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Abstract A mathematical model is presented for determining time histories of verticalimpact forces on platform horizontal structural members in the "splashzone". Interpretation is given in terms of the Morrison equation, with thecoefficient range illustrated as a result of the impulsive force nature. Applications are described for determining statistical properties, includingextreme values, as well as methods for evaluating fatigue life via structuralresponse analysis. Introduction When considering the various forces acting on fixed offshore platforms atsea, an important class of forces for which there is not a large extensivehistory of study are the impact forces that act on horizontal members in the socalled "splash zone" (see [1]). The "splash zone" is a regionwherein the particular horizontal members of the platform are not usuallyconsidered to have continuous contact with the waves, but which are located ata height relative to the mean water surface so that only occasional contactwith the water will occur. The nature of the forces that occur during suchcontacts is essentially impulsive, and thus somewhat similar to the forcesassociated with slamming of ships (see [2]), where the relative emersion andimmersion of a portion of the ship bow region with respect to the sea surfaceproduces impacts on the ship. In order to provide estimates of these impact forces for use in offshorestructure design, use is often made of the classical Morrison force formula [3]with the problem (as usual) being the determination of the values of thevarious coefficients entering into that equation. However, the Morrison formulais generally applicable only to portions of an immersed body that are in fullcontact with the water continually, and as such there is a question as towhether that particular approach can be considered applicable to the presentimpact force problem for horizontal members.