Assembly for and a Method of Absorbing Impact Shock Loads

This invention relates to a shock absorbing assembly having means for controlling the modal deformation of collapse and in particular to a shock absorbing assembly capable of absorbing the dynamic energy of impact caused by the rapid deceleration of heavy masses such as a generator being deposited on an offshore oil platform.

A variety of differing shock absorbing assemblies have been disclosed in the past for a variety of differing objects. In Hanusa, U.S. Pat. No. 3,345,245, the shock absorbing assembly comprises a base formed from corrugated cardboard having a polyurethane shock absorbing material secured to and covering the corrugated surface. Steimen, U.S. Pat. No. 3,311,331, discloses a shock absorbing assembly wherein the shock absorbing material has means for securing the material to a leg of a machine and means for preventing the machine from creeping off the shock absorbing material. O'Donnell, U.S. Pat. No. 3,362,666, discloses a shock absorbing assembly for an office machine which can be positioned in various ways on the shock absorbing assembly. Nathan, U.S. Pat. No. 3,107,377, discloses shock absorbing assemblies constructed so that the upper surface can move relative to the lower surface to provide compensation for the expansion contraction of bridge members. While these references show a variety of shock absorbing assemblies, none of these references discloses a shock absorbing assembly having means for controlling the modal deformation of collapse.

It is an object of this invention to provide a shock absorbing assembly having means for controlling the modal deformation of collapse.

It is another object of this invention to provide a shock absorbing assembly having means for controlling the modal deformation of collapse and capable of absorbing the dynamic energy of impact generated by the rapid deceleration of heavy masses.

The foregoing objects are accomplished by the instant invention by providing a shock absorbing assembly having means for controlling the modal deformation of collapse. This is accomplished by a shock absorbing assembly comprising a plurality of sections, which are arcuate in cross section, sandwhiched between two steel plates wherein a groove is ground in the soffit of each section to provide for the modal deformation of collapse. An elastomeric rubber compound is secured to and covers the top plate and if desired may also be secured to and cover the bottom plate. The elastomeric rubber compound comprises a plurality of rubber slabs bonded together with metal plates between the slabs. The plates and with metal plates between the slabs. The plates and the sections are formed from steel to provide the ability to absorb the dynamic energy of impact caused by the rapid deceleration of heavy masses such as the large generators used at offshore oil platforms.

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 is a top plan view of a shock absorbing assembly of this invention;

FIG. 2 is a side elevation of FIG. 1;

FIG. 3 is an end elevation of FIG. 1;

FIG. 4 is a cross section of a modification;

FIG. 5 is a top plan view with the top plate and elastomer removed; and

FIG. 6 is a cross section showing a shock absorbing assembly mounted on a surface.

The shock absorbing assembly of this invention is illustrated in the drawings and comprise a top plate 2 and a bottom plate 4. Sanwhiched between the top plate 2 and bottom plate 4 are a plurality of sections 6. As shown in FIG. 2, the sections 6 are arcuate in cross section and specifically are half round. As illustrated in FIG. 1, the sections 6 preferably extend across the short dimension of the plates. Although the plates 2 and 4 are illustrated as rectangles having a long and a short dimension, the plates 2 and 4 may be equilateral. A groove 8 is ground in the soffit of each section 6 to provide for the modal deformation of collapse. The groove 8 extends for substantially the complete length of each section and is located at the center of the soffit. The sections 6 are secured to the plates 2 and 4 by any suitable means such as by welding. An elastomeric rubber compound 10 is secured to and covers the top surface 12 of plate 2. If desired, an elastomeric rubber compound may be secured to and cover the bottom surface 14 of plate 4 as illustrated in FIG. 4.

The edges 16 of the sections 6 are welded to the top plate 2 with a full penetration weld along the entire length of each edge 16. The sections 6 are secured to the bottom plate 4 by tack welds preferably at the extreme ends of each section.

The elastomeric rubber compound 10 comprises a lamination comprising a plurality of rubber slabs bonded together with metal plates 18 bonded between some of the slabs. Any suitable means may be used for bonding the rubber slabs as long as they can withstand the horizontal shear forces occurred during installation.

In one embodiment of the invention, each plate has a length of about 610 mm, a width of about 406 mm and a thickness of about 13.4 mm. Each section comprises a half-round tubular section having a radius of about 30.15 mm, a wall thickness of about 3.2 mm and a length of about 396 mm. The groove 8 is ground into the soffit a distance of about 1.7 mm. The elastomeric rubber compound comprises a natural rubber having a Durometer of about 50, a minimum tensile strength of about 15.5 N/mm.sup.2, an elongation at break of about 450 percent, a compression modulus of about 3.45 MN/m.sup.2 .+-.15 percent and a shear modulus of about 0.81. Each steel plate imbedded in the elastomeric rubber compound has a length of about 573 mm, a width of about 363 mm and a thickness of about 6.7 mm. The total height of a shock absorbing assembly, illustrated in FIG. 1, is about 155 mm.

The shock absorbing assembly, illustrated in FIG. 1, is designed for a static weight distribution of about 68.7 tonnes, and dynamic weight distribution of about 100 tonnes for maximum capability continuous, i.e. >20 m sec. duration and about 116.7 tonnes for maximum short transients, i.e. <20 m sec. duration. The dynamic weight distributions are assessed from the following peak decelerations: Forces up plus about 1.75 g Absolute for maximum short transients from .ltoreq.20 m sec. to .ltoreq.5 m sec. and Forces up shall not exceed about 2.2 g Absolute for maximum short transients of .ltoreq.5 m sec. Limited velocity on impact is about 1 ft/sec.

In another embodiment of the invention FIG. 5, each plate has a length of about 610 mm, a width of about 406 mm and a thickness of about 13.4 mm. Six sections 6 each having a length of about 396 mm spaced apart equal distances are secured between the plates 2 and 4 and two sections 6a each having a length of about 85 mm are positioned adjacent each end and spaced therefrom a distance of about 35 mm. This embodiment is designed for a static weight distribution of about 131.6 tonnes, and a dynamic weight distribution of about 200 tonnes for maximum capability continuous, i.e. <20 m sec. duration and about 230.3 tonnes for maximum short transients, i.e. <20 m sec. duration. The dynamic weight distributions are assessed from the following peak decelerations: Forces up plus about 1.5 g Absolute for maximum capability continuous; Forces up plus about 1.75 g Absolute for maximum short transients from .ltoreq.20 m sec. to .ltoreq.5 m sec. and Forces up shall not exceed about 2.2 g Absolute for maximum short transients of .ltoreq.5 m sec. Limited velocity on impact is about 1 ft/sec.

The shock absorbing assemblies must be capable of absorbing the horizontal component of impact forces accruing from a 2.5.degree. slinging angle of tilt of the heavy mass during installation. This may be accomplished by tack welding the bottom plate to the surface on which the shock absorbing assembly is mounted. As illustrated in FIG. 6, this may also be accomplished by guide frames 20 secured to the roof 22 of the substructure.

In operation, the initial impact and any slight surface imperfections are absorbed by the elastomeric rubber compound. As the load reaches a critical value, the steel tubes plastically deform and the shock absorbing assembly compresses at near constant load maximizing the energy absorbing relations to peak force. The shock absorbing assembly is designed to absorb a certain amount of energy at a given peak deceleration but in the event of catastrophic impact, some impact absorption will still be retained at loads in excess of three times the design limit.

Shock absorbing assemblies made in accordance with this invention were used successfully to land two generators, each having a sling mass of 265 tonnes. Two shock absorbing assemblies, each providing a static weight distribution of 66.7 tonnes were mounted at predetermined locations on the roof of a substructure and one shock absorbing assembly providing a static weight distribution of 131.6 tonnes was mounted at another predetermined location on the roof of a substructure. A crane was used to transfer the generator from a cargo ship to an offshore oil platform. During installation, contact was made on the two shock absorbing assemblies first and then on the one. The shock absorbing assemblies functioned as described above with the initial impact being absorbed by the elastomeric rubber compound and the steel tubes plastically deforming to absorb the heavy impact forces.

While the preferred embodiment of the invention has been illustrated and described herein, it may be otherwise embodied and practiced within the scope of the following claims.