Expert: Oversizing a common issue in the use of precast concrete
The problem of overdesign arises from the incorrect assumption that precast concrete is weaker than site-cast concrete, expert says
The construction industry needs to do a better job at diagnosing weaknesses in building designs that use precast concrete in order to avoid oversizing, according to Halûk Sucuoğlu.
The director of the structural and earthquake engineering laboratory at Turkey’s Middle East Technical University told Construction Week that precast systems are typically viewed as weaker compared to site-cast concrete, an assumption that he said he disagreed with.
“That [perceived] weakness is compensated through overdesign, which is not rational,” said Sucuoğlu. “You don’t try to overcome a weakness by overdesigning. You address it by diagnosing the weakness properly. If the weakness is in the connections, then design and execute the connections better.”
One of the speakers at the Big 5 2017’s Innovation in Precast Summit, Sucuoğlu highlighted the need for performance-based seismic designs to boost the resilience to earthquakes of structures made of precast concrete.
“In the Middle East, cast-in-place concrete still probably dominates the market, but precast systems have the advantage of quality because they are produced in factories,” he said. “Safety-wise, there is no problem. Precast emulates reinforced concrete, and adheres to the same codes and [standards], so it doesn’t have any handicaps.”
Though not handicapped, precast concrete does have “special characteristics” that require attention, noted Sucuoğlu, adding that a precast system’s vulnerability to earthquakes tends to involve the connections made on site.
He explained: “The connection, which is made at the site, should be done properly, not only in the execution but also in the design, especially in seismic regions.
“There are certain methods of design that do not transmit earthquake forces to connections but dissipate them to other parts of the structure.”
Sucuoğlu added: “With the current system, [precast systems] are being designed similar to reinforced concrete, which receives damage during an earthquake anyway.
“But precast has the further advantage of being modular. This modularity can be explored and used as an advantage, since it means dissipaters between building elements and parts can be replaced after an earthquake, in the same way that a damaged part of a vehicle can be replaced.”
Although earthquakes are not as common a problem in Gulf countries like the UAE as they are in other parts of the world, the region is not free of seismic activity and must, therefore, work at improving the resilience of structures that make use of precast concrete, said Sucuoğlu.
“Precast is the construction system of the future […], so we need to develop new techniques that make precast systems less vulnerable to earthquakes. This is the way to go, but it is not so easy. Scientists and engineers are continuing to work on it,” he concluded.