A afierfiresented at a Meeting of the Ckicago Branclof the A nierican Institute of Electrical Engi--neers, Clhicago, Fe6 2S,' r9 5.

Copyright 1905. By A. I. E. E.

CEMENT IN CENTRAL STATION DESIGN.

BY EUGENE B. CLARK.

The Illinois Steel Company has just completed, and placedin operation at its plant in South Chicago, a new power-housefor the supply of power to its various mills at South Chicago,and at Buffington, 10 miles distant. This station cottains, atthe present time, two units, each consisting of a 2000-kw.,25-cycle, 2200-volt, three-phase generator, direct driven by a24-in. by 60-in. by 48-in. horizontal-vertical, cross-compourndenlgine. The addition of two more generating units, of a ca-pacity of 4000 kw. each, is contemplated in the near future"iThis alternating-current station operates in conjunction with Adirect-current station which has been in operation for sometime. The two power-houses are connected by means of sy'n-chronous converters. Both stations take steam from blast-furnace boiler-houses, in" which the fuel is excess blast-furnacegas. The supply of this excess gas is quite variable at times,and it is desirable under such conditions to be able to shiftthe load from one station to the other, as desired. Such an ar-rangement gives the opportunity of utilizing completely allexcess blast-furnace gas at either point. The principal pointsof interest with which we are concerned to-night, deal entirelywith the use of cement in the building of this and other power-houses.The foundations for the machinery and the building rest

upon piles and are made of slag concrete consisting of onepart cement, three parts torpedo sand, and seven parts crushedslag.' The cement used for those parts of the foundations'which are not exposed was of the brand known as Puzz'olanft;"for those parts which are exposed, Universal' 'Portlaiid 'eiennt

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56 CLARK; CEMENT IN [Feb. 28

was used. The foundations were started in the coldest weatherof last winter, and the concrete, which had to be mixed withwarm water and warm sand, to keep from freezing in the mixer,did freeze immediately after being tamped into place. Fillingwas used to follow up the foundations as rapidly as they wereput in place, so that the concrete was not permitted alternatelyto freeze and thaw as the warmer weather came on. The resultwas to obtain a thoroughly solid foundation, the concrete set-ting up firmly as it gradually thawed during the spring months.About the middle of summer the foundation was tested bydrilling a hole several feet deep into that part which had orig-inally been frozen. It was found that it had set up to makean extremely solid and strong concrete.A considerable amount of time and attention was devoted

to determining the most desirable method of floor construction.The power-house apparatus is controlled by electrically-oper-ated switchiing devices. The electrically-operated switches, to-gether with the bus-bars, control-pedestals, instrument-postsand feeder-panels, required for their accommodation the con-struction of galleries at one end of the engine-room. Two ofthese galleries were built, and the engine-room floor was used asanother gallery. On the engine-room floor were located thegenerator-switches; on the first gallery were located the bus-bars, the instrument-posts, generator-control pedestals, feeder-panels, etc.,; on the third gallery were located the feeder-switchesand the lightning-arresters. A transmission line, carrving apressure of 20 000 volts, was necessary to transmit the requiredamount of power to Buffirfgton, located 10 miles south of SouthChicago. At least 4500 kw. of transformers had to be locatedin the power-house. It was decided best to place these on theengine-room floor, under the first gallery, constructing anisolated transformer-room for that purpose. The transformer-room was isolated from the rest of the apparatus on the engine-room floor, by means of a wall about three inches thick and17 feet high, built of reinforced concrete, in accordance withthe method to be described later. This wall proved aftererection, to be thoroughly solid and substantial; as rigid, infact, as would have been a masonry wall 12-in. or 14-in.thick. It then became necessary to take wires carrying apressure of 20 000 volts through the operator's position on thefirst gallery. In order to harmonize these various requirements,it soon became evident that much additional space would be

1905.] CENTRAL STATION DESIGN. 57

required if it should prove necessary to have the usual steelbeams in the gallery floors, inasmuch as the beams would bein the way of the mnany wires which it would be necessary totake through these floors. These conditions pointed to theadvisability of using a floor construction of concrete slabs orof fire-proof tile. Careful consideration of the subject provedthat, even with the comparatively long spans for such heavyloads, the concrete construction would be far preferable, bothfrom the standpoint of cost and from the standpoint of fire-proofing. Experience at the Baltimore fire had shown thatproperly constructed concrete floors had withstood the test offire and water better than any other kind of floors.To make certain of the safety and conservatism of the pro-

posed design, a section of the floor, as proposed, was built andtested prior to the final decision as to the construction of thefloor for the building and galleries. After being allowed toset 21 days, this section of floor was tested by piling pig ironupon it, to the extent of 500 lb. per square foot. The test slabwas 7-in. thick and 15-ft. span, made of concrete, consisting ofone part Universal cement, two parts Torpedo sand, and fourparts 0.5 to one inch crushed limestone, reinforced with 0.5-in.steel rods, spaced five in. apart and laid on top of No. 10 gaugeexpanded metal placed one inch from the bottom of the slab.Upon test, the slab collapsed under a load of 550 11). per squarezfoot. An even distribution of the load over the surface wasobtained by covering the top of the slab with about four inchesof sand, upon which was piled the pig iron. Deflections weremeasured as the load increased. The deflection at the center-had risen to about 1.5 inches by the time the slab failed. Itwas determined that the expanded metal was comparativelyvalueless for purposes of reinforcement when used in conjunctionwith the 0.5 in. round rods, as all the tensio'n was taken bythe rods. These rods were bent at the ends for a distance ofabout 10 or 12 iIches through an angle of 1800, thereby insuringthat they would not pull out at these points. It was foundnecessary to bend the rod through 1800, and not through 900;for those which were bent only 900 showed a very decided ten-dency to crack the concrete at the corners and then to pullout. Round rods were used in preference to twisted or notched,or any other form of rods designed to prevent slipping or pulling-out of the concrete, and for two reasons: first, the round rodsare far cheaper; secondly, it was decided that nothing was gained

58 CLARK: CEMENT IN [Feb. 28

by preventing, the rods from pulling out of the concrete, pro-vided they were properly fastened at each end. The mixtureused in all the floor construction was one part Universal Portlandcement, two parts Torpedo sand, and four parts crushed lime-stone, 0.5- to 1-in. mesh. The shoring under all floors waspermitted to remain 28 days before removal. In the engine-room floor, for the very long spans, some floor beams wereused, but in all cases they were entirely covered with concrete,to give thorough fireproofing.Wherever generator-pits or fly-wheel pits were to be covered,

such covers were made of cement castings, reinforced with ex-panded metal, rather than of cast iron. These cover plateswere made to exact fit for each place as the work progressed,no drawings being necessary. The carpenter made a smallmould of the correct size, in which the cement worker cast hisfloor plate and finished it exactly as the rest of the floor. Thegallery floors were completed and the shoring removed beforeany work was done on the installation of the electrical controlapparatus or the supports therefor. Each gallery was treatedas independent of the one under it, so far as support Was con-cerned, though, in building up the switch-cells, the bus-barconstruction, and the barriers, the practical result was to give,additional support to each floor from the one under it. Theswitch structure was also constructed in such a way as prac-tically to be a beam in itself. Round iron rods were cast intothe lower part of the structure and allowed to extend throughfrom the first switch in the row to the last. The result was toprovide a construction of the switch-cells which, being in itselfa beam, would distribute the load to those points where theload might best be taken. In addition to this fact, the barrierwhich rose from the switch-cell to the ceiling above, taken inconjunction with the lateral barriers-all of which were builtmonolithic with the wall rising from the switch structure-formed a column of great strength. It would probably not bepoor engineering to depend, in a measure, upon the strength ofthis column to support the floor above it; but in the case whichis being described this was not done. Even though no attemptwere made to utilize the switch structure as a column, still, thefact was taken into consideration that there would be a naturaltendency, by reason of the presence of the switch structureto transmit load from one floor to the one under it, and there-fore to impose a greater load upon the lower floor than would be

1905.] CENTRAL STATION DESIGN. 59

accounted for by the weight actually upon that floor. Thiseffect was compensated for by giving the lowest floor additionalsupporting columns, which were placed between the basementand the engine-room floor. These columns were covered withexpanded metal and a cement plaster to insure against failure,in case a fire should occur, due to the storing of inflammablematerials. ItL had not been contemplated that such materialsshould be stored in the basement, but it was thouglht wise toprovide against this contingency.The roof of the engine-house was constructed of concrete

laid in place as is usual for sidewalks. In each bay a removablewooden frame was secured to the structural roof cords in sucha way as to permit of ready removal by knocking out wedgesafter the roof was in place. A thin layer of cement mortar,consisting of cement and sand, was placed on the top of thiswoodwork support. The function of this thin layer was togive a smooth coat for the finished interior of the roof. Theexpanded metal reinforcement was laid immediately on top ofthis preliminary coat, and was covered with about two inchesof concrete of about the same mixture as was used for the floors.On top of this was placed a thin layer of rich mixture, whichwas given a sidewalk finish on the side exposed to the weather.After 28 days, the wooden supports were removed from theinside, by knocking out wedges, and were lowered to the engineroom floor. The roof, made in this way, developed cracksafter drying out. These cracks were filled by pouring into thema thin grout consisting of cement and sand. The result wasto stop all leaks and insure a roof which was cheap andthoroughly fireproof. It has the disadvantage of being heavyand requires rather heavier roof-trusses than does a tile orslate roof; it is very strong and is not damaged by menwalking upon it, or by falling pieces of stone or other mate-rials. The latter consideration is an important one in thecase described, because the station is located near blastfurnaces, which, unfortunately, have the habit of throwingstone and ore out of the top at times. The advantage of usingexpanded metal on such a place as a roof, rested entirely inthe economy of labor in handling the material. The writerbelieves the disposition of material in expanded metal to be.uneconomical and, at times, disadvantageous. All of thatmaterial which lies transversely to the strain is wasted, andfurthermore it is the speaker's belief that there is a tendency

60 CLARK: CEMENT IN [Feb. 2&

on the part of expanded metal, when subjected to strain, toelongate the diamond-shaped meshes and to shear off the con-crete between the meshes. The tendency to shear the concretewould be trifling and unimportant if, in addition to this, therewere not a tendencv to break the concrete which is always placedbelow the expanded metal for fireproofing purposes. Thislower section of concrete is generally about one inch thick;being, in tension, it is apt to crack when the floor is heavilyloaded. After the lower section of colncrete cracks, there is atendency for the expanded metal to shift in position, andtherefore become ineffective. This belief of the writer's arises-from observations of heavy beams reinforced with concreteand tested to the breaking point. He does not mean to conveythe impression that for light beams, loaded comparativelylightly, expanded metal is not a desirable reinforcing material.The electrically operated oil-switches which are usually

mounted in a brickwork cell structure, were mounted in a cellstructure built up of concrete. A collapsable wooden mould wasmade, set up in the proper position for the switch, and filledwith concrete from the top. This mould was built similarly toa hinged flask standing on end, and was made large enoughto allow of casting two switches at one setting. The mouldwas properly lined up, leveled, and braced to prevent moving-while tamping the concrete. The bolts for holding the switchesin place were set in the concrete of the cell structure by means ofa template on top of the mould, just as foundation posts forengines are set. The concrete mixture was one part Universalcement, two parts Torpedo sand, and three parts screenedlimestone, which would go through a --in. mesh. After themould was constructed, the only skilled labor required wasthat of the carpenter, who lined up the mould each time it wasmoved into a new position. After the concrete had set forapproximatelv 48 hours, the mould was stripped and again setup for th3 next two switches. After all the switches of a'rowhad been cast, and the moulds removed, the cement workerwent over them to point up any voids which might have occurredin the corners, and to give the whole structure a finished appear-ance. The result was a pleasing one. It was decided thatthe mould-which in this case was built of dressed lumber, inthe attempt to give a smooth and finished appearance to theconcrete work-might better have been of rough lumber, itwhich case it could have been built for about $50. In case

1905.1 CENTRAL STATION DESIGN. 61

a large number of switches were to be built, however, the speakerwould recommend the construction of a metal mould, whichperhaps would cost $100. A mould constructed of metalwould be free from liability to warp, which always exists in thecase of a wooden mould. The wires leading from the oil-switcheswere separated from each other by means of barriers built upof thin slabs of concrete. The method of construction of thesebarriers was simple and effective. Pipes, or 0.5-in. rods, wereset up and tied together with wire in the form of the proposedcompartment construction. A light metal lath, such as is usedfor plaster partitions in building construction, was then wiredto the light framework. A cement mortar was then applied,in the same way as the plaster. The cement worker became soexpert in doing this class of work that he could build thesecompartments more rapidly than a draughtsman could makethe drawings for them. The bus-bar structure was built upin the same way as was the cell structure for the oil-switches.Where lines left the building, or where they were run in anyhorizontal position, barriers were suspended fronm the ceilingby allowing a piece of metal lath to project down at the timethe floors were put in. The barrier was plastered to this pieceof lath in the same way as just described. Where conductorwires were taken through the floor, which, of course, was fre-quently necessary, the insulators were set into the co,ncrete asthe floor construction progressed; therefore, when the floor andswitch construction was completed the wiremen had the insu-lators through which the wires were to be run properly located.One great advantage of this form of construction rests in theeconomy of space which it makes possible. ALny brick wallmust necessarily be four inches thick, whereas a concrete wallmay be put up only two inches thick, provided it is reinforced.In case brick construction is employed, where thin partitionsare desired, they must be built of soapstone or marble, Theconcrete is just as effective in most cases, and is much Cheaper.

In constructing the switch-cells and bus-bar structures, anattempt was made to obtain a perfectly smooth finish by dress-ing the mould smooth and coating it with shellac, as is customaryfor patterns. This was found to be a mistake, as the bubblesof excess water contained in the wet mixture tended to gatheron the smooth surface and 'make a rough finish to the work,It was found- preferable to leave the mould rough and to finishthe work with a final float-coat.

t62 CLARK: CE.11EA\T iNX [Feb. 28

The generator leads were brought from the machines inthree-inch bituminized fibre conduits, laid in the cement floorof the basement. Under the generator switches, they werebrought from the basement floor to the engine room floor in asolid concrete wAall. The lead sheathing was removed from thecables, and additional coating consisting of paper and shellacwas provided. After allowing a few days for this to dry, thecables were built into a wall of concrete. Inasmuch as the wallwas only a few inches thick, little difficulty would be encoun-tered in cutting the cables out, if necessarv; in fact, three cableswere cut out, under the mistaken impression that they wereimproperly connected. Little difficulty and slight expensewere involved in the operation; and the cables were found tobe in perfect condition. In the basement, no important wireor cable was permitted to be exposed. The result is that if afire should start in any material which might be stored thereit could not affect the connections to the generators or instru-ments, nor could it cause the collapse of the structure, due tothe failure of exposed steel columns. The instrument leadsand the control wires for the switches were buried in cement.It was originally intended to use for this purpose lead-coveredcable run in an iron-armore(d conduit, the latter being imbeddedin the floors. It was decided later, however, to do without theiron-armored conduit, and tolaythe lead-covered cables directlyinthe cement floor. For this purpose, a. top coat of 2.3 in. of cementon the floor was allowed, in additioln to the original cemenitfloor which was designed to support the full loads. Of this topdressing, two inches consisted of a mixture of cement, sand, andsawdust, in thle proportions. of one of cement, one of sand,and two of sawdust. The method of installation consisted oflaying the conductor cables on the top of the original, supportingfloor. When all the instrument wiring -was completed andtested, the cables were covered and imbedded in this mixtureof sawdust-cement, and on top of all was laid a 0.5-in. finishingcoat for the floor. The mixture of sawdust-cement is softenough to permit of chopping a cable out at any time withoutdamage to the cable, or to surrounding cables. The repair ofthe floor is very simple, and the floor is perfectly solid and toall intents and purposes the same as if constructed wholly ofconcrete. The necessity for chopping out cables is very remote,because, once properly installed, there is no chance for move-ment or damaging of the cables. The item of labor saved bv

1905.] CENTRAL STATIJON DESIGN. 63

making it unnecessary to draw into the conduit the very greatnumber of cables which are required for the installation ofelectrically-controlled switching apparatus is very considerable.The 20 000 volt wires which were led from the transformer

room on the first floor to the lightning-arresters and buildingoutlets on the top gallery were provided with thorough pro-tection where they passed through the operator's gallery. Foreach wire a chimney was built of 10-in. bituminized fibre con-duit. The three chimneys carrying the three wires of a circuitwere placed close together and were surrounded with a con-struction of expanded metal lath, covered with cement plaster.The result was, to outward appearance, a rectangular column.In effect, there was a thoroughly-insulated duct provided forthe conveyance of each high-pressure wire, which entirely pre-vented an operator coming into contact with these wires.

After the installation of all apparatus and connections thereto,the cement work was given a final finishing wash of whiting,glue, and a slight amount of dark coloring matter, producing auniform natural cement color over the whole job. It is im-possible to produce this without some such wash, since allcement work will discolor more or less as it dries out.The final result is most pleasing from both engineering

and artistic standpoints. Not much effort was taken at thestart to lay out the work with a view to insuring good archi-tectural lines, but even though this was not looked to as itmight have been, it was possible, by adding a touch here andthere, to get some very satisfactory effects from the standpointof appearance. Of recent years, most large power-houses aredesigned with a view to obtaining ,ood architectural lines onthe exterior, whereas the interior is generally designed froman engineering standpoint only. The possibilities of cementconstruction in inisuring artistic and decorative interior effects,with very slight increased cost, and without sacrificing engineer-inr, requirements, have so far received too little' consideration.