Apr 28, 2016 News Archive
In collaboration with Roy Cottrell, 3DENT has filed a provisional patent for an improved brace-to-hull connection, for possible application in semisubmersibles. The impetus for the improved connection is our understanding that these connections are usually heavily reinforced so they can meet the fatigue life requirements of the unit.
Some of the loading on these connections is due to direct wave pressure on the braces, but a large component of the cyclic loading is due to differential movement of the pontoons, induced by prying/squeezing or racking.
Given the relative stiffness of the braces compared with the deck, the majority of the differential pontoon wave load is transferred through the column to deck connection, and the braces simply move with the pontoons. Reinforcing the brace to hull connection increases the rotational stiffness of the connection, attracting more load and making this reinforcement an ineffective way to address the connection fatigue issues. Because the deck is so much stiffer than the braces, this reinforcement does not influence brace deflection significantly, and the racking deflection is not reduced by reinforcing the braces.
The invention presented here looks to reduce the rotational stiffness of the brace to hull connection, thereby reducing the bending moment and reducing the need for local reinforcement requirements of the connection needed to achieve the target fatigue life. By reducing the local reinforcement requirements, a reduced structural weight of the brace connection can be attained.
Figure 1 depicts the stress flow of a typical connection and that of the optimized connection. For the new brace to the hull connection, the bending stress is significantly reduced mostly due to the flex element suffering only axial loads. Figure 2 shows some details of the connection, with named components. A presentation with more details on the patented connection can be found in our website.
A presentation with more details on the patented connection can be found HERE.