Research On Damage Evaluation Of Steel Structures In The High-rise Building Based On TVCC Fire Disaster

The steel structures are widely used in the high-rise buildings due to their light weight, high strength, small occupied area, good seismic performance and rapid erection. However, the steel has a low fire resistance, and its mechanical performance is very sensitive to high temperature. The fire in the building may cause the bearing capacity of steel structure to achieve ultimate strength in a short time, further leading to severe damage to structural components or global collapse to the whole structure. In recent years, the fire accidents occurred in the high-rise building frequently. Though most fires did not cause the building to collapse, the structural components inside building suffered varying degrees of damage, which affecting the performance of the entire building structures. Therefore, studying on the fire damage to steel structures in high-rise building has important economic and social significance for guiding the the repair and reinforcement, and fire-resistant design of steel structures.Based on the fire accident of TVCC building, the steel space grid structures outside the building, and the combination of steel trusses, beams, and profiled sheet floors on the top of the building(called top steel trusses) are selected. Site investigation and inspection, laboratory test and numerical simulation methods are adopted to study the evaluation of fire damage to the two different types of steel structures. The main results are as follows:(1) Fire damage grade evaluation of steel space grid structure. The fire site investigation and inspection, steel and connection node mechanical tests after fire, typical embedded nodes of supports mechanical tests after fire are carried out, then the mechanical performance of structure material, connection node joints and supports after fire are mastered. Finally, the structural components of space grid structure are graded by considering the current existing fire damage grade standards for steel structure.(2) Steel and connection node mechanical tests after fire. For the steel Q345 B and fillet weld adopted by steel space grid structure, the affect of initial load to the strength of burnt steel, the deterioration of mechanical performance of steel and fillet weld are studied through laboratory test. For the butt weld and high strength bolt used in the top steel trusses, the strength decrease of butt weld and high strength bolt, and loss of slip coefficient of high strength bolt after fire are studied by fire test.(3) Embedded nodes of supports fire test. The scale model of embedded node specimens are made according to the serious burnt supports, the fire test with heating and cool process are carried out firstly, then the tensile and shear mechanical test are executed to study the loss of ultimate bearing capacity of specimen and failure mode.(4) Steel column node fire test. For the steel column node in the top steel structure, fire test and static loading test are carried out to study the nodes temperature variation in different positions of the column, and nodes carrying capacity variation, and column deformation after fire.(5) Numerical simulation of top steel trusses fire-resistance. Based on the result of fire site investigation for top steel trusses, the temperature field of its typical structural components and nodes are simulated, and the finite element model of the whole top steel trusses is builded up for the temperature-load coupling computation, and the fire affects to the stress distribution and deformation of the top trusses are analyzed finally.(6) Steel structural damage evaluation system after fire. Through the site investigation and inspection, connection nodes fire test, steel column node fire test, temperature field simulation of typical structural components and nodes, temperature-load coupling finite element analysis of overall top steel trusses, then the condition of steel material, connection nodes, structural components, and entire structures of top steel trusses after fire are understanded comprehensive, which provides reliable information for the damage evaluation of structural components. Thereby a comprehensive fire damage evaluation system for steel structure is established, which has great significance for the steel damage assessment after fire in future.