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.
Cast-Iron Floor Lights For Iron Beams in the form as shown in the plate opposite, are cast in one piece. The glass is 6 inches square by 3/4 inch thick. The section of rib A - B is 2 inches by 1/2 inch thick, the section C - D is 3 inches by 1/2 inch thick, and frames are usually made from 2feet square to 4X6 feet. The frames may be made longer than 6 feet, but should never be over 4 feet 6 inches wide: the deepest rib in all cases to extend the 4 feet 6 inch way.
The border shown at C is made 2 1/2 to 3 inches wide, with reeds continuous on four sides. If the border is not required, the frame need only extend to floor to receive the glass.
The rebate E which receives the glass requires to be 1/8 inch deeper than the thickness of glass to receive the putty, and 1/2 to 3/4 inch wide. The section of rib A - B is made deeper on the ends as shown at B. The outside frame is stiffened by the ribs E and secured to the beams by the bolt D.
Cast-Iron Floor Lights For Wooden Beams are made similar to the cast-iron floor lights for iron beams, but the frame is arranged somewhat differently (see illustration on page 104), and the ribs section C - D are 3 inches deep.
The particulars concerning rebates, glass and putty described in the preceding article apply also to this floor light.
This floor light (see page 105) has the same cast-iron frame as the cast-iron floor light, but the frame is slotted as shown at section E - F, to receive the principal bearing bars, which are of wrought iron.
Riveted to each side of these bearing bars, for a rebate, are 1" X 1/2" strips, as section C - D, with 5/16inch-diameter rivets placed 6 inches apart between centres, and sunk the thickness of glass and putty below the top. The one-inch-square crossbars, section A - B, also receive the glass, and extend in one piece through the bearing bars, the number varying to suit the length of glass and width of span. The glass is rough plate, three quarters of an inch to one inch thick, from 12 to 16 inches wide, with 1/8 inch clearance on each side for putty; the length should not be over 30 inches. But as the glass is liable to break unless it be perfectly flat, it is preferable to have it square: the smaller the square the more easily is it replaced when broken.
In calculating the strength of bearing bars, deduct the area of hole punched out for the one-inch-square bars. Then for safe load uniformly distributed use the following formula:
Safe load in tons =(2.6AD)/(3L), where A = area of section; D = depth of bar; L = span in feet. Example. To find the uniformly distributed load of a 6" X 1" flat bar used for a floor light with a span of 6 feet.
Deduct one square inch of area for loss of section by the one-inch cross-bar. The bar loses in area by the holes punched for the rebate bars, but gains again by the addition of the bars. Then by formula,
Safe load =((26x5x6)/(3x6)= 4.3 tons.
To find the deflection for the above bar under the same load uniformly distributed:
Deflection =(WL3/48AD2) = (4.3x216)/(48x5x36) = .107 of an inch.
To prevent the glass from being broken, the deflection should not be over .33 of an inch in centre of span.
In nearly every building a skylight in one shape or another is required, and almost invariably it is inserted for ventilation as well as light.
Single-pitch skylights should not have less pitch than two inches to the foot. In double-pitch hipped skylights the angle should be 33 degrees or 8 inches to the foot; for instance, a skylight with a span of 12 feet should have the ridge 4 feet high. The curb should be from 4 to 6 inches above the roof: if ventilators are placed in the curb, it should be from 12 to 16 inches high. For ornamentation various kinds of glass may be used - opalescent, crown disks, pressed, fancy, fluted, etc. The best glass for skylight purposes is rough plate or fluted, and the following thicknesses are proportionate to the sizes: 15" X 40" X 3/16" thick; 16" X 60" X 1/4" thick ; 20" X 100" X 3/8" thick. Rough plate is to be preferred to fluted; it will admit more light, while it is equally translucent. The flutes often become filled with dust and dirt, which will accumulate and be held in the recesses of the fluting.
2 1/2 "
8 1/2 "
12 1/2 "
For covering bars, ridges and curbs, galvanized iron is often used, and sometimes brass and copper. See section of flat skylight bar. B is the covering; A is the main supporting bar, of wrought iron, 1/2 inch thick by the height to suit the span ; C are small bars riveted to side, serving as a rebate for the glass. If the main bars are long and several layers of glass are required, the C bars should be made as steps following the different layers of glass. D is a cast-iron condensation bar, 1/4 of an inch thick, riveted to main bar.
It is a mistaken idea that galvanized iron does not require painting. It should always receive at least two coats of paint - applied one or two months after it has been exposed, as the paint adheres much better after the gloss is off, in the same manner as with tin roofs. The best kind of paint to use is the oxide of zinc or of lead.
Condensation caused by the heat within and the chilling influence of the cold atmosphere without, and also any leakage which might occur between the bars and glass, is taken up by a small condensation gutter.
Hip Skylight is made of wrought-iron bars for rafters (section C - D in plate opposite), with cast-iron condensation gutter riveted to bottom for support of glass. In this case the glass is 1/2 inch thick by 12 inches wide by 60 inches long. In considering the width and length of glass, it is best to use what is generally called stock glass; otherwise it may be difficult to get when needed. The shorter the lengths, the more easily they are handled and the less liable to break. If the span is long, several lengths may be necessary; these can be overlapped at, each joint. The rebates should then be raised on the condensation gutter by strips of iron of different thicknesses under each plate of glass, to keep them in one pitch as steps. This will be found best for the glass, as the putty may shrink and become dislodged by the action of the atmosphere, leaving a wedge-shaped opening under each sheet.
Section A - B is the ridge bar having 1" X 1/2" strips riveted to sides. The filling-in bars are tenoned and mortised into this ridge, while some are mortised into the bar H, which is secured to wall with expansion bolts or lag screws.
The section of wall shows a cast-iron gutter 1/2 inch thick, with a false bottom E. This bottom is cast with the gutter near the top of moulding on one end, pitching down to the opening F in bottom of gutter where the leader connects.
This gutter is cast in several lengths, and is accurately fitted and water-tight. On the inside where the bars rest the glass is secured by galvanized or copper strips to prevent the plates from sliding out (see section G).
The weight to be calculated, in addition to iron and glass, is that of snow at 40 pounds per square foot; and use the formula as adopted for wrought-iron floor lights.