# Should the corbel angle always be estimated as 60 degrees in masonry construction, or is there a formula to use instead?

In educational construction material as well as engineering publications, the corbel angle for significant excess loads, and also for substantial openings, in an ordinary brick wall is usually stipulated as being taken as 60 degrees to the horizontal.

For example: In the first illustration, the reduced load is spread out, in the second a distributed load is spread out, and in the third, a point load is spread out. There are no buttresses or other "out-of-plane" support. The wall can be imagined as an indefinite length ordinary 100mm thick brick wall.

I've tried to find the source of that 60 degree value, to check when it's applicable and how it's calculated, but I can find nothing whatsoever on the topic. The few mentions online of "corbel angle" are all of a form that just state/assume 60 degrees (with no reasoning). I can't find anything else.

Related to this, when dealing with an opening, which of these is the correct way to use the corbel angle, and why? They can't both be correct, as they contradict, but there doesn't seem to be an obvious reason why the answer should be one rather than the other.

In the first diagram, the reduced weight is treated as causing a reduced load in nearby masonry at 60 degrees outward; in the second the heavier surrounding weight is treated as causing an increased load at 60 degrees inward.

How does the corbel angle actually work in these typical situations, where there is an excess loads + openings at some point in an ordinary brick wall, and how universally appropriate is it to always assume it's 60 degrees in ordinary brick or concrete construction?

• Didn’t they work this out when building cathedrals etc But you may find this interesting : scielo.br/… Commented Mar 23, 2019 at 19:11
• Thanks S.M. - an interesting source! So they've modelled a protruding corbel as a section of masonry in tension, (the "tie") supported by a triangular section of masonry in compression (the "strut")? I can use that. But it's not directly applicable as it stands, to calculations on corbel in-plane spreading within masonry wall, such as these examples. Is there anything more directly relevant on these, and on the 60 degrees usually quoted? Ideally Eurocode if available, but anything really. Commented Mar 23, 2019 at 19:32
• 3 quick comments: 1) Mike is linking to an article on corbels in reinforced concrete, so be very careful in applying it to masonry. 2) Why would you expect to be able to calculate the load distribution angle? It looks like a purely empirical value to me. 3) Regarding your question on window openings: This angle is for distributing a concentrated load on a limited length of wall until it becomes evenly distributed on the entire length of the wall (assuming the wall is tall enough). (See also the figures in EN1996-1-1 section 6.1.3.) Commented Mar 23, 2019 at 21:29
• @ingenørd - Thank you! 1996-1-1 section 6.1.3 is perfect. Can you put this in an answer, so I can mark it? Commented Mar 23, 2019 at 22:25
• @Stilez, yes, sure, I've rewritten it in a slightly more answer-like format. Commented Mar 24, 2019 at 8:09