ABSTRACT The hot pot stress (HSS) of a tubular joint is considerable because of the existence of stress concentration along the welding seam. To study the strategy for control stress concentration factor (SCF) of tubular joints, a typical five-planar tubular Y-joints as the connection between diagonal braces and the central column of a five-pile substructure is selected and simulated using FE method. Moreover, the corresponding reinforced FE models with three stiffened rings are established and calculated. The SCF distributions along weld seam, extreme SCF values, and sensitivity analysis of geometries parameters are performed and compared. INTRODUCTION The weld and geometrical discontinuity of tubular joint cause stress concentration which is a detrimental impact on fatigue performance. Usually, the stress concentration due to the weld itself is included in the S-N curve, while the stress concentration due to the geometry effect of the actual detail is determined by means of calculation of hot spot stress. Generally, the hot spot stress is calculated from multiplying the nominal stress by stress concentration factor (SCF). There are many pieces of research of SCFs for tubular joints subjected to different loadings. The SCFs for simple tubular joints are listed in the fatigue design codes such as API (2014) and DNV (2016). Hot spot stresses at failure-critical locations for multi-planar tubular joints such as DK, DKT, X-type are derived by Dong, Moan and Gao (2011). Considering bending effect, Karamanos, Romeijn and Wardenier (2002) computed SCFs of DT-joint. To meet the demand for expending fatigue life, many stiffened joints are studied. Woghiren and Brennan (2009) carried out a parametric stress analysis of various configuration of plate stiffened multi-planar KK-joint using the finite element method. Shao, Lie, and Chiew (2010) proposed parametric SCFs equations for the tubular T-joint with reinforced chord under axial compression. Ahmadi, Mohammad and Shao (2012) established a set of SCF parametric equations for the fatigue design of internally ring-stiffened KT-joint.

ABSTRACT When using bracings to build a joint between the jacket base and the tower, it becomes complicated both in force capacity and fatigue performance due to its complex joint form and large sizes, which also make the empirical formulas recommended in DNV rules or other specifications no longer apply when calculating the joint stress concentration factors (SCFs). Based on above-mentioned, this paper focuses on the joint SCFs by calculating FE models with different load directions and structural parameters, tries to give their change rules or values variation range which can provide reference for the fatigue design of the offshore wind turbine (OWT). INTRODUCTION Jacket foundations are typical and reliable structures of marine engineering, also widely applied in offshore wind turbine (OWT) in recent years. There are different structure forms to connect the tower with the jacket base, using diagonal bracings to transfer load and support the tower is one form of these structures. The bracings and the tower form a joint which has much larger size than common joints of the jacket base, this results in difficulties when considering its fatigue properties. The stress concentration factor (SCF) of joints is hinge parameter especially in preliminary design stage to calculate the fatigue stress, because of the large size of the joints, the empirical formulas no longer suit for deriving SCFs. Studies on the joint SCF s began in 1970s, measures to get the SCF s are considerable developed over the past decades. Measuring the hot spot stress directly from large number of model experiments is considered to be first-hand and accurate (Cheng, 1999), empirical formulas to calculate SCFs were subsequently formed (Li, 2014). However, model test is not suitable for joint with large sizes, also the huge expense is another limitation. With the rapid development of the FEM, calculating stresses of tubular joint become convenient. The shell element and solid element are both wildly used according to the actual needs (Shao, 2006), concretely, using shell element means less computing burden, but it cannot model the attachment structures like the welds, on the contrary, the solid element brings larger amount of calculation but can fit reality more (Zhang, 2008).

ABSTRACT Fatigue is the significant factor resulting in the failure of the support structure for an offshore wind turbine (OWT) subjected to combined hydrodynamic loads and aerodynamic loads. The tubular joints are the weakest component leading to fatigue failure of the whole structure. But in current fatigue assessment method, the effect of torque loading applied on brace component is neglected. Considering the multi-pile foundation structure which is used widely in China, a three-planar tubular Y-joint as the connection between diagonal braces and central column of a typical tripod OWT substructure is selected to study the influence of torque loading on fatigue life. The study mainly focuses on three levels as follows: component internal stress analysis, the stress concentration factor (SCF) and the fatigue damage of OWT. INTRODUCTION With the continuous adjustment of worldwide energy structure to handle the energy challenge, offshore wind energy regarded as renewable energy has been strongly supported by many governments. A key problem of OWT substructure is fatigue damage, which caused by wind, wave, current, ice, earthquake and other environmental loads. Generally, most stress concentration can be found in the vicinity of connections, so, only the connection of marine structure need fatigue assessment while the tubular joints is the major part of connection. For now, the most popular fatigue assessment method is structural hot spot stress approach and correct calculation of hot spot stress is directly related to the accuracy of fatigue assessment. In fatigue research of tubular joints, stress concentration factor (SCF) is defined as the ratio of hot spot stress to nominal stress. It was recommended (CIDECT, 2001; API, 2014; DNV, 2016; IIW, 2016) that nominal stress and SCF are used to calculate hot spot stress which is given by: (equation) In order to calculate hot spot stress efficiently and accurately in practical engineering design, many studies have been carried out on the tubular joint SCF under various loading types including axial loading (AX), in-plane bending (IPB) and out-of-plane bending (OPB). Potvin, Kuang, Leick and Kahlich (1977) presented parametric equations covering T-, Y-, K-, and KT-joint configurations and utilize a modified thin-shell finite element (FE) program specifically designed to analyze tubular connections. The tubular connections were modeled without a weld fillet, and equations are merely expressed the location of the hot-spot as chord-side or brace-side. Efthymiou and Durkin (1985) proposed a complete set of SCF equations expressed in terms of joint parameters for the design of T-, Y- and K-joints under AX, IPB and OPB by using 3D shell elements. The hot-spot SCFs were determined on the base of maximum principal stresses linearly extrapolated to the modeled weld toe, with some consideration being given to boundary conditions (i.e. short chords and chord end fixity). Hellier, Connolly and Dover (1990) primarily developed the fracture mechanics to estimate remaining life for a joint rather than for tubular joint design, and proposed SCF equations covering T/Y-joint configurations. Also, the weld fillets were not modeled. Lee and Morgan (1997) suggested a set of parametric equations to determine the SCFs for tubular K-joints under AX, IPB and OPB. The equations were developed using a database of thin shell FE results to estimate the SCFs at key locations on both the chord and brace. Karamanos, Romeijn and Wardenier (1999) proposed a set of parametric equations to determine the SCFs for multi-planar welded CHS XX-connections. In this study, the weld profile was modeled using 20-node solid elements while 8-node shell elements were used to model the chord and brace. This research covered the various loading modes including reference and carry-over effect. Karamanos, Romeijn and Wardenier (2000) proposed SCF equations in multi-planar welded tubular DT-joints including bending effects. Special attention was focused on the location where critical stress concentration occurs, as well as on the so-called "carry-over phenomenon" and its implications on the hot-spot stress value. Shao, Du and Lie (2009) presented a set of parametric equations to predict the hot-spot stress distribution for tubular K-joints under AX, IPB and OPB. The equations proposed by Lotfollahi-Yaghin and Ahmadi (2010) can be used for prediction of SCF distribution along the weld toe of tubular KT-joints under the balanced axial loads. Using ANSYS, SOLID95 element was used to model chord and brace members and the weld profile. The equations proposed by Ahmadi and Lotfollahi-Yaghin and Aminfar (2011a, 2011b, 2012) were utilized for prediction of SCF distribution along the weld toe of tubular two-planar DKT-, uni-planar DKT- and three-planar KT-joints respectively. However, almost all these results are focused on the values of the SCF under AX, IPB and OPB. The SCF caused by TOR have been ignored. Although the results of these research efforts are useful, it is worth mentioning that attention should be paid on the influence of SCF caused by TOR.

Abstract Reliability-based low-cycle fatigue assessment for crack-stopping holes in severe sea states was formulated. The time to initiate a new crack at a crack-stopping hole in severe sea states is predicted by strain-life methods. The limit state function for low-cycle fatigue assessment for a crack-stopping hole is established by taking into account the potential severest sea state the cracked structure may encounter before it is repaired. Low-cycle fatigue reliability assessment for two crack-stopping holes on the deck of a tanker is then performed for demonstrating the capability of the method developed. The effects of the return period of the potential severest sea state, radius of crack-stopping hole, and environmental severity factor on the reliability not to initiate a new crack at crack-stopping holes were investigated.

Abstract The design of the new developed offshore supporting structure for wind energy converters PREON marine requires the use of thick walled rectangular (RHS) and circular (CHS) hollow sections. Since for joints made of these sections only little information on the fatigue behavior exists, the check of the fatigue limit state is hampered. Therefore, numerical investigations on symmetrical K-joints with gap made of RHS, CHS and made of combinations of RHS and CHS are carried out by the Center of Competence (CCTH) in Karlsruhe. Additionally, joints made of RHS and gusset plates are investigated. The results presented here form part of extensive numerical investigations (Herion et al, 2013).

ABSTRACT In this paper for PREON marine - a special offshore application - the SCFs for K-joints with gap×made of thick walled rectangular hollow sections (RHS 300 300 20 mm) are determined by using finite element calculations. The results are compared with the SCFs calculated on basis of the CIDECT Design Guide 8 and on a publication of Herion and Mang (1996).

ABSTRACT: Steel Catenary Risers (SCR) are known to be subjected to important cyclic loading often critical for the fatigue resistance of the structure. Normally, specifications for girth welding, in products destined to fatigue applications, express very strict requirements in terms of maximum allowable imperfections, with very small allowed embedded and surface flaws. In previous ISOPE Conference, a paper illustrating the model for suitable prediction in crack propagation regime was presented, offering indications for a proper calculation with some reduction in overconservativism with respect to a standard fatigue life prediction. In the present work, a Two Stage Model (TSM) for the fatigue defect tolerance calculations was developed, including the initiation and propagation stages. The number of cycles to crack initiation is modeled by a local strain approach using the Manson-Coffin equation, whereas the propagation phase is modeled by fracture mechanics adopting the Paris law. Such model is able to take into account the effect of the global geometry of the joint and of the local geometry considering weld toe, weld imperfections, residual stresses and consequent local rising of mean stress during stress cycling. The model was calibrated on the basis of a wide full scale experimental testing program and it was applied to predict fatigue life of X65 pipeline girth welded joints. In order to verify the accuracy of the presented model, the S-N plots constructed from the two-stage model and full-scale fatigue tests on X65 girth welds with welding imperfections were compared. INTRODUCTION Fatigue analysis presented in main design standards ( e.g. BS 7608–1993, "Code of practice Fatigue Design and Assessment of Steel Structures" ; DNV-RP-F204 2010 "Riser fatigue" ); are generally very stringent with respect to defect tolerance in components subjected to cyclic loads, referring to the highest levels of Good Workmanship Criteria.

ABSTRACT The circumferential welds on steel tubular berthing monopiles, namely pile splices, are potential fatigue hot spots. This paper presents the latest progress in linear elastic fracture mechanics (LEFM)-based fatigue safety assessment for welded splices of steel berthing monopiles. Particularly, the fatigue assessment against vessel impacts is studied at the current stage. Practical methods for determining stress intensity factor (SIF) and stress concentration factor (SCF) at the circumferential welds given bending moments are reviewed and summarized. This paper also proposes a new modification factor for Paris law, as well as a Beta distribution for characterizing the hot-spot stress range caused by vessel impacts, which is often doubly bound by operational water levels. The findings of this paper provides practical information for performing LEFM-based fatigue safety assessment of splice welds of steel berthing monopiles. INTRODUCTION Steel marine piles often work against cyclic and harsh operational and environmental loadings. Due to welding flaws or defects (undercuts, cracks, incomplete penetration, and gas pores), circumferential welds on steel piles, also known as splice welds, transversal welds, or girth butt welds, have been recognized as potential fatigue hot spots, given the frequently repeated loadings. Insufficient fatigue strength of welded pile splices may cause severe structural failures (Dailey et al., 1987a, 1987b; Weidler et al., 1987). This paper studies the fatigue reliability of circumferential welds of steel berthing monopoles. Fatigue loadings for a berthing monopile include berthing impacts, wave effects, current oscillations, etc. In many cases, for example well-sheltered harbours, the berthing impact dominates as a major fatigue loading for splice welds. The berthing impact normally leads to substantial bending moments on a monopile. This paper focuses on the cases dominated by berthing impacts. Typically, hot-spot fatigue strength can be assessed with either S-N curves or linear elastic fracture mechanics (LEFM).

ABSTRACT Fatigue of tubular T-joints under axial loading was investigated. Five models were tested, three with R-ratio R=−1 and two with R=0. Hot spot stress was evaluated for the brace and the chord based on strain measurements using the ECSC linear extrapolation procedure. Fatigue loading was applied in load control, to obtain through thickness cracking at a number of cycles in the range 5000 – 10 000 cycles. In addition, finite element analyses were carried out on the same geometries. The experimental data and the FE results were analysed and compared. Results were also compared with published data. Finally, an assessment was made on fatigue design criteria for tubular joints in the low cycle range. INTRODUCTION During the operational life time of offshore structures, waves represent the main fatigue loading. Consequently fatigue damage is mostly caused by cyclic loads with small amplitude, and fatigue damage accumulation occurs in the high cycle range, i.e. from 10 5 to 10 8 cycles. However, low cycle fatigue may be of interest in specific cases, such as transportation of jacket structures on a barge from shore to field. Low cycle fatigue failures have been reported by the industry during such operations. One refers to low cycle fatigue when the major contribution to cumulative fatigue damage is from stress ranges corresponding to a constant amplitude life less than 10 5 cycles. Because most fatigue failures occur in the high cycle range, SN curves for tubular joints are based on high cycle fatigue data (Health and Safety Executive (HSE), 1992). In recent design codes and guidance documents, e.g. UK Department of Energy (1995) and Det Norske Veritas/NORSOK (2004), SN curves were extrapolated by loglinearization from the high cycle to the low cycle range. Both British Standard (1993) and HSE (2004) have set a limitation to this procedure.

Rudder horn, in ship structures, is typically attached on the shell plate by welding. It is an important part of steering systems and has possibilities of fatigue crack due to various fluctuating loads. In this study, therefore, fatigue strength assessment for casting weld joint is carried out by making fillet weld joint specimens with cast steel and carbon steel in order to evaluate the fatigue behavior of a rudder horn. The specimens were fabricated and tested for three different conditions such as pre-heating effect, shape of weld joint effect and welding position effect. Test results of each case are represented in terms of S-N curves and are compared for evaluating the effect of fatigue strength improvement. INTRODUCTION Cast steel has a similar chemical composition with that of rolled steel or forged steel which are commonly used. Also cast steel is widely used in ships, railway cars and tools because it has excellent strength and damping compared to cast iron or other castings. The welding process is important for constructing structures with steel castings. It is used in two ways: in fabricating structures either by welding castings together (cast weld construction) or by welding steel castings to wrought steel products (composite fabrication), and in the correction of casting irregularities which may occur in the course of manufacture. Steel castings, as a component of weldments, are widely used because of possible cost savings. The use of steel castings is advantageous in regard to quality production, useful properties, and simplified design [1]. In ship structures, rudder horn is typically attached on the bottom shell plate by welding. It is made from steel castings to fix and support the rudder as an important steering system of a ship. And rudder structures in a ship are exposed to fatigue failure due to various cyclic loads such as hydrodynamic force and propeller force.

ABSTRACT This study performed a series of conventional triaxial tests to investigate composite behavior of soft marine clay reinforced by sand compaction pile. Test samples were prepared using kaolin and dense sand with the area replacement ratio of 0, 9.59, 23.58, 38.7 and 100%. Sand columns were prepared with a relative density about 70% and optimum water contents of 13.5%. Sand columns were installed in the center of the normally consolidated clay sample using freezing method. Series of tests are performed under the conditions of rate of strain and area replacement ratios to investigate the behavior of composite sample. From test results, effect of strain rate on stress-strain behavior, variation of effective internal friction angle, effective cohesion, peak stress, ultimate stress of composite sample according to the area replacement ratio were identified. INTRODUCTION The sand compaction pile (SCP) method forms a composite ground by installing sand pile into the soft ground, and is the one of the commonly used soil improvement for reinforcing and strengthening soft clay deposits in many countries for more than 30 years. It consists of wellcompacted sand piles which are installed in soft ground by using a vibrating casing pipe. This method has in fact undergone a greater process and found a wider application in Japan and Korea than in any other country. The SCP method can be applied to both sandy and clayey grounds by using the same equipment and machines. Especially, when the SCP method is set to a clay ground, the improved clay ground is called a composite ground. The application of the SCP method in the construction industry are wide and varied (Jung, 1998). Many researchers have been investigated the mechanical behavior of composite ground reinforced by sand compaction pile (Murayama, 1962; Aboshi et al., 1979; Kimura et al., 1983).

ABSTRACT This paper summarizes recent progress in modeling the fatigue behavior of simple, helically-served cable constructions subjected to cyclical tension or steady tension with cyclical bending over a circular sheave. The model computes all stress components acting on steel helical wires and compares these with the crossed-wire contact stresses developed between wire layers. The stress concentration occurring between contacting wires is treated as an "equivalent notch" and the fatigue analysis follows the conventional practice of designing machine components. Model results are compared with results of tests made on an aerostat cable and a 1×19 steel strand. Considering some variation in material properties of the as-built cable test specimens, model agreement with test results is promising. INTRODUCTION Fatigue failure of cables and wire rope is a major concern to designers of submarine communication, tether and complex umbilical cables, structural cables such as bridge and track strand and cable-stayed structures, and electric power transmission cables. Fatigue failures of cables used in any of these applications could result in significant financial loss or loss of life. The approach taken by the cable and rope industries to mitigate cable fatigue failures has been to verify cable performance in extensive prototype test programs. While this approach provides the best possible evaluation of a cable design, it frequently fails to provide insights needed to improve designs. It simply is not practical in cable testing to measure stress distributions and stress concentrations in the inner layers of cable and rope constructions. Thus, designers have no real means of understanding the weaknesses of their designs. This becomes especially problematic for new applications requiring significant departures from conventional design. To reduce the cost of developing new cable and rope designs for demanding applications and to improve cable performance for dynamic loadings, a cable fatigue modeling tool is needed.

ABSTRACT This study was performed in order to investigate fatigue characteristics of nitrided SACM 645 steel according to nitriding condition and notch shape. V-notches were made on the specimens and they were nitrided using the Nitemper method. The rotary bending fatigue test for each specimen was carried out at room temperature. The fatigue characteristics of the nitrided specimen were improved compared with that of the non-nitrided specimen because of compressive residual stress on the surface. The improvement of fatigue characteristics of the notched specimen was more effective than the smooth one. INTRODUCTION Currently, mechanical components are subject to severe condition of load, wear, and chemical erosion of surface. Therefore, various methods are applied to improve mechanical properties of surface like ceramic coating, surface treatment and so on (Murakami et al., 1989; De la Cruz et al., 1998). Nitriding method is a kind of surface treatment to improve and enhance mechanical properties at steel surface. It is performed in high temperature between 500 and 600°C for atomic diffusion of nitrogen into the steel material. Therefore, it improves hardness, wear resistance, erosion resistance, fatigue strength, etc (Genel et al., 2000; Ericsson, 1987). Hence, nitriding treatment was suggested to improve fatigue characteristics in this experimental research. In general, fatigue characteristics of nitriding treatment depends on residual stress, compound layer, diffusion layer, notch and inclusion. This study was object to evaluate quantitative investigation on mechanical properties and fatigue characteristics of nitempered SACM 645 steel through hardness test, tensile test, and rotary bending fatigue test, related with the state of diffusion layer, residual, compound layer and notch. In addition, the effect of stress concentration and fatigue notch factor on fatigue behavior was investigated for nitempered SACM 645 steel with five kinds of notch shape.

ABSTRACT From a view of fatigue strength, a critical review on thermo-mechanically controlled process (TMCP) steel was shown with picking up comparative test results in the past on fatigue strength for TMCP steels, including welded joint, to that of conventionally rolled plates and with introducing key experiments about important effect of softened HAZ on welded joint fatigue behaviors, for the purpose to bring greater attention for structure designer to obtain maximum advantages of TMCP steels such as excellent weldability, high toughness at HAZ and good performance in cost efficiency. INTRODUCTION At present TMCP steels are widely used in large-size welded structures. With comparing to conventionally rolled steel, TMCP steels has strong advantages such as better weldability and high toughness at heat affected zone (HAZ), that means with no preheating to heavy welding and reduced weld cracking at HAZ etc.. On the other hand, combination of low carbon equivalent and large heat input welding may result in softened HAZ growth, of which tensile strength is lower than that of the base metal so that it could reduce the welded joint strength locally. There are several types of TMCP plates, say accelerated water cooling type (Type-III) and non-water cooling type (Type-I and-II), and being low carbon equivalent is a common feature to all the types of TMCP steels. So that the effect of softened HAZ on the weldment strength had been an issue of wide importance to make clear and hence many studies and tests have done on the subject in Japan. In this paper from the viewpoint of fatigue, results of critical review will be shown on the past comparative fatigue tests on TMCP steels to conventionally rolled plates and the key experiments that deal with the effect of softened HAZ on the welded joint fatigue behavior.

ABSTRACT In the scope of CIDECT and DFG projects, L-joints made of CHS have been statically tested under tension and compression loading. The results of these investigations are to be published at the 9 th ISTS (International Symposium on Tubular Structures) in Diisseldorf, Germany, 3–5 April 2001. The fatigue behaviour of Ljoints made of CHS and RHS has also been investigated in the scope of these projects. These results are presented in this paper. For the determination of the fatigue resistance of L-joints made of CHS, numerical investigations have been performed. Solid finite elements have been used, since local stress and strain distributions are of interest in this case. The stresses in the joint area have been analysed and the stress concentration factors have been calculated. Using these SCF's, a design for L-joints made of CHS under fatigue loading is now possible (e.g. crane structures). The finite element mesh has been calibrated by comparison with the results of strain gauge measurements. Additional fatigue tests up to a maximum number of load cycles (Nf= number of cycles to failure) have been used for S-N lines and the classification of detail categories. These results can be used for establishing design standards for fatigue strength of L-Joints made of CHS and RHS. GENERAL L-joints made of Hollow sections are used in different structures, such as in cranes, portal frames, light roof structures, fairground structures, bridges etc. The static behaviour of L-joints made of RHS is already investigated (DIN 18808, 1984, EC3, 1993, Mang et al, 1981). For Ljoints made of CHS, a new design concept has been developed (Karcher 2001). Fatigue tests have been performed not only on L-joints made of CHS, but also on L-joints made of RHS. Classification of detail categories could therefore be made for both these cases.

ABSTRACT Fatigue damage in shipsides has been investigated for several decades. As a part of the FPSO Fatigue Capacity Joint Industry Project, stress concentration factors in longitudinals connected to transverse webframes are assessed. As FPSOs are operating between a ballast draft and a fully loaded draft continuously, a large r area of the shipsides are exposed to lateral dynamic load compared to conventional tankers. This study has focused on details typical for FPSOs operating in the harsh environment of the North Sea. Typical loads generated by lateral pressure are applied in the analyses. A conventional type of connection between longitudinal and transverse webframc is compared with an improved design of the connection. Angled profiles are compared with bulb profiles. The effect of different longitudinal dimensions is also investigated. The results are presented in terms of stress concentration factors in typical hot spots. The stress concentration factors are calculated based on a hot-spot stress and a nominal stress. The study documents stress concentration factors in critical hot spots for all analysed details, for 3 different load cases. By knowledge of the nominal stresses in the structure, fatigue life can be assessed. INTRODUCTION In the Joint Industry Project FPSO - Fatigue Capacity/1/, a part of the work have been concentrating on stress analyses of typical web frame/longitudinal connections. Such connections are conventional in a ship design with longitudinal stiffening of hull girder plates and transverse frames supporting the stiffeners. The longitudinal stiffeners are mainly loaded by longitudinal stresses due to hull girder bending and local bending stresses due to lateral panel pressure. In vicinity of the waterline, the lateral pressure is the most significant load, while at the top and bottom of the shipside, the longitudinal global load is the major load.

ABSTRACT This paper presents the design, construction and performance of ground treatment to support road embankment on refuse landfill in Korea. The long-term settlement characteristics of refuse landfill were analyzed by Sower(1973);Yen and Scanlon(1975). As a result of field test., the predicted settlement exceed the allowable settlement and ultimate bearing capacity is not satisfied. Therefore, refuse landfill was treated by stone columns. The effectiveness of dynamic replacement was verified by Standard Penetration Test(SPT), Plate Bearing Test(PBT), Pressuremeter TesffPlVlT) performed before, during and after construction of the stone columns. From the loading test, estimation of critical embedded ratio to classify the failure mechanisms, critical and yielding pressure on treated and untreated ground is suggested. Also deformation modulus of stone columns and untreated ground is suggested. The results indicated that the settlement of the treated foundation should be reduced to about 70 percent and the bearing capacity should be increased to about 60 percent comparing with the treatment. Due to the non-homogeneity of refuse landfill, stress concentration factors were distributed in wild range. INTRODUCTION Recently, the use of refuse landfill has been a growing concern. But most cases are faced with excess settlement and insufficient bearing capacity problems. Generally, many treatment methods such as dynamic compaction method, chemical grouting method are suggested for refuse landfill. In this site, stone columns are applied considering the insufficiency of aggregate and economics of construction problems. In this paper, SPT, PMT and PBT are performed to estimate the effectiveness of stone column in refuse landfill. The increase of bearing capacity, penetration resistance ratio and elastic modulus are measured before and after treatment with the stone columns. Also, the characteristics of settlement and the effectiveness of dynamic compaction are investigated. GROUND CONDITION The site consist of uncontrolled waste disposal landfill.

Abstract The Ursa Tension Leg Platform is located in the Gulf of Mexico in approximately 4,000 ft of water. The foundation design for the platform requires the installation of sixteen 96" diameter piles, each to be driven to a depth of 396 ft with an underwater hammer. The predicted hammer blow count necessary to achieve this design penetration resulted in driving fatigue damage becoming an important design issue. More than double the blow counts were expected for driving the Ursa piles than required for a previous deepwater project. This paper presents the methodology used in estimating the driving fatigue damages at the Ursa pile girth welds. First, pile driving stresses are generated by a pile driveability program. These records are then used in a simple one-cycle counting method to estimate fatigue damage based on Miner's rule. Second, the stress waves from the driveability program are used in a more comprehensive rainflow stress-cycle counting method based on Wirsching's algorithm. The selection of the design SN curve, along with the calculation of representative stress concentration factors, is discussed, and a revised thickness effect correction to the design SN curve is presented. The justifications for the selected design SN curve used in the fatigue damage ratio calculation and the allowable fatigue damage ratio, however, are not within the scope of this paper. 1.0 Introduction The Ursa Tension Leg Platform (TLP) is located, 130 miles southeast of New Orleans, in the Mississippi Canyon Block in the Gulf of Mexico in approximately 4,000 ff of water (Figure 1). The Ursa TLP foundation consists of sixteen 96" diameter piles with four piles at each corner of the TLP. Sixteen tendons (Figure 2) are to be directly connected to the tendon receptacles at the pile top, which is similar to the Mars and Ram/Powell TLP pile designs.

A method for evaluation of allowable stress concentration factors (SCFs) and hence the local geometry of structural details subject to complex loading is developed to meet a specified target fatigue life. The method is based on the local strain approach to fatigue, and takes into account the long term loading history. On the condition that cumulative fatigue damage equals unity, an upper bound of the allowable SCFs conditional on a selected mode of loading is found, and the corresponding changes to the initial detail geometry are determined. In the general case of multiple loading modes, the procedure normally needs to be repeated, until overall convergence in geometry occurs. The method is supported by necessary software and an SCF database. INTRODUCTION Fatigue life estimates are sensitive to small variations in the nominal stress and in the local conditions which control the crack initiation, in particular the stress concentration. One way of making the structural fatigue model less sensitive to these uncertainties is to directly base the fatigue evaluation on the theoretical stress concentration factors characterizing the local fatigue conditions in the structural detail. As a basis of such a model the local strain approach can be used. The approach is restricted mainly to the fatigue crack initiation period, wherein the local plastic strain range controls the conditions of the microscopic crack origination and the initial stages of macroscopic crack formation. Examples of structural details of interest include openings in the deck and outer plating at hatches, side-ports, and transverse frame webs slots in FPSOs and other floating structures. A typical feature of these details is the presence of a combination of global or geometric stress concentrations and more localized stress concentrations produced by the presence of welds. The material of the "process-zone" at a crack initiation site therein deforms nonlinearly due to the mechanisms of micro and macro-plasticity occurring under the total effect of these stress concentrations, leading to fatigue under cyclic loading.

ABSTRACT The API recommended practice for fixed offshore platform design has for many years provided guidance on fatigue design of welded connections in offshore structures. As this practice, designated API RP 2A is transformed into an international ISO document, the fatigue provisions, as well as many others are being re-evaluated. In light of the research on fatigue of welded connections and the different provisions of many European design practices, major changes can be expected from the current ones in API RP 2A. Areas covered include the choice of stress concentration factor; the appropriate design lines for fatigue; and changes to those design lines due to thickness, weld profile, and post-weld improvement. Each of these provisions can be expected to be modified from the current document as the ISO version is promulgated. INTRODUCTION The API recommended practice for fixed offshore platform design has for many years provided guidance on fatigue design of welded connections in offshore structures. As this practice, designated API RP 2A (API 1993), is transformed into an international ISO document, the fatigue provisions, as well as many others are being reevaluated. In light of the research on fatigue of welded connections and the different provisions of many national design practices, major changes can be expected from the current ones in API RP 2A. This paper will discuss the choice of stress concentration factor; the appropriate design lines for fatigue; and changes to those design lines due to thickness, weld profile, and post-weld improvement. Provisions in each of these areas can be expected to be modified from the current document as the ISO version is promulgated. The focus of the paper will be on simple, un-reinforced tubular joints, although some of the information will certainly apply to other cases.