Fire Performance Of Restrained Steel Reinforced Concrete Columns

Building structure in use is to ensure security during the event of fire. The current steel reinforced concrete structures have been widely used, and the columns of steel reinforced concrete frame are key factors to decide whether the structure collapsed in fire. So the fire resistance of such research is member significance. Previous scholars of steel reinforced concrete columns fire resistance mainly in simple single supported member, but actually, in steel reinforced concrete frame structure, steel reinforced concrete columns due to the restraints from beams and columns, the actual stress state of both ends of the frame columns are restrained. According to the nature of restraints, the restraints can be divided into axial restraints and rotational restraints. So further study in the fire resistance of such members is important to ensure the structural fire safety. The main research and achievements are as follows:1. Seven steel reinforced concrete columns with end restraints were tested in fire. The influence parameters of different load ratio, eccentricity and steel ratio on deformations and internal force of the restrained columns in fire were discussed. Test results showed that: in case of fire, due to the axial restraints, the vertical displacement of columns gradually expanded in the beginning and then presented gradually compression deformations. When the load ratio is relatively small(less than or equal to 0.5) and same, the greater the eccentricity, fire resistance of the columns increased accordingly; with increase of steel ratio, the fire resistance of the columns could be extended in a certain degree.2. Using the computer program of ABAQUS, the finite element models of steel reinforced concrete columns under thermal and mechanical coupling are builded. The finite element models have been validated with test results. Based on the finite element models, the temperature field distributions and mechanical properties of steel reinforced concrete restrained columns are studied. Post-processing program language is written based on Python. And the axial restraint stiffness ratio, rotational restraint stiffness ratio, load ratio, eccentricity, cross-sectional dimensions, steel ratio, reinforcement ratio, steel yield strength, reinforced yield strength, concrete compressive strength and the thickness of the protective layer are detailed conducted to resreach interal force, deformations and destruction regulars of steel reinforced concrete restrained columns.3. Influencing parameters on the fire resistance of steel reinforced concrete restrained columns are detailed analysis. The results show that the axial restraint stiffness ratio, load ratio, eccentricity, cross-sectional dimensions and concrete compressive strength are the main factors affecting the fire resistance of the restrained columns. Based on lots of simulation results respectively, practical calculation method for the fire resistance of restrained columns is proposed..4. For eccentric compression SRC restrained columns, inflection points are produced by the presence of the rotation restraints. The rotation restraints could significantly reduce the length factor of the columns. Without rotational restraints at column ends, there is no inflection points in column length, and the effective length is equal to 1. The existence of axial restraint will share the vertical load at top of the columns, significantly reducing the half-height moment of columns to improve the fire resistance. Rotational and axial restraints on the influence of force and deformation of steel reinforced concrete column could not stack.5. Under ISO834 standard heating curve, axial restraint stiffness ratio, rotational restraint stiffness ratio, load ratio, eccentricity, cross-sectional dimensions, steel ratio, reinforcement ratio, steel yield strength, reinforced yield strength, concrete compressive strength and the thickness of the protective layer are researched to bring out the influence on columns’ length factor and moment magnification factor at half-height of columns. By studying the above various factors on the influence regulars of column effective length coefficient, the length factor of steel reinforced concrete columns changes between 0.465-0.506 at the time of frie resistance. Under high temperature, eccentricity, axial restraint stiffness ratio and cross-sectional dimensions of the columns have great influence on moment magnification factor. Based on lots of simulation results of the main parameters respectively, practical calculation method for moment amplification factor of restrained columns is proposed..