Hold Downs - resistance from architect
Hold Downs - resistance from architect
(OP)
Hi All,
I am designing a house in a 110mph, exposure C zone, so we are designing per the WFCM. As always we have specfied hold downs at the ends of shear walls for the architect. The architect has posed a question back to us, asking if we can get rid of the hold downs and increase the sill plate anchorage, they claim other engineers hasve done this for them.... Am I missing something here? We have thousands of lbs of tension at these hold downs and feel that hold downs at the shear wall corners is the right answer. Anyone had this request/pushback in the past?
Thanks in advance.
I am designing a house in a 110mph, exposure C zone, so we are designing per the WFCM. As always we have specfied hold downs at the ends of shear walls for the architect. The architect has posed a question back to us, asking if we can get rid of the hold downs and increase the sill plate anchorage, they claim other engineers hasve done this for them.... Am I missing something here? We have thousands of lbs of tension at these hold downs and feel that hold downs at the shear wall corners is the right answer. Anyone had this request/pushback in the past?
Thanks in advance.






RE: Hold Downs - resistance from architect
RE: Hold Downs - resistance from architect
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Hold Downs - resistance from architect
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com
RE: Hold Downs - resistance from architect
If you find one of these, make sure he becomes a repeat customer. They are few and far between.
RE: Hold Downs - resistance from architect
Please remember: we're not all guys!
RE: Hold Downs - resistance from architect
KootK, that is the approach I took, trying to explain to the architect why we need them. Whether they fully believe me is another question.....
RE: Hold Downs - resistance from architect
SLTA: The architect simply responded to my markups showing the hold downs. I suppose it can't hurt for them to ask. He has not questioned me since saying, yes they are required. Just wanted to double check here since he is saying other engineers were able to design similar homes without hold downs.
TehMightyEngineer: I will take a look. Thanks.
RE: Hold Downs - resistance from architect
We often have the contractor stating that other firms or engineers "have done this for us".
We will often try to accommodate the request, but, more often than not, we tell them the bottom line is that the particular item, in your case, the holdown is simply necessary. In my experience, with most people, if you give them a reasonable explanation they will accept it.
On many occasions, i wonder if the comment, "other engineers will do this for us", is a bluff. I don't know!
RE: Hold Downs - resistance from architect
Shows what we know.
RE: Hold Downs - resistance from architect
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Hold Downs - resistance from architect
Please remember: we're not all guys!
RE: Hold Downs - resistance from architect
RE: Hold Downs - resistance from architect
A few HD8's are a small price to pay related to the total cost of the house. This is a ridiculous area to save money. Delete a few ornate Architectural details instead.
You are the structural engineer, not the other engineers, TO WHOM THE ARCHITECT DID NOT RETURN, BY THE WAY. Why?
Just say no.
Mike McCann, PE, SE (WA)
RE: Hold Downs - resistance from architect
1) Additional sill anchorage can help with direct tension uplift.
2) Additional sill anchorage, cannot help with uplift due to shear wall overturning? Except for the bolts right beside the chords of course.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Hold Downs - resistance from architect
3) Additional sill anchorage can help with uplift due to shear wall overturning! Technically, what's the difference between direct tension and overturning?
But, when uplift resistance can be accomplished in a single calc with (1) holdown, why would you consider the sill anchors? I suppose if you passed the threshold of allowable tension of the holdown? But, then either increase the holdwon size or add another holdown to the next adjacent stud(s) yielding (2) holdowns each end of shear wall. I've done that many times! (hopefully i haven't gone on too much of a tangent???)
RE: Hold Downs - resistance from architect
RE: Hold Downs - resistance from architect
I don't think you are missing anything.
I don't think anyone here is suggesting that properly designed, and, if necessary, (perhaps) "hybrid" sill anchors cannot resist uplift.
The OP was simply questioning the contesting of the architect who was wanting to get rid of the holdowns.
As jayrod said, "shearwalls without holddowns are possible". However, with "hybrid" contemporary architectural designs, the contemporary structure generally has to meet higher demands than that of the conventional past. The "typical conventional" sill anchor, at typical/conventional spacing, may not always be adequate.
RE: Hold Downs - resistance from architect
I'm pretty much suggesting this. Of course "properly designed" covers a lot of ground. If you take your conventional overturning hold down and distribute that capacity along the length of your wall then you fundamentally alter the distribution of shear in the shear wall panel. And you increase it on a unit shear basis as you reduce the effective depth of the shear wall. Also, rather than having a constant shear demand in the panel, the demand will step at each stud that is located near a tie down. Essentially, from a shear perspective, you are turning one shear wall panel into multiple, interconnected uniform shear panels that are divided at the tie downs. Can such a wall be designed? Sure. I've done something similar when using centrally located point loads to effectively tie down walls. That said, it's very unconventional way to design a shear wall and anyone attempting it needs to be aware of the ramifications. I've never once seen such a design appear in print.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Hold Downs - resistance from architect
RE: Hold Downs - resistance from architect
Link. For what it's worth, a good home has far more to do with the quality of the building envelope than the quality of the structure in my opinion. This document is probably better in that regard: Link.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Hold Downs - resistance from architect
RE: Hold Downs - resistance from architect
RE: Hold Downs - resistance from architect
RE: Hold Downs - resistance from architect
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com
RE: Hold Downs - resistance from architect
at first glance, I thought the concept was to have a bunch of architects attached where the holdown would normally go....
RE: Hold Downs - resistance from architect
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Hold Downs - resistance from architect
If that doesnt work hold-downs are required on walls that do not meet criteria, see this section.
RE: Hold Downs - resistance from architect
What I implied: don't do it.
What I wish that I'd said: do it carefully.
Complications <> prohibition. I shouldn't be implying that things can't be done simple because I'm concerned about whether or not others will fully appreciated the issues involved. My bad.
On a related note, I'm curious to know how others are interpreting the last sentence of SDPWS 4.4.1 and clause 4.3.6.2. While I don't think that these clauses prohibit the use of distributed uplift connections for overturning, I feel that they indicate that the authors were envisioning these systems having discrete tie downs for the OT uplift components in excess of self weight.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Hold Downs - resistance from architect
2. For out-of plane uplift, then the stud to plate connection in connection with the anchor bolts does function to resist any uplift if the dead load of the wall segment is insufficient.
I have always considered #1, but really never #2. I will concede that #2 does exist for walls normal to the applied lateral force.
Mike McCann, PE, SE (WA)
RE: Hold Downs - resistance from architect
On another note....110 mph is nothing to sneeze at for wind loading. Maybe it will never see that; however, I've seen structures fail at much lower wind speeds. Stick to your guns.
RE: Hold Downs - resistance from architect
that painted a picture in my mind I shall not soon forget
RE: Hold Downs - resistance from architect
The way I read it is that if your first wall anchor is sufficient to resist the tension force then you don't need a hold down. Looking at the tables, this only applies to really light loads. It looks like a dumbed down version of a perforated shear wall.
Never have used this section of the code and probably never will.