In-Plane Buckling and Semi-Rigid Joints of Tubular High Strength Steel Trusses
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Korkealujuusteräksisten putkiristikoiden puolijäykät liitokset ja tasossa nurjahtaminen
This thesis investigates buckling of hollow section members in tubular trusses. The existing codes and instructions do not take into account several factors that have been indicated to affect buckling lengths in tubular trusses. Furthermore, the existing formulae give -in many cases- buckling length factors that are excessively conservative or even underestimated results. Thus, buckling length of the bracing and chord members is investigated. The emphasis is on the in-plane buckling of K-joints. The influence of dimensional properties of truss members to the joint stiffness is examined. In general, obtaining buckling length is simple in the cases of fully rigid or hinged connections. Since braces are usually welded to the chords in steel girders, the connections can be semi-rigid. This makes the calculation of buckling challenging, because the stiffness of the connection needs to be determined. In this thesis, the the joint stiffness is determined by FE-modeling. The aim of this thesis is to confirm a wider applicability range for recently developed formulae. FE models are validated and verified, after which joint stiffnesses of new joints are derived. The validation is done with high strength steel, grade S500, joints. Buckling length factors are analytically calculated with the obtained joint stiffnesses.