Study On Fire Performance Of 500MPa Reinforced Concrete Columns Under Compression

The column as a vertical force component,once destroyed,will have continuous damage,in the concrete structure.At present,the research of fire resistance is mainly aimed at the concrete columns with ordinary steel bars,but the research on the concrete columns with high-strength reinforcement is not enough.By studying the mechanical properties of concrete columns reinforced with 500 MPa bars after fire,it can provide the basis for the damage evaluation,repair and reinforcement after fire,and further improve the fire resistance design theory in china.The fire on the column is mainly caused by the fire on both sides and on the three sides,but it is easier to control the influence factors by considering the single side fire,so the research method of single side fire is adopted.The full text from the experimental,numerical analysis of two aspects of research,the main contents and conclusions are as follows:1.In this paper,a total of 11 concrete columns were studied.First of all,7 of them were subjected to a single fire test under the ISO834 standard heating curve,and the temperature field distribution and axial displacement of the column were measured.The results showed that:(1)The temperature curve in the trend basically conforms to the ISO834 standard temperature curve,but the temperature is slightly lower,this is mainly because the fire stove Mifengbuyan,there is heat exchange with the outside world;(2)Measuring points from the fire face,the temperature reached 500 degrees.2.The 11 concrete columns under normal temperature was carried out to observe the failure phenomena,and the strain,later bearing capacity,axial displacement and lateral displacement of columns were measured.The results showed that:(1)Uniform compression concrete column process and compression process of ordinary concrete columns with 500 MPa steel,can be divided into elastic,crack development and failure of three stages;(2)With the increase of eccentricity gradually decreased when the eccentric bearing capacity;at the same time,along with the time by fire growth,bearing capacity gradually decreased.(3)After the section of the column passes through the high temperature,the section weakens,the neutral axis shifts,and the height of the compression zone decreases.Under the eccentric eccentric loading,the damage of concrete due to high temperature weakens ahead of time,which leads to large bias failure to be subjected to small bias failure.3.Analysis under ABAQUS were carried out to obtain the section temperature field distribution and the ultimate bearing capacity calculation results.The results showed that:(1)The section temperature field distribution was in accord with experimental results,the finite element analysis for temperature field can be used as a load analysis of second stage structure;(2)The calculation result and the test result error is very small errors were 4.5%,11 column bearing capacity limit of 4.4%,5.9%,8.3%,19% 2.8%,10.6%,14%,1.7%,1.6%,and 7.2%;(3)variation of axial and lateral displacement and close to the basic test.4.By comparing the simulation results and experimental data,the Nu-e and Nu-Mu curves are obtained,which provide intuitive data for the mechanical properties after fire.The results showed that:(1)From the average strain section,the assumption of plane section concrete columns with 500 MPa steel after the fire on the situation still apply,calculation formula of normal temperature can still be used in high temperature,but the strength of concrete should be reduced;(2)By the Nu-Mu curve under fire in column compression zone later,in the transfer limit of eccentricity of the concrete column will occur the size of the bias,the compression zone after fire will weaken the part of the concrete,the concrete destroyed early,large eccentric compression failure into small bias failure;(3)serious damage boundary section in layered specimens subjected to fire 1.5h,2h after injury depth are 36 mm and 46 mm.