ishvaaag
Structural
- Aug 17, 2001
- 3,665
To solve skew bridges engineer Peter Nicholson of the XIX century laid out a steorotomy based in a pair of two orthogonal helices, one more or less parallel to the visible faces. Thousands of masonry skew bridges are said to be built to this pattern.
Background at
I draw a notional 3D model of this stereotomy and find somewhat puzzling that the more stressed points of the spring lines, namely the convergence point of the obtuse angles in the barrel, receive the loads in a way prone to slippage. See attached drawing, bottom corner of the barrel.
The text above clearly expounds logarithmic line patterns were found to be more adequate to proper load path. It also says that was recommended not to use the method for half circle barrels -as my model is- yet even for segment of circle the fact so stands.
Now, without abandoning the pair of spirals scheme, the question is ... since the more stringent load path is arcing along a plan diagonal between the obtuse angles in the barrel -and assuming the corresponding acute angle abutments in their rear stay competent- couldn't be more convenient to tweak -rotate- the long pitch spirals to hold the main arch push? This way the primary mechanism of strength would be being preferred respect to the secondary, where strength at the stronger abutments at longer span is preferred, which is the situation in Nicholson's pattern.
Of course would reappear the issue of some push toward façades that would need to be cared for by interlock, friction or mortar action.
In all, this provisionally leads to me to the idea that the differences in limit strength of well built models to each pattern shouldn`t be quite big.
I would apreeciate your comments on this and as well some available pdf or so describing the logarithmic pattern more thoroughly.
Background at
I draw a notional 3D model of this stereotomy and find somewhat puzzling that the more stressed points of the spring lines, namely the convergence point of the obtuse angles in the barrel, receive the loads in a way prone to slippage. See attached drawing, bottom corner of the barrel.
The text above clearly expounds logarithmic line patterns were found to be more adequate to proper load path. It also says that was recommended not to use the method for half circle barrels -as my model is- yet even for segment of circle the fact so stands.
Now, without abandoning the pair of spirals scheme, the question is ... since the more stringent load path is arcing along a plan diagonal between the obtuse angles in the barrel -and assuming the corresponding acute angle abutments in their rear stay competent- couldn't be more convenient to tweak -rotate- the long pitch spirals to hold the main arch push? This way the primary mechanism of strength would be being preferred respect to the secondary, where strength at the stronger abutments at longer span is preferred, which is the situation in Nicholson's pattern.
Of course would reappear the issue of some push toward façades that would need to be cared for by interlock, friction or mortar action.
In all, this provisionally leads to me to the idea that the differences in limit strength of well built models to each pattern shouldn`t be quite big.
I would apreeciate your comments on this and as well some available pdf or so describing the logarithmic pattern more thoroughly.
