Fire Resistance Analysis Of A Typical Super High-Rise Concrete Frame-core Tube Structure

With the rapid development of high-rise buildings in recent years, the disaster prevention of high-rise buildings becomes a critical issue. Fire hazard is one of the main threats to the safety of high-rise buildings. A concrete frame-core tube structure, which is one of the most widely used structural types of high-rise buildings, is chosen as a typical example in this study to examine its fire resistance in the view of the overall structural level. The fire-induced collapse resistance under extreme fire is also discussed. Finally,the method is applied to practical engineering structures to investigate their fire performances, which provides a reference for the fire resistance design of high-rise buildings. The main works of this thesis are shown as follows:(1) The numerical models and the simulation processes for the fire resistance analysis of high-rise buildings are proposed and validated.(2) The effect of the thermal strains of materials on the mechanical behavior of reinforced concrete(RC) beams and columns exposed to fire is analyzed. The analysis indicates that the effect of thermal strains on the RC beams with three sides exposed to fire is small, but the effect of thermal strains on the RC columns with three sides or four sides exposed to fire is much larger. The thermal creep strain of concrete has very small effect in different components. Consequently, its influence could be neglected in the simplified calculation. Except the thermal expansion strain of steel bar, the influences of the other thermal strains of RC beams could be neglected in simplified calculations.(3) The overall fire resistance performance of a typical super high-rise RC frame-core tube structure exposed to conventional fire is analyzed. The analysis results show that the high-rise concrete structure itself has a good fire resistant performance and has sufficient bearing capacity when exposed to a conventional fire. However, the floor systems and the upper parts of the structure may experience very large deformation that will affect the normal use after the fire. Therefore, fire protection measures are suggested to protect these components.(4) The collapse resistance of a typical super high-rise RC frame-core tube building subjected to extreme fire is analyzed. Subjected to extreme fire, a partial progressive collapse may occur inside the fire-affected area. However, because of the large redundancy of the RC frame-core tube building, the structures outside the fire-affected area can avoid progressive collapse through alternative load path. The collapse of the RC frame is triggered by the flexural failure of the peripheral columns, which are pushed outward by the thermal expansion of the floor system.(5) The fire resistance performance of practical engineering structures is studied. The results show that the temperatures of most regions inside the cross section of the mega components have no significant change in the process of heating. Thus, the mega components have a good fire resistance. At the same time, the mega components will not experience flexural failure caused by the thermal expansion of the floor system due to its large lateral stiffness. However, the secondary frames and the floors of the structure need the corresponding fire protection to prevent the failure caused by large displacement under fire condition.