GB2176229A

GB2176229A - Formwork beams

Info

Publication number: GB2176229A
Application number: GB08610745A
Authority: GB
Inventors: Andras Szucs
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-05-02
Filing date: 1986-05-01
Publication date: 1986-12-17
Anticipated expiration: 2006-05-01
Also published as: GB2176229B; GB8511199D0; GB8610745D0

Abstract

Description is given of extruded aluminium structural beams (20) having their cross-sections shaped for cooperation with connecting means, said connecting means being used for assembling continuous support lengths of desired dimension in each application by connecting said beams in series with variable overlap of their ends. According to the invention beam (20) includes support surfaces (26,28) located on side of beam with lesser projection of flanges (25,27) said surfaces lying in planes convergent towards main axis (46) said axis being perpendicular to plane of flexure. Line of action (39) of support forces is directed towards plane of web (45) and has inter-section (47) with it within the cross section. In such arrangement internal stresses due to eccentricity of support forces are substantially reduced. Torsioin of the beam (20) due to support arrangement is lessened by the proximity of the shear centre (38) to the plane of joint (37). Joints of the beam are held together by bolt-heads engaging in T section slots at the end of the flanges. <IMAGE>

Description

SPECIFICATION Structural beam This invention relates to scaffolding, formwork and like structures that are constructed of reusable and demountable components in varying assemblies for each use.

Primarily the components would include a structural beam, hereinafter referred to as "of the type described". The cross section of such beam includes a web extending perpendicularly between flanges at its opposed ends, each said flange extending to a lesser extent -on one side of the web than on the other side and the said one side includes formations as means for connections. The components would further include connecting elements of various kinds that serve either to join two of the beams to each other or to join a beam to means of support.

Known types of beams in general use are mostly of symmetrical cross-section and their joints are made with centre line alignment.

These joints include end to end butting of beam ends for the provision of continuous line supports that are placed on vertical props.

This type of joining method has two disadvantages. One is that the combined length of the beam members is usually different from the working length required. The other is that on flexural members an end to end joint is weak and should preferably be located over a support. The current practice is necessitated by the use of structural beams that are such that their cross section is symmetrical about two perpendicular planes.

In my pending Application published as GB 2 147 344A there are descriptions of structural assemblies making advantageous use of beams not having axes of symmetry. These beams are of "the type described" and preferably so designed that their shear centre lies between that side of the web which is towards the lesser flange extensions and the plane that lies through the extremities of said extensions.

Generally the beam will include means on said one side of the web for attaching the beam to support means thereof such that all forces transmitted from the support means to the beam act on the beam in the region between said one side of the web and the extremities of the flanges on said one side.

In this way the beams are subject to low or even non-existent torsional forces at the support means enabling use of beams of lighter construction than that of conventional beams for a similar given application.

The support means may comprise a support stool, a support bracket or a like structural beam.

This invention lies in the presentation of beams of advantageous design for use in assemblies that were the subject of my earlier application referred to above. According to the invention there is given a beam of the type described whose cross section includes on the side, with formations for the engagement of connecting means one or more support surfaces whose plane or planes are inclined and converge with the major principal axis of inertia towards the other side of the beam.

It can be stated that the primary load transfer between structural beams and elements connecting them is effected through the respective contact surfaces of both beams and connectors. It can be assumed that these transmitted forces would be at right angles to the surfaces.

In the connections of beams of the type discrived forces that would be generated by structural continuity are parallel with both the plane of joint and the plane of the web. Accordingly the contact surfaces can be designed to be at right angles to the web to correspond to the location and direction of the support forces. However, in practice this is not the optimum arrangement.

It will be shown in the following that there are several advantages in choosing contact surfaces for load transfer on the structural beams whose plane is not at right angles to the plane of the web. According to the invention the contact surface formed on the flange should be closer to the centre of the beam at its joint to the web than it is at the side of the beam referred to as the plane of joint and is defined by the extremities of the shorter portions of the flanges.

The invention will be further apparent from the following description, with reference to the several figures of the accompanying drawings, which show, by way of example only, a number of structural beams of the kind referred to as embodying the invention, and means connecting with the beams enabling their use in a wide range of applications, which again are given only by way of example.

Of the drawings: Figure 1 shows a diagrammatic plan view of a formwork support comprised of beams of the type described carried on supporting props; Figure 2 is a cross section on the line B-B of Fig. 1 showing a supporting prop and two symmetrically carried support beams; Figure 3 is a cross section on the line C-C of Fig. 1 showing a supporting prop and single offset beam; Figure 4 is a cross-section on the line D-D of Fig. 1 showing two beams lapped side-byside and connecting means therefor; Figure 5 is a view similar to that of Fig. 4 utilising alternative connecting means bolted to the web at the end of one beam; Figure 6 is a cross section through a modified beam carried by a support stool; Figure 7 shows the cross section of a struc tural beam according to the invention.Some reference lines are marked to illustrate relationships of sectional characteristics; The invention will now be described with reference to the accompanying drawings.

Fig. 1 shows how beams of the type described can be used to support soffit formwork for a slab extending between four walls shown at 101-104 inclusive.

The falsework consists of vertical props which are shown at 10. These props are arranged on a rectangular grid and are interconnected by horizontal scaffolding tie members shown at 12. Similar ties at right angles to those shown are obscured by the beams above them. The beams 20 are carried by the props 10 and form primary support on the parallel grid lines.

It can be seen that there are various combinations of available beam lengths which can make up the required support length with one or two adjustable laps in this example. These laps may be located at midspan or over supports depending on the beams used.

The load bearing capacity of the props 10 depends in part on the eccentricity of the loads applied to their head plates. It will be understood that props carrying a single beam 20 are subjected to eccentric loads due to the offset of the beams. The design of beam 20 and support means therefor reduce the effective eccentricity.

The primary support beams 20 carry secondary beams 13 which support plywood sheeting onto which the wet concrete can be poured. In known use, as is shown, the required combined working length of the secondary beams can be effected by forming lap joints over a primary beam. It can be stated if beams of the type described are also used as secondary beams the laps to form combined lengths can be located independant of the position of the primary beams.

Figs. 2 to 4 inclusive show details of structural arrangement of beams 20 and prop 10 at typical positions indicated on Fig. 1.

Fig. 2 shows two beams of the type described located symmetrically over a prop.

It will be seen that each of the beams 20, which is an aluminium extrusion, has a cross section which includes a web 21 which extends perpendicularly between flanges 22 and 23 which extend to a lesser extent on one side of the web 21 than the other such that the shear centre of the beam 20 lies between said one side of the web 21 and the extremities of the flanges 22 and 23 on that side.

The shorter portions of each of the flanges 22 and 23 are of equal width. The shorter portion of the flange 22 is substantially thicker than the longer portion and shaped to provide a slot 24 of T-section which opens into the plane connecting the extremities of the shorter portions.

The slot 24 divides the shorter portion of flange 22 into a pair of limbs shown at 25 and 26. The designed strength of these limbs and that of the short portion 27 of flange 23 is such that all forces associated with the support of the beam can be transmitted through them to support means.

The width of the longer portions of the flanges 22 and 23 need not be equal. However, the overall geometry of the beam should preferably be so designed that the principal axes of inertia of the section be parallel and normal to the plane connecting the extremities of the shorter portions.

As shown, the two beams 20 are carried by a headplate 11. They are disposed in juxtaposed relationship with the plane of contact between the extremities of the shorter portions of the flanges 22 and 23 concentric with the prop 10.

Vertical loads on the formwork are transmitted to the top of the upper flanges 22 and passed down to headplate 11 through the underside of the lower flanges 23. The webs 21 are subject to compression but buckling is restrained by mutual buttressing.

As can be seen from Fig. 3 a support stool 30 is provided between each headplate 11 and an eccentrically positioned single beam 20.

The stool 30 comprises a baseplate 31 and upstanding cranked flange 32 and includes an abutment 33 that bears against the underside of the limb 26 on the upper flange 22 so that the beam is suspended preventing compression in the web 21 in the region of the prop 10 and transferring vertical forces to the headplate 11 with small eccentricity relative to the prop 10. The stool is secured to the beam by the engagement of a cranked top projection 34 in slot 24 in the flange 22.

It will be understood that headplates 11 carrying stools 30 are set at a lower level than the others so that all beams 20 lie in a plane parallel to the slab soffit.

Stool 30 which is an aluminium extrusion provides support for beam 20 for load transfer with least eccentricity. If more eccentricity is acceptable, similar means can be mounted on the side of a prop 10 at some intermediate level for the support of beam 20. These means would also effect primary load transfer from the upper half of beam 20.

The alternative means mounted on the side of the prop may include T headed bolts which by engaging in slot 24 provide for secure attachment to beam 20.

As shown in Fig. 4 where two beams 20 overlap, without underlying support, they are joined at both beam ends by connecting means 40 to prevent lateral separation and relative vertical movement.

Each connecting means 40 comprises an aluminium extrusion of h-shaped cross section having a long leg 42, a curved short leg 41 and a connecting crossbar 43.

To effect a connection the curved legs 41 of each of the means are inserted into slot 24 of one of the beams 20 respectively, and the means are rotated to align their long legs 42 with the slot 24 at the end of the other beam. After alignment the means are slid along the first beam to locate legs 42 in slot 24 of the second beam.

A stop is provided on one end of each means 40 to prevent excessive penetration of the second beam and to facilitate removal.

It can be seen that substantial vertical movement between the beams is prevented by the crossbars 43 which are subjected to shear in the plane of joint.

Fig. 5 illustrates alternative connecting means 50 for a lap joint of two beams 20.

These means include splice plates which are aluminium extrusions comprising of a web 51, two flanges 52 and 53 and a fin 55. The web and the two flanges are symmetrical about the vertical centre line of the web. This centre line lies on the plane of joint between the two beams when the latter are in side by side contact. As the fin 55 is located on one side of the centre line it would prevent the full face contact between the two beams. To allow such contact the fin is cut away from that portion of the splice plates which are placed within the length of the overlap. These said portions are provided with bores that can line up with respective bores on the end of each beam. The beam on right hand side has a splice plate attached to it by the use of bolts 57 located in the respective bores on the two components.On the portion of the splice plates that extends beyond the beam ends, fin 55 is retained and is provided with a bore 56.

A T-headed bolt not shown located in bore 56 can be brought into engagement in slot 24 of the beam on left hand side.

The foregoing is the description of the arrangement on one side of a lap joint between two beams 20. On the other side of the joint the roles of the beams are reversed.

It can be understood that two splice plates at either end of the overlap of two beams and bolts located in bores on the splice plates will prevent the sideways separation of the said beams. Forces acting on one beam in a plane parallel to the webs 21 and 51 are transferred to other beam through bearing contact of limbs 26 and 27 on flanges 52 and 53 respectively.

Fig. 6, wherein like parts are indicated by like reference numerals, shows a beam 60 of different cross section having the lower flange 23 profiled to provide a T sectioned slot.

The beam 60 has upstanding walls 61 and 63 which with the upper flange 22 (or part thereof) define a channel 62 to locate a timber nailing strip to facilitate attachment of secondary supports or plywood sheeting.

This beam section has no axes of symmetry but it is preferably so designed that the two axes of principal Moments of Inertia are parallel and perpendicular to the plane of the web respectively.

As before, beam 60 can be suspended on a support stool 30 of similar design to that described whose upper edge 33 bears against the underside of the upper flange 22 so that the beam is suspended preventing compression in the web 21 in the region of the prop 10 and transferring vertical forces to the headplate 11 with small eccentricity relative to the prop 10. The stool is secured to the beam 60 using a T-headed bolt engaging the slot 65 and a bore 66 in the flange 32.

Fig. 7 shows a sectional view of a symmetrical structural beam according to the invention.

The beam 20 has a web 21 extending between upper flange 22 and lower flange 23.

There is an axis of symmetry shown at 46 on which is located the shear centre 38.

The shorter portion of the upper flange is divided into two limbs 25 and 26 by the Tee slot 24. Similarly the shorter portion of the lower flange is divided into limb 27 and limb 28 by Tee slot 29.

Several reference lines are given on the drawing. These indicate the plane of joint 37, the centre of the web 45 and the line of action of continuity forces and support reaction 39.

The support forces of the shown beam when placed on vertical props are acting on the lower surface of limb 26. Similarly shear forces associated with the provision of flexural continuity will act on the upper surface of limb 28 and the lower surface of limb 26.

The force acting on limb 26 is assumed to act at the centre of the limb at right angles to the surface. It causes bending in the limb.

Similar action would be occurring on limb 28.

Appropriate material provision is made by having the thickness of the limb larger in the vicinity of 36 than in the vicinity of 35.

It can be seen from the diagram that the line of action of the force on limb 26 as shown at 39 converges with the centre line of the web 45 and intersects it at point 47. As the vertical shear is distributed along the beam through its web the internal stresses in the section due to the shear forces are minimised by the shown arrangement.

It should be noted that the horizontal component of the joint forces created by the inclined contact surface of the limb are compensated by friction and small additional tie forces normal to the web which need to be taken into account for the design of the connectors.

The connectors that are made to cooperate with the sloping bearing surfaces on limbs 26 and 28 have corresponding sloping surfaces.

It can be understood that displacement of the connectors relative to the beam in a direction at right angles to the web, while contact of the surfaces is maintained, is accompanied by relative vertical movement of the same parts. This can be regarded as a wedging arrangement for load taking and load release of support assemblies. Load release associated with simultaneous disassembly is particularly useful in temporary support structures.

Some connector means as was described in the foregoing (Fig. 5) could be of a size that would engage both limbs 26 and 28 simultaneously. Due to inaccuracies of the extrusions, the inclined contact surfaces on the limbs 26 and 28 would not in all cases be good match for the connectors. The wedge-like arrangement in the geometry of the sections can help in accommodating tolerances.

The sloping surface provision for contact surfaces as described in the foregoing can be included in structural beam sections by means other than the shaping of the divided inner limb or limbs of the shorter portion of the flanges.

It will be appreciated that it is not intended to limit the invention to the above example only, many variations such as might readily occur to one skilled in the art being possible, without departing from the scope as described in the foregoing.

Claims

1. Structural beam of the type described in whose cross section on the side provided with formations for connecting means there are included one or more support surfaces of inclined plane said planes being convergent with the major principal axis of moment of inertia of the beam towards its other side.

2. Structural beam according to Claim 1 whose shear centre is located within the area defined by the extremities of the shorter portions of the flanges, and the outside of the web near to that side.

3. Structural beam according to preceeding Claims 1 and 2 having inclined support surfaces located on the faces directed inwards of the shorter flange portions.

4. Structural beam according to preceeding Claims 1 to 3 inclusive in whose cross section at least one shorter flange portion is so shaped to define a slot of T section opening into the plane connecting the extremities of the shorter portion of the flanges.

5. A structural beam according to Claim 4 in whose cross section both said shorter portions are so shaped.

6. At least two structural beams according to Claims 1 to 5 inclusive included in an assembly providing combined length where the overlapping ends of said beams are connected side-by-side or in a close spaced arrangement using connecting elements located in the space between said beams for the transmission of forces from one said beam to the other.

7. An assembly according to Claim 6 including beams according to Claims 4 and 5 arranged with their webs parallel and disposed in a side-by-side relationship such that the entrances to the T section shaped slots of one of the beams are juxtaposed with the entrances to those in the other beam and including connecting means located in said oppositely disposed T section shaped slots for fastening the beams against lateral separation and vertical movement relative to one another.

8. An assembly according to Claim 6 including beams according to Claims 4 and 5 arranged with their webs parallel and disposed in a side-by-side or closely spaced relationship and including connecting means attached by bolts located in through holes to the end of one beam and also attached by hammer headed bolts to T section slots of other beam at a location intermediate of its ends.

9. Connecting elements used in assemblies according to Claim 8.

10. Structural elements and assemblies substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1 above have been deleted or textually amended.

New or textually amended claims have been filed as follows:

1. Structural beam of the type described in whose cross section on the side provided with formations for engaging connecting means there are included one or more inclined support surfaces directed towards the axis of major inertia of the section such way that the distance of said surfaces from said axis is less when measured near to the plane of the web than when it is measured near to the plane containing the edges of the shorter flanges.