Product category:
Hydraulic Components
News Release from: DavyMarkham | Subject: PLC-based electro-hydraulic actuation systems
Edited by the Engineeringtalk Editorial
Team on 08 November 2001
New Gateshead Millennium Bridge is under
control
Kvaerner Markham was responsible for the systems that control the tilting process and earn the newly opened Gateshead Millennium Bridge its nickname, the 'Blinking Eye'.
Hailed as the world's first tilting bridge, the newly opened Gateshead Millennium Bridge has attracted international acclaim for its unique structure and now forms a stunning landmark across the River Tyne The creative vision of client Gateshead Metropolitan Borough Council, the award-winning design by consulting engineers Gifford and Partners and architects Wilkinson Eyre, and the overall project management of main contractors Harbour and General have all been rightly praised as a result
This article was originally published on Engineeringtalk on 25 Jul 2006 at 8.00am (UK)
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So too has Sheffield-based Kvaerner Markham, part of Kvaerner E and C Manufacturing Division, which was responsible for the mechanical, electrical and hydraulics systems that control the entire tilting process and earn the bridge its nickname, the 'Blinking Eye'.
Employing the system design skills of its engineering team and the large-scale manufacturing capabilities of the Kvaerner E and C works operation, Kvaerner Markham developed and built the unique hinge mechanisms and sophisticated PLC-based electro-hydraulic actuation systems in-house.
That it was able to produce a world-first application that worked 'out of the box ' and was delivered on time, is a testament to the company's enormous engineering expertise and experience, its preliminary computer modelling to test and verify both designs, and its ability to work seamlessly with expert contractors in other fields, assembled on this ?22 million project.
Collaborating closely with the civil and structural design teams, alongside Gateshead Council and the architects, Kvaerner Markham's main challenge was to provide a safe and reliable system that would facilitate bridge opening and closing under all load conditions, at the same time meeting strict aesthetic and environmental requirements.
The bridge itself has just one major moving part, the whole structure, which turns on hinge assemblies on either side of the river to form a 25m high archway, under which taller ships can pass.
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Massive hydraulic rams push or pull against steel paddles attached to the hinges, rotating the parabolic bridge deck and its supporting arch through almost 40 degrees, then closing it again once the ships pass upstream.
The hinge or trunnion assemblies each consist of a cylindrical shaft, supported at either end by a spherical bearing and housed in a steel pedestal.
In its detailed proposals, Kvaerner Markham pointed out that the unique structure imposed axial/radial loadings and horizontal thrust forces not normally seen on a conventional lifting bridge, but that the company's extensive knowledge of large rotating structures would enable it to meet the technical challenges of shaft and bearing design.
It also proposed finite element analysis to optimise the design and manufacturing techniques for the pedestals, in order to marry the somewhat conflicting parameters of strength and aesthetics.
Computerised simulation of the electro-hydraulic operation and control system was also deemed essential by Kvaerner Markham, to ensure meeting stringent performance and safety criteria.
These included an opening/closing sequence of under four minutes, in wind speeds up to 14m/s, static overload relief in case of extreme loadings and precisely synchronised movement at each side, without relative oscillation.
Although the company was originally part of another consortium bid, the client was sufficiently impressed by Kvaerner Markham's presentation and engineering credentials to insist that the winning contractor worked with its team.
Starting in February 1998, its design specialists first addressed the task of designing relatively compact hinge pedestals, which would withstand the huge axial and radial thrusts produced during opening and closing, yet be visually attractive as well as functional.
Employing dedicated LUSAS finite element analysis software, Kvaerner Markham 's in-house design department optimised the profile and distribution of material to give minimum weight and cost for the applied loading, at the same time resolving on casting techniques for aesthetic reasons.
The two resulting pedestals, cast by Weardale Steel, are bolted to the concrete substructures and designed to withstand 4000kNm vertically, 7700kNm laterally and 4200kNm transversely; at the same time, the outboard bearings supporting each shaft can handle a maximum static load of 150mpa and a dynamic load of 90mpa.
The final hinge assemblies, each weighing in excess of 14 tonnes and almost 4 metres long, were assembled and tested at the giant Kvaerner E and C works in Sheffield, where the job could be readily accommodated, before being installed and commissioned by its engineering staff.
Possibly the greatest challenge facing Kvaerner Markham was synchronising the two hydraulic drives on opposite banks of the river, without a mechanical link between.
Thus, the initial development work centred on computer modelling the hydraulic and control circuitry to simulate how it would integrate with the bridge structure itself, employing the specialist resources and systems of Bath University's Centre For Power Transmission and Motion Control.
The hydraulic and electrical installation that emerged from this modelling exercise is housed in acoustically-insulated machinery rooms located on the north and south piers; each system comprises five electro-hydraulic pumpsets, three Rexroth Hydraudyne 450mm bore cylinders, fixed and proportional control valves, and associated PLC control architecture, linked by a communications cable running through the bridge.
The hydraulic cylinders, which operate between 215 bar and 350 bar, are sized so that only two in each group are able to raise and lower the bridge, in the event of ram failure.
Similarly, a standby diesel generator will operate the bridge at low speed, in case of a mains outage, and there is also provision for lowering the structure manually, by gradually releasing hydraulic fluid.
Separate control systems have been installed by Kvaerner Markham on either side of the river, which are based on advanced ControlLogix 5550 controllers and provide the processing power required in an easy-to-use environment.
During operation, the PLCs monitor the position of each bank of hydraulic cylinders, by means of a measuring system integrated into the cylinder rods; one on each side is designated the master cylinder and a deviation of more than 6mm between the two triggers an out-of-synchronisation warning.
As a backup, there is also a second form of position monitoring, based on encoders in the hinge bearing shafts and another dedicated PLC.
Each opening and closing sequence takes about four minutes and this is controlled by proprietary software running on the main PLCs, with deceleration at each end of the cycle to avoid oscillation.
Initially it moves at a fixed creep speed of 1mm/sec, then gradually accelerates to a maximum speed of 18mm/sec, by means of proportional control technology, before decelerating to zero.
At the highest point, back pressure is introduced so that the hydraulic cylinders pull rather than push the bridge, to prevent it going over centre.
The whole opening/closing process is fully automated and monitored on touchscreen displays in the main control room on the south bank, although there is also provision for manual operation.
Weighing more than 850 tonnes and sitting on 19,000 tonnes of concrete, the bridge is expected to open at least 200 times a year; Kvaerner Markham's engineering expertise, its use of the latest technology and ability to work closely with other contractors on such a ground-breaking project, should ensure it does so efficiently, over many, many years to come.
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