Structural integrity of deck

BigWaylon

BigWaylon

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How much would it be impacted if the cross braces were moved up similar to the red lines?

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Working on clearing out the backyard. Had a Jeep parked under that deck for the last 13 years or so, and sold it a couple months ago. Just had the idea today while burning a bunch of limbs in my newly acquired fire bowl that it would be nice to not looking at the boards at least when sitting on the patio.
 
Probably not as much as you might think. Looks about 4-ish feet? I seen it done all the time.
 
I play a Structural Engineer on a cable reality show. So take this accordingly.

Would it help if laterals came before the diagonal ones?

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Shouldnt matter too much if you move them up. The view will be nice.

Sent from my SM-G965U using Tapatalk
 
Jeppo said:
I play a Structural Engineer on a cable reality show. So take this accordingly.

Would it help if laterals came before the diagonal ones?

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Are you asking me that question? The lateral (as drawn) would be really annoying. Having the X gives a semi-high spot to walk under. The lateral would make that tougher and force the X to be a lot higher for the same visibility.
 
Djstorm100 said:
Probably not as much as you might think. Looks about 4-ish feet? I seen it done all the time.
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My thought was it wouldn’t really make much difference at all. I could move them up even higher as long as they were still angled.

what are you thinking is 4-ish feet?
 
And a follow-up question...

They’re currently staggered at the bottom...any problem buying longer bolts and having one hole with the boards attached on each side of the post? I think the top is that way. Heck, bolts might even be long enough already. I just need a bigger/longer drill bit than anything I currently own.
 
BigWaylon said:
Are you asking me that question? The lateral (as drawn) would be really annoying. Having the X gives a semi-high spot to walk under. The lateral would make that tougher and force the X to be a lot higher for the same visibility.
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I charge extra for advice that’s really valid. ;)
 
Jeppo said:
I charge extra for advice that’s really valid. ;)
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I wasn’t sure if you were asking me the question based on how it looked...or asking it in general for people that might know the engineering side of it. :D
 
BigWaylon said:
I wasn’t sure if you were asking me the question based on how it looked...or asking it in general for people that might know the engineering side of it. :D
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I was trying to make it appear I had something to contribute. :cool:

P.S. Not sleepy yet
 
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Been a long time since I’ve taken statics and my focus is electrical, but. ... if you consider zero degrees to be horizontal from the left fulcrum to right, each angled post is upporting y/x degrees of force where y is the height and x is the span. It’s the same in the second case. except the height Y has been reduced and now you’re asking the verticals members to take on a different, remaining below that height load. Of weight times y which is since tangents of new angle times the weight and the question is whether that exceeds the force limit of a 2x4 or 4x4 post as it may be.

Edit, it’s the tangent of the angle, not sine. Do your trig and multiply by the weight and see if it exceeds the limits of the structural member..this includes deck plus people. Then.... https://answers.yahoo.com/question/index?qid=20100724145848AAoICFX
 
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BigWaylon said:
My thought was it wouldn’t really make much difference at all. I could move them up even higher as long as they were still angled.

what are you thinking is 4-ish feet?
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Moving the braces up from their current location is 4-5 feet. Just guesstimating.
 
Don’t do it without an engineering sign-off. If something ever happened (next owner throws a hot tub up there and has a party) insurance could be looking for a way out.

Also not a structural engineer but it worries me. Looking at the far left diagonal as an example, it pulls on the base of the second pole right where it’s anchored in the ground. If shortened up it pulls right in the middle of the post where it’s not as strong.
Might work but I’d want somebody that knows that stuff to do the calculations.
 
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My tiny house is on 4x4s and when I researched it, they could withstand almost a ton each down. I used structural screws and not bolts for the cross members because they have even a greater shear rating than lag bolts and are easier. Each structural screw has a shear of like a thousand pounds. It is also integral to the wood as you aren't drilling a hole in the wood. They are in the screw section at lowes and home depot.
 
Me. said:
Why have X braces at all?

https://www.decks.com/how-to/82/deck-bracing

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images




EDIT:
Google ‘Design for Code Acceptance (DCA) 6 - Prescriptive Residential Wood Deck Construction Guide’. Your answer is in there, not here.
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This is Similar to how the deck is on our house. Can Get you pics and measurements if it helps.
 
Goofyfoot2001 said:
I used structural screws and not bolts for the cross members because they have even a greater shear rating than lag bolts and are easier. Each structural screw has a shear of like a thousand pounds. It is also integral to the wood as you aren't drilling a hole in the wood. They are in the screw section at lowes and home depot.
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After building a deck with those screws (TimberLok) I will never use bolts again, except where they are required... only in a few places, none of which were in my deck. We used them to fasten the beams to posts, railing posts to beams, and to make beams from doubled 2x10s.
 
If the support beam are properly set in the concrete and you have the correct span on bolts from the house thru the deck then cross braces are not needed. There is not enough info and pictures to determine that.
 
BlackGun said:
If the support beam are properly set in the concrete and you have the correct span on bolts from the house thru the deck then cross braces are not needed. There is not enough info and pictures to determine that.
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The patio was poured a year or so after the deck was built, so they’re not set in the concrete you see. Not sure if they were originally set in concrete or not.

the posts are 6x6...(I think 4x4 was mentioned by somebody earlier)
 
BigWaylon said:
The patio was poured a year or so after the deck was built, so they’re not set in the concrete you see. Not sure if they were originally set in concrete or not.

the posts are 6x6...(I think 4x4 was mentioned by somebody earlier)
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Dig down a bit around the post. I'd be 99%sure they are in concrete
 
Raising the cross braces up like you have shown will make them less effective in controlling frame sidesway. Will it be enough to cause collapse? Not sure. It depends on how tall the columns are and how much vertical and horizontal load is applied. I also am not familiar with home building codes.
 
If the posts aren’t anchored into the concrete via concrete, a base plate or at least L brackets with good lags and concrete anchors. I’d start there. If they are just sitting, the current x bracing is all that is keeping the 6x6’s from moving off the slab.

If the bases are securely anchored. There is honestly no need for the braces at all. (Laws,ordinances, etc should be considered)

If the deck is done properly, double banded, lags/structural screws/carriage bolts etc. into band at house and posts. Then hangers On the floor joists. That will easily prevent the deck twisting. The decking itself adds tons of rigidity to The rectangle of the deck. That’s all x bracing is for. Holding the deck square and plumb.

I would personally add diagonal bracing (2x4’s are fine) across the bottom of the floor joists from back band to front band just for more strength and make sure the posts are anchored FOR SURE to the concrete. Then remove the giant bracing all together.

Just my opinion. I’m no engineer:)
 
second Trevillan's points, Wonder if cable braces would do the trick if the posts are not anchored in concrete. If the posts are not anchored you should keep them from moving. Also maybe a railing at 3 feet would serve the purpose and also add privacy to the patio. For a railing, the lumber from the braces could be reused. I have only seen videos of a deck collapse but it would not be pretty.
 
Trevillian said:
If they are just sitting, the current x bracing is all that is keeping the 6x6’s from moving off the slab.
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Again...the patio was poured after the deck was built. The 6x6 posts are not in that concrete, or sitting on top of it.

I’ve just never paid any attention as to whether they’re buried in the dirt, in concrete, or just sitting on the ground. Something that’s easily figured out, I just haven’t gone out there during this discussion to check.
 
mikehrl said:
second Trevillan's points, Wonder if cable braces would do the trick if the posts are not anchored in concrete. If the posts are not anchored you should keep them from moving. Also maybe a railing at 3 feet would serve the purpose and also add privacy to the patio. For a railing, the lumber from the braces could be reused. I have only seen videos of a deck collapse but it would not be pretty.
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The patio is open on both ends. It’s woods behind us before crossing a creek (ok, drainage ditch) and hitting the backyard of another house. Privacy isn’t really a concern at this point. The rail would eliminate the ability to walk directly out from the patio to the backyard, which is what I’m trying to gain out of this (along with not staring at boards while seated).

I would definitely consider a rail on the two end sections of the back, and leave the larger middle one open to walk out from.

Don’t know anything about double banded, cable braces, etc...
 
BigWaylon said:
Again...the patio was poured after the deck was built. The 6x6 posts are not in that concrete, or sitting on top of it.

I’ve just never paid any attention as to whether they’re buried in the dirt, in concrete, or just sitting on the ground. Something that’s easily figured out, I just haven’t gone out there during this discussion to check.
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Right, I got that part. I was trying to make it clear that how those are set is step one to determining how necessary the current bracing is.
 
.......i think you should be good to go. I think.
.........the purpose of the braces is to unitize the seperate sections of the deck. It shouldn't matter if they tie into the bottom 1/3 of the post or the bottom 1/3. The graphic from @J R Green being the most common i remember seeing.
 
@Me. beat me to it. Make each column “Y” with 45-degree braces as shown. Take the 45’s to the mid-point of the girders. For example: if the span between columns is 10’ then each 45 brace would reach 5’ out and 5’ down. At the midpoint of each girder you should have a maximum vertical clearance of whatever the column height is.
 
9outof10mms said:
@Me. beat me to it. Make each column “Y” with 45-degree braces as shown. Take the 45’s to the mid-point of the girders. For example: if the span between columns is 10’ then each 45 brace would reach 5’ out and 5’ down. At the midpoint of each girder you should have a maximum vertical clearance of whatever the column height is.
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So you’re saying I’d end up with the red braces here?

A5CB6F28-C4A9-49D7-A108-7B3CBAA94263.jpeg

That’s what I get if I used the mid-point between posts as my reference to get 45° braces. The middle section is wider than the left and right, so those would be much lower.

Alternative plans would be:
1. Green = keep 45°, but reference off where the holes in the posts would be going away from the two middle posts.
2. Blue = use the mid-point of the center section to attach both braces, but stray from the 45° to attach at the same point on the posts
3. Not drawn...just use the 2’ distance shown in the diagram up thread

A variety of #3 would be to pick a distance close to 2’ but base it ok where the brace would fit between the joists...which all run from the house out the edge. The 2’ mark might not work, but the midpoint plan mentioned early might also not work depending on where those joists are.

I like both of those better than the red, as least aesthetically. But if it doesn’t make structural sense I wouldn’t do it.

I can also add two more at a 45° angle going from the two end posts back towards the house. There aren’t any braces in that direction right now.

I need to go out and measure the bolts tomorrow. I think they’re much larger than the 3/8” in the diagram earlier in the thread.
 
I have a similar setup. I’ll send some pics in the next day or two. I’ve got 2 bats with an opening in the middle to open it up a little bit. If you aren’t adding a hot tub or ton of weight up top you should have options. Then again there have been some deck collapses in the news when people cram 50 drunks on them.
 
BigWaylon said:
So you’re saying I’d end up with the red braces here?

View attachment 253558

That’s what I get if I used the mid-point between posts as my reference to get 45° braces. The middle section is wider than the left and right, so those would be much lower.

Alternative plans would be:
1. Green = keep 45°, but reference off where the holes in the posts would be going away from the two middle posts.
2. Blue = use the mid-point of the center section to attach both braces, but stray from the 45° to attach at the same point on the posts
3. Not drawn...just use the 2’ distance shown in the diagram up thread

A variety of #3 would be to pick a distance close to 2’ but base it ok where the brace would fit between the joists...which all run from the house out the edge. The 2’ mark might not work, but the midpoint plan mentioned early might also not work depending on where those joists are.

I like both of those better than the red, as least aesthetically. But if it doesn’t make structural sense I wouldn’t do it.

I can also add two more at a 45° angle going from the two end posts back towards the house. There aren’t any braces in that direction right now.

I need to go out and measure the bolts tomorrow. I think they’re much larger than the 3/8” in the diagram earlier in the thread.
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Good point—I didn’t see the wider separation between those columns.

You could stick with the same height as the adjacent ones for aesthetics. Won’t hurt anything. All this is doing is taking some away/wiggle out of the structure.

To be honest, the 45 “Y” configuration is likely more rigid than the “X” frame you currently have.
 
CZfool68 said:
I have a similar setup. I’ll send some pics in the next day or two. I’ve got 2 bats with an opening in the middle to open it up a little bit. If you aren’t adding a hot tub or ton of weight up top you should have options. Then again there have been some deck collapses in the news when people cram 50 drunks on them.
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Yeah, no hot tub. We built the house in ‘99...and there’s never been more than 6 people on it since then. Just a grill and a couple chairs. :D
 
CZfool68 said:
I have a similar setup. I’ll send some pics in the next day or two. I’ve got 2 bats with an opening in the middle to open it up a little bit. If you aren’t adding a hot tub or ton of weight up top you should have options. Then again there have been some deck collapses in the news when people cram 50 drunks on them.
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That usually happens as a result of improper fastening to the house structure or not having the perimeter frame of the deck resting on a notch in the columns. All of the weight is relying on the shear strength of the bolts used to fasten the frame to the column. For normal use, it’s ok. For a party with a bunch of people trying to take a group photo, the load can max out those bolts.
 
Ideally you don't want the braces to meet in the center of the gap. That only leaves 1 point of support. Use shorter ones and you have two.
 
9outof10mms said:
That usually happens as a result of improper fastening to the house structure or not having the perimeter frame of the deck resting on a notch in the columns. All of the weight is relying on the shear strength of the bolts used to fasten the frame to the column. For normal use, it’s ok. For a party with a bunch of people trying to take a group photo, the load can max out those bolts.
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Your momma so fat.......she could max out the shear strength of deck bolts.


Not your momma specifically. This reminds me of the end of Me, Myself and Irene.
 
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J R Green said:
Ideally you don't want the braces to meet in the center of the gap. That only leaves 1 point of support. Use shorter ones and you have two.
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The 45’s aren’t doing anything for vertical load support on the girders. They’re for lateral stability only. If the girders need vertical deflection support, they’re too small (height) for too long of a span.
 
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Me. said:
Where I’m from, we don’t build decks for the weight of the people, we build ‘me for the weight of the snow......


90
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Was that thing secured to the house with finish nails? Seems to follow what others have said, that the failures we see are due to improper fastening to the house.
 
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