I am not a structural engineer (or an architect for that matter). But one of the things that has come to greater light as a result of the devastating earthquake that hit Turkey & Syria last month is the number of "soft story buildings" throughout these countries.
Technically, a "soft story building" is exactly what the name suggests. It is a building where one floor is less than 70% as stiff as the floor above it, or less than 80% as stiff as the average of the three floors above it (source).
The typical application of this is a ground floor that has less structure (missing shear walls for example) and is more open. And it is usually done to accommodate things like parking and retail uses, and to, of course, build more cheaply.
However, there is a massive problem in that they are often structurally suboptimal! (Again, not a structural engineer.) This is why we saw so many of the buildings in Turkey "pancake" during its earthquake. The ground floor failed and then it brought down the rest of the building.
I am not a structural engineer (or an architect for that matter). But one of the things that has come to greater light as a result of the devastating earthquake that hit Turkey & Syria last month is the number of "soft story buildings" throughout these countries.
Technically, a "soft story building" is exactly what the name suggests. It is a building where one floor is less than 70% as stiff as the floor above it, or less than 80% as stiff as the average of the three floors above it (source).
The typical application of this is a ground floor that has less structure (missing shear walls for example) and is more open. And it is usually done to accommodate things like parking and retail uses, and to, of course, build more cheaply.
However, there is a massive problem in that they are often structurally suboptimal! (Again, not a structural engineer.) This is why we saw so many of the buildings in Turkey "pancake" during its earthquake. The ground floor failed and then it brought down the rest of the building.
I can appreciate that retrofitting older buildings is both difficult and expensive; but it is inexcusable to not work toward that and it is certainly inexcusable to not mandate that every new building meet whatever building codes are required to save lives.
I can appreciate that retrofitting older buildings is both difficult and expensive; but it is inexcusable to not work toward that and it is certainly inexcusable to not mandate that every new building meet whatever building codes are required to save lives.
If I were to make a broad generalization for the way that we typically design the structural systems for residential buildings and office buildings here in Toronto it would be as follows: office buildings tend to have a big structural core with perimeter columns and residential buildings tend to have a smaller core accompanied by both columns and shear walls (long structural walls essentially). There are a myriad of other differences, but for the purposes of this post, I'm going to run with this broad classification.
When something is typically done a certain way it often means that it is generally what the market wants and it is a cost effective solution. In the case of office buildings, this sort of structural system is essential for maintaining open plans and future flexibility. You can't have shear walls interrupting your floor plates. And because big office buildings also tend to have a lot of elevators, the structural core is usually what provides lateral stability to the building (or at least this is what the structural engineers tell me).
But this same imperative for open plans isn't usually there for residential buildings. In this case, the unit demising is often fairly fixed and the individual resident/tenant spaces tend to be smaller than in office buildings, which makes frequent structural elements a lot more palatable. And since the elevator cores also tend to be smaller (fewer elevators), there is usually a need to introduce other structural elements that can provide the building with lateral stability. (Again, this is what the engineers tell me.) So enter all the shear walls.
But every now and then, somebody in Toronto will ask: Is this the right way to be building? Other cities don't build their residential buildings with all of these shear walls and so should we really be limiting the future flexibility of our multi-family housing supply by constructing in this way? These are good questions. The short answer is that it tends to be easier/cheaper to build this way. Our market is used to it. And generally end-users are just fine with it.
However, this method of building isn't necessarily a universal truth. The structural system for One Delisle, for example, is far closer to that of an office building than it is to that of a typical residential tower. Much of this was driven by the building's architecture and its continually changing floor plates. I have also heard of instances where purpose-built rental developers are choosing to go column over shear wall so that there's greater flexibility in the future. There's certainly a case to be made for this.
As developers, it is impossible to know all there is to know about any one discipline. You need the right team in place for that. But we do have to look at the bigger picture, weigh all of the constraints, and then hopefully make a reasonably good decision. This is one example of that.
Image: Bay-Adelaide Centre North, Toronto
If I were to make a broad generalization for the way that we typically design the structural systems for residential buildings and office buildings here in Toronto it would be as follows: office buildings tend to have a big structural core with perimeter columns and residential buildings tend to have a smaller core accompanied by both columns and shear walls (long structural walls essentially). There are a myriad of other differences, but for the purposes of this post, I'm going to run with this broad classification.
When something is typically done a certain way it often means that it is generally what the market wants and it is a cost effective solution. In the case of office buildings, this sort of structural system is essential for maintaining open plans and future flexibility. You can't have shear walls interrupting your floor plates. And because big office buildings also tend to have a lot of elevators, the structural core is usually what provides lateral stability to the building (or at least this is what the structural engineers tell me).
But this same imperative for open plans isn't usually there for residential buildings. In this case, the unit demising is often fairly fixed and the individual resident/tenant spaces tend to be smaller than in office buildings, which makes frequent structural elements a lot more palatable. And since the elevator cores also tend to be smaller (fewer elevators), there is usually a need to introduce other structural elements that can provide the building with lateral stability. (Again, this is what the engineers tell me.) So enter all the shear walls.
But every now and then, somebody in Toronto will ask: Is this the right way to be building? Other cities don't build their residential buildings with all of these shear walls and so should we really be limiting the future flexibility of our multi-family housing supply by constructing in this way? These are good questions. The short answer is that it tends to be easier/cheaper to build this way. Our market is used to it. And generally end-users are just fine with it.
However, this method of building isn't necessarily a universal truth. The structural system for One Delisle, for example, is far closer to that of an office building than it is to that of a typical residential tower. Much of this was driven by the building's architecture and its continually changing floor plates. I have also heard of instances where purpose-built rental developers are choosing to go column over shear wall so that there's greater flexibility in the future. There's certainly a case to be made for this.
As developers, it is impossible to know all there is to know about any one discipline. You need the right team in place for that. But we do have to look at the bigger picture, weigh all of the constraints, and then hopefully make a reasonably good decision. This is one example of that.
