From a Reader:
Feel free to share the following information from a structural engineer in Alaska who is also a recently retired structural engineering professor at UAA.
I would only get concerned if walls are out of plumb, detached from their supports, or are “racked” (i.e. door openings and window openings are no longer square).
If floor systems as structurally detached from supporting walls, that would be another major concern.
We expect that sheetrock will be damaged (wall and ceiling) and that suspended ceilings will fall, so don’t think that there is structural damage if that is all that has happened.
I suspect that if windows are intact and doors open and close, than there is nothing to worry about.
There may be some hidden problems (like cracked beams or columns) but it is unlikely in a wood framed structure.
It would be prudent to have an engineer evaluate at some point if there are further concerns, but there should be no immediate danger if the above criteria is not met.
The most stable homes are the “boxes”, homes with a minimum of corners and offset features. Large custom homes with lots of openings and complex shapes are more likely to have issues.
One last thought, the level of design for seismic is life safety . This means that we do not design buildings to survive earthquakes. They are designed so that they don’t collapse and kill people. Any building that stays together enough so that people can get out is considered a success. Some buildings will have to replaced, or undergo serious repairs. From what I am hearing, though, it is doubtful that many homes will need more than cosmetic repair as this earthquake, while significant, is not as significant as the design earthquake.
T. Bart Quimby, P.E., Ph.D., F.ASCE
Quimby & Associates
For clarification, below I’ve made some of it more plain English
Sheetrock is not structural. It doesn’t support anything or hold any weight, so Sheetrock damage is not structural.
The ceiling grids that fell down in the schools are also not structural, the lights are supposed to hang like that in an earth quake. Most schools do not appear to have sustained much of any structural damage.
Out of plumb means not lined up. If you have a wall that moved two inches, you have a problem. If your foundation moved or is no longer square, as in the walls meet at the same angles, you have a problem.
Cracks, even in concrete, are not necessarily a problem. A structural failure mean something moved out of place. A wall, a foundation wall, etc.
The below picture (click the link) shows Sheetrock damage that occurred in a home with no structural or even significant damage at all.