Reinforcement in blockwork over steel lintels

[SillyBilly]

For a 3.6m opening in a 6.3m wall of  200mm Celcon blocks I will need reinforcement.  The wall will be internal and  loadbearing but  I would prefer stainless steel reinforcement rather than galvanised or expamet type as it is structural rather than crack control

 

I am looking at 3mm ladder type but this only comes in 2.7m lengths and width max is 100mm.  I understand the reinforcement should extend 600mm beyond the opening.  I asked the manufacturer what they recommend but their reply was that there were no standards  set. 

What width should the reinforcement be for a 200mm block wall and what overlap should there be at the centre.  Also how many rows above and below the lintels?

[PeterW]

20 minutes ago, SillyBilly said:

For a 3.6m opening in a 6.3m wall of  200mm Celcon blocks I will need reinforcement. 

 

 Why will you..??

 

Are you using a lintel or a steel, and what’s the height and loading ..??

 

 

[markc]

What is the opening for? will it be liable to impact ... garage etc.? Reinforcement will not help with compressive loads

[SillyBilly]

It is for an internal  single-glazed sliding door between two rooms in an open plan extension.  So no impacts.  Steel lintel over opening

[markc]

Just now, SillyBilly said:

It is for an internal  single-glazed sliding door between two rooms in an open plan extension.  So no impacts.  Steel lintel over opening

In t hat case i cant see why reinforcement would be needed or a benefit

[SillyBilly]

Because of the size of the opening and stresses at the ends, and to reduce the risk of cracks in blockwork.  Extension will be built over 2 years and the blockwork will be external and subject to wind forces.

[Temp]

2 hours ago, SillyBilly said:

For a 3.6m opening in a 6.3m wall of  200mm Celcon blocks I will need reinforcement.  The wall will be internal and  loadbearing but  I would prefer stainless steel reinforcement rather than galvanised or expamet type as it is structural rather than crack control

 

I am looking at 3mm ladder type but this only comes in 2.7m lengths and width max is 100mm.  I understand the reinforcement should extend 600mm beyond the opening.  I asked the manufacturer what they recommend but their reply was that there were no standards  set. 

What width should the reinforcement be for a 200mm block wall and what overlap should there be at the centre.  Also how many rows above and below the lintels?

 

I've never seen these used but down this page they suggest a 6-8" overlap..

 

https://www.masonrymagazine.com/blog/2015/06/24/joint-reinforcement-less-is-more/

 

 

 

 

[Temp]

PS The overlap doesn't have to be in the middle. Eg 2.7m length in the middle with two short lengths either side.

[PeterW]

1 hour ago, SillyBilly said:

Because of the size of the opening and stresses at the ends, and to reduce the risk of cracks in blockwork.  Extension will be built over 2 years and the blockwork will be external and subject to wind forces.

External ..?

 

1 hour ago, SillyBilly said:

It is for an internal  single-glazed sliding door between two rooms in an open plan extension.

 

Or internal ..?

 

Either way, not sure why you are looking for crack reinforcement as there are no shear loads that will cause issues. Has the SEng specified it ..?

[SillyBilly]

It will be internal when the single storey part is built but external until then: they dont recommend galvanised for external walls.

Why considered?

I have seen several cases where block walls have cracked possibly because of shrinkage after soaking, but am concerned because while the load is in compression the light weight blocks have little strength in bending, torsion, or tension.

[PeterW]

Then don’t use lightweights…?? Crack mesh won’t fix that issue. 

[Gus Potter]

1 hour ago, PeterW said:

Then don’t use lightweights…?? Crack mesh won’t fix that issue. 

Good point Peter.

 

SillyBilly looks like there is more to this than meets the eye. If the wall is going to be an internal wall at the end of the day then why lightweight insulating blocks? Is there an issue with the founds say and you are trying to reduce the loading?

 

The wall looks like it is 6.3m long , usually after about 6.0m you start to worry about significant shrinkage cracking in cement based blocks (as opposed to clay), assuming the materials have been looked after and the mortar mix is not too strong. Even with walls shorter than this you get some shrinkage cracks around the opening depending on the surrounding wall geometry.

 

Much also depends on the wall height, geometry and how the SE say has designed it. Vertically spanning, two way spanning and so on. To give you relevant pointers then a drawing or two would help.

 

If you are just worried about the wind loading in the temporary condition then your starting point is this. If you look at the probability of the wall being loaded by the wind over a two year period then the wind loading is reduced (by some 35  to 40 %) as the normally calculated wind loading is usually based on a 50 year return period. But the wall may have been designed with a certain amount of compression, say from the upper floors / roof. Often if you have a good weight on a wall then compression is beneficial as it counteracts the tension stress developed on one face of the wall by the sideways wind loading.

 

On the practical side you could consider introducing a couple of temporary wind posts on the outside of the wall, you may have the space to do this. We know that aerated type blocks are hard to get a good fixing to so when you are building the wall introduce some bent leg tie straps with a twist. The bent leg would turn down the inside face of the wall and where the strap comes out the outside face you have the twist. Now screw fix the strap to the side of your wind post, go for timber posts. Fix the posts top and bottom.

 

When ready remove the temporary timber wind posts and recycle.

 

The bed reinforcement looks great on paper but for a brickie it's another hassle and makes it harder to keep the coursing level. If you really need it SE wise then fine but the brickie will charge you more to bed it and for the extra time they will have to take to get everything level.

 

You also have the cost of the bed reinforcement and time to procure. If you're laying the blocks your self then make sure you have a practice with bed reinforcement as although the flattened type S/steal stuff looks great it still makes it harder to maintain level coursing if you are working on a 10.0 mm mortar bed and standard units sizes. If you deviate from this then you'll often find that you can't marry up the wall coursing where it ties into other walls.

 

Hope this gives you a few ideas.

 

 

 

 

 

 

 

 

 

[SillyBilly]

On 01/07/2021 at 21:52, Gus Potter said:

The bed reinforcement looks great on paper but for a brickie it's another hassle and makes it harder to keep the coursing level. If you really need it SE wise then fine but the brickie will charge you more to bed it and for the extra time they will have to take to get everything level.

 

You also have the cost of the bed reinforcement and time to procure. If you're laying the blocks your self then make sure you have a practice with bed reinforcement as although the flattened type S/steal stuff looks great it still makes it harder to maintain level coursing if you are working on a 10.0 mm mortar bed and standard units sizes. If you deviate from this then you'll often find that you can't marry up the wall coursing where it ties into other walls.

Thanks Gus for some useful comments.  I had in mind to use Ancon products which reduce difficulties on levels and embedment 

https://www.ancon.co.uk/products/masonry-reinforcement/ancon-amr-x

 

Edited July 3, 2021 by SillyBilly