Abstract:
Retrofitting a horizontal building roof having a pre-existing, composite-strength concrete roof having a corrugated steel deck with concrete poured over the deck top. Replacing the pre-existing roof with a dry-installed composite-strength roof having a rigid sheet installed over a corrugated steel deck, the rigid sheet attached to the deck by mechanical fasteners extending through the rigid sheet and the upper ribs of the corrugated deck. The newly installed roof restrains the upper ribs against lateral distortion under loading, thus forcing the corrugated deck to maintain shape and operate to composite capacities in excess of predictable flexural load capabilities of its components considered alone.

Description:
BACKGROUND 
     As buildings age across the United States, a great number of horizontal roof deck assemblies having poured concrete over a corrugated steel deck are in need of repair or replacement. In fact, under current building codes, namely as set forth in the International Building Code, many older flat roofs may be dangerous or classified as in a state of possible collapse. Many of these flat roofs are “composite roofs” or “composite strength roofs” which rely on the combined strength characteristics of their components, as installed, to meet load requirements and where the components considered individually are insufficient to meet those requirements. These roofs have aged and been damaged resulting in the bonding between the concrete and deck to fail. In other words, the concrete “pops off” the deck, cracking sometimes into numerous pieces of concrete rubble. Consequently, these roofs are in need of repair and methods are needed to economically effect these repairs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       A drawing of exemplary embodiments of the disclosure are annexed hereto so that the disclosure may be better and more fully understood, in which: 
         FIG. 1  is an illustration of an exemplary prior art horizontal, composite-strength roof deck assembly, generally designated, having a symmetrically corrugated steel deck secured to horizontal supports and overlaid with roofing concrete; 
         FIG. 2  is an exemplary flow chart of an exemplary composite roof replacement method according to an aspect of the disclosure; 
         FIG. 3  is an illustration of an exemplary dry-installed, composite strength roof deck assembly, installed according to aspects of the disclosure; 
         FIG. 4  is a cross-sectional, orthogonal, partial view of two corrugated deck panels positioned adjacent one another according to an aspect of the disclosure. 
         FIG. 5  is a cross-sectional elevational illustration of an alternate exemplary dry-installed, composite strength roof deck assembly installed according to aspects of the disclosure. Numeral references are employed to designate like parts throughout the various figures of the drawing. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     As explained above, repair or replacement is increasingly needed for horizontal composite strength roofs having poured concrete bonded to a corrugated steel deck below. The composite strength roofs employ a corrugated steel deck, supported by and attached to horizontal supports below, covered with roofing concrete. The roofing concrete is sometimes called, and herein includes, lightweight roofing concrete, lightweight insulating concrete, non-structural concrete, foam concrete, and the like. The composite strength of these roofs depends on sufficient bonding between the concrete and the corrugated deck such that the combined components, considered together as-installed, meet load requirements, such as gravitational load, wind uplift resistance, and diaphragm shear load. The concrete is bonded to the steel deck, typically by chemical reaction, and effectively stiffens the steel deck sections. Depth requirements for the concrete varied but were typically about two inches minimum above the upper rib portions of the corrugated deck. 
     Steel roof deck referenced herein is a corrugated, steel, roof deck, formed in generally flat sheets or panels and having parallel stiffening ribs extending across the sheet. The flat surfaces of the upper ribs provide a supporting surface for one or more layers of rigid sheet material. The corrugations define upper and lower ribs and, in a symmetrical deck, have an equal distribution of steel above and below a neutral axis lying in a plane passing through the center of the sheet and disposed parallel with upper and lower surfaces of the sheet. Symmetrically corrugated deck has been historically used for composite and non-composite cement roof assemblies, however non-symmetric deck is also known in the art. 
     More recently, symmetrically corrugated configuration has been used in flat roof, dry-installed, composite strength roof deck construction. For further disclosure to such, see U.S. Pat. Nos. 4,736,561, to Lehr, et al., and 5,584,153, to Nunley, et al., which are incorporated herein by reference for all purposes. Dry-installed composite strength roofing relies on the composite strength of the connected components of the roof deck assembly rather than the strength characteristics of the components individually. The roof components identified in the Lehr patent are a corrugated steel roof deck, attached to a rigid, high-density sheet above, by a plurality of fasteners (preferably threaded), and wherein these components are fastened together to create horizontal and vertical trusses. 
     As used herein, dry-installed composite strength roof assemblies (and similar) are those which rely on their composite strength characteristics, as installed, to meet load and resistance requirements. That is, the corrugated steel deck, rigid sheet, and fasteners, considered in composite together, as installed, provide sufficient strength characteristics, whereas the deck alone or rigid sheet alone fail to provide sufficient strength. As used herein, composite strength concrete roof assemblies (and similar) are those which rely on their composite strength characteristics, as installed, to meet load and resistance requirements. That is, the corrugated steel deck, and the overlaid and dried concrete, considered in composite, as installed, provides sufficient strength characteristics, whereas the deck or concrete alone fail to provide sufficient strength. 
       FIG. 1  is an illustration of an exemplary prior art horizontal, composite-strength roof deck assembly, generally designated  10 , having a symmetrically corrugated steel deck  12  secured to horizontal supports  14  and overlaid with roofing concrete  16 . 
     As explained above, the composite strength roof assembly is defined by the strength of the installed roof assembly; that is, the composite strength of the roof is the strength of the roofing components acting together to meet load requirements. The steel deck alone is not sufficient to meet load-bearing requirements. Similarly, the concrete alone fails to provide adequate strength. The concrete, once in place, dried, and bonded to the deck, stiffens the steel section and prevents the corrugations from “folding over” under shear load. Such roof assemblies have been widely used and many are now aged, damaged, or otherwise unfit for use and need repair or replacement. Horizontal supports as used herein includes various types of horizontal roof deck supports, such as purlins, rafters, beams, joists, etc. 
     Composite concrete roofs are horizontal, typically between zero and three degrees from horizontal or have a slope ranging from about 0.25/12 to 2/12. Low slope allows the poured concrete to set, or dry, without creating substantial uneven areas. 
     The steel roof deck  12  has symmetrical corrugations creating upper ribs  18  and lower ribs  20  or ridges extending longitudinally across the deck. Corrugated deck  12  has flat, substantially horizontal, upper and lower rib portions  22  and  24 , respectively, typically of substantially equal width, and pitched connector portions  26  extending therebetween. The symmetrical corrugation provides straight, parallel, regular, and equally dimensioned upper and lower ribs. Similarly, the deck defines symmetrical upper and lower hollows  28  and  30 , respectively. This deck configuration has a substantially equal distribution of surface area and weight of the corrugated deck above and below the neutral axis  32 . The dimensions of the corrugated deck vary depending on anticipated loads, span, etc. Typical steel decks are made of 28 to 20 gauge steel, sometimes higher. The most common deck shape is symmetrical, as explained above, however other shapes are known in the art. 
     In some prior art concrete roof assemblies, insulation board  34  was positioned between upper and lower layers of concrete  16 . Often referred to as “holey board,” such insulation boards have perforations  36  such that the concrete fills the holes, creating columns extending between upper and lower concrete layers. 
     A further feature of prior art composite concrete roofs is ventilation systems to assist in drying the wet-poured concrete. Ventilation systems employed in prior art composite concrete roofs include vented corrugations (e.g., having holes in the rib portions), vent passageways defined in the steel deck (e.g., lateral indentations extending across the deck ribs), and vent “clips” positioned between adjacent deck panels. It is not unusual to find concrete which has penetrated between adjacent deck panels during setting. 
     As composite concrete roofs age and experience significant loads and resulting deflections, it is common for the concrete to crack, break into pieces, or “pop loose” of the steel deck thereby breaking the concrete-to-steel bonding necessary to achieve composite strength. For example, significant roof deflection can be induced by severe or repetitive wind uplift or diaphragm shear loading. Concrete can also crack due to weather effects and common loading. Repairing or replacing aged or damaged composite concrete roofs is an expensive proposition. Repairing the roof typically includes removing the concrete and re-laying new concrete. If the roof deck is compromised, it must be removed and replaced as well. 
     The disclosed methods herein provide an alternative replacement process wherein a composite-strength concrete roof assembly is replaced with a composite-strength dry-installed roof assembly. Such dry-installed assemblies are typically less expensive and easier to perform. 
       FIG. 2  is an exemplary flow chart of an exemplary composite roof replacement method according to an aspect of the disclosure. In the method, the existing composite-strength concrete roof assembly is evaluated  100 , such as for concrete and deck damage, state of disrepair, type of concrete, gauge and configuration of steel deck, attachment of deck to horizontal supports, concrete-to-deck bonding, etc. 
     If it is determined that the existing roof is a viable candidate for the disclosed replacement method, then some or all of the existing roof assembly components, or portions thereof, are removed from the building. Removal can include the following, in no particular order: removing some or all of one or more concrete layers; breaking up, scraping off, prying off, or otherwise removing the concrete; removing some or all of the steel deck or panels thereof; removing holey board or insulation materials; removing pipes encased in the concrete; removing ventilation systems such as vent “clips;” and/or removing concrete from seams at adjacent deck panels. Breaking up, scraping off, or otherwise removing the concrete can be performed manually, such as by repeatedly striking the deck with a hammer, sledge-hammer, crowbar, or other blunt object. Alternately, such actions can be performed using suitable machinery, such as jack-hammers, breakers, demolition hammers, rotary hammers, mechanical scrapers, mechanical strippers, and small loading or dozing machinery. 
     Removal of the concrete at step  102 , according to exemplary and alternative method, can comprise various steps or actions, singly or in combination. For example, removal of the concrete can comprise removing concrete to expose the upper surfaces  25  of the upper rib portions  24 . Such removal allows for positioning of rigid sheets across the upper ribs. Further, concrete removal can include removing some or all of the concrete positioned in the lower hollows  28 . Concrete removal in some embodiments includes removing concrete to expose only portions of the upper surfaces  27  of the lower rib portions  22 . For example, removal of concrete to expose only some areas of the upper surfaces  27  of the lower rib portions can be performed to allow selective attachment of the steel deck  12  and horizontal supports  14 . Stated another way, removal of concrete can include intentionally leaving some concrete in place, namely, in the lower hollows  28  or on the upper surfaces  27  of the lower rib portions  22 . This can be time and labor saving, especially since the concrete may tend to crack through or break off at the top of the deck corrugations. Note that in some methods it is not necessary to remove ventilation systems, vent clips, encased pipes, etc., if such does not interfere with the replacement of concrete with dry-installed composite components. 
     Where the steel roof deck is also damaged, the method can optionally include repair or replacement of the deck, deck panels, or portions thereof, at  104 . Repair of the deck or panels can be performed by, for example, sanding, blasting, patching, welding, or coating all or part of a deck or panel. Where necessary, the replacement method can include removal and replacement of one or more deck panels or the entire deck. 
     Once the roof is prepared by removal of concrete, the method includes installation of dry-installed roofing components to form a composite-strength, steel deck and dry board deck assembly. 
       FIG. 3  is an illustration of an exemplary dry-installed, composite strength roof deck assembly, installed according to aspects of the disclosure. 
     The dry-installed composite roof deck assembly  48  includes a corrugated steel deck  50  attached to, and supported from below by, horizontal supports  14 . The deck is attached to the support by connectors  57 , which can be welds, fasteners, threaded screws, etc. Opposing edges of the corrugated deck, or panels thereof, are supported by generally parallel, horizontal supports, such that the deck creates a span between supports. A flat, rigid sheet  54  is secured from above by mechanical fasteners  56  to the corrugated deck. The aged or damaged composite concrete roof assembly is replaced with such a dry-installed composite roof assembly according to the disclosure. In some instances, it may be possible to use components, such as the steel deck, from the pre-existing composite concrete roof assembly in the replacement dry-installed composite roof assembly. 
     Depending on the construction procedures and materials used during initial installation of the composite concrete roof assembly, the corrugated deck may be attached to the horizontal supports by pre-existing connections such as a series of welds, screws, or other fasteners. The disclosed method in some embodiments includes identifying such pre-existing connections (including their number, pattern, state of repair, etc.), evaluating their sufficiency for use with the to-be-installed roof assembly, calculating the load bearing capacity of the pre-existing connections, etc., before step  106  of  FIG. 2 . 
     According to an aspect of the disclosure, at  106  of  FIG. 2 , fasteners  57  are applied to secure the corrugated deck  50  to the horizontal supports  14  in sufficient number and appropriate locations to meet load and code requirements. 
     In most instances, the pre-existing connections are a series of welds performed at or near the perimeters of the corrugated deck, or deck panels, attaching the deck to the horizontal deck supports. Additional welds may be located attaching the deck to intermediate horizontal supports, where present. Where welds are present and functional, they typically do not meet current load or code requirements. Consequently, according to an aspect of the disclosed methods, the corrugated deck is secured to the horizontal supports using a plurality of fasteners  57 , preferably threaded fasteners. 
     It may be possible to calculate the load bearing capacity of existing connections, calculate a required number and location of fasteners to supplement the pre-existing connections such that the combination of fasteners, pre-existing deck-to-support connections, and other dry-installed roof components, in composite, meet load requirements. It is unlikely that pre-existing welds are sufficient to meet load requirements, but if so, they are left in place. These methods are indicated, if applicable, at the decision node before step  106  of  FIG. 2 . 
     A typical composite concrete roof assembly uses multiple corrugated steel deck panels  68   a - b  positioned adjacent one another, defining panel seams  72 , to create the roof deck  50  as a whole.  FIG. 3  is a cross-sectional view of two corrugated deck panels  68   a - b  positioned adjacent one another according to an aspect of the disclosure. Adjacent deck panels  68   a - b  from the pre-existing composite concrete roof assembly typically have overlapping lower rib portions along the seams of adjacent deck panels. The adjacent panels, however, tend to not be mechanically fastened together by welds, threaded fasteners, and the like, in composite concrete roofs. Further, the concrete tends to flow into and between the seams  70  defined between adjacent panels  68   a - b  prior to hardening. Consequently, in some methods of the disclosure it is necessary to remove concrete from the panel seams  70 , at  106 . Further, at  106 , the method includes connecting adjacent deck panels  68   a - b  together proximate seams  72  to limit or eliminate relative movement between the panels  68   a - b  , thereby creating a functionally monolithic roof deck. Preferably, the adjacent panels are fastened together using threaded fasteners. Welds may be acceptable in some circumstances. 
     The disclosed methods include, at  108 , positioning a rigid sheet  54 , or one or more panels thereof, horizontally above the corrugated deck  50  and spanning adjacent upper ribs  18 . Where panels are installed, they are positioned adjacent one another and can be interlocked with cooperating tongue and groove or similar features. The rigid sheet, or panels thereof, is positioned to create a structural bridge over upper hollows  28 . 
     At  110 , the method comprises securing the rigid sheet  54 , or panels thereof, by threaded fasteners  56  to upper rib portions  24  of the corrugated sheet  50 . Fasteners  56  preferably have enlarged heads  60  on the end thereof which engage the rigid sheet  54 . Fastener holes formed in the rigid sheet  54  are preferably countersunk to receive the enlarged heads  60 , resulting in a uniform upper surface. 
     Threaded fasteners  56  are installed from above the rigid sheet  54  extending downwardly through the rigid sheet and through the upper rib portions  24 . Securing the rigid sheet  54  can further include securing a plurality of panels thereof adjacent to one another to cover the corrugated deck  50  or panels thereof. Spaced apart threaded fasteners  56  are secured from above the rigid sheet, through the rigid sheet and through the upper rib portions  24  of the deck  50 . The method can include securing the rigid sheet, or panels thereof, to create a structural bridge over upper hollows  28 . 
     The method includes, at  110 , securing the fasteners  56 , oriented in a selected pattern, and forming a series of generally triangular-shaped, horizontally-disposed, trusses T h  and a series of vertically-disposed trusses T v  throughout the length and width of deck spans between spaced horizontal supports  14  to increase resistance to horizontal and vertical planar deflection of the roof deck as seen in  FIG. 4 . The method includes providing flexural strength and diaphragm stiffness to the roof deck by securing the rigid sheet to the upper rib portions of the deck and restraining relative horizontal movement of the deck ribs using the rigid sheet and fasteners. The method includes forming a horizontal, triangular-shaped truss T h  in the horizontal plane of the rigid sheet, having a triangular segment of the rigid sheet  54  restrained by adjacent mechanical fasteners  56  to upper ribs  24  of corrugated sheet  50  in a span between horizontal supports  14 . 
     The upper deck ribs are in compression when a downwardly directed force is applied above the deck. The fasteners  56  are positioned such that buckling of the unsupported length of the upper rib portions is minimized. The rigid sheet  54 , or panels thereof, are relatively high density, relatively planar, fire and water resistant board selected to provide resistance to high impacts and concentrated loads without rupturing, and to contribute to the composite roof load capacity. The rigid sheet  54  may comprise a plurality of panels, which may have cooperating tongues and grooves formed thereon to provide continuous interlocking of panels. The method may include interlocking adjacent rigid sheet panels, and more specifically, interlocking adjacent panels using cooperating tongue and groove features  62 . 
     Fasteners  56  are secured through the rigid sheet and upper rib portions  24  and oriented in a pattern to form a vertical truss T v  comprising: a section of the rigid sheet spanning upper hollow  28  between adjacent upper ribs and between adjacent fasteners  56 , the adjacent fasteners  56 , and connector portions  26  of the corrugated deck between the ribs. 
     The method can include determining a functional fastener pattern for use in securing the rigid sheet to the corrugated deck, calculating necessary spacing between fasteners, using deck span measurements in such calculations, using length, width, and height measurements of the deck in such calculations, using roof shape in such calculations, and using horizontal support spacing measurements in such calculations. 
     The method can include, at  110 , spacing the trusses T v  and T h  from the horizontal supports  14  and preventing lateral and vertical distortion of the corrugated deck  50  as a result of force applied in the plane of the rigid sheet  54 . The method can further include maintaining the joint stability of adjacent rigid sheet panels using a selected fastener pattern or installed fasteners in such a pattern. 
     The composite roof deck functions as a structural diaphragm, providing rigidity. Fasteners  56 , oriented in a pattern at horizontally spaced locations transversely of the span, and at spaced locations longitudinally of the span, form a series of essentially triangular shaped trusses T h  and T v  in the horizontal and vertical planes throughout and across the span, between the horizontal supports, and stabilize and prevent lateral and vertical deformation of the individual ribs of the corrugated deck, increasing resistance to horizontal and vertical planar deflection of the deck. 
     The methods herein disclosed are typically required to be completed in a single day&#39;s work since the building is usually occupied or operational and must be kept in the dry. 
     The methods herein disclosed may further include, at  114 , application of a roof covering  78  to the upper surface of the rigid sheet or panels thereof. The roof covering is preferably a smooth, flat, single-ply synthetic material. Typical coverings are made of EPDM, TPO, or PVC, for example. The covering is preferably adhered to the rigid sheet. For example, a layer of asphalt can be applied to the upper surface of the roof and a covering of modified bitumen laid atop the asphalt or other adhesive. Alternately, some roof coverings can be applied to the upper surface of the roof and then heated in place to self-adhere to the below roof component. 
     The methods herein may further include, at  112 , application of insulation material  80 . The insulation material can be positioned in a sandwiched position between the corrugated deck  50  and the rigid sheet  54 , as seen in  FIG. 5 , or in a position above the rigid sheet  54 , as seen in  FIG. 3 . Where an insulation layer is applied, the above-described methods are modified accordingly such that securing of roofing components includes extending fasteners through the insulation layer. For further disclosure in this regard see the incorporated references. 
     The methods disclosed herein may further include, at  116 , installation of ventilating apparatus to control temperature and air pressure below the roof deck. Provision of ventilation apparatus to relieve pressure includes communicating air flow such that change in air pressure above the rigid sheet is accompanied by simultaneous change in air pressure in lower hollows below the rigid sheet. This minimizes the likelihood that sufficient pressure differential will exist to separate rigid sheets  54  from the stronger corrugated deck  50 . For further disclosure in this regard see the incorporated references. 
     The methods disclosed herein may further include, at  116 , installation of a heat exchanger or the like to eliminate condensation on the corrugated deck and form a vapor barrier between the interior of the building and the roofing. For further disclosure in this regard see the incorporated references. 
     From the foregoing it should be readily apparent that while the symmetrically corrugated deck, rigid sheet, and optional insulation layer are insufficient in strength characteristics to form a roof assembly when separately considered, the components installed and considered working together or in composite have superior strength. In view of the unorthodox characteristics and functions of the individual components when assembled in a dry-installed composite roof, mathematical calculation of composite strength is infeasible. However, strength characteristics and comparisons with existing structures have been observed by actual construction and testing. Empirical data has been analyzed and formulated into a predictable pattern by applying engineering principles. 
     The invention is defined by the claims appended hereto and the specification is not limiting to the claim interpretation. It is understood that other and further embodiments of the disclosed methods can be devised without departing from the basic concepts explained herein. Terms take their normal and ordinary meanings unless otherwise addressed herein. The various steps, actions, procedures, etc., described herein are limited in their respective order only when so indicated by the claims. Further, such actions can be omitted, repeated, changed in order, etc., as a person of skill in the art will recognize. Application of common sense by someone of skill in the art should educate use of the disclosed methods and any modifications thereof.