Structure stability calculations 2

[antonmichel]

Dear Engineers,

I am a civil engineer with a little experience, I have been asked by an architect to check if a building is stable or not. How can I check this?

I am not asked for detailed design or calculations, I have been asked just to check if the building is stable or not with very simple calculations, the building is a bit complex like the pictures shown.

Thank you all in advance,

Anton

 

[ukbridge]

I'm going to read between the lines here and give you some minor hints.

Think loadpaths - driver smashes into a column, will the building stand up? Are there any alternative ways for the building to stand up i.e. at the very least not collapse? There are other similar situations you will need to think about.

Its all about robustness. Make some simple sketches showing these loadpaths with some bullet points and a bit of explanation.

gl

 

[antonmichel]

Thank you for responding,

I didn't really understand what do you mean, i have a very little experience, can you please tell me how can i make a simple report with simple calculations to check the stability for an architect?

thank you,

Anton

 

[BridgeSmith]

There really are no simple calculations for detailed stability checks, especially for a complex structure. You have to rely on first principles (statics), and as ukbridge said, follow the load path. This may be one of those occasions where you have to recognize the limitations of your experience, and defer the work to someone with the experience to take on an analysis of this scope.

 

[ukbridge]

Anton,
I can't give anymore away than that - the rules are very clear here, hence me reading between the lines.

You need to think about the lifecycle of the building, from its conception to its demolition. What happens if a middle column collapses from a vehicle collision? Are there any alternative load paths?

A good example is a footbridge. Say a lorry smashes into the front of the footbridge, clearly the footbridge itself is not going to survive and need to be replaced. However at the very least it would not become unseated from its bearings and fall onto the road/traffic. While this itself would be a catastrophic event, as a structural designer we have at least somewhat mitigated the risk (it would be very uneconomic to design the members of a footbridge to take into account collision forces for an illegal vehicle driving on the road, that substantially violates the clearances we have designed for).

As an "architect" or client I would want you to think about scenarios like these, and be assured that my building at the very least would not fall down if the worst were to happen. You convey this in the form of simple cartoon like sketches. Don't overthink it, write some simple bullet points and scan in some basic line sketches with arrows for the forces i.e. a) building in normal use and b) with column/floor removed.

As HotRod10 says there are often no simple calculations to check these things; without coming across a bit pretentious we have to rely on our deeper understanding of structures and engineering judgement. Its an art as well as a science at the end of the day, this is how we'll always make our money as structural designers and (mainly) not be replaced by a black box.

If you really want a reference read over this

https://www.google.com/search?q=des...ome..69i57.3950j0j7&sourceid=chrome&ie=UTF-8.

 

[oldestguy]

How do you find the neutral axis of a complicated structural beam? Do it in two directions 90 degrees apart and there is the center of gravity for building.

 

[SlideRuleEra]

Anton - "Stable" can have more than one definition; here are two more:

Say, the second building:

Consider the top view:

Find the center of gravity (C.G.) and locate it's position on the top view. If the C.G. is outside the projection of the foundation, the building is unstable (it is likely to fall).

If the C.G. is inside the foundation projection but outside the foundation kern projection, the building is stable... with uplift on some of the foundation.

If the C.G. is inside the foundation kern projection, the building is stable... all of the foundation contributes to supporting the building.

http://www.SlideRuleEra.net

 

[chicopee]

In addition to evaluating static loading and impacts from vehicles, you have to ask yourself where is that building located. Is it next to a beach susceptible hurricane forces, is it in California where tremors from seismic events are taking place or is it somewhere in Colorado where the building may be exposed to avalanches or NYC where traffic from vehicles could impact or elevated train tracks transmitting vibrational forces, or excavated underground tunnels could lead the building to collapse. You got to know the surroundings and come up with plausible problem areas in order to satisfy the requirements of your boss. In my case back in the 1970's ago when I was designing microwave antennae for VHF and UHF transmition, I always made a point of evaluating for wind and ice loading since these antennae were mostly erected on top of mountains and buildings throughout the world. You got to know your exposures.