Wave Pressures On The Underside Of A Horizontal Platform

Abstract

ABSTRACT The destructive effects of shallow water wave action on the underside of horizontal floors, decks, and platforms is evident from the inspection of hurricane damage. In order to provide some knowledge of the pressure distribution under such conditions, a laboratory study was made. Results are generalized through the use of dimensionless parameters and are presented in graphical form. These graphs show maximum and minimum relative pressure intensity and distribution of relative pressure intensity along the underside of the platform, in the general direction of wave motion, for various conditions of relative wave height, relative clearance, relative width, and relative length. INTRODUCTION Inspection of structural damage due to hurricanes along the Gulf Coast has revealed that horizontal floors, decks, and platforms are susceptible to severe damage by shallow water wave action on the underside. In order to gain some knowledge as to pressure intensities associated with such conditions, a laboratory study was undertaken. Although hurricane conditions could not be simulated, the action of shallow water waves on a small scale structure provides useful information as to the nature of the problem. The study was designed to reveal the separate effects of wave height, clearance above still water surface elevation, width of structure, length of structure, and still water depth on pressure intensity along the underside of. the structure, in the general direction of wave motion. This was done by varying each quantity, except depth, from the value associated with a set of common or reference conditions. The results are generalized insofar as possible through the use of dimensionless parameters, length ratios with stillwater depth as the common quantity. There is reason to believe that the motion of a large, storm wave through relatively shallow water may be more nearly that of a solitary wave than that of a wave in an oscillatory wave train. Proceeding on this premise, the waves generated for this study were sufficiently far apart that they were considered to be independent of one another. This means that, for the purposes of this study, such quantities as wave period and wave length are not considered to be significant. DIMENSIONAL CONSIDERATIONS A rather common structural problem along coasts exposed to hurricanes is that having to do with pressure intensity on the rectangular, horizontal underside of floors, decks, and platforms as a result of shallow water wave action. If the study is limited to cases in which a centerline of the rectangular underside is parallel to the general direction of wave motion, the physical quantities which appear to enter the problem are those necessary to describe the pressure intensity, the location at which pressure intensity is determined, the characteristics of the water, the characteristics of the waves, the spatial relation of structure to water, and the geometry of the structure.