Bridge Structures 15 (2019) 121–138 DOI:10.3233/BRS-190151 IOS Press 121 Probabilistic analysis of the effect of the combination of traffic and wind actions on a cable-stayed bridge M. Nesterova a , F. Schmidt a,∗ and C. Soize b a Universit´ e Paris-Est, EMGCU, MAST, IFSTTAR, Marne-la-Vall´ ee, France b Universit´ e Paris-Est, MSME UMR 8208, UPEM, Marne-la-Vall´ ee, France Abstract. At the design stage of bridges, all possible actions and their combinations are to be considered. In certain cases, the influence of the environment must be taken into account in addition to design values of traffic loads. In order to assess the current state of an existing bridge, actual applied actions must be considered: updated traffic situation, monitored climatic actions, and their unfavorable combinations. Therefore, monitoring all actions makes it possible to adequately study a structure. Since only limited data are generally available, the important question is how the quality and the duration of monitoring influence the assessment of the structure. In the current study applied to the Millau viaduct, effects from monitored traffic and wind actions are evaluated. The statistical analysis of applied actions and caused effects is done according to the Peaks Over Threshold (POT) approach. Results include the comparison between confidence intervals of predictions, for each studied load case and for various periods of monitoring. In addition, this paper presents study of the influence of the length of monitoring data on predictions of future extreme load cases, and also proposes an alternative efficient algorithm for threshold choice in the POT approach. Keywords: Cable-state bridges, orthotropic deck, extreme values theory, peaks over threshold, wind actions, traffic actions, combination of actions, BWIM 1. Introduction The complexity of predicting the residual life of large complex unique bridges such as the Millau viaduct is an important topic for the modern civil engineering work. Due to the fact that many Euro- pean bridges, as well as bridges all over the world, are coming to the end of the design life, the question of the extension of their operational life is essen- tial [1]. Moreover, some bridges were not designed to the current loading and have to be re-assessed. Studying such structures allows for improving the assessment of existing structures and possibly, gain- ∗ Corresponding author. F. Schmidt, Universite Paris-Est, EM GCU, MAST, IFSTTAR, Marne-la-Vallee, France. E-mail: franziska.schmidt@ifsttar.fr. ing some profit from an economic point of view by avoiding unnecessary over-design or strengthening. Usually, in bridge engineering and development of standards or norms, such as background works on the Eurocodes [2], the Extreme Value Theory (EVT) is used for forecasting of return levels of actions for the period of the interest. One of the most efficient approaches to be used is the Peaks Over Threshold (POT) method, that was not used during the men- tioned background works, but which has proven to work well in diverse fields: wind engineering [4], pre- cipitation predictions with non-stationary data [5], electricity demand estimation with a time-varying threshold [6], etc. Here, it is used for two types of loading – loading from heavy vehicles and wind load- ing, and their combination. 1573-2487/19/$35.00 © 2019 – IOS Press and the authors. All rights reserved This article is published online with Open Access and distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0).