H1 Tie vs. A35 Clips
H1 Tie vs. A35 Clips
(OP)
For a couple years now I've been in the practice of specifying A35 clips at the top of all my shearwalls either connecting the top plate to the rim board of the floor above or the roof truss above (usually a gable end truss). I've also always shown a detail with an A35 clip connected to the "vertical" bird blocking where the trusses bear on the exterior walls. See detail (4) at this link:
http://design.medeek.com/cad/autocad/INTERIOR_SHEA...
I've had some builders complain that all this hardware is redundant. You will note that in the detail (4) I'm also calling out H1 ties at each rafter. I've given this some thought and went back to my Simpson Catalog to see if I could eliminate the A35 clips entirely and just use the F1 value of the H1 clip to take the shear load. If I do this then Simpson suggests a unity equation on page 198 of their Wood Construction Connectors Catalog (2015-2016). In other words you need to factor in the uplift and max. horz. reaction(s) of the truss along with the shear load to accurately size the connector.
u/U + f1/F1 + f2/F2 < 0
Their alternative method is to use 75% of the allowable published load to check against when utilizing the connector in simultaneous loading.
This seems like a lot of extra work in order to eliminate some clips, but in certain cases is will probably work since the H1 clips have a fairly good F1 allowable load. Don't try this with their SDWC truss screw though since its F1 allowable is surprisingly small.
http://design.medeek.com/cad/autocad/INTERIOR_SHEA...
I've had some builders complain that all this hardware is redundant. You will note that in the detail (4) I'm also calling out H1 ties at each rafter. I've given this some thought and went back to my Simpson Catalog to see if I could eliminate the A35 clips entirely and just use the F1 value of the H1 clip to take the shear load. If I do this then Simpson suggests a unity equation on page 198 of their Wood Construction Connectors Catalog (2015-2016). In other words you need to factor in the uplift and max. horz. reaction(s) of the truss along with the shear load to accurately size the connector.
u/U + f1/F1 + f2/F2 < 0
Their alternative method is to use 75% of the allowable published load to check against when utilizing the connector in simultaneous loading.
This seems like a lot of extra work in order to eliminate some clips, but in certain cases is will probably work since the H1 clips have a fairly good F1 allowable load. Don't try this with their SDWC truss screw though since its F1 allowable is surprisingly small.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com






RE: H1 Tie vs. A35 Clips
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: H1 Tie vs. A35 Clips
We commonly specify H2.5A clips @ 48" oc and A35 clips at each rafter bay. We have relatively low uplift forces though (110mph wind ASCE 7-10). Contractors in our area expect the A35 clips and frequently install them even when not specified.
With the slanted block we've done 2 things: either install a double block and have the outer one be decorative and not used for lateral transfer or use a LS clip instead of the A35. Those clips can be field bent.
I agree the bird holes can be problematic if they are too large or there are too many of them. We usually limit size and spacing to try and keep block in tact.
RE: H1 Tie vs. A35 Clips
RE: H1 Tie vs. A35 Clips
Go to your local Menards or Home Depot. An A35 (there's a big box of them) costs about 56 cents each. Yeah, there's labor involved and nails, but this has got to be the cheapest building material since dirt.
RE: H1 Tie vs. A35 Clips
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: H1 Tie vs. A35 Clips
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: H1 Tie vs. A35 Clips
...probably the reason a lot of structural engineers stay away from most residential. That and a much higher level of risk.
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RE: H1 Tie vs. A35 Clips
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: H1 Tie vs. A35 Clips
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: H1 Tie vs. A35 Clips
I agree with your take on spacing out the clips. Spacing should reflect the disposition of shear as it comes in from the roof deck.
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: H1 Tie vs. A35 Clips
RE: H1 Tie vs. A35 Clips
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: H1 Tie vs. A35 Clips
1. You have (usually) a first time owner/client who usually doesn't know much about construction and can be very paranoid.
2. You have an owner/client who has limited funds and can be very sensitive to costs or cost over-runs even if it is not your fault.
3. Typically smaller architect firms, or one-person architect firms, are involved and many times they do not have professional liability insurance.
4. If you have PL insurance and no-one else does, guess who gets sued?
5. Your fees for the structural in residential are usually (as you pointed out) fairly limited or small - thus the risk-reward is very unbalanced not in your favor.
6. Some residential efforts involve the structural sizing one or two beams or some footings. Once you touch the design of a part of the structure a litigious owner/client assumes you are responsible for it all.
7. Limited opportunity for repeat business from the client - therefore always some limit on personal relationship and developed trust.
8. Smaller contractors who tend to have less experience in structural engineering and details...thus struggle to get your details built correctly - or they ignore them entirely.
9. Residential wood construction has a lot of "traditional" and "standard" ways of framing that aren't always consistent with structural requirements or load paths. In other words, looking at how houses are stick framed is a structural engineer's worst nightmare.
10. There is usually less organizational structure, procedures and processes in place during construction with regards to inspections, requests for information, submittals and their review processes, etc. So things can get built different from design or simply wrong without you knowing about it and problems from that later can come back to haunt you via an angry owner/client (see items 1-2 above).
I'm sure there are other reasons/risks.
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RE: H1 Tie vs. A35 Clips
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: H1 Tie vs. A35 Clips
I live in oil country where our economy is wildly cyclical. In boom time, construction is astoundingly amateurish. My brother had his condo built when things were white hot and his condo board has now spent more on repairs than the condo's original purchase price. When they opened things up to investigate some problems, there we entire components of the envelope there were not merely installed poorly but, rather, simply not installed at all. Bathroom fans that just vent into the plenum space etc. Ron would have a field day. It's almost like a gang of elementary school kids decided to get together and build some homes. Lawsuits o'plenty.
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: H1 Tie vs. A35 Clips
Unless I misunderstand the situation, this just sounds wrong. Conservative, but wrong. You attach the diaphragm to the to top plates (chord) uniform-ishly along the diaphragm with the blocking and clips. You attach the top plates to the shear wall panel with diaphgragm boundary nailing for the wall unit shear.
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: H1 Tie vs. A35 Clips
Splice Capacity: 141 x 1.6 x 12 = 2,707 lbs
Cont. 2x6 DF No. 2 Capacity (tension): 1.5 x 5.5 x 575 x 1.6 = 7,590 lbs
Under most circumstances (typical residence) the drag force is probably less than these allowables but it is something to keep in mind.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com