an australian aqueduct: reflections on engineering

An Australian Aqueduct: Reflections on

Engineering Assessment and Heritage Politics

L. Huddle*, K. MacLeod^

Deakin University, School of Architecture and Building,

Woolstore Campus, Geelong, 3220, Australia

Email: [email protected]

^Gheringhap Street, Geelong, 3220, Australia

Email: [email protected]

Abstract

The monumental scale, structural ingenuity and aesthetic quality of the 800 metre (2,424 feet)long sewerage aqueduct and footbridge in Geelong, Australia make the retention of thisdecommissioned structure a priority for the community. It resembles the Scottish Firth ofForth steel bridge aesthetically and is designed upon the cantilever principle. The Australianengineer E. G. Stone in 1912-1916, used the French Considere concrete system in fourteensplayed cantilevers, at 53.7 metres (176 feet) centres, for this structure. The owners denyresponsibility for the ongoing maintenance, safety and costs associated with its retention andhave campaigned for a demolition permit.

Located on a natural flood plain, the gigantic web-like structure provides an astonishinglydelicate landscape feature when viewed from a distance. The community's response to thethreatened loss of this important engineering heritage, and the subsequent politicaldiscussions, have been important factors in the successful debate about the viability of theedifice.

Key stakeholders' assessments of the safety and integrity of this structure have differedsubstantially due to their assumptions of concrete strength, degree of degradation of theconcrete and reinforcing steel, and the mathematical model chosen to calculate membercapacities. A stakeholder's commitment to retention of the structure appeared to be asignificant influence on their assumptions. Adjudication of these assessments, together withmethods of repair and estimates of costs, was an important aspect of a government inquiryappointed to advise on whether the structure was to be retained.

Throughout the process, the professionalism and politics of cultural heritage in Australia,based on the requirements of the Burr a Charter, has served as a powerful force in shaping thedecisions concerning the retention of this structure.

The Barwon Aqueduct and Pedestrian Bridge Photo. M. Trengove 1991

Transactions on the Built Environment vol 26, © 1997 WIT Press, www.witpress.com, ISSN 1743-3509

26 Structural Studies, Repairs and Maintenance of Historical Buildings

AN ENGINEERING, POLITICAL AND PROFESSIONALCHALLENGE

INTRODUCTIONA decommissioned sewerage aqueduct does not have immediate appeal as astructure to preserve. However, the elegance, scale and structural ingenuity ofthis unique bridge enabled its heritage registration and thus, protection by law.

The preservation debate about this aqueduct is a case study for theinteraction and interdependence of community awareness and action, rigorousengineering assessment, and the consistent application of the principles of theAustralia ICOMOS Burra Charter by cultural heritage practitioners.

The extensive community support for E.G. Stone's reinforced concretesewerage aqueduct and footbridge is unusual for several reasons. Adjoining anindustrial and pastoral area six kilometres from the centre of Geelong, thedistant, web-like structure is barely discernible in the dusty light of theyellow-green flood plain landscape. However the remarkable aesthetic andtechnical qualities are clearly evident as one approaches the gigantic yet delicatebridge, and awe inspiring to walk the 800 metres through the centre of thestructure. Yet many people in Geelong did not know it existed.

The engineering issues of the preservation debate centred around the degreeof the remaining structural capacity, public safety and the likely costs offeasible rehabilitation. Engineers in support of the aqueduct proposed, as theappropriate approach to assess the structural capacity, a design reviewphilosophy based on structural mechanics first principles, (rather than currentdesign codes) and supported by the full scale test results at Pont D'lvry byConsidered 1903.

Since its inception in 1979 the Australia ICOMOS Burra Charter hasattained the status of the benchmark from which the assessment of heritageplaces are measured. Acceptance of this benchmark by all stakeholders in thiscase study greatly assisted the successful preservation outcome.

Recognition of the interdependence of these three perspectives was thebasis of the successful process to save the aqueduct from demolition.

KEY HISTORICAL EVENTS

CULTURAL SIGNIFICANCEThe construction of the Barwon River Ovoid Sewer Aqueduct commenced inJanuary 1912 as part of the sewerage system built to provide for the growingcity of Geelong, located in southern Victoria. It is remarkable for theinnovative use of the Considere system of reinforcement and concretefabrication, developed in France in 1900 and the cantilever truss structuralsystem, derived from the 1890 Firth of Forth steel railway bridge in Scotland.

E. G. Stone first used the Considere system in 1909 in the Bow Trussbuilding* but the aqueduct, built in 1912-16, is the only known extant structure


Structural Studies, Repairs and Maintenance of Historical Buildings 27

in which this method was used in Australia. Edward Giles Stone's creative anddaring structural systems challenged the basis of the architectural andengineering professions and the limits of construction technology in Australia,particularly in the reinforced concrete structure and components of theaqueduct and now destroyed wool stored Willingham notes in the Statement ofCultural Significance in 1991*

... The ovoid sewer aqueduct is of critical importance to the history ofthe engineering heritage in Australia, there being few survivingstructures of such monumental scale, structural ingenuity and aestheticquality built before the Great War. ... the aqueduct is an essentialdocument in the pioneering use of concrete in Australia and itspreservation is mandatory.

The cultural significance of the aqueduct has been acknowledged by allstakeholders.? That it requires substantial repairs and maintenance was alsoagreed.

DEMOLITION PROPOSALThe decommissioning of the aqueduct by Barwon Water in 1992 led toextensive debate on its future. As Barwon Water apparently had no further usefor the aqueduct, they stated their objective of disposing of their responsibilityfor its maintenance and preservation. The initial reasons given were criticismsof the use of reinforced concrete as a durable material and retention of a heritagestructure being argued as outside their core business activity.

Public debate on Barwon Water's proposal to dispose of the structuredeveloped on the basis that it was protected by the Heritage Act and requiredState Government Authority approval for works. Subsequently, BarwonWater applied for a demolition permit on the grounds that its poor structuralstate represented a danger to the public and the cost of repair and maintenancewas not part of their charter.

As the Aqueduct was listed on the State Government's Historic BuildingsRegister, thereby implying preservation, the attitude of Barwon Water and theensuing public debate led the Minister of Planning and Development toestablish a ministerial inquiry to determine an outcome. Broadly, the terms ofreference of this inquiry were to explore options for the extent of physicalconservation of the aqueduct in accordance with the principles of the Burr aCharter^ financial implications of its maintenance, the extent of its safemanagement and maintenance, and involvement of the Geelong community inthe preservation and management of the structure.

FORMATION OF THE GEELONG AQUEDUCT COMMITTEEAfter decommissioning of the aqueduct, Barwon Water called a meeting in 1994to explain their position and decision to dispose of their responsibility for theaqueduct.% Many present were unhappy about Barwon Water's decision. Inresponse, Barwon Water invited formation of a community based committee to



attempt to find alternative uses, ownership and funding for retention of theaqueduct.

The formation of the Geelong Aqueduct Committee was decisive in theeventual outcome of the problem. The committee consisted of representativesfrom the National Trust of Australia (Victoria) a large social pressureorganisation, the professional organisation ICOMOS Australia, prominentacademics from Deakin University, Monash University and the University ofMelbourne, and local organisations such as the Geelong Environment Council,Geelong Field Naturalists and Geelong Historical Society, as well as interestedindividuals. They presented a united front in efforts to retain the structure.Issues addressed by the Geelong Aqueduct Committee included methods forthe community to voice their opinions, measuring community support, futureuse in a wider planning context, potential sources of financial assistance for thecost of conservation, and engineering assessment. The diversity of expertisewas exploited by the formation of sub-groups such as fundraising, publicityand engineering.

To Barwon Water's surprise, the Geelong Aqueduct Committee took astrong stand that Heritage Act requirements for owners to maintain registeredstructures should be enforced.

PUBLICITY SUB-GROUP The Geelong Aqueduct Committee publicitysub-group used a variety of messages to counter the strong and frequent pressreleases by Barwon Water. The problem that many people in Geelong did notknow of the existence of the aqueduct was exploited by opponents of retentionas a lack of interest by the community. This proposition was countered by adatabase recording the number and type of letters to the editor, newspaperarticles, television segments, and calculating the percentage for and against.Over a period of three years 76 newspaper articles were noted and 82% ofthem were in favour of retention. 85% of these supportive articles werepublished in Geelong newspapers. Topics involved the issue of funding andadaptive use proposals (43%), retention, historical and contemporaryengineering analyses, and possible employment schemes which could beutilised for the aqueduct's restoration." These statistics and articles clearlyindicated the community's substantial support for the retention of theaqueduct.

Other publicity methods demonstrating community support included aradio and press spokesperson, a photographic exhibition, the entry of a float inthe local Gala Day street parade, jewellery depicting the aqueduct, a postercompetition and endorsement of the 700 member Geelong Historical Society.

ENGINEERING SUB-GROUP The Geelong Aqueduct Committeeengineering sub-group was critical in providing a professional evaluation ofBarwon Water's engineering assessment and disseminating it to other membersof the committee and to the public, in plain English.



Important engineering issues which arose were the notion of absolute safety,assumptions made when assessing the integrity of the structure, whether thecauses of deterioration of reinforced concrete are understood, whether"standard" methods for repair and maintenance exist and whether thesequestions apply to historic structures.

THE PROFESSIONAL PROBLEM

ICOMOS Burra CharterThis charter (1979) was derived from the Charter of Venice (1966), by theInternational Council on Monuments and Sites (Australia ICOMOS). It isregarded as a nationally important document on conservation philosophyand methodology.

Persons with appropriate conservation experience and currentlypractising within the terms of the Burra Charter are eligible to becomemembers. They are also required to give an undertaking that the individual ororganisation's conservation activities will continue to fall within the terms ofthe charter and its guidelines.^ The Burra Charter promotes a professionalapproach to the conservation of places which are of cultural significance tothe community.

Owners of culturally significant places are strongly encouraged to followthe philosophy and guidelines of the ICOMOS Burra Charter throughaccess to Government funding tied to the use of the Charter. Engineeringassessment of historic structures should be no different to architectural,historical or archaeological assessment in that they should be a balancebetween the needs of the client and the needs of the community. Themajority of ICOMOS members are archaeologists, architects, or historians.Few members are engineers.

THE POLITICAL PROBLEM

CHANGING VALUESAs society changes, so too does the attitude to our extant buildings.Demolition of some buildings, sanctioned for various 'good' reasons someyears ago may now be considered to be decisions that resulted in a grosswaste of energy and heritage. Repeatedly, a community is left with vacantland for several years and/or it is replaced with a mediocre structure.Testimony to this are the vacant sites of several former substantial woolstores in Geelong, including the site of the Internationally significant BowTruss wool store.^ That the buildings could have been reused isdemonstrated in the successful adaptive use of the Dennys Lascelles 1878bluestone wool store which is now the National Wool Museum and thehighly successful conversion of the Dalgety Woolstores into the sixthcampus of Deakin University.'& These events partially explain the reason



for strong community support for the aqueduct.Costs, estimated to be an initial $5.7 million for 'patch repair' of the

entire structure, with $2.2 million ongoing maintenance costs over 30 years,must be addressed in solving the problem. Barwon Water has stated thatthey allowed $540,000 in their budget, for demolition,^ but they did notbelieve Geelong ratepayers should be the only people to pay the costsinvolved in maintaining a structure which was of significance to allAustralians.

THE ENGINEERING PROBLEM

THE ORIGINAL DESIGN AND CONSTRUCTION

To create a river crossing for the new Geelong sewerage system, the thenWaterworks and Sewerage Trust (forerunner to Barwon Water) awarded adesign and construct tender to the firm of Stone and Siddeley in September191221

The accepted design^ was a reinforced concrete structure with 14 piers,each with a parallel pair of balanced cantilever trusses. The concrete ovoidsewer pipe was supported by a walkway through the centre of thecantilevers.

It was noted^^ 'that one of the advantages of the cantilever constructionwas that thermal movements are horizontal, thereby ensuring the particularlyflat grade of the sewer (1:2500) was unaffected by thermal movements of thestructure.'

E.G. Stone, the designer, adopted the Considere system of reinforcedconcrete construction for this structure, and the report on the constructionrecords the works as follows :

The reinforcement throughout is of ordinary commercial steel rods, andthe disposition of the bars throughout the structure is of extremeinterest, the full tensile strength being taken up by laps; in no place arethey mechanically connected. The rods in the upper boom are arrangedin concentric rings, the laps of which break joint along its length. Thediagonals are in tension, and the ends of the rods through them areaccurately bent around the rods in the upper and lower booms. Afootpath is also provided throughout the whole length, and its treatmentadds very considerably to the appearance of the work.The length from point to point of a cantilever span is 136 feet, andacross the gap of 40 feet are placed girders, which in each case are fixedat one end and free to move at the other. The handrail ing of the footpathis sufficiently reinforced to act as a girder; by this method it waspossible to maintain a continuous footpath form.An expansion joint is provided in each span, its design being similar tothat of an ordinary stuffing box.



The design approach of Considere and the ductile structures resulting werereported in Marsh and Dunn, 1906." Appendix 1 of this publication reportson Considered full scale test to destruction of a bow string reinforced concretegirder spanning 65.6 feet. It is probable that Stone would have been aware ofthis information, and as an exponent of reinforced concrete construction, awareof the many benefits of its ductile structural behaviour.

Apparently the construction technique used for the aqueduct departed fromthe true Considere system wherein casting of the tension members occurredafter the structure was unpropped. Following completion of the aqueduct in1916, cracking was first reported in the tension booms of the cantilevers in1922.

Maintenance of the Aqueduct was necessary from time to time during itsservice as an essential element of Geelong's sewerage disposal system untildecommissioning in 1992. The deterioration of the aqueduct over the years,and its apparent inability to cater for the increased sewerage dischargesgenerated by the development in Geelong lead to the decision by the WaterAuthority for its replacement by a siphon under the river.

SAFETY - A MATTER OF DEGREEToo often there has been hasty demolition of substantial and culturallysignificant structures because of a perceived safety problem. The Bow Trusswool store in Geelong is an unfortunate example. Nine engineers reports werecommissioned on this reinforced concrete structure. While it was acknowledgedthat there were serious maintenance problems, only one report, thatcommissioned by the owner, condemned the building as irreparable.^ Absolutesafety, found only in the land of Camelot, was similarly used as an issue in thecampaign to demolish the Geelong aqueduct.

Arguments by Barwon Water for disposing of the aqueduct were variouslybased upon information about the probable cost of repairs, and liability inrelation to public safety of an old structure. Consultants engaged to report onoptions for rehabilitation, with cost estimates, drew attention to their concernsas to the continuing degradation of the structure due to propagation ofcorrosion. The consultants indicted that there were significant reserves ofstrength in most members, but that the loss of cover concrete and corrosion ofthe encircling ligatures would require significant rehabilitation works.

The proponents of preservation argued that the inherent robustness of thestructure based on the Considere principle, required capacity assessment basedon first principles rather than the use of modern design codes (as apparentlyhad been used by the Barwon Water's consultants). Specifically, differences ofopinion were held on questions such as concrete characteristic strength, extentof reinforcement corrosion, anchorage of reinforcing at joints, end fixity ofindividual diagonal truss members, and the appropriateness of mathematicalmodels used in capacity analysis.

Subsequent studies by van der Molen, Alsop and Grigg-% using a



progressive collapse model indicate that the existing structure in its presentcondition has capacity not only to accommodate adequate load factors for deadloads, pedestrian live loads, but also for a material capacity reduction factor.

It is contended that the stakeholders assessment of the safety and integrityof this structure has varied substantially due to their differing commitments tothe retention of the structure. As a result, different assumptions have beenmade on concrete strength, degree of degradation of the concrete and thereinforcing steel, and different mathematical models chosen to calculate membercapacity.

The reality that the present decommissioned structure is stable, and standsunder its own dead load, wind and stream flow live loads, poignantlydemonstrated during and after the great flood in November 1995,-™ wasproposed as an essential starting point. Engineering debate based on theoreticalcalculations differed in their recognition of this reality - proponents of retentionarguing the standing structure assists in verifying their position; proponents fordemolition contending "imminent collapse".

The published information on the Considere system, and the full scale testto destruction of a bowstring girder span at the Pont D'lvry site in 1906, hasapparently only been considered by the proponents for retention. It isinteresting to note that Considere reported that the cover concrete is non-structural, and that the "shelling off of the cover concrete as a structure cameunder increasing load, provided an easily identifiable sign that the structure wasapproaching its capacity limit.

It would seem that current engineering designers (and some reviewers of thisstructure) were unaware of the principles of the Considere system.

CONCLUSION

Community support for the retention of the aqueduct grew in strength, breadthand consistency through the efforts of the united members of the GeelongAqueduct Committee. This was important in convincing the press andpoliticians that the issue was important to the broad community. Theexpertise of structural engineers on this group was essential to counter theengineering jargon presented by Barwon Water in favour of the argument that amajor issue was one of public safety.

It was the acceptance by the ministerial enquiry of the appropriateness ofthe Burr a Charter principles that assisted the ICOMOS shaped engineeringopinion of the Geelong Aqueduct Committee, to be regarded as credible andinfluential. The strength of the professionalism of cultural heritagepractitioners who are members of Australia ICOMOS, and therefore bound bythe Burra Charter, was clearly demonstrated in this case. Governmentauthority acceptance of the Burra Charter and membership of AustraliaICOMOS as a requirement for a balanced engineering assessment of theaqueduct, was consistent with their long standing requirement that Cultural



Significance be assessed according to the Burra Charter and funding forconservation works being tied to the application of the Charter.

As the ministerial inquiry was directed to investigate "the extent to whichthe structure can be physically conserved in accordance with the principles ofthe Burra Charter" it appointed a separate engineering consultant, who. as afull member of Australia ICOMOS, was experienced in engineering assessmentof historic structures, to weigh the views of the two sides of the debate. Theinquiry stated, "The Bar won Water proposal to demolish the river spans isassessed and rejected on a number of grounds" and preferred the engineeringassessment presented by the Geelong Aqueduct Committee and those alignedstakeholders.

In relation to funding of repairs, it was recommended that "contributionsshould come from all levels of government for Stage One and direct publiccontributions as an appropriate mechanism for funding later stages ofdevelopment - once greater public awareness of the existence and significance ofthe structure has developed."

The structure remains, and remains as yet unrepaired. It is argued that theremarkable success in retaining the structure against the potential for itsdemolition (partial or full) has been significantly influenced by the strength ofcommunity opinion for its retention. An essential aspect of this communitysupport has been the vocal engineering opinion, based on the tenents ofICOMOS, that assessment of the structure indicated its robustness andductility, and its strength capacity for use as a pedestrian bridge.

REFERENCES1 Geelong Advertiser, January 23, 1912, p5.2 M Lewis 200 Years of Concrete in Australia. Concrete Institute of Australia. North

Sydney, N.S.W. 1988. p!8.3 M. Lewis, 200 Years of Concrete in Australia, Concrete Institute of Australia, North

Sydney, NSW, p 18.4 M. Lewis: 200 Years of Concrete in Australia. Concrete Institute of Australia, North

Sydney, N.S.W. 1988. pi8. The building was officially known as the Dennys LascellesAustin wool store, designed by E.G.. Stone in 1909 and built in 1911-12. The BowTruss building was demolished, amid political controversy, in 1990. van der Molen,and Huddle, The Age, Features, 15 June 1990, p 11.

5 A. Willingham , Assessment of cultural significance preparation of a conservationplan for the ovoid sewer aqueduct at Breakwater Geelong Victoria, Geelong andDistrict Water Board, 1991. p 135

6 A. Willingham 1991. The full Statement of Cultural Significance is on p 135.7 These include Barwon Water, the owner of the aqueduct which was classified by The

National Trust of Australia (Victoria) in 1987, listed by the Australian HeritageCommission, and registered by the Historic Buildings Council of Victoria in 1991.

8 Barwon Region Water Authority, 'Meeting to Discuss Future of the Ovoid SewerAqueduct, Agenda', 28 Feb. 1994.

9 Barwon Region Water Authority, 'Letter to L Huddle Re: Sewer Aqueduct - Formation



of Working Party', dated 24 March 1994.10 The database and copies of the articles were recorded and analysed by David Rowe,

School of Architecture and Building Deakin University.11 Ggg/ong ve,Y/jg,\ 15. 7. 1991, 25.8.1992, Letter to the Editor, Ggg/ong /4dfvgrfz.?gr,

26.3.1994, 2.4.1994, GgeWg TVewj, 29.3.1994, 7%e Xgf, 22.4.1994.12 Randell Bell. Mark Trengrove and Jean Lucas were major contributors to this process.13 Dick van der Molen specialised in concrete construction in Europe and Australia and had

been employed several times as a consultant for repair works on the aqueduct; Peter Alsopwas a roads and bridges engineer who studied engineering in Paris and is now thePresident of the Geelong Historical Society and a member of Australia ICOMOS. KenMacLeod was the principal of a local firm of consulting engineers.

14 Australia ICOMOS Inc. Membership Information and Application Form.15 Government funding for works, loans, etc is tied to the practitioner demonstrating an

understanding and use of this charter.16 In February 1997, only 4 out of a total of 265 full members were both members of

ICOMOS and the Institution of Engineers, Australia, ICOMOS Secretariat Data Base.17 Demolished in April 1990.18 Both of these adaptive use designs were done by Geelong architects, McGlashan Everist

in conjunction with Geelong engineers, Hamilton MacLeod.19 Barwon Sewer Aqueduct Report by Independent Panel of Inquiry, 1996, May 1996 p(ii)20 The cost to the owner to demolish the aqueduct is estimated to be at least $540,000.

Taywood-Maunsell, 'Structural Integrity Assessment of the Barwon River Ovoid SewerAqueduct', Geelong and District Water Board, Geelong, April, 1991.

21 Geelong Advertiser, 16 October 1912, p 522 Geelong Advertiser, 16 October 1912, p 523 Concrete and Constructional Engineering Vol XI, No. 1, Jan 1916 p. 52-5224 Concrete and Constructional Engineering Vol XI, No. 1, Jan 1916 p. 52-5225 Marsh, C.F and Dunn, W. Reinforced Concrete, Constable & Co. 1906, p. 563-577.26 A. Willingham 1991 pi3527 Historic Building Council files on the Dennys Lascelles Austin wool store.28 Taywood-Maunsell, 'Structural Integrity Assessment of the Barwon River Ovoid Sewer

Aqueduct', Geelong and District Water Board, Geelong, April, 1991.29 J.L. van der Molen,, P.F.B. Alsop, and N. Grigg, Private communication Feb. 1997.30 This was the largest flood in 40 years. The full length of the bridge was standing in

the strong flowing water of the Barwon River when it broke its banks and immersed theflood plane.

31 Barwon Sewer Aqueduct Report by Independent Panel of Inquiry, 1996, May 1996.p(ii)


an australian aqueduct: reflections on engineering

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