STRUCTURAL INTEGRITY EVALUATION OF A FIXED PLATFORM USING VIBRATION CRITERIA.

A mathematical model of the structure is analyzed by the SAP IV computer program, taking into consideration the effects of mass, entrained water, soil support conditions, equipment, etc. The various parameters affecting the lower-mode vibration characteristics of the structure are considered separately and their quantitative effect on the natural frequencies is evaluated. The theoretical analysis provides a convenient way to incorporate changes of structural, inertial and foundation properties, together with their effect on the vibratory response of the structure. Results of computer calculations are presented to illustrate this capability. The method provides a way to confirm possible structural damage, especially damage below the waterline which is often difficult to detect. It is also particularly effective in detecting microcracks in concrete in structures such as reinforced concrete platforms. These microcracks are otherwise undetectable, and can lead to structural failure.