Expert: Arshad Khan - 1/16/2005

Question
-------------------------
Followup To
Question -
Hello Arshad,

I live in a small country town in Australia.  I did a materials engineering degree at university but am currently a high school mathematics teacher.  A friend of mine manufactures a masonry product called Timbercrete which is a brick made from fine pine-chip, sand and cement along with other binders.  He asked me if I would be able to determine for him the bracing value of a wall made from these bricks.  I said I would give it a try, but admitted that I was not a structural engineer and limited in my knowledge in that area.  In fact, with all the searching I've done so far, I cannot find any helpful information on this topic.  What do you know about bracing value?  Is there a relatively simple means of calculating this or is it something that is only determined through experimentation?

Regards

Mark Lowe
Answer -
Hi Mark,

I am not sure what you mean by bracing value, but if it is about lateral bracing of a building by using these blocks as in-fill panel within a framework, then you'd need to know the properties of the brickwork and the joints mortar - i.e. crushing strength and shear strength. From that you can work out approximately how much lateral bracing it can provide.

I hope taht helps!

Kind regards,

Arshad

I think that is what the bracing value is referring to.  My friend has obtain flexural strength and modulus of rupture from tests performed on the bricks.  Could this be used?  If so, are there specific formulae to calculate the approximate lateral bracing it could provide?

Mark

Answer
Hi Mark,

Design of blockwork is not an exact science, especially when you are assessing strength not prependicular to the bedding planes. Therefore,as a very rough calculation, depending on the geometry of your wall panel, you can work out the available stress (and therefore force) of resistance that a "band" of diagonal brickwork can safely resist. Remember that the strength of the mortar joints plays a role as well.  I would say as a rough guess, divide the rupture stress by 3 and use that to calculate the bracing force within the diagonal brace. As an example, for an in-fill wall panel (i.e. surrounded by columns and beams) of say 3m height and 6m width, you can assume an effective band of diogonal of between 0.75m and 1 m depth (and it will be through the thickness of the wall). Multiply the X-section area of this "brace" by the safe stress and then by triangular resolution, you can work out the horizontal bracing force along the plane of the wall panel.

I hope this helps!

Kind regards,

Arshad