An 18-foot steel column shakes in the grip of a vise on UC San Diego’s shake table.
The column would stand vertically in a building, and the shake table stimulates the stress of a building’s weight and the movement of a strong earthquake.
Ultimately, the column buckles and bends, which could cause a structure to lean or even collapse.
Building codes will likely be changing soon, following the shake table experiment, because the column is used in many California buildings.
The experiment are detailed in an article published in The Journal of Structural Engineering.
Jay Harris is a structural engineer who co-wrote the article. He said the problem is found in the column’s connecting spine, called the “web,” which has proven to be too slender.
“So it gets very thin — the slenderness gets very high. The column itself is at risk of buckling too much and losing some of its load-carrying capacity,” Harris said.
“If you lose the ability to carry those gravity forces you could be at risk for some type of collapse. Whether it’s a partial or a total collapse, that’s going to be specific to the building and the skeleton. And where that column is located … what it is carrying.”
One of the consequences of a buckling column is what’s called “story drift.” That occurs when the upper stories of a multi-story building sway in an earthquake, causing the building to lean.
Ironically, the use of the columns, which that failed the shake table test, became quite common following the Northridge earthquake. Engineers thought the beam's greater width would prevent lateral building movement in an earthquake.
“The Northridge Earthquake was a big shock to the engineering community, when it came to earthquake designs. What we were using was brittle in the welded joints,” said UC San Diego engineering professor Chia-Ming Uang, another co-author of the journal article on the shake table test.
Now that the wider columns have proven too have their own problems, Harris said those will be phased out with new building codes.
