Evaluation of vehicular dynamic effects for the life cycle fatigue design of short‐span bridges

Abstract

In current bridge design codes or specifications, the dynamic effects of vehicles are considered by using a dynamic amplification factor (DAF) or dynamic load allowance (IM). However, a DAF is defined based on the ratio of the maximum dynamic load responses to the static load responses, and it is more appropriate for maximum value-based strength design. For fatigue design, stress cycles other than the maximum stress ranges could contribute to fatigue damage accumulations. Meanwhile, on the capacity side, a reduction in fatigue strength due to structural deterioration, which is related to local environmental conditions, including temperature, humidity, etc., could introduce more uncertainties into structural safety and reliability evaluation. However, such multiple stress range effects and structural deterioration are not included in current bridge fatigue design. To evaluate the vehicular dynamic effects for the life cycle fatigue design of short-span bridges, the present study proposes a new dynamic amplification factor for life cycle bridge fatigue design (DALC), which is defined as the ratio of the life cycle nominal live load stress range to the maximum static stress range. In contrast to other traditionally defined dynamic factors, the newly defined DALC includes information about both the structural loading and the structural capacity. Therefore, the multiple stress cycles from vehicle-induced vibrations and the structural deteriorations from road surface conditions and corrosion of structural members are included. Parametric studies of DALC were carried out for multiple parameters and variables in the bridge's design life cycle, for instance, possible faulting days in each year, fatigue strength exponent, corrosion parameters and corrosion level. The stochastic properties and uncertainties from these variables are also considered in the DALC calculation.

Impact of Traffic Load Randomness on Fatigue of Steel Bridges

“…It is also used to determine maximum loads of structures under assumption that vehicles have identical dimensions and weight (Harman, et al 1983;Moses, et al 1975). Attempts to describe the results of field tests of road bridges in terms of this process have also been made (Croce, 2020;Wysokowski, 2018;Zhang, et al, 2017).…”

“…The influence of operational loads from heavy goods vehicles on the bearing capacity and fatigue capacity of steel bridge structures is relatively well understood regarding the impact of cyclically variable loads, it has been described in many publications, e.g. (Guo, Frangopol, & Chen, 2012;Kwon, & Frangopol, 2010;Wysokowski, 2001Wysokowski, , 2018Zhang, Wu, & Zhu, 2017). Fatigue tests of structural elements are carried out mainly using a cyclic model load, disregarding randomness of their amplitude.…”