Wrong grade threaded bar used for wall plate

[Ady88]

Hi can you help me with a problem please!

We have just realised we used standard grade 4.8 threaded bar for resin anchor fixings a wall plate to support a new suspended timber floor when we needed a minimum of grade 5.8 threaded bar:/

The old studs have to stay in place now and we have some spare locations to add a few extra bolts or we need to perhaps add a wall plate underneath to prop the original wall plate up.

What do you all think is best or do you have any other ideas???

 

[freddiemercurystwin]

Just add a few more but it won't be going anywhere in any case, most of forces on the fixings will be vertical trying to shear the studs not pulling on the threads.

 

[RandomGrinch]

I believe the yield and tensile strength of the grade 4.8 threaded bars could be at most around 20-25% less than that of a grade 5.8 bar.
As above, a few more fixings should do the job, but have you asked for any recommendations from your structural engineer?

 

[Ady88]

Thanks for replying,

I'm waiting to speak to my structural engineer and in the meantime I spoke to Fischer who told me the resin is tested with grade 5.8 and that has 500nm capacity whereas 4.8 has 400nm capacity and the .8 at the end means they will yield at 80% of that capacity.

We did space at just under 400mm centres so I do have soon room for extra bolts still. I'm thinking to use thunderbolt in those locations instead as they are easier to install now everything is up already.

You are both right..it's about 20-25% less tensile strength so should still be plenty right?

 

[tony1851]

The two most common grades of bolts are 4.6 and 8.8 (not sure if there's a 5.8?) 8.8 is usually used for steelwork, and 4.6 for timber work.

You didn't say what diameter of bolt you used (that is just as significant as the grade) and the spacing. If you know these, and the load on each bolt from the floor, it is relatively easy to check suitabilty.

As others have pointed out, you'll probably be OK; domestic floor loads are not that great.

 

[stevie888]

As Tony I think it should be 8.8 and that strength in the fasteneing is only really warranted for steel to steel connections so I wouldn't worry.

 

[RandomGrinch]

The two most common grades of bolts are 4.6 and 8.8 (not sure if there's a 5.8?) 8.8 is usually used for steelwork, and 4.6 for timber work.

I don't know if it's because we do a fair bit of machining, rather than building works, but grade 4.8 and 5.8 threaded rod (not bolts) are pretty standard for us....

 

[stevie888]

Everyday's a school day!

 

[Ady88]

Sorry I should have said - we used M12 threaded bar which is graded 4.8 (and I have understood this to mean it can handle 400n/mm2 and yield at 80% of that stress) with maximum 400mm centres. The wall here is a random rough cut stone wall so we had to find best places to resin the studs into.

Maximum spacing was 400mm and some as close as 300mm where it allowed.

The timber floor is going to carry a galley kitchen so that's why I was concerned about the weight. The joists span is 3600mm in total (the other side of the joists is sitting on the steel flange)

So I need to figure out how much load each stud is taking.

Dead load 0.5kn/M2 and live 1.5 on/M2 total is 2.0kn/M2 or 3.0kn m/2 with safety factor

1.8m (half floor span) x 3 = 5.4 kn/m run on the wall plate?

So 5.4 /2.5 = 2.16 kn = 2160 n per rod?
The m12 can handle 400 per mm2
Assume M12 circular is equivalent to 8mm as a square?
8*400= 3200 n per threaded rod?

Is this math correct

 

[^woody^]

The 4" nails we used back in the day need seem to be holding up well - even without resin.

 

[Ady88]

Haha woody I know what you mean.. I'm just making sure I have done enough

The 4" nails we used back in the day need seem to be holding up well - even without resin.

 

[Ady88]

The two most common grades of bolts are 4.6 and 8.8 (not sure if there's a 5.8?) 8.8 is usually used for steelwork, and 4.6 for timber work.

You didn't say what diameter of bolt you used (that is just as significant as the grade) and the spacing. If you know these, and the load on each bolt from the floor, it is relatively easy to check suitabilty.

As others have pointed out, you'll probably be OK; domestic floor loads are not that great.

If M12 threaded bar has a surface area of 113mm and it is grade 4.8 so 400nm per mm2 then does that mean each bar can handle 113*400 nm?

 

[tony1851]

Sorry I should have said - we used M12 threaded bar which is graded 4.8 (and I have understood this to mean it can handle 400n/mm2 and yield at 80% of that stress) with maximum 400mm centres. The wall here is a random rough cut stone wall so we had to find best places to resin the studs into.

Maximum spacing was 400mm and some as close as 300mm where it allowed.

The timber floor is going to carry a galley kitchen so that's why I was concerned about the weight. The joists span is 3600mm in total (the other side of the joists is sitting on the steel flange)

So I need to figure out how much load each stud is taking.

Dead load 0.5kn/M2 and live 1.5 on/M2 total is 2.0kn/M2 or 3.0kn m/2 with safety factor

1.8m (half floor span) x 3 = 5.4 kn/m run on the wall plate?

So 5.4 /2.5 = 2.16 kn = 2160 n per rod?
The m12 can handle 400 per mm2
Assume M12 circular is equivalent to 8mm as a square?
8*400= 3200 n per threaded rod?

Is this math correct

It's not just the strength of the bolts themselves that matters, its also how the bolts react with the timber they are fixing,
Here's an extract which which might give a clue as to your bolt-load capacity. Its for timber>timber connections but wont be far out for your purposes

 

[Ady88]

It's not just the strength of the bolts themselves that matters, its also how the bolts react with the timber they are fixing,
Here's an extract which which might give a clue as to your bolt-load capacity. Its for timber>timber connections but wont be far out for your purposes

Thanks for this.. it suggests 1.09 for perpendicular load long term with 45mm member thickness using the 4.6 grade.

I used 4.8 grade which is abit stronger so I would like to think the load capacity is higher than this so I should be fine as we used plenty extra studs.

Thanks for all the help!