ASCE 7-20 Non Building

[BPres]

I am a mechanical engineer designing a skid 6ft x 34ft with 8 legs holding process up about 6ft above grade. The customer wants it designed per "Non Building", ASCE 7-02, Section 9.14.

I have cross member bracing on the 8 legs. In the 34ft side, one end of each brace is welded at the bottom of one leg and the opposite end of the brace is welded at the top of the next leg. Does that design constitute a "Steel eccentrically graced frame, moment resisting, connection at columns away from links" per Table 9.5.2.2.

Finally, any recommended text books or handbooks for basic structural design and column-beam connections for a mechanical engineer?

 

[JStephen]

My first thought would be to use 9.14.5.2, "Rigid" non-building structures, which seems to simplify things.

AISC ASD and LRFD manuals have some structural detailing in them. You're not obligated to follow them necessarily.

On stuff like this, unless you're building a lot of identical units, it is sometimes more economical to modify the construction just to simplify the design. Use rectangular tubing instead of angles, for example.

 

[TFL]

sounds like an ordinary concenrically braced bay to me

 

[BPres]

We did a modal analysis on the frame and found T>0.06 so we couldn't use the rigid model method.

I thought "concentric" meant 2 braces (facing each other) connected at 2 columns and connected at the center of a common beam. As designed, I have 1 brace connected to the low end of 1 column and the top of the next column.

Am I helping or misunderstanding everything?

 

[TFL]

A conentric braced frame is one were all the members meet at nodes. essentially a concrentric braced frame is a truss. all the members are loaded in only axial compression or tension.a conncetric braced fram can have several configurations

****** ******* *********
* * * * * * * * * *
* * * or * * * or * * * *
* * * * * * * * * * *
* * * * * *

an eccentric braced brame is one where the members do not meet at a common point. Because the members do not meet at a common point the members induce bending in some of the members. A knee brace is an eccentric braced frame.

********** *******************
* * * * * * * *
* * or * * * *
* * * * * *
* * * *

in the first eccetric braced fraome above bending in induced in both column and beam, in the second ecb bending is only induced in the beam - sometimes called a link beam. The first ecb is actually very close to the behavior of a moment frame.

the reason it matters what system you use is becasue of the ammount of ductility the system can generate. concentric braced frames are very stiff not very ductile. moment frames are not very stiff. but very ductile. ecentric braced frames are soewhere in the middle

check out this link. be sure to click on the examples link at the bottom.

http://urban.arch.virginia.edu/~km6e/arch721/content/lectures/lec-02/home.html

 

[TFL]

i'm sorry the little "drawings" did not come out so well.

 

[TFL]

conncentric braced frames

or

or

or

 

[TFL]

eccentric braced frames

or

or

 

[TFL]

ok some more eccentric frames then i am going to bed

 

[BPres]

Thanks tfl! Big help.

 

[BPres]

Next question deals with ASCE 7-02, 9.5.2.4.2. For this skid, what r(max) do I use?

 

[BPres]

Never mind. Since A= floor area of immediate level above, and there is no level above, the reliability factor =2, right?

 

[TFL]

i don't have asce 7-02 i anly have 7-98 and that chapter references seismic zone d . i don't live in that world i only design for zone c so i am not familiar with that requirment.

however i would think there would have to have some area that you are supporting weather it be roof or mech equipment. the structure does not really care what you call it but you are supporting something with you brace.

 

[yellowbeetle]

Does anyone know when ASCE 7-05 will be released?

Thank you in advance.