Static strength of fabricated trunnion and x joint under shear and in plane bending moment

STATIC STRENGTH OF FABRICATED TRUNNION & X-JOINT UNDER SHEAR AND IN-PLANE BENDING MOMENT QUAH CHIN KAU NATIONAL UNIVERSITY OF SINGAPORE 2006 STATIC STRENGTH OF FABRICATED TRUNNION AND X-JOINT UNDER SHEAR AND IN-PLANE BENDING MOMENT BY QUAH CHIN KAU, M.Eng., B.Eng.(Hons) DEPARTMENT OF CIVIL ENGINEERING A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY NATIONAL UNIVERSITY OF SINGAPORE 2006 To God Be the Glory ACKNOWLEDGEMENTS I would like to express my sincere appreciation to my supervisors, Professor N. E. Shanmugam, Associate Professor Choo Yoo Sang and Associate Professor Richard Liew Jat Yuen for their invaluable support, guidance and encouragement throughout the course of this study. Special thanks also to the staff from the former CAE/CAD/CAM Centre and Civil & Structural Engineering Laboratory, Faculty of Civil Engineering, for their help and support in the computational and experimental investigations respectively. I also gratefully acknowledge the National Science & Technology Board, Singapore (NSTB), Sembawang Marine & Offshore Engineering (SMOE) and the National University of Singapore (NUS) for providing the necessary finances, equipment and research facilities to pursue the study. It was my mother, who struggled hard to put me through many years of education, that has the strongest desire to see her son succeed. I dedicate this volume to her: for her untiring perseverance, patience and believe in her son. Last, but not the least, my dear wife, who makes the journey during the course of the study more bearable and enjoyable. Everything is made possible by the grace of God. i TABLE OF CONTENTS ACKNOWLEDGEMENTS …………………………… …….… …………… i TABLE OF CONTENTS ………………………… ………….… …………… ii SUMMARY ………………………………………… ……….… …………… viii LIST OF TABLES …………………………………………….… …………… xi LIST OF FIGURES ……………………………………… ….… …………… xiii LIST OF SYMBOLS ………………………………………….… …………… xx CHAPTER ONE INTRODUCTION 1.1 Structural applications of hollow sections and trunnions ……… 1.2 Types of trunnions studied ……………………… …………… 1.3 Classification of joints ………………………………… ……. 14 1.4 Objectives and scope of research ……………………………… 16 1.5 Survey of previous research …………………………………… 19 1.5.1 Experimental research in trunnion …………………… 21 1.5.2 Research in tubular X-joints …………………….…… . 25 1.5.3 Finite element method …………………………….…… 29 1.6 Current design recommendations ……………………………… 31 1.7 Contents of Thesis …………………………………………… . CHAPTER TWO 35 EXPERIMENTAL INVESTIGATION ON SMALL PIPE TRUNNIONS 2.1 Introduction ……………………………………………………. 36 2.2 Research programme ………………………………………… 38 ii 2.3 2.4 2.5 2.2.1 Trunnion dimensions … … … … … … … … … … … … … 38 2.2.2 Fabrication of specimen … … … … … … … … … … … … . 41 2.2.3 6,000kN test rig … … … … … … … … … … … … … … … . 44 2.2.4 Instrumentation … … … … … … … … … … … … … … … 46 Governing failure mode of trunnion … … … … … … … … … … 48 2.3.1 Pure pipe trunnions … … … … … … … … … … … … … … . 48 2.3.2 Shear plate pipe trunnions … … … … … … … … … … … 51 2.3.3 Combined shear and pipe trunnions … … … … … … … … 54 Discussions of the test results … … … … … … … … … … … … … 58 2.4.1 Design strength pure pipe trunnions … … … … … … .… 58 2.4.2 Design strength of pipe trunnions with slotted shear plates only … … … … … … … … … … … … … … … … … … 62 2.4.3 Design strength of pipe trunnions with shear plates and pipes … … … … … … … … … … … … … … … … … … 65 Conclusions … … … … … … … … … … … … … … … … … … … … 67 CHAPTER THREE EXPERIMENTAL INVESTIGATION OF LARGE PIPE TRUNNIONS AND TUBULAR X-JOINTS 3.1 Introduction … … … … … … … … … … … … … … … … … … … … 69 3.2 Research Programme … … … … … … … … … … … … … … … … 71 3.2.1 Trunnion dimensions … … … … … … … … … … … … … 71 3.2.2 Fabrication of specimen for test … … … … … … … … … . 75 3.2.3 10,000kN test rig … … … … … … … … … … … … … … … 77 3.2.4 Instrumentation … … … … … … … … … … … … … … … 87 Governing failure mode of trunnion … … … … … … … … … … 90 3.3.1 90 3.3 Pure pipe trunnion … … … … … … … … … … … … … … . iii 3.4 3.3.2 Through pipe trunnion … … … … … … … … … … … … … 95 3.3.3 Combined shear plate and pipe trunnion … … … … … … 97 3.3.4 Tubular X-joints … … … … … … … … … … … … … … … . 101 Discussions of the test results … … … … … … … … … … … … … . 105 3.4.1 Design strength of pure pipe trunnions … … … … .… … 105 3.4.2 Design strength of through pipe trunnions … … … … 110 3.4.3 Design strength of combined shear plate and pipe trunnions … … … … … … … … … … … … … … … .… 113 3.4.4 Transition of shear and bending moment … … … … … … CHAPTER FOUR 116 FINITE ELEMENT ANALYSES ON TUBULAR JOINTS 4.1 Introduction … … … … … … … … … … … … … … … … … … … … . 120 4.2 Finite element programs and hardware used … … … … … … … 122 4.3 Main characteristics of finite element work on tubular joints … 123 4.3.1 Finite element mesh and boundary conditions … … … … 123 4.3.2 Finite element types … … … … … … … … … … … … … … 125 4.3.3 Loading of the joints … … … … … … … … … … … … … . 127 4.3.4 Modeling of the post-yield material property … … … … . 128 4.3.5 Iteration procedure and convergence criteria … … … … 129 4.3.6 Numerical modeling of weld geometry … … … … .… … 130 4.4 Numerical analysis for the experimental tests … … … … … … … . 131 CHAPTER FIVE NUMERICAL SIMULATION OF THE EXPERIMENTS 5.1 Research programme and general finite element aspects … … … 134 5.2 Numerical analyses … … … … … … … … … … … … … … … … … . 135 iv 5.3 5.2.1 Pure pipe trunnions . … … … … … … … … … … … .… … . 137 5.2.2 Shear plate pipe trunnions .… … … … … … … … … … … 140 5.2.3 Through pipe trunnions … … … … … … … … … … … . 141 5.2.4 Combined shear plate and pipe trunnions … … … … … . 143 5.2.5 Shear and bending loads on tubular X-joints … … … … 145 Comparison between the experimental and numerical results 146 5.3.1 Pure pipe trunnions … … … … … … … … … … … … … 147 5.3.2 Shear plate pipe trunnions … … … .… … … … … … … .… 151 5.3.3 Through pipe trunnions … .… … … … .… … … .… … … . 152 5.3.4 Combined shear plate and pipe trunnions … … … … .… . 154 5.3.5 Shear and bending loads on tubular X-joints … … … … 156 CHAPTER SIX NUMERICAL PARAMETRIC STUDIES 6.1 Assumptions for the numerical models … … … … … … … … … . 159 6.2 Pure pipe trunnions … .… … … … … … … … … … … … … … … 161 6.2.1 Research programme … … … … … … … … … … … … … . 162 6.2.2 Effective W ratio for trunnion design … … … … … … .… . 170 6.2.3 Effective E ratio for trunnion design … … … … … … … . 179 6.2.4 Selection and design approach for pure pipe trunnions 186 6.2.5 Proposed design formulation for pipe trunnions .… … 194 Through pipe trunnions … … … … … … … … … … … … … … … 196 6.3.1 Research programme … … … … … … … … … … … … … . 197 6.3.2 Comparison of ultimate load capacity of through pipe trunnions … … .… … … … … … … … … … … … … … … . 201 6.3.3 Design approach of through pipe trunnions … … … … . 205 6.3 v 6.4 Tubular X-joints … … … … … … … … … … … … … … … … … … . 208 6.4.1 Research Programme … … … … … … … … … … … … … 208 6.4.2 Interaction effects of shear and bending moment … .… 209 6.4.3 Proposed interaction equation of shear and bending moment … … … … … … … … … … … … … … … . 211 6.4.4 Effective width of trunnion brace … … … … … … … … … 216 CHAPTER SEVEN TRUNNION DESIGN CALCULATION 7.1 Design approach for fabricated trunnion … … … … … … … … … . 218 7.2 Rigging arrangement and design loads … … … … … … … … … … 7.3 Estimating lifting loads on the trunnion .… … … .… … … … … … . 220 7.4 Pure pipe trunnion option … … … … … … … … … … … … … … … . 221 7.5 7.4.1 Selection of pure pipe trunnion … … … … … … … … … … 222 7.4.2 Verifying chord and brace sizes … … … … … … … … … 224 Through pipe trunnion option … … … … … … … … … … … … … 227 7.5.1 7.6 7.7 220 Selection of chord and brace sizes … … … … … … … … . 227 Combined pipe and shear plate trunnion option … … … … … … . 230 7.6.1 Design load considerations and layout … … … … … … … . 231 7.6.2 Selection of main parameters … … … … … … .… … … … 234 7.6.3 Checks for trunnion brace … … … … … … … … … … … . 7.6.4 Checks for shear plate … … … … … … … … .… … .… … 237 7.6.5 Checks for chord wall … … … … … … … … … … … … … 239 Conclusions … … … … … … … … … … … … … … … … … … … … 240 235 vi CHAPTER EIGHT CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK 8.1 Overview of experimental study … … … … … … … … … … … … 241 8.2 Overview of numerical and parametric study … … … … … … … 243 8.3 Overview of trunnion calculations … … … … … … … … … … … . 244 8.4 Main findings and conclusions … … … … … … … … … … … … … 244 8.5 Proposals for future research … … … … … … … .… … … … … … 248 REFERENCES … … … … … … … … … … … … … … … … … … … … … … … … 250 vii Introduction current international design guidance on hollow structural section connections. One of the key elements in research in tubular joints was that the tubular joint is resilient and reliable in transferring the loads. Lalani (1990) discussed in more detail the reserve capacity and reliability of tubular joints as used in the offshore industry. However, although the list of researches on general tubular joint behaviour may be impressive, research on trunnions is dismal in comparison. This is interesting considering the fact that trunnion joints, necessary for heavy offshore lifting installation, are as critical as having a good structural frame. There is only one published work on the behaviour of plate trunnions subjected to shear loading by Choo et al (1995). This was a purely numerical study on the behaviour of plate trunnions subjected to shear loads. Since no experimental work was carried out in this paper, there was no calibration in terms of the numerical works carried out. However, this provided the initial impetus to pursue further into this area of research. More recent study was carried out by Choo et al (2001) where small-scale experimental and numerical work were carried out to extend this area of research. Results were presented from a study in which the relevant geometric properties were varied systematically. The effect of these parameters on the elasto-plastic responses of plate trunnions subjected to shear loads from the sling eyes was discussed. These studies were based on analyses using numerical methods with assumed boundary conditions. Two distinctive failure modes of the plate trunnion, namely main plate dominated failure or shear plate/trunnion pipe dominated failure have been highlighted. A proportional limit load has been defined for each specimen based on its load-displacement response. It was observed that trunnions with pipe diameter to 20 Introduction thickness ratio d1/t1 of 25 to 30 are more prone to buckling effects when loaded beyond the limit load. The current practice that considers only the shear plate to transfer the total sling load into the main plate appears to be conservative. The limit load was found to be about 1.5 times higher than the unfactored shear plate strength for a design with shear plate thickness less than the main plate thickness, and was found to provide a more rational reference strength than available in the current industrial practice. However, no prior works was carried out for pipe trunnions subjected to shear and bending moments. This is also a reason why the existing recommendations from Brown & Root (1990) and Shell (1992) not consider the brace to contribute towards the ultimate capacity of the trunnion. Since no research was carried out, there is no guidance on the behaviour of chord plastification effects and the amount of shear carrying capacity to be accounted for in the brace. During the course of this research, some papers were published to initiate discussions on this through Choo et al (2001c) and Choo et al (2001d). These papers provide the background and initial experimental results. Interesting discussions were featured and some of this feedback has been studied in this report. 1.5.1 Experimental research in trunnion Until a few years ago, no experimental test results on trunnions were available. Of the existing design codes, only Brown & Root (1990) and Shell (1992) provide some simple guidelines for designing plate trunnions. These guidelines are dealt mainly with geometrical dimensioning. These geometric dimensions are used in configuring the size of the trunnions without taking into consideration the different failure 21 Introduction mechanisms associated with trunnions since no experimental results were published to support the method used. The recommended parameters designing a plate trunnion only cover the overall shape and thickness of the various pipes and plate used. This is definitely insufficient to cover the complex behaviour that pipe trunnions and especially the load level that trunnions are able to handle. The behaviour of plate trunnions subjected to shear loading was reported by Choo et al (1995). The experimental and numerical results were presented. Two distinctive failure modes of the plate trunnion, namely main plate dominated failure and shear plate/brace pipe dominated failures have been highlighted. It was also highlighted that the current recommendations of not considering the strength contribution from the brace is overly conservative. The report proposes the following relations in configuring the trunnion components: (i) Shear strength of shear plate, Vs AISC (1989), Vs where, ˜ d s ˜ t s ˜ f ys (1.1) ds = depth of shear plate, ts = shear plate thickness, fys = yield strength of shear plate (ii) Shear strength of trunnion brace, V1 API (2000), V1 S ˜ d m1 ˜ t1 ˜ f y1 (1.2) 22 Introduction where, d1 = outer diameter of brace t1 = brace thickness, dm1 = d1 – t1, fy1 = yield strength of trunnion brace More recently, a research thesis by Quah (1998) provided an experimental and analytical study of the structural behaviour and strength of plate trunnions under shear loading. Based on the experimental tests of specimens, an empirical recommendation is given to support the conclusion that the current design codes are inadequate to accurately utilize the inherent strength of trunnions. The early design recommendations are also very conservative as the inherent reserve strength of the trunnion is shown to be very high. Looking into the new data from the set of experimental test results would definitely help to increase the factor of safety associated with the use of trunnions. The report also proposes a set of preliminary guides in determining the strength of plate trunnions. The observed two distinct failure behaviour of trunnions is confirmed by the experimental study of the specimens tested to failure. In this report, three different types of trunnions were studied, namely, trunnions with attached pipe, trunnions with slotted shear plate and trunnions with combined shear plate and brace. The trunnion with only slotted shear plate was configured to be tested to determine extent of strength contribution from the brace pipe which was neglected in the earlier recommended design of trunnion. It was concluded in the report that plate trunnions with only the pipe as the trunnion brace was able to resist the applied shear load effectively. By taking into account the experimental and computational results, a preliminary set of recommendations are 23 Introduction deemed to be suitable to be considered for the design of plate trunnions. The following are the set of design equations proposed: V1 = S dm1 t1 (0.4 fy1) (1.3) Vs = ds ts (0.4fys) (1.4) V1 + Vs = 0.4 (2 ds ts fys + S dm1 t1 fys) (1.5) Plate trunnions however comprise only a small section of the use of trunnions in offshore structures. When a plate trunnion is used for lifting, both sides of the brace are kept very close and this poses a problem since grommet (wire ropes) require sufficient bending radius to prevent undesirable failure of the wire ropes. Since a longer brace would result in additional bending moment effect, only the use of pipe trunnion is able to resolve the dilemma. The current research programme looks into the use of pipe trunnions used as lifting points. The built up of pipe trunnions is similar to the plate trunnion except that the main body in this case consists of a pipe (chord) instead of a plate. This allows the overall bending radius of the grommet to be sufficiently wide at the crane hook. The design of a pipe trunnion is more challenging than a plate trunnion due to the complication from chord plastification effects. The proportioning of the shear plate, brace as well as the chord is crucial in enhancing the load carrying capacity of the trunnion. 24 Introduction 1.5.2 Research in tubular X-joints Since the effectiveness of the trunnion brace is dependent largely on the amount of shear capacity that can be mobilised, the trunnion width, w1, is critical in ensuring that bending moment effects is kept to a minimum. The research programme also aims to cover the bending moment and shear interaction behaviour in using a set of tubular Xjoint. In this set of specimens, the length of the brace is extended beyond the initial length of 200mm from the side of the chord wall to 4d1 distance away. The contribution to the shear strength of the brace reduces, progressing as the trunnion width, w1, as the brace extends longer and longer. The brace length used is much longer than a normal pipe trunnion. A survey of the current research shows that available materials on the moment and shear effect on tubular X-joints are limited. So far, most of the study on tubular Xjoints revolves around the effect and behaviour of tubular joints loaded by axial or inplane bending. There was an early study by Gibstein (1976) that uses a very simple mechanism to test for shear and bending effects. However the specimens used were very small and the test was carried out using dated technology. The report recommends the following formula for the mean ultimate moment strength of uni-planar tubular X-joints under in plane loading: Mu 6.0 ˜ E ˜ J 0.5 ˜ f y ˜ t 02 ˜ d1 (1.6) Validity range is given as : 0.25 < E < 0.9 25 Introduction < J < 30 where, Mu = ultimate in-plane bending moment fy0 = yield strength of chord t0 = wall thickness of chord d1 = outer diameter of brace d0 = outer diameter of chord E 2J d1 d0 d0 t0 Other researchers including Mitri (1989) also provided some guidelines on the ultimate moment of tubular joint. Mitri recommended that the ultimate in-plane bending moment on a T or Y tubular joint could be obtained from in Equation 1.7. Mu where, t ˜d2 ˜ f y ˜ ˜ F ( w) ˜ F ( E ) ˜ F (T ) d M p sin T (1.7) fy0 = yield strength of the chord t0 = wall thickness of chord d1 = outer diameter of brace T = angle between brace and chord Mu = ultimate in-plane bending moment Mp = plastic moment capacity of joint 26 Introduction F ( w) § 2t · ¨¨1  w ¸¸ d1 ¹ © F (E ) 4˜ 5  (1  E 0.5 ) §S · F (T )  0.2 ˜ ¨  T ¸ ©2 ¹ This is compared to other researches that use the following formula to predict the ultimate strength of the tubular joint in Equation 1.8. Mu § t2 ˜ d · 6.1 ˜ f y ˜ ¨ ¸ ˜ E ˜ J 0.5 ¨ sin T ¸ © ¹ where, (1.8) fy0 = yield strength of the chord t0 = wall thickness of chord d1 = outer diameter of brace T = angle between brace and chord Mu = ultimate in-plane bending moment E 2J d1 d0 d0 t0 It is noted that this ultimate moment is related to the failure of the chord wall alone and assumes that the brace will not fail before the chord wall fracture. 27 Introduction The ultimate capacity from in plane bending moment effects was further investigated by and compiled in the latest CIDECT (1991) and recommends Equation 1.9 for the mean ultimate moment strength of uni-planar tubular X-joints under in-plane loading. This was an improvement from Equation 1.6. Mu 4.85 ˜ E ˜ J 0.5 ˜ f y ˜ t 02 ˜ d1 where, (1.9) fy0 = yield strength of the chord t0 = wall thickness of chord d1 = outer diameter of brace Mu = ultimate in-plane bending moment E 2J d1 d0 d0 t0 It was discussed by Vegte (1995) that the schematisation of the in-plane bending moments by two opposite forces leads to a strength formula for joints loaded by inplane bending which is directly related to the strength formula of axially loaded joints. The basic formula, resulting from the analytical “ring model” approach, can be used to describe the local strength behaviour on the tension and compression side of the brace. This simple formulation as proposed by Vegte (1995) is used to describe the observations of the shear and bending moment experienced on the trunnion. This formulation is given in Equation 1.10 below, where Mu is the ultimate bending moment capacity from the tension and compression actions. 28 Introduction Mu f y ˜ t0 ˜ d1 where, 5.1 ˜ J 1.04   ✁ 0.43   (1  0.4E )  (1  0.4E )   (0.4 E ) (1.10) J2 fy0 = yield strength of the chord t0 = wall thickness of chord d1 = outer diameter of brace Mu = ultimate in-plane bending moment E 2J d1 d0 d0 t0 These studies on the ultimate moment capacity of tubular joints provided some clues as to the interaction between moment and shear of tubular X-joints. 1.5.3 Finite element method The numerical research on the strength of tubular joints went as far back as the late 1970s when computational resources and advances in the finite element method were still limited. However this has not prevented early research from investigating the benefits of different element types such as the use of 3D solid elements, and thick shell and thin shell elements. Further developments were reported by Connelly and Zettlemoyer (1989), who presented numerical investigations on the behaviour of tubular joints primarily frame behaviour. Many researchers Cofer (1992), Vegte et al (1995) and Lu (1994), have indicated that the finite element method could be used to predict the ultimate behaviour of tubular joints if the following conditions are met: 29 Introduction Material Non-Linearity The material law should include nonlinear effects (plasticity and strain hardening) since the material is usually stretched beyond its elastic limit in tubular joints. Geometric Non-Linearity A large-deformation formulation of the finite element equations has to be adopted to better predict the possibility of buckling of the pipe wall. Fracture Criterion Where fracture is a dominant mechanism in the analysis, fracture criterion has to be included to predict better the formation and propagation of the cracks. Vegte et al (1991) and Cofer et al (1992) have reported several nonlinear analyses of the ultimate strength of tubular joints and they provide important affirmation that the finite element method can accurately predict the behaviour of tubular joints. Vegte (1995) reported on an extensive investigation on the uni-planar and multi-planar Xand T-joints. The numerical analyses utilize primarily eight-noded thick shell elements. Weld elements are also included in the numerical analysis by adding one layer of shell elements to the brace chord intersection. The application of weld simplification here was proven sufficient as calibrated from the experimental data. Davies et al (1996) also further improved the weld formulation from recommendations through the use of six-noded prism elements in combination with four-noded shell elements to model the fillet weld. To maintain compatibility of solid and shell elements, multiple point constraint methods were used. Weld geometry was 30 Introduction also investigated by Healy (1994) who presents many numerical studies on the strength of overlapped K- joints under in-plane bending and brace axial loading. In addition, Lee et al (1995) presented research on the accuracy of studies on mesh discretisation, boundary conditions and material properties in the numerical study of CHS DK-joints. In all these results, the ultimate strength were determined and used in the design recommendations, which highlights the great potential in the use of the finite element method to extend the scope of work not possible through experiment programmes. 1.6 Current design recommendations Current design recommendations for fabricated plate trunnions, Brown & Root (1990) and Shell (1992), indicate only the total sling load to be transferred by the shear plate alone to the main plate. There is no existing design guides on pipe trunnions. The trunnion pipe (on either side of the main plate) is only regarded as providing a bent circumference for the sling eye or grommet and is not expected to contribute towards the structural strength of the fabricated trunnion. The contribution of the trunnion pipe to the strength of the plate trunnion may be significant for certain geometric ranges and a detailed understanding of this strength contribution will lead to a more rational and thus cost effective design. The following are a list of specific requirements and recommendations given as shown in Figure 1.13: (i) The trunnion central stiffener plate (shear plate) should be slotted through the main plate or pipe and should be designed to transfer the lift point load 31 Introduction into the main plate or tubular section while neglecting the strength contribution of the trunnion brace. (ii) The main plate thickness, tm, (or, if more than one plate is used, the sum of the main plate thicknesses) should be equal to or larger than that of the trunnion stiffener plate, ts. (iii) In order to minimise the effect of bending loss the minimum diameter of a trunnion brace, d1, for a grommet should be the hook diameter or six times the grommet diameter, dsl, whichever is lower. (iv) To ensure that the sling bend efficiency will be higher than the splice efficiency, the minimum diameter of a trunnion brace for a sling doubled over the trunnion should be four times the sling diameter. (v) The diameter of a trunnion brace for a sling eye should not be less than the one sling rope diameter and should not exceed 1/6 times the sling eye length. (vi) As the sling will spread out at the contact area during lifting (where bearing width # 1.25 times sling diameter) the width of the trunnion contact area should be a minimum of 1.25 times the actual sling diameter plus 25mm. (vii) The cover-plate/keeper-plate should protrude about 75% of the sling diameter at the bearing area, with a minimum of 100mm above the centre of the pipe. Sling retainers should be provided to hold the sling in tension. (viii) All edges likely to be in contact with the sling or grommet during handling and transportation should be profiled to a minimum radius of 10mm. (ix) A clearance, c, of at least 1.5 times the sling diameter is required to facilitate the installation and removal of sling. In initial design, allowance should be made for a possible increase in sling rope diameter. 32 Introduction (x) The allowable stresses for the fabricated plate trunnion design should be in accordance with the requirements of the AISC Specification (1989) with no increase in allowable stresses. The allowable bearing stress is taken as 0.9 fy, the allowable shear stress as 0.4 fy and the allowable bending stress as 0.6 fy. 33 Introduction Sling Diameter Trunnion Diameter Trunnion Width Main Plate Trunnion Flange Clearance d sl > d sl for doubled sling d1 > d sl for grommet d1 > d sl for sling eye d1 < times of sling eye length wt = 1.25 d sl + 25 (mm) tm t ts f > 0.75 d sl c > 1.5 d sl d1 Trunnion Pipe dsl wt ts tm Sling Shear Plate c Main Plate f d1 Sling Retainer Figure 1.13 Recommended geometrical parameters for trunnions, Brown & Root (1990) 34 Introduction 1.7 Contents of thesis The previous sections in this chapter outline the importance of tubular sections and joints in offshore structural connections and the characteristics of CHS tubular joints. The basis of approaching this area of research is critical in providing a basic understanding of the influence of shear and bending loads on trunnions. Chapter and outlines the extensive experimental works that has been carried in order to provide a strong foundation to study the effects of shear and bending loads on the joints of a trunnion. Many combinations of the specimens were studied including two different sets of scale of specimens for greater confidence in the results. Chapter subsequently describes the general aspects of the numerical calibration approach for this work. This is necessary to provide a framework on which the future numerical works were carried out. Chapter describes the numerical works that have been analysed to compare the experimental results with the numerical works to pave the way for a greater scope of coverage in the behaviour of trunnions, which cannot be done through experiments due to limited resources available. Chapter reports on the extensive parametric study, which was carried out to understand the effects of shear and bending on trunnions. Chapter provides a sample calculation for a pipe trunnion using the proposed recommendations from the research. Chapter provides a summary and list of future works. 35 [...]... Fu1,expt ultimate capacity of pure pipe trunnion as obtained in experiment Fu,num ultimate load predicted by the numerical method taken at the load which corresponds to the deformation at experimental failure load M bending moment Mu ultimate in- plane bending moment Mu,ip* joint design resistance for in- plane bending moment Mp plastic moment capacity of joint Fip* applied force to effect the joint design... design receommendations define fabricated trunnions as consisting of a slotted shear plate and two side braces on each side of a main body It is used as a lifting point in the installation of heavy offshore structures There is very limited experimental and numerical work that has been conducted to study the behaviour and strength of trunnion subjected to shear and bending moment As a result, current... gap in the understanding of behaviour and strength of trunnion subjected to shear and bending moment The objective of this study is to close the gap and provide a more rational design approach through a comprehensive experimental and numerical research programme There is a three fold approach used in this study The experimental programme provides the basis in benchmarking the ultimate strength of trunnion. .. jacket installation or very tall towers in refinery plants Thus a good understanding of the structural behaviour of fabricated trunnions, especially its ultimate carrying capacity and failure mechanism, is important and critical in the successful installation of new and larger structures 2 Introduction In order to appreciate the scale and importance of fabricated trunnions, the following descriptions of. .. Table 6.12 Governing failure mode of through pipe trunnions Table 6.13 Dimensions and non-dimensional geometric parameters for X- joints Table 6.14 Shear and bending moment interaction from the numerical and experimental results Table 7.1 Failure mode of pure pipe trunnions Table 7.2 Failure mode of through pipe trunnions xii LIST OF FIGURES Figure 1.1 An effective use of a fabricated plate trunnions to... the offshore industry, installation of such structures is becoming a critical issue A fabricated trunnion, being a lift point, may be one of the weak links in the successful installation of offshore structures The main chord of a fabricated trunnion is usually welded directly onto the main structure so that it can provide a strong point as well as a pivot for upending sequence of operations for offshore... elastic linearity Fy,num yield strength of trunnion as obtained in numerical analysis corresponding to the point where the yield curve starts to deviate from elastic linearity Fyura load predicted by the numerical method corresponding to Yura deformation limit of 80VyE Fu,expt ultimate strength of trunnion as obtained in experiment Fus,expt ultimate capacity of pure shear plate trunnion as obtained in tests... Comparison of experimental and numerical results of the ultimate failure mode of small pipe trunnion C3 xvi Figure 5.3 Comparison of experimental and numerical results of the ultimate failure mode of small pipe trunnion CT3 Figure 5.4 Comparison of experimental and numerical results of the ultimate failure mode of small pipe trunnion CT5 Figure 5.5 Comparison of experimental and numerical results of the... failure mode of shear plate small pipe trunnion C5 Figure 5.6 Comparison of experimental and numerical results of the ultimate failure mode of shear plate small pipe trunnion CT6 Figure 5.7 Comparison of experimental and numerical results of the ultimate failure mode of shear plate small pipe trunnion CT7 Figure 5.8 Comparison of experimental and numerical results of the ultimate failure mode of shear plate... recommendations for trunnion cover generic specifications on the geometric dimensions only Further, it does not include brace shear strength as contributing to the overall static strength of a trunnion joint Thus, current trunnion joint design practice is very conservative The detailed engineering designs for trunnion are empirical and dependent on the ingenuity of experienced engineers using empirical equations . STATIC STRENGTH OF FABRICATED TRUNNION & X- JOINT UNDER SHEAR AND IN- PLANE BENDING MOMENT QUAH CHIN KAU NATIONAL UNIVERSITY OF SINGAPORE 2006 STATIC STRENGTH OF FABRICATED TRUNNION AND X- JOINT. 208 6.4.2 Interaction effects of shear and bending moment … .… 209 6.4.3 Proposed interaction equation of shear and bending moment … … … … … … … … … … … … … … … . 211 6.4.4 Effective width of trunnion. TRUNNION AND X- JOINT UNDER SHEAR AND IN- PLANE BENDING MOMENT BY QUAH CHIN KAU, M.Eng., B.Eng.(Hons) DEPARTMENT OF CIVIL ENGINEERING A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY NATIONAL