Stability of Single-Bolted Thin-Walled Steel Angle Members with Stochastic Imperfections

The focus of this paper is on the probabilistic estimation of the buckling capacity of single-bolted members from plain or lipped angle sections with stochastic geometric imperfections. A joint experimental-stochastic mechanics approach is adopted, employing in-house imperfection measurements of angle members in combination with detailed numerical models. Different slenderness values, plain and lipped angle sections, as well as single-brace or X-bracing diagonals are investigated in all cases accounting for the single-bolt connection. The member buckling loads are obtained via numerical analyses considering geometric and material nonlinearities with initial imperfections. The random variables are the geometric imperfections, the material properties, and the lateral load (wind pressure) on the member. Quatro-variate single-dimensional stochastic processes (the spectral representation method in connection with the method of separation) are used for the modeling of the geometric imperfections. It is shown that the influence of imperfections for typical lattice tower angle members is 3–6 times lower than the influence of material properties and lateral loading. All in all, current EU and US design provisions are found to be mostly conservative for the design of such members, while the use of equivalent imperfections in a numerical model can provide a more rational safety margin.