Advanced composites, such as glass fiber reinforced polymers (GFRPs), are strong, lightweight, durable materials that can be flexibly shaped to build large load-bearing structures.

Data logged from sensors placed on a GFRP structure at the 2016 Serpentine Architecture Programme, in London, now shows that it is possible to observe stresses borne by these advanced composite structures so as to give engineers a better understanding of how they react to different loads.

Dr. Wendel Sebastian, reader in structural engineering in the University of Bristol's Department of Civil Engineering, led a project in which sensors were distributed throughout the Serpentine Pavilion—an "unzipped wall" that transformed from a straight line at its top to a three-dimensional curved structure lower down. The project logged data on the structure’s response to both environmental (wind, temperature) and gravity (self-weight) loads.

Its advanced shape and assembly meant that the pavilion exhibited a complex structural response to applied loads. Image credit: ©Iwan Baan.“Advanced composites behave differently from traditional construction materials such as steel and concrete, so the improved understanding that we gain using data from a spectrum of real composite structures will help us use these materials even more creatively in the future,” Sebastian says.

Its advanced shape and assembly meant that the pavilion exhibited a complex and hybrid structural response—partly as a dome, partly as a frame—to applied loads. While safety factors were used in its design to ensure the structure was reliable, it was recognized that monitoring a real, as-built structure would present a unique opportunity to understand its true structural action and pave the way for additional safety factors in the design of future exhibition structures.

Working closely with the contractor responsible for taking down the structure at the end of the summer, Sebastian was able to log data that gave insight into the stresses released by the structure during dismantling. These stresses were locked into the structure from the beginning, owing to the need to overcome any lack of fit between the boxes during the original assembly of the pavilion. In reality, random differences from tolerances stated on engineering drawings mean that lack-of-fit stresses, which can be particularly important for structures made from slender members, are also random and are therefore difficult to predict with confidence.

Normally such stresses remain a secret of the structure. Given that the sensors were installed after the pavilion was built, it is only because these stresses, slightly modified over time, were released by dismantling that this rare opportunity existed to attempt their quantification from the sensor data.

Sebastian has also gathered sensor data from a GFRP road bridge used near Bristol. The lightweight bridge was prefabricated and quickly lifted into position using a low-power crane, thereby enabling the early removal of a seven-kilometer diversion required during the bridgeworks.

His findings will be presented at the Advanced Composites in Construction conference in September 2017.