Verifying masonry Arching Action for lintel designs???

[Kwaz]

I have read a lot of literature talking about when arching action can be assumed. The typical directive is to be sure there is enough masonry to resist the thrust at the base of the arch (triangle) and be sure there are no control joints located NEAR the openings. OK; how close is near??? I am not looking for a "rule-of-thumb, but rather a calculation to verify this.

I can calculate the thrust: [(total wall load and tributary roof load above half the length of lintel) - (half the triangular load)] x Cos 45-degrees.

I calculate the shear capacity through the "column" of masonry (acting as a column, but not reinforced as one) from the side of the opening (jamb) to the control joint (A-n) x fv. (A-n is calculated as face shell thickness x 2 + the area of solid cores in this "column".)

I have read that I would also need to verify the overturning (stability) of this "column" of masonry. Since both the opening jamb and the cells adjacent to the control joint are typically reinforced with a full-height vertical bar, I don't know if overturning really needs to be calculated. If so, I assume it should be calculated as a vertical beam???

I know that it is conversative to just analyze these lintels without arching action, but I would like to know when I can truly use arching action.

Thanks in advance!

 

[concretemasonry]

Take a look at the National concrete Masonry Association (NCMA) at ncma.org to access the free .pdf TEK Notes downloads on masonry design. There are over 100 standardson different masonry subjects that are written by professional engineers active on the normal code and standards (ACI, ASTM, IBC, etc.) domestically and internationally. they also have a huge lab (2-3 million pounds and 20+ high walls) where they love to do research for members and contract research for goverments and other associations.

In proper masonry design, you look at the masonry panels as a structural element because of the code design and construction requirements. Looking at a theoretical column in a contiguous wall is a very dangerous simplifying assumption. - I guess most assumptions can be dangerous in some cases.

Dick

 

[Kwaz]

Hi Dick -

Thanks for your reply.

I have to believe that I have virtually exhausted my research on this topic. I had also looked at almost all the Tek Notes on this subject. I have actually contacted them today to review their masonry lintel design. The next time I talk with them, I was thinking of suggesting that they demonstrate how to calculate for the thrust resistance.

Everyone seems to say the same thing; you must consider the thrust from the arching action. However, no one talks about how to analyze this thrust resistance.

I agree that my use of the term "column" may not be appropriate. I believe that I should have used the term "shear wall" instead?

 

[vandede427]

Try using the term "buttress" when researching info for the ends of an arch.

The buttresses actually do act as shear walls. Apply the thrust to the top of the wall, check the shear stress in the wall, check the overturning safety factor (I would be very conservative with the overturning of the buttress).

Question, why do the words "search" and "research" have similar meanings? Why do we "research" information? Why don't we just "search" for it?