CLT Shafts 2

[phamENG]

Working on a 4 story wood design. The initial plan was to use CMU shafts for LFRS. This is a wind dominated design. It's unlikely that a building designed to meet our wind requirements would not meet our (nearly) laughable seismic requirements, but I'll pay them due homage when the time comes. (I'm in Coastal/Southeast Virginia.)

The framer reached out to the design team today and suggested CLT in lieu of the CMU. At first glance, I love the idea. As far as the architect and I are aware, only one project has used CLT in this region - and that was a roof. So having an opportunity to work on what is likely to be the first lateral CLT project in the region is exciting.

Here's the rub - CLT lateral design info seems to be a bit lacking. I've found a few white papers, and read the lateral chapter in the CLT handbook, but I'm not coming away with the level of confidence I'd like to have. Most of them are limited to story height shear walls in platform construction - the idea here is to build the shaft full height (50' +/-) and the come back and build up around it like you would with a typical CMU/CIP shaft.

Does anyone have any insights into this? The benefits of CLT are clear, and I'm sure it can work in this situation, it's just a matter of figuring out how. Any resources or experiences would be welcome. Thanks.

 

[masonrygeek]

As the masonry guy on here, I have to say - just keep using masonry, you'll be fine! As for your framer, pham, do you think he would say anything else? Masonry walls or shafts do not take that long to build. As an example there was a elementary school gymnasium in WI (~90'x130'x32') that went up in three or four days. There was another project, again in WI, that had prefabricated shaft wall modules that were built offsite and craned into place. Be wary of folks giving blanket statements about cost or speed.

 

[phamENG]

masonrygeek - thanks. I agree. There are certainly ways of doing masonry quickly and efficiently. I've only met a few masons in my area who can pull that off, and unfortunately none of them are cheap!

We were certainly wary of it, and considered all the angles - material cost, material lead times, design changes (both cost and time to complete), local AHJ buy in (not guaranteed, since as a lateral system it isn't listed in ASCE 7-10), etc. That's why we're sticking with masonry on this.

We're still going to explore CLT for future use - Virginia Tech is currently doing some interesting research on using Virginia hardwoods in CLT production, and as I understand it some manufacturers are starting to expand the use of Southern Pine. Forestry and related products add about $25B to Virginia's economy annually, so I'm all for expanding the use of renewable products responsibly harvested and processed here in Virginia.

 

[molibden]

Wood contractor will like to use wood shafts if possible. That's reasonable enough I guess. So why not? For concrete or masonry shafts they need another subcontractor, it's extra cost, scheduling problems, tolerances are different for different materials. In my area everything is precut and brought to construction site in panels, so if a shaft is not built as designed we have a huge problem. But I'm all for hybrids and using best material for the job. I'm aware CLT shaft is not always the best solution.

 

[NorthCivil]

There has been a lot of full size shake table tests carried out in Japan.

I recall reading a paper that did a full scale shake table test on a 7 story CLT building. I will try to dig it up. author was an italian guy by the name of "carcetti" or something similar.

It had all kinds of connections that showed all kinds of different failure.

the long of the short of it was:
many small ductile fasteners > big bolts
long straps > small brackets
& you are wise to create a ductile fuse