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[Image] [Backward] [Home] [Index] [Visitors' book] [animation] [animation]Operation of the Storm Surge Barrier Trusses The trusses, each 240 metres in length, are a prominent visual part of the Storm Surge Barrier. Their function is to transmit directly to the ball-joint the loads exerted on the retaining walls in the closure process. During closure the truss will ride up and by approximately 40 centimetres into a camber, levelling out again when the load eases. 1. Dimensions 2. Loads 3. Manufacture 4. Assembly 5. Attachment to the retaining wall[Image] [Backward] [Home] [Index] [Visitors' book] Truss dimensions Each arm consists of two separate open- frame girders joining up at the ball- joint. Length: 240 metres Maximum height: 20 metres Main girder cross-section: 1.80 metres Main girder wall-thickness:40-90 mm Diagonals cross-section: 60-80 mm Diagonals wall-thickness: 12-30 cm Maximum compressive force: 300 MN Tensile force (given negative thrust): 50 MN Connection with hinge: - end-diagonal - tailpiece Camber: 8 cm The trusses were constructed with a camber of 500 mm. After removal of the supports a camber of 80 mm remained. [camber] [Image] [Backward] [Home] [Index] [Visitors' book] [photo of arm] Truss loads The loads on the trusses have been calculated with the aid of an influencing factor model (i.e. the finite elements model), in which the trusses - like the retaining wall - form part of an integral model of the total sector-gate. The model translates a unit of (bar) force on a given section of the retaining wall into bar forces in the truss. The hydraulic loads on the retaining wall are translated into a combination of unit loads; in this way the maximum and minimum normal forces in the truss can be determined. Apart from the hydraulic loads and the dead-weight of the truss, the loads imposed on the arms by wind, temperature, snow and ice-formation have also been allowed for in the calculations. [Image] [Backward] [Home] [Index] [Visitors' book] [photo of welding] Truss manufacture The main girders of the truss consist of 4-metre cylinders. These cylinders were rolled out of straight plates and then welded longitudinally. By means of a U- butt joint the cylinders were joined together to form girders of up to 60 metres in length. The main girders of the truss were supplied in 60-metre lengths. These sections were joined up at the construction site and the diagonals affixed between the girders. The diagonals of the open-frame consists of spiral-shaped welded pipes, constructed along the same lines as the cardboard tube inside a toilet roll. [Image] [Background] [Home] [Index] [Visitors' book] [photo of pipe] [photo train] Truss assembly Assembly at the construction site commenced with the positioning of temporary supports, on which the lower cylinder-girders of the truss were placed. Temporary supports or "A- frames" were then placed on the lower two main girders. Mobile cranes then lifted the upper girder sections into position, after which the diagonals were positioned between the upper and lower girders. The truss-sections were then welded together. On account of the wall-thickness (up to 90 mm) of the main girders, a single weld consisted of 102 layers, taking approximately 160 welding-hours. To permit welding under controlled conditions and to prevent pollution of the surface waters, welding tents were positioned around these connection- points, with lighting and dust- exhaustion facilities. [Image] [Backward] [Home] [Index] [Visitors' book] [photo of wall] Attachment of the trusses to the retaining wall The trusses are attached to the retaining wall when the latter is floating. By the admission of ballast water into the gate, by controlling the dock and outer water level and by manoeuvring with the aid of winches, the retaining wall is positioned in such a way that the first three main girders of the truss can be attached. The main girders were fixed in position by means of clamps. The retaining wall is once again manoeuvred in such a way that the three remaining main girders can be affixed in the correct position. All the main girders are then welded to the retaining wall. Finally the clamping structures are removed and the remaining diagonals, bottom props and the coupling- girder are positioned. [Image] [Backward] [Home] [Index] [Visitors' book]Operation of the Storm Surge Barrier Wetted works (sill structure) The sill structure on the bottom of the New Waterway has three functions: * The formation of a flat base and foundation for the retaining walls, which are positioned on the sill- blocks with the aid of fenders. * Cutting down the flow of water once the barrier is closed. * Holding in place the subgrade on which the blocks are based. 1. Sill-blocks 2. Bottom protection and filter-bed 3. Dredging works 4. Raking the surface 5. Dumping the filter-bed [Image] [Backward] [Home] [Index] [Visitors' book] [Image] [Backward] Wetted works sill-blocks A total of 64 sill-blocks have been installed on the bottom of the fast- flowing New Waterway at an average distance of 3.5 centimetres apart. The blocks were delivered by pontoon and positioned with the aid of a floating derrick. Various measuring instruments were used to enable the blocks to be positioned to within one centimetre. A 21-metre-high measuring tower was attached to each block, which remained just poking up above water after the block had been sunk into position. Since the sills are somewhat curved, the blocks are slightly wedge-shaped. In cross-section the blocks are also flared, thus preventing the tops of the blocks from "rubbing" against each other in such a way as to create a larger crack at the bottom than permitted. Two rubber toes have been fitted on one side of each block, with corresponding notches on the other side. [Home] [Index] [Visitors' book]Wetted works - bottom protection and filter-bed It was not possible for the sill-blocks to be simply placed direct onto the river- bed: rapid accelerations in current would otherwise create major turbulence beneath and in the vicinity of the blocks upon closure of the barrier. Furthermore the sill could be seriously destabilised if water were unable to pass beneath the sill blocks. For this reason the blocks rest on a porous filter-bed, in turn resting on substantial bottom-protection. Filter-bed Length: 60 metres Weight: 206 MN (206,000 tonnes) various materials, distributed over four layers: layer 1 sand 0.5-5 mm thickness 0.5 m (bottom layer) layer 2 gravel 3.5-35 mm thickness 0.5 m layer 3 (basalt) 30-140 mm thickness 0.5 m layer 4 rubble (basalt) 10-60 kg thickness 0.75 m (top layer) [Image] [Backward] [Home] [Index] [Visitors' book] Wetted works - dredging works In order to install the filter-bed and the bottom-protection, the new Waterway was dredged out from a depth of 14.5 metres below Amsterdam Ordnance Datum (NAP) to a maximum depth of 22.5 metres below NAP. In total 920,000 cubic metres of sand and sludge were dredged up. With the installation of the filter-bed the bottom was raised to a level of 17 metres below NAP. Three kinds of dredging vessels were used: * The tow-hopper for the coarse- dredging of the cunette (trench) in the New Waterway. A backhoe or grab was used to dredge the slopes. * The dustpan suction-dredger for smoothing the cunette and installing the bottom filter-layer. * The inclined stone-tipper for dumping the bottom protection and the other two filter-layers. [Image] [Background] [Home] [Index] [Visitors' book] [Image] [Backward]Wetted works - raking out A good seal was needed between the filter bed and the sill blocks. This was achieved by smoothing the top layer of the filter- bed. To this end a steel device with vertical teeth was mounted on the mouth of a dustpan suction-dredger to create a kind of rake. Following the good results obtained with a similar method on Neeltje Jans and in the Petroleum Harbour in the Europort area, this method was also applied in the New Waterway. [Home] [Index] [Visitors' book] Wetted works - dumping the filter-bed After extensive research it was considered feasible to dump the various filter materials on the river bed. This procedure involved two risks: * the risk of separation of the filter material (with larger particles becoming separated from smaller), thus potentially reducing the stability of the filter-bed. * the risk of mixing in sand when the filter material was dumped; the deposition of sludge between the various layers also reduces the stability of the filter-bed. Special measuring techniques were used in the dumping-process. It proved possible to dump the various layers on each other to within 10 centimetres of the required thickness. Vessels Various vessels were used in installing the filter-bed. A dredge was fitted out in order to suck up sand and to dump coarse sand and gravel. Another vessel (Jetsed) squirted air and water jets to prevent any sludge from being deposited between the various layers. The Jetsed is a self- propelling vessel that removes sediment deposits in the cunette between the filter layers. This is achieved by vertical air and water injection, thus throwing up the disturbed sediment, which is then borne away in the tidal currents. [Image] [Backward] [Home] [Index] [Visitors' book] [animation] [animation] [animation] [animation]Operation of the Storm Surge Barrier Operating equipment and parking dock Upon closure of the barrier, operating equipment drives the retaining walls out of the parking dock to close the New Waterway. This equipment is operated from control buildings on the north and south sides. The equipment consists of three elements: the operating equipment of the dock-gate, the locomobile and the ballast system in the retaining wall. [Image] [Backward] [Home] [Index] [Visitors' book] [photo of dock] [photo of dock] Operating equipment parking dock [detail of parking dock] The parking dock protects the retaining wall when the Storm Surge Barrier is retracted, thus creating a protected harbour for the retaining wall. When inside the dock the retaining wall cannot be rammed by passing vessels. With this in mind the dock has also been fitted with a special, extremely robust gate. One of the great advantages of the present Storm Surge Barrier design is that when at rest, the parking docks are dry, so that maintenance activities can be easily carried out. To facilitate maintenance still further, 14 concrete of support points have been installed in and beside the dock, thus leaving the wall some 2.5 metres off the floor of the dock. [Image] [Backward] [Home] [Index] [Visitors' book] [animation] Operating equipment - dock-gate [dock-gate] The dock-gate is designed to seal off the dock. In addition the dock-gate protects the retaining wall from being run into by vessels; the gate has been designed in such a way that vessels scraping the gate are warded off, while also providing maximum protection in the event of a head- on collision. The dock-gate may be compared with a safe-door (dimensions: 2 m thick, 12 m high and 20 m long), running backwards and forwards over a rail. Since sludge builds up on the rail, the dock- gate is opened once a month for the sludge to be bulldozered off. The dock-gate is opened immediately before the retaining wall is propelled into the main stream. Once the closure has been completed the dock-gate seals off the parking dock again. [Image] [Backward] [Home] [Index] [Visitors' book] [animation] [animation] [animation] Operating equipment - the locomobile [locomobile] In order to close the barrier, the locomobile on top pushes the retaining wall horizontally out of the parking dock. Upon completion of the closure the locomobile draws the retaining wall back into the dock. With the aid of running and guide wheels on railtracks, the locomobile rests with its own weight on the upper side of the retaining wall. It pushes off against the control tower and transmits its force to the retaining wall by means of a rack and pinion. The toothed wheels are constructed out of high-grade chrome nickel steel. The rack runs the entire length of the door. In the rest situation the locomobile also keeps the retaining wall in position horizontally. [Image] [Backward] [Home] [Index] [Visitors' book] Operating equipment - ballast system During closure the retaining walls move in two directions. Apart from the horizontal movement out of the parking dock the walls also move up and down in the waves when being sunk and refloated. The ballast system in the retaining wall facilitates the sinking and refloating of the retaining wall. When the remote-controlled inlet-valves are opened, water flows into the specially designed ballast tanks in the retaining wall. In order to ensure that the wall sinks stably, the water must flow into all the tanks evenly. Pumps set in the retaining wall expel the ballast water from the retaining wall when the latter needs to be raised again. Each retaining wall is fitted with 30 pumps and 14 chaser-pumps to remove the last remaining water. The capacity of the pumps varies from 1.6 kW to 40 kW.