Experimental Study On Mechanical Properties Of Damaged Steel Frame Structure

The safety performance of structures needs to be reevaluated because of local damage caused by the increase of service time,environment erosion and natural disasters,etc.For the steel structure,although some structures were damaged,they can still be used.So that,demolition these structures may cause huge waste.It is one of the urgent problems to be studied that whether the damaged steel structure can continue to meet the secondary use and how the structural mechanical properties will change.In this paper,the mechanical properties of the damaged steel frame are studied by means of experimental study,numerical analysis and theoretical derivation.The main contents are as follows:Through the experiment of material properties the relationship between the elastic modulus of Q345 steel and the damage level in the second loading period has been obtained with the trilinear.Finally a unified formula is obtained to express the Q235 and Q345 elastic modulus in the second loading.Through the experiment of the steel frame structure the damage has been simulated and the mechanical properties of the damaged steel frame have been researched.The experimental results show that after damaged,the lateral stiffness is decreased and the ultimate bearing capacity of the steel frame decreases.The change regulations of displacement and strain have been obtained through simulating the whole damage experiment by means of the finite element analysis software ABAQUS.In the first loading and the second loading process:the frame column top horizontal displacement obtained by experiment and those obtained by finite element method are compared.The comparison results are in good agreement;the two position strain(one third position on the left side of the frame beam and the upper end of the frame column on the right)obtained by the experiment and those obtained by finite element method are compared.The results are generally anastomosis.Finally in the parameter analysis,the influence of different degree of damage and different damage position on the frame lateral stiffness has been researched.Results show that the higher the degree of damage,the lower lateral stiffness;in the same degree of damage,the influence of the bottom damage on the frame lateral stiffness decreasing is greater than those of the top damage.A damaged structure calculation method is obtained by considering the cross section damage and lateral displacement and Fortran program is employed to achieve the theoretical calculation.In terms of column top displacement,the results of the first loading and the second loading are compared with the experimental results and the finite element results,and the results are in good agreement with each other.Finally,an example of 8-story single-span steel frame structure is analyzed.The results show that the larger the initial residual deformation under the same load,the greater the lateral displacement value under loading.The residual lateral displacements increase the bending moment of the damaged layer and also increase the bending moment on the adjacent floor.The farther away from the damaged floor,the small increase.