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The Fire-trap Modern "Sky-scraper"

by William Sooy Smith

In view of the great height and consequent great weight of our principal buildings, it is important that materials should be used in their construction which unite in the highest degree lightness and strength with the other qualities of good building materials. And so steel naturally came to the front, with the strongest sinews and head erect-too proud to bend and too strong to break-saying to the architect and engineer: "Pile your mountain loads on my shoulders and place them in the firm grip of my hands and I will hold them for centuries, though the storm wrestles with me and the earth quakes beneath my feet." The men of science accepted the proffered service and the men of affairs poured out their money to pay for it.

And as a great building now goes up in Chicago a gaunt skeleton of steel first rises aloft, and this is gradually clothed from story to story with rigid flesh of stone and brick, title and mortar; and such integument it becomes a habitable edifice.

But with each change of temperature the steel skeleton expands and contracts-becomes a creeping, drawing thing, apparently striving to tear off its clothing-especially if exposed to such heat as results from the burning of great quantities of combustible materials, such as are collected and stored in a mercantile building, or from the occurrence of great heat in the burning of adjacent buildings, and this last danger may threaten even an office building, which itself contains very little combustible material.

Witness the Manhattan Savings Bank building, Broadway and Bleeker street, New York, which was destroyed a few weeks ago by the heat generated in the burning of the Keep building next to it.

And this in spite of the means usually employed to protect the metal from heat by the tile covering put upon it; for this covering will become so hot as to conduct enough heat to the steel to expand it and crack off the coverings.

I know of no fireproofing that has yet been used to protect the steel in composite buildings that has proved effective when exposed to a hot fire.

If the terra-cotta or other material used is not put together air-tight hot air will enter and, heating the iron or steel which it incloses, cause it to expand. This expansion will further open the joints in the fireproofing, and, as instances of this kind have shown, throw it off entirely-exposing the metal to the full heat of the surrounding flames or hot air. This occurred in the case of the fire that partly destroyed the Athletic Association building in this city. And notably at the burning of the Tribune building in Minneapolis, about three years ago, which resulted in its entire destruction.

The fire at the Athletic Association building occurred during the construction, and as the woodwork finishing material supplied the only fuel that was consumed, it was a hot one, but of very short duration. Nevertheless, much of the tile fireproofing (?) was thrown off the columns, exposing them to the full effect of the heat, and it is evident that if this heat had continued but a little longer the whole structure would have fallen.

The rate of expansion or contraction of iron and steel, which are practically the same, is one one-hundredth of an inch per ft. for a change of temperature of 100. If a vertical post or column of iron or steel is 150 feet in height, the total expansion for a change of 100 in temperature will be one and one-half inches; and for a change of 1,000 (to red heat), fifteen inches; and this change frequently occurs during a fire.

While a column changes its length fifteen inches, the integument of stone, brick, or tile expands or contracts much less, and so a "war to the death" takes place between the component part of what we call "steel buildings."

There may be steel buildings in which the fireproofing has been so well done that they will pass through an ordinary fire without such failure. But if the steel becomes even moderately heated its stiffness will be measurably diminished, and the strength of the upright members so reduced as to cause them to bend and yield. This is more likely to occur, as the horizontal beams and girders will at the same time expand (unequally from the different degrees of temperature) and throw the posts out of vertical and into buckling positions. This is the third difficulty.

It is as if a man were required to stand upright and take upon his shoulders all he could stand under, then take a strong dose of physic and have his knees pushed from under him.

Under these circumstances, if floors were built of perfectly rigid materials the unequal settlement would crack them into pieces and ruin them. The elasticity of the steel beams now used in the floor systems partially obviate this difficulty, but not wholly, as many floors in which they are employed, notably those of our postoffice and custom house building, are badly demoralized and broken up by unequal settlements. Here is the fourth difficulty, and our present system does not provide for it satisfactorily.

Now, supposing that we have succeeded in overcoming the great difficulties already pointed out-if steel and iron are used as principal parts of our buildings and these parts are not perfectly protected from corrosion, the building will be comparatively short-lived.

There are many imperfections in minor details, such as weakness of brackets and their fastenings, want of proper provision for resistance to strains resulting from wind pressure, etc. which we need not here describe or discuss. They are only alluded to because they are liable to occur in the class of building we have under consideration, unless they are guarded against by the architect who designs the superintendent or contractor who builds the structure. There is little danger of such defects in the buildings planned by many of our excellent Chicago architects and erected by first-class Chicago builders. The well do not need prescriptions; they are only for the sick.

Having thus considered the difficulties to our problems, let us endeavor to discover proper remedies for them, for we perform the most valuable service when we do not merely discover a difficulty, but when we point out the best way to overcome it.

The third difficulty, resulting from the expansion and contraction of the metals employed in the construction of tall buildings, may be obviated by protecting these metals absolutely from any considerable change in temperature, if this be possible, or by throwing out the metals altogether and substituting tile, brick, and stone, as far as may be practicable. As the weights to be borne by the vertical members of buildings, such as we have described, are very great, it becomes necessary to use materials and models of construction which will make these vertical members as small as may be in cross section, consistently with the loads they have to carry, and the strains they have to resist, in order to economize floor space, which is the revenue-producing part of the building.

Now, first class cut stone masonry, laid in hydraulic cement mortar, has about one-fourth the compressive resistance of the stone of which it is composed. If, therefore, the stones themselves can be placed in absolute contact, without the interposition of mortar, it is fair to presume that much greater compressive resistance of the material would be obtained. To test the truth of this supposition I had a square pillar of Lemont limestone made by the Western Stone Company, one square foot in cross-section, and about nine feet high. It was composed of seven stones, taken from their thickest stratum, and so cuts as to lay on the natural bed in the pillar when this was set up. The bearing surfaces of the blocks were planed perfectly true. I sent this pillar to the government testing machine, at Watertown, Mass., and asked that it be set up by simply washing the beds with a very thin grout of the best English Portland cement This pillar was subjected to the entire crushing power of the machine, 800,000 pounds, and it was only when the full strength of the machine was employed that the pillar showed the slightest symptom of yielding. Then small flakes were chipped off of the outside surfaces of two of the blocks, which is proof that the pillar was on the point of yielding. If pillars or columns having a cross section of four square feet instead of one were used, the total resistance of such pillar to crushing would be far more than four times 800,000 pounds, for it is a well-known fact that the crushing resistance of any substance increases in greater ratio than the area of cross-section of such substance.

If, however, we assume that the strength was increased in that simple ratio, a pillar two feet square of Lemont limestone made as already described would sustain a weight of 3,200,000 pounds. One-third of that load, or say 1,000,000 pounds, would be a safe load for such pillar. If we add a covering 2 inches thick on all sides of a pillar, which is sufficient to afford it all necessary protection from fire, if a method is used which will shortly be described, the whole size of the pillar so protected would be but two feet four inches each way, which is but little larger than many of the steel columns now used with their fireproofing. These pillars would, of course, decrease in size as the loads decrease, story by story, from bottom to top of the building. The blocks of which they are composed may be doweled by a steel rod running down through the center of the pillar and connecting cap plates of cast iron that should be put on the pillars at the level of each story.

If limestone or any other kind of stone which does not resist heat well is used, it can be protected by a covering of agolite or any other very refractory, non-conducting and non-expansive material. I have seen a slab of "agolite" only one inch in thickness that was held over a flame at white heat half an hour and then turned over and carried off on a man's hand, without burning it. With such material properly put on and secured to a non-expansive stone column, there would be little danger of any injury to it by fire.

But to avoid absolutely the injury that might come to it by any cause that might crack or remove the covering and so cause its destruction, (as in the case of the steel column), a strong and very refractory stone should be selected for the columns, such as that used in the lining of blast furnaces, which resists for months the white heat to which it is exposed. Of course, such stone would need no fireproofing.

Plates or cap stones can project sufficiently to furnish support to arches of tile, or beton coignet, which should be used for the floor systems. In wide buildings the pillars should be set in line at right angles to each other, and at suitable distances to make it practicable to construct the whole floor by a groined arch or dome system supported by these pillars.

This system off floor construction is by no means new, as it has been in use for centuries in Spain and Italy. It has been recently introduced into this country by a Spanish engineer, Mr. Guastavino, and has rapidly come into use in our eastern cities.

It has been found practicable to make strong floors with a very slight rise of the arch in proportion to its span. Steel rods have recently been built into the material of the floors thus constructed, protected from heat or corrosion, and so placed as to take and resist the horizontal thrust of the arches.

There is a balancing and neutralizing of this thrust throughout the entire system of arches except the exterior ones next the outside walls, and it is only in the case of these exterior arches that special provision must be made to take up this thrust.

This may be done by building in twisted steel or rods as above described, or by horizontal tie rods thoroughly protected from the effects of fire by a thick covering of agolite or asbestos. And the outside walls should for this purpose and for better security from fire in an adjacent building be made heavy and strong.

If the mode of construction here pointed out is adopted, the building would be practically unchanged in its dimensions, indestructible by fire, abundantly strong and as durable as the materials of which it is composed.

It also seems, from the best estimates I can make, that a building constructed in this way will cost less than one with steel and iron framing.

Tile, brick and stone do not corrode, and, while mistakes may be made and imperfections in design and workmanship are quite as likely to occur in the use of these materials as in that of iron and steel, these can be obviated in both cases by skill and fidelity, without which no system of building can be made successful.

Chief Bonner, of the fire department of New York, says in reference to the destruction of the Manhattan Bank building:

I don't want to pose as a sensationalist, for this is a subject which has too many serious bearings upon the safety of life and property to dismiss with anything but the most careful sort of consideration. But this I insist upon: We shall have in this city, unless the citizens of New York are warned in time, a calamity by fire which will rend their hearts. It will be due, too, to nothing else than their confidence in fire-proof buildings.

I believe that any fire-proof buildings constructed previous to the laws of 1892 is not proof against fire. The Manhattan bank fire shows that so little fire-proof are these structures that they are susceptible to fire from without and fifty feet away from them. Here is exemplified what a fire-proof building of admirable material will do when subjected to intense heat. The Keep building was only twenty-five feet wide, though it had a length of a block along Bleeker street, yet it generated sufficient heat to act as a furnace upon the Manhattan building, just as though the latter had been a piece of coal. And this brings out the first principle of building in defense of fire.

The heat from the Keep building acted directly upon the exposed iron work of the Manhattan building. The iron resisted the first-that is, it did not blaze, but so far as the safety of the building is concerned, it did something infinitely worse. It expanded under the heat and forced out the ends of the iron beams and girders from their resting places on the supporting piers.

The result was inevitable. Without the support which the buildings gave the floors down they came and brought with them the mass of fire brick used as flooring.

The roof was brought down by the pulling of the other floor columns, and the destruction was complete. It demonstrated anew that, like a chain, the strength of a fire-proof building is only that of the weakest link. The pier irons warped and the structure gave away.

The heat thrown from a large burning building of any height is immense. Remember that the Keep building was only twenty five feet wide. Take a building like the one at Houston street and Broadway, with a frontage of 100 feet, and once ablaze you could not stand within two blocks of it. Think what a chance there would be of saving adjoining structures under such conditions.

I am prepared to declare, from my experience, that a building of brick and yellow pine in case of fire is easier to manage, and the contents have more chance of being saved than the modern fire-proof building. In the former structure the fire burns more slowly and has no chance to concentrate its heat as in the iron and steel structure.

Chief Swenie, of the Chicago fire department, is quoted in an article recently published as follows:

"I think very much as Bonner does," said Fire Marshal Swenie to-day, when his attention was directed to a statement of the chief of the New York fire department to the effect that the modern skyscraper is a veritable firetrap. The New York chief is reported as saying that there is not a fire-proof building in New York city, and that all cities "should be warned that they are leaning upon rotton (sic) staves" when they believe that their splendid structures will not burn, and that they are not dangerous. "A building of brick and yellow pine," he declares, "in case of fire is easier to manage and the contents have more chance of being saved than the modern fire-proof building."

I am on record as having said the same thing four or five years ago, he said to-day, after indorsing the New York chief's remarks. Some four or five years ago I read a paper before the Northwestern Insurance Men's Convention, in which I called attention to this very matter. In that paper I stated that no style of construction and no building material that has ever come under my observation would render fire-proof a building filled with inflammable goods. Fire in a room so filled with goods might in very short time gain such headway as to imperil seriously the entire structure by the expansion, warping or twisting of the iron or steel framework.

No storage warehouse or building of any kind in which inflammable goods are stored should ever exceed 125 feet in height, and might with advantage be much less. This is not because we cannot throw water high enough. But suppose such goods are stored in a twelve-story building; a fire breaks out, say on the sixth floor, and gets to burning furiously. The heat ascends and causes the pillars and beams to expand. The expansion first raises all that part of the building above where it takes place. At the same time the whole weight above continues on the expanded metal. before you know where you are something is going to give, and what will be the results? They will be too fearful to contemplate.

A good deal has been said about the fire-proof qualities of our high buildings. Well, I know one thing: It does not take a great amount of heat to cause steel and iron to expand, and when beams and columns begin moving something has got to break. Suppose a fire breaks out in one of these buildings. We work at it from below, and the steel beams expand, the ceiling breaks and the floor above comes down. We do not know how much above is going to follow for we cannot see it.

The outside walls of the modern Chicago buildings are mere shells, veneers of tile. A fire starts in one and as we are not very particular where we throw water we pour against the walls. The natural consequence will be a sudden cooling which will cause them to crumble and fall. If a building in the rear of the skyscraper should be ablaze the eighteen-story structure would assuredly go, and there would be 180 feet of debris from the upper twelve floors. A fire on the alley side of the Masonic Temple would subject it to a terrific heat beyond our reach. That is where a great deal of the danger comes in.

And in a personal interview I had with the chief he repeated much of the statement above quoted, and in the most earnest and emphatic manner expressed his fears that terrible catastrophes are likely to result from the destruction by fire of tall buildings constructed as many of them are in this city. He dwelt particularly upon the extreme difficulty of making any building absolutely fireproof, and declared that in his belief none such now exist in the city of Chicago, meaning, as he explained, that there is no building that will withstand the heat of such conflagrations as we have had in the past, and may have in the future.

After listening to a brief description of my proposed method of construction, the chief said that a building so constructed would in his opinion, withstand any fire.

From what is herein set forth it is hoped that the duty of architects, owners and all interested in buildings, here and elsewhere, is made apparent to use such materials and adopt such methods of construction as will make buildings as safe as possible from the destructive effects of fires, small or large.

William Sooy Smith.



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