Concrete Construction Part 35

Labor:

Cofferdams, excavation and pumping $ 3,000 Forms, falseworks and centers 2,000 Mixing and placing concrete 4,000 Placing reinforcement 400 Removing falseworks, forms, etc. 1,200 One coat pitch and paper 150 Building plant, etc. 2,250 ------- Total $13,000

Mr. Harrison states that including plant cost, delays, floods and incidentals the cost per cubic yard of concrete was $8 and that excluding these items the cost was $6 per cu. yd.

~COST OF CONSTRUCTING CONCRETE HIGHWAY BRIDGE, GREENE COUNTY, IOWA.~--The following is the itemized cost of constructing a reinforced concrete slab highway bridge, one of several built by the Highway Commissioners of Greene County, Iowa, in 1906. The figures are given by Messrs. Henry Haag and D. E. Donovan, the last being the foreman of the concrete gang doing the work. All bridges consist of 10 to 12-in. slabs reinforced with old steel rails and of abutments and wing walls reinforced with old rods, bars or angles selected from junk. This junk metal cost 0.6 cts.

per pound and the rails cut to length cost 1.15 cts. per pound f. o. b.

cars. The work was done by a special gang, the men receiving $1.50 per day and board. As a rule the footings were made 2 ft. wide and as high as need be to get above the water and dirt. Before the footing concrete set steel rods, bars or angles were placed; they were long enough to reach the height of the wall and 3 to 6 ins. into the slab. The forms for the abutment and wing walls and for the floor slab were then erected complete before any more concrete was placed. No carpenter was employed, every man on the job having been taught to take his certain place in the work, then, the forms being erected, every man had his particular place in the work of mixing and placing the concrete. The foreman saw that the reinforcement was properly placed and watched over the accuracy of the work generally. The concrete was allowed to set on the centers for from 30 to 40 days; the other form work was taken down after three days and travel over the bridge permitted after three or four days. The concrete was mixed wet. The bridge whose cost is given was 22 ft. wide and 16 ft.

span with 2-ft. wing walls.

The foundations are 4 ft. deep and 2 ft. wide. The walls on top of the foundations are 7 ft. high, 18 ins. wide at the base, and battered up to 14 ins. at the top for wings and 12 ins. at top for walls. The floor is 22 ft. by 18 ft. and 1 ft. thick. The wheel guard is 12 ins. thick by 14 ins. wide and 32 ft. long. The itemized cost of this bridge, containing 73 cu. yds. of concrete, is as follows:

Materials. Total. Per cu. yd.

70 cu. yds. gravel at 70 cts $ 49.00 $0.6726 10 cu. yds. broken stone at 70 cts 7.00 0.0959 75 bbls. cement at $2.20 165.00 2.2603 7,000 lbs. steel rails at 1.15 cts 80.50 1.1027 1,000 lbs. junk rails at 0.6 cts 6.00 0.0819 200 ft. B. M. lumber wasted at $29 5.80 0.0794 15 lbs. nails at 3 cts 0.45 0.0061

Labor and Supplies: 2 days excavation at $14 28.00 0.3835 day foundation at $14 10.00 0.1369 1 days building forms at $14 21.00 0.2876 2 days filling forms at $14 28.00 0.3835 Hauling lumber and tools 8.00 0.1096 Hauling cement and tools 18.00 0.2465 Taking off forms 2.30 0.0315 1,000 lbs. coal at $4 per ton 2.00 0.0274 ------ ------- Total cost $431.05 $5.9054

In round figures the cost per cubic yard of concrete in the finished bridge was $5.90. Summarizing we have the following cost per cubic yard of concrete in place:

Item. Per cu. yd.

Cement $2.26 Steel 1.22 Lumber 0.22 Gravel and stone 0.76 Labor 1.41 Coal 0.03 ----- Total $5.90

The average cost of concrete in place for all the work done in Greene County by day labor was $6.25 per cu. yd. In the job itemized above the bank caved in, causing an extra expense for removing the earth. The gravel used in this bridge was very good clean river gravel.

~METHOD AND COST OF CONSTRUCTING TWO HIGHWAY GIRDER BRIDGES.~--The following account of the methods and costs of constructing two slab and beam highway bridge decks on old masonry abutments is taken from records kept by Mr. Daniel J. Hauer. The first bridge was a single span 15 ft. long that replaced wooden stringers and floor that had become unsafe; the second was two short spans of a steel bridge that was too light for the traffic of the road, and it was torn down and moved elsewhere, by the county authorities. The work was done by contract, and in each case consisted of building the reinforced floor and girders on the old masonry walls that were in good condition. While the work was going on traffic was turned off the bridges, fords being used instead.

Figure 154 shows a sketch of the cross-section of the floor and girders.

In Example I the girders had a depth below the floor of 12 ins. and were of the same width. In Example II the girders were 14 ins. wide and had a depth below the floor of 18 ins. The floors on both bridges were 6 ins.

thick. Kahn bars were used for reinforcement.

[Ill.u.s.tration: Fig. 154.--Cross-Section of Concrete Girder Bridge.]

_Example I._--This bridge was but little more than 5 ft. above the stream, which was shallow and not over 7 ft. wide, unless swollen by floods. The bottom for several hundred feet on either side of the bridge was covered with coa.r.s.e sand and gravel, that had pebbles in it from the size of a goose egg down. This was taken from the stream by men with picks and shovels and hauled to the site of the work with wheelbarrows, and then screened so as to separate the gravel from the sand. As it was found that the sand was so coa.r.s.e that it would take more cement than the specifications called for in a 1-2-5 mixture, some much finer sand was bought and mixed with it. For the privilege of taking the sand from the stream $1 was paid the property owner. This was done to get a receipt and release from him, rather than as an attempt to pay royalty on the gravel and sand. This dollar is included in the cost of the labor in getting these materials.

The cost of materials per cubic yard for the bridge was as given below, the mixture being as stated above. The cement cost $1.40 per barrel, delivered at the bridge.

Per Cu. Yd.

Steel $2.50 Gravel and sand .75 Sand (bought) .30 Cement 1.57 ----- Per cubic yard $5.12

It is of interest to note the cost of the gravel and sand, as this includes the cost of digging it, wheeling it in a wheelbarrow an average distance of 100 ft., and then screening it and putting it in two stock piles. The proportion of bought sand used with the creek sand was one-half.

The old wooden floor and stringers had to be torn down. This was done at a cost of $1.30 per M. ft. B. M., and furnished 60 per cent. of the lumber needed for forms. The floor boards were 3-in. yellow pine planks, and the stringers 612-in. timbers, rather heavy, but money was saved by using them. The 612-in. timbers were used for props for the centering.

Additional lumber was bought, delivered at the site of the bridge, for $20.84 per M. ft. B. M.

In framing and erecting the forms the carpenter had laborers helping him, he doing only carpenter's work, the laborers carrying and lifting all pieces wherever possible. The carpenter's work was about 40 per cent. of the total labor cost, which was as follows per cubic yard of concrete:

Tearing down old bridge $0.08 Lumber .85 Nails .15 Labor, carpenter .77 Labor, laborers .96 ----- $2.81

The forms were torn down by laborers, with the a.s.sistance of a man and his helper, who were given the boards for this labor and to haul them away. This reduced this item somewhat, as it only amounted to 20 cts.

per cu. yd.

The cost of the forms per thousand feet board measure was:

New lumber $20.82 Nails 1.44 Labor, carpenter 7.60 Labor, laborers 9.50 Tearing down 2.00 ------ $41.36

All the men, including the carpenter, worked 10 hours per day, and were paid at the following rates:

Carpenter $2.50 Sub-foreman 2.00 Laborers 1.50

A regular foreman was not employed, but an intelligent and handy workman was given 50 cts. additional to lead the men and look after them when the contractor was not present.

A gang of six men did the work of mixing and placing, and as the stock piles were close by the mixing board no extra men were needed to handle materials. Water was secured from the stream in buckets for mixing. The mixture was made very wet. The cost per cubic yard for the entire structure was as follows:

Preparing for mixing $0.04 Cleaning out forms .06 Handling steel .03 Mixing and placing 1.15 Ramming .23 ----- $1.51

The cost of the contractor's expense of bidding, car fare, etc., is listed under general expense, and gives a total cost per cubic yard of:

Materials $ 5.12 Erecting forms 2.81 Tearing down forms .20 Labor 1.51 General expense 2.00 ------ $11.64

_Example II._--For this bridge both the stone and sand had to be bought.

The bridge floor was nearly 14 ft. above the bottom of the stream, which was shallow. The wages paid were as follows for a 10-hour day:

Foreman $3.00 Laborers 1.50

Carpenters were paid $3 for an 8-hour day and time and a half for all overtime, which they frequently made.

For the girders a 1-2-4 mixture was used. The cement, delivered at the bridge, cost $1.21 per barrel, there being 8 cts. a barrel storage and 8 cts. a barrel for hauling included in this. The sand was paid for at an agreed price per cartload delivered, which averaged $1.34 per cu. yd.

The stone was crushed so as to pa.s.s a 1-in. ring in all directions. It was delivered at the bridge for $2.75 per cu. yd. This makes the cost per cubic yard for materials as follows:

Steel $1.41 Cement 2.18 Sand .67 Stone 2.75 ----- $7.01

For the floor a 1-3-5 mixture was used, making a cost for material of:

Steel $1.02 Cement 1.69 Sand .67 Stone 2.75 ----- $6.13

Two-inch rough pine boards were used to make the troughs for the girders, while 1-in. rough boards were used for the floors. These were all supported by 34-in. pine scantlings. This lumber cost delivered $17.50 per M. ft. B. M. Carpenters did all the framing, and erected it with the help of laborers. All the carrying of the lumber was done by laborers. This reduced the cost of the work, as the laborers' wages amounted to one-third of the whole cost. As soon as the forms were all in place, which was before the mixing of concrete commenced, the carpenters were discharged. The cost per cubic yard for forms was:

Lumber $2.82 Nails .05 Labor, carpenters 1.24 Laborers .62 ----- $4.73

The tearing down of the forms was done entirely by laborers at a cost of 61 cts. per cu. yd.

On concrete work it is also advisable to keep the cost of forms per thousand feet board measure, so as to have such data for estimating on new work. The cost per M. ft. on this job was:

Lumber $17.50 Nails .30 Labor, carpenters 7.65 Laborers 3.85 Tearing down 3.80 ------ $33.10

The concrete was mixed by hand, water being carried in buckets from the creek. Ten to twelve men were worked in the gang under a foreman, and the concrete was wheeled from the mixing board to the forms in wheelbarrows. The mixture was made wet enough to run. The cost per cubic yard for the girders in detail was as follows:

Foreman $0.41 Preparing for mixing 0.14 Cleaning out forms 0.07 Handling materials 0.30 Handling and placing steel 0.40 Mixing and placing 0.87 Ramming 0.45 ----- $2.64

The cost of labor for the floor was: