Description of the Prior Art Shock pads, also known as bridge pads or derrick pads, are used in various industries to provide a shock absorbing joint between two load bearing structures that are subjected to varying loads. Shock pads generally include alternating layers of rigid plates and elastomeric blocks arranged in a"sandwich"configuration. Examples of uses of shock pads can range from supporting delicate instrumentation to the legs of an offshore drilling rig.

A variety of methods have been devised for quantifying the load being applied to a shock pad. For example, when jacking a rig using an electric jacking system, load can be determined by monitoring the power required to move the load. Hydraulic jacking systems may use similar indirect measuring systems. While these methods are applicable for quantifying varying load, these methods are not applicable for measuring static loads. These methods also suffer from accuracy in that they are indirect methods of measurement.

Also, these methods cannot generally be used to isolate part of the structure and to detect load specifically in the structurally isolated areas.

It is the object of this invention to provide a load sensing shock pad having means for detecting static load as well as varying load.

It is a further object of this invention to provide a load sensing shock pad having means to directly detect the amount of load being applied to the shock pad.

It is a further object of this invention to provide a load sensing shock pad which allows for structural isolation and isolated detection of a load.

It is yet a further object of this invention to provide a load sensing shock pad system, which allows for detection and summation of load being applied to the shock pad system.

These and other object and advantages of this invention will be apparent to those skilled in the art from a reading of the application including the attached drawings and appended claims.

BRIEF SUMMARY OF THE INVENTION The load sensing shock pad of this invention comprises first and second plates with a block of elastomeric material positioned and bonded between the plates. A load sensor, or fluid filled cavity, is located in the elastomeric block for sensing the compressive stress in the elastomeric material as the load on the pad changes. A load communicating means or transducer converts the compressive stress in the elastomer'to load on the pad, i. e. pounds, tons, kilograms, or the like.

The load sensor comprises a sealed reservoir located within the elastomeric block and a fluid contained within the reservoir. The load communicating means includes a pressure measuring device for measuring pressure imparted

on the fluid in the reservoir by the compression of the elastomeric block.

In a preferred embodiment, the load communicating means further comprises a calculation means for correlating the pressure imparted on the fluid in the reservoir to the load on the shock pad. The reservoir of a preferred embodiment is lined with a bladder which is sealably connected to the first plate. A plug can be used to secure the bladder in place. The first plate or the plug defines a passage, or passageway, for transmitting the fluid from the reservoir cavity to the pressure measuring device, thus communicating pressure changes in the reservoir cavity to the pressure measuring device to indicate the pressure imparted on the fluid by compression of the elastomeric block. This load sensing shock pad can be used, among other things, for supporting a portion of the weight of a structure that is subject to varying loads such as a supporting column of a bridge or a leg of a mobile offshore drilling rig.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side elevation of a load sensing shock pad of this invention when load is not being applied.

Fig. 2 is a side elevation of the load sensing shock pad when load is being applied.

Fig. 3 is another preferred embodiment of this invention with the passage defined by the plug securing the bladder in place.

DETAILED DESCRIPTION OF THE INVENTION The load sensing shock pad of this invention is illustrated in the drawings showing first plate 1 and second plate 2. As bearing load is applied to the first and second plates of the pad, reactive pressure is induced in elastomeric block 3, such that load applied to the plates compresses the elastomeric block 3. In a preferred

embodiment, this elastomeric block is rubber. Reservoir 4 is formed in the elastomeric block 3 thus creating a cavity which is integrally formed in the structure of the shock pad. Reservoir 4, in a preferred embodiment, is lined with bladder 5 which is sealed against the first plate such that the liquid contained in the reservoir does not come into physical contact with the elastomeric block. In this manner, the bond between the elastomeric block and the plate is not relied upon to seal the liquid under pressure.

Figures 1 depicts a preferred embodiment in which the first plate 1 defines a passage, or passageway, for transmitting fluid (not depicted) from cavity 6 defined by reservoir 4 to pressure measuring device 7. Pressure in cavity 6 indicates the pressure imparted on the fluid by compression of the elastomeric block. In this fashion, the reservoir acts as a load cell. A passage 8 is defined by the first plate such that fluid can flow from the reservoir through the passage to pressure measuring device 7. In a preferred embodiment, a plug 9 secures the bladder in cavity 6 and provides for continuity of the fluid passage from the reservoir into the plate. By thus enclosing the fluid within the cavity of the reservoir, the cavity acts as a blind cavity.

Figure 2 depicts a load being applied as indicated by directional arrow 11. This load creates compression of the elastomeric block as shown by arrows 12, resulting in the induced pressure deformation of the cavity.

Figure 3 depicts another preferred embodiment with the plug defining passage 8'such that fluid can flow from the reservoir through the passage to pressure measuring device 7'.

A pressure transducer, pressure gauge or other common pressure measuring device can be used as pressure measuring device 7 which is connected to outlet 10 of passage 8. The induced fluid pressure measured by the pressure measuring device can be equated to the load applied to the pad. Any

common pressure measuring equipment suitable for the prescribed installation can be used for this function by calibrating the equipment to display the load applied to the shock pad. Likewise, any common pressure measuring device can be used as pressure measuring device 7'which is connected to outlet 10'of passage 8'.

Another embodiment includes the use of multiple shock pads as a shock pad system to support a structure where load applied to each of the pads is totalled to determine a total structure load. An example of such a system involves using three separate shock pads mounted independently to support one leg of a drilling rig. Each shock pad to be monitored incorporates the features discussed above including cavity 6 filled with fluid and pressure measuring device 7. The pressure determined by the pressure measuring device for each shock pad is transmitted to a processor or calculation means (not depicted) which computes a summation of all measured pressures. This summation of induced fluid pressures, as measured by all of the pressure measuring devices, is equated to the load applied to the pads and is displayed as the total structure load.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus and structure.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

While preferred embodiments have been described and illustrated, it will be understood that the invention is not limited thereto since many modifications may be made and will become apparent to those skilled in the art.

For example, a shock pad can have multiple elastomeric blocks stacked one upon the other, any one or more of which could be monitored for an applied load in the manner described in this invention. The multiple elastomeric blocks can be separated by plates to provide for greater deflection between the two structures between which the pad is installed. Finally, this invention encompasses any item acting as a shock pad including, but not limited to, bridge bearing pads, anti-vibration bearings and seismic isolation bearings. These and other such modifications which would be apparent to those skilled in the art are encompassed by and are within the scope of the current invention.