GB2487759A - A method of building construction with joists having a support nib. - Google Patents

Abstract

The building construction has a wall 130 on which rests a joist 210. The joist has a section removed from the end 116 to provide a support nib 118. In use, the support nib is longer than the planned length so that the joist provides a shorter hanging length 26 to enable the joist to locate between the masonry walls even when the dimension between the walls is smaller than planned. The overall length of the joist is increased by increasing the length of the support nib in use as opposed to the planned length, thus the load bearing value is maintained even when the dimension between the walls is larger than planned.

Description

METHOD OF BUILDING CONSTRUCTION

The present invention relates to building construction and in particular, though not exclusively, to a method of building construction which removes the reguirement for site adjustment of top and bottom hung joists.

During building construction, it is common to erect masonry walls of block or brick which support joists or beams to create floors, ceilings and roofs of the building. The joists or beams may be of solid timber with a rectangular cross-section or, more typically, are I beams or open web beams. In the latter cases, two strips or chords of wood are arranged to provide upper and lower surfaces, the strips are then joined via either; a slim vertically arranged panel, forming the characteristic cross-sectional I'; or, open webs of metal strips which form a zig-zag arrangement on the sides of the strips.

There are a number of ways in which the joists may be supported. For example, each end of the joist can be laid upon a course of bricks so that it is fully supported by the walls, further bricks are laid around and over the full height of the joist to complete the wall. Alternatively, a hanger can be located in the masonry wall, providing a support for the joist to rest against the inside face of the wall.

These construction methods have a number of disadvantages.

Supporting the entire joist end requires cutting of bricks and due to the height of the joist, the mortar located around the joist end has a tendency to settle and sink, thereby creating gaps so that the wall is not sealed. Hangers are of metal construction and thus increase building costs. Hangers also require careful placement and a high tolerance of the joist length to fit in oppositely arranged hangers between two walls.

To overcome these disadvantages, joists are provided to be top or bottom hung. For I joists and open web joists, the top (or bottom) chord is extended to create a nib support. For solid timber, a section is removed from an end of the timber to leave an extension as the nib support. The nib support rests on the supporting masonry wall, while an end face of the joist hangs' on the inner face of the masonry wall. These arrangements provide less joist material to be mortared into the wall and, in the case of solid timber, the height of the nib support can be selected to match the brick height, to reduce the amount of cutting required.

While top and bottom hung joists provide some advantages, they also have a major disadvantage in masonry construction.

Masonry walls can be constructed off plumb and not square resulting in the dimension between the opposing walls being either smaller or larger than the plan. This can cause a problem for joists that are designed to have a nib support built into the supporting wall. The problem when the dimension is too large is that there may not be a large enough bearing area on the joist to support the design load. The problem when the dimension is too small is that the hanging' section of the full height joist will not fit between the opposing walls.

The problem is compounded if the joists are pre-assembled as a floor cassette as any modification on-site to remedy the situation would be difficult if not impossible.

It is therefore an object of the present invention to provide a method of building construction which overcomes at least

some of the disadvantages of the prior art.

It is a further object of the present invention to provide a method of building construction which removes any requirement to modify joists on-site to fit between masonry walls.

According to a first aspect of the present invention there is provided a method of building construction, the method comprising the steps: (a) providing a design plan for a construction; (b) determining a minimum design value for sufficient load bearing, from the plan, for a joist hanging from a masonry wall and supported on the wall by a support nib at an end of the joist; (o) determining a planned overall length of the joist and a planned hanging length of the joist from the design value; (d) providing an engineered joist having an overall length at least as long as the planned overall length and a hanging length less than the planned hanging length; (e) constructing the masonry wall; and (f) locating the engineered joist upon the masonry wall such that the hanging length lies inside the wall and the support nib lies on the wall.

By profiling the joist to provide a narrower hanging length, the joist will now locate between the masonry walls even when the dimension between the walls is smaller than planned. By increasing the overall length of the joist, the load bearing value is maintained even when the dimension between the walls is larger than planned. Thus the building can be oonstruoted without having to modify the joist on-site, or compromise the load bearing performance.

Preferably, the distance between the overall length and the planned overall length is equal to the distance between the hanging length and the planned hanging length. This simplifies the calculation and ensures that the minimum load bearing on the supporting wall is maintained by ensuring the surface area of the joist on the wall is maintained.

Alternatively, the overall length is egual to the planned overall length. This may be the case when the minimum load bearing capacity is calculated with a relatively large safety margin.

The method may include the use of I joists, open web joists or solid timber joists. Alternatively, the joist may be a solid timber joist wherein a reinforcing member is located adjacent the support nib. Such a joist is described in Applicant's co-pending patent application GB 1013134.0.

The method may include the step of determining a height of the support nib for minimum load bearing capacity. This height will be predetermined for I joists and open web, being the height of the chord. Preferably, the height of the support nib in a solid timber joist will be greater than half the height of the joist. Preferably also, the height of the support nib in a solid timber joist including a reinforcing member will be less than half the height of the joist. In this way, an engineered solid timber joist can have a support nib height comparable to I joists and open web joists without compromising performance.

The method may be adapted for a joist having a support nib at each end, with the joist being supported on two oppositely arranged masonry walls. This would allow an engineered joist to be brought to site, knowing that the hanging length will fit between the walls and the load bearing capacity is maintained, regardless of how off-oentre' eaoh wall is with respeot to the other.

The method may include the step of arranging a plurality of the engineered joists in parallel and applying a supporting member aoross the joists to thereby oreate a floor cassette.

The cassette may be used as a ceiling cassette if the supporting member is laid on an opposing edge of the joist. In this way, the cassette can be lifted onto a construction and no adjustment will be required to get the cassette to fit between masonry walls. This greatly speeds up construction time.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figure 1(a) is a schematic illustration of a planned joist hung from a masonry wall; Figure 1(b) is a schematic illustration of an engineered joist hung from a masonry wall according to a an embodiment of the present invention; and Figure 1(c) is a schematic illustration of the engineered joist of Figure 1(b) hung from a masonry wall according to a further embodiment of the present invention.

In modern building construction, a design plan is created by the architects and engineers, which provides a list of the building materials required, including the quantity and sizes.

By bringing pre-cut timbers and exact quantities of components to a site, the build time and costs are reduced as time is not wasted in cutting timbers on site, expensive skilled labour is not required for a majority of the build, and there is minimal waste material to be disposed of.

For a masonry oonstruotion having joists whioh are top or bottom hung, the design plan must include oalculations for the dimensions of the joists to ensure that there is suffioient load bearing oapaoity from the supporting wall. In a typical design plan, the joists will be sized to have a hanging seotion fitting between oppositely arranged walls or other supports, while a supporting nib of the beam has a suffioient length to provide a load bearing surfaoe adequate to support the joist and an expeoted load located upon it. Material oosts are saved in making the length of the nib and oonsequently the overall length of the joist as short as possible.

Referring now to Figure 1(a) of the drawings there is illustrated a joist, generally indioated by referenoe numeral 10. The joist 10 is a planned joist, its dimensions being determined in a design plan for the overall building in whioh the joist 10 will be boated. The joist 10 is oonsidered to be of reotangular oross-seotional area (typioally 220mm x 40mm) and has a height measured between an upper surfaoe 12 and a lower surface 14. The joist 10 is designed to be top hung, with a section removed from an end 16 to provide a support nib 18. Support nib 18 is an elongate portion having an upper surface 20 which is co-linear with the upper surface 12 of the joist 10. The support nib 18 has a lower surface 22 created when the section was removed. Similarly, removal of the section creates a face 24 on the end of a hanging section 26 of the joist 10.

In the design plan, the distance between the inner face 28 of a supporting masonry wall 30 and an end location of the joist (not shown) is determined. This is defined as the planned hanging length of the joist 10. Using this oaloulation, the area of the surface 22 of the support nib 18 is calculated to give a minimum design value for sufficient load bearing. With the calculated area, the depth of the support nib 18 is determined. The depth defines the length between the end 16 and the face 24. The planned overall length of the joist 10 is then the combined length of the planned hanging length together with the depth of the support nib 18.

It is noted in Figure 1(a) that the design plan assumes that the joist 10 will be a close fit to the supporting wall 30.

The lower surface 22 of the support nib 18 rests entirely on the top 32 of the masonry wall 30. Perpendicular to the surface 22 is the face 24 of the hanging section 26. The face 24 of the hanging section 26 is intended to meet the face 28 of the wall 30.

In typical building construction, the masonry walls can be constructed off plumb and not sguare. Accordingly, the wall 30 can splay inwards, see the wall 130 shown in Figure 1(b), or outwards, see the wall 230 shown in Figure 1 (c) . The Figures 1(a)-(c) are drawn to similar scale and like parts have been given the same reference numerals as Figure 1(a) with the addition of 100' for Figure 1(b) and the addition of 200' for the Figure 1 (o) As can be seen by comparing Figures 1 (a) and (b), if the wall splays inwards, off plumb, the planned joist 10 would not fit when brought on site as the planned hanging length is longer than the available space on construction of the wall 130. A carpenter would have to chisel or saw a further portion from the planned joist 10 to get it to fit. This both wastes valuable construction time and is expensive to keep a carpenter available. Additionally, the on-site amendment of the joist 10, will require its own quality control on site.

Similarly, as can be seen by comparing Figures 1(a) and (b), if the wall splays outwards, off plumb, the planned joist 10 will fit. However, the entire depth of the support nib 18 will not be supported on the top 32 of the wall 30. A portion of the surface 22 will not rest on the top 32, as a gap will exist between the inner surface 28 of the wall 30 and the face 24 of the hanging section 26. Consequently, the load bearing is now below the minimum design value. This compromises the build.

The present invention overcomes these difficulties by amending the planned joist 10 at the design stage. Joists 110 and 210 are identical. Each joist has the same height both on the hanging section 126,226 and the support nib 118,218. However the depth is increased to increase the surface area of the lower surface 122,222 of the support nib 118,218. This is achieved in two steps. The planned hanging length is shortened and the planned overall length is increased. Consequently a longer joist 110,210 is engineered with a deeper profile below the support nib 118,218.

The engineered joist 110,210 can now be brought to the construction site, in the knowledge that it will fit regardless of whether the masonry wall 30,130,230 is plumb or tilted inwards or outwards.

Figure 1(b) illustrates the engineered joist 110 located upon a masonry wall 130 which is off centre, tilting inwards so that the planned hanging length is shortened. Joist 110 has the face 124 of the hanging section 126 set back, to reduce the hanging length. Additionally the support nib 118 is elongated to provide a greater area and depth to surfaoe 122.

While a gap 134 is shown between the edge 136 where the inner faoe 128 of the wall 130 meets the top 132 of the wall 130, and the oorner 138 where the surfaoe 122 of the support nib 128 meets the faoe 124, this need not be the oase and there is space for the wall 130 to be further off centre. There will, however, always be a gap between the edge 140 where the lower surface 114 of the joist 110 meets the face 124 of the hanging section 126 and the inner face 128 of the wall 130. This is because the face 128 of the wall 130 and the face 124 of the hanging section 126 are non-parallel.

Figure 1 (b) also shows that the depth of the surface 122 of the support nib 128 almost entirely rests on the top 132 of the wall 130. The load bearing is therefore at least maintained.

Figure 1(c) illustrates the engineered joist 210 located upon a masonry wall 230 which is off centre, tilting outward so that while the joist 210 fits easily into place, the gap 234 between the edge 236 where the inner face 228 of the wall 230 meets the top 232 of the wall 230, and the corner 238 where the surface 222 of the support nib 228 meets the face 224, is increased so that a smaller portion of the surface 222 of the nib 218 rests on the top 232 of the wall 230. If the overall length of the joist 210 was that of the planned joist 10, an insufficient area of the nib 218 would be supported by the wall 230 and consequently the load bearing would be seriously compromised. The increased overall length of the engineered joist 210 ensures that the minimum design value for load bearing is maintained.

While a solid timber joist is shown, it will be appreciated that the method works equally for I joists and open web joists where the support nib is formed from the chord. Equally, the joists may be top or bottom hung. For the timber joist illustrated, the height of the support nib is less than half the height of the joist at the hanging section. It is more typical for the nib to extend over a majority of the height of the joist. This provides greater support for the nib.

However, the present applicant's have found that narrower nibs can be achieved if a reinforcing member is located adjacent to the corner where the lower surface of the support nib meets the face of the hanging section. This reinforcing member may be a plate located on one or both sides of the joist.

It will also be realised that the method finds particular benefit when the joist has a support nib at either end. The method is applied independently to each end of the planned joist and the engineered joist will fit in the space between the masonry walls regardless of the direction of the tilt on either of the walls.

The engineered joists can also be incorporated into a cassette by fixing the joists together in a parallel array with a supporting member, which may be a floor. Typically, a floor cassette for a masonry wall cannot be constructed from joists with support nibs as the joists cannot be adjusted on-site as it's too difficult to know which joists need to be adjusted and to give access to a carpenter. By ensuring that all the joists will fit before the cassette leaves the factory, the cassette becomes a valuable labour saving addition to the construction.

The principle advantage of the present invention is that it provides a method of construction which negates the need for site adjustment of top or bottom hung joists.

Further advantages of the present invention are that it provides a method of construction which provides joists which will always fit, speeds up construction time, removes the requirement for skilled tradesmen on site, produces negligible on-site waste, is simple, inexpensive and does not require any additional on site fitting or construction procedures.

It will be appreciated by those skilled in the art that modifications may be made to invention herein described without departing from the scope thereof. For example, the dimensions of all the components can be varied to suit the designer.

Claims (12)

1. CLAIMS1. A method of building construction, the method comprising the steps: (a) providing a design plan for a construction; (b) determining a minimum design value for sufficient load bearing, from the plan, for a joist hanging from a masonry wall and supported on the wall by a support nib at an end of the joist; (c) determining a planned overall length of the joist and a planned hanging length of the joist from the design value; (d) providing an engineered joist having an overall length at least as long as the planned overall length and a hanging length less than the planned C\J hanging length; r (e) constructing the masonry wall; and (f) locating the engineered joist upon the masonry wall such that the hanging length lies inside the wall O20 and the support nib lies on the wall.
2. 2. A method of building construction according to claim 1 wherein the distance between the overall length and the planned overall length is egual to the distance between the hanging length and the planned hanging length.
3. 3. A method of building construction according to claim 1 wherein the overall length is egual to the planned overall length.
4. 4. A method of building construction according to any preceding claim wherein the engineered joist is selected from a group comprising: I joists, open web joists and solid timber joists.
5. 5. A method of building oonstruction according to claim 4 wherein the engineered joist is a solid timber joist including a reinforcing member which is located adjacent the support nib.
6. 6. A method of building construction according to any preceding claim wherein the method includes the step of determining a height of the support nib for minimum load bearing capacity.
7. 7. A method of building construction according to claim 6 wherein the height is predetermined for I joists and open web, being the height of the chord.
8. 8. A method of building construction according to claim 6 wherein the height of the support nib in a solid timber r joist is greater than half the height of the joist.
9. 9. A method of building construction according to claim 6 O20 wherein the height of the support nib in a solid timber joist including a reinforcing member is less than half the height of the joist.
10. 10. A method of building construction according to any preceding claim wherein the method is adapted for a joist having a support nib at each end, with the joist being supported on two oppositely arranged masonry walls.
11. 11. A method of building construction according to any preceding claim wherein the method includes the step of arranging a plurality of the engineered joists in parallel and applying a supporting member across the joists to thereby create a floor cassette.
12. 12. A method of building oonstruction aooording to olaim 11 wherein the oassette is used as a oeiling oassette and the supporting member is laid on an opposing edge of the joist. c\J r c\J