Built to last?
McMaster University civil engineer Samir Chidiac on the evolving process of quake-proofing buildings.
Civil engineers from around the world will be meeting in Hamilton, Ont., next week to discuss sustainable structures: buildings designed and constructed to incorporate conservation and the recycling of waste materials and to handle extreme stresses like earthquakes.
With the notable exceptions of British Columbia and, to a lesser degree, Quebec, Canada has very little seismic activity. Nevertheless, sustainable construction is an area where Canadians are among the leaders in research, says Samir Chidiac, the McMaster University associate professor chairing the conference. He spoke with CBCNews.ca about the state of earthquake-proofing technology.
What do you need to consider when assessing whether a building can withstand an earthquake?
There are four main issues. One is the issue of [the building] code: what are the standard requirements and does it meet those standards? Another is design. One of the things we're seeing in China is that these kinds of buildings may not have been designed to sustain that kind of load. They were certainly not designed to withstand an earthquake of 7.9. This is a large earthquake.
The other two issues are construction and maintenance. It doesn't matter how well you design it, if it's not built as specified, then you don't have the building you think you have. This is what we're seeing is happening quite often, especially if you are looking at Turkey, Iran. China would not be an exception. This is one [issue] that's very hard to deal with in a country where there is no quality control.
The last [issue] also relevant here in Canada is maintenance of existing structures. It doesn't matter how well built the building is, it will age, which means its properties are changing, and if we don't address those, then potentially we'll have a problem.
How do engineers design better buildings?
Unfortunately, how we learn is when there's an earthquake. A building is designed for a certain magnitude of earthquake, let's say 7.0, which means it is designed to handle certain acceleration in both the horizontal and vertical direction, to put it in a layman's terms.
If you look back at the 1995 earthquake in Kobe, Japan, one problem that came about was that they were using two different types of construction. They were using concrete, and then there was steel on top of it, and there were failures.
We also learned something from the collapse of bridges at Kobe, because before, we really didn't pay too much attention to vertical acceleration. As a result of that earthquake, vertical acceleration became more important, and that's why you see the [building] code has changed, even in Canada.
Because of that, it gives impetus to research. People want to work on relevant things, but sometimes, it's hard to presume what is relevant, except, unfortunately, when something goes wrong.
You say vertical, or up-and-down, stresses from earthquakes are being taken into greater consideration. How has that changed the way buildings are made today?
It's how columns and beams and walls are reinforced. We've identified where the weaknesses should be. This is not necessarily new technology per se, but the way it's being implemented is new.
Typically, when we were looking at earthquakes, we were concerned with the lateral load, that everything is moving more or less in the lateral direction, or in the horizontal plane, if you want to simplify it. But now, we recognize that there is also an up and down movement, and that can become a problem, depending on the construction.
If you look at masonry, it has been designed in the past only to handle gravity loads, to have force pushing it down. The minute you bring an acceleration upwards, guess what, you don't have the same interaction between the masonry, which means it will loosen and create problems for us if it's not reinforced.
If you look back, a lot of the collapsed buildings have a reinforced concrete frame structure with a lot of masonry infill, and for a big earthquake, that's not the preferred type of structure.
Have there been any technological innovations in the last decade?
Isolation is one innovation, where you try to isolate the building from the ground to a certain extent dynamically so that it would dampen the vibrations from the earthquake. It's not necessarily new … but its implementation has more or less taken place in the last five to seven years.
Typically, what you do is instead of the foundation resting on your soil or the rock, you put a medium in between so that it provides a cushioning effect to reduce the energy transfer from the ground to the building.
There are different types of material you can use. At McMaster, a colleague of mine, Michael Tait, is doing work where they are looking at using FRPs — fibre-reinforced polymers — to create isolators for masonry. What you are looking at is energy dissipation and [whether] the isolator will dissipate more energy without taking damage, because you cannot change them every time [an earthquake hits]. … You want to design them to a certain level so they will be able to absorb the energy with minimal distortion.
Another thing we're looking at here at McMaster are tuned liquid dampers. What you do is put almost like a water tank at the top of the building and use that to counteract the lateral load from the earthquakes or from wind load. (Vancouver's One Wall Centre, completed in 2001, was the first skyscraper to use this technology.)
As the earth is moving, that energy goes from the bottom to the top of the building and back again on a highrise. If you put a mass on the top or you put that energy dissipater at the top, it will allow the building to reduce that movement, so it acts as a counterweight. How well it works in earthquakes, we're [still] looking at, but these have been very effective in high winds for highrises.
It seems like the early history of civil engineering is littered with broken careers — the bridge builder who is a genius until his bridge collapses, and then he's a pariah. Does that environment still exist?
Not anymore. Before, these guys were pioneers. They had no code and no standards; they had their vision and their knowledge of the mechanics. Whereas now, typically, we open a text: this is the load, and you design for it. Now, engineers lose their career if they are not trained to design for [an] earthquake and they don't do the proper reinforcement, which could happen.