Description of Invention

From one aspect, the present invention relates to the monitoring of a structure wherein a mass is suspended by means of a plurality of elements connected in parallel with each other between the mass and a support therefor. The invention has been devised primarily for use in monitoring a boiler structure comprising a number of rods, by means of which pipework and other members are suspended from a support. The invention is also useful in a suspension bridge.

There exists a number of large boiler installations, each comprising pressure vessels, tubes and pipework suspended by 400 to 900 rods from a support structure which lies above the pipework, pressure vessels and tubes. It will be understood that the output required from the boiler varies from time to time, that the rate of consumption of fuel is varied accordingly, that this results in changes in the temperature of various components of the boiler and that changes in temperature are accompanied by expansion or contraction. Lower end portions of the suspension rods, which are in the vicinity of the pipework, pressure vessels or tubes are subjected to elevated temperatures, for example temperatures in the region of 300°C to 570°C.

It has been discovered that the respective loads to which the suspension rods of a boiler structure of the kind described are subjected vary substantially with time, primarily because the load is dependant upon the temperature of the rod and upon the temperature of the member suspended by the rod. The overall load is not distributed evenly to all of the rods and the distribution of the load varies when the operating conditions change. In consequence of this discovery, there is a requirement for continual or continuous monitoring of the load to which individual suspension rods are subjected under various operating conditions pertaining to the boiler. One use of such

information is to enable an assessment to be made as to whether existing suspension rods are able to sustain safely the loads to which they are subjected during operation of the boiler.

It is known to apply electrical strain gauges to structural members and the use of strain gauges enables the load to which a member is subjected to be monitored continually or continuously. However, in order to calibrate a strain gauge fitted to a structural member, it is necessary to isolate that member and to subject it to known loads. Strain gauges could not conveniently be fitted to and calibrated on the suspension rods of an existing boiler structure. Furthermore, the low stress in the suspension rods of a boiler structure and the necessity for in- situ calibration impairs the accuracy with which the load in a suspension rod can be measured by an electrical strain gauge.

It is known to attach a block to an upper end portion of a suspension rod and to interpose between that block and the supporting structure an hydraulic load cell. The hydraulic pressure required to raise the block slightly relative to the supporting structure then provides an indication of the instantaneous load to which the suspension rod is subjected. However, an hydraulic load cell is unsuitable for providing a continual or continuous indication of the load to which a boiler suspension rod is subjected.

Attempts to ascertain the loads to which suspension rods of a large boiler are subjected during operation have been made. These attempts involved fitting electrical strain gauges to suspension rods whilst the boiler was out of commission and calibrating the strain gauges by use of an hydraulic load cell as described in the immediate preceding paragraph. These attempts are regarded as failures, owing to the unreliability of the indications of load during operation of the boiler which were obtained. The method of installation and calibration of the strain gauges and the position of the strain gauges give rise to inherent inaccuracies in measurement of the loads to which the suspension rods are subjected. Furthermore, electrical strain gauges which failed in service could not be replaced, without again taking the boiler out of commission.

It has not been known that the loads to which individual suspension rods are subjected change significantly during operation of a boiler.

According to a first aspect of the present invention, there is provided a method of monitoring a structure wherein a mass is suspended by means of a plurality of elements connected in parallel with each other between the mass and a support therefor, the method comprising the steps of interposing in the load- transmission path through each of said elements to the support a respective load- indicating device and interrogating continually, continuously or intermittently the load-indicating devices.

Information about the respective loads to which the elements are subjected can be stored for future use.

The stored information can be processed to provide a visual or other representation of the absolute loads to which individual suspension rods are subjected, variations in those loads with respect to time and the relationship between the respective loads in selected suspension rods. Such representations are valuable in the assessment of whether existing suspension rods can safely support the loads which may be imposed on them during operation of the boiler.

In the preferred method, the respective load indicating device is connected with a portion of each said element, driving means is associated with each load indicating device, the driving means is operated to move said portion of the element relative to the support sufficiently to divert the load through the driving means, the load indicating device is adjusted, the driving means is relieved of the diverted load, the diverted load being imposed on the load indicating device, and the driving means is removed, leaving the load diverted through the load indicating device.

The same driving means may be associated with each load indicating device in turn. The load indicating device may be connected with the portion of said element before, during or after association of the driving means with the load indicating device concerned. The load indicating device is adjusted to a condition

in which it is adapted to transmit the load from said portion of said element to the support.

The discovery that the respective loads to which the suspension rods of a boiler structure of the kind described are subjected vary substantially with time has lead also to a requirement for intermittent measurement of the load to which a suspension rod is subjected, in order that the increase or decrease in that load over a period of time can be determined. This period of time may be several days. For example, the load to which a suspension rod is subjected may be measured whilst the boiler is cold and then measured during operation of the boiler, after the boiler has been operating for several days. Thus, the intermittent interrogation of the load indicating devices may be as infrequent as interrogation on two occasions. The information about loads to which individual suspension rods are subjected and variations of those loads with respect to time may be recorded electronically or manually. Electronic recording is suitable when the load indicating devices are interrogated continually or continuously. Manual recording is suitable when the load indicating devices are interrogated intermittently.

The step of connecting the load indicating device with a portion of the element may include the steps of attaching to the element a respective load block having transfer means for transferring the load from the load block to the support, the step of operating the driving means may involve driving the load block relative to the transfer means in a direction away from the support, adjusting the device may involve retaining the transfer means in an operative position relative to the load block, the driving means may be relieved of the load by permitting the load block to move towards the support to impose the load on the transfer means and the transfer means may be provided with a load-indicator capable of providing a signal representing the magnitude of the load transferred by the transfer means from the load block to the support.

The load indicator is preferably applied to the transfer means prior to assembly of the transfer means with the load block. Accordingly, the load- indicator can conveniently be calibrated.

In a case where the load indicating device is to be interrogated continually or continuously, the load indicator preferably remains associated with the transfer means of a single load indicating device and may be permanently attached to or permanently incorporated in the transfer means. In a case where the load indicating device is to be interrogated intermittently, the load indicator may be applied temporarily to the transfer means and a single load indicator may be used in the interrogation of a number of load indicating devices. However, there is preferably incorporated in each load indicating device a respective load indicator which can remain with the device more or less permanently. This facilitates intermittent or more frequent interrogation of the device.

According to a second aspect of the invention, there is provided apparatus suitable for use in a method according to the first aspect and comprising a load block having means for attaching the load block to a selected one of said elements and transfer means for transferring a load from the load block to the support, the transfer means being adjustable relative to the load block, a load indicator capable of providing a signal representing the magnitude of a load transferred by the load transfer means from the load block to the support, and driving means for driving the load block relative to the transfer means in the direction of adjustment of the transfer means.

The driving means is preferably separable from the load block, after the transfer means has been retained in an operative position relative to the load block. The driving means can then be used in the application to a further element of a load block and transfer means.

The transfer means preferably comprises a plurality of load-transfer members which are spaced from each other around a centre of the load block and which act in parallel with each other to transfer the load from the load block to the support. In this case, the load indicator may be associated with one only of

the load-transfer members. Alternatively, respective load indicators may be associated with two or more of the load transfer members which act in parallel with each other. The load transfer members may be relatively small components and therefore relatively highly stressed in use, so that an electrical strain gauge can be used to provide a signal which represents the load in the elongate element with a fairly high degree of accuracy.

According to a third aspect of the invention, there is provided apparatus for use in a method embodying the first aspect of the invention, the apparatus comprising clamping means suitable for clamping a portion of said elongated element, adjustable transfer means for transferring load from the clamping means to the support, driving means for driving the clamping means relative to the support and a load indicator capable of providing a signal representing the magnitude of a load transferred by the transfer means from the clamping means to the support. Preferably, the transfer means includes a hollow load block, a rod extending from the clamping means through the load block and an adjustable retainer for retaining the transfer means in an operative condition, in which it can transfer load from the clamping means to the support.

The retainer may be adjustable relative to the load block and/or relative to the rod. _

According to a fourth aspect of the invention, there is provided apparatus for use in a method embodying the first aspect of the invention, the apparatus comprising first and second clamping means suitable for clamping said element at respective positions which are spaced apart along the element, driving means for driving the clamping means towards each other to operative positions and retaining means for retaining the clamping means in the operative positions when the driving means is removed.

According to a fifth aspect of the invention, there is provided a support structure comprising an elongated element which is subjected to a load in use, a support for receiving the load, a load block fixed with respect to a portion of the elongated element to receive the load from the elongated element, transfer means

for transferring the load from the load block to the support and load-indicating means associated directly with the transfer means or load block for providing an electrical signal representing the magnitude of the load transferred by the transfer means.

In the preferred structure, the load indicating means is associated directly with a portion of the transfer means and the transverse cross sectional area of said portion of the elongated element is substantially larger than the corresponding area of said portion of the transfer means. With this arrangement, said portion of the transfer means will be stressed more highly than is the elongated element and load indicating means in the form of an electrical strain gauge will provide a signal representing the magnitude of the load with greater accuracy than could be achieved by use of the same electrical strain gauge, if associated directly with the elongated element.

According to a sixth aspect of the invention, there is provided a support structure comprising an elongated element which is subjected to a load in use, a support for receiving the load, first and second members clamped to the element at respective positions spaced apart along the member, a load transfer means connected with both said members for transmitting load between them and a load indicator on the load transfer means for providing a .signal indicating the magnitude of the load transferred by the load transfer means.

Examples of methods embodying the first aspect of the invention, in which methods there is used apparatus embodying the invention and which methods result in support structures according to the invention will now be described, with reference to the accompanying drawings, wherein:

FIGURE 1 is a diagrammatic illustration of an upper end portion of a suspension rod and of parts associated with the suspension rod during performance of the method, ig.

FIGURE 2 is an isometric representation of the resulting structure,

FIGURE 3 is a diagrammatic illustration of an intermediate portion of a further suspension rod and of parts associated with the further suspension rod during performance of the method,

FIGURE 4 shows certain of the parts of Figure 3 in cross section in the plane IV-IV of Figure 3 and

FIGURE 5 is an isometric view of a part of a further suspension rod and parts associated with that suspension rod during performance of the method. The particular methods represented in the accompanying drawings involve modification of an existing support structure for a boiler and subsequent monitoring of loads in that support structure. The boiler comprises pipework, pressure vessels and other members (not shown) suspended from a deck structure by means of a number of suspension rods, a portion of one of which is represented in Figure 1 and identified by the reference numeral 7. In a typical boiler, there are several hundreds of such primary suspension rods, many being identical one with the other and the intention of the designer of the boiler structure would be that the overall load imposed on the suspension rods should be distributed so as to achieve approximately even stress margins between those rods. The present invention enables ^* the load in all of the suspension rods or in selected ones of the suspension rods to be monitored continuously, continually or intermittently.

In both the original boiler structure and in the modified structure embodying the present invention, the suspension rod 7 is supported by a support 9, through which an upper end portion of the rod 7 extends. The support 9 rests on the support deck of the boiler structure. The upper end portion of the rod 7 is formed with a male screw thread with which a nut 8 cooperates. During initial installation of the rod 7, the nut 8 rests on the support 9 and is screwed along the rod 7 tojj^djust the position of the suspension rod. In carrying out the method of the present invention, there is interposed in the load-transmission path between the suspension rod 7 and the support 9 a device capable of providing an indication of the load to which the rod 7 is subjected.

The load-indicating device comprises a hollow load block 1 formed with a female screw thread which is complementary to the male thread of the suspension rod 7. Two or three through bores are formed in the load block, these being spaced equally from each other around the central, threaded opening of the load block, spaced equally from that opening and having respective axes which are parallel to the axis 13 of the central opening. As viewed in plan, the load block may be square or otherwise rectangular. Alternatively, the load block may be triangular, as viewed in plan. This shape is particularly appropriate in a case where three bores are formed in the load block.

The device further comprises load-transmitting means for transmitting load from the load block 1 to the support 9. In the example illustrated, the load transmitting means comprises a number of load transmitting members, one for each bore of the load block 1. Two of these members are identified in Figure 1 by the reference numerals 2 and 3. Each of these members is of substantially cylindrical form and has a diameter such that it is a free, sliding fit in the corresponding bore of the load block 1. An upper end portion of the member is formed with a male screw thread on which there is screwed a retainer in the form of a nut, identified by the reference numerals 11 and 12 respectively. At their lower ends, the load transfer members 2 and 3 have respective slightly convex faces which are substantially perpendicular to the longitudinal axes of the members.

Releasable holding means is provided for holding the load transfer member 2 in an inoperative position (not illustrated) with respect to the load block 1. In the inoperative position, the load transfer member is withdrawn further into the load block than is the case when the load transmitting members are in the intermediate position represented in Figure 1. Corresponding holding means are provided for the other load transfer member or members. The holding means may comprise a respective grub screw for each load transfer member, the grub screw being disposed in a respective bore in the load block 1 transverse to the bore in which the associated load transfer member is received.

There is directly associated with the load transfer member 3 a load indicator 10 suitable for providing an electrical signal representing a compressive

load imposed on the member 3. Since the load transfer members are subjected to equal loads, the signal will also represent the load to which the rod 7 is subjected. The load indicator 10 may be a known electrical strain gauge. If required, a substantially identical strain gauge may be applied to the other load transfer member or respective strain gauges may be applied to the other load transfer members. However, we have found that the provision of a single strain gauge is sufficient to obtain a reliable and accurate indication of the load in the suspension rod 7.

Whilst, for convenience of illustration, we have represented in Figures 1 and 2 a surface-mounted strain gauge, alternative load indicators may be used. For example, an electrical strain gauge which lies on the neutral axis of the load transfer member may be used. Furthermore, a load indicator other than an electrical strain gauge may be used. This may be a known device for detecting changes in the length of the transfer member 10, for example by means of ultra¬ sonic sound waves.

A suitable, electrical strain gauge which lies on the neutral axis of a component is supplied under the designation "Strainsert" and is available from AJB Associates (Electronics) Limited of 54, High Street, Wells, Somerset, England. A suitable ultrasonic device is designated the "Raymond Ultrasonic Bolt Gage" and is available from W. Christie (Industrial) Limited of 58/62 Seaward Street, Glasgow, United Kingdom.

It will be understood that the load block 1 is subjected to strain, since it bears the load transmitted by the load transfer members to the support 9. Accordingly, the load indicator could be associated directly with the load block, rather than with a load transfer member.

The apparatus represented in Figure I further comprises driving means for driving the load block 1 relative to the load transfer members 2 and 3 in a direction along the axis 13 of the central opening of the load block. The driving means comprises an hydraulically actuated jack 14, a bridge member 15 and a jacking frame 6. In use, the jack 14 is interposed between the bridge member 15

and the frame 6. The bridge member 15 comprises a pressure plate 5, on which the jack 14 rests, and a number of plungers, one for each of the load transfer members. These plungers are rigid with the pressure plate 5 and extend therefrom into the bores of the load block 1 to bear on the load transfer members. The plunger which bears on the member 10 is identified in Figure 1 by the reference numeral 4. The plungers are a free sliding fit in the bores of the load block.

The frame 6 rests by an intermediate portion on the jack 14 and limbs 16 and 17 depend from the intermediate portion of the frame to the load block 1. Each of these limbs has a respective inwardly projecting abutment which engages beneath a corresponding step formed on the load block so that the frame is anchored against upward movement relative to the load block.

In carrying out the method, the load block 1 is screwed onto the thread of the suspension rod 7 from the upper end of the rod. During this step, the load transfer members are held in their respective inoperative positions so that they do not interfere with rotation of the load block. Typically, the load block is driven along the thread of the suspension rod until the upper surface of the load block is approximately flush with the upper end of the suspension rod. The load transfer members are then released for movement from their inoperative positions into engagement with the support 9. The bridge member 15 is then applied to the load block so that the plunger 4 rests on the load transfer member 3 and the other plunger rests on the corresponding load transfer member. The jack 14 is placed on the bridge member 15 and the frame 6 is slid over the jack and beneath the steps of the load block until the centre of the frame lies substantially on the axis 13 of the central opening of the load block.

Hydraulic fluid is supplied under pressure to the jack 14, thereby driving the frame 6 upwards relative to the bridge member 15 and thus driving the load block 1 upwards relative to the load transfer members 2 and 3. This is continued until the nut 8 is raised from the support 9. This condition may be ascertained by visual inspection or by use of a feeler gauge. The retaining nuts

11 and 12 are then driven upwards on their respective load transfer members into firm engagement with the load block 1, thereby retaining the members 2 and 3 in respective operative positions relative to the load block.

Once the load transfer members are retained in their operative positions, the jack 14 is relieved of hydraulic pressure and permitted to collapse. The frame 6 is then removed from the load block 1, the jack is removed and the bridge member 15 is removed. The nuts 11 and 12 bear on the underside of the load block 1 and prevent movement of that load block towards the support 9 so that the nut 8 does not bear on the support. The entire load in the suspension rod 7 is transmitted to the support 9 via the load transfer members 2 and 3.

Figure 2 shows the modified structure for supporting the suspension rod 7, after the driving means has been removed.

The procedure is repeated in relation to other suspension rods and the electrical strain gauges are all connected with a common sampling, data storage and data processing system (not shown) suitable for interrogating the strain gauges continually or continuously, storing information about the signals provided by the strain gauges and processing that information. The information may be processed, for example, to provide a visual representation of the loads in the tension rods. Changes in these loads occurring over a period, for example 24 hours, can be represented in a single print or display, the load in each rod being sampled at intervals of one minute, for example.

The aggregate cross sectional area of the load transmitting members 2 and 3 in a plane perpendicular to the axis 13 is substantially smaller than the cross sectional area in the same plane of the suspension rod 7. Accordingly, the load transmitting members are stressed more highly than is the suspension rod. This contributes to the accuracy of the indication of the load in the suspension rod which is provided by the strain gauge 10.

It will be noted that the suspension rod 7 is not relieved of its load during modification of the structure. Furthermore, the relationship between the nut 8 and the suspension rod is not disturbed. In the event of failure of the load

block 1 or load transmitting members 2 and 10, the nut 8 would support the suspension rod 7 once more.

The modification procedure can readily be carried out in reverse to restore the means for supporting the suspension rod to its original condition.

In a case where a load indicator other than an electrical strain gauge is used, the load indicator may be interrogated by direct inspection and a manual record may be made of the indicated load or of some other parameter related to load. This procedure is suitable when the load indicator is to be interrogated only once after installation of the load indicating device or only a small number of times after installation. Thus, the signal provided by the load indicator may be a visual indication representing the load. However, the signal is preferably electrical in character, since information carried by an electrical signal can be stored and processed electronically without the intervention of a person and the risk of error which accompanies such intervention.

In Figure 3, there is shown an intermediate portion of a suspension rod 20 which incorporates a clevis joint. The clevis joint comprises a female part 23, a male part 24 and a sheer pin 25 extending through aligned apertures in the male and female parts to connect them together. The method illustrated in Figure 3 may be used where the upper end portion of the suspension rod is inaccessible, where there is no or insufficient exposed thread at the upper end of the suspension rod to receive a threaded load block and also in a case where there is insufficient space above the upper end portion of the suspension rod to permit the temporary installation of a load frame and jack as represented in Figure 1. Suspension rods comprising clevis joints as illustrated in Figure 3 are commonly incorporated in boiler structures having primary suspension rods as represented in Figure 1. The support for the suspension rod 20 is not shown in the accompanying drawings and may be the support deck which supports the suspension rod 7 of Figure 1.

In carrying out the method of the invention, as applied to the jointed suspension rod 20 of Figure 3, the load in the suspension rod is diverted through

a load indicating device from that part of the suspension rod which includes the clevis joint. Thus, the load indicating device is interposed in the load-transmission path between a lower portion of the suspension rod and the associated support. The load indicating device of Figure 3 comprises an upper pair of clamping members 26 and 27 and a lower pair of clamping members 28 and 29, these pairs being spaced from each other along the suspension rod 20. A portion of the suspension rod lying above the clevis joint is clamped by the members 26 and 27 and a further portion of the suspension rod, lying below the clevis joint, is clamped by the members 28 and 29.

As shown in the drawing, the clamping members 26 and 27 preferably act on the suspension rod 20 indirectly, via respective pads 30 and 31 which collectively form a split block embracing a portion of the suspension rod. The lower clamping members 28 and 29 also act on the suspension rod through respective pads which together constitute a further split block.

The load indicating device further comprises load transferring means connected with both the upper pair of clamping members 26 and 27 and the lower pair of clamping members 28 and 29 for transferring between these pairs of clamping members the load which is diverted from the suspension rod 20. The load transferring means includes a pair of tie rods 32 and 33. Each of the clamping members 26 to 29 has a respective hole through which a corresponding one of the tie rods extends. The tie rod 32 has at its lower end a head 34 which abuts the underside of the clamping member 28. A male screw thread is formed on an opposite end portion of the tie rod 32 and this end portion carries a nut 35 which bears on the upwardly facing surface of the clamping member 26. The threaded portion of the tie rod protrudes above the nut 35. The tie rod 33 has a corresponding head 36, nut 37 and threaded upper end portion.

The clamping members 26 and 27 are carried by a common carrier 38 which partly overlaps both of the clamping members, as the assembly is viewed in Figure 3 in a direction towards the suspension rod 20. The clamping member 26 is connected with the carrier 38 for pivoting relative thereto about a pivot axis

defined by a pivot pin 39. The pivot axis is perpendicular to the longitudinal axis 40 of the suspension rod 20 and is perpendicular to a line extending from the tie rod 32 to the tie rod 33. The pivot pin 39 is nearer to the pad 30 than to the tie rod 32 but is spaced a short distance from that pad. A portion of the clamping member 26 which bears on the pad 30 is formed as a cam so that pivoting of the clamping member 26 on the pin 39 drives the pad towards the axis 40 of the suspension rod or permits movement of the pad away from that axis. The arrangement is such that downwards movement of that portion of the clamping member 26 on which the nut 35 bears clamps the suspension rod 20 more firmly.

The clamping member 27 is connected with the carrier 38 in a similar manner by means of a further pivot pin 41 and the clamping member 27 also is formed as a cam such that increasing the tension in the tie rod 32 clamps the suspension rod 20 more firmly. The carrier 38 conveniently comprises two identical members, one supporting first ends of the pivot pins 39 and 41 and the other supporting the opposite ends of the pivot pins.

The clamping members 28 and 29 are carried by a further carrier 42 which is identical with the carrier 38 and the clamping members 28 and 29 also are formed as cams to act on the associated pads. However, these cams are so formed that upwards movement of those portions of the clamping members on which the heads 34 and 36 bear clamps more firmly that portion of the suspension rod which lies below the clevis joint.

Prior to installation of the load indicating device, an electrical strain gauge 43 is applied to the tie rod 33 and is calibrated. The load indicating device is then assembled around the tie rod 20. The pads of the split blocks may be held together and held on the suspension rod by fasteners (not shown).

In preparation for driving the pairs of clamping members towards each other, a bridge 44 is placed on the clamping member 26 so that the threaded portion of the tie rod 32 protrudes through the bridge. An annular, hydraulically actuated jack 45 is placed on the bridge and a nut 46 is then screwed onto the threaded end portion of the tie rod and tightened down to the jack. A

corresponding bridge, jack and nut are applied to the tie rod 33. The jacks are connected in a common hydraulic circuit with a pump so that the jacks will be subjected to the same hydraulic pressure. This pressure is then increased, by means of the pump, until the load is diverted from the clevis joint to the load indicating device.

Relieving the clevis joint of the load may release the sheer pin 25 so that the pin can readily be turned. If so, this can be used as an indication that the load has been fully transferred to the load indicating device. If the sheer pin is prevented from turning, for example by corrosion or because it has been welded to the male part 24 of the clevis joint, alternative means are employed for determining when the sheer pin has been relieved of the load. One such alternative means is illustrated in Figures 3 and 4.

Figures 3 and 4 show means for detecting a change in the length of the sheer pin 25. When the sheer pin is loaded normally, it is curved. As it is relieved of the load, the degree of curvature becomes smaller. This can be detected by means of the gauge 47 represented in Figures 3 and 4. The gauge includes pointed contact elements which are in firm engagement with respective ends of the sheer pin at positions which are either as far below the longitudinal axis of the sheer pin as practicable or as far above that axis jis practicable. One of the contact elements can be adjusted towards the other to achieve the required contact with the sheer pin. An electrical strain gauge 48 is mounted on the gauge 47 and this responds to movement of the contact elements towards or away from each other by providing an electrical output signal. If this output signal is monitored during diversion of the load from the clevis joint to the load indicating device, full diversion of the load will be indicated by an end to the change in the output of the electrical strain gauge 48.

Once the load has been diverted fully from the clevis joint to the load indicating device, the nuts 35 and 37 are tightened down onto the clamping members 26 and 27 to retain the tie rods 32 and 33 in respective operative

positions relative to these clamping members. The jacks can then be relieved of the hydraulic pressure and removed, together with the associated bridges.

It will be noted that operation of the jacks urges the clamping members to pivot in respective directions such as to increase the clamping of the suspension rod concurrently with diversion of the load from the clevis joint.

The electrical strain gauge 43 is connected with the common sampling, data storage and data processing system. If required, a corresponding electrical strain gauge may be provided on the tie rod 32 also but we have found that a strain gauge on one only of the tie rods provides a reliable indication of the load to which the suspension rod 20 is subjected.

In Figure 5, there is represented at 220 an upper end portion of a further suspension rod which is supported from the support deck from which the suspension rod of Figure 1 is supported. In the particular example illustrated in Figure 5, the suspension rod nut 208 bears on a pad with a convex lower face which, in turn, rests on a pad corresponding to the support 9 of Figure 1. There is no substantial threaded portion of the suspension rod 220 protruding above the nut 208.

In application of the method of the present invention to the suspension rod of Figure 5, the load is diverted from an upper end portion of the suspension rod through a further load indicating device to the support deck. The load indicating device comprises a pair of clamping members 228 and 229 which clamp between them a portion of the suspension rod 220 below the level of the support deck. The clamping members 228 and 229 may be identical with the clamping members 28 and 29 and act on the suspension rod via pads which together form a split load-block. The clamping members are carried by a carrier identical with the carrier 38.

The load indicating device of Figure 5 further comprises load transferring means which includes a pair of tie rods 232 and 233. The tie rod 232 has a head at the underside of the clamping member 228 and extends upwards through a hole in that clamping member and through the support deck and a

further hole in a support pad 226. This pad rests on the support deck. A nut corresponding to the nut 35 bears on the upper face of the pad. The tie rod 233 is arranged in a similar manner with a nut and a pad adjacent to its upper end.

In order to divert the load in the suspension rod 220 to the load indicating device of Figure 5, bridges, hydraulic jacks and nuts corresponding to the bridge 44, jack 45 and nut 46 are applied to the tie rods 232 and 233 and the procedure hereinbefore described is used. The pressure is increased in the hydraulic jacks until the nut 208 rises from the pad on which it normally rests. This condition may be detected visually or by means of a feeler gauge. The respective nuts on the tie rods are then tightened down to the pads. Once this has been done, the jacks are relieved of hydraulic pressure and are removed, together with the bridges.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.