This section is from the "Architectural Iron And Steel, And Its Application In The Construction Of Buildings" book, by WM. H. Birkmire.. Also see Amazon: Architectural Iron And Steel, And Its Application In The Construction Of Buildings.
Circular Stairs are used where circumstances prevent the construction of a straight staircase. The treads and risers, as shown in the detail, are cast in one piece, placed over and secured to a 4 or 6 inch diameter wrought-iron pipe extending the full height of stairs.
In adjusting the plan, it is important that the head-room be sufficiently large to allow passage up and down: it should not be less than 7 feet from top to bottom of treads. The landing, as shown in top plan, has a square platform, well-hole, railing, and cast-iron fascia.
The treads may be of slate or marble, or of cast iron, solid or open pattern.
A cast-iron post, as shown at section A, is set into a socket, on the top of pipe, giving it a finished appearance.
The angle knee H is for connecting the deck beam to floor beams of stair well.
The post G is made to cover the connection of string. The risers are secured to the face of blocking pieces on face string, and to the projecting flange E on wall string. The wall string projects from the wall line and receives the plastering as shown at C. The railing bars D are bent over the treads and secured to the blocking pieces.
Channel Strings as shown at Fig. 2, are constructed as close strings, the treads and risers being secured to the channels by cast-iron or wrought-iron angles formed to the shape of the treads and risers.
The face of channel at flanges can be filled with cast-iron mouldings, and webs ornamented with rosettes.
Plate And Angle Strings are constructed similarly to "channel strings." Cast-iron mouldings and rosettes may be applied in the same manner.
This is a more expensive stairway than any of the others previously described, and is used only in cases of long flights and heavy traffic. The wall strings can be constructed of cast iron for any length of span if placed directly against walls, for the reason that dowels or expansion bolts are used to tie the string to wall for support. It will also be found to give a better finish and connection with base moulding, which is generally continued around landings and platforms.
Treads are generally made of slate, 1 1/4, 1 1/2, 1 3/4, and 2 inches thick, and risers of iron, 1/4 and 3/8 inch thick. Where stairs have little light and dependence is placed upon skylights, the treads and risers are frequently made of cast iron perforated. Where a first-class finished staircase is adopted, the treads are made of white Italian marble, and the cast-iron riser is faced with marble.
Tiling can also be applied to the risers and treads by making the outer border and body of riser and tread solid iron and setting the tiling in recess.
The landings and platforms of all stairways should have fascias the size of outer strings, and should project a few inches below ceiling line to receive plastering, and a few inches above to receive finished floor. The casting can be made as thin as 3/16 of an inch.
Posts Or Newels are to be placed in all corners where necessary, extending above and receiving the rail, and to have a finished "drop" below ceiling at G.
These brackets are used on landings, corridors, and wall side of stairway, for the hand rail to rest in, and made of a 3/4-inch-diameter brass or wrought-iron bar. The distance of pipe from wall at A is generally 2 inches.
To give the staircase a finished appearance in every respect, it is very important that the work should be carefully constructed. The wall strings should extend along all landings and finish with some post or door trim.
The slate and marble for the treads and platform should not be too large (not over 4 X 5 feet), with small beams, tees, or cast-iron bridge pieces for their support.