Buckling resistance of compression members with back‐to‐back connected angle sections

Abstract

This paper focusses on the buckling resistance of compression members made of back-to-back connected angle sections. The studied built-up members are connected through bolted packing plates. Due to the flexibility of this connection, these members generally do not fully work as a single member but the connection stiffness has to be accounted for. In Eurocode 3 Part 1-1 it is currently admitted to neglect the effect of the connection stiffness if the packing plates possess a maximum distance of 15 imin (imin is the minimum radius of gyration of one individual angle section, also called "chord"). Elsewise the influence of the packing plates on the member resistance should be accounted for. The limit distance of 15imin appears to be much lower than the past practice, consequently leading to a more conservative design and a complexification of the fabrication. This paper therefore presents a sensitivity analysis focusing on the influence of several parameters as: the distance of packing plates, the presence of clearance in bolt holes and the influence of preloaded bolts. These parameters are studied with a numerical model based on solid finite elements. Owing to the use of solid elements, it is possible to model explicitly the bolts, the packing plates and all contact regions.

Resistance of Closely Spaced Back‐to‐back Connected Equal Leg Angle Sections

“…The observation presented in references [8] and [9] are again confirmed by the numerical results shown in Figure 20. In this figure, the results are presented with reference to the member length and not to the relative slenderness in order to facilitate the lecture of the results.…”

“…As the battens and the chords are also subjected to shear forces, an additional contribution to the total displacement between two battens may arise from the shear deformation. This effect has been quantified in references [2] and [4] as shown in Equation (8).…”

“…As an alternative to preloaded bolts, snug tight bolts may be used if neither fatigue nor loosening of the bolt nuts is an issue or if loosening is prevented by specific measures. The numerical sensitivity study presented in references [8] and [9] has highlighted that in case of snug tight bolts, the distance between the battens does not have an impact on the resistance of the members. The reason for this observation is the fact that if the bolted connection is simulated with a clearance (even a very low clearance of 0,5 mm), the bolt shaft does not get in contact with the bolt hole before the buckling failure load is reached.…”

Load carrying capacity of star‐battened angle members made of S460 steel in compression

“…For the contact between the nut and the angle and the contact between the packing plates and the angle, a friction coefficient equal to 0,2 is applied; this value is considered as a lower bound. Nonetheless, as the bolts are not preloaded, the value of the friction coefficient has been shown to have very low influence [12]. In addition, a clearance of 2 mm in bolt holes has been modelled, in order to account for the sliding before contact.…”

Telecommunication and transmission lattice towers from angle sections – the ANGELHY project

“…The numerical results show that a small clearance degrades the resistance and that preloading of bolts, even at low levels, is necessary to attain the full connection case. More information is provided in [18]. The same procedure is applied to a single support and dead-end tower, as well as a complete power transmission line under consideration of the uncertainty of wind and ice loads.…”