Hold Downs - resistance from architect 6

[JONNH]

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.

 

[KootK]

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.

 

[MillR]

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.

 

[andriver]

Thanks KootK!

 

[Huevo]

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

 

[TehMightyEngineer]

Nice reference Huevo, good info there.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[Triangled]

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....

 

[medeek]

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

http://www.medeek.com

 

[BSE05]

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.

 

[KootK]

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.

 

[msquared48]

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)

 

[Ron]

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.

 

[Triangled]

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

 

[CBSE]

@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.