Design of a Rubble and Mortar Building Wall

[Ussuri]

I am looking at determining the structural capacity of a laterally loaded rubble and mortar wall. The wall is approximately 150 years old and forms an exterior leaf on an old farmhouse.

Does anyone know of any references which would give an indication of determining capacity? The problem being that these things can be so variable in terms of material and construction I would expect it is very difficult to quantify.

 

[valleyboy]

Hello Ussuri

There is no guidance given in BS 5628 for flexural resistance of random rubble masonry for the very reasons you state - the extreme variability of the quality of construction.

Just out of interest, why are you carrying out the assessment ? Perhaps a more prudent approach would be a visual assessment that the wall is plumb and not showing signs of distress etc.

Alternatively, another approach would be to demonstrate that no net tension is developed in the masonry due to lateral loads (P/A +/- M/Z) - but this usually requires very massive walls for success.

VB

 

[Ussuri]

Valleyboy

Cheers for the reply.

BS5628 does give a little guidance (clause 19.1.10) allows you to take the characteristic strength as 75% of the equivalent if it were a natural stone construction. It further reduces it if lime mortar is used by 50% of mortar class M2.

As you can see its very rough and I have no idea where the 0.75 and 0.5 come from and on what justification.

I'm looking at this as a favour for a friend. She is doing some internal modifications to her house and needs to submit to building control for a building warrant. The wall they want to remove is load bearing and their builder has just told them to replace it with a flitch beam.

That's is all well and good, however, the wall is also 'possibly' (I haven't been to have a look yet) an internal return to the exernal wall. This is more of a concern as if this is the case removing it will effectively reduce the exterior wall to a one way spanning panel. And due to the age of the building I expect there to be little or no structural connection at the wallhead to the intermediate floor diaphagm.

I am expecting I will need to include a pier or at worst case a small internal portal. I guess I have to wait and see until after I have had a nosey.

 

[bridgebuster]

You might try "Structural Analysis of Historic Buildings" by J. Stanley Rabun, published by Wiley.

There is a section on buildings with brick and dimension masonry walls.