th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 MOVABLE SPAN BRIDGES OF NSW: A NEW CLASSIFICATION SYSTEM I. Berger 1, D. Healy2 and Mark Tilley2 1 2 NSW Roads and Maritime, North Sydney, NSW GHD Pty Ltd, Newcastle, NSW ABSTRACT NSW Roads and Maritime Services manage 26 movable span bridges of which 11 are still operational. These bridges were the subject of a recently completed study undertaken jointly by RMS and GHD Newcastle which focused on the components of each bridge for the purposes of detailed heritage assessment, conservation and operational enhancement. The majority of bridges within the study can be broadly categorized as the bascule or vertical lift type. Detailed assessment has led to the recognition of particular subtypes within these broader groupings. This paper will explore the international origins of movable span bridges and detail the defining characteristics of these subtypes and suggest a new naming convention for each. INTRODUCTION Roads and Maritime Services (RMS) currently manages twenty six movable span bridges in NSW and of these fourteen are still operational. Between 1802 and 2005 there were five distinct types of movable bridge types built which included pontoon, lift, bascule, swing and sliding spans. In total 66 movable span bridges were constructed in NSW but many of these have now been demolished or are permanently closed. The detailed historical research into the development of movable span bridges in Europe and America has enabled a better appreciation of the influences that affected the design of the 48 vertical lift span and bascule bridges built in NSW between 1882 and 2005. Through a comparative analysis of the lifting mechanisms of these bridges it has been possible to develop a classification system that identifies each of these bridges as belonging to one of 13 types; 8 for the vertical lift span bridges and 5 for the bascule bridges. The first generation of 6 vertical lift span subtypes identified can be properly recognised as Australian adaptations with no international equivalent. The movable span bridges in NSW were split into three main types: 1. Vertical Lift Span Bridges 1.1. First generation – Old 1.2. Second generation – New 1.3. Table – Pit 2. Bascule Span Bridges 2.1. First generation – Drawbridge 2.2. Second generation – Bélidor 2.3. Third generation – Modern 3. Swing Span Bridges The design and development of swing span bridges in NSW are not discussed in this paper. © ARRB Group Ltd and Authors 2014 1 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 Within each movable span bridge type there were identified a number of subsets as shown in Table 1. This classification provides a better understanding of the performance and shortcomings of those movable span bridges that are still operational as these issues appear common to all bridges within a type. Table 1 – Movable span bridges by generation including subset types Type / No. I I.i 1 Study bridges Informed the study Built Balranald TYPE Balranald North Bourke 1882 1883 VERTICAL LIFT SPAN BRIDGES First Generation – Vertical Old Brewarrina TYPE Brewarrina 1888 Mulwala TYPE Mulwala Wentworth Tocumwal TYPE Tocumwal Wilcannia 2 3 4 5 6 Swan Hill TYPE Swan Hill Dunmore Bridge Tooleybuc Bridge Abbotsford Hinton Bridge TYPE Hinton Cobram Bridge Barham Bridge Second Generation – Vertical New Robinvale TYPE 9 10 Gonn Crossing Mororo Robinvale Boyds Bay Martin 11 12 13 14 15 16 I.iii 17 Nyah Ryde TYPE Ryde Hexham Batemans Bay Wardell Harwood Table Lift Wentworth © ARRB Group Ltd and Authors 2014 1895 1896 1896 1899 1925 1928 Murwillumbah 7 8 I.ii 1893 1893 1901 1901 1902 1905 1925 1926 1935 1937 1940 1941 1935 1952 1956 1964 1966 1969 2 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 . Type / No. II II.i II.ii 18 Study bridges Informed the study Built Belmore Camden Haven Sheas Creek Kinchela Creek 1891 1891 1892 1893 Telegraph Point (timber) Swansea (first - timber) 1902 1909 1905 1905 1906 1912 1922 1925 BASCULE SPAN BRIDGES First Generation Drawbridge TYPE Second Generation Bélidor TYPE Glebe Darling Point 19 McFarlane 20 Carrathool II.iii Third Generation – Modern Bascules Strauss TYPE Kyalite Sheas Creek Rail Spit (first) Menindee 21 Narooma Lansdowne Barney Point 23 24 25 Rolling Lift - Rall TYPE Grafton Simple Trunnion TYPE Swansea (north bound) Spit Swansea (south bound) III SWING SPAN BRIDGES 22 26 Pyrmont TYPE Pyrmont Glebe Island © ARRB Group Ltd and Authors 2014 1924 1927 1931 1934 1936 1932 Broadwater (Council owned) 1955 1958 1989 2005 Wentworth Park Pyrmont Glebe Island Hay Gladesville Fig Tree 1850 1857 1862 1873 1884 1885 1902 1903 3 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 TYPE ONE: VERTICAL LIFT SPAN BRIDGES Vertical lift span bridges are movable bridges which rise vertically and remain horizontal throughout operation. The first generation of vertical lift span bridges in Australia are of particular interest as there is a fascinating evolution in designs, with a number of distinguished Australian engineers contributing to the body of knowledge of each subset. European origins The history of the vertical lift span bridge dates prior to 1840, with one of the first bridges built over the Danube River at Vienna. This bridge consisted of a 30 ft. opening and could raise approximately 6.5 ft. Another vertical lift bridge was built in the Netherlands at Amsterdam over the Poldervaart Canal during 1846, however both of these designs have limited information available and the earliest detailed account is of a vertical lift bridge completed in England in 1848 (Tyrrell, 1912). The need for this vertical lift span bridge arose in 1846 when the late London and Croydon Railway Company wanted to connect its main line with the river Thames line at Grove Lane Dock. The connection line was to be only 1 mile in length; however it required crossings over the Grand Surrey Canal. The Parliament passed an Act in the same year approving the new line though it was stipulated in the Act that no more of the Canal Company’s land should be taken than was absolutely requisite for laying down the rails. These stringent requirements rendered the implementation of a swing-bridge unacceptable as the central pier of the bridge would occupy an excessive amount of land. The “telescope” type bridge and “bascule” type bridge were also considered, however the telescope type also occupied excessive land and the bascule type appeared less advantages for both efficiency and economy (Hood, 1850). The design that met the fore mentioned requirements was proposed by R. J. Hood for a new type of moveable bridge which he generally named a “vertical lift bridge”. The design broadly consisted of a platform that was to be suspended at all four corners by wire ropes which pass over pulleys fixed on four pairs of cast-iron standards. Hand gearing, shafts and counter weights were the components of the mechanism that would cause the lift motion, with a mechanical advantage of twenty six times achieved by the design (Hood, 1850). Figure 1 – Second design lift bridge over the Grand Surrey Canal by Hood (Humber, 1857) Due to unknown circumstances the original bridge was removed within 10 years of completion and was replaced by a second similar vertical lift bridge also designed by R. J. Hood (Figure 1). Variations of this type of bridge received limited usage on other canals and across small rivers. North American influences Vertical lift bridges built to Hood’s design were characterised by their small size and application to mainly canals or small inland rivers. This design was sufficient in most respects for applications in Europe. However in the USA there was a requirement to provide movable bridges crossing over larger rivers. This led to the next notable evolution in vertical lift span bridge designs prepared by the American engineer Squire Whipple and first constructed in the 1873 Erie Canal Bridge in Utica. The designs of Whipple continued to progress in the USA and Canada though no bridges of this type were built in NSW. © ARRB Group Ltd and Authors 2014 4 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 The development of vertical bridges continued in the USA with a design prepared by Dr J. A. L. Waddell. The first design was for a vertical lift span bridge over the Chicago River and it was opened in late 1893 (Griggs, 2006). This bridge became the template for a number of large span vertical lift bridges, though further improvements took place to the designs and lifting mechanisms and opening span arrangements. The striking features of the design are the large towers that have sufficient inherent stiffness to prevent encroachment on the span, also the movable span is a truss and mechanical components consist of heavy machinery and motorised components not previously used in vertical lift span bridges. Waddell type bridges were widely adopted in NSW. Figure 2 shows a Waddell Bridge built in 1913, and there are many similarities that are apparent and it provides a clear comparison to the NSW Ryde Bridge built in 1935. Figure 2: Rail bridge over the Williamette River at Salem, Oregon (Source: Gerald W. Williams Collection, Oregon State University Archives, Corvallis Oregon) Simultaneous with the design of large scale movable bridges was the improvement of vertical lift span bridges over small rivers and canals. Waddell’s firm designed a number of relatively small vertical lift span bridges that used steel plate posts for vertical components and web plate girders as the movable span (Waddell, 1916). This design was adopted for the St. John and Quebec Railway Bridge over the Oromocto River in New Brunswick. It is likely that such designs influenced the second generation vertical lift bridges in NSW, such as Gonn Crossing and is evident when comparing the two bridges (see Figure 3). Figure 3: St. John and Quebec railway bridge over the Oromocto River in New Brunswick and Gonn Crossing over the Murray River (Source: RMS) NSW Vertical Lift Span Bridges First Generation: Old The era from 1840 onwards realised various vertical lift span bridge designs and numerous bridges were built throughout Europe and USA before the first vertical lift span bridge appeared in NSW at Balranald in 1882 (Figures 4 and 5). © ARRB Group Ltd and Authors 2014 5 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 It is difficult to ascertain how this design was informed, though it is plausible that the designs of bridges over canals in Europe were used as a basis. Reviews of early European designs against the Balranald drawing set do show a number of similarities, specifically with the tower arrangement and sheave orientation. Figure 4: Paddle Steamer passing Balranald Bridge in the 1890s (Source: DMR HO23720) The first generation designs were continually improved upon and a number of ingenious modifications were implemented by different Australian engineers over this early period. The following is a summary of this evolution of designs, the issues that were encountered and how they were overcome by each successive vertical lift span bridge. The Balranald Bridge completed in 1882 and designed by J. H. Daniels was a wrought iron lattice bridge with independent towers and longitudinally oriented chain wheels. This design had trouble with the towers deflecting inwards and pinching the lift span. In addition the lifting mechanisms at each end of the span were independently operated which created difficulty in achieving a uniform lift making jamming more susceptible during operation. This design was also adopted for the North Bourke Bridge built in 1883. These two bridges form the first subset of vertical lift span bridges in NSW and are hereafter referred to as the “Balranald Type”. Figure 5: Balranald Bridge Elevation – 1882 (Source: RMS) To improve operation Percy Allan made modifications to the design of the Brewarrina Bridge completed in 1888 (Figure 6). The modifications were simply to add longitudinal girders to the superstructure, therefore minimising the differential tower deflections and to connect the chain wheels by shafts. Although this design was an improvement, retaining the dual winch lift mechanism still resulted in unsatisfactory operating performance. Allan’s design innovations were limited to this one structure which forms the sole member of the second subset known as the “Brewarrina Type”. © ARRB Group Ltd and Authors 2014 6 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 Figure 6: Brewarrina Bridge 1888 (Source: RMS) In 1896 modifications to the mechanisms of Balranald and North Bourke Bridges were made by E. M. De Burgh. These modifications included the introduction of extra chords to the tower braces and replacing the lifting mechanism with a wire rope arrangement. It is noteworthy that the addition of the tower brace chords changed the member to a lattice girder from a Warren type truss girder. The next design progression was due to alterations made by J. A. McDonald in his plans of the Mulwala (Figure 7) and Wentworth Bridges both built in 1893. These are both described hereafter as the “Mulwala Type” forming the third subset of vertical lift span bridges and introduced new concepts which enabled future design and operational improvements. This is the first time that wire ropes were used as an improvement over the chains used previously as this reduced weight and friction in the operating system. Also for the first time the lifting mechanism was designed to be operated by a single person as all the sheaves were mechanically linked by shafts thus ensuring a uniform lift. Nevertheless, issues arose with the design due to the weight and location of the overhead winch mechanism causing excessive deflections to the longitudinal girders thus pinching the shafts and inducing additional torsion (Dare, 1896). There were also some issues with the ropes unwinding. Figure 7: Mulwala Bridge 1893 (Source: RMS) J. A. McDonald made a second attempt at improving vertical lift span bridges in 1895 with his design of Tocumwal Bridge (Figure 8). The modifications made included changing the direction of the sheaves to be transverse and the counter weights were also hung on the outsides of the towers. Despite these improvements, the shafts were still pinching due to deflections most likely arising from inadequate tower bracing and further enhancements were still required. The Wilcannia Bridge over the Darling River completed in 1896 also adopted a similar design. Collectively these form the “Tocumwal Type” as the fourth subset of vertical lift span bridges. Figure 8: Tocumwal Bridge 1895 (Source; RMS) © ARRB Group Ltd and Authors 2014 7 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 In 1896 the Percy Allan design of Swan Hill Bridge (Figure 9) became the new standard for NSW vertical lift span designs. It represents a transition from the designs of J. A. McDonald and it is interesting to note that an alternate set of drawings were created for Swan Hill and signed by J. A. McDonald (Figure 10). The design was similar to Tocumwal Bridge however it was never built. The main alterations introduced by Percy Allan were to redesign the lifting mechanism by lowering the previously overhead winch back down to deck level and connecting all sheaves via longitudinal and transverse shafts. These design improvements appear to have prevented the bridge from jamming during operation. This design was adopted for Dunmore Bridge over the Paterson River built in 1899, Tooleybuc Bridge over the Murray River built in 1925 and Abbotsford Bridge over the Murray River built in 1928. These four bridges collectively make up the “Swan Hill Type” which forms the fifth subset of vertical lift bridges. Figure 9: Swan Hill Bridge Design (Constructed) by Allan dated 1896 (Source: RMS) Figure 10: Swan Hill Design (Alternate) by McDonald drawings dated 1893 (Source: RMS) Hinton Bridge was completed in 1901 to a design by De Burgh with the sheaves oriented back in a longitudinal direction (Figure 11). The design also linked the sheaves at either end of the span with wire ropes as opposed to shafts thus effectively reducing the amount of friction in the mechanism. In 1895 De Burgh first tried this arrangement whilst enhancing the operational performance of Brewarrina Bridge. Hinton Bridge marked the first opportunity to apply this design on a new structure. This arrangement was adopted for another three bridges designed by De Burgh, with each having slight improvements including the implementation of extra ropes into the system, improving aesthetics of transverse tower braces and adding road gates. These bridges include the Murwillumbah Bridge over the Tweed River built in 1901, Cobram Bridge over the Murray River built in 1902 and Barham-Koondrook Bridge also over the Murray River built in 1905. Collectively these four bridges form the “Hinton Type” as the sixth subset of vertical lift bridges. Figure 11: Hinton Bridge 1901 (Source: RMS) © ARRB Group Ltd and Authors 2014 8 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 NSW Vertical Lift Span Bridges Second Generation: New The second generation of NSW vertical lift bridges is defined by a close replication of bridge types widely used in North America. NSW’s design input is much less apparent from this time onwards. The next generation commenced with the design of the Robinvale Bridge over the Murray River built in 1925. This design was of steel construction with the most striking feature being the adoption of slender steel columns for the tower components. Further modifications were made to the counterweights with two larger weights being implemented instead of four smaller weights at each corner. This style was applied with very little change to another four vertical lift bridges including Gonn Crossing over the Murray River built in 1926 (Figure 13), Mororo Bridge over the Clarence River built in 1935, Boyds Bay Bridge over Terranora Creek built in 1937 and Nyah Bridge over the Murray River built in 1941. Collectively these five bridges form the “Robinvale Type” as the seventh subset of vertical lift bridges. Figure 13: Robinvale Type: Gonn Crossing Bridge 1926 (Source: RMS) The Ryde Bridge completed in 1935 was an adoption of the American Waddell type vertical lift span bridge design which had been built from 1893 onwards. The bridge is considerably larger than previous vertical lift span bridges built in NSW and the components consist of a truss lift span, independent towers and a machinery house. Operation for the bridge was provided for the first time by electrical motors with a backup petrol motor installed in case power outages were experienced. This design was typically adopted when a larger span with greater waterway clearance was required. Another four bridges of this type were completed including Martin Bridge built in 1940, Hexham Bridge built in 1952 (Figure 14), Batemans Bay Bridge built in 1956, Wardell Bridge built in 1964 and Harwood Bridge built in 1966. These five bridges collectively form the “Ryde Type” as the eighth subset of vertical lift span bridges. Figure 14: Ryde Type: Hexham Bridge 1952 (Source: Karmalsky Design Report, RMS) In addition, two steel truss bridges were designed so that conversion to a Ryde type bridge would be possible if conditions on the waterway required. These were the Iron Cove Bridge at Drummoyne and the Karuah Bridge on the Pacific Highway at Karuah. The designs reveal that the central piers were reinforced to carry the extra weight of the towers and the deck joints on the adjacent span made readily removable to facilitate opening. © ARRB Group Ltd and Authors 2014 9 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 NSW Vertical Lift Span Sole Table Bridge In NSW the first and only table bridge was constructed over the Darling River at Wentworth in 1969. Due to the large time lapse between the early European table bridges and the design adopted for Wentworth, it is difficult to ascertain whether these designs informed the bridge. The European bridges do however provide a reference point and knowledge of their existence may have been sufficient to initiate its use in NSW. The design consists of four hydraulic rams positioned at each corner of the movable span (Figure 15). No other mechanical advantage is provided by means of a counterweighted system and the hydraulic mechanism is solely relied upon for the operation of the bridge. Figure 15: Wentworth Bridge (Source: RMS 1969) TYPE TWO: BASCULE BRIDGES The term “bascule” originates from the French language and translates as “a balance” (Waddell, 1916). They are defined as those bridges which operate by raising the load-carrying side whilst lowering the balancing side, for example the action of a simple seesaw. This action can be achieved through considerable variations in geometry, mechanisms and operation leading to a great diversity of designs. Notwithstanding this, components common to all bascule bridge designs include: leaf spans which pivot off a horizontal trunnion, variable force counterweights, locks and gearing. The bascule bridge design is utilised when there is a need for infinite headway at a river crossing. This was often the requirement on coastal rivers where masted vessels were frequent users of the waterway (Dare, 1896). Further advantages of the design included the speed of operation and keeping the deeper river passage clear from pier obstructions as is the case with the often large central pier of swing bridges (Waddell, ibid). European origins The bascule bridge is an evolution of the common medieval drawbridges that were utilised mainly as military devices. When fully raised they would prevent passage across a channel or moat thus providing protection to inhabitants (Hovey, 1926). It appears that the size of the spans was originally limited due to the reliance on manual haulage to operate the drawbridge (Figure 16). Usually, it was a pulley, on one side of the entrance wall. The mechanical advantage of this arrangement means that the effort required to lift the span begins at a maximum then dissipates as the drawbridge reaches the top of its motion so there is a controlled closing of the drawbridge. However, if a constant counterweight is used the drawbridge will accelerate and crash into the support tower with the subsequent difficulty of lowering the drawbridge against an unbalanced system (Fraser, 1985). This problem has been solved by various mechanisms that ensure the variation in the lifting force is matched with a variation in counterweight force. Early attempts consisted of seesaws, complex lever arrangements, rollers and draw pits. © ARRB Group Ltd and Authors 2014 10 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 Figure 16: Typical medieval castle drawbridge operated by a compact pulley and chain attached to the entrance wall (Source: Unknown) This led to the eventual introduction and evolution of counterbalanced systems to provide the required mechanical advantage. The overhead balanced seesaw arrangement, known as the Dutch method, was developed during the early years of the Industrial Revolution and has been successful and remains a viable modern day design (Figure 17). Figure 17: Dutch draw bridge (Source of Drawing: Hovey, 1926) and modern Dutch bascule bridge at Yarmouth, England (Source: Unknown) Balance is the key feature of any bascule bridge design with engineers and mathematicians having devised and analysed many mechanisms, particularly in the USA through the late 1800s and early 1900s where patents abounded. An ingenious alternative system was devised by Bernard Forest de Bélidor c irca 1729 by replacing the conventional drawbridge arrangement with a counterweight that rolled down a rear curved track. This was originally used exclusively for military fortresses. The Fortress of Bonifacio in Corsica is cited as the earliest known example of this style (Hovey, 1926). Credit for the first analysis of this system was attributed to the French mathematician Guillaume de l’Hopital, in correspondence with the Swiss mathematician Johann I Bernoulli during the late 16th century which contained the curve equations. It was published in Latin by Bernoulli in 1695, who recognised the equation as that of a cardioid (heart-shaped, Figure 18) (Barpi & Deakin, 2012). Belidor had suggested a sine curve. The Bélidor bascule bridge design (or cardioid curve) operates by the principle that the rolling counterweight provides maximum lifting force when it is vertical and at its peak (maximum height). From here the counterweight rolls down the curve where the curved track radii increases so that the vertical load of the of the counterweight decreases to keep in balance with the rising centroid of the bascule span. This design was popularised in French publications (Figure 18) and there are a considerable number of bridges with this design built in the 1700s including the Königstein fortress in Germany, the Exilles in Italy and the Esseillon and the Fort l’Écluse in France. © ARRB Group Ltd and Authors 2014 11 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 Figure 18: The cardioid orientation where the track occupies only the broad red line section (Source: Barpi & Deakin, 2012) and sketch (Source: La Science de Ingenieurs, 1754) The next evolutionary development in the design of bascule bridges were the trunnion bascules. These were distinct from previous bascule designs with the introduction of a heavy counterweight mounted on a frame at the fixed end of the span. The bridge rotates around a fixed pivot point and as the span is raised the counterweight swings down (Waddell, 1916). The earliest recorded trunnion type bascule bridge was built at Selby, England in 1839 and was noted to provide practical service as a rail bridge (Price, 1879). North American influences In comparison to the relatively slow development recorded in Europe, the intense competition in the USA to have patents led to an explosion of subtypes of bascule bridges being developed with extensive variations of mechanisms and geometry between the 1890s and 1920s. The potential of the Bélidor bascule as an elegant and energy efficient movable bridge design was described in an influential 1896 paper in the Railroad Gazette, by Assistant Chief Engineer of the American Bridge Company, Otis E. Hovey (1926). Hovey’s comprehension and knowledge of the Bélidor bascule was pivotal in the successful adaption of the design to road and rail bridges. He designed a number of these bridges in USA displaying their practical advantage. Two examples of Hovey’s designs built in 1896 include the Bridge across the West Branch of the Chicago River (Figure 19) and the Berry’s Creek Bridge on the Erie Railroad. Figure 19: Chicago River Bridge by Hovey (Source: Scientific America, 1896) The US rolling lift bascules had two important forerunners; these were the 40 ft. track girder built at Le Havre, France, before 1824 and another rotating on a wheel built at Bregere and documented by Waddell (1916). By contrast the rolling lift bascules are distinctly different in operation as the movable span rolls backward on curved extensions of the bridge girders. As it does this, the leaf rises and the counterweight drops. The fixed counterweight makes this very economical to operate. © ARRB Group Ltd and Authors 2014 12 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 The Scherzer bascule was first developed in 1893 by William Scherzer of the Metropolitan West Side Elevated Railroad Company of Chicago. The bridge design was patented and vigorously advocated and widely used in the USA and in other countries. The type was popular on account of its simplicity and the small power required for operation (Hovey, 1926). No examples of this type were built in NSW. The Rall bascule bridge is an interesting variant of the rolling bascule type. The design appears to have arisen in part as a way around the patents held by the Scherzer Bridge Company. The design was developed and patented by Mr. Theodore Rall and was controlled by the Strobel Steel Construction Company of Chicago. The Rall patent involves large moving rollers and is considered suitable for a double deck bridge (Grafton Bridge, Figure 25). The most significant bridge built to this specification was the Broadway Bridge across the Willamette River in Portland, Oregon opened in 1913 (Figure 20). Figure 20: One of the Rall wheels on Broadway Bridge (Source: Tilly) Following the Scherzer design, Joseph Strauss developed another variant bascule bridge in 1905. This design was patented by the Strauss Bridge Company of Chicago. There have been more bascule bridges built from the Strauss designs than any other single type of bascule. This series comprises designs of three general “Strauss Types”:    Type 1: Vertical overhead counterweight (Narooma and Menindee Bridge, Figure 24) Type 2: Underneath counterweight (no examples built in NSW) Type 3: Heel-trunnion (first Spit Bridge, Figure 21). Figure 21: First Spit Bridge (Source: MSBSR 579, RMS photographic archives) © ARRB Group Ltd and Authors 2014 13 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 NSW Bascule Bridges First Generation: Drawbridges In NSW the earliest bascule bridges were built in the 1890s to designs by J. A. McDonald (Fraser, 1985). These designs consisted of an entirely timber structure encompassing a latti ce tower, longitudinally oriented sheaves and counterweights hung inside the tower cavity. The span was raised at one end by a cable which passed over the sheaves and onto the counterweights. Tower stability was provided by tie rods from the top of the tower restraining it to the side spans (Figure 22). Allan (1924) noted that the stiffness of the towers was not adequate to prevent excessive deflection during operation however the design still met the operational requirements. This type of bridge was built at four locations (see Table 1) and is known collectively as the “Drawbridge Type”. Figure 22: Drawbridge Type: First generation bascule bridge, essentially a drawbridge (Source Dare, 1896) and Shea’s Creek Bridge (Source: Don Fraser collection, RMS archives) An interesting feature of these first generation designs was the method adopted for retaining a balance of the lift span during operation. J. A. McDonald used a set of metal disc weights of decreasing diameters to balance the opening span as it rose. The discs were picked off by matching lugs inside the tower; hence the amount of active counterweights was balanced against the position of the opening span. NSW Bascule Bridge Second Generation: Bélidor Type The early drawbridge designs were most likely informed by British engineering technology (Fraser, 1985). The Bridge over the Wilson River named Telegraph Point was designed by Harvey Dare in 1902 and he noted that the bridge was designed on a principle applied in several structures in the United States (Dare, 1904). The inherent complexity of a bascule bridge is how the mechanical advantage, centre of gravity and load continually varies during operation. As the lift span is raised the weight of the span and centre of gravity is shifted towards the pivot and consequently less force is required from the lifting mechanism as the bridge rises. Further bascule bridge developments continued in the USA, taking the European designs as a basis. Bridge engineers in the USA continued to innovate in two distinct basic patterns; the trunnion and the rolling lift types. The trunnion type was an evolution of the Selby Bridge described above, with the key feature of a fixed pivot point. The solution adopted by Dare was the Bélidor curved balance counterweight track. Where the counterweight rolls down the track and the vertical component of force diminishes as the track levels out. These changes in force are matched to ensure that there is minimal weight differential during the entire lifting operation which is achieved by increasing the diameter of the curve track as the rolling counter weight approaches the base. Dare was already using the graphical method from America to set out the cardioid to scale (Figure 18). He changed to a practical piece of curve-fitting using sections of circular curves to closely match the progressively changing radii of the true cardioid. Metal fabricators wer e quite familiar with shaping metal sections to fit circular curves. The Telegraph Point Bridge was of timber construction with a curved track incorporated into the adjacent fixed span. The counterweight travelled along the track during operation and as noted previously this results in a varying counterweight force that retains the balance in the system (Figure 23). The Swansea Channel was also bridged by a similar design in 1909 which remained in service for 46 years. © ARRB Group Ltd and Authors 2014 14 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 Figure 23: Bélidor Type: Telegraph Point Bridge track curve (Source: Dare, 1904) The Telegraph Point Bridge bascule span was relatively short and therefore the use of a timber tower was adequate. The later Bélidor type bridges designed by Dare needed to span greater distances and hence metal was required (Dare, 1904). Coraki Bridge was the first of this type and was completed in 1905. However, it was designed on the same principle, the scale was increased with the tower and adjacent truss subsequently reinforced with additional diagonals. Five other bridges of this type were completed including the Darling Point Bridge built in 1905, McFarlane Bridge over the South Arm of the Clarence River built in 1906, Kyalite Bridge over the Wakool River built in 1912, Carrathool Bridge over the Murrumbidgee River built in 1922 and Shea’s Creek rail bridge built in 1925 (Figure 24). These bridges collectively form the “Bélidor Type” bascule bridges. Figure 24: Shea’s Creek Railway Bridge, Alexandria replaced 1985 (Source: SRA archives) NSW Bascule Bridges Third Generation: Modern Bascules The third generation bascule bridge designs are primarily categorised as those derived from US designs patented and operational between the period between 1896 and 1913. These are distinct through sophistication of their mechanical systems and relatively large size. In 1924 the first Spit Bridge over Middle Harbour was completed and the design adopted was a double-leaf “Strauss Type 3” heel-trunnion bascule (Figure 21). This design positions the trunnion at the top of the tower where the driving force rotates the counterweight and lever arm which raises the span. The bridge over the Darling River at Menindee (Figure 25) was the first vertical overhead counterweight “Strauss Type 1” bridge built in NSW. The Bridge was completed in 1927 and the design consists of a counterweight supported laterally by a rear tower. The driving force of the bridge is provided by a rack and pinion mounted at the rear of the span. This design was also adopted for the bridge over the Wagonga Inlet at Narooma built in 1931, the bridge over the Lansdowne River at Coopernook built in 1934 and Barneys Point Bridge built in 1936. These bridges, along with the first Spit Bridge, collectively form the “Strauss Type” bascule bridges. © ARRB Group Ltd and Authors 2014 15 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 Figure 25: Strauss Type: Menindee Bridge 1927 (Source: RMS) The Grafton Bridge completed in 1932 was a unique design for Australia. It is based on the Rall type bascule bridge (Figure 26). Key features include the mechanism which rotates and traverses horizontally on a large roller (rall) during operation and the truss bascule span. The bridge has a double deck and is designed to provide passage for both road and rail traffic. This bridge is the sole entry in the “Rall Type” bascule bridge category. Figure 26: Rall Type: Grafton Bridge 1932 (Source: RMS) In 1955 the Bélidor type bascule bridge over the Swansea Channel was replaced with a trunnion type design shown in Figure 27. This type of bridge is electro-mechanically driven, with electric motors operating a rack and pinion mounted on the rear quadrant of the span. The 1958 Spit Bridge was also designed on a similar principle. These two bridges collectively form the “Simple Trunnion Type” bascule bridges. Figure 27: Simple Trunnion Type: Twin Swansea Bridges (Source: RMS) © ARRB Group Ltd and Authors 2014 16 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 The second Swansea Bridge built in 1989 is similar in many respects to the adjacent 1955 design however there is a progression in the operating mechanism. The driving force is provided by hydraulic luffing cylinders that are mounted near the trunnion of the spans. This type of movable bridge is considered as a hydraulically actuated trunnion bascule and the design was published in a USA patent by G. Mooney and E. Driver from 1967. The application of hydraulics to a bascule bridge was also adopted in the design of the second Spit Bridge and the Broadwater Bridge over the Richmond River. Broadwater Bridge bascule span was built through the relocation and reuse of the Barneys Point Bridge and the circumstances leading to the adoption of a hydraulic driving system by Richmond Valley Council is not clear. The bridge consists of a steel web plate girder and the span pivots on a reinforced concrete pier that is founded on concrete piles. The pier construction and bridge relocation was completed in 2005. CONCLUSION The Movable Span Bridge Study was completed by GHD in conjunction with RMS. The study will play a vital role in assisting RMS in assessing and managing their heritage movable span bridges into the future. The new classification provides a better understanding of the performance and shortcomings of those movable span bridges that are still operational as these issues appear common to all bridges within a type. One significant benefit of this classification is that it should enable the standardisation of maintenance strategies across each type and the development of more consistent heritage and conservation management practices. REFERENCES 1. J. A. L. Waddell (1916) Bridge Engineering Volume I, John Wiley & Sons, Inc. London: Chapman & Hall, Limited. 2. H. Harvey Dare (1896), The Opening Bridges of New South Wales, Sydney University Engineering th Society, 25 November, 1896. 3. Otis Ellis Hovey (1926), Movable Bridges (V.1). New York: J. Wiley sons, inc.; London: Chapman Hall, Limited. 4. D. J. Fraser (1985). Movable Span Bridges in New South Wales Prior to 1915, Multi-disciplinary Engineering Transactions. 5. Barpi, F. and Deakin, M., A., B. (2012) The Bélidor Bascule Bridge Design. International Journal for the History of Engineering & Technology, Vol. 82 No. 2, July, 2012, 159-75. 6. Bélidor, M. (1754) La Science des Ingénieurs. 7. Price, J. (1879) Movable Bridges. Institute of Civil Engineers Min. Proc. Vol. LVII Part III, 1878. 8. Percy Allan (1924), Highway Bridge Construction – The practice in New South Wales: Movable th Bridges. Industrial Australian and Mining Standard, 11 September, 1924. 9. Tyrell, H. G. (1912). “The evolution of vertical lift bridges.” University of Toronto Engineering Society, Toronto. (reprinted in Applied Physics 1912). 10. Hood, R. J. (1850). “Description of a vertical lift bridge, erected over the Grand Surrey Canal on the line of the Thames Junction Branch of the London, Brighton, and South Coast Railway.” Trans. Inst. Civil Eng, IX, 303-309. 11. Griggs F. E. (2006), “Development of the Vertical Lift Bridge: Squire Whipple to J. A. L. Waddell, 1872-1917. Journal of Bridge Engineering, ASCE September/October 2006. © ARRB Group Ltd and Authors 2014 17 th 9 Austroads Bridge Conference, Sydney, New South Wales 2014 AUTHOR BIOGRAPHIES Ian Berger joined the RTA in 2002 and works as a Heritage Officer in Environment Branch. By trade an archaeologist, he provides support and advice to project teams and designers on the upgrade and repair of heritage structures including bridges. Mark Tilley is a Principal Bridge Engineer at GHD and a Fellow of the Institution of Engineers Australia and an Engineers Australia accredited Heritage and Conservation Engineer. He specialises in opening, heritage, timber, steel and concrete bridges including repairs, rehabilitations, upgrades, inspections, asset management and brownfield rail and road bridge replacements often during short shutdowns. © ARRB Group Ltd and Authors 2014 18