Design and optimization of FRP traffic decks considering uplift bolt forces

Abstract

This research is about which geometry of FRP slabs is the most optimal, in terms of costs, to use for a given load and boundary conditions taking the occurring uplift bolt forces into account. The first part of the report focuses on the calculation of the uplift forces in the bolted connections caused by the moving loads. For this, first a detailed numerical model is made in Abaqus. Based on this most detailed numerical model, different simplifications are made to make the calculations easier and less time-consuming. Numerical models with linear bolts instead of non-linear bolts and with load superposition using a one-wheel load instead of a complete vehicle are considered. Next to this, equivalent material properties are calculated to make a model with an orthotropic deck plate instead of modeled geometry of skins and webs. For the numerical model with this orthotropic deck, the same simplifications are applied. Next to the numerical models, different analytical beam and plate models are considered. All different numerical and analytical models made, are compared on possibilities, calculation and modeling time and accuracy. Based on the comparison between the models and the capacity of the connections, it is concluded that the uplift design of the bolted connections does not need to be taken into account in the optimization of the slabs.

The second part of the graduation work is about the optimization of the FRP slabs considering the global behavior of the deck, for which a genetic algorithm is used to detect the most optimal geometry. The most important parameters for the design are the height of the deck, the spacing of the webs and the layup of the topskin, bottomskin and webs. The layup of the different elements is dependent on the number of plies, the ply orientation and the overlapping length. During the optimization process, design and initial (global) strength, stability and stiffness checks are performed. First, optimization is done for the same deck that is considered in part one of the research. Next to this case, different cases for the distance between the supports are considered for which standardization is done with respect to engineering and production of the slabs.

Based on the performed research it is concluded that the uplift bolt forces are in a range of 0.5 to 21.5 kN. Simplifications can be done by the use of an orthotropic deck with equivalent material properties. The maximum difference using this simplification is 2.9 kN, while the calculation time needed is reduced by a factor of 4-5. Other simplifications that can be done are the use of linear bolts and/or load superposition. Using linear bolts gives a maximum difference of 0.5 kN and load superposition a maximum difference of 0.3 kN, both without an improvement of the calculation time. The optimal geometry for different boundary conditions is given as a standard design with a variable number of plies for the topskin and a variable height based on intervals for the distance between the supports.