Problems and features of FPP suspended boiler metal framework calculation under seismic impacts

DOI: 10.37153/2618-9283-2023-5-53-73

Authors:  
Rubric:     Design, building and reconstruction of aseismic constructions   
Key words: frame–boiler system, metal frame, suspending steam boiler, earthquake resistance, damping, antiseismic bracing, FE-analysis
Annotation:

Introduction. Metal frames of suspended steam boilers are responsible structures, damage to which during seismic impacts can lead to major man-made disasters with loss of life and significant material damage.

The tasks of ensuring the seismic resistance of such objects are currently complicated by the fact that there are a large number of contradictions in the regulatory documents regulating the calculations of building structures and boiler equipment, there is no clear methodology for carrying out calculation justifications in terms of forming calculation schemes that take into account the interaction of elements of the frame and boiler equipment, determining the parameters of damping of the frame-boiler system and technological requirements safe operation of the system, modeling of antiseismic bracing elements and damping devices.

Purpose and tasks. Based on the analysis of existing regulatory experience, scientific and experimental research, as well as considering calculations performed at various times by specialists of LLC "CVS" for Russian and foreign (Bulgaria, India, Vietnam) projects, to develop approaches to assessing the seismic resistance of boiler frames and designing an antiseismic bracing system.

Methods. The methodology for performing the calculation justification of the seismic resistance of suspended boiler frames as part of the "frame–boiler" system is based on the provisions of the current version of SP 14.13330.2018 on determining the calculated seismic loads, considering the three-component seismic impact, using the method of direct dynamic analysis in calculations for a control earthquake. Additionally, the norms of boiler inspection, supplementing and developing the provisions of the building codes of rules, are taken into account.

The calculation justifications are made using the FE software complexes SCAD Office and ANSYS.

Research and results.

Dry friction in the contact zones between the elements of the boiler and the frame can make a significant contribution to the dissipation of vibration energy, comparable to the level of structural damping of the frame-boiler system; considering friction can lead to a decrease in horizontal seismic displacements and all components of internal forces in the elements of the frame by up to 15...35%.

Effective means of regulating the dynamic reaction of the frame-boiler system are elastic-plastic elements of antiseismic bracing, which can be designed considering the geometric features of the frame-boiler system using numerical methods. Their installation makes it possible to multiply reduce the relative displacements of the boiler and the frame; varying the number and places of installation of elements provides acceptable levels of displacement at different levels of seismic impact (from 0.1 g to 0.4 g).

The boiler suspension system associated with the overlap of the frame can have extremely uneven loading. When equalizing the forces in the suspension rods on a real object, the specified installation operation must be correctly modeled in a software package for analyzing the work of structures. The refined FE-element analysis of suspensions allows avoiding excessively conservative estimates of their stress-strain state, analyzing the operation of the system nodes important from a technological point of view, on which its overall stability depends.

Conclusion. The assessment of the seismic resistance of suspended boiler frames involves consideration of the "frame–boiler" system and consideration of a number of technological requirements along with the requirements of strength and stability of elements of metal structures. When assessing the seismic resistance of suspended boiler frames, a higher level of damping is assumed than the recommended SP 14.13330 for steel structures, including considering the damping of vibrations by friction forces in the contacts of the system elements. The use of elastic-plastic elements of antiseismic bracing is a simple and at the same time sufficient means to effectively regulate the dynamic reaction.

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