Hanging Doors

[MTbowels]

I've always been fascinated by the way heavy internal doors are hung in hospitals and offices etc. Invariably there are three hinges on the doors, no doubt to carry the extra weight of the door. However, it's the spacing of these hinges that puzzles me. The bottom hinge is roughly where it would be on any internal door, but the top hinge is higher up than on a normal two hinge door. The third hinge is about 20cm below the top hinge. Why isn't the third hinge at the middle point of the height of the door? Why does the door need the extra support near the top?
The only other thing I've noticed is that some of these door have oil filled closure devices fitted. Could this be the reason or is simply because the doors are heavier?

[davebro]

because the weight bears mostly on the top half - that's why there are 2 hinges higher up

[davebro]

the bottom hinge is in compression, a middle hinge would be neutral, the upper hinges carry the weight.

[The Builder]

Dave's right.
Just to confuse you even more MT ................

In my own house, I have entrance doors that are 1.1 metres wide (3.6 feet).
Fully glazed. They're so heavy I used a trolley jack to lift them while I screwed in the hinges. It's because they're triple glazed and take two people to carry them.
They are fitted with four 100mm hinges.
Two near the top, one in the middle, and one at the bottom.

Nothing to do with fitted closers. They are usually oil-filled (hydraulic) and are adjustable for different weight doors.

[Atheist]

Davebro; do you mean the the upper hinge is subject to a sideways pull away from the frame? The weight (if regarded as the force acting vertically downwards) would be the same on all hinges if they are correctly spaced.

[The Builder]

Atheist... the load is a rotating "moment" calculated from the centre of gravity of the door (exact centre of door - vertically and horizontally.)

That's if I remember correctly from A-level Applied Maths, but that was 50 years ago ;o)))

[davebro]

The weight acts vertically downwards but the centre of gravity is in the middle of the door so there is a outward pull at the top & an inward force at the bottom hinges.

[Togo]

The principles of hanging a door and the "science" and practicalities are also applied in the glazing industry. With the advent of bigger panes of glass being available, after the invention of float glass, and subsequently more weight/load on the opening casements the heel and toe method of glazing become desirable if you did not want the then wooden openers to "drop". It was even more important when double glazing was introduced, and the correct heel and toe packing of the units was paramount to prevent hinge damage in alloy or pvc frames. Of course, all this is preceded by the use of the Z framed 5 bar gate which has the diagonal bar with the bottom on the lower hinge of the gate post which transfers the weight to that hinge and stops the gate from dropping and resting on the ground.

Window pane packing for heel and toe.

https://nulinewindows.com.au/blogimage/uploads/Heel-and-Toe-Bifold-door-6.jpg

[Togo]

Further to that if you remember the old cottage style doors that were basically planks laid side by side with a top and bottom rail there was also a diagonal rail and the door was hung to transfer weight to the bottom of the door on the hinge side. THese doors if they were wide or made of quality heavy wood also had a middle rail giving a double Z construction. Again both diagonals had the lower point on the hinge side.

[The Builder]

Yup....same for "ledged and braced" doors Togo :o)

[Togo]

Evening Builder. This stuff actually fascinates me ... I am a nerd. Haha.

[Togo]

Thing is Builder, I have seen these doors hung the wrong way up and glazing units toe and heeled the wrong way around. I am sure you have too.