×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Seismic action on a combined foundation

Seismic action on a combined foundation

Seismic action on a combined foundation

(OP)
I have two large stoves approx 30m tall, 7.7m diameter, 10m apart weighing about 1700tonnes each. Seismic forces will govern strength design of an (unfortunately) combined foundation.

Obtaining seismic forces is pretty straightforward but the question is ----

In the event of an earthquake, can the two stoves go "out of phase" of each other or will they always have forces acting on each of them in the same direction.

If they oscillate like a tuning fork then both can move in towards each other and bend the hell out of my foundation. Looking in the orthogonal direction, if one goes one way and the second goes the other way then the foundation suffers a huge torque or twisting action which will double my reinforcement.

Is it possible for the earthquake to induce oscillations in the stoves such that they move in different directions and effectively “fight” each other using my foundation.

I am inclined to think it is possible (mainly because I’m not sure and feel the need to design for it). However we are talking about a fairly sizable increase in build costs and there are some people trying to argue that it can’t happen and that earthquake forces from the two vibrating structures will always act in the same direction.

This alternative arguement is that it is the footing that moves under the stoves and the stoves are mearly trying to "catch up with" the footing. If this is so then I can see that the forces cannot oppose. But my arguement against this is pictures from Kobe which clearly showed that close  buildings smashed into each other indicating opposing oscillations.

The two stoves are essentially the same.

Any views would be appreciated.

RE: Seismic action on a combined foundation

I think that you have to assume that the stoves will "fight" to some degree.  Since the earthquake loading can arrive at different times at each stove, they can (will?) be largely out of sync during a seismic event.

I understand that there are some fairly sophisticated modelling structural engineering computer programs that can use past earthquake events and finite element techniques to try and predict probable structural behavior.  But I suspect that level of effort is beyond the scope - and needs - of your assignment.

Perhaps a structural engineer with relevant experience will respond - hope my message keeps yours "near the top."  

Good luck -

RE: Seismic action on a combined foundation

You could justify allowing for non-synchronous movements by the stoves, by addressing their behaviour (i) during construction, (ii) during operation, where one may be shut down for maintenance, (iii) during a major overhaul, where one stove continues in operation, and the other may be partly dismantled.  This is likely to increase the phase shift of movement caused by the difference in arrival times of seismic forces.

Happy New Year!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources