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Sydney Harbour Bridge

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  2. Building The Bridge
  3. Why Sydney Harbour needed a bridge: a missing link
  4. The Contract
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The Contract

How did the government of New South Wales go about arranging for the construction of the Sydney Harbour Bridge?

The task was to provide an adequate crossing of Sydney Harbour and to balance this function in relation to giving the people of New South Wales value for their money. The government organisation assigned to control the work to be done was the Department of Public Works (DPW) who eventually handed over the completed construction to the Department of Main Roads, later to become the major component of the Roads and Traffic Authority of today.

Within the DPW, Bradfield had the title of Chief Engineer, Sydney Harbour Bridge and Railway Construction. It is of interest to look at a few of the possible ways that Bradfield and his colleagues could have used to deliver the desired result because these options and their variations still exist in the building and construction industries.

1. Direct Labour

In this option, often referred to as “day labour”, no construction contracting company is used for any major part of the works which means that the individual labourers, carpenters, excavator drivers, etc., are employed and paid directly by the organisation requiring the work to be done. This approach is subject to the criticism that there is less competition with regard to cost reduction than with full contracts. On the other hand, the direct labour approach has been found to be useful in special circumstances such as long-term construction of development works where funds are released on a year-to-year basis. It is also possible to start a project without designs and other documents being complete for the later stages, such as in ventures referred to as being “fast-tracked”.

A successful example of the direct labour approach – which, of course, could be traced back to the convict era – was the construction of Warragamba Dam which is the largest of the storages serving the Sydney metropolitan region.

The organisation promoting this project was Sydney Water Board. The work proceeded in two stages, the first and smaller one being of an emergency nature resulting from a drought in the 1930s.

Construction of the main dam started after World War 2 and was completed in 1960. A township housing 3,500 persons was built by the Board, including educational and medical facilities for workers’ families.

A review of Australia’s rainfall and runoff in the 1980s indicated that many dams and drainage areas needed to upgrade their ability to handle more severe events. In the case of Warragamba, the decision was made to greatly increase the spillway capacity. However, by 1999 the views on direct labour construction had changed and the new spillway section, completed in 2002, was built by means of a contract (see below) awarded to a construction company: Abigroup.

2. Lump sum contract

A very common occurrence is when complete knowledge and documents relating to a project are available at an early stage. This allows any interested construction contractor to examine the proposal, to calculate the cost and to put in an appropriate bid for carrying out the entirety of the work. In this way a number of bids from different contractors can be compared and understandably it is usually one of those asking for the lower sums of money that is selected for the work.

In this way, an element of competition is introduced into the system.

In theory the work will be carried out for the sum submitted by the contractor but in many cases there are claims for additional payments (“extras”) usually due to circumstances not foreseen at the time the contract was signed. Defective soil in the foundation area is often not detected, even by the most conscientious of test borings and sometimes faulty drawings fail to reveal underground services through which the contractor apparently has to excavate. Extreme weather conditions are frequently mentioned.

But all worthwhile “conditions of contract” documents include procedures for dealing with claims and to allow for increase in costs due to inflation on long jobs. In most cases, disputes are resolved by a process of arbitration by experienced engineers, rather than by having the matter end up in the law courts.

There are increasingly popular variations to the lump sum process in which a formula is used either to target a lower sum for the construction and/or to provide a financial benefit to the contractor if completion is ahead of the date specified in the contract. After all, it is to the owner’s benefit to obtain earlier possession of the project and its earning capacity. There is nearly always also a time-based penalty for late completion.

If the owner (or “principal”) has in-house engineering staff, then it is likely that they will be employed for the preparation of the design and tender documentation to present to the competing bidders. But in many cases, an owner/developer does not have these skills to hand. In such circumstances an engineering consultant is called in for this purpose, additionally advising on the selection of the successful tenderer and then supervising the construction as the owner’s representative.

3. The construction package

The proposed bridge to cross Sydney Harbour was always going to be exceptional by world standards. A large vertical clearance was needed for shipping that used Darling Harbour and other western wharves. Furthermore, the contours of the Harbour bottom and acceptance by the public would be contrary to the use of intermediate supporting piers for the spans.

These factors logically point towards a structure having a main span of around 500 metres. The Quebec Bridge, Canada, of 1917 has a main span slightly greater than this. (The longest span in Australia at that time was the 1892 Northbridge Suspension Bridge, Sydney, at 152 metres.) Other bridges of long span were being planned overseas and this inspired the concept of competition on an international scale. Novel and practical ideas for the unusually large structure would be likely to appear if international contractors were asked to supply their own design on which they based their tender.

By adopting this procedure, the New South Wales government hoped to tap the world’s best creative engineering talents and construction skills.

This process makes it necessary for the owner or promoter of the project to state the final performance requirements. In the specification for the Sydney Harbour Bridge, the following items were among those listed for the tenderer to conform to.

The detail set out in the contract for the tenderer can be seen by examining just a few sections from the specification, little was left to chance;

Section 1 This contract is to include the whole of the work required for the Manufacture, Supply, and Delivery of all Metalwork, and the Construction and Erection complete and ready for traffic of a Cantilever Bridge or an Arch Bridge from Dawes Point to Milson’s Point carrying four lines of railway, a roadway 57 feet wide between kerbs, and two footways each 10 feet wide, across Sydney Harbour, also the approach spans thereto, in accordance with this specification, the Plans and General Conditions as set forth herein.”

Section 3a The Arch Bridge to consist of two hinged steel spandrel braced main trusses, set in the vertical plane, spaced 98 ft 6 in apart centre to centre, the clear span centre to centre of hinges being 1650 ft, the rise of the centre line of bottom chord at centre of span above the centre of hinges is to be 370 ft.

Section 4 The Bridge is to provide for:-

  1. Four lines of railway 4 ft 8 1/2 in gauge, spaced in pairs as shown …
  2. A roadway 57 ft wide between kerbs …
  3. Two footways, each 10 ft wide …”(DPW, 1923, 13)

The contract specification also provides guidance for tenderers for items such as;

Minimum span clearances,
Live loads to be carried on the rail and road,
Weights of materials: steel, concrete, asphalt, etc. to be used,
Properties of materials -content and strength of different types of steel, concrete, and masonry.

Bridge cross-section
Compare this cross section of the bridge with the as-built cross section in the 'Engineering Graphics' component of this website

In addition, the tenderers were required to describe the proposed method of construction for approval by the DPW. In smaller projects, this is often not done as there is less of an interest in just how the work is carried out as long as the final structure does the job required. However, with such a large structure and with so much at stake, it is clear that the DPW had concerns for the safety and conduct of the project throughout. (The latter part of the “Report on Tenders” digitisation on this website includes such a review.)

As described elsewhere, this approach attracted twenty proposals from six contractors of high status. Included were suspension bridge designs which did not conform to the “cantilever bridge or an arch bridge” requirement of the specification. Disappointing at first must have been the failure of the Cleveland Bridge Company, England, to put in a tender because they had been strong supporters of an arch design. The matter was put right when they passed all their calculations to Dorman, Long & Company together with the services of Ralph Freeman whom they had been using as a consultant.

The practice of getting the contractor to supply at least part of the design has gained favour in recent times in common with a tendency to outsource work, particularly by government organisations. The version of the general conditions of contract (see earlier) for a lump sum contract published by Standards Australia as standard AS4000 has a parallel standard, AS4300, to be used for design-and-construct projects.

General supervision of the project and the checking of the properties of materials used were carried out by Bradfield and his team. On completion of the Bridge, this culminated in taking observations of deflections under various combinations of load as illustrated elsewhere on this website.

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