The evolution of bridges over the past decades has been impressive. In the future, it is estimated that bridge spans could reach about 3 kilometers in length. As bridge structures become capable of spanning larger gaps, new technology should evolve to make them more efficient.
Scientists from the Technical University of Denmark (DTU) and COWI, an international consulting group established in Denmark, evaluated the potential to optimize bridge structures reducing their weight and making them more environmental-friendly.
The research team investigated changing the fundamental design of a suspension bridge by utilizing topology optimization, a technique that optimizes the material arrangement used at a given project considering the loads applied, the constrains and the boundary conditions. This method is widely used in aerospace and automotive engineering but it has not been introduced in structural engineering.
The ultimate purpose of this technique is to reduce the structural materials used in a bridge's girder, filling the rest of the part with air without impacting its loading capacity. Scientists studied a girder measuring 30x5x75 meters which was divided into two billion voxels in order to be analyzed. A voxel is the corresponding unit of a pixel in 3-dimensional space and is defined in x,y,z coordinates. A topology optimization technique was then utilized to reduce the amount of sufficient materials. "The topology optimization method is used for determining whether each individual voxel should consist of air or steel material. The result is a bridge girder design that uses the least possible steel without impairing the strength of the structure,” Niels Aage, co-author of the study and a Professor at the Department of Mechanical Engineering, DTU, stated.
According to the results of the study, a method that would save structural material and reduce the weight of the structure includes making the conventional transverse diaphragms of a bridge's girder, curved. This approach could theoretically reduce the materials used in bridge decks by up to 28% and the total materials used in the structure by 20%. A similar reduction in carbon emissions would also take place in that scenario, a fact that is critical since the building and construction industry are responsible for 39% of the total carbon emissions worldwide.
Such modifications would affect the construction processes and the feasibility of a bridge. However, according to Dr. Mads Jacob Baandrup, the lead author of the study and an engineer in COWI's bridges department who was involved in the aforementioned analyses during his Ph.D., the design alterations proposed are applicable and can be implemented without increasing the cost of the structure.