Aluminium Marina Gangway FEA to Eurocode 9: Strength Check and Hinge Redesign

A pontoon and marina equipment maker in Europe needed proof that a long aluminium gangway, the walkway that links a floating pontoon line to the shore, would carry its design pedestrian load safely. The bridge is a welded truss in 6005A aluminium with a GRP grating deck, hinged at one end and sitting on pontoons along its length.

Shirsh Technosolutions carried out an aluminium gangway FEA in ANSYS Mechanical, checked strength and deflection against Eurocode 9 (EN 1999), found that the hinge zone of the first design did not meet the ultimate limit state, and then verified a simple fix on the full model.

Building the model. The 3D model was built from the client's 2D drawings, including the side trusses, handrails, deck profiles, cross members, clamps and hinge plates. We meshed it with second-order solid elements and treated the joints as bonded or frictional contacts, depending on how each part is actually connected. Mesh quality was checked for aspect ratio, Jacobian ratio and warping, and the reported error stayed within the usual FEA guidance in the general regions.

Loads and supports. Self weight came directly from the 6005A aluminium density, the GRP grating was added as a distributed mass, and the pedestrian live load was applied as a uniform pressure over the walkway area. The hinge and roller ends were modelled with remote displacement supports at the real hinge plates. Under the deck, the pontoons were replaced by springs, with a stiffness worked out from the total load and the expected pontoon sinkage, so the frame could settle on its floating supports as it would on the water.

Stability first. Before the strength run we did an eigenvalue buckling analysis of the whole bridge. In Eurocode 9 terms, the critical load factor tells you how sensitive a frame is to instability and whether second-order effects need attention. It also shows the first buckling shapes, so we could see which members to watch.

Strength and deflection. A static structural run under dead plus live load gave total deformation and equivalent stress for the full bridge and for each deck profile. Mid-span deflection was compared with a span/500 serviceability limit. Peak stress was compared with the aluminium strength using the EN 1999 partial factor.

Finding and fixing the weak spot. On the first design, deflection was within the limit, but the hinge plate area at the shore end did not meet the ultimate limit state. The stress plots showed a sharp concentration where the plate meets the frame. We reported this to the client and proposed two changes at that zone: gussets added near the hinge plates, and a thicker clamp plate. The revised geometry was re-run straight away. Peak stress at the hinge came down sharply, the partial factor check passed with margin, and deflection stayed within the limit. The final report and the updated 3D geometry were issued to the client.

Common questions

How do you check an aluminium gangway or footbridge to Eurocode 9? Build a detailed FE model of the truss, deck and connections, apply self weight and the pedestrian live load, and check stress against the aluminium strength with the EN 1999 partial factor and deflection against a span-based limit. Run an eigenvalue buckling check too, because aluminium frames are slender and stability can govern.

How are floating pontoon supports modelled in a gangway FEA? Replace each pontoon with a vertical spring. The stiffness comes from the load the pontoons carry and how far they are allowed to sink, so the bridge settles on its supports realistically instead of sitting on rigid bearings.