IN-SITU QUASI-STATIC AND DYNAMIC BEHAVIOURAL RESPONSE OF STEEL TUBULAR FRAMES SUBJECTED TO LATERAL IMPACT LOADS

Abstract

STEEL TUBULAR MEMBERS ARE WIDELY USED AS PRIMARY AND SECONDARY STRUCTURAL FRAMING MEMBERS IN OFFSHORE OIL AND GAS PLATFORMS. A PLATFORM IS INHERENTLY LIABLE TO COLLISIONS FROM SHIPS WHICH CAN CREATE SEVERE STRUCTURAL DAMAGES IN THE RIG. THE EFFECT OF THIS DAMAGE HAS BEEN STUDIED BY A NUMBER OF RESEARCHERS THROUGH INVESTIGATING THE IMPACT BEHAVIOUR ISOLATED TUBULAR MEMBERS. THIS IS WHILE, THE IN-SITU RESPONSE OF A MEMBER LOCATED IN A STRUCTURAL FRAME, TO LATERAL IMPACT LOADS, IS NOT NECESSARILY THE SAME AS THE RESPONSE OF AN INDIVIDUAL ISOLATED IMPACTED MEMBER. IN THIS PAPER THE BEHAVIOUR OF A CHORD MEMBER FORMING PART OF A TUBULAR FRAME, SUBJECTED TO IMPACT LOADS, HAS BEEN INVESTIGATED. THE TUBULAR FRAME WAS TESTED EXPERIMENTALLY BY OTHER RESEARCHERS AND REPORTED IN THE LITERATURE. THE NON-LINEAR NUMERICAL MODELS OF THE FRAME PRESENTED BY THE AUTHORS HAVE BEEN VALIDATED AGAINST THE EXPERIMENTAL RESULTS. THESE VALIDATED MODELS HAVE BEEN EXAMINED UNDER BOTH QUASI-STATIC AND DYNAMIC IMPACT LOADS WITH OPERATIONAL PRE-LOADING APPLIED. IT HAS BEEN FOUND THAT, IN A PRE-LOADED FRAME, QUASI-STATIC IMPACT LOADING RESULTS IN THE FAILURE OF THE IMPACTED MEMBER. INTERESTINGLY, DYNAMIC MODELLING OF THE IMPACT RESULTS IN THE DYNAMIC INSTABILITY OF AN ADJACENT BRACING MEMBER. IT HAS BEEN NOTICED THAT, UNDER A DYNAMIC IMPACT, THE IMPACTED IN-SITU MEMBER (LOCATED IN THE FRAME) BEHAVES RATHER SIMILARLY TO A PIN ENDED ISOLATED MEMBER. WITH A QUASI-STATIC IMPACT, THE IMPACTED IN-SITU MEMBER FOLLOWS FAIRLY CLOSELY THE RESPONSE OBTAINED FOR A FIXED ENDED ISOLATED MEMBER.