Coach screws vs bolts

[DJM]

When securing a beam from behind using coach screws instead of coach bolts (to avoid bolt heads showing externally) is there a method for calculating how many coach screws are required in lieu of bolts? This is for both ends of a 250x50 F7 softwood beam, span 5.8m.

[Pulse]

You can probably substitute them 1 for 1, same diameter, provided that they penetrate deeply enough into the post. Shear strength is the main factor.

Cheers
Pulse

[Carpenter]

I reckon the coach bolt has been superceded by the batten screw. Available in 75, 100 & 150mm it is much easier to use having an internal hex drive countersunk style head. You need to drill a pilot hole in hardwoods & its handy to have a long series drill bit on hand.

[Barry_White]

I really don't think Batten Screws are big enough in diameter to hold beams to posts especially on verandah posts and beams that can be spanning up to 3 metres.

Batten screws usually are only fixing battens at a maximum of 1200mm.

Why not recess the bolt heads into the beams and fix a wooden plug into the holes to cover the bolt head.

[Garves]

I agree with Barry White (ohhhhh yeah ), use bolts. My BHP reference manual states the working design stress of M12 Bolts to be 6 kN in shear and 12.1 kN in tension. M16 are 11.4kN in shear and 22.6kN in tension. You will have a hard time using coach screws to acheive that capacity.

The hold on to the timber is where your concern is. A coach screws thread holds on to the timber, where as the bolts thread holds on to a nut and clamps the timber.

[julianx]

What is the beam holding up, 5.8 metres is a huge span especially for F7 softwood. I think the question should be how many more supports not how many coach screws

[DJM]

Good advice. Thanks all. I think I'll look at recessing & plugging bolts.
Julianx - rafters are only supporting own weight plus light tin sheeting (no battens). 240x45 is capable of spanning 6.7m (10kg/m2) according to AS1684, in fact 190x45 listed for 5.8m span but I've bumped up to next size.

[Barry_White]

Good advice. Thanks all. I think I'll look at recessing & plugging bolts.
Julianx - rafters are only supporting own weight plus light tin sheeting (no battens). 240x45 is capable of spanning 6.7m (10kg/m2) according to AS1684, in fact 190x45 listed for 5.8m span but I've bumped up to next size.

DJM

Does this take into consideration of the wind load. The dead load of the construction materials is insignificant.

The wind loading on any construction is the one that does all the damage.

An open construction without sheeting is fine but as soon as you add sheeting to the equation everything changes. It is not just the downward load it is also the upwardload with windloads.

I have seen in a violent storm 450mm dia by 1500mm deep concrete piers lifted out of the ground on open fronted sheds and just lay them on the ground.

IMHO I would get an engineer to look at the construction. I know engineers aren't cheap but they are cheaper than having to rebuild it if it blows down or away.

[jaws]

Have you had a look at the topic 'connecting verandah beam to post' ?
it might be worth a look.
Cheers,
John