US3398491A - Building construction and method - Google Patents

Description

Aug. 27, 1968 H. N. BABCOCK BUILDING CONSTRUCTION AND METHOD 2 Sheet 1 Filed May 13' 5 VEN Henry N, gubcock ATTORNEYS Aug. 27, 1968 H. N. BABCOCK BUILDING CONSTRUCTION AND METHOD 2 Sheets-Sheet 2 Filed May 13, 1965 Hvw/ u h I I I I l LEEUI I IH H FIG. 7

INVENTOR Henry N. Bobcock BY f ATTCIDFZ? United States Patent TBUILDING CONSTRUCTION AND METHOD Henry N. Babcock, 4 Quintard Ave., Old Greenwich, Conn. 06870 Filed May 13, 1965, Ser. No. 455,429 17 Claims. (Cl. 52-90) ABSTRACT OF THE DISCLOSURE The present invention relates to a structural building system and more particularly to a building system employing flat sheet metal for enclosing a frame structure where the strength characteristics of the metal sheets are utilized by tensioning the sheets after they are placed over the frame structure so as to develop a predetermined integral strength in the entire structure that is sufficient to withstand predetermined variable loads to which the building, and in particular the covering, will be subjected.

For many types of building constructions, it is conventional to form the roof and or sides of the building of corrugated or ribbed metal panels that are pre-fabricated from rolled sheets. Where pre-fabricated corrugated panels are employed in covering building structures, they are usually supported on purlins that are commonly made of metal. Thus supported, they operate similar to beams resting over one or more purlins. There is, however, no structural continuity from one sheet to another as they pass over the roof of a building. Each sheet operates independently of the other, each is fastened by itself and there is no transfer of load or attachment from sheet to sheet. Also, in coverin a building with corrugated metal sheets, certain minimum strength characteristics must be maintained. For example, the metal covering must be capable of withstanding the various dead and live loads to which it will be subjected, and the sheets must be capable of remaining taut on the building framework regardless of temperature changes in the ambient atmosphere that will tend to cause the sheets to expand.

Overall tautness of the building covering is important to the extent that loosenness of the covering will permit the sheets to deflect and vibrate under varying load conditions and thus subject the entire building to forces that tend toweaken its strength. Load requirements of buildings covered with corrugated sheets are met primarily by the strength of the underlying framework and by the gauge of metal used in forming the corrugated sheets. In addition, the corrugations that are pre-formed in the sheet give the individual sheets the strength required to withstand expected loads that will be encountered between the supporting portions of the framework. To maintain the required tautness in the sheets, they are normally rigidly attached to the framework at spaced intervals with the spacing between the points of attachment made small enough so that any expansion of the sheets that might be caused by changes in the temperature of the ambient atmosphere will be limited in extent.

Although building constructions employing corrugated sheets have found a widespread use, they do possess certain cost and strength disadvantages. To begin with, the pre-fabrication of these metal panels to produce the corrugations reduces the coverin or usable area of the sheets. A flat sheet sixty inches in width, for example,

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will, after being corrugated, have an efiective width of only thirty-six inches. Not only does this pre-fabrication reduce the covering area of the metal sheet, but, in addition, by requiring a separate manufacturing operation, it increases the cost of the sheet as supplied to the user. Also, the inherent structural tensile strength of the metal is not used to amaximurn due to the formed corrugations.

In accordance with the teachings of the present invention, the disadvantages of pre-fabricated corrugated sheet coverings are avoided by using flat sheet metal panels and by tensioning these panels over the various load bearing beams that form the buildings frame structure. Panels stressed over the load bearing beams in this manner provide a unique structural system. The stressed sheet, when anchored on one side of a building, stretched up the side walls, over the roof and down the other side and then tensioned, enhances the integral strength of the structure, provides greater bearing strength for the roof and deck loadings and reduces the quantity of structural materials required to support such a cover. In addition, such a construction reduces the cost and time of installation of the building enclosures, eliminates most of the fabricating procedures usually required in such a structure, reduces the dead weight design requirements of the covering system and provides a structure which is basically stronger and has a longer life.

For maintaining the sheets relatively taut between the adjacent supporting beams over which they are stretched, the amount of induced tension or stress created in each sheet may be made sufiiciently great to efiectively compensate for the normal expansion of the sheet that will be caused by ambient temperature variations encountered in the location where the building is erected. In other words, each sheet may be stressed by a predetermined amount such that when the sheet subsequently expands as the ambient temperature increases, the stress then remaining in each sheet will still be adequate to maintain a sufiicient degree of tautness for effectively resisting the predetermined loads to which the covering will be subjected.

The sheets that are used in carrying out the teachings of the present invention may vary in width depending on what the various mills are rolling and what best fits the particular project. Sheets are presently available up to 72 inches without special order, and with a 72 inch sheet, a roof covering area of approximately 66 inches per sheet would be produced. If the normal corrugated metal sheet were used in succession, the coverage would be approximately 60% less per sheet due to the necessary rib or fluting required.

When a building has the tensioned or stressed cover of the present invention, the requirements for such things as cap flashing and ridge flashing are eliminated. In addition, the number of joints in such a building as compared to one using corrugated sheets is reduced by over 60%. Also, the gauge of metal required as compared to a normal corrugated sheet is reduced by a considerable amount as well as is the number of supporting purlins required. Other advantages obtained with the present invention are the reduction of the poundage of structural steel required to support such a building and the amount of foundations required to support such as structural system.

There will be little possibility of vibration of the metal sheet due to wind loads both positive and negative. Because of the strength afforded by the system of the present invention, lighter, faster, and cheaper constructions become possible; and where the sheets are made of stainless steel, a construction requiring little if any maintenance is produced.

A more complete understanding of the present inven- 3 tion including both the structural details and the method of construction will be obtained from the following description with reference being made to the accompanying drawings of which:

FIG. 1 is a perspective view of one embodiment of a building constructed in accordance with the teachings of the present invention;

FIG. 2 is a detailed blowup of the encircled portion designated A in FIG. 1;

FIG. 3 is a detailed blowup of the encircled portion designated B in in FIG. 1;

FIG. 4 is a detailed blowup of the encircled portion designated C in FIG. 1;

FIG. 5 is a detailed blowup of the encircled portion designated D in FIG. 1;

FIG. 6 is a perspective view of one of the wedge shaped shims shown in FIG. 5;

FIG. 7 is a schematic end view of a modified embodiment of the present invention; and

FIG. 8 is a schematic view of still another embodiment of the present invention.

As shown in FIG. 1, the building system of the present invention generally includes a foundation 1 comprised of concrete footings 2 and concrete piers 3. The foundations are provided in the form of elongated members which extend parallel with all load bearing members or beams indicated generally at 4. These beams are in turn supported by vertically disposed posts or columns 5 by suitable means such as welding or attaching plates, not shown. Each of the load supporting beams consists of a web 6, an upper flange 7, and a lower flange 8 with the edges of the upper flange beveled or rounded as more fully described below.

Once the foundations have been laid and the posts and supporting beams connected in place, the resulting frame- Work is ready to receive a covering. According to one embodiment of the present invention as shown in FIG. 1, the covering comprises a plurality of elongated flexible metal sheets 9 such as stainless steel sheets that are placed over the supporting beams 4 in overlapping relationship with each other and secured to the foundations so as to provide both the roof and wall portions of the building. The sheets used in the building system of the present invention are flat in nature as opposed to corrugated sheets and may be of any desired width depending on the particular project being constructed. For example, rolled sheets 72 inches in width may be used and placed in overlapping relationship with an overlap at each longitudinal edge of three inches so as to provide an eflective covering area of about 66 inches for each sheet.

The covering of the building starts at one end 11 with a first sheet 9' which may be unrolled from a supply roll fed up one side 12 of the building, over the roof 13, and down the other side 14. The sheet is then cut from the supply roll and the opposite ends 15, 16 anchored on the piers 3 against movement with respect to the load bearing beams 4 as by means of anchor angles 17. Since this first sheet has a portion that is stretched down the side of the end columns 5, an anchor angle will be used for the remaining portion of the sheet adjacent the columns and the portions of the sheet in alignment with the columns may be secured directly to the side of the piers 3 as shown in FIG. 1. It will be noted from FIG. 2 that the heel of the anchor angle is rounded to prevent cutting or creasing of the sheet at this point. Similarly, it will be noted that the appropriate edges of the load bearing beams 4 are also rounded where they engage the sheet metal.

After the first sheet 9' is anchored to the piers, a second sheet 9" is erected in a similar fashion with several inches of overlap being provided with respect to the first sheet 9. At the point of overlap, a weathertight gasket, such as a butyl rubber bead 18, is installed. This procedure is repeated with succeeding sheets down the length of the building until the opposite end 19 is reached.

After the building is completely covered with the re quired number of sheets tightened and anchored to the piers 3, the center posts of columns 5' are raised a pmdetermined number of inches or fractions thereof to tension the sheets longitudinally. For the purpose of raising the columns 5, wedge shaped shiins 20, such as disclosed in my United States Patent 2,943,716,. are -employed. These shims are inserted between column base plates 21 attached to each of the columns 5' and foundation base plates 22 attached to the piers 3 as shown in FIG. 5. The shims are then driven between these two plates, raising the columns the proper amount to, in turn, tension the individual sheets the required amount. As the sheets are tensioned, they will compress the intermediate gaskets 18 to effect a watertight seal between the sheets.

The amount of tension induced in the sheets will depend on the loads to which the building will be subjected during use and this will in turn depend on the geographical location of the building. Of importance in determining the amount of tension necessary to withstand the loads is the temperature variations that will be encountered where the building is erected. The sheets used in covering the building have the characteristics of contracting and expanding as the temperature of the ambient atmosphere changes. The higher the temperature, the more the sheets will expand and as the sheets expand they tend to become loose between the adjacent supporting beams 4. As such they are subject to deflection and vibration that would tend to be caused by wind loads, for example. In addition, loose sheets are less capable than tensioned sheets of withstanding load conditions produced, for example, by accumulated snow.

According to the teachings of the present invention, the sheets are tensioned to a stress value suflicient to enable them to resist any appreciable deflection and to withstand the variable loads to which they will be subjected as they expand and contract with temperature variations in the ambient atmosphere. To calculate the tension stress forthe sheets of a building to be constructed in any given location, the maximum loads including, for example, live,'

dead, and wind loads to which the building will be subjected are first determined. To these maximum values a safety factor may be added if desired or required by local building codes. Next, the temperature range for that location is found and from this, the maximum amount of sheet expansion calculated. These values are then correlated with the previously tested loads which the sheets are capable of withstanding under various degrees of tensions; and the sheets are then tensioned to a stress value which will be suflicient to resist these loads under the assumed range of temperatures.

Usually, if the sheets are tensioned an amount sufficient to compensate for temperature expansion so that when the sheets are fully expanded they will have enough tension to resist deflection and vibration and to withstand the loads that will be encountered at this temperature, this value of tension will be more than enough to enable the sheets to withstand the loads encountered at other temperatures. Accordingly, in most situations, the sheets need not be tensioned to completely prevent deflection as they expand, the important criteria to be considered being the amount of loading to which the building will be subjected in relation to the expected temperature of the ambient atmosphere at the time of such loading. Most often, the higher loads to which the building and covering will be subjected will occur with lower temperatures. At these temperatures, however, the sheets are normally in a more contracted state and thus inherently more able to withstand high loads even though the amount of induced tension at the maximum temperature is less than that required to prevent deflection. For example, one type of loading to which the building and covering will be subjected is that created by the accumulation of snow on the roof. This type of loading, however, will occur at low temperature values under which conditions the sheets will have contracted to increase their induced tension and the sheets will therefore be in a state most capable of withstanding such snow loads; In addition, wind loads which are usually accompanied by storms with-resulting temperature decreaes, are similarly counteracted by the sheets contracting with the falling temperature. Thus, it will 'be seen that the building system of the present invention actually takes advantage of the changing conditions of nature to strengthen the building at the time such additional strength is needed to withstand the loads to which it will be subjected. Of course, in any unusual situation, as-for example, when the loads will be a maximum at the higher temperatures, this will be taken into account in originally tensioning the sheets.

Instead of tensioning all of the sheets at one time as describedabove, they may be tensioned successively after they are placed over the adjacent portions of the load bearing members and before the next succeeding sheet is erectedFor-example, where a number-of vertically adjustable columns 5' are provided down the length of the building, and most advantageously where one of such columns is positioned directly beneath each sheet of covering, the column disposed below a particular sheet maybe raised immediately after the corresponding sheet has been erected. Where this procedure is followed, the original tension applied to each succeeding sheet may be made less by progressively decreasing amounts than the desired final tension so that when the last column is raised the required amount, it will in turn finally increase the tension of all the sheets by the last increment necessary to" produce the desired overall results.

Also, the tension in adjacent sheets need not necessarily be equal to each other as long as the tension of each sheet is at least of a minimum value that will enable that sheet to withstand the required loads. Accordingly, where the vertical columns are to be raised successively after the succeeding sheets are erected, the raising of each succeeding column down the length of the building need only be of such an amount to assure the creation of this minimum value without particular'regard to the increased tension induced in the preceding sheets as the erecting and tensioning operation progresses from one end of the building to the other.

In another embodiment of the present invention as shown in FIG. 7, stationary columns 23 are employed and each sheet 9 is tensioned individually after it is erected over the load bearing beams 4. As with the embodiment of the invention shown in FIG. 1, the sheets are applied in overlapping relation. Here, however, each sheet is'cut after erection and the free ends 15, 16 are attached through suitable stress gauges 24 to tensioning lines 25 which are in turn connected to a power winch 25. By actuating the power winch in the clockwise direction as viewed in FIG. 7, the sheet 9 is tensioned over the load bearing beams 4 and such tensioning is continued until the gauges 24 show the desired value. Next, the tensioned sheet is anchored at its endsby the anchor angles 17 and the tensioning device disconnected. After the first sheetis properly tensioned and anchored, the succeeding sheets are then successively erected in a similar fashion with the desired overlap and sealing gasket being provided until the entire length of the building is covered;'

In a variation of this last described embodiment of the present invention, the tensioning device and which may be eliminated and the required tension produced in each sheet by deflecting the trailing end of the sheet before it is cut from its supply. As shown in FIG. 8, a truck 26 having two suppliesand 10' of sheet :metal is provided, the supply'roll 10 being positioned on a vertically adjustable support 27. This truck may be used to deliver the sheet metal directly from the mill where it is rolled to .the particular'project being constructed. To erect any one sheet over the load bearing beams 4 of the building, the truck isbrought into the position shown' in'FIG. 8 and the sheet unrolled from the'supply roll-10; fed -un der the elevated supply roll 10'-, passed-'overthe load bearing beams 4 and anchored 'atitsleadingend mane foundation 1 on the right side of the building as viewed in FIG.8. To induce the required tension into this sheet, the supply roll 10 is then fixed against rotation and the supply roll '10', which is mounted on the vertically adjustable support 27, lowered onto the sheet 9 passing" thereunder. This sheet will accordingly be deflected and "thereby induce a tension in a direction along the length of the -sheet, the required amount of tension being provided by" con trolling the extent to which the supply roll 10' is lowered. After the first supply roll has been exhausted, tensioning of the sheets fed from supply roll-10- may then be effected by means of the tensioning device shown in' FIG. 7. Alternatively, the supply roll 10' may be moved to the position originally occupied by "the supply" roll 10 and a-suitable weight placed on the adjustable'support 27 for creating the required tension."

Where it is desired to reduce the stress required in the metal sheets due to temperature changes, this may be done by applying a thermal insulating material to one or both sides of each sheet before it is tensioned. For example, an insulating material such as urethane foam which is self-bonding, can be sprayed to the top side and and/or underside of the metal sheet in the manner described in my copending patent application No. 349,669 entitled Structural Systems Employing Foaming-In- Place. As such, the metal sheet is considerably insulated from temperature changes, and when, for a temperature change of uninsulated sheets would normally be stressed for a temperature change of about if a safety factor of 30 is to be included, the addition of in sulation of one inch urethane on the top side and /2 inch on the underside, will produce a sheet such that a 100 temperature differential will only produce a direct temperature differential on the sheets of 15. Thus with this insulation system, the sheets will only have to be stressed for a temperature differential of about 20'to 25. With the installation of rigid foam on both sides of this system, a stronger sheet is also obtained because of the trength of the bond and with the installation of a sprayedin-place fireproof foam insulating material, the cheapest possible fireproof or fire resistant structure is available. A variation of the above-described "procedures can be used for roof covering only. In such 'a situation, the sheets will be attached to opposite eaves of the building and then the median supporting columns shimmed up the required distances to stressthe'sheet properly. Inthis case, the exterior columns will remain stationary; Tensioning of the sheets in this situation can also be effected by wedging beam connections in the roof system, if such is found desirable or by using" stationary columns and tensioning the individual sheets after they are applied in a manner similar to that described with 'reference to FIG. 7.

Where openings are required in a roof system or wall system, they can be cut in at a later date as the sheet is erected and stressed as long as the openings leave en'ough' cross-sectional areas of the covering sheet to provide-the required tension. If the opening is too large for the remaining parts of the sheet to carry the required tension, a reinforced sheet can be attached to the existing tensioned sheet to increase the required cross-sectional area for cut out purposes or a thicker tensioned sheet can be used at this point.

Also, it is not essential that the sheets be stressed over the width of a structure. They may be stressed in the opposite direction by laying the firt sheet at the eaves and overlapping each sheet thereafter until the ridge of the roof is passed and by then progressing down the other side of the roof.

7 The system of the present invention has an added advantage in that it may be erected in almost any weather because the workman does not have to walk on'steel. Also, there are less joints for possible leakage. With sprayed insulation, heat losses are reduced to a minimum and with sprayed urethane foam, corrosion is eliminated on these sheets. Expansion provisions do not have to be taken care of in the length of the sheet other than by stressing the sheets longitudinally; and in the width of the sheet, expansion can take-place over the flexible sealant such as butyl. Thus,emany of the normal building expansion joints are eliminated. When the roof or wall system receives a temperature differential, reducing the induced tension in the sheet, the supporting structural system will also have an induced expansion which will tend to counteract the tension reduction in the sheet due to the temperature diiferential.

The system of ,the present invention can be installed on a flat or sloping roof. It will have a vapor transmission rate of zero, and if a stainless steel sheet is used, will have an exceedingly long life expectancy.

If a steel sheet is used with urethane insulation on the top and bottom sides, a protective coating of paint for corrosion purposes will not be required. The urethane foam on the outer surface can have a compressive strength of from 20 p.s.i. to over 3000, whatever is required. The outside of the metal deck or the foam can be painted or coated with all presently known materials, if so desired. The installation of a foam on the underside will provide a considerable acoustical value in addition to its corrosive protection, insulation protection, fire protection, and structural value.

Although the above description of the present invention has been made with reference to certain preferred embodiments, it is to be understood that the teachings of the invention are equally applicable to erecting other types of building constructions that are to be covered with sheet metal, as for example storage tanks, and that various other changes can be made without departing from the scope of the invention as set forth in the following claims.

I claim: 1. In a self-supporting building construction, the combination comprising:

(a) a set of spaced load bearing members; and (b) at least one sheet of flat metal capable of contracting and expanding with temperature variations to alter any tension induced therein, each of said sheets being slidably supported solely by said members and extending transversely thereacross with the ends of each sheet disposed on opposite sides of said set of members being anchored against movement to place each sheet under an induced permanent tension applied thereto in a direction extending transversely of said members, said tension being of a value sufficient to enable each of said sheets to resist deflection intermediate said members as said sheet expands and contracts transversely of said members due to temperature variations in the ambient atmosphere. 2. In a self-supporting building construction adapted to withstand predetermined variable loads, the combination comprising:

(a) a set of spaced load bearing members defining a framework for said building; and

(b) at least one continuous sheet of fiat metal capable of contracting and expanding with temperature changes slidably supported solely by said load bearing members and extending along a predetermined path transversely across said load bearing members, said sheet having its ends disposed on opposite sides of said set of load bearing members anchored against movement to induce a predetermined permanent tension in said sheet along said path so that as said sheet contracts along said predetermined path due to temperature decreases, said tension will increase to'in turn' increase the load bearing capabilitie's' of said sheet. 3. In a self-supporting building constructioniadapted'to withstand predetermined yariable loads, the combination comprising:

(a) a set of parallel spaced load bearing beams;

(b) a plurality of elongated flat flexible metal sheets capable of contracting and expanding with temperature variations to alter any tensioninduced therein,

, said sheets being supported by saidbeams and ex- I tending transversely therea'crossj'with longitudinal edges of adjacent sheets overlapping eachiother' in shingle-likt'e'formation, the endsof each sheet b'eing anchored against movement on opposite sides of said set of beams to place each of said sheets under a predetermined induced and permanent tension applied in a direction extending along its length, said predetermined induced tension being of a value sufficient to enable said sheets to withstand said predetermined loads as temperature variations in the ambient atmosphere cause said sheets to expand and contract longitudinally; and

(c) a sealing gasket disposed between the adjacent overlapped edges of said sheets and extending the length thereof.

4. In a building construction as set forth in claim 3 wherein:

(a) said sealing gasket is of compressible material held in compression between said sheets.

5. In a building construction as set forth in claim 3 wherein:

(a) each of said sheets is coated with a layer of thermal insulating material.

6. In a building construction as set forth in claim 5 wherein:

(a) said insulating material is self-bonding foam and is aflixed to both sides of said sheets.

7. The method of constructing a building adapted to withstand predetermined variable loads comprising the steps of:

(a) erecting a plurality of parallel rows of vertical columns with the columns of each row being in spaced relation;

(b) supporting a load bearing member on each row of columns;

(c) covering said load bearing members with at least one section of flat metal sheet capable of contracting and expanding with temperature variations with opposite ends of said sheet disposed on opposite sides of said set of load bearing members;

(d) permanently tensioning said sheet in a direction transversely of said load bearing members to a value sufiicient to enable said sheet to withstand said predetermined loads as it expands and contracts in a direction transversely of said load bearing members due to temperature variations in the ambient atmosphere; and

(e) anchoring the ends of said sheet against movement with respect to said load bearing members.

8. The method of constructing a building as set forth in claim 7 wherein:

(a) the opposite ends of said sheet are anchored against movement with respect to said load bearing members before said tension is applied.

9. The method of constructing a building as set forth in claim 7 wherein:

(a) the opposite ends of said sheet are anchored against movement with respect to said load bearing members after said tension has been applied.

10. The method of constructing a building as set forth in claim 7 wherein:

(a) one end of said sheet is anchored against movement with respect to said load bearing members before said tension is applied; and

(b) the opposite end is so anchored after said tension has been applied.

11. The method of constructing a building as set forth in claim 7 wherein:

(a) a plurality of said sheets are placed over said load bearing members with the edges of adjacent sheets extending transversely of said load supporting members overlapping each other in shingle-like formation.

12. The method of constructing a building as set forth in claim 11 further including the step of:

(a) positioning a compressible sealing gasket between the overlapped edges of each sheet.

13. The method of constructing a building according to claim 12 wherein:

(a) the tension is applied to each sheet individually before the tension is applied to the next adjacent overlapping sheet.

14. The method of constructing a building according to claim 12 further including the step of:

(a) covering at least one side of each sheet with a thermal insulating material.

15. The method of constructing a building adapted to Withstand predetermined variable loads comprising the steps of:

(a) erecting a plurality of parallel rows of vertical columns with the columns of each row being in spaced relation and with the columns of at least one row being adjustable in height;

(h) supporting a load bearing beam on each row of columns;

() covering a first portion of said load bearing beams with a first elongated sheet of fiat flexible metal capable of contracting and expanding along its length with temperature variations, said first sheet extending in a direction transversely of said load bearing beams with the ends thereof disposed on the opposite sides thereof;

(d) anchoring the ends of said first sheet against movement with respect to said load bearing beams;

(e) successively covering succeeding adjacent portions of said load bearing beams with additional elongated sheets of said flat flexible metal with each successive sheet overlapping the next preceding sheet in shinglelike formation;

(f) anchoring the ends of each successively applied sheet against movement with respect to said load bearing beams; and

(g) increasing the height of the adjustable columns to tension all of said sheets in a direction along their lengths to a value sufiicient to enable said sheets to withstand said predetermined loads as they expand and contract in a direction along their lengths due to temperature variations in the ambient atmosphere.

16. The method of constructing a building as set forth in claim 15 further including the step of:

(a) positioning a compressible sealing gasket between the overlapped edges of each sheet.

17. The method of constructing a building adapted to withstand predetermined variable loads comprising the steps of:

(a) erecting a plurality of parallel rows of vertical columns with the columns of each row being in spaced relation;

(b) supporting a load bearing beam on each row of columns;

(c) covering a first portion of said load bearing beams with a first elongated sheet of flat flexible metal capable of contracting and expanding along its length with temperature variations, said first sheet extending in a direction transversely of said load bearing beams with the ends thereof disposed on the opposite sides thereof;

(d) permanently tensioning said first sheet in a direction transversely of said load bearing beams to a value sulficient to enable said first sheet to withstand said predetermined loads as it expands and contracts in a direction transversely of said load bearing beams due to temperature variations in the ambient atmosphere;

(e) anchoring the opposite ends of said first sheet against movement with respect to said load bearing beams;

(t) covering succeeding adjacent portions of said load bearing beams with succeeding sheets of said flat flexible metal overlapping the next preceding sheet in shingle-like formation with a compressible sealing gasket disposed between the overlapped edges of adjacent sheets; and

(g) successively permanently tensioning and anchoring each overlapping sheet in the manner of said first sheet and before the next following overlapping sheet is so tensioned and anchored.

References Cited UNITED STATES PATENTS 2,427,021 9/1947 Rapp 52222 2,827,138 3/1958 Roy a- 52222 X 2,943,716 7/1960 Babcock 52122 X 2,988,810 6/1961 Wilken 52222 X 3,057,119 10/ 1962 Kessler 52222 X 3,113,403 12/1963 MacMillan 5263 X 3,277,219 10/1966 Turner 52309 X 3,295,267 1/1967 Lundell 52222 X 2,382,357 8/1945 Watter 52222 FRANK L. ABBOTT, Primary Examiner.

P. C. PAW, Assistant Examiner.

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