An integrated approach to reliability assessment of spatial metal structures

Introduction. Some results of implementation of the integrated approach to reliability assessment of design solutions of buildings and structures of increased level of responsibility (large-span rod and sheet metal structures, vertical cylindrical tanks of large volumes) with load-bearing metal structures are presented.Materials and methods. The initial stage of the developed approach to assess the reliability of buildings and structures of increased responsibility is the formation of refined finite element design schemes based on the detailing of nodal connections and geometric schemes of designed structures, which allows to identify the features of the stress-strain state (SSS) and perform a refined assessment of the stability of structural elements. Some general patterns obtained based on such detail are given for large-span structural coatings and structures of vertical cylindrical tanks. To realize the next stage of assessment of the propensity of the designed system to avalanche collapse, a special algorithm for calculating the SSS of the structure, implemented in a geometrically and structurally non-linear formulation, was developed and presented. At the same time, for the considered calculation situation, during the multi-stage calculation, a set of key elements is determined, the failure of which, on the one hand, initiates the beginning of avalanche-like destruction, on the other hand, allows using the established set of elements to determine the upper bound of the numerical value of the probability of failure (or the reliability index) of a repeatedly statically indeterminate system. At the final stage, if necessary, optimization of the obtained structural solution is performed using the Nelder – Mead method according to the specified failure probability indicators for key and minor elements.Results. The proposed approach allows to determine reliability indices of multiply statically indeterminable systems with acceptable practical accuracy. This is especially relevant for unique structures of increased responsibility. The mechanism of loss of stability of compressed rods of structural structures of the MARHI system was clarified, the methodology of correction of the µ coefficient determination taking into account the obtained results was proposed; the data of change of the aerodynamic coefficient of cylindrical tanks of large volumes V = 10,000–30,000 m3 were obtained. This allowed us to determine the following features for the constructions under consideration: with an increase in the volume of the reservoir, there is a change in wind pressure in the area of the ladder junction, compared with a reservoir without a ladder; the maximum discrepancy with the normative values (up to 20 %) was noted in the negative pressure zones (opening effect on the wall); in the active pressure zone, there is a decrease in the vacuum pressure, depending on the size, up to 6 %.Conclusions. A complex algorithm is proposed, which allows, on the basis of detailed design schemes and assessment of the propensity of the designed structures of high level of responsibility to avalanche-like destruction, to perform a refined assessment of their level of design reliability. On the basis of the algorithm, an optimization procedure of the initial design solution is proposed, based on the use of the Nelder – Mead method and currently implemented to minimize the target function in the form of the mass of the main structural elements (rods and connector nodes).

metal structures, numerical methods, avalanche failure, reliability, structural constructions, geometrical nonlinearity, structural nonlinearity, structures of increased level of responsibility