Reliability Analysis Of Box-shaped Steel Column Subjected To Blast Loading

The collapse and destruction of building structures caused by terrorist explosion and accidental explosion occur from time to time.For Steel structures which are widely used at present,the damage and destruction of steel structures are easily caused by the action of explosive load,in particular,the vertical load-bearing member box-shaped steel column,and then lead to the continuous collapse of the steel structure,resulting in huge economic losses and casualties.However,the explosion load acting on the building structure is affected by many factors,such as the quality of the explosive,the position of the initiation point,the complicated environment of the city,the ambient temperature and humidity,etc.There is some volatility.At the same time,the structure itself,such as the static and dynamic properties of materials,the geometric dimensions of structural components,also has uncertainty.Therefore,in order to study the damage mechanism and reliability analysis of box-shaped steel columns under blast loading,this paper systematically carried out the following work:(1)The propagation mechanism of explosion and the simplified overpressure time-history curve of blast load acting on building structure are introduced.Based on comparison between the experimental data of previous explosion load and the empirical formula,charts and computer code Conwep summarized by the simplified model of explosion load,it is concluded that there is has a strong fluctuation for the explosion load.According to the assumption that the peak reflected overpressure P_r and duration of overpressure t_d of the parameters of explosion load are subject to normal distribution,the best fitting curve of the mean value,standard deviation and coefficient of variation of the peak reflected overpressure P_r and duration of overpressure t_d under different proportional distances Z is obtained through statistical analysis.(2)Based on the finite element numerical simulation method,the mechanical response and failure mode of box steel column under blast loading are studied.Through parameter analysis,the influence factors such as section size,yield strength and constraint conditions of box steel column are further studied.Meanwhile,the failure modes of box steel column under different explosion loads under impulse load,quasi-static load and dynamic load are analyzed.Meanwhile,the failure modes of box-shaped steel columns under impulse load,quasi-static load and dynamic load are analyzed.The results show that there are three main failure modes of box-shaped steel columns under blast loading:global bending failure,local deformation failure and combined local and global deformation failure.(3)An efficient method is established to evaluate the damage degree of steel box columns under blast loading.Based on the damage criterion of the global deformation and the local deformation of the box-shaped steel column under explosive load,the pressure-impulse(P-I)curves are established for predicting damage degree of the global and the local deformation of the box-shaped steel column under explosive load.At the same time,the prediction formula of P-I curve of steel column with arbitrary size is fitted,and the established prediction formula is compared with the numerical simulation method.The results show that the proposed method can save a great deal of computation time on the premise of ensuring the calculation accuracyand and is convenient to be used in engineering practice.(4)Based on the P-I damage curves with different damage indexes and the Monte Carlo method method,the reliability analysis is carried out to establish the calculation method of the cumulative damage index distribution probability and the failure probability of the steel box column under the uncertain explosion load.At the same time,the effects of betweem certain explosion load or certain structure size and volatility with explosion load as well as structure size on the cumulative probability of damage index of steel box columns are compared and analyzed.The results show that the mass and proportional distance of the explosive have an important influence on the reliability of the structure,and the importance of the random fluctuation of the explosive load and the structure size to the reliability of the steel box column under the explosive load is taken into account,the cumulative probability of damage index distribution is affected most by the random fluctuation of the peak value of reflected overpressure.