In 2010, current practice for the design of lock gates and approach structures is a relatively standard activity for a suitably experienced engineering company if the design requirements and the load cases are clearly specified.
Relevant, robust, reliable and effective software is available to assess the strength (stress, deformation, buckling, damage limitations, etc.) of lock gates and approach structures even if extreme load cases must be considered. The design aspects other than strength, such as opening and closing arrangements, service life, water tightness, sensitivity to vibrations, installation, maintenance, who pays for gate repairs (administration or vessel owner), etc. are the matter of the designers' specialisation and experience in hydraulic structures.
Steel gates share many design aspects with ships and the estimation of the collision resistance of ships is a fairly matured task using numerical methods. Similarly, in the auto industry, it is normal practice to perform numerical simulations of crash tests on new models of cars even before they are built and tested as prototypes. These simple examples show that the numerical tools to study the effects of ship impacts on lock gate structures are available.
So what are the design issues to be considered in determining the effects of ship collision on gate structures and approach works? In general terms, these are:
- What is the mass and hull form of the vessel?
- What should be the design speed(s) to consider for collision?
- Is the collision from and up or down bound ship?
- What shape(s) of the vessel in collision cause the most severe damage?
- What is the effect of added hydrodynamic mass?
- What level of damage can be accepted?
- How should the analysis be carried out and how can such analysis be verified against real events?
- How can the design be implemented to deliver the required robustness and ductility levels?
- What are the recommended measures to prevent/minimise collision damage?
- Which collision energy is dissipated in the vessel and which in the gate?
- What are (and what are not) the recommended repair methods and other practices after the collision
Obviously, there are probabilistic issues within these problems. The probability of a minor collision on a gate or approach structure on a regular basis which causes no significant degradation of capability or performance is relatively high for most lock gates or structures, but the general probability of having a major collision which causes substantial damage and its potential ramifications is much more complex to assess.
