An analysis of the cost of forms for an eight-story building is given by R. E. Lamb (Concrete Engineering, December, 1907). The basis of his estimate is made on using 7/8-inch by 6-inch tongued-and-grooved lumber for slab forms; 1 3/4-inch dressed plank for the sides and bottom of the beams and girders; posts 4 by 4-inch spaced 6 feet center to center; and on the fact that it cost $20.00 per thousand feet of lumber to make and set one floor of forms; that it cost $15.00 per thousand feet to strip the forms and reset them on the next floor; and that it cost about $8.00 per thousand feet to strip the forms and lower them to the ground.

Fig. 159. Form for Reinforced Concrete Slab between I Beams.

Fig. 159. Form for Reinforced-Concrete Slab between I-Beams.

Fig. 160. Form for Floor Slab on I Beams.

Fig. 160. Form for Floor-Slab on I-Beams.

Fig. 161. Beam and Slab Forms for Locust Realty Company Building.

Fig. 161. Beam and Slab Forms for Locust Realty Company Building.

With the size of the beams and girders as shown in Fig. 163, Mr. Lamb states that it will take an average of 4 feet, board measure, to erect each square foot of floor area.The basis of his estimate is as follows: that 1.5 board feet of lumber per square foot of floor is required for the slab; that for every square foot of beam surface, including the bottom, 3.2 board feet per square foot is required; and that for each square foot of girder, including the bottom, 3.G board feet of lumber is required. Taking these figures, for the panel shown, the slab will require 1.5 board feet per square foot; the beams, which are 8 by 18-inch, will have 3 feet 8 inches of surface per linear foot; and multiplying this by 3.2 board feet per square foot, and dividing by 7.5 feet, the distance center to center of beams, we find that 1.56 board feet per square foot of floor surface is required. Taking the girder in the same way, with 4 feet 8 inches of surface, multiplied by 3.6 board feet, and divided by 18 feet, the distance center to center of girders, we find that .94 board foot per square foot of floor is required. The total of the lumber required, then, is 1.5 board feet for the slab, 1.56 board feet for the beam, and .94 board foot for the girders - a total of 4 board feet per square foot of floor area.

Fig. 162. Column Forms for Locust Realty Company Building.

Fig. 162. Column Forms for Locust Realty Company Building.

In this estimate for an eight-story building, three sets of forms were used:

Fig. 163. Diagram of Forms.

Fig. 163. Diagram of Forms.

Roof: Stripping the sixth floor, resetting, altering to form valleys, and finally stripping roof and lowering forms to ground, 4 board feet at 2.6 cents

$ .104

Eighth Floor: Stripping the fifth floor, resetting, and finally stripping and lowering forms to ground, 4 board feet at 2.3 cents

.092

Seventh Floor: Stripping the fourth floor, resetting, and finally stripping and lowering forms to ground, 4 board feet at 2.3 cents

.092

Sixth Floor: Cost, same as for the fourth floor

.060

Fifth Floor: Cost, same as for the fourth floor

.060

Fourth Floor: Stripping the first floor, and resetting, 4 board feet at 1.5 cents

.060

Third Floor: Cost, same as for the first floor

.184

Second Floor: Cost, same as for the first floor

.184

First Floor: Making and setting forms, 4 board feet a1 2 cents

$.080

Material, 4 board feet at 2.6 cents

.104

.184

9)1.020

Average cost per square foot of surface

$ .113

To this average cost of 11.3 cents, 10 per cent should be added tor waste, breakage, nails, etc.; and if two sets of forms are used, the third floor would cost 6 cents per square foot, and the seventh floor 6 cents, giving an average of 9.6 cents per square foot.

In estimating the cost of the forms for the columns, it is assumed that making and placing the forms for the basement columns will cost about $26.00 per thousand; the cost of stripping and resetting, $16.00 per thousand; and 3.1 square feet of lumber is required for each square foot of column surface.

Eighth Story: Stripping sixth story, resetting and altering, finally stripping eighth story, and lowering to ground 3.1 board feet at 2.2 cents

$.068

Seventh Story: Stripping fifth story, resetting, and finally stripping and lowering to ground 3.1 board feet at 1 9 cents

.059

Sixth Story: Cost, same as second story

.050

Fifth Story: Cost, same as second story

.050

Fourth Story: Cost, same as second story

.050

Third Story: Cost, same as second story

.050

Second Story: Stripping basement columns and resetting 3.1 board feet at 1.6 cents

.050

First Story: Cost, same as for the basement columns

.162

Basement: Material, 3.1 board feet at 2.6 cents

$.081

Making and setting 3.1 board feet at 2.6 cents

.081

.162

.162 9) .701

Average cost per square foot of surface

$.077

To this average cost of 7.7 cents per square foot of column surface, should be added 10 per cent for bolts, nails, waste, etc. If three sets of forms are required, the second-story cost would be 16.2 cents, and the sixth story 5.9 cents, giving the average cost per square foot, of 9.1 cents.

The student should remember that this lumber has a value after it has been removed from the building, and that this value should be deducted from the total cost of the forms, to find the actual cost of forms.