elongation fails to meet requirements of acceptance specification in the straightening process of the steel coils.It is often used as beam and column stirrups and in floors.The engineering circle generally worried about that the the concrete member and earthquake-resistant ductility of structure will be affected due to brittle mechanical property.The displacement loading pattern is adopted to conduct of full-process loading test of concrete confined with HPB300 “thin” stirrup on the basis of test of concrete confined with “thin” HPB235 stirrup,so as to study effect of HPB300 “thin” stirrup on confined concrete constitutive model.The main content shows as follows:1 、 Given the rate of thin of “thin” stirrup is between 10%~18%,the HPB300 steel bars with 17.6% of the average rate of thin from many groups are conducted tensile test.As a result,the average elongation of“thin” steel bars are 12.8%,the total average elongation with the maximum force is 3.17% and average yield strength has increased by 21.7%.The elongation of HPB300 steel bar after breakage and “thin” is obviously less 25% than value stipulated in national standard as well as less 10% than value stipulated in national standard for elongation the with maximum.2、From the test on 8 rectangles with volume stirrup ratio between 0.51%~1.74%and rectangular diamond composite stirrups,when the stress in ascent stage reaches to 80% of peak stress,the surface of this specimen appears obvious cracks with rapid development.When concrete prismoid arrives in before and after peak stress,the“thin” stirrup begins to yield and increase deformation significantly.However,until the stress in descent stage decreases to 50% of peak stress,the protective layer fell off severely,concrete in the core area is crushed,longitudinal bar is pressed to bend and specimen is broke seriously.There has no broken phenomena in “thin” stirrup.However,the phenomenon of disconnecting with hook occurs in three prismoid specimens due to bend of longitudinal bar.There has no obvious differences betweencomplete stress-strain curve of all specimen and stress-strain curves and that of components normal stirrup confined with concrete from Guo Zhenhai-Zhang Xiuqin model.3、8 prism concrete specimen are broken finally because of crush and falling off of concrete.The specimen ductility equals to that of prism model with normal stirrup confined with concrete,which shows ductility and materials are two concepts for components and they are not the entirely identical.Although “thin” stirrup has a bad ductility,it can meet needs of ability to restrain deformability of concrete.Therefore,the ductility of component doesn’t decrease.4、The prismoid is analyzed through adopting ABAQUS finite element software,which found the better coincidence between stress-strain curve calculated through this software and testing result.It turns out that the ABAQUS concrete damaged plastic model can simulate exactly full process of elasto-plastic deformation for prismoid.5、Since the discreteness exists in cracking and fall-off for concrete,involving in many fracture force problems.besides,the plastic damage model of concrete belongs to continuous model,which cannot stimulate completely lateral deformation development of concrete strained by “thin” stirrup and can result in big differences obtained from stirrup stress-curve with finite element modeling and test.So research of stirrup strain should regard test as the core.6、Adopt actual area of “thin” stirrup and yield strength to calculate characteristic value for providing stirrup,and use Guo Zhenhai-Zhang Xiuqin model also can describe constitutive model of concrete restrained by “thin” stirrup. |
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