Comparison of Failure Criteria of a Slender Wood Structure under Stochastic and Quasi-Static Wind Loads

Abstract

A stochastic model of a wood pole under wind loads is addressed in order to study its failure under different criteria. In order to evaluate wind loads on a structure, the Argentine standard CIRSOC 102-2005 proposes simplifications that take into account the effects of shape, location and dynamics of a load variable in time, resulting in an equivalent quasi-static action, which simplifies the strength and deformations assessment of a given structure. However, if a temporal and spatial varying record of the wind load is considered in detail, the results should be comparable to those obtained with the standard load. The structural model consists of a wood utility pole with one end embedded in the ground and the other end free, with deterministic geometry and material properties values. The pole is subjected to a wind load along its length. The stochastic dynamic wind load as a temporal function derived from a Power Spectral Density Function using the Spectral Representation Method and taking into account spatial and temporal correlations. The structural model is discretized with FEM and the realizations are analyzed with Monte Carlo method. In the study, the maximum displacement at the tip is assumed as the failure threshold. This work seeks to explore results from different failure criteria for dynamic loads and to compare them with the results of a pole under quasi-static deterministic wind load. The criteria are the first passage, the dwell time above the failure threshold, the extreme values distribution, the crossing rate and the cumulative proportion of displacements above the threshold of all the realization. A comparison is carried out by means of the fragility curves to assess the suitability of each approach.