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The fatigue life estimate by the LEFM concept of the tube joints exposed to axial load

Djoković J. M., Nikolić R. R., Bujňák J., Hadzima B.

Roczniki Inżynierii Budowlanej

2017

z. 17

35--41

In the tube joints the crack growth usually appears along the weld’s edge, i.e. at the spot where the chord and the brace are connected. The semi-elliptical crack the most frequently develops from the initial flaw that originated during the welding. The abrupt change in the material’s structure and response to loading are increasing the normal stresses in the lateral tube at certain spots around the crossing of the main and lateral tubes, producing the “hot spot” stress. Sensitivity to fatigue depends on combination of the cyclic loading, initial defects, environmental influences and the “hot spot” stresses which are the result of the tube walls bending during the loading of the structure. The principles of the Linear Elastic Fracture Mechanics (LEFM) are applied in this paper to analysis of the crack propagation behavior of a thin tube joints. Influence of various parameters was investigated individually and independently, and the share of the fatigue crack growth and subsequently the working life of the welded joint were estimated.

Buckling of variable cross-sections columns in the braced and sway plane frames

Nikolić R. R., Djoković J. M., Bujňák J.

Roczniki Inżynierii Budowlanej

2016

z. 16

31--39

Columns of the variable cross-sections are used in order to decrease the costs of the structure, for the purpose of easier maintenance, or for architectural reasons. Buckling of such columns is a problem that could appear in many steel structures, and could cause the loss of the structural stability. The critical buckling loading and the effective buckling lengths of such columns are analyzed in this paper for the cases of columns in the braced frame with the fixed and the sway frame with the movable nodes. Results are presented on corresponding diagrams what enables pinpointing the exact moment at which the particular column would lose its stability. The comparison of obtained results for the two types of frames are presented, as well.