Patent Publication Number: US-2005120669-A1

Title: Bottom flange hanger

Description:
CLAIM OF PRIORITY  
      This application claims the benefit of U.K. Patent Application No. 0324445.6, “Bottom Flange Hanger,” filed on Oct. 20, 2003, which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a joist hanger for use in the construction industry.  
      2. Description of the Related Art  
      A known method of floor or roof construction in residential buildings typically comprises the step of providing a number of approximately parallel supporting joists. Thereafter flooring or roofing is positioned atop the supporting joists. However, there are many situations during the construction of a floor or roof in which it is necessary to create an aperture, usually rectangular, through the floor or roof e.g. for a staircase or roof light. In these situations it is known to split the span of one or more supporting joists thereby forming trimmed joist(s). The cut ends of the trimmed joist(s) are supported by trimmer joist(s) positioned adjacent the aperture and the trimmer joists are usually supported between adjacent supporting joists. This is illustrated in  FIG. 2 . Joist hangers are generally provided at the junction between (a) one end of a trimmer joist and a supporting joist; or (b) one end of a trimmed joist and a trimmer joist.  
      A traditional joist hanger is shown in  FIG. 11  wherein the joist hanger  100 , comprises a joist bearing slot  200  formed by opposed approximately parallel spaced apart side flanges  300 ,  400  and a joining bottom flange  500 , the side flanges are joined to an angle bracket  600  by weld lines  700 . The angle bracket  60  is arranged such that a first face thereof provides a back flange  610 , attached to the joist bearing slot, whilst a second face thereof, provides a top flange  620  arranged at a right angle to the back flange  610 . In use, the joist hanger  100 , is set with the back flange  610  tight against a support. The top flange  620 , is at this point resting on a top surface of the support. Hangers folded from a single piece of metal are also known. An example of a hanger produced of a single piece of metal is the well known ITT™ hanger sold by Simpson Strong Tie.  
      There are a number of different forms of floor joist used in construction, three main types being: traditional rectangular solid sawn timber; engineered timber ‘I’ shaped joists comprising a narrow web and rectangular top and bottom flanges; and engineered timber truss joists comprising rectangular timber top and bottom flanges which are spaced apart by a lattice work of metal webs.  
      Known joists of solid timber suffer from the problem that they are prone to shrinkage and distortion. To address this problem ‘I’ joists have been developed which typically consist of two rectangular flanges attached by a web. A cross sectional view of an ‘I’ joist is shown in  FIG. 1 . The flanges are usually either solid sawn or composite laminated timber and the web is usually manufactured from panel timber such as plywood or oriented strand board (OSB). In the case of flooring, the ‘I’ joists are provided with their flanges lying in horizontal planes and their webs positioned vertically.  
      However, as disclosed in GB2376700 (Cullen Building Products Limited), it is difficult to make an orthogonal junction of ‘I’ joists because connection to one or both flanges of an ‘I’ joist can cause rotation of the flange(s) relative to the web and this limits the load bearing capacity of the joist. In the past, as shown in  FIGS. 3A and 3B , this has been facilitated by packing the gap between the web and the flanges of the ‘I’ joist with a backer block, thereby limiting rotation. However, it has been found that the backer blocks are costly, time consuming and difficult to install correctly often resulting in inadequate installation. In addition, if the backer blocks have high moisture content when installed they can subsequently shrink on drying and create a gap to the underside of the top flange enabling rotation to take place.  
      GB2376700 suggests that this problem should be addressed by a hanger having a first bracket having first and second side members with an intermediate member therebetween capable of supporting a flange of one end of a first ‘I’ joist, and a second bracket having first and second side members and an intermediate member therebetween adapted in use to overlie the upper flange of a second ‘I’ joist. Fixing apertures are provided in all the side members particularly to facilitate connection of the upper flange of the end of the first ‘I’ joist to the first bracket.  
      A need exists for new equipment for facilitating the erection of a building structure which can be used easily, which reduces the burden required to secure a first joist to a second joist, which is strong and which facilitates the use of all known joists including joists of “I” shaped section.  
      It is an aim of the invention to solve or reduce at least one of the problems set out above.  
     SUMMARY OF THE INVENTION  
      An embodiment of a joist hanger which is the subject of this invention, addresses or solves one or more problems of the prior art by inclusion of a bottom flange which can be fixed (e.g. by one or more nails) to the underside of the supporting joist bottom flange. Advantageously, it has been found that this feature creates a connection capable of resisting rotation.  
      Accordingly, in a first aspect, the invention provides a joist hanger which comprises first and second side flanges, a seat, at least one back flange and at least one bottom flange; wherein the seat is provided between the first and second side flanges to form a stirrup for supporting a first joist; a back flange adjoins at least one of the side flanges in a plane approximately perpendicular to planes including the adjoining side flange and the seat; a bottom flange adjoins the back flange proximal to the seat and in a plane approximately parallel to a plane including the seat; and the back flange and the bottom flange form a bracket for abutting a lower surface and a side surface of a second joist.  
      At least one of the side flanges defines one or more fixing apertures for receiving a fixing (e.g. a nail or screw). In one embodiment, the fixing apertures are positioned to facilitate fixing to the flange(s) of an ‘I’ joist. In addition, the fixing apertures may be staggered to minimize the risk of splitting wooden flanges of an ‘I’ joist.  
      In a second aspect the invention provides a method for connecting a first and second joists which comprises the step of fixing a joist hanger according to a first aspect of the invention to the second joist and fixing the first joist to the joist hanger.  
      Advantageously, it has been found that when a first joist is connected to a second joist according to an embodiment of the method, the ability of the bottom flange of an ‘I’ joist to rotate relative to the web of the ‘I’ joist is greatly reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Embodiments of the invention will now be described in detail with reference to the drawings in which:  
       FIG. 1  shows a cross sectional view of a typical ‘I’ joist.  
       FIG. 2  shows a view of a typical arrangement of supporting joists, trimmer joists and trimmed joists.  
       FIGS. 3A and 3B  show views of rotation of the flanges of an ‘I’ joist and how this rotation can be restricted by the positioning of backer blocks.  
       FIGS. 4A and 4B  show views of one embodiment of a joist hanger according to the invention without and with ‘I’ joists, respectively.  
       FIGS. 5A and 5B  show views of an alternative embodiment of a joist hanger according to the invention without and with ‘I’ joists, respectively.  
       FIGS. 6A and 6B  show views of a further alternative embodiment of a joist hanger according to the invention without and with ‘I’ joists, respectively.  
       FIGS. 7 A and 7B  show views of a further alternative embodiment of a joist hanger according to the invention without and with ‘I’ joists, respectively.  
       FIGS. 8A and 8B  show views of a further alternative embodiment of a joist hanger according to the invention without and with ‘I’ joists, respectively.  
       FIGS. 9A and 9B  show views of a further alternative embodiment of a joist hanger according to the invention without and with ‘I’ joists, respectively.  
       FIGS. 10A and 10B  show views of a further alternative embodiment of a joist hanger according to the invention without and with ‘I’ joists, respectively.  
       FIG. 11  shows an embodiment of a typical known joist hanger. 
    
    
     DETAILED DESCRIPTION  
      For the purposes of clarity and a concise description features are described herein as part of the same or separate embodiments. However it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.  
      Referring to  FIGS. 4A and 4B , one embodiment of a joist hanger ( 10 ) according to the invention is formed/folded from a single piece of metal (e.g. steel). Therefore, it is more economic and efficient to manufacture compared to the known joist hangers. In addition, unlike a welded two part hanger it does not require secondary protective coatings such as hot dip galvanizing for durability, because unlike the known products an embodiment of the invention can be produced of steel sheet which is pre-galvanized. Alternatively the hanger ( 10 ) is formed from multiple pieces which are connected by for example welding, riveting etc. An embodiment of a hanger ( 10 ) may be formed of plastics material or timber.  
      The hanger ( 10 ) comprises first and second side flanges ( 30 ,  40 ), a seat ( 50 ), two back flanges ( 61 ) and two bottom flanges ( 80 ).  
      The seat ( 50 ) is provided between the first and second side flanges ( 30 , 40 ) to form a stirrup for supporting a first joist ( 1 ,  2 ,  3 ). The stirrup is tapered in width from the mouth ( 110 ). A taper provides the advantage of taking account of tolerance in the dimensional width of a joist and allows a joist to be tightly gripped as it is driven into the hanger.  
      The back flanges ( 61 ) adjoin the side flanges ( 30 ,  40 ) in a plane approximately perpendicular to planes including the adjoining side flanges ( 30 ,  40 ) and the seat ( 50 ).  
      The bottom flanges ( 80 ) adjoin the back flanges ( 61 ) proximal to the seat ( 50 ) and in a plane approximately parallel to a plane including the seat ( 50 ).  
      The back flanges ( 61 ) and the bottom flanges ( 80 ) form a bracket for abutting a lower surface and a side surface of a second joist.  
      The back flanges ( 61 ) project outwardly from the side flanges ( 30 ,  40 ).  
      Alternatively, the back flanges ( 61 ) project inwardly from the side flanges ( 30 ,  40 ) as shown in  FIGS. 10A and 10B . In one embodiment, a single back flange ( 61 ) adjoins both side flanges ( 30 ,  40 ). In yet another embodiment, the back flange ( 61 ) adjoins both side flanges ( 30 ,  40 ) and the seat ( 50 ).  
      Fixing apertures are defined by the top flanges ( 62 ), bottom flanges ( 80 ), side flanges ( 30 ,  40 ) and back flanges ( 61 ). The apertures receive fixings (not shown) and facilitate connection to the upper and lower flanges ( 1 ,  3 ) of one or more ‘I’ joists.  
      The hanger ( 10 ) can be used to provide restraint of the supported joist ( 1 , 2 , 3 ) against rotation/lateral movement at its upper flange ( 1 ). The hanger side flanges ( 30 , 40 ) are therefore of sufficient height in relation to the supported joist height to enable the supported joist top flanges ( 1 ) to bear against the inner faces of the side flanges ( 30 , 40 ). This obviates the need for timber blocking pieces ( 7 ) to be installed to the supported joist web ( 2 ) to create the required contact with the side flanges ( 30 ,  40 ) to resist lateral movement of the upper part of the supported joist ( 1 ).  
      An embodiment (10) can also be used for, and gives similar benefits, on open web beams which have a top and bottom flange connected by metal webs/struts ( 2 ). The joist hanger ( 10 ) can be applied to solid rectangular timber joists where the benefits of reduced flange rotation and load sharing between the flanges are not required.  
      Joist hanger ( 10 ) is sized to receive a standard size of joist. An embodiment of a hanger ( 10 ) according to the invention can accommodate any type of joist and a range of sizes allows joists of different types and sizes to be accommodated.  
      Although the stirrup ( 30 ,  40 ,  50 ) is described as enclosing the end part of a joist ( 1 ,  2 ,  3 ), it will be appreciated that there may be gaps or holes formed in the joist hanger such that the stirrup ( 30 ,  40 ,  50 ) only partially encloses the joist end.  
       FIGS. 4A, 4B ,  5 A,  5 B,  6 A,  6 B,  7 A and  7 B show various embodiments of the invention. In  FIGS. 5A, 5B ,  6 A,  6 B,  7 A and  7 B, the top flange(s) of an embodiment of the invention are part or full width of the supporting joist top flange ( 1 ). As shown in  FIGS. 4A and 4B , the top flanges extend a part of the width of the supporting joist tip flange ( 1 ). As shown in  FIGS. 5A and 5B , they extend over the full width of the supporting joist top flange. The length of top flanges ( 62 ) corresponds to the width of the flange ( 1 ) of an ‘I’ joist. In  FIGS. 6A and 6B , the top flanges ( 62 ) adjoin upper return legs ( 90 ). The length of top flanges ( 62 ) corresponds to the width of the top flange of an ‘I’ joist and return legs ( 90 ) adjoin the top flanges. The upper return legs ( 90 ) project downwardly from the top flange ( 62 ) for abutting the side of a joist flange ( 1 ) distal to the stirrup of the hanger ( 10 ). Alternatively, shown in  FIGS. 7A and 78 , is an embodiment of the hanger ( 10 ) has no top flange(s) ( 62 ); top flanges ( 62 ) are absent.  
       FIGS. 7A, 7B ,  8 A,  8 B,  9 A and  9 B, show additional embodiments of the invention including variations to the bottom flange(s). As shown in  FIGS. 7A and 7B , the bottom flange(s) extend a part width of the supporting joist bottom flange ( 3 ). As shown in  FIGS. 8A and 8B , the bottom flange(s) extend over the full width of the supporting joist bottom flange and adjoin return legs ( 91 ). The length of bottom flanges ( 80 ) corresponds to the width of the flange of an ‘I’ joist and return legs ( 91 ) adjoin the bottom flanges. The lower return legs ( 91 ) project upwardly from the bottom flange ( 80 ) for abutting the side of a joist flange ( 3 ) distal to the stirrup of the hanger ( 10 ). In another embodiment, the bottom flanges ( 80 ) extend from the back flanges ( 61 ) proximal to the seat ( 50 ) as shown in  FIGS. 7A, 7B ,  8 A and  8 B. Alternatively, as shown in  FIGS. 9A and 9B , an alternative embodiment of the hanger ( 10 ) has a single bottom flange ( 80 ) which is coplanar with and extends from the seat ( 50 ) of the stirrup.  
      Referring to  FIG. 10 , back flanges ( 61 ) of an embodiment of a hanger ( 1 ) according to the invention project inwardly toward each other from side flanges ( 30 ,  40 ).  
      It will be apparent that, in one embodiment of the invention, the top flange(s) ( 62 ), back flange(s) ( 61 ) and bottom flanges ( 80 ) together define a ‘c’ shape. The opening of which comprises a mouth ( 110 ). However, the embodiments of the invention include within their scope any combination of the top and bottom flange variations described herein.  
      In the various embodiments set forth above, the top flange(s) ( 62 ), upper return leg(s) ( 90 ), back flange(s) ( 61 ), side flange(s) ( 30 ,  40 ), bottom flange(s) ( 80 ) and lower return legs ( 91 ) may include fixing apertures for receiving fixings. However, it will be apparent that the fixing apertures could be absent or present. The fixing apertures are optional and any combination is possible. The fixings (not shown) facilitate connection to one or more joists ( 1 ,  2 ,  3 ). In the embodiment of  FIG. 4 , suitable locations of fixing apertures are shown. It will be recognized that any number of fixing apertures may be utilized.  
      In addition, the seat may define one or more fixing apertures for receiving a fixing (e.g. a nail or screw). In one embodiment, the fixing apertures are positioned to facilitate fixing to the flange(s) of an ‘I’ joist. In addition, the fixing apertures in the seat may be staggered to minimize the risk of splitting wooden flanges of an ‘I’ joist.  
      In another embodiment, at least one of the back flanges includes one or more fixing apertures for receiving a fixing (e.g. a nail or screw). Again, such fixing apertures are positioned to facilitate fixing to the flange(s) of an ‘I’ joist. In addition, the fixing apertures in the back flange may be staggered to minimize the risk of splitting wooden flanges of an ‘I’ joist.  
      In addition, the bottom flange(s) may include one or more fixing apertures for receiving a fixing (e.g. a nail or screw). Again, such fixing apertures are positioned to facilitate fixing to the flange(s) of an ‘I’ joist. In addition, the fixing apertures in the bottom flange may be staggered to minimize the risk of splitting wooden flanges of an ‘I’ joist.  
      Still further, at least one of the top flanges may include one or more fixing apertures for receiving a fixing (e.g. a nail or screw). Such fixing apertures may be positioned to facilitate fixing to the flange(s) of an ‘I’ joist. In addition, the fixing apertures in the top flange may be staggered to minimize the risk of splitting wooden flanges of an ‘I’ joist.  
      In use, an embodiment of a joist hanger according to the invention can be fixed to a supporting joist wherein the bottom flange abuts a bottom surface of the supporting joist and the back flange abuts a side surface of the supporting joist. The stirrup of the joist hanger projects from the supporting joist and is capable of receiving and supporting a further joist.  
      In the various embodiments set forth above, where a top flange is present, the top flange may adjoin a back flange distal to the seat and in a plane approximately parallel to a plane including the seat. The bottom flange, back flange and top flange may form a bracket for abutting a lower surface, a side surface and an upper surface of a joist.  
      In embodiments of a joist hanger according to the invention which include at least one lower return leg, the leg may adjoin the bottom flange such that the back flange, bottom flange and the lower return leg forming a bracket for abutting a joist.  
      In embodiments of a joist hanger according to the invention including at least one upper return leg which adjoins the top flange, the back flange, top flange and the upper return leg may form a bracket for abutting a joist.  
      In various embodiments, the upper and/or lower return legs lie in a plane or planes approximately parallel to a plane including the back flange(s).  
      The upper and/or lower return leg(s) may include one or more fixing apertures for receiving a fixing (e.g. a nail or screw). Such fixing apertures may be positioned to facilitate fixing to the flange(s) of an ‘I’ joist. In addition, the fixing apertures may be staggered to minimize the risk of splitting wooden flanges of an ‘I’ joist.  
      Tests carried out demonstrate that an embodiment of a hanger according to the invention has a significantly higher failure load compared to hangers which fall outside the scope of the invention.  
      In one test, performance of an embodiment of the invention as shown in  FIG. 4  was compared to a similar joist hanger having no bottom flanges.  
      In the test, a joist hanger having no bottom flanges having a thickness of about 1.5 mm was fixed to appropriate joists and subjected to a load in a downward direction for a period of 10 minutes. The test was repeated a number of times and the mean failure load was 11.66 kN.  
      Thereafter, an embodiment of a hanger according to the invention as shown in  FIG. 4  having a thickness of about 1.5 mm was fixed to appropriate joists. One nail was used to fix each bottom flange to a supporting hoist. The embodiment was subjected to a load in a downward direction for a period of 10 minutes. The test was repeated a number of times and the mean failure load was 13.91 kN.  
      The test demonstrates that the tested embodiment had a failure load 20% higher than a similar joist hanger falling outside the scope of the invention.  
      All papers and documents which are referred to herein are hereby specifically incorporated herein by reference.  
      It will be appreciated that there are many different variations of hanger which may be envisaged incorporating the teachings of the present invention. Wherever joists are referred to in this description, the skilled artisan will realize that such a term is used by way of example only and that other forms of supporting structure may be used in conjunction with embodiments of the invention.  
      Accordingly, in a second aspect the invention provides a method for connecting a first and second joists which comprises the step of fixing a joist hanger according to a first aspect of the invention to the second joist and fixing the first joist to the joist hanger.  
      Advantageously, it has been found that when a first joist is connected to a second joist according to an embodiment of the method, the ability of the bottom flange of an ‘I’ joist to rotate relative to the web of the ‘I’ joist is greatly reduced.  
      Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. In addition, all of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.  
      It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art.  
      Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications are covered by the appended claims.  
      The foregoing detailed description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The described embodiments were chosen in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.