Patent Publication Number: US-5896716-A

Title: Joist splice shoe

Description:
INTRODUCTION 
     The present invention relates to a new piece of hardware for repairing damaged lumber joists of residential buildings. 
     In current practice, a distressed lumber joist is repaired by scabbing plywood or lumber with nails on both the vertical sides of the joist. With such methods, the task of carrying out repairs tends to be a strenuous one. 
     The primary object of the present invention is to provide an alternative hardware for repairing a damaged lumber joist that is sound from an engineering point of view, and easy to use. The invented hardware is a joist splice shoe, which is a U-shaped plate made of steel or any other suitable metal, with unitary prongs used as fastening means. When a single joist splice shoe is attached to a damaged lumber joist across the line or zone of distress, it effectively resists tensile and shear stresses transmitted from the lumber joist. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     The present invention will be more readily understood by reference to the following detailed description when read in conjunction with the attached drawings. 
     FIG. 1 is an isometric view of a typical residential house showing a lumber joist in distress, to which a joist splice shoe of the present invention is attached. 
     FIG. 2 is an isometric view of the distressed lumber joist of FIG. 1 along with the joist splice shoe. 
     FIG. 3 depicts a plan view of the joist splice shoe before bending to its final U-shape. 
     FIG. 4 is an isometric view of a unitary prong of the joist splice shoe. 
     FIG. 5 is a side elevation view of FIG. 2 for illustrating details of the attachment position of the joist splice shoe at the zone of distress. 
     FIG. 6 is a cross-sectional view taken along lines V--V of FIG. 5. 
     FIG. 7 is a side elevation view illustrating another embodiment of the joist splice shoe attached to a damaged lumber joist using nails. 
    
    
     DETAILED DESCRIPTION 
     Repair methods used at the present time mostly depend upon the extent of damage in a lumber joist. In these methods, restoration of a damaged or cracked lumber joist is either by replacing the joist or by scabbing the joist using lumber or plywood and nails. Invariably, this creates the task of carrying out repairs of a distressed lumber joist to be a strenuous one because the repair material used is heavy and unwieldy. The structural adequacy of such a repair is also doubtful. 
     The basic contribution of the present invention involves reduction of the overall weight of repair material by using a joist splice shoe so as to enable convenient repair of a distressed lumber joist. The invention also provides a novel alternative to conventional fasteners by using unitary prongs that add to the ease of affixing a joist splice shoe to a distressed lumber joist. As a single joist splice shoe is used at the zone of distress, repair can be carried out with ease and a minimum of labor. 
     In the FIG. 1 layout of a typical residential house, a distressed lumber joist is indicated by 1, and a metallic U-shaped plate of the present invention known as joist splice shoe is indicated by 2. 
     The lumber joists of FIG. 1 support vertical loads of overlying floors. In each joist, the maximum tensile stress is developed along the lowermost fiber, and is the maximum midway of the length of the joist. Once a crack 3 develops in the lumber joist 1 as shown in FIG. 2, it is the lower portion of the joist which is the most vulnerable. Hence, repair of the lower portion of a distressed lumber joist assumes importance. 
     The novel feature of this invention involves laying out a system to efficiently transfer the developed tensile and shear stresses in a lumber joist at the zone of distress to a plate made of steel or any other suitable metal having higher strength than lumber. 
     FIG. 3 depicts a joist splice shoe before bending to its final U-shape, having length 4 which is dependent on the magnitude of the load supported by the distressed lumber joist or the maximum tensile stress developed in the joist. Numeral 5 indicates lines along which the joist splice shoe is bent, and the numerals 6 &amp; 7 indicate dimensions that depend on the size of the distressed lumber joist to be repaired. 
     The U-shaped joist splice shoe has unitary prongs formed in the sidewalls as means for attachment to a distressed lumber joist. The unitary prongs are indicated by 11, and the isometric view of a unitary prong is shown in FIG. 4. These unitary prongs eliminate the requirement for non-unitary fastening means such as nails. Each unitary prong has an elongated, curved portion tapering to a penetrating end. The penetrating ends are directed towards the surface of the joist to which the joist splice shoe is to be secured. The extremities of the penetrating ends do not extend inside the space between the sidewalls. 
     In its final U-shape, the axes of the unitary prongs in each sidewall are oriented substantially parallel to the plane of the bottom wall. For each sidewall, the center line that is perpendicular to the plane of the bottom wall defines a line of symmetry about which the penetrating ends of corresponding prongs are directed. Because of this arrangement, the grip of a joist splice shoe over a distressed lumber joist increases upon application of load. 
     Orientation of the joist splice shoe 2 with respect to the line of distress 3 of the lumber joist 1 is depicted in FIG. 5. For a proper repair of the distressed lumber joist, effective transfer of stresses to the joist splice shoe is necessary. This is ensured by keeping the joist splice shoe free of unitary prongs or holes along portion 10 of FIG. 5 and along portion 6 of FIG. 6, so that these portions envelop the distressed zone of the lumber joist from three sides, and resist tensile and shear stresses transmitted from the lumber joist. 
     As the first step of attachment of the joist splice shoe, the bottom portion 6 is brought into contact with the bottom surface of the distressed lumber joist ensuring that the middle of portion 10 lies just below the line of distress, and the unitary prongs in portions 9 are flattened with a mallet to ensure complete clasping on the lumber joist at the undamaged portions adjacent to the distressed zone. 
     An alternative embodiment of the joist splice shoe has no unitary prongs and is indicated by 13 in FIG. 7. This alternative embodiment is secured to a damaged joist 1 using nails 12 through its sidewalls at locations corresponding to the locations of unitary prongs 11 of the preferred embodiment indicated by 2. 
     While specific configurations have been set forth for the purpose of describing the novel features of the invention, it should be recognized that such specifics can be varied by relying on the technology as taught, without departing from the principles of the invention. Therefore, in determining the scope of the present invention, reference shall be made to the appended claims.