AMERICAN SOCIETY OF CIVIL ENGINEERS

INSTITUTED 1852

TRANSACTIONS

Paper No. 1173

A CONCRETE WATER TOWER. [A]

BY A. KEMPKEY, JR. , JUN. AM. SOC. C. E. [B]

WITH DISCUSSION BY MESSRS. MAURICE C. COUCHOT, L. J. MENSCH, A. H. MARKWART, AND A. KEMPKEY, JR. 

The City of Victoria is situated on the southern end of VancouverIsland, in the Province of British Columbia, Canada, and is the capitalof the Province. 

In common with all cities of the extreme West, its growth has been veryrapid within the last few years. The population of the city proper, together with that of the municipality of Oak Bay, immediately adjacent, is now about 35, 000. 

The Victoria water-works are owned by the city and operated under thedirection of a Water Commissioner appointed by the City Council. Byspecial agreement, water is supplied to Oak Bay in bulk, thismunicipality having its own distributing system. 

The rapid increase in population, together with the fact that in recentyears very little had been done toward increasing the water supply, resulted in the necessity for remodeling the entire system, and thereare very few cities where this would involve as many complex problems ora greater variety of work. 

Water is drawn from Elk Lake, situated about five miles north of thecity; thence it flows by gravity to the pumping station about four milesdistant, and from there is pumped directly to the consumers. 

The remodeling of the system, as recently completed, provided for:

1. --Increasing the capacity of Elk Lake by a system of levees. 

2. --Increasing the capacity of the main to the pumping station byreplacing about two miles of the old 16-in. , wrought-iron, riveted pipewith 24-in. Riveted steel pipe. 

3. --Increasing the capacity of the pumping station by the installationof a 4, 500, 000-gal. Pumping engine of the close-connected, cross-compound, Corliss, crank-and-fly-wheel type. 

4. --The construction of a 20, 000, 000-gal. Concrete-lined distributingreservoir in the city. 

5. --The entire remodeling of the distributing system, necessitating thelaying of about 1/2 mile each of 18-in. And 27-in. Pipe, and about 1mile of 24-in. Riveted steel pipe; also about 3, 000 tons of cast-ironpipe, varying in size from 4 to 12 in. 

6. --The provision for a high-level service by means of an elevated tankof approximately 100, 000 gal. Capacity, water being supplied to the tankby two electrically-driven triplex pumps, each having a capacity of100, 000 gal. Per 24 hours, against a dynamic head of 150 ft. , andarranged to start and stop automatically with a variation of 3 ft. Inthe elevation of the water in the tank. These pumps are located aboutone mile from the tower, and are controlled by a float-operatedauto-start, in the base of the tower. 

A description of the elevated tank, which is novel in design, with thereasons for adopting the type of structure used, the method ofconstruction, and the detailed cost, form the basis of this paper. 

The tower is on the top of the highest hill in the city, in the heart ofthe most exclusive residential district, beautiful homes clusteringabout its base. The necessity for architectural treatment of thestructure is thus seen to be of prime importance. In fact, theopposition of the local residents to the ordinary type of elevated tank, that is, latticed columns supporting a tank with a hemispherical bottomand a conical roof, rendered its use impossible, although tenders wereinvited on such a structure. 

It is believed that under the conditions of location, three types ofstructure should be considered: First, an all-steel structure, theornamentation being produced by casing in with brick or concrete;second, a brick-and-steel, or a concrete-and-steel, structure, such asthe one actually erected; third, a typical reinforced concretestructure. 

Considering only that portion below the tank, the amount of materialrequired to case in a structure of the first type would be substantiallythe same as that used to support the tank in a structure of the secondtype. Consequently, the steel substructure, for all practical purposes, would represent a dead loss, and, therefore, the economy of this type isopen to serious question. 

A tender was received for a reinforced concrete structure identical inoutward appearance with the one built, but, owing to the naturalconservatism of the local residents regarding this type of construction, it was not acceptable. 

The tower, as built, consists of a hollow cylinder of plain concrete, 109 ft. High, and having an inside diameter of 22 ft. The walls are 10in. Thick for the first 70 ft. And 6 in. Thick for the remaining 39 ft. , and are ornamented with six pilasters (70 ft. High, 3 ft. Wide, and 7in. Thick), a 4-ft. Belt, then twelve pilasters (12 ft. High, 18 in. Wide, and 7 in. Thick), a cornice, and a parapet wall. 

A steel tank of the ordinary type is embedded in the upper 40 ft. Ofthis cylinder. To form the bottom of this tank, a plain concrete dome isthrown across the cylinder at a point about 70 ft. From the base, thethrust of this dome being taken up by two steel rings, 1/2 in. By 14 in. And 3/8 in. By 18 in. , bedded into the walls of the tower, the latterring being riveted to the lower course of the tank. 

The tank is covered with a roof of reinforced concrete, 4 in. Thick, conical in shape, and reinforced with 1/2-in. Twisted steel bars. Thedesign of the structure is clearly shown in Fig. 1. 

The tower is built on out-cropping, solid rock. This rock was roughlystepped, and a concrete sub-base built. This sub-base consists of ahollow ring, with an inside diameter of 20 ft. , the walls being 5 ft. Thick. It is about 2 ft. High on one side and 7 ft. High on the other, and forms a level base on which the tower is built. The forms for thissub-base consist of vertical lagging and circumferential ribs. Thelagging is of double-dressed, 2 by 3-in. Segments, and the ribs are of 2by 12-in. Segments, 6 ft. Long, lapping past one another and securelyspiked together to form complete or partial circles. These ribs are 2ft. From center to center. 

[Illustration: FIG. 1. --(Full page image)

WATER TOWER VICTORIA, B. C. WATER-WORKS]

Similar construction was used to form the taper base of the towerproper, except, of course, that the radii of the segments forming thesuccessive ribs decreased with the height of the rib. Tapered laggingwas used, being made by double dressing 2 by 6-in. Pieces to 1-3/4 by5-13/16 in. , and ripping on a diagonal, thus making two staves, 3 in. Wide at one end and 2-3/4 in. Wide at the other. This tapered laggingwas used again on the 4-ft. Belt and cornice forms, the taper beingturned alternately up and down. 

[Illustration: FIG. 2. --FORMS FOR WATER TOWER VICTORIA, B. C. ]

The interior diameter being uniform up to the bottom of the dome, collapsible forms were used from the beginning. These forms wereconstructed in six large sections, 6 ft. High, with one small keysection with wedge piece to facilitate stripping, as shown in Fig. 2. There were three tiers of these, bolted end to end horizontally and toeach other vertically. 

Above the taper base and except in the 4-ft. Belt and cornice, collapsible forms were used on the outside also. There were six sectionsextending from column to column and six column sections, all boltedtogether circumferentially and constructed as shown in Fig. 2. Threetiers of these were also bolted together both vertically andhorizontally. 

Having filled the top tier, the mode of operation was as follows:

All horizontal bolts in the lower inside and outside forms were removed, as was also the small key section on the inside; this left each sectionsuspended to the corresponding one immediately above it by the verticalbolts before mentioned. It is thus seen that in each case the centertier performed the double duty of holding the upper tier, which was fullof green concrete, and the sections of the lower tier, until they werehoisted up and again placed in position to be filled. 

These lower forms were then hoisted by hand--four-part tackles beingused--and placed in position on the top forms, their bottom edges beingcarefully set flush with the top edge of the form already in position, and then bolted to it. On the outside, the column forms, and on theinside, the wedge and key sections were set last. A 3-lb. Plumb-bob on afine line was suspended from the inner scaffold and carefully centeredover a point set in the rock at the base. This line was in the exactcenter of the tower, and the tops of all the forms, after each shift, were carefully set from it by measurement, thus keeping the structureplumb. 

The first 23 in. Of the barrel of the tower was moulded with specialoutside forms, constructed so as to form the bases of the largepilasters. After eleven applications of the 6-ft. Forms, these 23-in. Sections were reversed to form the capitals, thus making thesepilasters, 69 ft. 10 in. Over all. 

The forms of the 4-ft. Belt and beading were made in twelve sections ofsimple segments and vertical lagging, as shown in Fig. 2. 

Two sets of the outside forms were split longitudinally, as shown inFig. 2, and used to form the small pilasters. The first set was put inplace, filled, and the concrete allowed to harden. The bolts wereloosened and the forms raised 5-1/2 in. Vertically, again bolted up, andthe second set was placed in position, bringing the top of the secondset up to the bottom of the cornice. The bases and capitals of the smallpilasters were moulded on afterward. 

The cornice forms are clearly shown in Fig. 2. The small boxesseparating the dentils are made of light stuff, and tacked into thecornice forms so that, in stripping, they would remain in place andcould be taken out separately, in order to prevent breaking off thecorners of the dentils. A number of outside and inside sections weresawed in half horizontally in order to provide forms for the parapetwall. 

The inside diameter of the tank is 8 in. Greater than the insidediameter of the base. Two sets of inside forms were split longitudinallyand opened out, as shown in Fig. 2, and another small section was addedto complete the circle. The remaining set was left in place to supportthe dome forms. 

The dome forms were made in twelve sections, bolted together tofacilitate stripping. All ribs and segments were cut to size on theground, put together in place, and then covered with lagging and two-plytar paper. The lagging on the lower sharp curve was formed of a doublethickness of 3/8-in. Spruce, the remainder being 1 by 4-in. Pine, sizedto a uniform thickness of 7/8 in. Fig. 3 shows the construction of theseforms and the method of putting on the lagging. 

The roof forms were made in eight sections and bolted together tofacilitate stripping. All ribs and segments were cut to size on theground, put together in place, and covered with 1 by 4-in. Lagging, dressed to a uniform thickness of 7/8 in. , and two-ply tar paper. Fig. 3shows the construction of these forms. The segments being put inhorizontally instead of square with the lagging, gave circles instead ofparabolas, making them much easier to lay out, and giving a form whichwas amply stiff. 

The question of using an inside scaffold only was carefully considered, but owing to the considerable amount of ornamentation on the outside, necessitating a large number of individual forms, it was not thoughtthat any economy would result. 

Fig. 4 and Figs. 1 and 2, Plate XXIII, show clearly the construction ofthe scaffolding. 

[Illustration: PLATE XXIII, FIG. 1. --SCAFFOLDING FOR WATER TOWER. ]

[Illustration: PLATE XXIII, FIG. 2. --COMPLETED WATER TOWER. ]

All concrete was mixed wet, in a motor-driven, Smith mixer, and handledoff the outside scaffold, being sent up in wheel-barrows on the ordinarycontractor's hoist and placed in the forms through an iron chute havinga hopper mouth. This chute was built in three sections bolted together, either one, two, or three sections being used, depending on the distanceof the forms below the deck. When the top of the forms reached theelevation of any deck, the concrete was put in through the chute fromthe deck above. The chute was light and easily shifted by thewheel-barrow men, assisted by the man placing the concrete, during theinterval between successive wheel-barrows. 

[Illustration: FIG. 3. --FORMS FOR WATER TOWER VICTORIA, B. C. ]

The concrete, except that for the roof and parapet, was composed of sandand broken rock, the run of the crusher being used. That for the roofand parapet was composed of sand and gravel. The only reason for usinggravel for the concrete of the roof was the ease with which it could beobtained in small quantities, the supply of broken rock having been usedup, and this being the last concrete work to be done. 

The concrete used was as follows: 1:3:6 for the sub-base and taper base;1:3:5 for the barrel of the tower and tank casing; and 1:2:4 for thedome and roof. The dome was put in at one time, there being no joint, the same being true of the roof. Vancouver Portland cement, manufactured on the island about 15 miles from the city, was usedthroughout the work. 

Before filling, the inside of the tank was given a plaster coat, consisting of 1 part cement to 1-3/4 parts of fine sand. This proved tobe insufficient to prevent leakage, the water seeping through the domeand appearing on the outside of the structure along the line of thebottom of the rings. Three more coats were then applied over the entiretank, and two additional ones over the dome and about 8 ft. Up on thesides, and, except for one or two small spots which show just a sign ofmoisture, the tank is perfectly tight. 

The barrel of the tower was carried up to a height of 66 ft. A specialset of inside forms, about 2 ft. High, extending to the springing lineof the dome, was then put in, and the dome forms were set up on it. Theidea was that this 2-ft. Form could be knocked out piece by piece andthe weight of the dome form taken on wedges to the last 6-ft. Form, these wedges being gradually slackened down in order to allow the domeform to settle clear of the dome. As a matter of fact, this was done, but the dome forms, being very tight, did not settle, and had to bepried off a section at a time. A similar method was used for slackingdown the roof forms, with similar results. 

After the dome forms had been put in, the concrete was carried upapproximately to the elevation of the bottom of the rings. Small neatcement pads were then put in and accurately leveled, and on these thesteel rings were placed, and the steel tank was erected. 

In order to insure a perfectly round tank, each course was erectedagainst wooden templates accurately centered and fastened to the insidescaffold. The tank is the ordinary type of light steel, the lower coursebeing 3/16-in. , the next, No. 8 B. W. Gauge, the next, No. 10 B. W. Gauge, and the remaining four, No. 12 B. W. Gauge. 

Work on the foundation was started on August 15th, 1908, and the towerwas not completed until April 1st, 1909. Much time was lost waiting forthe delivery of the steel, and also owing to a period of very coldweather which caused entire cessation of work for about one month. 

The tower as completed presents a striking appearance. In order toobliterate rings due to the successive application of the forms and tocover the efflorescence so common to concrete structures, the outsidewas given two coats of neat cement wash applied with ordinarycalcimining brushes, and, up to the present time, this seems to havebeen very effective in accomplishing the desired result. 

[Illustration: FIG. 4. --(Full page image)

SCAFFOLD FOR WATER TOWER]

Irregularities due to forms are unnoticeable at a distance of 200 or 300ft. , and the grouting gave a very uniform color. 

The application of two coats of cement wash cost, for labor, $97. 68, andfor material, $15. 18, or $1. 32 per 100 sq. Ft. , labor being at the rateof $2. 25 per 8 hours and cement costing $2. 53 per bbl. Delivered on thework. 

The tower was designed by Arthur L. Adams, M. Am. Soc. C. E. , underwhose direction the plans for all the work of remodeling the water-workssystem were prepared and executed. The forms, scaffolding, etc. , weredesigned by the writer, who was also in immediate charge of theerection. 

Tenders received for the construction of the tower covered an extremelywide range, and indicated at once the utter lack of knowledge on thepart of the bidders of the cost of a structure of this kind. Inasmuch asnone of them had had previous experience in this class of construction, the engineer deemed it the part of wisdom and economy to retain theconstruction under his immediate supervision, and, therefore, the workwas done by days' labor. 

Table 1 gives the cost of the structure. The total herein given will notcoincide with the total cost as shown by the city's books, for thereason that various items not properly chargeable to the structureitself have been omitted, the principal ones of which are the cost ofthe site, the laying of about 600 ft. Of sewer pipe to connect with theoverflow, and considerable expense incident to the construction of awagon road to the tower. 

The rates of wages paid, all being on a basis of an 8-hour day, were asfollows:

Common labor $2. 25 and $2. 50Carpenter 4. 00Carpenter's helper 2. 75Boiler-maker 3. 50Holders on 2. 50Boiler-maker foreman 5. 00Plasterers 6. 00Plasterers' helpers 3. 00

The cost of material was as follows:

Cement, per barrel $2. 53Sand, per yard 1. 47Rock, per yard 0. 80Lumber, per 1, 000 ft. B. M. 14. 00 and 16. 00

All these prices are for material delivered on the work. 

An examination of the cost data, as given, will show that for the mostpart the unit costs are very high. This is due chiefly to the continuedinterruption of the work, during its later stages, owing to bad weather, particularly in the case of the erection of the steel tank. The materialcost in this case was also exceedingly high. 

In the case of the concreting, inability to purchase a hoist and motorand the high cost of renting the same, together with the delaysmentioned, added greatly to the unit cost. 

When it is considered that the cost of plastering covers that of fourcoats over the entire inside of the tank and three more over aboutone-third of it, it does not appear so high, especially in view of thehigh rate of wages paid. 

The cost per yard for concrete alone was $25. 126, and this is probablyabout 25% in excess of the cost of the same class of work executed undermore favorable conditions as to location, weather conditions, etc. 

TABLE 1. --COST OF HIGH-LEVEL TOWER, VICTORIA WATER-WORKS. (412 cu. Yd. )

============================================================================= | TOTAL COST. | UNIT COST. ---------------------+---------+--------+----------+---------------+--------- | Rate | | | | | per | Amount. | Complete. | Labor. |Material. | hour. | | | |---------------------+---------+--------+----------+---------------+---------Preliminary Work: | | | | | Labor, Carpenter |$0. 50 |$11. 00 | | | Labor | 0. 344 | 64. 94 | | | " | 0. 281 | 249. 67 | $325. 61| $0. 790 | Material | | 133. 62 | 133. 62| | $0. 324 | | | | |Forms: | | | | | Buildings, shifting | | | | | and stripping: | | | | | Labor, Carpenter | 0. 50 |1, 832. 99| | | Labor | 0. 344 | 80. 85| | | " | 0. 281 | 563. 84| 2, 477. 68| 6. 014 | | | | | | Material: | | | | | Lumber | | 583. 49| | | Hardware | | 325. 51| | | Miscellaneous | | 13. 90| 922. 90| | 2. 240 | | | | |Scaffold: | | | | | Erecting and | | | | | tearing down: | | | | | Labor, Carpenter | 0. 50 | 693. 00| | | Labor | 0. 344 | 350. 59| | | " | 0. 281 | 117. 27| 1, 160. 86| 2. 818 | | | | | | Material: | | | | | Lumber | | 487. 77| | | Hardware | | 202. 79| 690. 56| | 1. 676 | | | | |Concreting: | | | | | Labor | 0. 50 | 142. 00| | | " | 0. 344 | 11. 00| | | " | 0. 281 | 947. 81| 1, 100. 81| 2. 672 | Material: | | | | | Rock | | 317. 30| | | Sand | | 385. 72| | | Cement | |1, 581. 97| | | Motor and Hoist: | | | | | Rental | | 406. 56| | | Power | | 83. 53| 2, 735. 08| | 6. 638 | | | | |Plastering | | | | | (3, 000 sq. Ft. ): | | | | | Labor, Plasterers | 0. 75 | 116. 50| | | Labor | 0. 46-7/8| 15. 00| | | " | 0. 37-1/2| 198. 52| | | " | 0. 281 | 105. 66| 435. 68| 14. 52 | | | | | per sq. Ft. | Material: | | | | | Sand | | 8. 64| | | Cement | | 66. 10| | | Alum and Potash | | 16. 00| 90. 74| 3. 25 | | | | | per sq. Ft. | | | | | |Cement Wash | | | | | (8, 560 sq. Ft. ): | | | | | Labor | 0. 48-3/4| 50. 00| | | " | 0. 281 | 47. 68| 97. 68|1. 14 per | | | | | 100 sq ft. | Material: | | | | | Cement | | 15. 18| 15. 18| 0. 18 " " " " | | | | | |Windows, doors, | | | | | and scuttle: | | | | | Labor | 0. 50 | 49. 00| 49. 00| | Material: | | | | | 1 door, | | | | | 7 windows, etc. | | 47. 26| 47. 26 | | | | | | |Equipment: | | | | | 40% of $461. 46 | | 184. 58| 184. 58| 0. 448 | | | | | |Superintendence | | | 1, 241. 45| 1. 506 | | | | | |Steel Tank: | | | | | Labor, Carpenter |$0. 50 | $124. 24| | | Helper | 0. 344 | 2. 75| | | Boiler-makers | | 382. 57| | | Holders on | | 147. 33| | | Labor | | 40. 61| | | Foreman | 0. 625 | 186. 25| $883. 75|$0. 0441 per lb. | | | | | | Material: | | | | | Tank, rivets, etc. | | | | | (20, 000 lb. ) | | | 1, 740. 69| | $0. 0875 | | | | |Iron-work: | | | | | Spiral stairway, | | | | | inlet, and overflow| | | | | pipes, ventilator, | | | | | reinforcing steel, | | | | | etc. : | | | | | Labor, Machinists | 0. 50 | 89. 50| | | Helper | 0. 344 | 240. 16| | | Labor | 0. 281 | 100. 79| 430. 45| | | | | | | Material | |1, 814. 71| 1, 814. 71| |---------------------+---------+--------+----------+---------------+--------- Total | | |$16, 578. 29| |=============================================================================

DISCUSSION

MAURICE C. COUCHOT, M. AM. SOC. C. E. (by letter). --It appears to thewriter that in the design of this structure two features are open tocriticism. The first is that such a high structure was built of plainconcrete without any reinforcement. Even if the computation of stressesdid not show the necessity for steel reinforcement, some should havebeen embedded in the work. As a matter of fact, the writer believesthat, with the present knowledge of the benefit of reinforced concrete, a structure such as this should not be built without it. This appliesmainly to the tower below the tank. 

The second feature, which is still more important, refers to theinsertion of a shell of smooth steel plate to take the stresses due tothe hydrostatic pressure, and also to insure against leakage in thewalls of the tank. The 6-in. Shell of plain concrete outside the steelshell, and the 3-in. Shell inside, do not work together, and arepractically of no value as walls, but are simply outside and insidelinings. Although the designer provided lugs to insure the adhesion ofthe concrete to the plate, such precaution, in the writer's opinion, will not prevent the separation of the concrete from the smooth steelplate, and, at some future time, the water will reach and corrode thesteel. It would have been better to have reinforced the wall of the tankwith rods, as is generally done. The full thickness would have beenavailable, and less plastering would have been required. Furthermore, the adhesion of concrete to a smooth steel plate is of doubtful value, for, in reinforced concrete, it is not the adhesion which does the work, but the gripping of the steel by the concrete in the process of setting. 

L. J. MENSCH, M. AM. SOC. C. E. (by letter). --This water-tower isprobably the sightliest structure of its kind in North America; still, it does not look like a water-tower, and, from an architectural point ofview, the crown portion is faulty, because it makes the tank appear tobe much less in depth than it really is. 

The cost of this structure far exceeds that of similar tanks in theUnited States. The stand-pipe at Attleboro, 50 ft. In diameter and 100ft. High, cost about $25, 000. Several years ago the writer proposed tobuild an elevated tank, 60 ft. In diameter and 40 ft. Deep, the bottomof which was to be 50 ft. Above the ground, for $21, 000. 

Among other elevated tanks known to the writer is one having a capacityof 100, 000 gal. , the bottom being 60 ft. Above the ground. [C] The totalquantities of material required for this tank are given as 4, 480 cu. Ft. Of concrete, 23, 200 lb. Of reinforcing steel, and 27, 600 ft. , b. M. , ofform lumber and staging. Calculating at the abnormally high unit pricesof 40 cents per cu. Ft. For concrete, 4 cents per lb. For steel, and $50per 1, 000 ft. , b. M. , for lumber, the cost of the concrete would be$1, 792, the steel, $928, and the form lumber and staging, $1, 380. Addingto this the cost of a spiral staircase, at the high figure of $7 perlinear foot in height, the total cost of this structure would be $4, 598. The factor of safety used in this structure was four, but some engineerswho are not familiar with concrete construction may require a higherfactor. By doubling the quantities of concrete and steel, which wouldmean a tensile stress in the steel of only 8, 000 lb. Per sq. In. , and acompressive stress in the concrete of only 225 lb. Per sq. In. , the costof the tank would be only $7, 318, as compared with the $16, 578 mentionedin the paper. This enormous discrepancy between a good design and anamateur design, and between day-labor work and contract work should be alesson which consulting engineers and managers of large corporations, who prefer their own designs and day-labor work, should take to heart. 

A. H. MARKWART, ASSOC. M. AM. SOC. C. E. (by letter). --It is thewriter's opinion that the steel tank enclosed within the concrete of theupper cylinder, to take up the hoop tension and presumably to provide awater-tight tower, will not fulfill this latter requirement. If aplastered surface on the dome-shaped bottom provided the necessaryimperviousness, it would seem that plastered walls would have provedsatisfactory. 

Apparently, the sheet-metal tank is intended to exclude the possibilityof exterior leakage, but it occurs to the writer that it will fail to beefficient in this particular, because, under pressure, the water willforce itself under the steel tank and the dome thrust rings and out tothe exterior of the tower just below the tank, thus showing thatinsurance against leakage is actually provided by the plastered interiorsurfaces and not by the sheet-metal tank, and, for this reason, ordinarydeformed rod reinforcement, in the writer's opinion, would have provedcheaper and better, and more in line with other parts of thereinforcement. 

Mr. Kempkey states:

 "Before filling, the inside of the tank was given a plaster coat, consisting of 1 part cement to 1-3/4 parts of fine sand. This proved to be insufficient to prevent leakage, the water seeping through the dome and appearing on the outside of the structure along the line of the bottom of the rings. Three more coats were then applied over the entire tank, and two additional ones over the dome and about 8 ft. Up on the sides, and, except for one or two small spots which show just a sign of moisture, the tank is perfectly tight. "

This substantiates the writer's contention that water-tightness wasactually obtained by a liberal use of cement plaster, which would alsohave been true had the reinforcement been rods. 

As a further comment, it might be stated that a water-tight concrete forthe tank could have been obtained by adding from 8 to 10% of hydratedlime to the 1:2:4 mixture. This seems advisable in all cases where awater-tight concrete is necessary. The interior plastering could thenhave been done as a further precaution. 

A. KEMPKEY, JR. , JUN. AM. SOC. C. E. (by letter). --Mr. Couchot'sstatement, that the 3-in. Inside and outside sheets forming the tankcasing do not act together, is quite true, and it was not expected thatthey would, other than to protect the steel and form an ornamentalcovering for it. 

There is certainly adhesion between concrete and steel, even though thesteel be in the form of a thin shell, and in a structure of this kindwhere the steel is designed, with a low unit stress, to take all thestrain, and where the load is at all times quiescent, it is difficult tosee how this bond can be destroyed; the writer feels no concern on thisscore. 

Mr. Markwart's statement, that the steel tank enclosed within theconcrete of the upper cylinder, presumably to provide a water-tighttower, will not fulfill this latter requirement, is not true, as shownby the statement in the paper that the only leakage which occurred wasthat which passed under the tank, the entire remaining portion beingabsolutely tight. The amount of leakage, while insignificant, was, untilremedied, sufficient to spot the outside of the tower, making itunsightly; and this, in the writer's opinion, is just what would havehappened had the tank been constructed in the ordinary manner, withdeformed bars, except that it would have extended over more or less ofthe entire surface, instead of being localized, as was actually thecase, and would have required more instead of less plastering. It isalso doubtful whether the addition of hydrated lime would have produceda tight tank, in the sense that this structure was required to be tight. 

In the paper the writer endeavored to bring out the fact that this isone of the few instances where the ęsthetic design of a structure ofthis sort is of prime importance, and cost a secondary consideration. There is, therefore, no use in comparing its cost with that of astructure in no way its equal in this respect and the use of which wouldnot have been permitted any more than the use of the ordinary type ofsteel structure, even though the estimated cost were 75% less. 

Mr. Mensch has been pleased to term this design amateurish, presumablybecause of the conservative character of the stresses used and becauseof its cost; at the same time, he sets up the design to which he makesreference as a good one simply because of its cheapness. He will findthe "enormous discrepancy, " to which he calls attention, accounted forby the fact that the "good design" would not have been tolerated becauseof its appearance and because of the fact that the excessively highunit stresses, of which Mr. Mensch is an exponent, did not commendthemselves either to the designer, in common with most engineers, or toVictorian taste; while the design used has proven eminently satisfactoryto a more than usually conservative and discriminating community. 

Mr. Mensch's statement of unit costs, even though applied to a muchplainer structure, is not calculated to inspire confidence in thesoundness of his deductions in any one familiar with Victoriaconditions. 

 FOOTNOTES:

 [Footnote A: Presented at the meeting of March 16th, 1910. ]

 [Footnote B: Now Assoc. M. Am. Soc. C. E. ]

 [Footnote C: "The Reinforced Concrete Pocket Book, " p. 124. ]