Concrete Construction Part 51

"Six 16-ft. sections of these forms were built, and three were used each day on each end, as shown by the diagram MN, Fig. 256, which gives the day for the month for the completion of each of seven 48-ft. sections.

"A gang of men simply s.h.i.+fted on alternate days from end to end of the conduit, although several sections were in progress at one time; and of course, finally, when a junction was made between any division, say of 1,000 ft. to another 1,000 ft., one small form was left in at this junction inside of the conduit, and had to be taken down and taken out the entire length of the conduit.

"The centers for a 16-ft. length of this conduit cost complete for labor and material, $18.30, but they were used over and over again; and, after this conduit was completed, they were taken away for use at other points, so that the cost is hardly appreciable, and the only charge to centers that we made after the first cost of building the centers, was on account of moving them daily. Part of this conduit was built double (two 6-ft. conduits) and part single, the only difference being that, where the double conduit was built, two forms were placed side by side, and not so much was undertaken in one day.

"These conduits, when completed and dried out, rung exactly like a 60-in. cast-iron pipe, when any one walked through them or stamped on the bottom."

Mr. Woollard gives the following a.n.a.lysis of the cost per cubic yard of the concrete-steel conduit above described:

Per cu. yd.

1.3 bbl. cement $1.43 10 cu. ft. sand 0.35 25 cu. ft. stone 1.10 26 sq. ft. expanded metal, at 3 cts. 0.78 Loading and hauling materials 2,000 ft.

to the mixing board (team at $4.50) 0.50 Labor mixing, placing, and ramming 1.38 Labor moving forms 0.60 ----- Total $6.14

Wages were 17 cts. per hr. for laborers and 50 cts. per hr. for foremen. The concrete was 1-2-5, a barrel being a.s.sumed to be 3.8 cu.

ft. The concrete was mixed by hand on platforms alongside the conduit.

The cost of placing and ramming was high, on account of the expanded metal, the small s.p.a.ce in which to tamp, and to the screeding cost. When forms were moved they were sc.r.a.ped and brushed with soft soap before being used again.

From Mr. Morris R. Sherrerd, Engineer and Superintendent, Department of Water, Newark, N. J., we have received the following data which differ slightly from those given by Mr. Woollard. The differences may be explained by the fact that the cost records were made at different times. Mr. Sherrerd states (Sept. 26, 1904,) that each batch contains 4 cu. ft. of cement, 8 cu. ft. of sand, and 20 cu. ft. of stone, making 22 cu. ft. of concrete in place. One bag of cement is a.s.sumed to hold 1 cu. ft. He adds that a 10-hour day's work for a gang is 63 lin. ft. of single 6-ft. conduit containing 47.4 cu. yds. of concrete and 1,260 sq.

ft. of expanded metal. This is equivalent to cu. yd. of concrete per lin. ft. The total cost of material for one complete set of forms 64 ft.

long was $160; and there were 7 of these sets required to keep two gangs of men busy, each gang building 63 lin. ft. of conduit a day. Since the total length of the conduit was 3,850 ft., the first cost of the material in the forms was 18 cts. per lin. ft.

Cost of Labor on 6-ft. Conduit:

Per day. Per cu. yd.

1 foreman on concrete $ 3.35 $0.07 1 water boy 0.75 0.01 11 men mixing at $1.75 19.25 0.39 5 men mixing at $1.50 7.50 0.16 4 men loading stone at $1.40 5.60 0.12 4 men wheeling stone at $1.40 5.60 0.12 2 men loading sand at $1.40 2.80 0.06 2 men wheeling sand at $1.40 2.80 0.06 1 man placing concrete at $1.75 1.75 0.04 6 men placing concrete at $1.50 9.00 0.19 2 men supplying water at $1.50 3.00 0.06 1 man placing expanded metal at $2. 2.00 0.04 1 man placing expanded metal at $1.50 1.50 0.03 ------ ----- Total labor on concrete $64.90 $1.35

Cost of Labor Moving Forms:

Per day. Per cu. yd.

4 carpenters placing forms $13.00 $0.27 2 helpers placing forms 4.00 0.08 1 carpenter putting up boards for outside forms 2.75 0.06 1 helper putting up boards for outside forms 2.25 0.05 2 helpers putting up boards for outside forms 3.50 0.07 1 team hauling timber 4.50 0.09 1 helper hauling lumber 1.75 0.04 ------ ----- Total labor moving $31.75 $0.66

It will be noted that it required two men to bend and place the 700 lbs., or 1,260 sq. ft., of expanded metal required for 63 lin. ft. of conduit per day, which is equivalent to c per lb., or 3 cts. per sq.

ft., for the labor of shaping, placing and fastening the metal.

~CIRCULAR SEWER, SOUTH BEND, INDIANA.~--In building 2,464 ft. of 66-in.

circular reinforced concrete sewer at South Bend, Ind., in 1906, the method of construction ill.u.s.trated in Figs. 257, 258 and 259 was employed. The sewer has a 9-in. sh.e.l.l b.u.t.tressed on the sides and is reinforced every 12 ins. by a 3/161-in. peripheral bar in the sides and roof and 3 ins. in from the soffit. Each bar is composed of three pieces, two side pieces from 15 ins. below to 6 ins. above springing lines and a connecting roof bar attached to the side bars by cotter pins. Two grades of concrete were used, a 1-3-6 bank gravel concrete for the invert and a 1-2-4 bank gravel concrete for the arch. The invert was given a -in. plaster coat of 1-1 mortar as high as the springing lines.

[Ill.u.s.tration: Fig. 257.--Form for South Bend Sewer (First Stage).]

[Ill.u.s.tration: Fig. 258.--Form for South Bend Sewer (Second Stage).]

[Ill.u.s.tration: Fig. 259.--Form for South Bend Sewer (Third Stage).]

Forms and Concreting.--In constructing the sewer the trench was excavated so as to give a clearance of 1 ft. on each side and was sheeted as shown by Fig. 257. The sewer was built in 12 ft. sections as follows: The bottom of the trench was shaped as nearly as possible to the grade and shape of the base of the sewer. Four braces to each 12 ft.

section were then nailed across the trench between the lowest rangers on the trench sheeting. A partial form consisting of a vertical row of lagging was set on each of the outside lines of the sewer barrel as shown by Fig. 257. Each section of this lagging was held by stakes driven into the trench bottom and nailed at their tops to the cross braces as shown by Fig. 258. A template for the invert was then suspended from the cross braces by pieces nailed to the four ribs of the template and to the cross braces as shown by Fig. 257. The concrete was now placed and carried to the top of the template, which was then removed. The side pieces of the reinforcing bars were then set and fastened as shown by Fig. 258. The side forms extending up to the springing lines were then placed. They were held in position by braces nailed to their ribs at the tops and by other braces fitting into notches in the ends of their ribs at the bottom. The concrete was then carried up to the springing lines, the arch centers in two pieces were placed; the arch bar of the reinforcement was placed and the extrados forms erected up to the 45 lines, all as shown by Fig. 259. The placing of the arch concrete completed the sewer barrel. The outside forms and bracing were removed about 24 hours after the completion of the arch and back filling the trench was begun immediately, but the inside forms were left in place for two weeks; they were then removed by the simple process of knocking out the notched braces. By building several lengths of invert first and following in succession by the side wall construction and then by the arch construction, the form erection and the concreting proceeded without interruption by each other. It was also found that, by making bends in the form of polygons with 10 ft. sides instead of in the form of curves, there was a material saving in expensive form work. To overcome the friction of the angles in such bends an additional fall was provided at these places. All concrete was made in a Smith mixer mounted on trucks so that it could be moved along the bank of the trench and discharging into a trough leading to the work.

_Labor Force and Cost._--With a gang of 12 men from 24 to 36 ft. of sewer was built per 10-hour day, working only part of the time on actual concreting. The disposition of the force mixing and laying concrete and the wages were as follows:

Item. Per day.

Six wheelers, at 18.5 cts. per hour $11.10 One mixer, at 22.5 cts. per hour 2.25 One dumper, at 18.5 cts. per hour 1.85 Four placers, at 22.5 cts. per hour 9.00 ------ Total $24.20

There were 0.594 cu. yd. of concrete per lineal foot of sewer and its cost is given as follows:

Item. Per cu. yd.

Cost of gravel $0.774 Cost of sand 0.36 Cost of cement 1.50 Cost of steel reinforcement 0.84 Cost of labor, mixing and placing concrete 1.094 Cost of moving forms, templates, etc. 0.757 Cost of forms, templates, etc. 0.589 Cost of finis.h.i.+ng, plastering, etc. 0.639 Cost of tools and general expenses 0.841 ------ Total $7.394

~SEWER INVERT, HAVERHILL, Ma.s.s.~--In constructing sewers with concrete inverts at Haverhill, Ma.s.s., in 1905, use was made of the traveling form or mold shown by Fig. 260. The form consists of an inner and an outer sh.e.l.l, the annular s.p.a.ce between which forms the mold; in operation the annular s.p.a.ce is filled with concrete, then the outer sh.e.l.l is pulled ahead from underneath, leaving the inner sh.e.l.l in place. A second inner sh.e.l.l is then adjusted to the outer sh.e.l.l in its new position, the annular mold is concreted and the outer sh.e.l.l again pulled ahead.

Continued repet.i.tion of the operations described completes the invert.

The merit of the device lies in the fact that the inner sh.e.l.l is not moved until the concrete has attained some degree of rigidity; when, in such devices, the inner mold is slid ahead on the green concrete it is likely so to "drag" forward the material that a rough and pitted surface results.

_Mold Construction._--Referring to the drawings of Fig. 260, A is the outer mold of sheet steel bent to the required shape of the outer surface of the conduit to be constructed. A rib, or angle, B, is riveted to the inside of the mold at its front end and a diaphragm C of plank is securely fastened to the rear side of the rib. The opposite or rear end of the mold is open. Angles D forming tracks are riveted inside the mold a short distance below the edges and reaching their full length. The inner mold comprises a steel sh.e.l.l E curved to the form of the inside of the conduit; inside this steel sh.e.l.l is a reinforcing lagging, and at each end there is a wooden diaphragm F. Pa.s.sing through both end diaphragms and having its ends flush with the end planes of the mold is a timber G. Rearward projecting lips e are secured to the lagging at the rear end of the mold and on each side of the timber G. The diaphragms F have each two arms f which project horizontally beyond the surface of the inner mold and engage the tracks D; locking dogs H are pivoted to the arms f so as to hook under the track angles D and hold the inner form from rising. Setting on the inner mold is an inverted V-shaped deflector I; its edges are flush with the sides of the mold and its purpose is to facilitate the placing of the concrete. There is also a movable diaphragm K, fitting loosely inside the outer mold A and bearing against the end of the inner mold E. The length of the inner mold E is about one-half that of the outer mold A; as a rule several inner molds are provided with one outer mold.

[Ill.u.s.tration: Fig. 260.--Traveling Invert Form for Sewer Construction.]

_Mode of Operation._--In using the device described the outer mold A is first placed in the trench with its rear end at the end of the trench. An inner mold E is then suspended on the tracks of the outer mold and locked therein by the dogs H, with its rear end flush with the rear end of the outer mold. The part.i.tion K is then placed in position against the forward end of the inner mold and a jack J of any suitable form is interposed between diaphragms K and C, the jack being extended sufficiently to press diaphragm K firmly against the front end of the inner mold. The deflector I is next placed in position on the inner mold and the concrete is forced down with an iron rammer between the two molds, so as to fill completely the annular s.p.a.ce. The deflector aids in directing the concrete into this s.p.a.ce, as will be obvious. After the mold has been filled and the concrete compacted as much as possible, the jack is operated to separate the diaphragms K and C, and as the part.i.tion K is pressed against one end of the ma.s.s of concrete which has been laid, the opposite end of which abuts against the end of the trench, it follows that any backward movement of the diaphragm K will compress the concrete. This movement will be practically inappreciable in distance, but enough to compact thoroughly the concrete and fill any voids. The action of the jack will also push forward the diaphragm C and the outer mold A, the latter being withdrawn from beneath the inner mold and the newly laid concrete, the tracks D of the outer mold being drawn from beneath the arms f of the inner mold, leaving the latter behind resting on the freshly laid concrete. Further compression of the concrete after it has been left by the outer mold will fill the s.p.a.ces between the inner mold and the surface of the trench. The outer mold is moved forward in this manner a distance equal to the length of the inner mold, and then the diaphragm K is drawn forward and another inner mold is lowered into the outer mold exactly as was the first one. The jack is then placed, the concrete deposited and the outer mold again advanced exactly as before. As the outer mold advances, the inner molds become disengaged one after another and are set ahead; in practice, enough inner molds are provided to enable the concrete to harden sufficiently to keep its position when it becomes necessary to take up successively the rearmost molds and place them ahead.

_Haverhill Sewer Work._--The work at Haverhill, Ma.s.s., previously mentioned in which the form just described was used, was a 24-in.

circular sewer with 6-in. walls. The outer form was 36 ins. in diameter and 6 ft. 2 ins. long; the inner form was 24 ins. in diameter and 3 ft.

long. Angle B was 3 ins. and the track angles D were 1 ins.; diaphragm K was made of two thicknesses of 3-in. plank and diaphragm C of one thickness of 3-in. plank, the other diaphragms were of 2-in. plank. The sh.e.l.ls of the molds were of -in. steel plate; the jack was an ordinary screw jack. Eight inner molds were used.

The form used at Haverhill was built by the city carpenter, the metal portions being made in a boiler shop. Its cost was not ascertained, but was, it is thought, about $75. The concrete used was a 1-3-5 stone mixture, with cement costing $2 per barrel, sand $1.50 per load of 36 cu. ft., and stone $2.50 per load of 36 cu. ft. The men were paid 25 cts. per hour. Records kept on 265 ft. of invert, or, theoretically, 19.3 cu. yds. of concrete, gave the following figures:

Per Per lin. ft. cu. yd.

Labor, setting and moving forms, 42 hours, at 25 cts. $0.05 $0.67 Labor, mixing, placing and wheeling concrete, 179 hours, at 25 cts. 0.16 2.19 ----- ----- Total labor cost $0.21 $2.86

With the ordinary 1-3-5 mixture the cost of materials would run about as follows:

Per cu. yd.

Cement, 0.96 bbl., at $2. $1.92 Sand, 0.47 cu. yd., at $1.13 0.53 Stone, 0.78 cu. yd., at $1.88 1.47 ----- Total cost materials $3.92

Two men were worked in the trench, one alternately ramming the concrete into place and working the jack, and the other shaping the trench ahead and a.s.sisting in bringing the rear forms ahead.

The form described was invented by Mr. Robert R. Evans, of Haverhill, Ma.s.s., and has been patented by him.

~29-FT. SEWER, ST. LOUIS, MO.~--The following account of the method and cost of constructing 162 ft. of very large sewer section at St. Louis, Mo., is compiled from information furnished by Mr. Curtis Hill.

The cross-section of the sewer is given by Fig. 261, which also shows the arrangement of the reinforcing bars. Johnson corrugated bars, old style, are used for reinforcement. The sections of the various reinforcing bars are: Longitudinal bars, 0.18 sq. in.; invert bars, 0.7 sq. in., and arch bars, 0.7 sq. in. The s.p.a.cing of the bars and the arrangement of the splices are indicated on the drawings of Fig. 261.

All splices have a lap of 36 ins. Some gravel concrete has been used in the invert, but most of the concrete has been crushed limestone and Mississippi River channel sand. The proportions were 1-3-6 in the invert and 1-2-5 in the arch. The arch was computed by Prof. Greene's method.

The ultimate strength of concrete in compression was taken as 2,000 lbs.

per sq. in. and the working strength at 500 lbs. per sq. in. The elastic limit of the reinforcing bars was taken at 50,000 lbs.

[Ill.u.s.tration: Fig. 261.--Harlem Creek Sewer, St. Louis, Mo.]

The trenching was done by wheel sc.r.a.pers to the amount of waste. Then a cableway was erected spanning the entire length of the section and the remainder of the material taken out. The last 4 or 5 ft. in depth were in limestone and the excavated rock was taken by cableway to dump carts which took it to the crusher and returned with crushed rock to be used for concrete. This rock foundation was taken advantage of to reduce the amount of invert concrete.

In constructing the sewer proper the invert was first concreted to template to the height shown in Fig. 262. The arch forms were then placed as shown in Fig. 262, and the roof arch concreted. Both templates and arch forms were constructed of wood. The arch forms were moved ahead on iron rails and jacked into place. The ribs were 210-in. pieces and were s.p.a.ced 4 ft. on centers; the lagging was 2-in. tongue and grooved stuff and was smeared with crude oil. The reinforcing bars shown in Fig.

261 were bent to proper radius by means of a wagon tire bender and were held in place by templates. The concrete was all mixed by two Chicago Improved Cube mixers operated by electric power.