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The hinge-connector units of the Venice flood prevention system
The “heart” of the mobile barriers consists of the buoyancy flap-gates and the hinge-connector units which provide anchorage and supply power and compressed air to the gates - these units are steel structures weighing 45 tons each, marked by a compact solution despite the multiple functions and the high forces resisted.
Location: Venice, Italy.
Client: Consorzio Venezia Nuova, concessionary of the Ministry for Infrastructure and Transport - Venice Water Authority.
Cost of total Works: 220,000,000 € (hinge-connector units).
Services: Detailed design of hinge-connector units at the four lagoon inlets; prototype specifications and assistance for testing activities on a full-scale model.
The solution chosen to protect Venice by recurrent tides includes, as major work, the temporary closure of all the lagoon inlets by means of a row of mobile gates. The MOSE barrier has been designed to protect Venice lagoon from high tides up to 3 m, assuming a sea level raise as much as 60 cm for the next 100 years.
Any barrier consists of several steel flap gates (variable in number between 18 and 21) connected to the housing caissons by means of a couple of connectors for each gate. Starting from the gate level, the main components of the connector are:
- Male element, steel carpentry with a lower part matching with the socket of the female element and with an upper part fork-shaped which supports the spherical hinge of the gate, weighing 12 t;
- Hinge, junction between the beams of the gate and the male of the connector, done by means of a huge stainless steel pin enclosed by a spherical bush;
- Female element, steel box about 3.5 m large and 1.2 m thick provided of a cone-shaped seat in the middle that matches with male element, weighing 30 t, grouted on the roof of the caisson and anchored with 10 post-tensioned bars;
- Coupling unit, a long hammerhead steel rod which connects male and female elements with a pretension of 3000 kN, moved, rotated and tensioned by hydraulic systems completely automated and remote controlled.
The components (1) and (2) are installed on the gate and therefore removable from the barrier in occasion of the gate maintenance operations; the remaining elements (3) and (4) are fixed to the roof of the caissons.
The hinge-connector units, equipped with rubber hoses, valves, spherical bearing, underwater electrical connector and mechanical inclinometer, meet the following requirements:
- Restrain the gate with a couple of hinges, enabling a free rotation between the rest position and the max amplitude of oscillation assessed by the physical models.
- Withstand the severe loading conditions due to the marine events (tide, sea level rise, waves) acting on the barrier.
- Connect the gate to the foundation, joining a steel box to a reinforced concrete slab, allowing the gate removal for maintenance but preventing the entry of water in the underlying tunnels.
- Assure compressed air and power supply along with signal transmission (exchange of data with all the instruments installed inside the gate).
- Lifetime of 100 years for all connector’s parts fixed to the caisson.
- Gate placement in barrier must be carried out with a misalignment between the two connector elements that have to be coupled (male element on the gate and female element on the caisson) up to 50 mm in any direction.
In barrier 156 fully interchangeable units are installed, with several level of protection against corrosion as epoxy paints, cathodic protection (sacrificial anodes), parts of stainless steel, special cladding for components in steel alloy, extra-thickness of steel. Reference electrodes fixed on the female elements will monitor the efficiency of the cathodic protection.
FEM analysis have been carried out on a complete model (including part of the concrete supporting structure) and several refined local models, introducing non linearity of materials and mechanical contacts, to examine load effects (radial forces acting on the hinge up to 8000 kN for ULS) on stresses, displacements and fatigue life.
First studies on hinge-connector began with the trial module Mo.S.E.; the experimentation lasted four years and were able to provide important data about the behaviour of the gate and its connector in the lagoon environment. More recently, the experience continued with other four years of activities, dedicated to the construction and testing of a full-scale prototype of the connector. In this occasion the most suitable method of construction has been selected, taking into account construction and installation tolerances, durability, tightness and the multiple connections. The functionality of the coupler units and their instruments has been tested as well as mechanical strength and tightness under the worst design conditions (water head applied with a pressure bell). A load spectrum equivalent to the design condition (6 millions of cycles for 100 years) was applied to investigate fatigue effects.
Technical Drawings & Renderings
Key components of the hinge-connector units
Gates and caissons coupled by hinge-connector units
Focus: gates and caissons coupled
Hinge-connector unit with key components highlighted
Compressed air path through the connector