Changein the stress-strain state of elements of the «base – foundations – load-bearing structures» system dueto a possible progressive collapse
DOI:
https://doi.org/10.32347/2410-2547.2024.112.273-284Keywords:
numerical simulation, progressive collapse, pile foundation, load-bearing elementsAbstract
The calculation of a building for stability against progressive collapse using the LIRA SAPR-2019 software is considered. Two calculation approaches are compared: using a quasi-static formulation and direct integration of dynamic influences overtime. The first approach to calculating the local failure of an element used the force application principle defined for this element under normal operating conditions, but with the opposite sign (dynamism coefficient Kd=2, “pulldown” loading). These cond calculation approachis characterized by the dependence of the system response on the loading rate and the rate of removalof structures. To take into account damping, Rayleigh coefficients were determined by natural frequencies for two dominant modes of natural vibrations (No. 7, 10) based on the modal analysis of the system.The local failure time of the element was assigned as 0.1T (oscillation period) for natural vibration mode No.7, as the closest to the expected response of the system to the removal of the pylon. According to the calculation results, in the quasi-static formulation, a qualitative changein forces was recorded, where in stead of compression, tension appeared in the chain of pylons, which are located above the remote one, and in the dynamic formulation, a decrease of 70...90% in the magnitude of longitudinal forces in the pylons was recorded, that is, work was recorded on the principle of a hanging scheme. An increase in the load on the piles under the vertical load-bearing structures around the removed element is predicted under the scenario of a local failure of the structure; depending on the calculation method, the expected increase in the load on adjacent piles is 15...25%. Based on the results of the study, in order to increase the survivability and ensure the protection of building structures from progressive collapse, a decision was made to increase the reinforcement area by 30...35% for pylons in the entrance area to a dual-use structure, as well as in the radius of influence of a remote element, in order to absorb increasing forces by these elements when redistributing loads when removing an adjacent building element and assessing the load-bearing capacity of the remaining elements. It has been established that in this case, progressive collapse does not occur for this building.
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