Vibration Characteristics Of Beams Of The Overall Structure Under Fire

The research on fire resistance of steel structure is lagged behind though the number of steel constructions is increasing all the time. The fire resistance test of a overall -steel building have been carried out and a large number of research results are obtained at abroad, but there are few experiements about that in domestic research. Because of the non-linear material behavior at elevated temperatures and constraints from surrounding conditions, the component fire response of the overall structure is very complex. In order to obtain the real reaction of components of the overall structure under fire and provide effective recommendations for fire resistant design. Fire resistance tests of a single-span beam and a two-span continuous beam of a full-scale overall structure, which is 3-floor steel frame building (3?3bays) with floor and wall, have been carried. The work is shown in the following:(1) First, a fire test furnace is built according to the requirment of the test beam. According to the ISO834 fire curve, the fire resistance test of a single-span beam and a two-span continuous beam of the overall structure under a static load is carried out. Then the beam deflection, the up and low flange deformation, the column lateral deformation and the concrete slab and steel beam section temperature are measured. Finally, the relationship among deflection, temperature and time are studied. The results show that the grads of temperature exist on the section. The deformations of concrete and steel, which are exposed to fire in the test, are incompatible because of the different thermal conductivity. Due to the heating expansion and cooling shrinkage deformation of the beam, a great number of push and pull force occurred on columns and causes the column lateral deformation. Therefore, the beam-column joints will be splitted by the tension, which is generated by the cooling shrinkage deformation of the beam.(2) Using the vibration test equipment, the acceleration response of the single-span beam and the two-span continuous beam are measured, the random signal of acceleration are obtained. The self-spectral analysis results show that, the vibration frequency of composite beam of the overall structure under fire is decreasing fluctuant. At last, the study of vibration characteristics can provide the theoretical basis for health inspection of structures under fire.This paper presents valuable reference and theoretical basis for engineering's by general laws and conclusions, which are obtained from the research of the single-span beam and the two-span continuous beam of the overall structure under fire.