On the Issue of Determining the Design Lengths of Elements in Structural Constructions of the Kislovodsk Type

Introduction. The article looks at the issue of determining the design lengths of rods of the structural construction of the Kislovodsk type. While examining the existing structure of the coating of the shopping center, in the design documentation for the object, the authors found that the design length coefficient equal to 0.8 was used in the calculations of the rod structure. The value of 0.8 is due to the results of the tests performed at Kucherenko Central Research Institute in 1987. However, according to the current regulations, a coefficient of design length equal to one is to be used. The aim of the article is to justify the value of the design length coefficient in calculations of such structures.

Materials and Methods. A standard unit of attaching rods to a nodal connector is considered. It was decided to study the work of both a separate structural unit and rods together by modeling in the Femap with Nastran software package. The paper considers the effect of a nodal joint on the stability of an individual rod. To this end, a nodal structural element with a support at the contact connection of a compressed rod and a calculation of a separate rod for stability was modelled. A system of rods is then considered in order to determine the critical force, taking into account the influence of adjoining elements. The scheme consists of four rods of the lower belt and four rods of the braces connected in one node and loaded with a compressive or tensile load.

Research Results. The considered separate joint of the rod with the connector, where compressive forces are transmitted through a tight contact, is very close to rigid fastening by the nature of the work when checking the stability of the rod. The design length coefficient for compressed elements ranges from 0.77 to 0.88, depending on the force values in the elements and their cross sections. Based on this, it can be unambiguously concluded that the application of a coefficient of 0.8 for all compressed rods cannot be theoretically justified.

Discussion and Сonclusion. The coating studies show that the requirements of SP 16.13330.2011 "Steel Structures" are correctly applied in terms of determining the design length of a compressed rod equal to 1, and the use of a coefficient equal to 0.8 cannot be theoretically justified. Reducing the metal consumption while using reduced design length coefficients in calculations does not lead to significant savings for the overall structure and is not feasible. 

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