The Creeper Cranes.

From Engineering Heritage New South Wales


   The arch span of the Sydney Harbour Bridge was erected using two cranes which were aptly named ‘Creeper Cranes’ as they moved forward onto the bridge truss that they had just built to create the next panel, until the half arches met it the middle of the span. While the general concept of this procedure is well known among admirers of the bridge, the details of the scheme evolved through the design process. The cranes which ultimately did the job were remarkable machines.

   It was by no means necessary that a single crane (or two cranes – one on each half span) would carry out the whole task. David Anderson, whose firm had designed the Tyne Bridge in Newcastle UK, built simultaneously with the Sydney Harbour Bridge by Dorman Long, commenting on Freeman’s and Bradfield’s papers on the work, delivered to the British Institution of Civil Engineers in 1934, pointed out that that bridge had been built using a 5-ton derrick-crane which built a 20-ton derrick-crane which built the bridge and lifted the smaller crane ahead to move the larger crane to a new position to erect more of the bridge. He thought that the Sydney creeper cranes were expensive and must have set up heavy bending stresses in the bridge trusses. Freeman replied that the cranes were indeed expensive - £45,000 in the UK and £50,000 by the time they were erected in Sydney, but that the great width of the Harbour Bridge in relation to its panel length made the leap-frog technique impossible. The bridge structure had been designed to carry the erection loads imposed and in retrospect he thought that the cranes were perfect appliances. They had done every duty that had been imposed on them without a hitch from beginning to end and if the same problem had to be faced again he did not know a better way of dealing with it.[1]

   The draft erection procedure for the bridge as it existed in March 1924, when Dorman Long’s tender had just been accepted, included a creeper crane, slightly less in weight (536 tons) than that actually used but of much greater in lifting capacity (160 tons). It would have been employed as far as the tenth panel of the fourteen in the half arch only. A much lighter crane (180 tons), perhaps a stiff leg derrick crane, would have been used for the last four panels and apparently the erection of the deck. The prospect of having a 600-ton crane at the end of an 825-foot cantilever was not one to be glossed over.

   An article in The Sydney Mail on 26 March 1924, written by Kathleen Butler from the notes of J. J. C. Bradfield, includes the words:

The cranes weigh 536 tons each, and have been specially designed for this work, to lift members up to 160 tons weight.

In the fourth stage, as soon as sufficient cable is provided to sustain the reaction, the cables secured to the end post will be slacked, and the crane will continue to erect successive panels until the tenth panel is reached, leaving four panels on each side of the centre-line to be erected.

The remaining panels will be erected by means of a lighter crane, whose total weight is only about, 180 tons.

The accompanying drawings in the articles, sketchy as they are, illustrate these concepts. They are presumably sourced from Dorman Long as the publication date is only two days after the signing of the contract.

The erection procedure as envisaged in 1924. A large crane has built out as far as the tenth panel. Note that the tie-back arrangements shown are not those eventually used. The Sydney Mail 26 March 1924.
The smaller crane has built the last four panels on both half arches. The large crane is not shown, so must have been intended to have no further part in the work. Subsequent images in the series show the small crane building the deck. The Sydney Mail 26 March 1924.<


   With hindsight it is easy to ask how the light crane could have lifted the deck cross girders which were among the heaviest lifts on the bridge, but that would be to second guess the evolution of the design and the arguments that were had between the skilled and experienced men who carried out the work.

   The final design was to use a 600-ton machine with a lifting capacity of 120-tons all the way to the centre of the span to erect the arch and then on its return trip to erect the deck. Heavy and expensive as they were, two cranes were manufactured. Much of the other gear for the bridge erection was moved back and forth across the harbour so as to make double use of only one set, but this was not possible for the cranes.

   The creeper cranes were built specifically for the job in England by The Wellman Smith Owen Engineering Corporation Ltd. of Darlaston and one was erected on a stage approximating the slope of the Bridge top chord in Middlesbrough for testing before shipment to Sydney.

One of the cranes test assembled and operational at Dorman Long's works at Middlesbrough before shipment to Sydney. The Dorman Long Bridge Book. 1932.
An elevation drawing of the crane. Note the main jib, the wall crane on the front of the undercarriage and the derrick crane(s) at the rear of the traversing carriage. There are two of these cranes, but in this elevation view only the nearer one is drawn. The jigger hoist is shown at the lower end of its travel, very close to the carriages. ICE 1934. <


   The machines were much more than a single high-capacity crane. They had five independent cranes carried on the same chassis.

   The main crane – the one which would lift the heaviest components of the bridge – had a capacity of 120 tons. It could derrick, that is move the point of lift forward and back, under full load, by means of two large (9 inch) screws moving in phosphor-bronze nuts built into the crane jib, and could traverse across the width of the bridge to 25 feet beyond the arch trusses, on a track 148 feet long. The extreme point of lift was 10 feet outside the edge of the main truss and the speed of lift for maximum loads was 12½ feet per minute, meaning that a lift from a pontoon on the harbour to the higher parts of the bridge would take half an hour. Twice this lift rate was available for lighter loads up to 65 tons. The crane could traverse with a full load at 30 feet per minute, though this was automatically reduced to 10 ft. per minute at the ends of the travel.

Elevation of the crane looking along the bridge centreline. The tracks on the centre, deeper, part of the chassis of the crane are those for the travelling wall crane. An apparently minor part of the drawing is the 'small' steel section on which the crane bears - it is the bridge top chord, almost lost in the drawing. ICE 1934.
A drawing of the crane after it had moved off the part of the ramp where it was assembled and onto the extension of the ramp, into a position from where it could erect the first panel of the arch. Note the tie-back cables with their lower sections held in place but upper sections hanging limp pending the crane moving away and the ramp being dismantled, allowing access to their attachment point to the bridge. ICE 1934. <


   The traversing carriage was supported on a heavy box section underframe spanning between the bridge trusses and cantilevered beyond them. For travelling, the underframe was supported on four four-wheel bogies with unflanged wheels running on the flange plate of the chord directly above web plates inside the section. Once in position the front bogies were relieved of load using powered screw jacks. The carriage was hauled along the top of the bridge by a winch driven by a 50 H.P. electric motor through cables attached to points in the top chord at the further end of the panel just erected. The anchorage used was a keep plate grooved to clear rivet heads and secured through an access manhole in the flange of the box section bridge chord. Advance was at a speed of one foot per minute, or about an hour to advance one panel.

The front end of the undercarriage. Note the bogie for travelling and the rigid strut on which the crane rested once it was in the working position. The heavy safety chain and tension mechanism is to the right with the loose end of the chain hanging below. ICE 1934.
The southern crane being erected on the ramp on the abutment tower. 21 August 1928. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685.<


   The carriage was fitted with guide rollers on the outside of the flanges and clips locking it against overturning. Mechanisms were in place to ensure that both sides of the undercarriage moved forward at the same rate. The greatest worry however in the moving process was that a failure of the winch or cables could result in the heavy mass falling back until some check mechanism cut in. It was considered that the impact of the 600-tons falling one inch would result in the complete loss of the half truss and however remote, this was not acceptable. To avoid the possibility of any slip the moving undercarriage was also secured by four heavy link-and-pin chains, a pair on each chord, around a sprocket at the outer end of the chain. An electric motor driving though a worm gear maintained a tension force in the chains and had the weight of the crane fallen on to them there would have been minimal movement before they held the full load.

The jib of the southern crane being erected. The enthusiasm of the photographer must be admired as it would seem that he has carried his camera to the top of the 25-ton erection crane, or the derrick crane on the creeper crane itself. 21 August 1928. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685.
The southern crane ready to begin assembly of the end frame, but not yet moved forward to the end of the assembly ramp.The vantage point must be the jib of the floating crane Titan. 10 October 1928. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685.<


   There was only one set of chains and tensioning mechanism, and it was moved between Dawes Point and Milsons Point for the relatively infrequent movements of the cranes. The inclination of the top chord was a challenging 1 in 2 at its steepest but as it reduced with the curve of the arch and the cranes reached the flatter part, after the eighth panel, a simpler mechanism was used with a single chain with two pawls, one of which was always engaged. The attachment of the chain to the bridge after the eighth panel was a simple pin. For the return journey of the cranes once the two halves of the arch had been joined, the motor, worm and sprocket mechanisms were left in the centre of the bridge and the chain extended successively with panel-length sections of cable for each movement. The chain was run through the machine to the north or south side as the respective cranes were lowered.

All five cranes on the creeper crane. The jigger hoist is working near the end of the ramp with the left derrick crane visible behind and above it. The wall crane on the front of the traversing carriage is directly in front of the derrick crane at the right of the other end of the carriage. 10 October 1928. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685.
The crane has moved forward, with the safety chains seen draped over the end of the ramp. The first section of the lower chord is in place on the bearing and the end post is being assembled in three sections. 1 November 1928. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685.<


   Beneath the jib of the main crane was a trolley carrying the lifting point for the jigger crane. This had a capacity of 20 tons. It traversed with the main crane, but its point of lift could move along the length of the main crane's jib. Its main purpose was as a supplementary point of attachment to loads to control their inclination. Although in major lifts it hoisted at the same rate as the main crane, it could also independently lift lighter loads at twice the speed. Both hoisting and traversing were driven by 50 H.P. electric motors. Under full load the trolley could traverse the full length of the jib in two minutes.

A feast of cranes. Apart from those on the creeper crane proper, the 25-ton crane which erected it and the 5-ton crane building the pylon tower are seen. 21 January 1929. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685.
An image taken below the crane undercarriage. On the right is the end panel of the bridge with the diagonal strut locking it to the abutment tower. On the crane ramp at the right is the rigid strut locking the front end of the crane with a keyway onto the keeper plate. Behind it is the travelling bogie, for the present not carrying any load. The built-up link frame resting on the ramp with the pulley and rope is the climbing mechanism for the complete creeper crane. Temporary tie-back cables are visible above the engineer climbing the ladder and the safety chains are draped to the right. 21 January 1929. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685.<


   Along the front girder of the crane undercarriage a 5-ton wall crane operated independently. Its travelling capacity was 50 feet and by using both this and the slewing capacity of its 39-feet jib, it could reach any point in the bridge width. It had a hoisting rate of 60 ft. per minute and could traverse the whole length of its track in a minute. It was used for movement of stages and workers. A frame attached to the back of the traversing carriage supported two 2½-ton derrick cranes with 70-feet jibs for dealing with riveting stages, stores, tools, etc. The frames for the cranes were adjustable to allow for the angle change as the main crane travelled up the arch, and they could reach any point in the preceding panel and lift at 40ft. per minute.

A view down the temporary ramp. The temporary tie-back cables are at the bottom of the picture, the girders are the ramp and the safety clip to preclude the creeper crane toppling forward under overload is locked under the flange of the ramp girder. 21 January 1929. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
Workers riveting the portal frame, eventually to be above the roadway, of the end frame. The safety chains and tensioning mechanism are at extreme right top. The assembly method of the steel sections is well illustrated - some of the holes have tapered drifts, some have temporary bolts and the some are empty ready for rivets, a few of which have been placed. 21 January 1929. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685<


   The five-cranes-in-one machines were erected on the deck level of the abutment towers by the 25-ton derrick cranes which had built the approach spans. The creeper cranes were erected on temporary ramps at the same inclination as, and aligned with, the top chord of the truss which they would build. Their first task was the erection of the end panel of the bridge. The usual path from workshops to crane hook was via a barge, but at Dawes Point the creeper crane, standing on the pylon could not reach the harbour side so the floating crane ‘Titan’ lifted components from barge to shore and within reach of the creeper crane. At Milsons Point ‘Titan’ was not required as sections were brought directly from the workshops by rail.

Assembly of the northern creeper crane. It would seem from the photo that the 25-ton derrick crane was erected on the creeper crane undercarriage so as to more readily erect the jib of the main creeper crane. 7 June 1929. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
The northern crane from the abutment tower deck. The gear in the centre of the undercarriage is the mechanism to haul the whole 600-ton assembly up the slope of the top chord of the bridge. 6 July 1929. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685<


   With the end frame erected the crane ramp was extended to it and the crane moved forward to a point where it could erect most of the first complete panel, before moving forward again to erect the cross members in the lateral bracing system. The ramp occupied the position where the permanent cable anchorages for the half-truss would eventually be and so a temporary tie-back point was made lower on the end post.    With the first panel complete the creeper crane moved fully onto it, the ramp was dismantled and taken to the northern side of the harbour to repeat the process. This allowed the permanent tie-back arrangements to be set up at the end of the top chord.

All three front facing cranes are used on a lower chord section. The 120-ron crane has lifted it; the jigger hoist is controlling its inclination and the wall crane is lifting some light gear. On the right, against the post, tension cables, which will soon be used to hold the chord section until the truss diagonal member is lifted, hang limp. 16 October 1929 Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
The top chord near the top of the bridge. Only one safety chain is in use and it does not have the tensioning mechanism. The keep-plate for the next movement of the crane is set up, with a projecting key ready to receive the keyway on the strut under the crane. Riveters are joining the two halves of the chord with a cover plate. 29 July 1930. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685<


   Erection of the next thirteen panels on each side of the harbour was a repetitive process with the crane erecting a panel and then moving on to it. The southern half arch was built in advance of the northern, but at panel 8 the southern work stopped to allow the northern to catch up and for them to then advance together.

The jibs of the two creeper cranes caught in a single photo at the top of the arch. The arrangement for the jigger hoist is clearly shown, with a trolley running on rails beneath the jib of the larger crane. 12 August 1930. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
Ennis' and Freeman's illustration of the process of modifying the creeper cranes for their downward journey. ICE 1934.


   On their outward journey on the steepest parts of the top chord the cranes were able to lift 122 tons at 41 feet in advance of the panel point on which they were standing and 65 tones at 61 feet ahead. On their return journey they needed to be able to lift the 100-ton deck cross-girders and on the near horizontal upper parts of the curve could not derrick sufficiently to a radius short enough to lift this load. This required the derricking range of the jibs to be adjusted. Provision had been made for this in the design by allowing for some members of the jib truss frame to be removed.

Workers removing a panel from the jib of the main crane to change its derricking range so as to allow it to lift the deck structure on its return trip to the ends of the bridge. 20 September 1930. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
Workers removing a panel from the jib of the main crane to change its derricking range so as to allow it to lift the deck structure on its return trip to the ends of the bridge. 20 September 1930. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685<


   Freeman and Ennis write:

It had been anticipated that this process would be somewhat hazardous and difficult, because until the two cranes met at the top of the bridge they had always been regarded as independent, and while they were so the change-over would certainly have been a very anxious undertaking. The change was, however, conveniently carried out at the centre of the bridge, the jibs of the two cranes being allowed to rest against each other while the back members were removed.[2]

A view of the top of the bridge from the jib of the northern creeper crane. The safety chains and tensioning gear have been set up with the short, one panel-length, chains extended for each cycle with panel-length sections of erection cables. As the crane is still on the flatter part of the arch only one cable is in use. 5 November 1930. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
Workers adjusting two safety chains as the cranes are well into the steeper sections of the arch. 1 December 1930. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685<


   For the erection of the deck there were inherent limitations with the cranes now above the completed trusses. The deck cross-girders were directly below cross-members in the bracing in the planes of the upper and lower chords. This could be worked around with relatively light tackle, but a more challenging problem was the deck hangers which were directly below the chords and quite inaccessible to the crane hook. A frame for hoisting and rotating the slender sections was devised and this allowed them to hang perfectly vertically, offset from the crane hook by half the width of the chord.

The horizontal lifting beam placing sections of the bridge beyond the nominal range of the crane hook. 31 January 1931. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
A diagram from Ennis' and Freeman's 1934 ICE paper showing the technique used to lift the hangers into a position directly under the chord.<


   A number of pieces of the deck structure were situated outside the reach of the creeper crane and, to place these in position, a pair of railway stringers braced together, forming a box 60 ft. long and 7 ft. 6 in. wide, was used as a horizontal lifting beam. This beam was slung by means of four straps in an unbalanced position and the members to be lifted were attached to the light end; with the addition of this weight the lifting beam assumed a position practically horizontal and the member to be lifted could be placed into position some distance from the hoist. This lifting device was adopted for the chord members of the deck lateral system, the footway spans, and the painting gantry girders beneath the arch ribs.[3]

The crane lowering system with the crane on the steep part of the bridge. Two cables are in use, with the chains and tensioning device at the highest point of the arch. The built-up link frame, the pulleys and the ropes are the actual hauling device which had raised the crane and is now lowering it. 2 December 1930. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
The tensioning mechanism for the safety chains at the top of the bridge. 2 December 1930. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685<



End view of the tensioning mechanism for the safety chains at the top of the bridge. A descent must be about to begin as the chains are on the other side of the sprockets and the cables which connect to the crane are taut. 2 December 1930. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
Side view of the tensioning mechanism for the safety chains at the top of the bridge. A descent must be about to begin as the chains are on the other side of the sprockets to the load, and the cables which connect to the crane are taut. The mechanism could work in either direction to control either north or south cranes. 2 December 1930. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685<


   By the time that the creeper cranes had returned to the ends of the main span the 25-ton derrick cranes from the approach span erection had gone and the concrete and stone pylons were being erected by 7-ton cranes on 80 -feet high timber towers. These smaller cranes re-erected the 25-ton cranes including an extended jib, on similar timber towers, also 80 feet above the deck. The 25-ton crane dismantled the creeper crane and then the 7-ton crane dismantled the 25-ton crane.


One of the cranes, probably the northern one, has reached the end of the bridge and with its work done is ready to be dismantled. 20 March 1931. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
Workers beginning the task of dismantling the crane. The 25-ton derrick crane has been specifically erected for the job and has a flying jib for the extreme reach to the end of the creeper crane jib. 13 April 1931. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685<



The 25-ton derrick crane on 80 ft. tall timber towers and with a very long reach to dismantle the creeper crane. 13 April 1931. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
Dismantling the northern creeper crane, but now without the fly jib as the extreme end of the jib has been removed. A smaller derrick crane is building the pylon towers. 16 April 1931. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685<



Dismantling the southern creeper crane with the fly-jib. The northern crane was dismantled first. Probably there was only one fly-jib and the southern work could not begin until the gear was released from the north. 20 April 1931. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
A side view of he dismantling pf the southern creeper crane. 21 April 1931. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685<



Removing the derricking screws from the northern creeper crane. 30 April 1931. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685
Dismantling the upper section of the undercarriage. The track for the crane has been extended with a light ramp. Perhaps these heavier parts of the structure needed to be moved closer to the crane to be lifted safely. 15 May 1931. Museums of History. Sydney Harbour Bridge Photographic Albums. NRS12685<



Sources
Sydney Harbour Bridge, Dorman Long and Company Limited 1932
Transactions of the Institution of Civil Engineers 1934. Papers by Ralph Freeman, Lawrence Ennis and John Bradfield.
Sydney Harbour Bridge Photograph Albums. NRS 12685. NSW Museums of History.


  1. ICE 1934 p 330
  2. Proceedings ICE 1934 p212
  3. Sydney Harbour Bridge, Dorman Long. 1932
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