Hello!
In the countryside, countless barns and sheds have been built over the centuries with logs cut from wood from their own forest, instead of today's glulam/steel beams. Does anyone here know of a sizing table or similar for this old-fashioned beam type? Or maybe some of you even have a barn with a door about 6 m wide with a beam above it? Since many with their own forests still mill their own timber, that type of sizing knowledge must exist somewhere...
An example: One imagines a free opening with a width of 6m. Over the opening, a timber beam is placed on which rafters are positioned 1.2 m apart. Horizontal battens are laid on the rafters, and the metal roof is screwed into them. That is, no insulation, decking or similar. The rafter span is 7.2 m in the form of a gabled roof. What dimension of the solid wood log beam over the opening is needed then, measured in inches?
I’m excited to hear if there is a sizing table for this and similar questions concerning "real" timber beams.
In the countryside, countless barns and sheds have been built over the centuries with logs cut from wood from their own forest, instead of today's glulam/steel beams. Does anyone here know of a sizing table or similar for this old-fashioned beam type? Or maybe some of you even have a barn with a door about 6 m wide with a beam above it? Since many with their own forests still mill their own timber, that type of sizing knowledge must exist somewhere...
An example: One imagines a free opening with a width of 6m. Over the opening, a timber beam is placed on which rafters are positioned 1.2 m apart. Horizontal battens are laid on the rafters, and the metal roof is screwed into them. That is, no insulation, decking or similar. The rafter span is 7.2 m in the form of a gabled roof. What dimension of the solid wood log beam over the opening is needed then, measured in inches?
I’m excited to hear if there is a sizing table for this and similar questions concerning "real" timber beams.
No. There is no such 'dimension table'. What exists is what is called proven experience. That is, they built and took a chance on it holding. In this way, they obtained empirical data for future constructions. If it didn't hold, the dimension was increased for the next time, and so on.
It was first when Mr. Hooke launched his theories on strength through his theory of elasticity that a method to calculate strength was obtained. At the same time, it became clear that the external forces (calculated using statics and dynamics) would be balanced by the internal forces (strength) in the mtrl and constr. Before that, they more or less groped in the dark about how forces behaved and what withstood them. A textbook in building construction is the right way to learn statics (the study of forces at rest) and dynamics (the study of forces in motion). Follow that up with a book on the mechanics of materials, and it will become clear how it all fits together.
One of the reasons the warship WASA sank is precisely due to a lack of knowledge. The shipbuilder thought it seemed too weak as instructed and added a few more inches to the timber to ensure it held. But the right inch in the wrong place is of no help. It wasn't an inch here or there on the timber that caused the ship to capsize. It was ignorance of how to calculate equilibrium.
It was also the lack of knowledge about equilibrium that almost caused a church in Rome (the Pantheon) to collapse. The roof consists of a dome with a round hole in the middle to allow air and light in. The dome exerts pressure forces on the walls that want to move outwards due to the pressure. When the construction was finished, it began to crack. By Leonardo da Vinci using a measuring chain to demonstrate how it was, they tightened an iron band around the walls just below the roofline. Since then, it has held.
They discovered this late in ordinary house constructions as well. A beam that is 45x220 in dimension has a greater bending moment than a beam of 100x100 despite having a 100 mm^2 disadvantage in area between them. The difference in bending moment is 272250 - 125000 = 147250 mm^3, i.e., 45x220 is from a strength perspective more than twice as strong as a 4"x4". Therefore, all older constructions were built with almost square dimensions, now they are replaced with thinner and higher profiles since it is the 'inch' in height that is beneficial from a strength perspective.
Addition:
We should also not forget that it is from this ancient empirically determined knowledge that today's engineering science has arisen.
______________________
Byggaren
It was first when Mr. Hooke launched his theories on strength through his theory of elasticity that a method to calculate strength was obtained. At the same time, it became clear that the external forces (calculated using statics and dynamics) would be balanced by the internal forces (strength) in the mtrl and constr. Before that, they more or less groped in the dark about how forces behaved and what withstood them. A textbook in building construction is the right way to learn statics (the study of forces at rest) and dynamics (the study of forces in motion). Follow that up with a book on the mechanics of materials, and it will become clear how it all fits together.
One of the reasons the warship WASA sank is precisely due to a lack of knowledge. The shipbuilder thought it seemed too weak as instructed and added a few more inches to the timber to ensure it held. But the right inch in the wrong place is of no help. It wasn't an inch here or there on the timber that caused the ship to capsize. It was ignorance of how to calculate equilibrium.
It was also the lack of knowledge about equilibrium that almost caused a church in Rome (the Pantheon) to collapse. The roof consists of a dome with a round hole in the middle to allow air and light in. The dome exerts pressure forces on the walls that want to move outwards due to the pressure. When the construction was finished, it began to crack. By Leonardo da Vinci using a measuring chain to demonstrate how it was, they tightened an iron band around the walls just below the roofline. Since then, it has held.
They discovered this late in ordinary house constructions as well. A beam that is 45x220 in dimension has a greater bending moment than a beam of 100x100 despite having a 100 mm^2 disadvantage in area between them. The difference in bending moment is 272250 - 125000 = 147250 mm^3, i.e., 45x220 is from a strength perspective more than twice as strong as a 4"x4". Therefore, all older constructions were built with almost square dimensions, now they are replaced with thinner and higher profiles since it is the 'inch' in height that is beneficial from a strength perspective.
Addition:
We should also not forget that it is from this ancient empirically determined knowledge that today's engineering science has arisen.
______________________
Byggaren
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