Research On The Vibration Characteristics Of The Slab Fire Damage And Safety Performance

Reinforced concrete slabs are commonly used components in building construction, as the horizontal architecture of building structure, it has a significant impact on the bearing capacity and the overall stiffness of the structure. Currently, researchers at room temperature vibration characteristics of reinforced concrete slab has been relatively mature, and widely been used in the identification and reinforcement plate. The study of vibration characteristics of reinforced concrete structures under fire is also less, and has been not form a mature theory yet, Therefore, this paper takes vibration characteristics analysis of one-way simply supported slabs and two-way slabs simply supported on four sides that after the fire, and consider their safety performance by calculating the bearing capacity after the fire and resonance. The main results are as follows :1. By reading a lot of literature, has carried the induction and summary on the thermal properties and mechanical properties Of steel and concrete under fire. On this basis, by using the finite element software ABAQUS on simply supported one-way slab and two-way slab simply supported on four sides of the temperature field numerical calculation, and define the damage depth, then import the temperature field calculation into the mechanics model, and take modal analysis on the two conditions of the salbs. The results showed that : Temperature distribution in two salbs of concrete and steel are basically the same, in line with the one-dimensional heat conduction law, concrete surface thickness of 30 mm since the fire within the scope of temperature gradient is bigger, with the increase of temperature, the temperature gradient increases, as the thickness increases, the temperature gradient gradually moving to flat; Fire can cause vibration of reinforced concrete slab, but the high frequency vibration is difficult to be excited, this paper obtained the one-way slab and two-way slab 6 order and 7 order frequencies and corresponding vibration mode, the amplitude of the fundamental frequency in their post fire decreased respectively 66.7% and 62.74%, stiffness has a great loss.2. In this paper, the object of study are the sheet, according to the basic theory of thin plate bending, proposed one-way slab simply supported and simply supported two-way slabs of the natural frequency of the general formula. According to the temperature field of existing analytical solutions, combined with the mechanical properties of steel and concrete at high temperatures, in their thickness direction of one-way slab simply supported and simply supported bidirectional plate stiffness integral, get the relationship between stiffness and temperature under the condition of known thickness. Assume that the mass density of reinforced concrete at high temperature is constant, introduce stiffness and temperature relationship into the natural frequency of the general formula, got the relation between the natural frequency and temperature in the process of fire. To analyze stiffness variation of the two slabs at high temperatures, on the basis of the relationship between stiffness and temperature, got the stiffness reduction factor at high temperatures.3. Introduced the calculation method of equivalent cross section of bearing capacity of reinforced concrete structures after fire into the slab, and consider the reduction of bond steel bar and reinforced concrete under high temperature, first bond failure may occur at high temperatures, introduce the critical bond, to further improve the equivalent section method.4. Adopting JP5050 multidimensional force platform and the corresponding data analysis system for the load test on foot, analysis the fast walking stride frequency at the time of evacuation, then consider the effect of damping, discussion the determination method of slab resonance with people walking after fire. The results showed that : People after the fire evacuation quick walking pace around 2 Hz, and fall in the range of 1.90 Hz ~ 2.08 Hz; Resonance will not occur between simply supported one-way and two-way slab and fast walk stride after the fire.