A NOVEL REINFORCED CONCRETE CLEAR WATER BASIN
Within the limits of the city of Pittsburgh there are many large industrial establishments which are situate along or adjacent to the banks of the Allegheny, Monongahela or Ohio rivers. It is therefore possible for each to secure a water supply either from the municipality or from a plant of their own, taking water front the rivers or from the sand and gravel beds adjacent. The municipality furnishes filtered water to peninsular Pittsburgh and the South Side, and unpurified Allegheny River water to the North Side. The charges for the water are the same in either case, now being on a sliding scale from 18 cents per 1,000 gallons for the first 250,000 gallons to 10 cents for all over 1,000,000 gallons, the average for a very large consumer being about 10.2 cents. This relatively high charge has compelled many of the large users to install their own waterworks system and rely on the city service for fire protection only. H. J. Heinze Company has its main factory and administrative buildings on Progress street, North Side, Pittsburgh. Established in 1869, this company has experienced a phenomenal growth, until to-day the main plant has 24 acres of tloor space, occupying 25 buildings. The buildings are of unit construction, and most of them about 100 by 140 feet and five stories high. Situated as they are on the North Side. Pittsburgh, where the water supplied by the city is raw Allegheny River water, and being engaged in a business where pure, wholesome water is a necessity, it would be necessary to filter the city supply before using the same. To purchase this water at a price of 10.2 cents and then filter it proved very expensive, much more so than to secure its own supply.
In 1907 the first investigation towards a private supply was undertaken. This consisted of sinking a well. 20 feet in diameter, to rock. The walls were of brick, resting on a cast iron shoe. As the excavation was removed from within the weight of the walls forced the shoe and wall down until a solid foundation was reached. A number of two-inch pipes were built into the walls of the well; these permitted the water from the sand and gravel beds to gain entrance to the interior. The first test on this well developed a rate of 300 gallons per minute without any perceptible lowering of water level. This rate was increased to 600 gallons per minute by drilling 16 small holes outside of the well and a short distance from it and exploding in each a charge consisting of 20 pounds of dynamite.
The water from the well was first used for washing and general factory purposes, and while being so used was analyzed daily. The character of the water as determined from this long period of analyses showed that it was free from impurities or objectionable chemical compositions and could be used for the more important operations where it came in contact with foods Since placing this well in service the quality has been very satisfactory. The maximum temperature is 55 degrees, the minimum 18 degrees and the average 51 degrees. The water is at all times perfectly clear and not affected in any way by the changes in the turbidity of the river, about 300 feet away.
In 1911 two 12-inch wells were drilled to a depth of 80 feet. Recent tests on these wells show a capacity of 250 gallons a minute and no abatement therefrom with continuous pumping. The total available private supply at present is thus about 1,100 gallons per minute. In order to store the extra water pumped in the 14 night hours so that it might be used in the shorter period of 10 working hours, it is necessary to have a basin or reservoir of about 800,000 gallons capacity.
A clear water basin was designed and built adjacent to the present factory. It is 99 feet 8 inches long, 88 feet wide over all. and has a depth of 17 feet. The basin is divided into two equal compartments by a reinforced concrete wall, so that either side may be used while the other is empty. Each compartment is equipped with an independent inlet, outlet and drain. The overflow from the basin is through a 12-inch pipe back into the well. The structure is of reinforced concrete, supported on a concrete pile foundation The loadings were so considered in design that a five-story factory building may be erected upon the basin, using it as a basement structure.
In deciding upon this rather unique scheme the value of land in the vicinity was a governing factor. The growth of H. J. Heinz Company has made necessary a constant increase in factory space, and with a corresponding need of land upon which to build, this has naturally caused an increase in the value of land in the neighborhood. It is, therefore, uneconomical to use for water purposes, only, any considerable area of land. It is also unwise in this ease to store water in a standpipe, on account of the great fluctuation in water level which would be incidental thereto, making a larger first cost due to extra head and affecting the operating cost of pumping. By designing the basin as a foundation for a building, only a very small part of the value of the land occupicd is to he charged against water and a large and comparatively shallow basin could be built, thus causing a minimum pumping charge with great storage.
Loadings.—In diterminng the loads to be carried by the basin walls, columns and footings, the first floor was considered as having a live load of 400 pounds per square foot; the second and third flooras having 300 pounds per square foot, and the fourth and fifth floors as having a loading of 150 pounds per square foot. In addition to this, a section of the first floor was designed to carry, whenever necessary, a mechanical filtration plant over the four hats in the southeast corner, bringing tin* load on this section up to 700 pounds per square foot.
It was further necessary to design against several combinations of loads, due to the floods in the local river rising at times as high as the top of the basin. We, therefore, considered:
First—The basin entirely empty and a flood level with the top of the basin ;
Second—With the basin full and a flood level with top of the basin ;
Third—With the reservoir full and with ground water level at low water in the river.
These three combinations were further complicated by the fact that the factory building will not he built for a year or more, thus making it necessary to consider, first, only the weight due to the basin itself, and second, the weight due to the entire five-strov structure. The combination of loadings, giving maximum stresses, varied in different members. For instance, the worst condition in the walls would he with the basin empty, a flood in the river and the factory building not yet built. The maximum stresses in the foundation under the walls would be with the basin full, no flood conditions, and the entire structure built.
Foundations.—The investigation of the strata of the ground was made by auger borings and later these data were verified by drilling two 8-inch holes to rock. It is believed that the determination of such accurate data, by preventing the necessity for guessing and gambling by contractors, saved the Heinz Company many times its cost. The ground was largely fill, and the character of the material may he seen in plate No. 2. Originally at this location there existed an old creek channel. The drainage previously flowing in this open channel now is confined to a larger sewer known as the Butchers’ Run Sewer. Rock was encountered in these drillings at about 50 feet below the surface. The soil found was not eapable of supporting the load due to the building, so it was necessary to use piles. Investigations were made as to the best type for this work and the concrete pile was selected, on the basis of carrying about three times the load of a wooden pile and being proof against deterioration, so characteristic of the latter, and at the same time costing only about three times that of wooden piles.
Conerete Piles.—The concrete piles were grouped in clusters under the columns and arranged in a double row under the wall. Each pile was calculated to carry 30 tons. The specifications were so worded that bids could be made on three general types of concrete piles, i.e.:
- Concrete piles, made by the driving of a shell, provided with a foot piece, and filling with concrete as the shell is being withdrawn;
- Concrete piles, made by driving a shell and a collapsible core: after being driven the core is withdrawn, leaving in place a light iron form, which is then filled with concrete;
- Concrete piles, with steel reinforcement, molded on the ground and then driven.
Twelve contractors bid on the work. The average of all bids on type (a) pile was $1.07 ; type (b) was $1.20, and type (c) was $1.13 per linear foot. The contract was let at a price of $1 per foot to the Cummings Structural Concrete Company, driving a type (c) pile, i e., molded on the ground and then driven.
The piles were cast horizontally in lengths of 25 and do feet, the probable length being first ascertained by driving two wooden test piles. The side forms were made to wedge in place and were readily knocked down. 1 he pile consisted of a fabricated steel reinforcement cast into a concrete mass, octagon-shaped, in cross-section: 9 inches in diameter at the base and with a taper of 1 inch in 10 feet.
The principal features of the piles were:
Plate No. 1 shows the pile-yard. The fabricated steel reinforcement is seen near the wagons in the foreground, the forms or molds and the operation of pouring concrete on the left of the casting platform; the storage pile, derrick and handling arrangements appear in the center of the picture. The concrete consisted of a 1 : 2 : 4 mix. Universal cement and Allegheny river sand and gravel were used. After pouring the concrete the pile was allowed to stand for several days. The forms were then removed, without in any way disturbing the pile. The pile was left on the casting platform until sufficiently hardened to allow of its being picked up and placed on the curing pile, where it remained for about fifteen days, or until needed on the work. The head of each pile was marked with the date of casting and selection for driving was made in accordance with these dates.
Driving Piles.—Two pile drivers were placed on the work—one a drop hammer, the other a steam hammer. The steam hammer proved less satisfactory for this particular work, and it was later replaced with a drop hammer. The hulk of the pile work was done with the latter, weighing12,000 pounds—the heavy hammer appearing to have much advantage over a lighter one. In driving each pile was fitted with a cylindrical cast-iron cap. the pile extending into the cap 6 to 8 inches. Immediately on the pile there was placed a cushion consisting of old hemp rope, and a wooden driving block was placed on top of this cushion. The hammer in this way hit the wood and the blow was eased up somewhat on the concrete. Plate No. 2 shows the heavy drop hammer and some of the piles as driven. Plate No. 3 shows several pile clusters for column footings.
Footings.—The footings resting on the piles were designed so that the center of gravity of the load coincided with the center line of the cluster of piles. Under the walls, where there are two rows of piles, they were arranged so that one row is located under the line of pressure from the walls when the basin is empty; the other row is located so that the center of the two rows of piles will coincide with the line of presure due to the load of the walls and that due to the water. The footings are all designed for concentrated loads due to the pile reactions and not as distributing the column loads uniformly over the area of the base of the footings. The heads of piles were all imbedded in the concrete footings and vertical reinforcement from the piles extends up and into the footings. Plates Nos. 4 and 5 show the arrangement of steel reinforcement for wall and column footings.
Columns.—The columns are all circular in crosssection designed with 2 per cent, reinforcement, consisting of eight vertical rods resting on a castiron ring and spirally wound with spiral steel hoop.
Walls.—The walls of the basin are of gravity type, 32 inches thick. The joints were all located so as to permit a convenient day’s work and also at a place where they could be easily cared for. In order to prevent leakage at these joints, due to expansion and contraction, strips of lead, extending 2 inches into the wall on each side of the joint, were placed from the bottom to the top.
Roof System.—The roof system is of the girded and T-beam type of construction, with slabs 5 inches thick, having fabricated steel reinforcement. 1’he beams and girders are reinforced with loose bars. The roof system, as a whole, contains about 0.6 per cent, reinforcement. Plate No. 6 shows the roof slab reinforcement, also the tower and chute for placing concrete. Plate No. 7 shows the completed roof of the basin, which will later be the first floor of the factory building. With the basin in use water is pumped into it from the large excavated well by a 5-inch Worthington centrifugal pump, operated by a 20-horsepower umbrella type motor on a vertical shaft. Water will also be pumped from each of the two 12-inch wells, which are equipped with Dean pumping heads, each operated by a 7 1/2-horsepower motor. The pumping machinery is automatically controlled so that the height of water in the clear water basin will either break or make a circuit and start or stop the motors and thus the pumps. From the clear water basin the water flows by gravity through a 12-inch line, a distance of 340 feet, to two American steam pumps, with a capacity of 1,200 gallons a minute. The pumps work against a head of 150 feet and supply water throughout the factories. As a spare tor this service there is installed a 14 x 20 x 14 x 36-inch Union steam pump in the 20-foot well, which may take its suction either from the well or from the basin. Plates Nos. 8 and 9 show the interior of the basin, looking toward the gate chamber, and give a good idea of the massive footings, columns and girder construction. There is a 100,000-gallon reservoir centrally located in the yard across the street, which will also be fed by gravity from the new clear water basin or through the discharge from the pumps in the well. From this basin a Knowles fire pump, with a capacity of 1,000 gallons a minute, takes its suction.