WARose
Structural
- Mar 17, 2011
- 5,594
Recently I had to design some masonry (which I haven’t messed with for years)……it was a pretty heavily loaded wall that had some openings that needed a lintel above them. For the purposes of the lintel design, I assumed arching action. (There was sufficient masonry above it for such an assumption.)
The literature on this subject (i.e. in most masonry texts) is a bit vague on what this “arching action” actually consists of. (BIA’s Technical Note 31A was somewhat helpful as far as thrust loads go.)
In the case I had, the wall was so heavily loaded that I wanted to follow the load path from stem to stern to be sure I understood what was going on and to get accurate loads. So what I did was declare a zone/area above the lintel as being my “arch”. I made the apex where the lines intersect (i.e. where you come off the end(s) of the lintel at a 45 degree angle) and selected a depth that seemed logical with the geometry. (I didn’t let the depth get into the triangle zone (that the lintel carries) except at the apex.) The thickness was obviously the wall thickness.
Given that, I analyzed the “arch” on some FEA software (modeling the arch only (uncracked), with the proper loading)……got my moment, shears, thrust, etc. I checked the arch itself (vs. the allowables in the code, and not forgetting it is a curved beam for stress calculations) and then checked the adjacent wall for the thrust and other forces. (To my surprise, (given that this was a major arch) some significant moment did develop in the arch, but the axial compression force tended to cancel out the net tensile force from bending [not always though].)
All that being said……does the approach sound right? I would assume this is what is intended with the so-called “arching action” over lintels (i.e. that is the mechanism as to how they are intended to behave)…..but the problem is (in a survey of the available literature), I just don’t see it gone into detail….in this case (due to the loads), I couldn’t just let it go.
Thanks.
The literature on this subject (i.e. in most masonry texts) is a bit vague on what this “arching action” actually consists of. (BIA’s Technical Note 31A was somewhat helpful as far as thrust loads go.)
In the case I had, the wall was so heavily loaded that I wanted to follow the load path from stem to stern to be sure I understood what was going on and to get accurate loads. So what I did was declare a zone/area above the lintel as being my “arch”. I made the apex where the lines intersect (i.e. where you come off the end(s) of the lintel at a 45 degree angle) and selected a depth that seemed logical with the geometry. (I didn’t let the depth get into the triangle zone (that the lintel carries) except at the apex.) The thickness was obviously the wall thickness.
Given that, I analyzed the “arch” on some FEA software (modeling the arch only (uncracked), with the proper loading)……got my moment, shears, thrust, etc. I checked the arch itself (vs. the allowables in the code, and not forgetting it is a curved beam for stress calculations) and then checked the adjacent wall for the thrust and other forces. (To my surprise, (given that this was a major arch) some significant moment did develop in the arch, but the axial compression force tended to cancel out the net tensile force from bending [not always though].)
All that being said……does the approach sound right? I would assume this is what is intended with the so-called “arching action” over lintels (i.e. that is the mechanism as to how they are intended to behave)…..but the problem is (in a survey of the available literature), I just don’t see it gone into detail….in this case (due to the loads), I couldn’t just let it go.
Thanks.
![[bigglasses]](/data/assets/smilies/bigglasses.gif "[bigglasses] [bigglasses]")
