SHOCK ABSORBING SUPPORT

Abstract: A shock absorbing support (10) comprises a base (21, 22), an anchor element and at least three deformable arms (30) each having first and second ends (30A, 30C). The first ends (30A) of the arms (30) are linked together and to the anchor element. The second end (30C) of each arm is attached to a respective base member (21, 22). The arms (30) are arranged symmetrically and the base (21, 22) has resilient means on its underside and adjustable clamping means for clamping the base (21, 22) to a fixed structure at a variety of distances from a mid-point of said base.

Description: SHOCK ABSORBING SUPPORT The present invention relates to height safety systems and, in particular, to a shock absorbing support for use in supporting an elongate safety line such as a wire cable or the like which forms part of a height safety installation. Most particularly, the invention relates to a shock absorbing support for mounting to lightweight roof panels as part of a personnel fall arrest system. Personnel fall arrest systems generally comprise an elongate safety element such as a rail or a stranded wire cable or cable network for linking a worker's personnel safety harness to a rigid structure such as a building. If a fall occurs, it is desirable to reduce the shock loading experienced when the fall is arrested, primarily to reduce the severity of injury to the falling person, but also to minimise the forces applied to the elements of the fall arrest system and to the rigid building structure. Further, personnel fall arrest systems generally include elements which should be replaced or inspected after a fall arrest event has occurred. Accordingly, it is desirable to provide a clear, permanent, visual indication that a fall arrest has occurred. A shock absorbing support is known from the present Applicants' co- pending British Patent Application No. GB 2 325 719. The device disclosed in this earlier application is adapted to be attached to structural members of a building, for example rafters and purlins, through the fabric of a lightweight roof panel. One of the disadvantages of the known shock absorbing support is that it requires attachment to structural members beneath the lightweight roof skin. In some roof constructions, structural members are accessible in only one orientation, which makes attachment of such shock absorbing supports problematic. For example, certain roof constructions are provided only with purlins across the width of the roof span, and there are no associated rafters. Also, lightweight roof structures vary considerably in form and configuration so that it is difficult to supply a universal shock absorbing support that suits all roof types. One way of dealing with this latter problem is to provide shims or spacers that conform to the roof panel profile for a particular building. However, it will be appreciated that the number and types of shims or spacers which must therefore be held as stock items soon becomes inconvenient. It is therefore an object of the present invention to provide a shock absorbing support that is capable of being affixed to a lightweight roof structure without necessarily requiring attachment to underlying structural elements and which is capable of absorbing shock loading by undergoing plastic deformation prior to the occurrence of any buckling in the roof panelling to which it is attached. It is also an object of the present invention to provide a shock absorbing support that is adapted to conform to a wide variety of roof panel profiles. It is a further object of the present invention to provide a shock absorbing support having omnidirectional shock-absorbing capability and which gives a clear visual indication when it has been subjected to a high load such as might be encountered in a fall arrest situation. The invention is a shock absorbing support comprising a base, an anchor element and at least three deformable arms each having first and second ends, the first ends of the arms being linked together and to the anchor element and the second end of each arm being attached to the base, said base having resilient means on its underside and adjustable clamping means for clamping the base to a fixed structure at a variety of distances from a mid-point of said base. Preferably, there are four arms are arranged in orthogonal pairs about the anchor element and the base has a pair of strap elements arranged in a cross formation. The invention will now be described, by way of example only, with reference to the drawings, in which: Figure 1 shows a partial side sectional view of a shock absorbing support according to the invention; Figure 2 is a top plan view of the shock absorbing element of Figure 1 ; Figure 3, views (a) and (b), respectively, show a top plan view and a side view of a resilient seal for attachment to the underside of the shock absorbing support of the invention; Figure 4, views (a) and (b), respectively, show a top plan view and a side view of a resilient pad for attachment to the underside of the shock absorbing support of the invention; Figure 5 is a close-up cross-sectional view of one of the fixing points of the shock absorbing support of Figure 1 , and Figure 6 shows an arm element of the shock absorbing support of Figure 1. Referring to the Figures, a shock absorbing support (10) is shown. The support is formed by a pair of base members (21 , 22) and a pair of arm elements (30). The base members (21 , 22) are substantially planar strips of type 316 stainless steel, typically 60 mm wide and 3 mm thick. In the embodiment shown, base member 21 is considerably longer than base member 22, their lengths being approximately in the ratio 2:1 . Base member 21 is intended to be the primary means of fixing the support (10) to a lightweight roof structure, whilst base member (22) serves as a cross-strap. The two base members (21 , 22) are secured together at their mid-points in a cruciform configuration by a bolt (not shown). Referring now to Figures 3 and 4, these views show a resilient foam material that is attached to the underside of base members (21 , 22). Figure 3 shows a resilient foam seal that is adapted to extend the length of base member (21 ) and which is attached to the underside thereof by double-sided adhesive tape. Figure 4 shows a resilient foam pad adapted to be attached in like fashion to the underside of a portion of base member (22). In practice a foam pad of this type is attached to each end portion of the base member (22) . As best seen in Figure 1 , the foam seal may be cut away in the region of the bolts that secure the arms (30) to the base members (21 , 22). In an especially preferred form of the invention, the resilient material is a low density polyethylene foam having a density of aproximately 18 kg/m 3 . Figure 5 is a close-up cross-sectional view of one of the fixing points of the base member (21 ) to a roof structure. A bolt (70) passing through a saddle member (71 ) has a toggle formation (72) at its lower end. The toggle formation (72) acts in conventional fashion for securing the bolt (70) to the rear of hole formed, for example by drilling, in a fixed structure. The saddle may be moved along the base member (21 ) to one of a plurality of bolt holes (80) provided in the end portion of the base member (22). In this way, the shock absorbing support is provided with adjustable fixing capability. Turning now to Figure 6, each arm element (30) is formed as an "A" frame type arrangement by bending a strip of type 316 stainless steel 50 mm wide and 3 mm thick to define a symmetrical truncated triangle shape having two planar arm elements (30A), each 300 mm in length, a planar attachment region (30B) linking the arms (30A) at first ends thereof and a pair of feet (30C), with one foot (30C) being formed at a second end of each arm (30A). The arm elements (30A), attachment region (30B) and feet (30C) are linked by curved sections. A bolt hole (30D) is provided in the attachment region (30B) and a bolt hole (30E) is provided in each of the feet (30C). Each of the arm elements (30) is secured to a respective one of the base members (21 , 22) by a pair of bolts (50) passing through the bolt holes (30E) in the feet (30C) and through co-operating bolt holes (not shown) in the respective base member (21 , 22). The two arm elements (30) are secured together by a bolt (60) which passes through each of the bolt holes (30D) in their respective attachment regions (30B) . The bolt (50) may also secure an anchor element (not shown) to the two arm elements (30). In an especially preferred arrangement, the anchor element would be a ring suitable for supporting a lifeline in the form of a flexible cable. The ring could, of course, be replaced by other suitable anchor elements as required. The base members (21 , 22) preferably comprise a planar central section and two planar end sections, the arrangement being such that the end sections are both in a common plane parallel to the plane of the central section. The end sections are linked to the central section by kinked portions. A plurality of bolt holes (80) for securing the base member (21 ) to a structural element of a roof or similar rigid support structure is formed in each of its end sections. Base member (22) has a single bolt hole (90) at each of its ends. The kinked portions of the base members (21 , 22) are arranged to be just outboard of the positions at which the feet (30C) of the arm elements (30) are bolted to the base sections. The depth of the kinked portions such that the end sections of each base member (21 , 22) are displaced by half the thickness of the base member. In the illustrated example, this is 1.5 mm. The base members (21 , 22) and the arm elements (30) are arranged so that the base member which overlies the other base member is bolted to the arm element which overlies the other arm element and the two base members are arranged opposite ways up so that the base member which overlies the other base member has its end sections lower than its middle sections while the base member which underlies the other base member has its end sections above the middle section. This arrangement allows the cruciform shock absorbing support to be formed from two identical arm elements (30), thereby minimising the variety of stock parts that must be held, whilst ensuring that the end portions of the base members (21 , 22) lie in a common plane. This avoids pre-stressing or distortion of the shock absorbing support (10) during installation. In use, the shock absorbing support (10) transmits loads from the anchor element (not shown) to the rigid structure and for low loads acts as a substantially rigid unit. If a load of greater than 3.5 kN is applied to the anchor element approximately parallel to the base members the shock absorbing support will distort due to plastic deformation of the arm elements (30) . This plastic deformation will start with the curved sections linking the arm (30A), support (30B) and foot (30C) sections of each arm element rolling and will progress to bending of the arm portions (30A) of the arm elements (30) if the loading is sustained. In practice, it has been found with a loading of 8 kN parallel to the base members (21 , 22) the shock absorbing support distorts sufficiently to move the anchor element by 170 mm sideways. The distortion of the shock absorbing support absorbs some of the energy applied to the shock absorbing support and so reduces the instantaneous shock loads applied to the rigid support structure and the cable, or other arrangements, attached to the anchor element. Such instantaneous shock loads could damage or destroy the rigid support structure or the cable or other arrangement. In particular, in a fall arrest system such shock loading can injure the falling person. Further, the distortion of the shock absorbing support provides a clear, permanent, visual indication that a high load has been applied to the support. This would not normally occur with a device incorporating resilient means, eg springs as the energy absorbing means. In a fall arrest system, a load of 3.5 kN or greater will normally only be applied to the system in the event that fall arrest has occurred. The distortion of the support will act as a visual reminder to users to check and replace elements of the system as required. The symmetrical arrangement of the arms (30A) ensures that the shock absorbing support has an approximately omnidirectionally constant response to loads. This approximately omnidirectional constant response to loads includes both the threshold level at which distortion and plastic deformation of the shock absorbing support begins and the profile of load against time or load against distortion exhibited by the shock absorbing support if a load above this level is applied. Instead of an A-frame like arrangement, the arms (30A) could be formed individually. Alternatively, all of the arms could be formed integrally, for example, by cutting or pressing from a sheet. Bolting is, of course, only one method of assembly and the elements could be secured together by any other convenient means such as welding. Similarly, the inclusion of bolt holes to allow attachment of the shock absorbing support to a rigid support structure is not essential but is convenient. In order to provide the necessary symmetry of the arms it is necessary that at least three arms are provided. In the described example, the arms are formed by bent strips having a uniform width and thickness. In order to provide a desired threshold value for deformation to begin and the desired profile of deformation against time, the arms could be given a variable width or thickness or could be provided with ribs or cutaways or any other strength varying feature. The arms (30) could also have forms other than planar strips, such as rods. A threshold for distortion of 3.5 kn is often desirable in fall arrest systems but the shock absorbing support can be arranged to have any desired threshold value by suitable dimensioning, shaping and/or choice of materials. The materials and dimensions described herein should be regarded as merely illustrative. The shock absorbing support of the invention can be made from a wide range of materials in any desired size suitable for the intended use.

Claims: CLAIMS 1. A shock absorbing support suitable for use in a personnel fall arrest system, said support comprising a base, an anchor element and at least three deformable arms each having first and second ends, the first ends of the arms being linked together and to the anchor element and the second end of each arm being attached to the base, said base having resilient means on its underside and adjustable clamping means for clamping the base to a fixed structure at a variety of distances from a mid-point of said base. 2. A shock absorbing support as claimed in claim 1 wherein there are four arms are arranged in orthogonal pairs about the anchor element and the base has a pair of strap elements arranged in a cross formation. 3. A shock absorbing support as claimed in claim 1 , in which the arms are symmetrically arranged about an axis perpendicular to the plane of the base and passing through the anchor element. 4. A shock absorbing support as claimed in claim 3 in which the base comprises a plurality of substantially planar elongate base members joined together at their centres and each attached to both of the second ends of the arms of a respective integral pair. 5. A shock absorbing support as claimed in claim 4, in which each base member has two ends and is provided with securing means for securing the support to a further structure adjacent each of said ends. 6. A shock absorbing support as claimed in claim 5, in which each base member has a central section at which it is joined to the other base member lying in a first plane and two end portions provided with the support means lying in a second plane parallel to and offset from the first plane so that all of the end portions of the base members lie in a common plane. 7. A shock absorbing support as claimed in claim 6, and comprising four arms and two base members, in which the base members have the same thickness and the offset between the first and second planes of each base member is half the thickness of the base members. 8. A shock absorbing support as claimed in claim 7, and comprising two identical integral pairs of arms. 9. A shock absorbing support as claimed in any preceding claim, in which each integral pair of arms is formed from a single strip of material by folding.

Inventors: WOODLEY MARK, WOODLEY, MARK
Applicants: LATCHWAYS PLC, WOODLEY MARK, LATCHWAYS PLC., WOODLEY, MARK
Application year: 2000
Main classification: E04G21
IPC codes: F16F1, F16F3, F16F7