EP1752584A2

EP1752584A2 - Access cover

Info

Publication number: EP1752584A2
Application number: EP06254026A
Authority: EP
Inventors: David Henry Edmonds; Brian Mills
Original assignee: Wreckin Welding & Fabrication Engineering Ltd; Wrekin Welding and Fabrication Engineering Ltd; Atlanta Impex Ltd
Current assignee: Wreckin Welding & Fabrication Engineering Ltd; Wrekin Welding and Fabrication Engineering Ltd; Atlanta Impex Ltd
Priority date: 2005-08-02
Filing date: 2006-08-01
Publication date: 2007-02-14
Also published as: EP1752584A3; GB0515846D0; GB2429228B; GB2429228A

Abstract

A ground surface access cover (12) includes a substantially planar part (20) and a reinforcement arrangement (16). The reinforcement arrangement (16) is located on an underside in use of the planar part (20), and includes an elongate main reinforcement part (22). The reinforcement arrangement (16) further includes deformation reducing means (24, 26). The deformation reducing means (24, 26) includes an elongate auxiliary reinforcement part (24) which is located substantially alongside the main reinforcement part (22) and aligned substantially in the same direction as the main reinforcement part (22).

Description

The present invention relates to access covers, and in particular to ground surface access covers such as manhole covers.
Access covers undergo a variety of tests which are related to the type of application in which the access cover will be used, in accordance with regulatory standards. Currently, access covers are specified in accordance with European Standard EN124. This standard specifies that the cover is subjected to a permanent set test to test permanent deformation of the cover under load, followed by an ultimate load test. In the permanent set test, the cover is subjected to five load cycles up to two-thirds of the ultimate load, after which the permanent deformation is recorded. In the ultimate load test, a specified ultimate test load is applied for a specified period of time.
Conventionally, the design of access covers has been relatively crude, but as the cost of raw materials has increased, designers have increasingly sought to match the design of the cover to the requirements of the regulatory standard. The use of sophisticated design techniques such as finite element analysis (FEA) and computer aided design using three dimensional models has helped designers to minimise material requirements while maximising the strength of the covers, in particular in meeting the ultimate load test specification. However as designs become more complex, the ability of computer aided design and FEA programmes to accurately model the performance of the designs of the covers is reduced, and in particular, such techniques are generally poor in modelling and predicting permanent set.
Typically covers are provided as component parts of access assemblies, each assembly comprising a cover or pair of covers which is received within and supported by a frame. In testing the assembly is arranged to simulate a roadway installation with the cover or covers supported within the frame.
For certain applications the or each cover must be prevented from rocking in the frame during trafficking, and a common means of achieving a non rock support is for the cover to be supported on a three point mounting. This has led to the use of triangular covers, and "double triangular" pairs of covers within rectangular or square frames.
Each cover conventionally includes a main reinforcement beam which spans between two of the mountings and beneath the area over which the load is applied. Simple examples of such beams can be relatively easily modelled and designed to provide sufficient strength for the covers when tested to meet the ultimate load test specification. However, it can be difficult to model the performance of more complex beams such as curved beams and more difficult still to model the permanent deformation of more complex beams. In such situations, the designer often resorts to scaling the design of the beam by a factor to allow for the permanent set requirements. However such designs are not optimal in that material requirements may be higher than necessary. In the case of covers formed of ductile iron, failure more commonly occurs in the permanent set test due to deformation rather than the ultimate load test.
Testing has shown that the use of a curved main beam is relatively efficient, and allows a weight saving in material. However the curved beam is relatively "springy" and tends to have a relatively high permanent set in comparison with a linear beam. As the amount of material used is reduced, it has been found that the initial effect is upon an increase in permanent set rather than a reduction in the ultimate load.
According to the present invention, there is provided a ground surface access cover, the cover including a substantially planar part and a reinforcement arrangement, the reinforcement arrangement being located on an underside in use of the planar part and including an elongate main reinforcement part, the reinforcement arrangement further including deformation reducing means which are arranged so that when the cover is tested in accordance with regulatory standards, the permanent set recorded falls within the regulatory requirements.
Preferably, the deformation reducing means are arranged so that when the cover is tested in accordance with regulatory standards, the permanent set recorded is substantially zero.
Preferably, the deformation reducing means are arranged so that under load a deformation of one part of the cover acts against a deformation of another part of the cover, to reduce the overall deformation of the cover and hence reduce the permanent set recorded.
Preferably, the deformation reducing means connect the one part of the cover to the other part of the cover, to permit the deformation of the one part to act against the deformation of the other part.
The one part of the cover may be the main reinforcement part. The other part of the cover may be the planar part.
Preferably, the deformation reducing means include an elongate auxiliary reinforcement part. Preferably, the main and auxiliary reinforcement parts are located substantially alongside each other.
Further according to the present invention, there is provided a ground surface access cover, the cover including a substantially planar part and a reinforcement arrangement, the reinforcement arrangement being located on an underside in use of the planar part and including an elongate main reinforcement part, the reinforcement arrangement further including deformation reducing means, the deformation reducing means including an elongate auxiliary reinforcement part, the main and auxiliary reinforcement parts being located substantially alongside each other.
Preferably, the main and auxiliary reinforcement parts are aligned substantially in the same direction.
Preferably, a test load area is defined on an upper side in use of the planar part, over which area in use a test load is applied. The main reinforcement part and auxiliary reinforcement part may both extend directly underneath the test load area.
Preferably, the cover includes a plurality of mountings, and may include three mountings. Preferably, the main reinforcement part extends substantially between first and second mountings. Preferably, the auxiliary reinforcement part is aligned between the first and the second mountings.
Each of the mountings may be located at a corner of a right angled triangle. The triangle may have a longer side and may have two shorter sides, which may be of substantially the same length. Preferably, the planar part has a shape in plan which corresponds to that of the triangle.
Preferably, the first and second mountings are the mountings at each end of the longer side.
The main reinforcement part may be non linear in a longitudinal direction, and may be curved in the longitudinal direction. Preferably, the main reinforcement part curves convexly towards the third mounting, which may be the mounting between the two shorter sides. Preferably, the auxiliary reinforcement part is located on the side of the main reinforcement part away from the third mounting.
Preferably, the auxiliary reinforcement part lies along a chord of the curved main reinforcement part. The auxiliary reinforcement part may extend along only part of the chord.
Preferably, the main and/or auxiliary reinforcement parts are symmetrical about an axis, and may be symmetrical about the same axis. Preferably, the axis of symmetry extends through the third mounting, and may substantially bisect the longer side.
Preferably, the deformation reducing means include a web, which may extend between the main and the auxiliary reinforcement parts. More preferably, the deformation reducing means include a pair of spaced substantially parallel webs, which may extend between the main and auxiliary reinforcement parts. Preferably, the depth of the web at one end is substantially the same as the depth of the auxiliary reinforcement part. Preferably, the depth of the web at the other end is substantially the same as the depth of the main reinforcement part.
Preferably, a fillet extends between the main reinforcement part and the planar part. Preferably, the fillet extends transversely from the main reinforcement part. Preferably, the fillet extends from the main reinforcement part towards the mounting between the two shorter sides.
Preferably, the cover is formed of a ductile material, and may be formed of ductile iron, and may be formed by casting. Preferably, the cover is formed integrally in one piece.
Preferably, the main reinforcement part tapers in thickness downwardly in use from the planar part. Preferably, the auxiliary reinforcement part tapers in thickness downwardly in use from the planar part.
Preferably, the auxiliary reinforcement part is shallower in depth than the main reinforcement part. Preferably, the auxiliary reinforcement part is between 40% and 60% of the depth of the main reinforcement part, and may be approximately 50% of the depth of the main reinforcement part.
Preferably, the auxiliary reinforcement part is substantially similar in length to the test block. Preferably, the auxiliary reinforcement part is shorter in length than the main reinforcement part. Preferably, the auxiliary reinforcement part is between 30% and 50% of the length of the main reinforcement part, and may be approximately 40% of the length of the main reinforcement part.
Preferably, the regulatory standard to which the cover is tested is European Standard EN124.
Further according to the present invention, there is provided a surface access assembly, the assembly including a frame defining an opening and at least one cover as defined in the preceding statements, which in use is supported by the frame in the opening.
Preferably, the assembly includes a pair of substantially similar covers which may be supported side by side. Preferably, the assembly is arranged so that in use, the test load is applied substantially equally to each of the covers.
An embodiment of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:-

Fig. 1 is a perspective view of an access assembly according to the present invention;
Fig. 2 is a perspective view of the access assembly of Fig. 1 with a test block in position;
Fig. 3 is a perspective view of a cover according to the invention with the test block in position;
Fig. 4 is a perspective view from below of the cover of Fig. 3;
Fig. 5 is a view from below of the cover of Figs. 3 and 4 with the test block in position;
Fig. 6 is a view from one side of the cover with the test block in position;
Fig. 7 is a sectional view of two covers with the test block in position as indicated by the section line in Fig. 2;
Fig 8 is a schematic sectional view along an axis of symmetry of part of a cover not according to the invention undergoing testing; and
Fig 9 is a schematic sectional view along an axis of symmetry of part of the cover of Figs 1-7 undergoing testing.

Fig. 1 shows a ground surface access assembly 10 including a pair of covers 12 which are seated in a frame 14. The general arrangement of the covers 12 and frame 14 is relatively conventional, each cover 12 being substantially triangular in plan and being seated within a substantially square opening defined by the frame 14.
Fig. 3 shows one of the covers 12 on its own for clarity. Each cover 12 includes a planar part 20 which in use forms an upper surface of the cover 12. In plan, the shape of the planar part 20 is a right angled triangle, having a longer edge 50 and two shorter edges 52 of substantially equal length. At corners 64, the angle between the longer edge 50 and each of the shorter edges 52 is approximately 45°, and at corner 66, the angle between the two shorter edges 52 is approximately 90°. Extending downwardly in use from each of the 45° corners 64 are first and second mountings 54, 55 respectively, and extending downwardly in use from the 90° corner 66 is third mounting 56. Each of the mountings 54, 55, 56 is in the form of a protrusion, the mountings 54, 55, 56 together forming a non rock three point mounting for the cover 12.
Figs. 4 and 5 are views of the cover 12 from below. The cover 12 includes a reinforcement arrangement 16 which is located on an underside in use of the planar part 20. The reinforcement arrangement 16 includes a main reinforcement part in the form of a curved main beam 22. As shown in Fig. 6, the main beam 22 is deeper in section at its middle, and as shown in Fig. 7 the section thickness reduces with the depth away from the planar part 20.
The reinforcement arrangement 16 includes deformation reducing means including an auxiliary reinforcement part in the form of a linear auxiliary beam 24, which is located close to and parallel with the longer edge 50. As shown in Fig. 6, the auxiliary beam 24 is relatively short in comparison with the length of the main beam 22, and also relatively shallow in depth in comparison with the depth of the main beam 22. The auxiliary beam 24 includes a lowermost substantially flat face 70, at each end of which a sloping face 72 extends upwardly to the planar part 20 at an angle of approximately 45°.
The main beam 22 and the auxiliary beam 24 are located substantially alongside each other, and are aligned in the same direction, and both extend directly beneath a test load area 42 defined on an upper side in use of the planar part 20, over which area in use a test load is applied through the test block 40.
The main beam 22 extends between the first and second mountings 54, 55, and the auxiliary beam 24 is aligned between the first and second mountings 54, 55, on the side of the main beam away from the third mounting 56. The auxiliary beam 24 lies along a chord of the curved main beam 22.
The main beam 22 and the auxiliary beam are both symmetrical about an axis of symmetry 44 which bisects the longer edge 50 and extends through the 90° corner 66.
The deformation reducing means include a pair of spaced, substantially parallel webs 26, each of which extend between the auxiliary beam 24 and the main beam 22 to connect the auxiliary beam 24 to the main beam 22. Each of the webs 26 includes a lowermost face 74 which extends from the lowermost flat face 70 of the auxiliary beam 24 to a lowermost concave edge 76 of the main beam 22. Thus the depth of each of the webs 26 at one end is substantially the same as the depth of the auxiliary reinforcement beam 24 and the depth of each of the webs 26 at the other end is substantially the same as the depth of the main beam 22.
The cover 12 includes a pair of projecting nibs 32 which project from the underside of the planar part 20 and are located on the longer edge 50. Each of the projecting nibs 32 defines an aperture 34 for receiving a fastener such as a bolt (not shown) to loosely connect one cover 12 to a second cover 12 in use.
A fillet 28 extends between the main beam 22 and the planar part 20 via a keyway compartment 30 on the side of the main beam 22 away from the auxiliary beam 24. The fillet 28 extends from substantially the full depth of the main beam 20 at its deepest point.
The reinforcement arrangement includes a pair of curved lateral beams 36 extending from the side of the main beam 22 away from the auxiliary beam 24 to the 90° corner mounting 56, the lateral beams 36 being of lesser depth relative to the main beam 22. These lateral beams 36 provide some stiffness but because of the mode of failure of the cover 12 in testing are of relatively little consequence in reducing the permanent set.
In use, the frame 14 is installed over, for instance, an inspection chamber and the covers 12 located in the frame 14. In a typical construction in situ, only the top most edge of the frame 14 and the upper surfaces of the covers 12 will be visible. In a roadway, the covers 12 will be subjected to a range of dynamic loads as vehicles pass over the covers. The forces transmitted include both horizontal and vertical components as the vehicles brake, turn, and/or accelerate over the covers.
The approach to setting test specifications for access cover assemblies has been to not to try and attempt to simulate such varying load conditions in a test situation, but to apply a simple static load to the access cover assembly, the load including factors of safety to account for the different loading conditions experienced in practice. Thus, for example, a 38 tonne heavy goods vehicle having five axles with a total of 12 wheels will only apply a load of a little over 3 tonnes per wheel. However, the EN124 test specification for a cover suitable for use in a roadway for trafficking by heavy goods vehicles specifies five loading cycles up to 270kN after which the permanent set is measured, followed by loading to an ultimate test load of 400 kN, or approximately 40 tonnes, for a period of 30 seconds.
EN124 specifies that the permanent set after the five loading cycles should be no more than 0.2% of the opening. Thus, for example, for a 600mm opening, the limit for permanent set is 1.2mm.
Fig 2 shows the access assembly 10 with the test block 40 in position on the upper surface of the covers 12. The test block 40 transmits the test load substantially equally to each of the covers 12. Fig 7 is a sectional view of two covers 12A, 12B with the test block 40 in position with the section taken along line VII-VII of Fig 2, which is also the axis of symmetry 44 as shown in Fig 5. Along this section line, the main beams 22A, 22B are at their greatest spacing from each other, and extend directly beneath an outer region of the test load area 42.
A cover similar to that described above but without the auxiliary beam 24 and thus not in accordance with the invention was tested in accordance with the EN 124 test specification. After the permanent set load cycling test, the permanent set was measured at 1.8mm, exceeding the allowable limit of 1.2mm. Ultimate load failure occurred at 480kN, in comparison with the allowable limit of 400kN. Thus the cover exceeded the requirements for ultimate load, but failed the permanent set test. The use of simple 45° fillets on each side of the main beam appeared to make little difference to the permanent set recorded, even when those fillets extended to the full depth of the main beam.
The cover 12 according to the invention and including the auxiliary beam 24 and webs 26 was then subjected to testing. Some reduction in the permanent set was anticipated, and had been predicted by finite element analysis methods, but the effect of the auxiliary beam 24 and webs 26 exceeded expectations, in that the permanent set measured was around approximately zero mm. The ultimate load was similar to before. The test was repeated with alternative covers of similar design, with similar results.
The reason for this result is not yet clearly understood, and permanent set is not accurately predictable by finite element analysis methods. It will be noted however that the auxiliary beam 24 extends directly underneath the test load area 42 and is of substantially similar length to the diameter of the test load area 40. The intention was that rather allowing the cover 12 to deform progressively along the length of the longer edge 50 to a maximum at the mid point of the longer edge 50, the extra stiffening of the auxiliary beam 24 would reduce the deformation directly underneath the test block 40.
However there also appears to be an interaction between the auxiliary beam 24 and the main beam 22 via the webs 26. Figs 8 and 9 attempt to illustrate what might be happening. Fig 8 shows a cover 11 not in accordance with the invention, without an auxiliary beam 24. The test block 40 applies a load over a test load area 42 on the upper surface in use of the planar part 20. The load as indicated by arrows A is evenly distributed over the area 42. The load causes the planar part 20 to deform by (as it were) creasing along the axis of symmetry 44, the planar part 20 in the region of the axis of symmetry 44 deforming downwardly relative to the planar part 20 in the region of the mountings as shown by arrow B.
As this deformation occurs, the main beam 22 deforms so that the middle region of the concave edge 76 of the main beam 22 moves towards the longer edge 50 to flatten the curve of the concave edge 76 and accommodate the deformation of the planar part 20, the deformation of this region of the main beam 22 being shown in Fig 8 by dotted lines and indicated by arrow C.
Fig 9 shows the cover 12 of the invention undergoing a similar load test to that described in Fig 8. The load acts to deform the planar part 20 and auxiliary beam 24 downwardly as shown by arrow B, and to deform the middle region of the concave edge 76 towards the longer edge 50 as shown by arrow C. The webs 26 transmit these deformations towards each other to act against each other to reduce the overall deformation of the cover and hence the permanent set recorded. Careful design (or happy accident) can result in the deformations substantially cancelling each other out, and there being no permanent set recorded. In another example, a negative permanent set was recorded. Thus the auxiliary beam 24 and the webs 26 form deformation reducing means.
The depth of the auxiliary beam 24 could be between 40 and 60% of the greatest depth of the main beam 22, and in one example could be approximately 50% of the maximum depth of the main beam 22.
The maximum length of the auxiliary beam 24 could be between 30 and 50% of the maximum length of the main beam 22, and in one example was approximately 40% of the maximum length of the main beam 22.
Various modifications may be made without departing from the scope of the invention. The main beam could be of any suitable design, and could be of any suitable height, degree of curvature and section shape. The auxiliary beam could be of any suitable length, height and section shape. The webs between the main beam and auxiliary beam could be of any suitable design. A different number of webs could be provided. The main beam, auxiliary beam and webs could be configured differently, and could be located in different positions under the planar part. The planar part could be of different shape. For example, the planar part could be circular.
There is thus provided a cover which meets the requirements of the regulatory test specifications for ultimate load and deformation, with a reduction in the material used in manufacture. In one example, for a casting weighing 90 kilograms, a reduction of 6 kilograms was achieved, a reduction in material usage of just over 6%. For heavy items such as iron castings, transport costs can be significant, and therefore the cover of the invention allows a saving not only in the cost of material, but also provides a reduction in the cost of transportation.
Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

A ground surface access cover (12), characterised in that the cover includes a substantially planar part (20) and a reinforcement arrangement (16), the reinforcement arrangement being located on an underside in use of the planar part and including an elongate main reinforcement part (22), the reinforcement arrangement further including deformation reducing means (24, 26), the deformation reducing means including an elongate auxiliary reinforcement part (24), the main and auxiliary reinforcement parts being located substantially alongside each other, and aligned substantially in the same direction.
A cover according to claim 1, in which a test load area (42) is defined on an upper side in use of the planar part, over which area in use a test load (40) is applied, the main reinforcement part and auxiliary reinforcement part both extending directly underneath the test load area.
A cover according to claims 1 or 2, in which the main reinforcement part extends substantially between first and second mountings (54, 55).
A cover according to any of the preceding claims, in which the auxiliary reinforcement part is aligned between the first and the second mountings.
A cover according to claims 3 or 4, in which the cover includes three mountings (54, 55, 56), each of the mountings being located at a corner of a right angled triangle, the triangle having a longer side and two shorter sides, the first and second mountings (54, 55) being the mountings at each end of the longer side and the third mounting (56) being the mounting between the two shorter sides.
A cover according to any of the preceding claims, in which the main reinforcement part is curved in the longitudinal direction.
A cover according to claim 6 when dependent on claim 5, in which the main reinforcement part curves convexly towards the third mounting.
A cover according to claim 7, in which the auxiliary reinforcement part is located on the side of the main reinforcement part away from the third mounting.
A cover according to any of claims 6 to 8, in which the auxiliary reinforcement part lies along a chord of the curved main reinforcement part.
A cover according to claim 9, in which the auxiliary reinforcement part extends along only part of the chord.
A cover according to any of the preceding claims, in which the deformation reducing means include a web (26), which extends between the main and the auxiliary reinforcement parts.
A cover according to claim 11, in which the deformation reducing means include a pair of spaced substantially parallel webs (26), which extend between the main and auxiliary reinforcement parts.
A cover according to claims 11 or 12, in which the depth of the or each web at one end is substantially the same as the depth of the auxiliary reinforcement part.
A cover according to claim 13, in which the depth of the or each web at the other end is substantially the same as the depth of the main reinforcement part.
A cover according to any of the preceding claims, in which the cover is formed integrally in one piece.
A cover according to any of the preceding claims, in which the auxiliary reinforcement part is shallower in depth than the main reinforcement part.
A cover according to claim 16, in which the auxiliary reinforcement part is between 40% and 60% of the depth of the main reinforcement part.
A cover according to claim 17, in which the auxiliary reinforcement part is approximately 50% of the depth of the main reinforcement part.
A cover according to claim 2 or any claim dependent thereon, in which the auxiliary reinforcement part is substantially similar in length to the test load area.
A cover according to claim 2 or any claim dependent thereon, in which the auxiliary reinforcement part is shorter in length than the main reinforcement part.
A cover according to claim 20, in which the auxiliary reinforcement part is between 30% and 50% of the length of the main reinforcement part.
A cover according to claim 21, in which the auxiliary reinforcement part is approximately 40% of the length of the main reinforcement part.
A surface access assembly (10), characterised in that the assembly includes a frame (14) defining an opening and at least one cover (12) as defined in any of the preceding claims, which in use is supported by the frame in the opening.
A cover according to claim 23, in which the assembly (10) includes a pair of substantially similar covers (12) which are supported side by side.