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.
Ribbed Base Plates are used where large columns and heavy weights are carried to the base stone on these bases. The plate is ribbed to distribute the load over a greater area on the granite,generally 1000 pounds per square inch safe load on granite, 200 pounds per square inch on brickwork, 150 pounds per square inch on concrete, 60 pounds per square inch on earth.
The ribs (D) should be the thickness of the body of base, or they may disconnect (after casting) with the body of column in cooling. The A in section is a flange which will be found very useful in keeping the outer edge of plate straight in cooling and will also give considerable strength to the plate. E is a large hole 2 inches diameter in centre of plate; G are small holes I inch in diameter in bottom plate (for explanation see "Grouting"). C is the flange; 3 inches wide, as at B, with holes (F) for connecting with column flange.
The body of base (H) and flange (C) should be the thickness of column above; the bottom the same. The flanges (A) should be the thickness of bottom by 1 1/2 inches high on inside.
The distance from top of base stone to finished floor is to be taken into consideration when designing these bases. It is a good plan to make the height of the rib equal to its base; that is, K equal to J, as J will be found when the number of square inches required on granite is established and bottom made into a rectangular base.
The height of rib (K) may be two thirds the projection of J, and be found to be a good angle to resist bending.
Flat Base Plates are used in most cases for small columns, or columns with light loads, also plain plates without the bevel A. The ring is used for fitting in the column in each case. This plate is also used for heavy loads; it may be strong enough, but the deflection is so great as to throw load on centre of cap, instead of distributing the weight over entire area of base stone.
To grout a base plate properly, allow one half to three quarters of an inch space between base stone and plate, with the base stone trimmed off true and level; set plate in its proper place (also level); make a bed of cement on all sides of bottom, to prevent mixture from spreading outside. Mix Portland cement with water until it runs smoothly (not like paste); then fill the body of the ribbed base plate until it is about half full. If the mixture is properly made, it will begin to ooze up at small holes in the bottom of plate. (These holes are necessary in every plate grouted, as they show that the mixture has filled under thoroughly).
If cement is used entirely, being quick-setting (except in freezing weather), grouting is found to be practically sufficient for base plates.
After the base stone is trimmed off level and true, make the mixture the consistency of paste, spread it equally over the stone from one to two inches in thickness. Set the base plate in its proper place, ramming it down solid, true and level.
Wooden columns connected by iron dowels are equally as objectionable as dowelled iron columns. The dowels for the former are made in two shapes, square and circular ended as shown, of 3/4-inch metal 5" X 10" by the height of the girder, with raised sockets for inserting the top and bottom of posts, and a lip on each top and bottom plate.
The lip on plate at A is usually 1 1/2 inches, and the lower lip (B) 2 inches by 3/4 of an inch thick.
Wrought-Iron Pins And Cast-Iron Star-Shaped Dowels are also used similarly to the above.
In each case the holes for inserting the dowels are first bored through the wooden girder before setting same on the columns.