https://share.icloud.com/photos/0a0VoDHfDyzthn84VYO6y3FnQ

Why so many bolts?

Especially as the last pair of bolts seems to be beyond the end of the steel plate!

Maybe because they're unusually small bolts - usually in this type of application you get say three fat 18 or 20mm bolts, usually in incredibly slack holes. Maybe the Engineer is aware to spread the considerable rotational load into the timber with multiple tighter-fitting bolts over the full contact area.

See how, on the adjoining rafter ends, it looks like that rotation has happened anyway, the ridge has sagged/dropped, the rafter pitch has flattened, considerably.

I like the stop-chamfer on each rafter under-arris. If using planed timber, this kind of detail makes a huge difference - as carpenters knew routinely till early-20C. The 'modern' eco-aesthetic is to use rough-sawn timbers instead, which in my experience works fine as green unseasoned - cut the doug fir one day, saw it the next, nail it up the day after, no green-stain 'presertvative', no shipping round the world, no stockpiling at the builders merchant - why isn't it cheaper by far?

Hey, suddenly twice in a row (and a third experimental time) I'm getting fostertom auto-filled into the Whisper box, so it gets Whisper/messaged to me. Anyone else?

Posted By: tonyWhy so many bolts?

Same reason there's so many nails in a nail plate? Whatever that is. Bolts aren't used often in positions where they're shear-loaded I think, and have to be specially rated to be so used. Maybe the shear loads are large?

So it should - it could all be pin-jointed.

Several small holes in timber fastening are stronger than less larger holes. Timber retains it's strength. Like drilling holes in joist to run services you have smaller holes spaced out rather then big holes. I once had an aluminium framework to form an atrium and had problems with it moving but manufacturere would not listen until I consulted my own structural enginner who condemned it as being poorly designed. One of the comment he made was that the holes bolting the members of the structure together were too close to the edge ok in steel but not in aluminium.( The structure was replaced with a steel frame designed by my SE)

Posted By: djhSame reason there's so many nails in a nail plate?

The nails used in these situations are square twisted nails jobbing builders eraneously use galvanised nails

Bolts and nails can all be used in shear up to their capacity. But they usually don't need to be, because they act in tension to clamp two plate-like surfaces tightly together. The shear force is transferred by friction between those two surfaces, rather than relying on the nails or bolts.

In the example of a nail plate, you could imagine removing all the nails and replacing with a super sized G-clamp to clamp the plate hard against the timber. The G clamp has no shear strength itself, but the clamping friction means the timber cannot slide out past the plate and the truss would stand up. The nails or bolts are driven or tightened to a high tension to give the clamping effect.

Bolt holes are sometimes made over sized so the sides of the bolt don't touch the material and there's no shear force on the bolt, only tension.

Relying on friction with timber is a big no-no. Even if pulled up so tight it squeaks, timber always shrinks or moves, even a little bit, even if so-called kiln dried (is never 'seasoned' 2-5yrs these days). Result, friction disappears or greatly reduces. All the shear ends up on the bolts, or nails if it's a gang-plate, then the plate ends up taking all the bending moment. That's prob why bolts in these situations usually seem so oversized. Engineers may specify the bolts to take all the shear, but everyone overlooks that the holes are usually drilled (even specified) very sloppy/oversized. At best, the joint overall functions as a pin-joint. A tight pin joint is the only one that's not going to move around unpredictably, and the structure has to be designed on that assumption. Then you're free to use sawn green timber, which will warp and shrink laterally but hardly shrinks at all lengthwise, so if pin jointed the truss or whatever stays reliably in shape.

An experiment!

Find a smooth shiny wire nail and knock it into a piece of wood. Now pull it out again with your fingertips.

It won't come?

That's because of the friction of the wood fibres, even against the smooth steel surface.

Now try again with a Victorian nail in a roof?

Nope, still won't come out, even after 150 years seasoning and oxidation .

Friction is why buildings stand up, it's vastly under rated!

Posted By: Peter_in_Hungarythe other type is a plate full holes, good for on site construction and for these I always use screws but for nailing either twist nails or ribbed nails would do but I find screws quicker. (I don't have a nail gun)

Screws are unsuitable they are already weakened by the thread and the plate holes sit in the thread so you have a point load. I helped a friend build his house and he had problems when fixing I beam rafters to the ridge. Many of the screws broke as the structure moved. They were qualiity SPAX countersunk screws and they broke the head off. Perhaps pan heads would have been better more surface contact bearing on the plate. When I built my roof sq twist nails were specified and the BCO checked that I had used them.I did use screws to prefix timbers in position as that was easier than trying to hold timber and plates in place whilst holding hammer and nail. Once couple of screws in place reverted to nails then swapped the screws for nails. BCO spent an awful amount of time checking the tinbers were correctly braced and straps in place. Being in an exposed area think that was the reason. If you make a mistake with sq twist nails they are one hell of job to get them out.

Posted By: revor

Posted By: Peter_in_Hungarythe other type is a plate full holes, good for on site construction and for these I always use screws but for nailing either twist nails or ribbed nails would do but I find screws quicker. (I don't have a nail gun)

Screws are unsuitable they are already weakened by the thread and the plate holes sit in the thread so you have a point load. I helped a friend build his house and he had problems when fixing I beam rafters to the ridge. Many of the screws broke as the structure moved.

The screws I use are rated for structural use. they don't have countersunk heads but rather flat head with the thread stopping before the head. They are put in with a torx bit. A bit like e.g.
https://www.screwfix.com/p/fastenmaster-headlok-spider-drive-flat-self-drilling-structural-timber-screws-6-3mm-x-70mm-50-pack/378pp

PiH, those screws are structural-rated so OK on that front. That's an important qualification. But they look to be rather larger diameter than the holes in any nail plate I've seen?