Foundation Reactions 1

[SteelPE]

I have a job where I am not responsible for the design of the foundation system. I have all of my loads broken down into service dead, live, wind and seismic values. I prepare my reactions this way so that the foundation engineer can properly design his foundations.

The reactions have been submitted to the foundation engineer who is refusing to design the foundation until I give him worst case loading on his foundation system. Basically he is asking me to interpret the load combinations of the code for him. I avoid doing this because of the increased liability.

What do you guys do with providing reactions to another engineer to design foundations?

I understand with computer programs today, it is easy to export the reactions after they have been run through the load combinations.

 

[slickdeals]

I find it surprising that he is asking you to do his work. The equations are not too many or too complicated. I agree that you are taking on liability because you may have different combinations controlling the design.

We are Virginia Tech
Go HOKIES

 

[ToadJones]

I agree with Slick here....
I worked for a firm at one time where we did very little foundation work so we were issuing foundation reactions all the time.
Your foundation guy should be figuring out his own load combo's.
We usually factored the loads up quite a bit and issued them as "not to exceed" since they were often required early on in the job. We had to leave ourselves some wiggle room since we were essentially promising "not to exceed" them.
So we factored them up and I am sure the foundation guy threw some extra safety in there too....all said and done we probably had foundations that were 2 times bigger than they needed to be.

 

[ToadJones]

...still baffled that he is asking you what the worst case load is on his system.
That would be like the building designer asking a code official or a equipment vendor what is the worst case load on the building.

 

[nutte]

Looking at it from the foundation engineer's perspective, a lot of it has to do with how the reaction data is described and provided to the foundation engineer. I've seen lots of metal building drawings with several wind load cases (up, down, left, right, wind on parapet or eave only) and different dead load cases (building framing, collateral). If these are merely labeled W1, W2, W3, etc., how is the foundation engineer supposed to make sense of it? In cases like these, where interpretation of the submitted reactions is difficult or likely to result in error, it is completely understandable for the foundation engineer to ask for the worst case reactions.

 

[ToadJones]

nutte-
I can see your point there, but it sounds like he has his reactions pretty solidly labeled.

 

[SteelPE]

Nutte,

I have designed metal building foundation systems many times and I hear your frustration with the way the reactions are presented. However, it is very easy to cut through the BS and figure out what loads are applied to the foundation system. To ask the metal building mfr. to make this interpretation for you is risky. How do you know they are even giving you the proper reactions for your foundation design? Do you back check them, or just say that it is not your responsibility and place a not on your drawings stating the reactions you designed your foundation for were provided by (fill in the blank)?

 

[JAE]

Write the engineer a letter:

[blue]Dear Mr. Engineer:

My building reaction loads are as follows:
DL = xx lbs
RLL = xx lbs
RSL = xx lbs
RWL1 = xx lbs
(etc.)

The building code outlines several load combinations that are required. You, as the foundation engineer, can simply take the above load cases and combine them in accordance with the code using simple high school algebraic methods.

Should you require assistance with these basic procedures, we would be happy to assist you in developing a comprehensive plan and solution to your calculation needs.

Attached are our standard hourly rates that would be applicable should you choose to utilize our services.

As an estimate, we would expect the fees for these services to be between $3,000 and $4,000. Please advise us if you desire to pursue this and we will quickly get you a fee proposal contract form. A retainer fee in the amount of 50% of the above estimated fee will be required.

Sincerely,

xxxx
[/blue]

So my thoughts - shame them into doing their own work.

 

[ToadJones]

off subject, but we actually had a utility company tell us once that we had to show them, on a drawing, where THEIR utilities were running underground before we could get a permit. The reason we were calling this utility was to get them to mark their lines.
I was totally baffled....

 

[Oversee]

He might only ask for a favour from you.

By the way, it may not be conservative to have one ‘worst’ case to check. I did have combo reaction forces from my colleague who worked on superstructures. But I have to make my judgement to figure out the worst cases, e.g. a smaller vertical reaction is likely to a worse case when checking stabilities (overturning or sliding). Section 1605 of ASCE7-05 should be followed in your case.

 

[SteelPE]

Oversee,

I completely agree. How am I to know what is going to control the design of the foundation system. I have a general idea, but since I am not the designer it is not my responsibility.

 

[LowLax]

The engineer should be able to do it himself, but I see some metal building suppliers print the reaction envelopes for each column. I always appreciate it. The code dictates the load combinations. The building supplier is designing the building for these combinations. Why not just print the results? That being said, I would never ask if they weren't provided, I'd just figure it out.

 

[dcarr82775]

Toadjones,

We were doing an excavation bracing job about 40' deep requiring tiebacks. The phone company told us that their west coast trunkline was under the street behind the cut somewhere, but for security reasons they couldn't tell us where.....

 

[graybeach]

For bridge foundations, I generally provide a table of loads in all 6 DOF for each of the required load combinations. I clearly label the point at which the loads apply, and I state whether the loads are service or factored. All of this is necessary to design the foundations and should be developed by the structural engineer. There is no way I would or could choose one of the load combinations and say it is the worst case.

 

[SteelPE]

The code requires use to use superposition to define the loads on the foundation system. However, under the new AISC procedures, we are required to do some form of a P-Delta analysis on our structure. With a P-Delta analysis, the theories of superposition do not apply because the loads due to a P-Delta analysis are non-linear. This means giving the pure dead, live, wind and seismic loads would not be accurate?

What effect does this have on the overall question above?

 

[ToadJones]

dcarr-

I think their security "reasons" looked a lot like donuts and coffee

 

[frv]

SteelPE..

That may be true of the superstructure (and specifically internal stresses in the members), but the reactions are the reactions.. The foundation engineer can use the loads and decide whether he is to carry out a linear or non-linear analysis of the foundation system.


I'm with the majority on this one.. seems like the foundation engineer doesn't want to do his job.

 

[SteelPE]

Getting the engineer to do his job is proving to be very difficult. It's like dealing with a little child. He refuses to begin the process without the "minimum and maximum" loads on the foundation. The owner just wants the job done and doesn't care who does the work. Unfortunately, everyone wants me to resolve the problem at my own cost.

 

[ToadJones]

It actually scares me a little that he wants "minimum" and "maximum" loads.
Is he just going to use those loads only?

when doing my own buildings and foundations, I may have tons of load combos for the steel design.
When it comes to foundation time, I just use all my service level reactions and make up some new combinations...i have never just used the load envelop and designed the foundation for that!

 

[SteelPE]

ToadJones,

And nobody realizes why I want no part of this (at least outside of this forum)! You need strength level loads to properly design the concrete in the foundation system. How are min and max loads going to help him with this.