Bridges

Cover of Economical Design for Impact Actions on Bridge Structures
Economical Design for Impact Actions on Bridge Structures
  • Publication no: ABC2017-017-17
  • Published: 20 April 2017

Vehicular barriers are essential for highway bridges, and are often under the risks of vehicular impact. However, the current highway codes of practice use the force-based design which ignores the inertial resistance arising from the mass of the target structure.

Substantial construction costs have been incurred by the overdesign of the bridge barriers, the cantilevered slabs (in support of the barrier) flanking a bridge deck, the bridge pier and its foundation. This paper proposes the use of a displacement-based approach by treating a bridge segment as a 3 degrees of freedom (3DOF) system for estimating the displacement behaviour of the bridge elements, for a give impact scenario. The 3DOF includes: horizontal displacement of barrier, vertical displacement of deck, and horizontal displacement of pier.

The derivations of the analytical solutions are explained in detail. The advantage of the proposed solution is its simplicity, as it can easily be implemented with the use of spreadsheet such as Excel. Once the displacement demand is determined, it can be translated into equivalent design forces, and hence design bending moments and shear forces.

The proposed approach which can result in a much more economical design of highway infrastructure, including bridges, has been validated using a FE software package LSDYNA. Parametric studies have also been carried out to show the importance of considering the mass of the bridge components. The results show a counter-intuitive phenomenon: although the increase in target height/length increases its displacement, it reduces the resulting design force. This is due to the increase in target mass, and thus its inertial resistance. It again shows the importance of considering the masses of bridge barrier, deck and pier, as they all have substantial effects in reducing the design forces, and hence saving design costs.