Australian researchers are turning to advanced analytical computing methods to uncover means of further heightening the efficiency and resilience of structural steel frames.
Researchers at the University of Sydney have been conducting a project which aims to change the paradigm of steel structural design. The goal is find more consistent reliabilities for a wide range of structural systems, and shorter, more flexible and more efficient structural design processes.
Steel structures can buckle despite their apparent stability and may do so in different ways simultaneously. The strength and weight of the materials used are key to designing reliable steel frames, but the integrity of the structural components and the parts that connect them as a whole is paramount.
The current method for steel frame design entails two stages: the analysis of forces and moments in the steel frame itself, followed by detailed safety checks of columns, beams and connections against prevailing structural steel standards. Current procedures rely on hundreds of equations stipulated in national codes for calculating the strength of individual components of structural frames, such as columns and beams.
Led by Professor Kim Rasmussen, head of the School of Civil Engineering at the University of Sydney and chairman of the Centre for Advanced Structural Engineering, the team is basing the research on advanced geometric and material analysis in which both the analysis and capacity checks are carried out in a single step, thus removing the need for member and connection capacity checks to a structural steel standard.
At the core of the research is a rigorous statistical assessment of the system strength which considers structural redundancy, consequences of failure and statistical variations in loading and variables affecting frame strength.
Rasmussen says design-by-analysis will simplify and speed up steel frame structural design and deliver greater accuracy and safety.
He came up with the idea following conversations with members of the University of Sydney’s architecture faculty.
“Their design programs increasingly call on analysis programs that design structural components to find dimensions for things like floor slabs,” he said. “The same programs would benefit from analysis programs that can design the complete structural frame so that the dimensions of columns and beams are known, thus allowing clear floor space and floor heights to be determined accurately during architectural design, avoiding a second iteration after structural design is completed.”
Twenty years ago when the first advanced analysis programs were developed, they required high-cost, high performance computers only available at research institutions. Rasmussen says advanced analyses of large structural systems can now be run on low-cost desktop computers
“Codes in design-by-analysis will stipulate the reduction factors (resistance factors in engineering design) to account for variabilities in key parameters like material strength, imperfections and loads. We aim to derive these factors for a wide range of steel frame applications,” he said.
“Our method is superior to current member-based design to a national code: it is faster; provides more uniform reliability; and is versatile, being applicable to both common and unusual types of structural frameworks.”
Rasmussen’s team of PhD students has been running as many as 100,000 advanced analyses of various frames, using Monte Carlo probability modelling to generate random structures with random values for administering, checking and processing.
To date, the set of resistance factors that Rasmussen and his team have gathered from a wide range of 2D structural frame types is remarkably consistent. From a structural design engineer’s viewpoint, this as a positive result, minimising the number of resistance factors that will need to be incorporated.
The project is a truly global collaboration. In addition to Dr Hao Zhang, also from the University of Sydney, the team includes leading international researchers in the fields of steel structures and structural reliability from the Georgia Institute of Technology and Johns Hopkins University in the US, and the Harbin Institute of Technology in China.
Rasmussen hopes the project will lay the foundations for the widespread use of computer-based design-by-analysis, integrating architecture and engineering, and fostering greater innovation in structural design. He sees no reason why the design-by-analysis method will not be adopted throughout the world.