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T-girder bridges, Part 5.1

Girder bridges replaced prior to 1998: Page 1.

Our original study, culminating in the publication Monash Bridges, concentrated on bridges extant in the late 1990s. Many more T-girder bridges were built by the Reinforced Concrete & Monier Pipe Construction Company under Monash's direction. A large number of these were replaced prior to our study, as traffic needs increased. A few were destroyed by extreme floods. This section of our website outlines the stories of most of these bridges.

Bungaree Bridge.

Former Location:On the "Springs-road", Brown Hill, near Ballarat, over Yarrowee Creek.
Former Municipality:Shire of Bungaree.
Description:Single 4.9m span.
Activity:April to June 1913.
Status:Demolished.

Tenders for this bridge appeared in The Age on 12 April 1913. On 14th, Monash wrote to the Shire Engineer, Julius S. Lazarus, C.E., at the Shire Office, Leigh Creek. The advertisement called for a bridge in "Ferro Concrete", the term associated with RCMPC's rival, the Ferro-Concrete Company of Australasia. Would Lazarus accept a tender from RCMPC? The reply was positive and on 3 May, Monash submitted a tender for £183, noting that his Factor of Safety for concrete strength was 10, and that for steel 5. He emphasised that RCMPC had considerable experience, having built almost 100 bridges in Victoria to that date.

On 6 May, RCMPC was notified that the tender had been accepted. RCMPC's drawings were sent to G Kermode at the Public Works Department for approval. Monash told Lazarus that he was keen to start work before winter set in. H Brockwell was appointed as RCMPC's foreman, and sent his first daily report from the site on 24 May. On 18 June 1913 he advised that the bridge was almost complete.

This was a simple bridge with a single clear span of 16 feet. It was 19 feet wide and had four longitudinal girders. The abutments and wing walls were of unreinforced rubble concrete.

University of Melbourne Archives holds a historic image (Location Number BWP/23943) showing the bridge side-on, taken from the creek.


Bradshaw's Creek Bridge.

Bradshaw's Creek Bridge under test. University of Melbourne Archives, Location No. BWP/24136.
Reinforced Concrete & Monier Pipe Construction Co. Collection.

Former Location:2.4 km from Bradshaw Railway Station.
Former Municipality:Shire of Ballan.
Description:15.2m long, 6.1m wide. Two spans.
Activity:Feb. 1914 to Dec. 1914.
Status:Demolished.

On 12 February 1914, the Shire Engineer of Ballan, Piers Kelly, was at the Public Works Department head office, accompanying a deputation from the Shire seeking a grant to construct this bridge. He put in a phone call from there to Monash's office, asking for a quotation. The bridge, situated 1.5 miles from Bradshaw Station, was to be 50 feet long and 20 feet wide. The call for formal tenders appeared in The Argus on 26 September 1914. RCMPC"s bid of £424 was accepted on 16 November. Alex Lynch reconnoitred the site, and reported on 30 November. Drawings were prepared by J A Laing in December 1914 and January 1915. T Harrigan was appointed as foreman. Monash had only slight involvement with this project in the lead up to his departure for World War 1.

University of Melbourne Archives holds a historic image (Location Number BWP/24137) taken at deck level, showing a group standing in front of the traction engine observed by a dog. This may be seen on the internet at: UMAIC or Picture Australia. To view this image within UMAIC, search under Record ID for image UMA/I/6491.
Further images relevant to this bridge held by UMA are:
BWP/24133: previous bridge (timber)
BWP/24134: construction at deck level
BWP/24135: completed bridge
BWP/24136: completed bridge with traction engine (reproduced above)
BWP/24137a: similar to BWP/24137
Any enquiries to UMA concerning these images should refer to their Location Numbers.


Elsternwick Bridge.

Former Location:Carried Point Nepean Road (now the Nepean Highway) over the canalised Elster Creek.
Former Municipality:Joint City of Brighton and City of Caulfield.
Description:More a culvert than a bridge. 14 orthogonal portal frames, with minor beams diverging from end portals to cater for skew. Road width 20.1m. Length of culvert approx 25.6m. Skew 37.6°.
Activity:Aug. 1906 to May 1907.
Status:Replaced during reconstruction of highway, 1965.

The story of this bridge is of interest because of the interaction that occurred between Monash and two notable Melbourne consulting engineers. The bridge carried Point Nepean Road (now the Nepean Highway) over the canalised Elster Creek. It lay on the boundary of the suburban cities of Caulfield and Brighton. The project was handled mainly by the City Engineer for Brighton - a role filled by the father-and-son partnership of John Montgomery Coane and Henry Edward Coane. On 25 June 1906, T B Muntz, the Engineer for Caulfield, wrote to Monash: "Coane and I are going into the question of a new bridge on Pt Nepean Road ... He has designed a steel girder bridge in 2/12' spans … it occurred to me after inspecting the S Kilda St Monier bridge over same Creek that that might compete in price. We confer 2.30 tomorrow at his office. Meantime you might give me an approx. idea of the cost of say an equally efficient [reinforced concrete] bridge (say 22' span) with a roadway, say 40 feet. The abuts. would be about 7' high to underside of girder … " In reply, Monash quoted £200-£250, and Muntz promised to get Coane to allow for tenders employing reinforced concrete instead of steel.

12 feet = 3.6m   22 feet = 6.7m.   40 feet = 12.2m   7 feet = 2.13m

The bridge was required to carry a 15-ton steam roller. Monash's structural calculations, dated 21 July, include one of the earliest bending moment diagrams in RCMPC's records. He submitted his full tender and specification to the Brighton Town Clerk on 15 September, and a week later asked Catani to speed the decision-making process. After an unsuccessful attempt to see the State Premier (Thomas Bent) Catani talked to Coane, who simply guaranteed to recommend Monash's design if he felt it to be the most suitable. It was obvious that he had reservations. At Catani's urging, Monash indicated he was willing to alter his reinforcement to suit; but Coane said he had not had time to look at the documents and was too busy to discuss the matter.

Muntz then supplied Monash with a copy of an unsigned three-page report critical of the reinforced concrete design, presumably written by the Coanes. Monash prepared a forceful rebuttal, and analysed the Coanes's original brick-and-steel design to show that his own factor of safety was comparable with theirs. He claimed that the critic showed "only a nodding acquaintance with the elementary principles of Reinforced Concrete"; had "fallen into several grave errors, not unusual to beginners in the subject"; and had "been at pains to overstate the case against my design at every step". He added: "I will vouch for my design as being well within the Official Regulations of the German Empire and of New York City Building laws". He pointed to successful tests of girders with the same cross-section but larger span, and concluded: "I will take all responsibility for the ample strength of my design".

On 1 October, J M Coane asked to see the calculations for the reinforced concrete girders "and learn what you consider to be your factor of safety therein". Before replying, Monash double-checked his calculations which were based on French and German texts and regulations. For two independent checks on bending strength he referred to design tables prepared by Professor Warren of Sydney University and others by a Professor Kaufman. These both suggested the use of smaller, more highly reinforced cross-sections than Monash's, but this was not necessarily a better solution.

On 10th Coane finally accepted RCMPC's tender at £485, provided that Monash redesigned the girders using the method set out in Buel & Hill's text on reinforced concrete, and using bending moments specified by Coane. Further, the Brighton Council was anxious about the "very heavy and constant traffic" that the structure would have to carry, and wanted a performance bond of £250 for 12 months. Monash accepted these terms, but said that his directors would want the bond placed with someone like Coane, rather than with the Council. The nearest competitive tender for the bridge had come from W T Grant, for £510-14-0.

The Councils then decided that the width of the bridge should be increased so that the parapets would continue the building line on both sides. Monash took the opportunity to revise the layout of the structure. Originally he had aligned the girders with the direction of traffic. Now he rotated them through a horizontal angle of 38 degrees, to run at right-angles to the channel walls. The Councils beat Monash's price for the widening down to £140, making a total of £625.

It was only on 8 December that Monash sent his clerk to copy Coane's specifications for the bridge and found them not to his liking. The concrete mix was specified as 1:2:3 (cement, sand, stone) whereas the customary mix was 1:2:4. Monash also considered the required ultimate strength of steel (26 tons per square inch, or 400 Mpa) to be too high. However, Coane refused to budge.

Monash sent the first requisition for materials to RCMPC's Richmond depot on 14 December 1906. The contract was formally signed on 22nd. A progress payment of £275 was authorised by Coane on 14 February 1907, and the bridge was completed sometime in March. Monash submitted his final statement of accounts on 23 April, and the bridge was tested with a 15-ton roller on 16 May, 1907.

Note for engineers. I have not investigated the disagreement between Monash and Coane in depth, but offer some initial observations. The girders rested on short columns built integral with the abutment walls. Monash described the girders as "encastré", but used formulas for bending moment that implied only partial fixity. The drawings of December 1906 show no connection or lapping between the top bars at the ends of the girders and the outer bars of the columns, and thus a lack of continuity in the reinforcement around the outside of the knee joint. For uniformly distributed dead load, JM used WL/10 for the 'positive' bending moment (tension on lower face), implying a ' negative' end moment of WL/40.

Monash took advantage of the fact that in T-beams subjected to positive bending moment, the compressive force in the concrete is spread over a certain width of deck slab, reducing the intensity of the stress in the concrete. His critic checked the size of the girders by taking a rectangular cross-section of width equal to the stem of the T, thus using 10" × 21" (254 × 533mm) for gross concrete cross-section, rather than the 58" x 21" (1470 × 533mm) taken by JM. The critic assumed the neutral axis to be "one inch [25mm] below the centre of the beam", and thus estimated the effective depth to be 15" (381mm), leading to a higher estimated stress. (Monash had assumed the NA to be level with the bottom of the deck, giving him an effective depth of 18" or 457mm.)

The critic checked the size of JM's T-beams against tables for rectangular sections prepared by Professor Warren of Sydney University and others by Kaufman. Again he ignored T action. He obtained cross-sections of shallower depth than JM's, with heavier reinforcement, and impled that JM's sizes were wrong.

In this era before the invention of the slope-deflection and moment-distribution methods, both JM and the critic depended on simple formulas such as WL/8 and WL/10 for bending moment. (No attempts at frame analysis have been found.) It was accepted that the governing case for live load would be the 15-ton roller, so there is no mention of uniformly distributed live load. Differences arose over the choice of formula, especially for the effect of the roller, and to allow for end fixity, if any; over the value of the dead load; and over the 'effective span' to be fed into the formulas.

The critic also queried shear reinforcement of the girders and punching shear strength of the deck - probably aware of problems that had arisen with Monash's first reinforced concrete girder bridge at Stawell St, Ballarat East. Further criticisms were that a Clerk of Works would have to be in attendance at all times to ensure quality of the concrete; that JM's girders were spaced further apart than those in the steel design; and that "the heavy dead load of the concrete structure is against it".

When Monash consulted Gummow and Baltzer in Sydney regarding the calculation of shear reinforcement they referred him to the methods of von Emperger; Sanders & Weske; and Ramisch. As noted above, Monash based his approach to design of reinforced concrete mainly on von Emperger's serial Beton und Eisen and the text of the Belgian engineer, Paul Christophe, backed up by the German Imperial Regulations and those of New York City. Coane evidently relied on Buel and Hill.


McIsaac's Bridge, alias Kilmore Bridge.

Former Location:On the McIvor Rd over Kilmore Creek, 6 km from Moranding, 8 km from Kilmore.
Former Municipality:Shire of Kilmore.
Description:2 spans of 7.6 m.
Activity:Sept. 1906 to June 1907.
Status:Replaced.

Bridge at McIsaac's, Kilmore.
Photo: University of Melbourne Archives, Reinforced Concrete & Monier Pipe Construction Co Collection, Location Number BWP/24362.

McIsaac's Bridge was near the home of Councillor McIsaac, where McIvor's Road (now the Northern Highway), crosses the Kilmore Creek, about 5 miles (8 km) from Kilmore. The previous structure had been washed away in the flood of 9 September 1906, severing the road that led on to Pyalong and Heathcote. Monash contacted the Kilmore Shire Engineer, H J Hunt, and on 20th jotted down his ideas for a replacement bridge. Hunt called at the RCMPC office on 26th to discuss worries about the "doubtful foundations".

On 12 October, Hunt reported that he had not yet been able to get a decision from the Council on the question of reinforced concrete. He and Councillor Fennelly had attended the recent test of RCMPC's bridge over Deep Creek four kilometres east of Lancefield and had been impressed that the deflection under test load had been "scarcely perceptible". It was likely that Fennelly, who was a civil engineer would recommend the choice of reinforced concrete.

This was probably R Fennelly, who was Engineer and Secretary to the Shire of Pyalong, and an Associate Member of the UK Institution of Civil Engineers (equivalent to the present grade of Member).

In mid-November, Hunt reported to his Council on claims made to the Public Works department for funds to repair flood damage, and mentioned that he had had a "reasonable offer" for the reconstruction of McIsaacs Bridge in Monier (reinforced concrete) similar to that at Deep Creek. On 19th he was able to tell Monash that the Council had "at last" decided to call for alternative tenders in timber and reinforced concrete. However, he advised that "from the nature of the ground it will be better for you to visit the site …" which he had investigated by sinking trial pits. He offered to meet Monash at the site. Tenders were duly advertised, closing on 4 December.

At this time Monash was preoccupied with a number of major initiatives, and sent W W Harvey, one of his two assistant engineers, to reconnoitre the site. Harvey prepared a map extending from Kilmore East railway station to Pyalong township. This showed the McIsaacs site in relation to useful railway stations and sidings, connecting roads (with comments on their grades and surface), and sources of sand and stone. An important feature was the nearby hotel, run by Miss Griffith, which could provide accommodation as well as refreshment for the workers. Harvey also sketched the conventional timber bridge that Hunt had designed in his duty as Shire Engineer.

Harvey estimated the cost of a reinforced concrete bridge at £260-6-0. He allowed £39-14-0 for sundries, to give a total cost of £300. Adding a clear margin of £105 suggested a tender price of £405. Harvey estimated the tender price for Hunt's timber design would be £384. By this stage, Monash was well used to convincing Councils that the slightly lower capital cost of a timber bridge would be outweighed by the greater cost of maintenance.

The drawing for the bridge shows four main girders in parallel, having two spans, nominally 25 feet (7.6m) each. The central pier is composed of four columns carrying a spreader beam and sitting on a strip footing on rock. The specification (provided by RCMPC as was customary) included a test by a 14 ton traction engine.

In his covering letter to the tender, Monash pointed out that the new bridge provided double the waterway (basically the clear span) provided by the previous bridge. In an "unofficial" letter to Hunt, Monash noted that the tender should serve to convince the Council that "Councillor Fennelly was not quite well informed when at a recent meeting he stated that a Monier Bridge would cost 'fully double that of a timber one' ". He added that the proposed bridge would be fully guaranteed. In his opinion "a permanent structure of this nature is worth fully double that of a timber one, though costing little, if any, more". Furthermore, "I am quite sure that Mr. Catani [Public Works Engineer] will concur in this view. We have carried out several of these bridges for his Dept., and there are now over 50 in existence in various parts of this State." He gave Hunt "the hint" that both the Minister of Public Works, and its Inspector-General Davidson required all tenders for loan or grant works to be submitted "and will recommend reinforced concrete even if [the price is] substantially higher, which is not likely". "This is a course of action they have taken on several recent occasions." On 17 December, Monash was informed that his tender was lowest. The price was later increased by £15 to allow for iron rather than timber handrails.

It may have been Fennelly who persuaded the Council to send the drawing and specifications to consulting engineer T W Fowler for a second opinion on its "strength and efficiency". Fowler, in addition to being an extremely busy consultant in many fields, was a lecturer at the University of Melbourne. Monash was regularly in touch with him in both capacities. Fowler asked Monash to contact him so he could "go into the matter". He altered the central pier to become a solid wall 18" (457mm) thick, and slightly increased the reinforcement in the abutment walls. This resulted in a further increase in price of £14. (A letter in November 1907, concerning another bridge, suggests that the pier as completed was "solid rubble concrete 10' × 2' × 30' high".)

The contract was signed on 8 March 1907, for £422. It was only then that Monash supplied a drawing showing full details of the reinforcement. This was marked "Confidential" in the hope of preserving his intellectual property. Construction commenced on 4 April, under foreman D Giggins, and was complete by 5 June. At this date, Works Manager Alex Lynch visited the bridge and removed the remaining formwork and temporary supports. He reported that the structure looked good. Traffic was to be kept off it for another week to allow the concrete to gain full strength.

Monash sent in a claim for a "progress payment" for the contract price of £422, plus extra materials £2-2-0, and return of his deposit of £20, ready for the Council meeting of 5 June. It turned out that Hunt had not prepared the necessary voucher approving the quality of the work. The Chairman commented "This is a serious matter. We can't put these people [RCMPC] off like other contractors." Payment of £250 was approved, with the remainder to be considered at the next meeting on 19th.

On 10 July, Hunt advised Monash that the Council had inspected the bridge, and wanted the pier and abutment walls surface-finished, as they currently had "an apparent unfinished outward appearance". Monash was asked to send men to float over or cover the surfaces with cement mortar. "By doing so you will be adding another good 'Advertisement' to your Mode of Bridge Construction".

The bridge was formally declared open soon after. The Kilmore Advertiser reported: "The Kilmore Shire Council was represented by the President (Cr. M. McManus), and Crs. Fennelly, McIsaac, Wortley, Skehan, and O'Neill. After a thorough inspection of the bridge had been made … refreshments were provided, and the President, in formally declaring the bridge opened for traffic, dealt with its construction, and the reasonable cost of same. Cr Skehan said they had every reason to be proud of the new bridge, and the council had taken the precaution to have the expert advice of two officers outside of the shire in its construction. Cr Fennelly said that Mr R. L. Argyle, the member for the district, deserved a special vote of thanks for the trouble he had taken in securing a vote from the Government in connection with the construction of the bridge and for flood damages in the shire. Cr McIsaac said he was pleased that the bridge had at last been opened, as no one felt the want of it more than he did. Mr H. J. Hunt, shire engineer, also spoke. Mention was also made of the services rendered by Mr Thomas Walker Fowler, consulting engineer, in connection with the preparation of the plans for the bridge, and to Major Monash for his supervision. The new structure is one that will last for many years, but some additional waterway will have to be provided for on the north side."


Cochrane St Bridge, Elwood.

Former Location:Carried Cochrane Street over the Elwood Canal.
Former Municipality:City of Elwood.
Description:3 spans, nominally 5.2m. 5.5m, 5.2m.
Activity:May to Nov. 1907.
Status:Replaced.

Cochrane St Bridge, Elwood 1907. Elevation showing concrete outline on the left, reinforcement details on the right. From a RCMPC drawing in the J Thomas Collection.

The first intimation of this project in the RCMPC file is a note dated 13 May 1907 from Clerk John McNaught, to say that a clerk from the Public Works Department had left a plan [showing the outlines] of the required bridge, to be based on Monash's earlier Elwood bridge. The PWD wished Monash to follow "exactly the same procedure". On 23rd, assistant engineer S J Lindsay traced a drawing showing Monash's "amended design" for the new bridge. Like the other Elwood bridges, it was to have three spans, nominally 16 ft, 17 ft, and 16 ft. There were to be six parallel girders supported by six columns at the abutments and the piers. The deck was to be 24'-6" wide.

As usual, the RCMPC office designed and costed a timber version of the bridge, so as to calculate what price might be offered by competitors. Monash tendered a total price of £428, including £352 for the bridge structure plus wing walls, fence, and roadway; £66 for the approaches; and £10 for "provision". The contract was signed on 26 June 1907. Work started within a few days, and the final account was submitted early in November.


Asling St Bridge, Elwood.

Former Location:Carried Asling St over the Elwood Canal.
Former Municipality:City of Elwood.
Description:3 spans, nominally 5.2m. 5.5m, 5.2m.
Activity:Feb. to July 1908.
Status:Replaced 1975.

In February 1908, Carlo Catani, Engineer for Roads and Bridges with the Public Works Department, asked Monash to provide a bridge to carry Asling Street over the Elwood Canal, similar to the one recently built for Cochrane Street. It appears that an outline drawing of the proposed bridge was prepared in Catani's office by his assistant George Kermode, leaving Monash to provide the precise details of concrete dimensions and reinforcement. Monash said the bridge would be about the same price as that at Cochrane Street (£428) plus a £20 allowance for an increase in the price of cement. Catani asked for a definite tender for a bridge 24 feet (7.3m) wide with slightly larger span and greater skew, and then increased the width further, to 32'-6" (9.9m). Kermode produced a revised outline drawing and Monash tendered a price of £579. The contract was signed on 13 March 1908.

As usual, Monash had refrained from carrying out a full stress analysis until he was sure of the contract. He then realised that, despite the longer spans, the girders could be the same size as at Cochrane Street (10 inches [254mm] wide and projecting 14 inches [356mm] below the deck slab) and that the same reinforcement would suffice. To avoid awkward questions about the higher price he had quoted, he told Works Manager Alex Lynch to make the Asling St girders project 15 inches (381mm) nevertheless. Owing to the high rate of construction of Monash's Elwood Canal bridges, Lynch was told he would have to work from his knowledge of Cochrane Street, noting the following differences:

Early in July 1908, Monash informed Catani that the concrete superstructure had been completed about 15th May. "Mr Brown asked me on 16 June if it was safe to carry roller and I said yes."


Waterford Bridge.

Former Location:Carried the Stratford-Dargo road over the Mitchell River.
Former Municipality:Shire of Avon.
Description:5 spans of 9.1m.
Activity:Sept. 1907 to July 1908.
Status:Destroyed by build-up of debris during heavy flood, 27 September 1916.

Relevant Global coordinates: Stratford -37.965854, 147.080154; Waterford -37.515581, 147.204652.

General views of the bridge.

A general view of the bridge may be seen in the online image collection of the State Library on Victoria, Image No. b52678, Accession No. H21136. It shows the recently-built reinforced concrete structure in front of the old timber bridge. The view is taken from the approach from Stratford. The road to Dargo curves away on the opposite bank. (See sketch map below.) A view from a similar vantage point, probably taken when the bridge was undergoing test by a wagon loaded with rocks on 10 September 1908, is reproduced in Christie (1994), p.52.

History

Preliminary negotiations

Late in 1907 the Avon Shire Council in Gippsland planned to replace the deteriorating timber bridge that carried the Stratford-to-Dargo road over the Mitchell River. Carlo Catani, Chief Engineer of the Public Works Department of Victoria, suggested the replacement be in reinforced concrete and alerted Monash, whose firm claimed sole rights to the Monier licence.

It was unusual for Monash to accept a project so far from the sources of cement and steel. The closest convenient railway station was at Stratford, 222 km (138 miles) from Melbourne. Loads would then have to be hauled by horses 69 km (43 miles) into the mountains to Waterford. The inconvenience of travel also meant that reconnaissance and investigation of the site would be more expensive than usual. Monash obtained an agreement that if preliminary reconnaissance showed that a concrete bridge could be built for £1400 or less (competitive with timber) he would be guaranteed a contract. He recognised that the Council would have to depend on his firm's fairness to charge less, should the cost prove lower; but promised that if it proved to be more, the Reinforced Concrete & Monier Pipe Construction Co would bear the extra cost.

Shire Engineer Johnson's sketch plan of the locality. University of Melbourne Archives, Reinforced Concrete & Monier Pipe Construction Co Collection, File 743A.

Further negotiations, investigation, and design

The Shire Engineer, A L Johnson, was concerned about the danger presented by floods. In mountainous regions these are often violent and carry fallen trees and branches. If this debris becomes lodged against a bridge it forms a dam. The pressure thus exerted may break up or overturn the structure, while the increased velocity of flow may scour the foundations and undermine it. Johnson argued that, to reduce the danger of debris being caught, the piers should be 50 feet (15.2 m) apart, and the deck 30 feet (9.1 m) above the river bed. Monash argued that the difficulty of ensuring proper supervision at long range meant it would be safest to limit spans in reinforced concrete to 30 feet. [This would also have been advisable for reasons of strength and stiffness.] Johnson continued to put his point of view throughout the lengthy negotiations but Monash prevailed, and the bridge, 150 feet long (45.7 m), was designed with five 30-foot spans, necessitating four piers in the waterway.

The Public Works Department had allocated only £1200 for the job, but a visit from Mr M Kileen, the Shire President, extracted the extra £200. Monash's Works Manager, Alex Lynch, reconnoitred the site in mid-November. His instructions from Monash included:

The question of communication between the work site and the Melbourne office was of critical importance. Lynch reported that urgent telegrams sent to Dargo, 10 miles (16 km) further up the mountain, would be sent back to Waterford by "any one who happened to be travelling in that direction". The local constable (Ryan) had promised to look after them. Letters posted to Waterford via Bulgoback left Stratford on Tuesdays and Fridays. Outward mail was conveyed by the postman on Mondays and Thursdays, and at other times by "any one travelling to Stratford". Lynch advised that the river was at the time 100 feet wide (30.5 m), and only 18 inches deep (0.5 m) and that bedrock was 5'-6" (1.7 m) below the surface. No doubt impressed by local accounts of Mitchell River floods, he suggested that solid wall piers should be adopted as at Kilmore, rather than trestle piers. He also mentioned that the Shire Councillors and Johnson were very keen to get started. Monash felt obliged to point out to Johnson that the PWD would not allow the Shire to deal direct with RCMPC, and that the Local Government Act required at least the formality of calling tenders.

Monash was beginning to favour trestle piers in rivers prone to flooding (as later at Janevale) because the greater spread of the legs provided more security against overturning in the direction of the stream. However, they offered more opportunity for floating branches and trees to become entangled.

Preparing to tender, Monash estimated the basic cost of the bridge at £851-16-03. To this he added £48-03-09 for "all works contingencies", and £100 for "all design contingencies", and rounded off the total to £1000. Adding a margin of one third gave £1333. He considered quoting this figure if the width (12 feet) were to be measured between handrails, or £1415 if between gravel beams. His formal tender, submitted on 14 December 1907, was for the latter figure.

Technical Note. The Specification (written as usual by Monash as specialist contractor) was for a rolling live load of 14 tons or 3½ tons per wheel. Concrete in the foundations, piers, and abutments could contain up to 40% by volume of "rubble spawls" (large stones) set in concrete having a ratio of 1:3:5 cement/sand/stone, with clean broken stones not greater than 2". Concrete in the superstructure (girders and deck) was to be 1:2:3 cement, sand, and aggregate, where the aggregate was to be gravel, shingle or screenings. Cement was to pass tests specified by the PWD. Reinforcing steel was to have an ultimate tensile strength of at least 24 tons per square inch (371 MPa) and "high ductility".

Tender and contract

On 16 December, Johnson wired that the Council had accepted RCMPC's tender and would send it to the PWD for approval. Monash promised to apply pressure there to hurry things along. He and Johnson exchanged assurances that they would deal fairly with each other regarding any matters left unclear by the Specification, and unforeseen problems revealed by excavation. Johnson was worried that some of the foundations were shown well above rock, but Monash assured him that the Dargo abutment could be founded on "a good earth stratum". If changes were needed, they could be covered by extras. He trusted that none would be needed, but if they were, he would abide by Johnson's decision as to whether claims for extra cost were justified.

Final computations for the girders were completed on 10 January 1908, and the first requisition for materials was issued the next day. Monash's instructions to Works Manager Lynch were that the Stratford abutment and all four piers should go down to solid bed rock. If this was lower than expected the extra volumes should be recorded, but he should try to avoid extras. He should find "fairly solid earth" 3 or 4 feet below the surface for the Dargo end. If not, he should sink a shaft at each corner of the abutment, as had been done at Staughton Vale. Lynch should remember that the piers were very tall and thin, and might need to be propped until the deck had been constructed. "The stability of the whole bridge depends upon the Abutments, and not on the piers." It might be necessary to protect the Dargo end from scour with heavy rocks (beaching).

Monash again felt it necessary to pressure the Shire Engineer to "look carefully at the question of formalities … you will doubtless agree that it is in the interest of both parties that the requirements of the Local Government Act and of the Companies Act should be properly adhered to. This company can only properly contract under seal, and I fancy that the same observation applies to a Shire …"

Construction

When the first bags of cement from David Mitchell's factory began to arrive at Stratford, it was found that they had been badly tied, and due to rough handling on the railways, some cement had been spilt. Johnson had them put into cornsacks (three bags per sack) to protect them for the journey up to Waterford. This part of the trip was handled by D Hurley, a former councillor of the shire, who had resigned to take on the contract. There were some delays in the early stages, and Monash asked Johnson to push Hurley along.

The RCMPC records leave doubt about this image, but it is likely that it shows early construction work on the Waterford Bridge. At left is a 'forest' of props intended to support the formwork for the deck. Within the 'forest' are the grey shapes of two completed wall piers. Formwork for another pier may be under construction at centre, behind the lady in a white dress. The two abutments and their wing walls have been completed. The state of the work fits that described by Alex Lynch after his visit on 26 March 1908. (The curved line at top is a break in the glass plate.) Photo: University of Melbourne Archives, Reinforced Concrete & Monier Pipe Co Collection, GPNB-1250. There is another glass plate negative in the collection, GPNB-1133, showing a closer view of a portion of this scene.

The start of construction work brought the usual problems. For information about subsurface conditions, Johnson had relied on the memory of A G Traill, who lived near the existing bridge and had worked on its foundations. However, the new site was just downstream of the old. The rock proved to be further below the surface than expected, and extra excavation and concreting was necessary. There was also more water in the river than expected, and it was necessary to make cofferdams. One of these "leaked like a sieve" and the few hand-pumps available were inadequate to cope with the inflow. Traill, who was apparently employed as Johnson's Clerk of Works or Inspector, reported to Lynch that in making plans "we all made too little of the water in the river". (With Waterford a 70 km horse-ride from Stratford, Johnson was able to make only a few visits to the site during construction.)

Foreman Thomas Wood proved a little too enthusiastic and stripped the formwork from the first pier only two days after it had been cast. Supported by very little reinforcement, the still-fresh concrete slumped into the river. Johnson asked Monash: "Please take action to prevent a recurrence of this unseemly haste". However, Johnson was complimentary about Wood's work in general: "He is always keen in your interests yet withal conscientious, energetic and obliging". The shire engineer and foreman made an arbitrary decision to take the Dargo abutment face wall right down to rock. Owing to what Lynch described as an oversight, the wing walls were not taken down, but were founded on earth protected by beaching. Monash was concerned when he learned of this, because he felt the face wall should have been widened in the direction of the stream, to compensate for its increased height and guarantee stability in that direction.

Monash was grateful for Johnson's occasional reports from the distant site, and his willingness to sort out minor hitches at Stratford. "Permit me to thank you most cordially for your very clear and detailed information regarding conditions and progress of the work. It is only right to say that it has seldom been my experience to receive such cordial and sympathetic assistance in furthering building work in hand as you have been good enough to render me in this matter." He was glad to know that the critical work was now over and looked forward to rapid progress with remainder.

Johnson's next report was disturbing. Relations between the carpenter and foreman had deteriorated. According to Hurley, they had spread "gossip" about each other at Dargo. Specifically, the carpenter accused Wood of putting insufficient reinforcement in the piers. At this early stage in the introduction of reinforced concrete to Victoria many people viewed the "new" material with suspicion, and its advocates were fearful of anything that might bring it into disrepute. Johnson raised this point with Monash, and was also concerned for his own reputation, as he had "so strongly recommended the technique".

If the piers at Waterford were similar to one built at Thornton Bridge in 1914, the reinforcing cage was intended merely to help hold the concrete together, rather than to strengthen it. They were in effect mass concrete piers. See Comments below.

During his visit, Lynch decided to recruit better workers, though he feared they might be poached by the shire engineer. "I have a person in Stratford looking for three good labourers, & if he is successful they will proceed to Waterford & replace the local men. I pointed out to Mr Johnson the unfairness of taking these men away until the job is finished." He reported that both abutments; Piers 1 and 2; and the footings for piers 3 and 4 were finished. All props and staging for supporting the sole plates of girders in two-and-a-half bays were complete. Sand and gravel was on site ready to complete piers 3 and 4. The Stratford approach had been filled, and the Dargo approach half filled. "The work completed is of the best quality and finish. I feel sure the bridge will be a good sound job. The sand and cement are of the best."

Completion and Load Test

Work was complete by the end of May 1908, and Monash commenced negotiations over the extras, totalling just under £200. While these were going on, Johnson began to make arrangements for a public load test. Monash was now sufficiently confident to refuse to conduct or take part in such tests, seeing them as a waste of time and money. However, Johnson was keen to go ahead "for the experience itself and in order to silence for all time the many wise-acres who predicted failure in such blatant tones". Also, the Council was "anxious for the bridge to go through the ordeal". The structure was designed to carry a 14-ton moving load, but it would have been difficult and costly to arrange for one in the mountains. Monash therefore suggested that the integrity of the bridge could be demonstrated by measuring the deflection of the girders under the weight of a wagon containing 10 tons of rocks. Hurley was reluctant to risk his horse team in such a venture, so it was proposed to pull the wagon across with a block-and-tackle. Johnson was very keen for Monash to attend the formal opening of the bridge, and wrote to ask how many representatives from RCMPC would be coming so that he could arrange horses for them. John Gibson, RCMPC's Managing Director, jotted a note on the letter saying: "Mr Monash. What about this?". A second note, probably by P T Fairway reads: "Above not mentioned to Mr Monash". Johnson also hoped the Inspector General of Public Works, W Davidson, and his Chief Engineer, Carlo Catani, would attend, but the result was probably the same. The test was finally conducted on 10 September 1908.

Destruction by flood.

On 17 June 1909, the Gippsland Times reported that the river had risen 18 feet - two-thirds of the way up the piers of the new bridge, and "a fearful amount of huge logs and other debris collected about the bridge". On that occasion the structure was able to withstand the pressure of the backed-up water. However, late in 1916 the entire State of Victoria was subject to disastrous floods that swept away many bridges. The river at Waterford must have risen even higher, carrying even more debris, and Johnson's fears finally proved justified. The bridge was destroyed on 27th September 1916. It was replaced in 1917 by a bridge designed by the recently-formed Country Roads Board, incorporating a central span of 70 feet (21.3m) with two steel plate-girders encased in concrete. The 40-foot approach spans were of reinforced concrete T-beam construction.

Remains of the first reinforced concrete bridge at Waterford. View of the partly destroyed abutment at the Dargo end. The abutment of the old timber bridge is to its left. University of Melbourne Archives, Reinforced Concrete & Monier Pipe Co Collection, NN1160.

Remains of the first reinforced concrete bridge at Waterford. View of the partly destroyed abutment at the Stratford end. The abutment of the old timber bridge is to its right. University of Melbourne Archives, Reinforced Concrete & Monier Pipe Co Collection, NN1161.

There are two prints in the UMA Collection showing further views of the remains, both dated 2 May 1917. These are: BWP24245 showing portions of the destroyed bridge lying just downstream of the site; and BWP24246 showing an oblique view of the Dargo end.


Upper Thornton Bridge (Eildon).

Former Location:Over the Goulburn River at Upper Thornton (now Eildon).
Former Municipality:Shire of Alexandra.
Description:7 × 9.1m plus 2 × 12.2m spans.
Activity:January to July 1914.
Status:Destroyed during flood of September 1916.

Note 1. This project was known to Monash and his colleagues as "Thornton Bridge". However, the site was not in the town, but at Upper Thornton. Between 1915 and 1929 a dam was constructed nearby to form the Sugarloaf Reservoir. A construction township was established and took its name from Eildon, a local property founded in 1846. The dam was increased in size in 1929 and 1935, and a major enlargement began in 1951. Both the dam and reservoir now go by the name Eildon. It is possible that the site of RCMPC's bridge has been submerged. (The structure itself was destroyed by severe flood in September 1916.)
Note 2. Early in 1914, Monash's engineering work, plus a militia camp and other matters, obliged him to postpone his annual holiday until March. However, he was closely involved in the early stages of the Thornton Bridge project, aided by his Assistant Engineers J A Laing and P T Fairway. On 9 August, following the declaration of war, he was asked to act as Chief Censor and assumed duty on 17th, but by then the structure of the bridge was complete.

Thornton Fig. 1. The (Upper) Thornton Bridge nearing completion. Falsework is still under the spans at left. At right is Pier No.1, which was re-designed as a wall pier, rather than a trestle, when excavation revealed that it would sit on a narrow outcrop of bed rock. Photo: University of Melbourne Archives, Reinforced Concrete & Monier Pipe Construction Co Collection, NN/909.

Winning the contract

On 10 January 1914, J G W C Short, Engineer for the Shire of Alexandra, called at Monash's office to enquire about the cost of a reinforced concrete bridge to replace a timber bridge partially destroyed in floods. Monash was not present, but wrote to Short, asking him to send technical information and tender forms. Concerned about competition from new firms moving into the field, he added: "I presume you will only advertise in the local papers, because, if you were to advertise in Melbourne, you might get all sorts of silly proposals from people who might imagine they know something about reinforced concrete, but would afterwards leave you in the lurch". Short replied with a sketch showing the profile of the river bed. He indicated that the floods of September 1912 had reached Reduced Level 92.00 feet, and set the deck level for the new bridge at RL 94.00.

"Reduced Level" is a term used by surveyors when measuring height above an arbitrarily defined datum. As Eildon is about 230m above sea level, Short's datum must have been a local one.

One of Monash's Assistant Engineers, J A Laing, made preliminary calculations and on 28 January estimated the basic cost of the bridge as £1129. He added a margin of 40% to give a quotation price of £1594. Monash explained that the trestle-shaped piers would "have a wide spread so as to greatly increase the stability of the bridge and resist any tendency for same to be overturned in the event of a heavy flood". This meant extra cost and a higher price, "but I hope that the advantages of giving the piers a good spread and thus insuring the structure against being washed away will be fully taken in consideration when the tenders are being compared".

The drawing shows a bridge of nine spans: two of 40 ft (12.2m) and seven of 30 ft (9.14m). The elevation, plan, and cross-section were shown; but for commercial reasons, they included only a nominal indication of the reinforcement in the trestles. No details were provided of reinforcement for the girders or deck.

Thornton:   Fig. 2a, Elevation.   Fig. 2b, Trestle Pier.

In submitting the tender to Short on 30 January, Monash argued that the price was very reasonable. RCMPC's bridge at Cremona was 186 feet long and 15 feet wide and had been built at a price of £1881, or 13/6d. per square foot of roadway proper. The Thornton bridge would be 290 feet by 12 feet and so would cost only 9/- per square foot. This was due partly to the better foundations and smaller approach work; but RCMPC was tendering as low as possible to support Short's advice to Council that reinforced concrete should be chosen rather than timber. The bridge would be "a monolith and so designed as to be quite impossible to be swept away by flood".

The State Government was slow to grant funds for the project, and the Shire Council decided to hold the tenders until further notice. P T Fairway kept pressing for news of developments, arguing that RCMPC were very busy and needed to plan ahead. The work force and plant earmarked for the project would soon need to be allocated to other tasks - and as winter approached, it became urgent that work begin before the river started to rise. Monash remained hopeful that Cabinet would act, "seeing that the Chairman of the Roads Board is so insistent that the work should go on immediately".

Construction

RCMPC eventually commenced work on 16 April under foreman J Stevens without a contract; dismantling the remaining portion of the old timber bridge, clearing logs from the river, and blasting for pier foundations. The wing walls of the abutments and the pier footings were to be of mass concrete. The full working drawing for the whole bridge, showing all reinforcement details, was issued to Stevens on 22nd, signed on Monash's behalf by J A Laing. Progress was surprisingly rapid, despite a hold-up when it was discovered that Pier 1 would be sitting on an outcrop of rock and would need to be redesigned as a wall pier, rather than a trestle (see below). Pier 2 was concreted on 29 April and Pier 1 by 8 May. On 30 May, Shire Secretary Harry Wood sent the contract documents to be signed, explaining that Short had been laid up for some weeks by a buggy accident. The girders and deck of Span 1 were cast on 1 and 2 June, Span 2 on 3rd and 4th, Span 3 on 6th and 7th, and Span 4 on 9th and 10th. Attention then turned to the abutments. By 27 June, all piers had been cast, and Stevens continued construction of the deck working from the other end, through Spans 9, 8, and so on. On 10 July, Works Manager Alex Lynch reported the bridge complete. The appearance was very good, the piers in perfect alignment, and the finish of the concrete especially good. It would be ready for use by light traffic from 17th.

Contractual matters

The Alexandra Shire Council must have given written notice to proceed about the middle of March (1914), when it lobbied the Minister for Public Works. Monash sent several early requests that a formal contract be signed. On 29 May, with work well advanced, he felt it necessary to warn the Shire that it was laying itself open to challenge from the Auditor. "We shall be asking for a progress payment in about a week from date, and it is really high time that the matter was put in proper order. I should be obliged, however, if you will in any case acknowledge receipt of this letter stating how the matter stands, as my two previous letters on the subject have not been acknowledged and may possibly not have reached you." This at last evoked the response that the Shire Secretary had been laid up, and the contract documents were forwarded for signing.

On 3 June, Monash assessed the value of work done so far at £600. He asked for a progress payment of £450 or £500. Having received no response, he put the value of work done by 18th at £900 and asked for £675. "I shall also be pleased to hear when we may expect a remittance." On 26th he pointed out that he had had no reply to his previous letters. The bridge was nearing completion "and we have so far not had a penny advanced in respect of it". On 30th he reminded Wood of a promise that a progress payment would be discussed at the next Council meeting on 6 July, and that by then the bridge would be complete except for three girder spans and some details. The value would be over £1400. He asked Engineer Short for a certificate for at least £1000, and promised not to trouble him after that until the bridge was complete. RCMPC submitted its final account, for £1651, on 29 July, 1914, but was still attempting to obtain the last £54 of its claim in October 1915.

As often happened there were problems with slow delivery on the railways and this caused some inconvenience at the start of the job. A T Elliott was contracted to cart material from Alexandra to the bridge site and may have under-quoted, because towards the end of April he refused to continue carting gravel, though he was still willing to handle timber and steel. RCMPC's Melbourne office contacted J S Webb of Alexandra for a quotation for gravel; but it appears that Elliott resumed. J Cameron of Darlingford was awarded the contract for supplying earth fill at 11d per cubic yard.

Because of Monash's concern about intellectual property, Short was not supplied with full details of reinforcement until 13 May. This was only because he requested them, and the request was made only after he was informed that Pier 1 had been re-designed in anticipation of his concurrence. He requested "all particulars of all reinforcement &c in piers, girders, deck, [and] abutments". Monash complied, but wrote: "I judge that you will doubtless understand that it would be unfair to us if our drawings by any mischance got into the hands of would-be competitors. Consequently I trust you will not take it amiss if I ask you to treat them as confidential, and have them filed in such a way that no unauthorised person can have access to them".

The delay in supplying full working drawings might explain the Council's reluctance to sign the contract.

Redesign of Pier 1

As mentioned above, the trestle type of pier had been chosen for Thornton with the intention of providing good resistance to the effects of flood-borne tree debris. Caught in the piers, this could form an effective dam, causing the water to back up and exert large horizontal pressure on the bridge. The trestle piers were to have wide-spread legs to resist the danger of overturning - and at Thornton the feet were to be firmly based on rock. However, the first excavations revealed that the rock below Pier No.1 was not flat, but consisted of a ridge about 17 feet wide (measured in the direction of flow). It was therefore decided to redesign it as a wall pier, with the intention of deriving the same resistance from a narrower base.

Fig. 3a. Type drawing for trestles of the [Upper] Thornton Bridge. From the contract drawing of 29 Jan 1914.
Fig. 3b. Pier No.1 redesigned as a wall pier. From a sketch of 29 April 1914.
Both extracts from drawings in the J. Thomas Collection.

The wall pier was built 18 inches (500mm) thick throughout its height and 17 feet (5.2m) wide at the base, narrowing to 8 feet (2.44m) wide at the top. The vertical reinforcement consisted of only six bars 7/8 inches (22mm) in diameter. Horizontal reinforcement consisted of a pair of ¼ inch (6mm) diameter bars, laid every 18 inches of height. As an economy measure, 30% of the volume of Pier 1 consisted of large stones (known as 'spawls' or 'spalls') employed to minimise the amount of cement concrete needed.

Thornton Fig.4. Horizontal cross-section through Pier No.1. Detail from the sketch of 29 April.

Monash explained the idea to Short in a letter of 1 May. "It turns out that the rocks dip rapidly away on either side of the centre line, so that it would not be possible to get a bearing for the legs of the spread pier as originally designed without sinking cylinders and a considerable quantity of extra concrete below water, the cost of which would run into anything from £25 to £50. To avoid this considerable extra, we have decided, anticipating your concurrence, to somewhat modify the design of this particular pier by making the spread less, and by making the pier solid, so that the load of the superstructure will be carried down direct upon the block of rock on the centreline. This alteration involves an extra quantity of about 3 cubic yards of concrete, which we value at £7/10/-, and we trust that in view of the saving of the considerable extra foundation expenditure, you will recognise the fairness of approving of this sum as additional payment for the work. We will, of course, take full responsibility for the soundness of the alteration."

On 4 May, Lynch reported that he had inspected the No. 1 Pier foundation and had decided to put in a solid block of concrete 2 feet (610mm) wide and averaging 2 feet deep in the rock. The length of this block was 17 feet (5.2m), and so the pier would be 17 feet wide at the base. (It had been designed as 14 feet wide.) "No further trouble need be anticipated in regard to foundations for this bridge." Mr Short was "well satisfied".

Destruction by flood, 1916

Late in September 1916 there was severe flooding throughout Victoria. Townships were isolated, livestock and houses washed away, and a great many bridges destroyed. On 26th, the Argus reported: "It is generally agreed that the flood which has swept the Goulburn Valley during the last day or two is the greatest since 1870 and many consider that it is the greatest since the district was first settled … In the Shire of Alexandra the engineer considers that £5,000 is a conservative estimate of the damage done to bridges and roads. There is practically not a bridge in the shire that has not suffered more or less. A concrete bridge over the Goulburn at Upper Thornton, erected a few years ago at a cost of £1,600, and guaranteed to stand a strain of 1,000 tons, has been swept away, pushed down by the huge masses of timber and debris which banked up against it …" The partly-built Eildon Weir had "suffered a good deal", and "all the bridges between Alexandra and Thornton are gone."

Photographs from the Archives

The best general impression of the nearly-completed bridge is the long-range side-view reproduced in Fig.1 above, based on negative NN-909, from the Reinforced Concrete & Monier Pipe Construction Co Collection at the University of Melbourne Archives. An image in their online database UMAIC shows a view looking along the bridge at deck level, taken slightly off-centre so that the legs of the trestles can be seen (Record ID UMA/I/6595). Enquiries to UMA concerning this inage should quote Location No. NN-907. Another negative, NN-910 (not online) is similar to NN-907, but taken from the other end. All these photographs were taken on 10 July 1914, the date on which Alex Lynch reported all structural work complete.

There are two photographs on UMAIC showing construction work, with the formwork in place for Pier 2 (trestle) and men at work on the footings of Pier 1. These have Record IDs UMA/I/6727 and UMA/I/6594 and Location Nos. NN-905 and NN-906 respectively.

There are two images online showing remains of the bridge after its destruction. An image in UMAIC shows the river still in flood (Record ID UMA/I/6596 and Location No. BWP/24081). An image on the website of the State Library of Victoria (b10934) shows debris exposed as the waters retreat, with Pier 8 still intact.

UMA holds several views of the remains of the previous timber bridge, with Location Nos. NN-900 to NN-904. An image on the State Library website (H92.200/719), entitled "Goulburn Bridge, Upper Thornton", might be a view of the former timber bridge intact.


Reflections on the loss of Waterford and Thornton Bridges

Knowing and not knowing

As the saying goes: "There are some things we know; some things we don't know; some things we know we don't know; and some things we don't know we don't know". This aptly fits our understanding of the loss of the Waterford and Upper Thornton bridges.

We know that even with modern technology and capital expenditure, bridges still get washed away by flood water. From the start of European settlement in Victoria in the 1830s and 1840s, up the time that Monash was introducing reinforced concrete, destruction of bridges during floods was much more common. In the floods of September 1916 that destroyed the Waterford and Thornton bridges, a total of 11 bridges were destroyed in the Shire of Alexandra, including all bridges on the Goulburn River between Alexandra and Thornton. At the township of Dargo, upstream from the Waterford Bridge, the river rose 3½ feet (1 metre) in an hour around midnight on 24th, and by 26th was 21 feet (6.4m) above its normal level. Scores of bridges were lost throughout the state of Victoria.

For an impression of the devastation caused by the floods, see e.g. The Argus from 25 to 30 September 1916 onwards at NLA Newspapers. The information on river levels at Dargo is in the edition of 29th. For an illustration of the problems caused when bridges went missing, see (NLA Newspapers online, The Argus, 7 June 1900, p.9, "Country News", dateline Bruthen.) A photograph in the University of Melbourne Archives Image Collection (UMAIC) shows flood water squeezing through the Benalla bridge on 10 Sept 1921 (search under Record ID for UMA/I/4815).

We also know that Monash was convinced of the superior flood-resistance of his reinforced concrete girder bridges by the survival of his Lancefield Bridge which was completely submerged in the flood of September 1906. One abutment was undermined, but was quickly made good. Following the floods of September 1909, he told a Shire Engineer: "Upwards of forty of our bridges were within the flood area, but we have not heard of one penny worth of damage". He was convinced that with foundations, piers, girders, and deck forming an integral whole, reinforced concrete bridges were less likely than steel, timber or composite bridges to break up under pressure of floating debris. While Monash was its Engineer, the Reinforced Concrete & Monier Pipe Construction Co designed and built a total of about 60 girder bridges, almost all of which performed satisfactorily until replaced in the latter decades of the 20th Century, to cope with heavier traffic.

However, a modern engineer might wonder about the following features of the design and construction of the lost bridges:

  1. the decision to use 30-foot spans at Waterford, rather than provide a 50-foot central span.
  2. the rudimentary nature of the sub-surface investigation,
  3. the use of spread footings where rock was not close to the surface, rather than taking foundations all the way down to rock, or using piles,
  4. the use of mass (unreinforced) concrete in footings, abutments and piers.

It may well be that the last three were decisions that any engineer at the time would have made, in view of the relative isolation of the site, and the need to produce a proposal that took account of current economic conditions and competed with alternative forms of construction. Only a close study of the work of similar engineering firms at the time would provide a definite answer - assuming that sufficient records have been preserved. It need hardly be said that Monash was not a risk-taker. Some comments are offered below on each of these features in turn.

Monash worked to a factor of safety of four (ultimate strength/design stress) and took as his yardstick the Imperial German Regulations of 1905, which he considered the most advanced for their time.

Use of 30-foot, rather than 50-foot spans

The reasons Monash put forward for avoiding a large central span in reinforced concrete were that:

There are additional technical reasons why such a long span would have been inadvisable. The obvious solution was to turn to steel, but this was something Monash was reluctant to do, as he felt it detracted from the image of reinforced concrete.

* The bending strength required of a girder simply to carry its own weight and the weight of the deck increases as the square of the span, so that a 50-foot span must be 25/9 (or 2.78) times as strong as a 30-foot span, even before the weight of traffic is considered. Thus, as the span increases, the designer is locked in a vicious cycle - more weight requires more strength, which requires more weight. The only way to break out is to adopt a different form of construction or a material with a higher strength-to-weight ratio.
* In the period covered by our research (up to 1915), deflection and creep in reinforced concrete beams were not well understood and were likely to be under-estimated. We have not sighted any calculation of deflection in the RCMPC records.
* An example of Monash's reluctance to use steel occurs in the design of the balconies of Kither's Building, which he admitted would be most logically done in steel.

The bridge that replaced the RCMPC bridge in 1917 was designed by the new Country Roads Board, a department of the State Government. They adopted a central span of 70 ft (21.3m) using concrete-encased steel girders. This bridge enjoyed a long life; but whether that was because of its large central span is something that we may not be able to know.

Sub-surface investigation

In later times in Australia, government engineers organised the site investigation (and normally the structural design) for bridges before calling tenders for construction - then supplied the resulting information to all tenderers. It seems that Monash was obliged to make a specific request for such information. Perhaps the builders of timber bridges had had less need to know of sub-surface conditions - these would have been revealed as they drove the legs of their trestles into the ground. The cost to Monash of conducting a full site investigation, especially in a relatively remote area, would have reduced the competitiveness of his bid. (The pressure of competition meant that he was always reluctant even to spend time on detailed structural design of a project until he was sure that he had won a contract.) The Shire Engineer's information was usually based on probing with steel rods or, if considered worthwhile, digging small exploratory shafts. Bores were drilled only for the more important bridges. It must be remembered also, that the major advances that placed the science of soil and rock mechanics on a firm basis would not be complete until the 1920s, so there was less point than nowadays in a scientific investigation. Design was normally based on textbook values of 'safe bearing pressure' on soils categorised broadly under headings such as "firm sandy clay" and "sandy loose gravel".

Use of spread footings

Monash was well aware of the danger of scour undermining abutments and footings resting simply on alluvial materials. Regarding Waterford, he wrote to Shire Engineer Johnson: "It would be, of course, impossible for us to incur the slightest risk by putting our heavy piers and abutments upon a bottom which is in the slightest degree liable to disturbance by a heavy current …" One alternative was to take the foundations down to solid rock, provided it was not too far below the bed of the river. The second was to support the structures on piles driven either to reach the rock surface, or until friction with the soil provided sufficient resistance to support the load. Both at Waterford and at Upper Thornton, however, he felt confident that spread footings situated at the edge of the flood plain, well away from the main channel, could be satisfactorily protected from scour by a bank of heavy rubble. Later experience was to show that this faith was not always justified (see for instance the Cremona Bridge). Monash had acquired expertise in the design, casting, and driving of reinforced concrete piles for his Hindmarsh River bridge, tested in 1907, but their use would have greatly increased the cost of the bridge, especially at Waterford. Less expensive timber piles were perhaps ruled out because of his reluctance to use materials other than reinforced concrete, but the final decision in favour of spread footings was most probably based on cost-benefit assessment.

Mass concrete in abutments

The use of what was effectively mass concrete for abutments may appear strange to a modern engineer, but in Monash's time it was still quite common. Only a decade earlier, mass concrete made with lime, rather than Portland cement, was used for the foundations and abutments of some of Monash & Anderson's Monier arch bridges. However, Monash had used abutments formed from a row of reinforced concrete columns for the abutments of the Lancefield bridge, and these had performed well in flood despite their footings being seriously undermined. Once more, the idea at Waterford and Thornton may have been to avoid the cost of transporting reinforcing bars. In his initial proposal, Monash stated: "The piers and abutments could be built practically of rubble masonry bedded in and held together by a comparatively small proportion of concrete". The abutments at Thornton, as late as 1914, are shown with only nominal reinforcement (¼" at 6" centres) just below the surface of the face wall. In other respects they were mass concrete.

Mass concrete in piers

Although the working drawings for Waterford are not in the J Thomas Collection and there are no sketches in the relevant RCMPC file at UMA, it is fairly certain that the piers at Waterford were built in what was basically mass concrete. Monash proposed to Johnson that "The piers and abutments could be built practically of rubble masonry bedded in and held together by a comparatively small proportion of concrete". Thirty per cent of its volume was to consist of large stones (known as 'spawls' or 'spalls') employed to minimize the amount of cement concrete needed. We know that the carpenter was concerned that not enough reinforcement was going into the piers (though there is no reason to doubt that they were built according to the drawings). The photograph of work at Waterford shows wall-piers aligned in the direction of stream flow, and this is confirmed in the correspondence. They were relatively slender, described in early correspondence as 2 feet thick (610mm) and about 30 feet (9m) high. The re-designed Pier 1 at Thornton was only 18 inches thick and about 27 feet high. Monash would not have designed such piers unless he had found examples in the engineering literature, either texts or journals. The piers at Waterford stood for eight years, and we must remember that bridge engineers of the time routinely supported steel girders and timber trusses on piers of unreinforced brick or stone masonry. However, the nominal reinforcing cage shown on the Thornton drawing is unlikely to have confined the concrete sufficiently to allow its full strength to develop in compression or to resist significant tension.

We have come across no other instances of the use of mass concrete piers in Monash's reinforced concrete girder bridges. Thus, the decisions taken at Waterford (tendered December 1907) and Thornton (tendered January 1914) must have been made as part of the routine balancing of cost against risk, having regard to local conditions and economic and commercial pressures.

Stability of bridge as a whole

Monash's early instructions to Alex Lynch for Waterford emphasised that "… the piers are very tall and thin and will not be very stable till after [the] deck has been put on" and "The stability of the whole bridge depends upon the Abutments, and not on the piers." He also told Lynch that when the earth for the approaches was packed behind the abutment walls, it had to be brought up equally behind each abutment, so as to avoid displacing the deck longitudinally. Such movement would have pushed the tops of the piers away from the vertical and caused eccentric loading.

It is tempting to speculate that Monash might also have envisaged the deck as a horizontal girder spanning between the abutments, thus resisting movement of the tops of the piers in the direction of stream flow, and helping to resist the pressure of water dammed up by tree debris. Records of other projects show that he would have been aware of the potential for the deck to act in this way.

The Argus of 26 September 1916 reported that the bridge at Upper Thornton had been guaranteed to withstand a force of 1,000 tons. This information must have come from Monash. As the bridge had been destroyed by "huge masses of timber and debris which banked up against it", the implication was that it was designed to resist a horizontal force of this magnitude. There is no sign in the RCMPC project file of calculations made to justify this, but based on checks carried out to determine the resistance to overturning of structures such as lighthouses, retaining walls and dams, Monash and his colleagues probably assumed that bodily rotation would take place about the downstream toes of the trestles (or of the Pier 1 wall-pier). Knowing the gravity load applied to the trestle, and assuming the level at which the resultant force of dammed-up water would be applied, a simple triangle of forces would have then permitted calculation of the horizontal force that would cause overturning.

Diversions from plan

In addition to the original design decisions, a number of decision were made 'on the run' which may have affected the flood-resistance of the two bridges. At Waterford, Monash had decided not to take the Dargo abutment down to rock. During construction, Shire Engineer Johnson issued an on-the-spot instruction that this be done. Monash was not pleased. "I feel very great anxiety about this abutment, and it is only now that one can fully realise the error committed in rushing in to such a vital departure from the plan without first referring the matter to me. In my opinion, the Dargo abutment, if it had to be made so much deeper, ought to have been made correspondingly wider also." This would presumably have been to maintain its resistance to overturning in the direction of the stream. The photograph of the remains of the Dargo abutment suggest that the face wall and the upstream wing wall disappeared.

At Thornton, it was thought that a reasonably level rock surface would be found throughout the site, not far below the river bed. Monash depended on the Shire Engineer for this information. The rock surface proved deeper than expected at Pier 8, but all footings were successfully taken down to rock. At Pier 1, however, the rock surface proved to be a narrow ridge, rather than a flat surface. As explained in the history above, the RCMPC response was to re-design the pier as a wall rather than a trestle. It is possible that the rock may have sheared off at this footing. However, the fact that all piers except No.8 were lost suggests that the failure was a more general one.

Summary

To summarise: the rudimentary site investigation, the decision to use spread footings on alluvium for some piers and abutments; the use of mass concrete in abutments and some piers; and the adoption of 30-foot spans at Waterford, may be attributed to the following factors:

The histories of the two bridges on this web page and the notes above show that Monash was aware of all these factors and carefully weighed them before coming to his decisions.

What may have happened?

The main threats posed by floods are:

Only eye-witness accounts of the destruction of the bridges, if any exist, could tell us whether any of the factors listed above did have an effect on the flood-resistance of the bridges, or contributed to the failures in any way. We do not know whether the two bridges overturned bodily or were dismembered; which parts gave way first; or whether the foundations were undermined. There are no analyses of the failures in the RCMPC records, and the few photographs in the firm's records showing the debris provide little information.