PORTAL FRAME CONSTRUCTION

Abstract: A portal frame construction, for a building, comprising a stanchion (15), a rafter (17) secured at one end to the stanchion (15) at an angle thereto, and a haunch member (21) spanning the corner defined between the stanchion (15) and the rafter (17), the stanchion (15) and the rafter (17) each being defined by two elongate members of channel-shaped cross section positioned back-to-back with their base walls in contact, and characterised by said haunch member (21) being connected at one end to the rafter (17) by a connecting piece (36) including a plate (39) fastened in facial contact with at least one of the co-planar side walls of the channel members of the rafter (17).

Description: 1 PORTAL FRAME CONSTRUCTION This invention relates to a portal frame assembly, and a method of manufacturing a portal frame assembly, for a steel framed building construction. A steel frame building having a pitched roof will have at least two portal frames, one at each gable end of the building, and may have a plurality of intermediate portal frames parallel to the gable end portal frames and defining intermediate bays of the building construction. Conventionally each portal frame will consist of first and second spaced, parallel, upright members generally referred to as stanchions, each being connected at its upper end to an elongate, inclined roof support member generally referred to as a rafter. The two rafters extend upwardly and inwardly towards one another to be joined at the ridge line of the building construction. The corner defined between each stanchion and its respective rafter is spanned by a strut generally referred to as a haunch member connected at one end to the ratter at a point spaced from the connection of the rafter to the stanchion, and connected at its other end to the stanchion at a point below the point of connection of the rafter with the stanchion. There may well be a plurality of further vertical support members extending upwardly from the building floor pad to the rafters, and intermediate horizontal members bracing the vertical members. However these additional members are not of significance to the present invention. It is possible to form the stanchions and rafters from hot rolled metal beams of l-shaped cross-section. The invention is however not concerned with such constructions. As an alternative construction method the stanchions, rafters, and haunch members are formed from elongate lengths of back-to-back, paired, cold rolled, mild steel, rectangular C-shaped channel section. In such a construction conventionally the joints between the ends of each haunch member and respectively the rafter and the stanchion are made by flat steel fixing or gusset plates which are sandwiched between the back-to-back base walls of the channel sections, and so space the two channel sections of the stanchion, the rafter, and the haunch member apart by the thickness of the fixing plate. The spacing of the base walls of the back-to-back channel sections of the rafter and stanchion is disadvantageous to the load carrying capacity of the portal frame, and necessitates the use of spacers or packers where bolts and the like are to pass through the base walls. It is an objective of the present invention to provide a portal frame construction in which these disadvantage are minimised. In accordance with the present invention there is a provided a portal frame construction comprising a stanchion, a rafter secured at one end to the stanchion at an angle thereto, and a haunch member spanning the corner defined between the stanchion and the rafter, the stanchion and the rafter each being defined by two elongate members of channel-shaped cross- section positioned back-to-back with their base walls in contact, and said haunch member being connected at one end to the rafter by a connecting piece including a plate fastened in facial contact with at least one of the co-planar side walls of the channel members of the rafter. In accordance with a further aspect of the present invention there is provided a method of manufacturing a portal frame construction comprising securing first and second channel sections back-to-back with their base walls in contact to form a stanchion, securing third and fourth 3 channel sections back-to-back with their base walls in contact to form a rafter, securing the rafter at one end to the stanchion at an angle thereto, and securing a haunch member spanning the corner defined between the stanchion and the rafter, said haunch member being connected at one end to the rafter by a connecting piece including a plate fastened in facial contact with at least one of the co-planar side walls of the channel members of the rafter. Preferably each haunch member is connected at its opposite end to the respective stanchion by a connecting piece including a plate fastened in facial contact with at least one of the co-planar side walls of the channel members of the stanchion. Desirably each connecting piece includes a plate fastened in facial contact with both co-planar side walls of the channel members of the ratter or stanchion. Preferably a stiffening element is secured within each channel member of the rafter in that region of the channel member engaged by the plate of the connecting piece. Preferably a stiffening element is secured within each channel member of the stanchion in that region of the channel member engaged by the plate of the connecting piece. Preferably said stiffening elements are L-shaped in cross-section. Desirably the plate of each connecting piece is secured to the side wall of the respective channel member by a bolt or bolts passing through the plate, the side wall of the channel member, and one limb of the stiffening 4 element housed within the channel member. Preferably the second limb of each stiffening element engages the inner face of the base wall of its respective channel member, there being a bolt or bolts passing through the second limbs of the stiffening elements and the intervening channel member base walls to secure the stiffening elements and the channel member base walls together. Preferably each stiffening element includes a fin protruding at right angles to its respective channel member to facilitate securing thereto of a further structural component. One example of the invention is illustrated in the accompanying drawings wherein: Figure 1 is a diagrammatic representation of the steel frame of a building incorporating four portal frame assemblies, Figure 2 is a diagrammatic side elevational view of part of one of the four portal frame assemblies of Figure 1 , Figure 3 is a transverse cross-sectional view on the line 3-3 in Figure 2, Figure 4 is a view similar to Figure 3 illustrating a prior art arrangement, Figure 5 is a side elevational view of a jointing member illustrated in Figures 2 and 3, Figure 6 is a view in the direction of arrow A in Figure 5, Figure 7 is a side elevational view of a stiffening element illustrated in Figures 2 and 3, Figure 8 is a view in the direction of arrow B in Figure 7, and Figure 9 is a view similar to part of Figure 2 illustrating a modification. Referring first to Figure 1 of the drawings, it can be seen that the steel frame construction of the building includes four portal frame assemblies 1 1, 12, 13, and 14. The portal frame assemblies 11 and 14 are at opposite gable ends of the building and the intermediate portal frame members 12 and 13 are equally spaced between the gable end members 11 , 14, thus defining a building having three bays. Each portal frame assembly comprises first and second vertical stanchions 15, 16 anchored at their lower end to the floor pad of the building, the spacing between the stanchions 15, 16 being the width of the dimension of the building. In addition, each portal frame assembly includes first and second rafters 17, 18 anchored at one end to the stanchions 15, 16 respectively and extending inwardly and upwardly therefrom to interconnect at their opposite ends along the ridge line 19 of the roof of the construction. Each portal frame assembly further includes a haunch member 21 spanning the corner defined between the stanchion 15 and the rafter 1 7, and a second similar haunch member 22 spanning the corner defined between the stanchion 16 and the rafter 18. In addition, each portal frame may incorporate further upright members 23 supporting the rafters 17, 18 at various points along their length, and horizontal bracing rails 24. Side rails 25 and eaves beams 26 extend horizontally between stanchions 15, and similar side rails and eaves beams extend horizontally between stanchions 16. Purlins 27 extending lengthwise of the building between parallel rafters 17 and similar purlins extend in a similar manner between rafters 18. In addition the building construction may include further struts and bracing members not of significance to the present invention. Stanchions and rafters can be formed from hot rolled beams of l-shaped cross-section, but the invention is not concerned with such constructions. Hot rolled I beams are relatively massive, and for many applications it is preferable to utilise cold rolled channel-sections in the construction of the stanchions and rafters. It is known to produce stanchions and rafters from channel-shaped sections which are positioned back-to-back as shown, for example in Figure 4 of the accompanying drawings. It is also know to produce the haunch members 21 from pairs of channel-section members positioned back-to-back and in such portal frame assemblies the haunch members 21 , 22 are connected to their respective stanchions 15, 16 and rafters 17, 18 by planar metal gusset plates sandwiched between the mutually presented base walls of the channel-sections. Bolts pass through the base walls and the gusset plates to secure the components together. However, inevitably within each stanchion, and within each rafter the two channel-sections have their mutually presented base walls spaced apart by the thickness of the gusset plates. Such spacing of the channel-sections away from one another is disadvantageous in a number of respects. Firstly, the spacing prejudices the structural integrity of the portal frame assemblies since rafters and stanchions can twist more easily if the base walls of their back-to-back channel-sections are spaced apart. Furthermore, where bolts are to pass through the base walls then in order to prevent deformation of the base walls (or alternatively loose fixings) it is necessary to provide packing pieces between the base walls at the points where the bolts are to pass through. Figure 4 illustrates a pair of lipped, rectangular C-shaped channel-sections 31 , 32 with a gusset plate 33 sandwiched between the mutually presented base walls 31 a, 32a of the channel sections. It can be seen therefore that the base walls 31 a, 32a are spaced apart by the thickness of the gusset plate 33, the positions of fixing bolts being illustrated by dotted lines 34, 35 in Figure 4. In accordance with the present invention the channel-sections of the stanchions and of the rafters are positioned back-to-back with their base walls in facial contact. An embodiment of such an arrangement is illustrated in Figure 3 which is a sectional view through a rafter 17 of a portal frame assembly illustrated in part in Figure 2. It is to be recognised that the construction which will be described hereinafter, with reference to Figure 2, applies to each stanchion and rafter assembly of each portal frame assembly. Referring now to Figures 2, 3, and 5 to 8, each stanchion comprises a pair of rectangular, lipped, channel-sections positioned back-to-back with their base walls in facial contact. The channel-sections are cold rolled mild steel and are galvanised. Each rafter is also formed from a similar pair of back-to-back channel-sections 31 and 32 (Figure 3). A pair of generally L- shaped cleats 28 secure the channel-sections 31 , 32 at one end to the stanchion 15. Each cleat 28 has a first limb which extends within its respective channel-section 31 , 32 and a second limb which abuts the outer face of the side wall of a respective channel-section of the stanchion 15. Bolts extend through the first limbs of the cleats 28 and the base walls of the channel-sections 31 , 32 to secure the cleats to the channel-sections 31 , 32 and to secure the channel-sections together. The other limbs of the two cleats 28, which extend away from one another are bolted to the co- planar side wall of the two channel members of the stanchion 15 by bolts which pass through the second limbs of the cleats and the side walls of the channel sections. In addition, the bolts pass through first limbs of 8 respective L-shaped stiffeners 29 which are housed within the channel sections of the stanchion 15. The first limbs of the stiffeners 29 lie in contact with the inner faces of the co-planar side walls of the channel- sections of the stanchion 15 and the other limbs of the stiffeners lie in contact with the inner faces of the base walls of the channel-sections forming the stanchion 15. Bolts extend through the second limbs of the stiffeners 29, and the base walls of the channel-sections to clamp the stiffeners to the base walls, and to clamp the base walls in facial contact with one another. It is to be understood that references herein to bolts denote, except where the context dictates otherwise, nut and bolt fasteners extending through the sheet metal components and clamping them together. The haunch member 21 is also formed from a pair of back-to-back channel-sections, but as the haunch member is relatively short in length, and does not have other components normally bolted thereto, it is not critical that the channel-sections of the haunch member are positioned with their base walls in facial contact. Accordingly, in order to secure the haunch member 21 to both the stanchion 15 and the rafter 1 7 there is provided, at each end of the haunch member 21 , a jointing member 36, 37, the jointing member 36 being illustrated in more detail in Figures 5 and 6. The jointing member 36 comprises a leg 38 and a plate 39 welded thereto and lying in a plane at right angles to the plane of the leg 38. The plate 39 is disposed at an angle to the length of the leg 38 equal to the angle which the haunch member 21 is required to make with the rafter 17. The leg 38 is sandwiched between the base walls of the two channel-sections of the haunch member 21 at one end thereof and four bolts pass through the base walls and the leg 38 to secure the two together. The plate 39 seats 9 beneath the rafter 17 and thus makes facial contact with the outer faces of the lower, co-planar, side walls of the two channel-sections 31 , 32. Disposed within the channel-sections 31 , 32 immediately above the plate 39 are respective L-shaped stiffening elements 41, 42. Each of the elements 41 , 42 has one limb lying in facial contact with the inner surface of the lower side wall of its respective channel-section and the other limb in facial contact with the inner face of the base wall of the channel- section. Bolts pass through the plate 39, the respective channel-section side wall and the respective first limb of each element 41 , 42 to fix the rafter channel sections 31 , 32 to the plate 29 and to fix the elements 41 , 42 in position within their respective channel-section. Further bolts pass through the other limb of each element 41 , 42 and the base walls of the channel-sections 31 , 32 to fix the channel-sections together, and fix the elements 41 , 42 to the channel base walls. Each of the stiffening elements 41 , 42 has a fin 41 a, 42a welded thereto, and extending at right angles thereto. The fins 41 a, 42a thus project within their respective channel members 31 , 32 at right angles to the length of the rafter 17 to form an anchorage point to which respective purlins can be bolted in use. The jointing member 37 at the opposite end of the haunch member 21 is as described above with reference to the jointing member 36 except in that the plate and the leg of the jointing member subtend a different angle, appropriate to the angle made between the haunch member 21 and the stanchion 15. Stiffening elements 43 similar to the elements 41 , 42 are positioned within the channel-sections defining the stanchion 15 and each of the stiffening elements 43 has a fin 43a to facilitate connection of a side rail. 10 It will be recognised that if it is desired to ensure that the channel-sections of the haunch member 21 are positioned with their base walls in facial contact, then generally L-shaped cleats can be utilised in place of the jointing member 36, 37. There will be two cleats at each end of the haunch member each cleat having a first limb lying within its respective haunch member channel-section, and a second limb in facial contact with the outer surface of the lower side wall of the respective channel-section 31 , 32 of the rafter 1 7. Bolts will pass through the cleats and the base walls of the haunch channel-sections, and further bolts will pass through the other limbs of the cleats, the side walls of the channel sections 31, 32 and the lower limbs of the stiffening elements 41 , 42. The limbs of the cleats 28 which are bolted to the side walls of the stanchion channel-sections can, if desired, be extended to project beyond the edges of the side walls of the stanchion channel-sections to provide a fixing point for anchoring eaves beams 26 to the stanchions at their upper ends. Conveniently the rafters 17, 18 of each portal frame assembly are joined by flat chevron shaped joining plates which lie within the channel-sections 31 , 32 and which are secured in place by shouldered bolts passing through the plates and the base walls of the channel-sections 31 , 32, the included angle of each chevron shaped plate being the angle at which the rafters 1 7, 18 must subtend to provide the appropriate pitch angle for the roof. The bolts are arranged to be a close fit in corresponding holes in the plate and the channel sections, the use of close tolerance shouldered bolts overcoming the risk of "in use" relaxation, with consequential unacceptable flexure, of the bolted apex joint. 11 The stiffening elements disclosed above are of L-shape cross-section and bolt to a side wall and the base wall of their respective channel section, the limb which bolts to the base wall being short in relation to the width of the base wall.. Figure 9 illustrates a modification of the arrangement described above in which the stiffeners 29 at the upper ends of the stanchions are replaced by L-shaped stiffeners 49 having a limb extending across substantially the full width of the base wall of the respective stanchion channel section. Such an arrangement permits the use of single eaves beams 26 spanning adjacent stanchions, rather than the paired eaves beams 26 illustrated in Figure 1 , without impairing the structural integrity of the construction. Additionally the rafters are raised slightly in relation to the upper ends of the stanchions and the upper ends of the stiffeners 49 project beyond the ends of their respective stanchion and are cut at angle corresponding to the pitch angle of the rafters so as to form a continuation of the top face of the associated rafter and simplify the secure fixing of roof cladding members. L-shaped cleats 51 for securing the eaves beams to the stanchions are bolted to the base walls of the stanchion channel sections by bolts which pass also through the long limbs of the stiffeners 49. It is to be understood that in some applications the use of U-shape cross- section stiffening elements may be selected, the U-shape cross-section stiffener seating within its respective channel section and in some cases being bolted to both of the side walls and the base wall of the respective channel section The channel sections, cleats, jointing member, chevron plates and stiffening elements will all be formed from galvanised mild steel strip or sheet.

Claims: 12 CLAIMS :- 1 . A portal frame construction, for a building, comprising a stanchion (15), a rafter (17) secured at one end to the stanchion (15) at an angle thereto, and a haunch member (21) spanning the corner defined between the stanchion (15) and the rafter (17), the stanchion (15) and the rafter (17) each being defined by two elongate members of channel- shaped cross-section positioned back-to-back with their base walls in contact, and characterised by said haunch member (21) being connected at one end to the rafter (17) by a connecting piece (36) including a plate (39) fastened in facial contact with at least one of the co-planar side walls of the channel members of the rafter (17). 2. A portal frame construction as claimed in claim 1 characterised in that each haunch member (21 ) is connected at its opposite end to the respective stanchion (15) by a connecting piece (37) including a plate fastened in facial contact with at least one of the co-planar side walls of the channel members of the stanchion (15). 3. A portal frame construction as claimed in claim 1 or claim 2 characterised in that each connecting piece (36, 37) includes a plate fastened in facial contact with both co-planar side walls of the channel members of the respective rafter (17) or stanchion (15). 4. A portal frame construction as claimed in any one of claims 1 to 3 characterised in that a stiffening element (41, 42, 43) is secured within each channel member to which the plate of a connecting piece (36, 37) is fastened, the stiffening element being positioned in that region of the channel member engaged by the plate of the connecting piece. 13 5. A portal frame construction as claimed in claim 4 characterised in that the or each said stiffening element (41 , 42, 43) includes a region of L- shaped cross-section. 6. A portal frame construction as claimed in claim 5 characterised in that the plate of each connecting piece (36, 37) is secured to the side wall of the respective channel member by a bolt or bolts passing through the plate, the side wall of the channel member, and one limb of the stiffening element (41 , 42, 43) housed within the channel member. 7. A portal frame construction as claimed in claim 6 characterised in that the second limb of each stiffening element (41 , 42, 43) engages the inner face of the base wall of its respective channel member, there being a bolt or bolts passing through the second limbs of the stiffening elements and the intervening channel member base walls to secure the stiffening elements and the channel member base walls together. 8. A portal frame construction as claimed in claim 4 characterised in that each stiffening element (41 , 42, 43) includes a fin (41 a, 42a, 43a) protruding at right angles to its respective channel member to facilitate securing thereto of a further structural component. 9. A method of manufacturing a portal frame construction characterised by comprising, securing first and second channel sections back-to-back with their base walls in contact to form a stanchion (15), securing third and fourth channel sections back-to-back with their base walls in contact to form a rafter (17), securing the rafter at one end to the stanchion at an angle thereto, and securing a haunch member (21) spanning the corner defined between the stanchion and the rafter, said haunch member being connected at one end to the rafter by a connecting 14 piece (36) including a plate fastened in facial contact with at least one of the co-planar side walls of the channel members of the rafter. 10. A method as claimed in claim 9 characterised in that each haunch member (21 ) is connected at its opposite end to the respective stanchion (15) by a connecting piece (37) including a plate fastened in facial contact with at least one of the co-planar side walls of the channel members of the stanchion (15). 1 1. A method as claimed in claim 9 or claim 10 characterised in that each connecting piece (36, 37) includes a plate fastened in facial contact with both co-planar side walls of the channel members of the respective rafter (17) or stanchion (15).

Inventors: BURNS ROY JOHN, BURNS, ROY, JOHN
Applicants: BURNS ROY JOHN, METSEC PLC, BURNS, ROY, JOHN
Application year: 1999
Main classification: E04B1
IPC codes: E04B1, E04C3