GB2340141A - Cold rolled steel joist - Google Patents

Description

2340141 1 STEEL JOIST This invention relates to joists particularly joists

for use in floor joist systems.

Conventional floor joist systems incorporate timber joists and have a primary requirement of supporting applied floor loads as well as floor finishes, ceiling materials and fixings underneath. Although they are largely cost effective in their design and application, there are a number of areas where improvements are possible.

Conventional timber floor joist systems require large cross sections and depths for attaining spans greater than approximately 5 metres. The provision of services between floors and ceilings is an essential aspect of modern construction. Current conventional floor joist systems do not easily cater to these requirements and generally, joist modifications in the form of holes and cut-outs are required to facilitate the distribution of sewage, plumbing, gas, ventilation and electrical wiring services. Without adequate control, the structure can be compromised.

According to the present invention a joist is made from shaped pieces of cold rolled steel, preferably galvanised, connected to form an open framework or lattice. In the preferred form two shaped lengths of cold rolled steel are connected by struts to form the framework or lattice. Preferably the lengths are similar T-sectioned lengths and the struts are angle sectioned.

2 The prime structural advantage of the steel joist is its light weight and the potential for achieving long spans without the need for large joist depths and cross sections. It also has advantages such as accessibility and material performance which apply to any span. The lattice construction of the joist in accordance with the invention has sufficient voids within its basic framework to allow service pipe work and cablings through the joist without any extra effort required on site or any structural modifications.

In terms of material degeneration, steel performs far better than timber and degeneration as a result of infestation is not possible. Galvanised steel gives extra corrosion protection in comparison with plain carbon steel.

With advantage each stem of a T-sectioned length is of double thickness with a foid at the base and the outer ends of the angled sectioned struts are folded inwardly. This provides a safeguard against fretting or damage of service pipe work, wiring or cabling.

In the preferred construction the T-sectioned lengths have their stems extending towards one another in a common plane and the struts are connected between these stems on opposite sides thereof with the struts on one side extending at an angle to the vertical sloping in the opposite direction from the struts on the other side. These struts are preferably at an angle of about 45', for example in the range 35-551 to the vertical. The struts and T-sectioned lengths may be connected by any convenient means such as by punch riveting.

Preferably the joist is provided with end pieces of box sec tion providing a vertical channel. The box sectioned end pieces are formed in one piece from cold rolled galvanised steel and are provided with a pair of outwardly extending parallel spaced flanges for connection to the stems of the T-sectioned lengths.

3 Preferably the joist is provided in combination with one or more joist hangers adapted to be connected to the joists and formed from connected pieces of cold rolled steel. In one form each joist hanger comprises a pair of angled section pieces connected into a T-formation with the stem of the T having two parallel legs spaced apart and the arms of the T connected to a further angle or channel sectioned piece.

The invention extends to such joist end pieces and joist hangers independently of the joist.

One embodiment of joist and alternative end pieces and alternative joist hangers for use therewith will now be described, by way of example only, with reference to the accompany drawings of which- Figure 1 is a perspective view of a floor joist; Figure 2 is a side view of the joist on an enlarged scale; Figure 3 is an exploded view of the joist on a still further enlarged scale; Figure 4 is a perspective view of one T-sectioned length for such a joist; Figure 5 is a perspective view of one angle sectioned strut for such a joist; Figure 6 is a perspective view of one end section for the joist; Figure 7 is a perspective view of an end cap for the end section of Figure 6; 4 Figure 8 is a perspective view of an alternative end cap.

Figure 9 is a perspective view of one form of joist hanger; Figure 10 is a perspective view of a modified joist hanger; and Figure 11 is a perspective view of a further form of joist hanger in combination with an I-sectioned beam.

As seen generally in Figures 1, 2 and 3 a joist is formed from two similar T-sectioned lengths of Z28 pre-galvanised steel 12 connected by a plurality of angle sectioned struts 13 to form a lattice. Each of the lengths 12 is cold rolled from steel strip so that the stem 14 of the Tsection is of double thickness with a fold at its base 15 and with the two arms 16 extending horizontally outwardly from one another. Each of the struts 13 is cold rolled from steel strip to an angle section having a relatively long arm 17 and a relatively short arm 18 having respective inwardly turned edges 19 and 20. Two lengths 12 are located one above the other with their stems 14 extending towards one another in a common plane so that the arms 16 form essentially horizontal top and bottom surfaces of the joist. The struts 13 are connected between the stems 15 of the two lengths 12 at angles of approximately 450 to the vertical with the struts on one side of the stems sloping in one direction to the vertical and the struts on the other side of the stems sloping at the opposite angle to the vertical. The struts have the outside surface 21 of the longer arm 17 connected to the stems 15 so that the folded edges 19 and 20 are on the outside.

The folded bottom edge 15 of the stem of each T-section provides a safe working edge for the carrying of the joist and also as a safeguard against fretting or damage of service pipe work, wiring or cabling. The angled section of the struts provides structural strength as well as strong buckling resistance. The folded edges of the struts provide a safe edge for the component, thus making the joist easy to handle and more manageable. In addition the safe edges reduce the likelihood of fretting of service pipe work, cabling and wiring fed through the voids between the struts. In addition the presence of folded edges serves to stiffen the components and improve structural rigidity and buckling resistance. Dutch folding also leads to work hardening of the material situated about the fold, thus increasing the yield stress of the steel at the section edges and providing a material strength at areas of high stress concentration, namely at the strut ends towards the joist extremities.

The joist can be fabricated through the use of any appropriate fastening connecting the angle section struts to the top and bottom Tsectioned lengths. For example the parts may be punch rivetted together.

As seen in Figure 2, the angle section struts end before the ends of the joist leaving parts of the T-sectioned pieces extending outwardly. Preferably steel end pieces 24 are positioned at the joist ends between the protruding parts of the T-sections.

As seen in Figure 6, an end piece 24 preferably consists of a box section 25 with two protruding connecting flanges 26, 27, the whole being manufactured by folding a single piece of sheet metal. The end piece 24 is connected to the basic joist by the attachment of the connection flanges 26, 27 to the inside surfaces of the arms 16 of the top and bottom T-sections 12. The bottom surfaces 28 of the top T-section are in contact with the top edges 29 of the flanges 26, 27 and likewise the upper surfaces 30 of the bottom T-section contact the bottom edges 31 of the connection flanges 26, 27. The end pieces 24 provides structural reenforcement at the highly loaded ends as well as providing a vertical enclosed channel for the purpose of sealing built in joists within brickwork and attachment of noggins for plasterboard connection. The noggins are attached to the box section surface 32 facing in the direction of the main joist axis, furthest away from 6 the joist end. The vertical height and lateral (with respect to the main joist axis) width of the box section are dimensioned to correspond with and provide a tight fit within the outer edges of the T-sections.

For applications of the floor joist system where the joists are built in to the external brickwork of the house, a plastics end sleeve 35 (Figure 7) is placed over the end of the joist over the top and bottom Tsectioned lengths and covering the end piece 24. The plastic end sleeve 35 is made from a polymer material which provides the necessary material properties to meet standard criteria for fire resistance, and when adequately packed into the brickwork it acts as a seal against smoke movement through the joist cavity. The plastic end sleeve also prevents water seepage through to a joist end and provides thermal insulation between the wall cavity and the end of a steel joist.

As an alternative, shown in Figure 8, a slotted end cap 55 of insulating material such as plastics or wood could replace the separate steel end piece 24 and plastics end sleeve 35. The end cap 55 comprises a pair of parallel vertical hollow box sections 56 connected to an end plate 57. The box sections are dimensioned to slot into the end of the joist contacting the inner surfaces of the two T-sections and providing attachment points with the end plate against the joist end. This provides thermal insulation, and a water and smoke seal.

Figures 9, 10 and 11 show three types of joist hanger which are particularly designed to be associated with a joist system using the joists as described. A steel end hanger 40, as seen in Figure 9, is formed of three angle sectioned lengths 41, 42 and 43 of metal connected to provide a vertical support for a joist at a wall face. Two similar ones 41, 42 of the angle sections have their larger arms 44 in parallel with a gap 45 between them to allow the web of a joist upper T-section to be inserted. The height of the joist hanger is selected such that the top and bottom surfaces of the 7 longer arms 44 are in contact with the inner surfaces 28, 30 of the arms 6 of the top and bottom T-sectioned lengths. The other two shorter arms 46 of the angled sections extend in a common plane away from one another and are secured to the body 47 of the third angle section 42 having a horizontally outwardly extending arm 48 which is used to fix the hanger into the brickwork. The two parallel angled arms 44 provide direct support to the joists and are vertically offset from the outwardly directed support arm 48 to provide a level finish between the top of the floor joist and the top surface of the third angle section 42.

The second type of joist hanger 50, as shown in Figure 10, has a basic shape and function similar to that of Figure 9 except that the third angle section 43 is replaced by a channel section 51. The channel section flanges 52 may be fixed to the internal faces 28, 30 of the top and bottom joist T-sections at any required point along the span of a joist. The joist is designed to have a clearance of a few millimetres between the strut ends and the inner surfaces of the top and bottom T-sections. A joist may then be hung off the hanger 50 perpendicular to the joist to which the hanger is fixed. The parallel angle sections 41, 42 provide a similar function to those of the end hanger 40, namely to providing vertical support to the connecting joist.

An alternative version of this joist hanger is shown at 53 in Figure 11 and is similar except that the two vertical sections 41, 42 are offset vertically at greater distance below the top flange 52 of the channel section 51. This hanger is used when connecting a steel joist to a hot rolled I-beam section 54. The vertical offset of the two parallel angled arms 44 ensures that the correct joist height is achieved with respect to the flooring and plasterboard height.

Claims (13)

8 CLAIMS

1 A joist produced from shaped pieces of cold rolled steel and connected to form an open framework or lattice.

2. A joist as claimed in Claim 1 in which the cold rolled steel is galvanised.

3. A joist as claimed in Claim 1 or Claim 2 comprising two shaped lengths of cold rolled steel connected by struts to form the framework or lattice.

4. A joist as claimed in Claim 3 wherein the lengths are similar T sectioned lengths and the struts are angle sectioned.

5. A joist as claimed in Claim 4 wherein each stem of each T-sectioned length is of double thickness with a fold at the base and the outer ends of the angled sectioned struts are folded inwardly.

6. A joist as claimed in Claim 4 wherein the T-sectioned lengths have their stems extending towards one another in a common plane and the struts are connected between these stems on opposite sides thereof with the struts on one side extending at an angle to the vertical sloping in the opposite direction from the struts on the other side.

7. A joist as claimed in Claim 6 wherein the struts are at an angle in the range 35-551 to the vertical.

8. A joist as claimed in Claim 7 wherein the struts and T-sectioned lengths are connected by punch riveting.

9 9. A joist as claimed in any one of the preceding claims provided with end pieces of box section to define a vertical channel.

10. A joist as claimed in Claim 9 wherein the box sectioned end pieces are formed in one piece from cold rolled galvanised steel and are provided with a pair of outwardly extending parallel spaced flanges for connection to the stems of the T-sectioned lengths.

11. A joist as claimed in any one of the preceding claims provided in combination with one or more joist hangers adapted to be connected to the joists and formed from connected pieces of cold rolled steel.

12. A joist as claimed in Claim 11 wherein each joist hanger comprises a pair of angled section pieces connected into a T-formation with the stem of the T having two parallel legs spaced apart and the arms of the T connected to a further angle or channel sectioned piece.

13. A joist substantially as herein described and as described with reference to Figures 1 to 11 of the accompanying drawings.