Exploration for oil and gas is moving towards deeper waters. Steel has been the most common riser material. Related to deep water concepts titanium has become an alternative to steel for these applications. Several codes exist today for predicting collapse loads for marine pipes. However, the capacity formulas are developed for steel. If the formulas are applied directly to titanium several parameter uncertainties will be unknown. Ideally, extensive model testing of titanium pipes is required. This thesis discusses and investigates utilisation of experimental material test data and a supplementary numerical approach based on finite element analysis. The relationship between material model parameters as input to the analysis and the collapse capacity is investigated by performing a series of nonlinear FEM analyses. Statistical models for the input material model parameters are established based on tests on small specimens cut from titanium pipes. These models are subsequently combined with results from the FEM analyses by application of response surface methods. As output from the analysis, the probability distributions of the pipe capacity with respect to local buckling/collapse are obtained. Finally, the data from the nonlinear finite element analyses are compared to a relevant design code. Suggestions for a possible basis for design formulas to check for the local collapse capacity of deep water titanium risers are provided.

In this investigation strength and structural behaviour of prestressed concrete is studied with one full scale test of one flat slab, 16000 mm x 19000 mm, and three slabs on ground each 4000 mm x 4000 mm with thickness 150 mm. The flat slab was constructed and tested in Aalesund. This slab has nine circular columns as support, each with diameter 450 mm. Thickness of this test slab was 230 mm and there were two spans in each direction, 2 x 9000 mm in x-direction and 2 x 7500 mm in y-direction from centre to centre column. The slab was reinforced with twenty tendons in the middle column strip in y-direction and eight tendons in both outer column strips. In x-direction tendons were distributed with 340 mm distance. There were also ordinary reinforcement bars in the slab. Strain gauges were welded to this reinforcement, which together with the deflection measurements gives a good indication of deformation and strains in the structure. At a live load of 6.5 kN/m2 shear failure around the central column occurred: The shear capacity calculated after NS 3473 and EuroCode2 was passed with 58 and 69 %, respectively. Time dependent and non-linear FE analyses were performed with the program system DIANA. Although calculated and measured results partly agree well, the test show that this type of structure is complicated to analyse by non-linear FEM. Prestressed slabs on ground have no tradition in Norway. In this test one reinforced and two prestressed slabs on ground were tested and compared to give a basis for a better solution for slabs on ground. This test was done in the laboratory at Norwegian University of Science and Technology in Trondheim. The first slab is reinforced with 8 mm bars in both directions distributed at a distance of 150 mm in top and bottom. Slab two and three are prestressed with 100 mm2 tendons located in the middle of slab thickness, and distributed at a distance of 630 mm in slab two and 930 mm in slab three. Strain gauges were glued to the reinforcement in slab one and at top and bottom surface of all three slabs. In slab two and three there were four load cells on the tendons. Each slab were loaded with three different load cases, in the centre of slab, at the edge and finally in the corner. This test shows that stiffness of sub-base is one of the most important parameters when calculating slabs on ground. Deflection and crack load level depends of this parameter. Since the finish of slabs on ground is important, it can be more interesting to find the load level when cracks start, than deflection for the slab. It is shown in this test that crack load level was higher in prestressed slabs than in reinforced slab. There was no crack in the top surface with load in the centre, but strain gauges in the bottom surface indicate that crack starts at a load of 28 kN in the reinforced slab, and 45 kN in the prestressed slabs. Load at the edge give a crack load of 30 kN in reinforced slab, 45 kN and 60 kN in prestressed slabs. The last load case gives crack load of 30 kN in reinforced slab, 107 kN and 75 kN in prestressed slabs. As for the flat slab, FE analyses were performed for all of the three slabs on ground, and analyses shows that a good understanding of parameters like stiffness of sub-base and tension softening model, is needed for correct result of the analyses.

During this Master Thesis, leg-segments of jacket platforms subjected to supply vessel impacts have been considered. Finite element analyses (FEA) have been conducted using the explicit solver LS DYNA. The FEA results have been discussed and compared against simplified calculation methods and basic theory. In order to investigate the effect of the surrounding structure, two sets of boundary conditions have been considered for the columns:-Perfectly clamed boundary conditions-Axial flexible boundary conditions. The results have shown that the effect of the surrounding structure should be included. The effect is most important of the strength of the column is small relative to the striking ship. Parameter studies of the column-design with respect to column diameter and thickness have been performed. Three column diameters have been considered, namely 1.0 m, 1.5 m and 2.0 m. The thickness has been varied from 30 mm – 70 mm. Force-deformation relationships for the different columns have been compared and discussed. Based on the available amount of impact-energy, the different column-designs have been categorised as strength-designed, ductile-designed or shared-energy designed. The parameter study shows that if strength-design is aimed for, a column thickness of 70 mm in the case where the diameter = 1.5 m is required. If the column diameter is 2.0 m, strength design is achieved with a column thickness of 60 mm. Strength design was not achieved for the column with diameter = 1.0 m. However, based on the results, strength design of the 1.0 m column would probably require a thickness above 70 mm. The resistance against local indentation for the different columns have been considered and compared against resistance curves recommended by NORSOK N-004. The NORSOK-curves give a reasonable estimation of the strength for the weakest columns but becomes quite conservative compared to the strongest columns. An empirical design curve which takes the gradual increasing contact area into account was suggested based on the results. The resistance against global deformations have been compared against a simplified collapse mechanism. The results show that the accuracy of the simplified model is very dependent on the load definition and whether or not effects of reduced capacity due to local indentations are included. Two impact-scenarios have been considered: beam impacts and stern impacts. The beam impacts scenario proved to be the critical case in most cases. Finally, the effect of ring stiffeners applied in the collision-zone of the platform leg has been considered. 4 different designs have been evaluated. However, it was found that the effect on the column strength is larger if the column thickness is increased.

The oil price continues to increase while oil companies search for oil in new areas. There is assumed that 25% of the world’s hydrocarbons are located in the arctic area. Operating in these areas will be a huge challenge due to extreme low temperatures and ice condition Today one can predict with good accuracy how a ship will manage in different ice condition. Research on ship operating in ice the last decades has resulted in many different formulas for predicting ice resistance on a ship hull. Analytical and numerical methods are developed to estimate the resistance working on the ship hull under different ice conditions. Model test will still be the most accurate prediction, but the other methods may give you some guidelines on what to expect. This thesis contain a theoretically study of ice physics and mechanics. The formation and development of sea ice has been reviewed. The Ice Load Monitoring system tested on the Norwegian coast guard vessel KV Svalbard is described. Three different analytical ice resistance calculation methods are described. The three methods are Lindqvist (1989), Keinonen et al. (1996) and Riska et al. (1997). Data obtained from the Ice Load Monitoring system are used to estimate the full scale ice resistance on KV Svalbard. The three analytical methods are calculated with KV Svalbard as a reference ship to be able to compare with the full scale measurements. MATLAB is used for the calculations.