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Hold Downs - resistance from architect
5

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.

RE: Hold Downs - resistance from architect

I can't comment on your specific case, however shearwalls without holddowns are possible. Here north of the 49 there's factors that are applied to shearwall capacities that don't have dedicated holddowns.

RE: Hold Downs - resistance from architect

I have had that request. And I don't think that you're missing anything. With the exception of perhaps the bolts right next to the wall chords, the additional sill plate anchorage doesn't do anything much to improve hold down. It can be a delicate conversation but, if you explain it well to your client, there may be an opportunity for you to come of the situation looking quite competent relative to your competition. Of course, that assumes that your architect gives a damn about proper engineering.

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

The architect wants you to design the shear walls and sill anchor bolts for combined shear and uplift. There are provisions in the SDPWS for this. Sometimes this does make sense but other times it's clear that hold downs will be a less expensive option.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com

RE: Hold Downs - resistance from architect

Quote (KootK)

Of course, that assumes that your architect gives a damn about proper engineering.

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

I've pulled out the "thanks very much for your input but I enjoy having my license too much" gem before, when the architect starts questioning things like that. What is the pushback arising from? Or, why does the architect care?

Please remember: we're not all guys!

RE: Hold Downs - resistance from architect

(OP)
Thanks for the responses.

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

(OP)
This is a large house, 60ft x 32ft x 32ft tall and essentially on the ocean. The hold down forces are quite large, 7000 lbs at some locations.

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

Several years ago, it was a state plan reviewer, who possessed enough structural knowledge to question the lack of strength in the sill plate anchorage, that caused me to investigate Simpson Holdowns. I've been using holdowns ever since. I still specify the sill plate anchor, but, only as an auxiliary not due to lateral wind.

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

FWIW, has anyone ever witnessed a racking failure of a beach house? All the videos that I have seen shows the whole house getting pulled off the foundation as a unit.
Shows what we know.

RE: Hold Downs - resistance from architect

I have a structural engineer colleague who purchased a house on a steep slope. The leeward side faces our majestic mountain range and, consequently, is packed with windows. Initially, the house would vibrate noticeably and creak distressingly in strong winds. The addition of an interior shear wall alleviated the problem. That's all that I've got for real world anectodes.

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

Racking would be due to a lack of shearwalls, not lack attachment of shearwalls to the foundation.

Please remember: we're not all guys!

RE: Hold Downs - resistance from architect

(OP)
Great conversation here, thanks for the responses.

RE: Hold Downs - resistance from architect

2 to 3 stories with HD8's or the equivalent? I would not rely on the type of anchorage the Architect desires. Maybe on a small rambler with a lot of shear walls where the dead load from the truss package suffices to resist the overturning.

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

Just to be clear, are we agreed that:

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

Kootk:

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

Maybe I am missing something, but why can't additional sill anchors resist uplift and/or overturning if the anchors, sill, etc are designed accordingly. Not saying that you won't end up with larger, closer spaced anchors, just that I think it is theoretically possible (but unconventional). If shear walls are rigid enough to "span" between hold downs, then they should be able to get anchored anywhere along the span if the sill plate is designed to resist the anchor force

RE: Hold Downs - resistance from architect

Motorcity,

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

Quote (BSVBD)

I don't think anyone here is suggesting that properly designed, and, if necessary, (perhaps) "hybrid" sill anchors cannot resist uplift.

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

Can anyone provide reference material to understand typical home construction/engineering? As a structural guy in heavy industries I deal with heavy concrete and steel structures. I would like to know more about smaller commercial/residential construction out of curiosity but also for my own benefit when buying a home.

RE: Hold Downs - resistance from architect

Quote (andriver)

Can anyone provide reference material to understand typical home construction/engineering?

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

The architect is your client and you have to keep him reasonably satisfied. His client is the owner, or contractor, who has a specific cost in mind. Nobody ever cares what structure provides, only what it costs (until lawsuit time, then it is all your fault). So the first thing they look at is "over engineering" and if you are working in an environment of casual backcheck (most of America), you, as the structural engineer, are adding cost by requiring structure. By the numbers, the holddowns are required. By the checkbook, we've been doing it this way for thirty years. It just is what it is.

RE: Hold Downs - resistance from architect

Thanks KootK!

RE: Hold Downs - resistance from architect

2
Simpson did a test of a shear wall with and without hold downs. The cross grain tension in the sill plate scared me away from doing this in the past. Link

RE: Hold Downs - resistance from architect

Nice reference Huevo, good info there.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com

RE: Hold Downs - resistance from architect

2
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

Before we moved out to Washington State we had a two story home in Orem Utah. When the wind blew you could physically feel the house sway back and forth ever so slightly from the master bedroom on the second floor. I was doing some remodel work prior to selling the house just before we moved and determined that there were no actual OSB/Plywood shearwalls in the house only those ridiculous diagonal metal straps in X-patterns stretching between the top and bottom plates. The house had a 3/4" foam board covered with aluminum siding, built approximately 1984. One of these days in a 100 year storm that house is going to fold up like a house of cards...

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Hold Downs - resistance from architect

The IRC residential building code has a prescriptive design (without holddowns) based on lengths of full height sheathing. I have used a table on the drawings showning required and actural lengths for each walls and story, referencing the table.

If that doesnt work hold-downs are required on walls that do not meet criteria, see this section.

RE: Hold Downs - resistance from architect

I'd like to revise the view that I expressed above regarding the use of sill anchorage to resist overturning induced anchorage:

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

1. For in-plane uplift, if the dead load is insufficient, the holddowns at the end "shall" be provided to give the required safety factor against uplift.

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

Triangled.....Can't use architects for hold downs....they have no tension or compression capacity....somewhat akin to a box of feathers......from which they'll fashion a nice boa.

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

@Ron
that painted a picture in my mind I shall not soon forget bigsmile

RE: Hold Downs - resistance from architect

@Kootk

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.

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