New research leads to lighter and greener bridges

June 03, 2020

The past 60 years have not seen any fundamental change to the design of bridge decks for suspensions bridges - best known in Denmark from the Great Belt Link. To accommodate the request for ever longer bridges, the Technical University of Denmark (DTU) and COWI, studied how to optimise structures to reduce the weight of the bridge deck, in particular increasing the span. Recently published in the recognised scientific magazine Nature Communications, the results of that research project indicate vast potential.

"We applied different methods for examining how to better utilise materials, which primarily consist of steel and concrete. Initially, we sought to optimise their use in traditional structures by using transverse diaphragms in the bridge deck, thereby achieving a theoretical weight reduction of up to 14 per cent," says Mads Jacob Baandrup, who carried out the analyses in connection with his PhD project and today works as an engineer in COWI's bridges department.

New curved design makes the difference

With a view to achieving additional savings, the researchers looked at the possibility of altering the structural design. That was done by using topology optimization, a method known in car and aircraft industries, that had not previously been used for large-scale building structures.

"In popular terms, it's about 'emptying' a bridge girder of its existing elements, providing complete freedom for choosing a new design. The inner volume of the bridge girder is then divided into a structure of very small voxels (3D pixels), like small dice. The topology optimisation method is then 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," says Associate Professor Niels Aage, DTU Mechanical Engineering, who is one of the world's leading scientists in large-scale optimization and was responsible for the project analyses.

Specifically, a bridge element measuring 30 x 5 x 75 metres was analysed, divided into two billion voxels, each no bigger than a few centimetres. The result was an incredibly extensive calculation performed by a supercomputer, which would have taken an ordinary computer 155 years to do and is the largest structural optimisation ever carried out.

Carbon saving and economically interesting solution

The computer calculation presented input for how to best structure the design space of the bridge deck. Among other things, that meant curving part of the currently straight transverse diaphragms, making it possible to shave off 28 per cent of the material that is used for bridge decks and thereby achieve a corresponding reduction of the CO2 emissions generated by the production and transport of concrete and steel.

"We interpreted and adjusted calculations so the result became a suggested bridge girder structure with the optimum design that can be carried out without too costly production methods. The economic aspect is important in order for the design to be a realistic option for future bridge projects," says Mads Jacob Baandrup.

Valuable knowledge for tomorrow's suspension bridges

Naturally, additional analyses will be required before the new design can be used for building bridges, but COWI is confident that the results of the research project add valuable knowledge to tomorrow's suspension bridges.

"The new bridge girder design can be converted into a weight and CO2 reduction of up to 20 per cent for the entire bridge, which of course benefits the climate. COWI is also involved in a wide range of the world's largest bridge projects, so a potential new design will also benefit our customers and society," says Technical Director Henrik Polk, COWI, who participated in the research.

DTU is also very excited about the results.

"We believe there are huge perspectives to using topology optimisation for ensuring the sustainable design of other large building structures, such as high-rises, stadiums or highway bridges. We want to explore that field, and since the construction industry accounts for 39 per cent of global CO2 emissions, almost any reduction can be of interest," says Professor Ole Sigmund, DTU Mechanical Engineering.

The calculations for the topology optimisation were carried out on a PRACE (Partnership for Advanced Computing in Europe) supercomputer.

* The COWI Foundation: 450.000 DKK

* Innovation Fund Denmark: 668.518 DKK

* COWI's Bridges International department: 205.000 DKK

Technical University of Denmark

Related Emissions Articles from Brightsurf:

Multinationals' supply chains account for a fifth of global emissions
A fifth of carbon dioxide emissions come from multinational companies' global supply chains, according to a new study led by UCL and Tianjin University that shows the scope of multinationals' influence on climate change.

A new way of modulating color emissions from transparent films
Transparent luminescent materials have several applications; but so far, few multicolor light-emitting solid transparent materials exist in which the color of emission is tunable.

Can sunlight convert emissions into useful materials?
A team of researchers at the USC Viterbi School of Engineering has designed a method to break CO2 apart and convert the greenhouse gas into useful materials like fuels or consumer products ranging from pharmaceuticals to polymers.

Methane: emissions increase and it's not a good news
It is the second greenhouse gas with even a global warming potential larger than CO2.

Tracking fossil fuel emissions with carbon-14
Researchers from NOAA and the University of Colorado have devised a breakthrough method for estimating national emissions of carbon dioxide from fossil fuels using ambient air samples and a well-known isotope of carbon that scientists have relied on for decades to date archaeological sites.

COVID-19 puts brakes on global emissions
Carbon dioxide emissions from fossil fuel sources reached a maximum daily decline of 17 per cent in April as a result of drastic decline in energy demand that have occurred during the COVID-19 pandemic.

Egregious emissions
Call them 'super polluters' -- the handful of industrial facilities that emit unusually high levels of toxic chemical pollution year after year.

Continued CO2 emissions will impair cognition
New CU Boulder research finds that an anticipated rise in carbon dioxide concentrations in our indoor living and working spaces by the year 2100 could lead to impaired human cognition.

Capturing CO2 from trucks and reducing their emissions by 90%
Researchers at EPFL have patented a new concept that could cut trucks' CO2 emissions by almost 90%.

Big trucks, little emissions
Researchers reveal a new integrated, cost-efficient way of converting ethanol for fuel blends that can reduce greenhouse gas emissions.

Read More: Emissions News and Emissions Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to