Conceptual design of a deployable vehicular bridge structure using shape and geometric optimization for post disaster relief applications

Abstract

In the aftermath of a natural disaster, all efforts are dedicated to a common goal: repairing and bringing the affected communities back to their fully functioning condition. However, it is frequently encountered that infrastructure and roads providing access to these communities are also damaged. As this can slow down the community response time significantly, there exists a need for light, easy to install, and effective temporary infrastructure for immediate restoration of communication. This thesis presents a new design concept for a deployable bridge structure composed of scissor-like translational units. The proposed structure satisfies the deployment constraints and the stress limits determined by AASHTO LRFD Bridge Design Specifications. The used design approach uses multiple existing deployable geometries and performs a comparative analysis between the different systems. Given the particularity of SLE units, a standard finite element analysis method was enriched to match our conditions and enhance the accuracy of the modeling and analysis. This includes the implementation of master/slave node constraints and zero length rotational springs at the element nodes. The design problem is formulated as a formal optimization problem with a nested equilibrium condition. Our objective function minimizes the total weight of the structure for a deployable bridge subjected to H15 design loads and stress limits delineated by AASHTO. A design A design exploration is performed to compare the best designs for different bridge geometries, angles of element inclination and member cross sectional areas. The optimization problem is solved using a genetic algorithm which, at each iteration, uses our beam finite element analysis to check that structural equilibrium is satisfied. Given the potential lack of resources after a natural disaster, providing a light weight extendible structure which would therefore require less force and resources for installation, can have a positive impact in the recovery process.