Structural Engineering Program Needed

[msquared48]

Got a problem...

Designing a 5 story wood frame over three levels of PT concrete parking. "Woodworks" will analyze vertical and lateral for wood only, no concrete, and "Risa3D" will analyze vertical, concrete shearwalls and frames, but not wood shear walls. Risa will not include wood shear wall analysis in their building design program for about two years. Is there any program out there now that will do the whole building analysis without having to break the building into two solutions, one for the wood and one for the concrete?

Mike McCann
McCann Engineering

 

[csd72]

Design it as two separate buildings.

Apply the results of the timber analysis as loads to the top of the concrete carpark.

As an aside, you also need to consider the implications of anchoring the timber structure into the post tensioned structure.

csd

 

[msquared48]

This is what we are doing, but we were looking for a program to do both the wood and concrete as one building, vertical and lateral. Can't find one yet.

Mike McCann
McCann Engineering

 

[cldea8]

Mike,

We recently designed a 3-story cold-formed steel structure over a 2-story parking garage. The irony is, in order to look at the buildings separately (like csd72 suggests) they almost need to be modeled together. The seismic procedure (analyzing a building on top of another building) for this simplified method requires that the lower portion be 10 times stiffer than the upper structure and the period of the entire building to be no more than 10% over the period of the upper structure. (This is according to IBC...not sure on your building code..)

We actually modeled the upper portion in RISA (as we had rod-braced walls) and the lower portion in Etabs (by another firm--this was somewhat of a dual EOR project). We then combined the results using simple lump mass models. The seismic requirements proved to be somewhat challenging.

To directly answer your question...no I am not aware of fully comprehensive software tailored to building modeling. It seems diaphram type construction is modeled seperately from frame based software. We recently upgraded and did an extensive search and settled with RISA because it seems to offer the widest variety of components and systems. There are finite element packages out there such as SAPP and Tekla Structures but I don't think they are well tailored for building component modeling (not as much canned information). You would have to model building elements on a much more thorough and mundane level.

You may be able to add some type of lump mass model on top of your concrete frame in Risa? You could also possibly model the upper stories using spring constants in lieu of shearwalls?

Good Luck,

cldea8

 

[msquared48]

cldea8:

Thanks for the info - I will look into modeling the wood shearwalls that way - not sure offhand if RISA will do that though.

Mike McCann
McCann Engineering

 

[cldea8]

I have modeled shear walls using spring constants and have had success verifying hand calculated story drifts. I typically calculate my deflection (by hand) of each shear wall with a 10 kip point load. I translate this into a rigidity (1/deflection) and then use this value on a spring constant boundary condition at the top of the shear wall. I am only recently familiar with Woodworks and have not had a chance to see if it calculates deflections or story drifts?

If your upper building is regular and repetitive per floor (if the center of rigidity and mass are in the same locations) you may be able to lump your mass per floor onto stacked columns representing an equivalent stiffness (per floor) in order to check your periods?

Make sure you are getting good mass participation in RISA. The help file on this is rather thorough. Also we have had good luck with getting suggestions from the engineers at RISA.

cldea8

 

[RareBugTX]

Just curious. Did you say 5 story wood frame over concrete?
Sounds like a little bit too much of wood for a building that high.What type of occupancy are we looking at. Just curious.


Regards,


Rarebug

 

[woodengineer]

I was not aware you could frame 5 stories out of wood in the scenario you described. I have seen it done where the average grade placed most of the last level below grade and only a portion was a walk-out condition framed of wood with 4 stories above. Will Woodworks analyze 5 stories? In any case...it sounds like an inteesting project.

woodengineer

 

[msquared48]

The local jurisdiction allows you to go five stories of wood if it is sprinklered. I have not found 5 stories to be a problem with Woodworks, yet...

Mike McCann
McCann Engineering

 

[cldea8]

I think it can be done. We have looked into the story height issue w/ wood and found that it basically depends on local fire and building code (provided you are not restricted by your site seismic class).

In one instance we traced it back to whether or not the local fire department had a ladder truck long enough to reach a certain elevation.

But I agree, it is unconventional and we typically see the bottom story partially underground and constructed out of concrete.

cldea8

 

[jdonville]

I've only just dipped my toes into the structural analysis software pool, but ROBOT Millenium claims to work with any material. See

http://www.robobat.com/n/en/

for more details.

Jeff

 

[Pkass]

Hi,

Luckly, I have not met a problem like that. As I do steel and concrete design only.

However, to solve this problem I would go critical,

I would design and check the 5 + 3 as one material (concrete in your case) and get what I need for the first 3 floors, and then go tback and assume all building as wood and pick up what I need for the upper 5 floors.. Sounds crazy, but safe.

regards,

 

[cldea8]

Pkass,

How would you deal with the seismic requirements...differences in stiffness and period? That may be counter productive.

I am in Missouri (one of the highest seismic zones in the nation) so I naturally gravitate to those requirements. It may not be an issue @ this site or w/ this code.


cldea8