Analysis of 100 yr old Granite masonry 1

[VAStrEngr]

Does anyone have any experience analyzing a 100 year old masonry wall built of large granite boulders? If so, what documentation did you find for allowable stresses?

How about the mortar, does anyone have a good reference for determining the allowable stress in the mortar for what was common at that time?

 

[dik]

Is it constructed of stone (selected, but not cut) or is it constructed of cut blocks?

The mortar will have to be analysed. Master masons of a century ago had to source their own hydraulic materials. Check Sliderules website for some information on historic masonry.


Dik

 

[VAStrEngr]

It appears to be cut blocks.

I am trying to convince the owner he needs to have it analyzed but so far unsuccessfully.

Thanks for the website, I will check it out.

 

[ishvaaag]

For rough granite limit (squashing without buckling) compressive strength is 7 to 25 kgf/cm2.

For cut granite limit (squashing without buckling) compressive strength is 40 to 80 kgf/cm2

Divide by your safety load factor to get your allowable, say 1.6 or 2.

 

[dik]

If the client is looking at maintaining the integrity and the look, the mortar should be tested... I absense of that, a high lime mortar with masonry cement may be adequate... but, a mason specialising in restorative work should be employed.

For stone walls, I would look to a SF of approx 5 to 10...

Dik

 

[bridgebuster]

Is this a retaining wall or is it part of a building?

 

[VAStrEngr]

Part of an existing building being analyzed for a surcharge loading.

 

[dik]

Are there any signs of distress? Mortar, confined in a joint is a lot stronger than the cube tests will indicate. If simulating a load, try to test it in a confined state.

Dik

 

[ishvaaag]

I put 1.6 to 2 safety factor because the related codes with such estimates were then (the seventies') around 1.7. Undoubtedly for a 1 century old masonry the quality of the mortar shold be investigated because many mortars have suffered severe weather and chemical degradation. Fortunately if the mortar is in reasonable state it will have moderate impact on the allowable strength for the walls.

Respect the safety factors, note that code piet 70 was already a model code on limit strengths, and the design (characteristical) strengths above are values expected to be stood say 95% of the times. So the statements of the (limit) design crushing strengths above may not be in big disaccord with dik view of safety factors on the 5 to 10 order IF on average crushing strength (not the characteristical value).

So in my view, if normally one would use the 1.7 safety factor with the values above of characteristical design strength on the section once the buckling effects have been added, the main remaining question is to what extent we must increase the safety factor over such 1.7 to account for mortar degradation, an issue that can only reasonably be approached by direct investigation of its current state.