Lesson twenty-two Examples of offshore Structures By far the most common type of fixed offshore structure in existence today is the template, or jacket, structure illustrated in Fig. 1. This type of structure consists of a prefabricated steel substructure that extends from the seafloor to above the water surface and a prefabricated steel deck located atop the substructure. The deck is supported by pipe piles driven through the legs of the substructure into the seafloor. These piles not only provide support for the deck but also fix the structure in place against lateral loadings from wind, waves, and currents The construction and installation or a template structure plays a central role in its design. The substructure is usually prefabricated on its side at a waterside facility and then placed horizontally on a flattopped barge and towed to its offshore location. At the installation site, the substructure is then slid off the barge and uprighted with the help of a derrick barge and allowed to sink vertically to the seafloor. Once the substructure is in place, pipe piles are inserted through its legs and driven into the seafloor by means of a piles are driven to predetermined depths, they are cut off at the top of the substructure and the prefabricated deck stabbed into the piles and connected with field 解 Fig. 1 Artist's rendering of a modern template structure In its completed form, the deck weight is carried entirely by the piles, with the substructure providing bracing against their lateral movement. a typical oil drilling and production platform is shown in Fig. 2. This structure is located off Louisiana in about 300 ft of water in the Gulf of Mexico. The deck measures approximately 60*120 ft and, with operating equipment, weight about 2million pounds. The weight of the substructure is about 4million pounds. The eight pipe piles driven through the legs of the substructure have outside diameters of 4 ft and wall thicknesses of about 1 in in addition to
Lesson Twenty-two Examples of Offshore Structures Template Structures By far the most common type of fixed offshore structure in existence today is the template, or jacket, structure illustrated in Fig.1. This type of structure consists of a prefabricated steel substructure that extends from the seafloor to above the water surface and a prefabricated steel deck located atop the substructure. The deck is supported by pipe piles driven through the legs of the substructure into the seafloor. These piles not only provide support for the deck but also fix the structure in place against lateral loadings from wind, waves, and currents. The construction and installation or a template structure plays a central role in its design. The substructure is usually prefabricated on its side at a waterside facility and then placed horizontally on a flattopped barge and towed to its offshore location. At the installation site, the substructure is then slid off the barge and uprighted with the help of a derrick barge and allowed to sink vertically to the seafloor. Once the substructure is in place, pipe piles are inserted through its legs and driven into the seafloor by means of a piles are driven to predetermined depths, they are cut off at the top of the substructure and the prefabricated deck stabbed into the piles and connected with field Fig. 1 Artist’s rendering of a modern template structure In its completed form, the deck weight is carried entirely by the piles, with the substructure providing bracing against their lateral movement. A typical oil drilling and production platform is shown in Fig.2.This structure is located off Louisiana in about 300 ft of water in the Gulf of Mexico. The deck measures approximately 60*120 ft and, with operating equipment, weight about 2million pounds. The weight of the substructure is about 4million pounds. The eight pipe piles driven through the legs of the substructure have outside diameters of 4 ft and wall thicknesses of about 1 in. in addition to
8 main piles -48-in diameler wetted at we 300p# 4 skirt Fig. 2 Typical offshore template structure off Louisiana in the Gulf of Mexico (a)------installed(b)-----substructure illustrating skirt pi these, four skirt piles are placed around thethe base of structure. All piles are driven 200 to 300 ft into the seafloor. The structure is designed to withstand a result lateral force of about 3 million pounds from wind, waves, and currents during extreme hurricane conditions. Because the wave forces are greatest near the water surface, this resultant force acts near the top of the structure The structure is therefore also designed to withstand a base-overturning moment of the order of 700 million foot-pounds. These loads and moments are five to seven times those caused by extreme winds on a typical 25-story, 300-ft-tall building on land For structures designed for waters greater than about 350 ft, two variations of the basic eight-leg template design have been considered. The first has been to increase the number of legs of the structure so that, with skirt piles, the structure can carry additional deck loads and resist the increased lateral loading and overturning moment A second modification has been based on the observation that, with taller structure and increased base widths, the interior piles become less effective in resisting overturning moments. As an alterative to the eight-pile structure, consideration has thus been given to the four exterior corners of the structure Template structures, as described earlier, are especially suited to soft-soil regions such as the Gulf of Mexico, where deeply driven piles are needed to fix the structure in place and carry the required deck loadings. In regions where hard soil conditions exist and pile driving is more difficult, an alternative structural form has been developed which, in place of piles, relies on its own weight to hold it in place against the large lateral loads from wind, waves, and current. These structures have large foundational elements which, when ballasted, contribute significantly to the required weight and which spread this weight over a sufficient area of the seafloor to prevent failure. Such structures are generally referred to as gravity structures In their more popular form, gravity structures. Are constracted with reinforced concrete and consist of a large cellular base surrounding several unbraced columns which extend upward from
Fig. 2 Typical offshore template structure off Louisiana in the Gulf of Mexico (a)------installed (b)------substructure illustrating skirt piles these, four skirt piles are placed around the the base of structure. All piles are driven 200 to 300 ft into the seafloor. The structure is designed to withstand a result lateral force of about 3 million pounds from wind, waves, and currents during extreme hurricane conditions. Because the wave forces are greatest near the water surface , this resultant force acts near the top of the structure. The structure is therefore also designed to withstand a base-overturning moment of the order of 700 million foot-pounds. These loads and moments are five to seven times those caused by extreme winds on a typical 25-story, 300-ft-tall building on land. For structures designed for waters greater than about 350 ft, two variations of the basic eight-leg template design have been considered. The first has been to increase the number of legs of the structure so that, with skirt piles, the structure can carry additional deck loads and resist the increased lateral loading and overturning moment. A second modification has been based on the observation that, with taller structure and increased base widths, the interior piles become less effective in resisting overturning moments. As an alterative to the eight-pile structure, consideration has thus been given to the four exterior corners of the structure. Gravity Structures Template structures, as described earlier, are especially suited to soft-soil regions such as the Gulf of Mexico, where deeply driven piles are needed to fix the structure in place and carry the required deck loadings. In regions where hard soil conditions exist and pile driving is more difficult, an alternative structural form has been developed which, in place of piles, relies on its own weight to hold it in place against the large lateral loads from wind, waves, and current. These structures have large foundational elements which, when ballasted, contribute significantly to the required weight and which spread this weight over a sufficient area of the seafloor to prevent failure. Such structures are generally referred to as gravity structures. In their more popular form, gravity structures. Are constracted with reinforced concrete and consist of a large cellular base surrounding several unbraced columns which extend upward from
the base to support a deck and equipment above the water surface. Structures of this kind were installed in the North Sea during the mid-1970s. figure 3 illustrates the main features of these structures.This particular structure is referred to as a CONDEEP(concrete deep-water)structure and was designed and constructed in Norway One advance was of the gravity structure over the template type is the reduced time needed for on-site installation. This is especially important in hostile areas such as the North Sea, where unpredictable weather conditions make it highly desirable to limit the construction time needed to 时国场 斜 一E. Fig 3 Illustration of a concrete gravity platform used in the North Sea fix the structure in place. Another advantage is the very decks weights that can be carried by the massive concrete columns Deep-water design forms For water depths greater than about 1000 ft, the weight and foundation requirements of traditional offshore structures make them less attractive than other design forms Two such forms re the guyed tower and tension-leg platform The guyed tower concept is illustrated in Fig 4. It consists of a uniform cross-sectional support structure held upright by several guy lines that run to clump weights on the ocean floor. From the clump weights, the lines then run to conventional anchors to form a dual stiffness mooring system Under normal operating loads, the clump weights remain on the seafloor and lateral motion of the
the base to support a deck and equipment above the water surface. Structures of this kind were installed in the North Sea during the mid-1970s. Figure 3 illustrates the main features of these structures. This particular structure is referred to as a CONDEEP (concrete deep-water) structure and was designed and constructed in Norway. One advance was of the gravity structure over the template type is the reduced time needed for on-site installation. This is especially important in hostile areas such as the North Sea, where unpredictable weather conditions make it highly desirable to limit the construction time needed to Fig. 3 Illustration of a concrete gravity platform used in the North Sea fix the structure in place. Another advantage is the very decks weights that can be carried by the massive concrete columns. Deep-water design forms For water depths greater than about 1000 ft, the weight and foundation requirements of traditional offshore structures make them less attractive than other design forms. Two such forms are the guyed tower and tension-leg platform. The guyed tower concept is illustrated in Fig.4. It consists of a uniform cross-sectional support structure held upright by several guy lines that run to clump weights on the ocean floor. From the clump weights, the lines then run to conventional anchors to form a dual stiffness mooring system. Under normal operating loads, the clump weights remain on the seafloor and lateral motion of the
structure is restrained, However, during a severe storm, the clump weights are lifted off the seafloor by loads transferred from the structure to the clump weights through the guy lines. This action permits the tower to absorb the environmental loadings on it by swaying back and forth without overloading the guy lines. The guyed-tower concept is presently considered to be applicable to water depths of about 2000 ft Figure 5 illustrates the tension-leg concept. In this design, vertical members are used to anchor the platform to the seafloor. This upper part of the structure is designed with a large amount of excessive buoyancy so as to keep the vertical members in tension. Because of this ? Fig 4 Guyed tower concept for deep water tension, the platform remains virtually horizontal under wave action. Lateral excursions are also limited by vertical members, since such movements necessarily cause them to develop a restoring force. A major advantage of the tension-leg concept is its relative cost insensitivity to
structure is restrained, However, during a severe storm, the clump weights are lifted off the seafloor by loads transferred from the structure to the clump weights through the guy lines. This action permits the tower to absorb the environmental loadings on it by swaying back and forth without overloading the guy lines. The guyed-tower concept is presently considered to be applicable to water depths of about 2000 ft. Figure 5 illustrates the tension-leg concept. In this design, vertical members are used to anchor the platform to the seafloor. This upper part of the structure is designed with a large amount of excessive buoyancy so as to keep the vertical members in tension. Because of this Fig. 4 Guyed tower concept for deep water tension, the platform remains virtually horizontal under wave action. Lateral excursions are also limited by vertical members, since such movements necessarily cause them to develop a restoring force. A major advantage of the tension-leg concept is its relative cost insensitivity to
Fig 5 Tension leg concept for deep water increased water depths. At present time, it appears that the main limitation on the tension-leg platform arises from dynamic inertia forces associated with the lateral oscillations of the platform in waves. These become significant at water depths of about 3000 ft From"Offshore Structural Engineering,, by Thomas H. Dawson, 1983 Technical Terms 1. template structure导管架平台(结构)9. current潮流 2. fixed offshore structure固定式近海平10. flat topped barge平顶驳船 台(结构) 1l. derrick barge起重船 3. jacket structure导管架平台(结构) 12. pile driver打桩船 4. prefabricated steel substructure预制钢13. bracing撑杆,拉紧连杆 质导管架(底座) 14. oil drilling and production platform石油 5. seafloor海底 钻井和生产平台 6.deck甲板(平台) 15. skirt piles裙桩 7.(pipe)pile(圆管)桩 16. hurricane飓风 8.leg桩腿,支线 17. base overturning moment对基倾覆力矩
Fig. 5 Tension leg concept for deep water increased water depths. At present time, it appears that the main limitation on the tension-leg platform arises from dynamic inertia forces associated with the lateral oscillations of the platform in waves. These become significant at water depths of about 3000 ft. (From “ Offshore Structural Engineering”, by Thomas H. Dawson, 1983 Technical Terms 1. template structure 导管架平台（结构） 2. fixed offshore structure 固定式近海平 台（结构） 3. jacket structure 导管架平台（结构） 4. prefabricated steel substructure 预制钢 质导管架（底座） 5. seafloor 海底 6. deck 甲板（平台） 7. (pipe)pile （圆管）桩 8. leg 桩腿，支线 9. current 潮流 10. flat topped barge 平顶驳船 11. derrick barge 起重船 12. pile driver 打桩船 13. bracing 撑杆，拉紧连杆 14. oil drilling and production platform 石油 钻井和生产平台 15. skirt piles 裙桩 16. hurricane 飓风 17. base overturning moment 对基倾覆力矩
18. gravity structures重力式平台(结构)26. uniform cross-sectional support structure 19.soft-soil软质土壤 等截面支持构件 20. cellular base蜂窝(式)基础 27. guy line牵索 21. unbraced column无撑杆立柱 28. clump weight水泥块 22.on- site installation现场安装 29. dual stiffness mooring system双重刚性 23. hostile area气候恶劣区域 系泊系统 24. guyed tower牵索塔 30. lateral excursions侧向偏移 25. tension- leg platform张力腿平台 31. oscillation振荡 Additional Terms and Expressions 1. pile supported platform桩基式平台 21. carrIer载管 2. concrete shaft混泥土柱身 22. moon pool月池,船井 3. concrete column混泥土柱身 23. Christmas tree采油树 4. continental shelf大陆架 24. mode of operation工况 5. caisson沉箱 25. shallow earthquake浅表性地震 6.mat沉垫 26. ground motion地壳运动 7. drilling derrick钻井架 27.sea-bed海床 8. free standing derrick轻便井架 28.sub-soil底土 9. drilling operation钻井作业 29. heaving compensator垂荡补偿器 10. drill stem-test(DST钻柱试验 30. fire protection coating防火涂层 11. drilling string钴井管柱 31. surface protection表面防护 12. blow out井喷 32. accidental load偶然性载荷 13. blow out preventor(BOP)防喷器 33. environmental load环境载荷 14. blow out panel防爆盖板 34. deformation load变形载荷 15. weather cladding风暴盖 35. collision load碰撞载荷 16.mast活动钻塔,桅 36. punching shear load冲剪载荷 17. guide fixture导向固定装置 37. heat load热载荷 18. block/crown天车 38. explosion load爆炸载荷 19. cellar deck井口甲板 39. live load活载荷 asng套管 40. dead load固定载荷 Notes to the Text 1. Offshore structures原意为“离岸结构”或“近海结构”,这里根据文中的意思译为“固定式 平台 2. By far the most参见第三课注6 3. This type of structure consists of a prefabricated steel substructure that extends from the seafloor to above the water surface and a prefabricated steel deck located atop the substructure E a> This type of structure consists of a prefabricated steel substructure and a prefabricated steel deck
18. gravity structures 重力式平台（结构） 19. soft-soil 软质土壤 20. cellular base 蜂窝（式）基础 21. unbraced column 无撑杆立柱 22. on-site installation 现场安装 23. hostile area 气候恶劣区域 24. guyed tower 牵索塔 25. tension-leg platform 张力腿平台 26. uniform cross-sectional support structure 等截面支持构件 27. guy line 牵索 28. clump weight 水泥块 29. dual stiffness mooring system 双重刚性 系泊系统 30. lateral excursions 侧向偏移 31. oscillation 振荡 Additional Terms and Expressions 1. pile supported platform 桩基式平台 2. concrete shaft 混泥土柱身 3. concrete column 混泥土柱身 4. continental shelf 大陆架 5. caisson 沉箱 6. mat 沉垫 7. drilling derrick 钻井架 8. free standing derrick 轻便井架 9. drilling operation 钻井作业 10. drill stem-test(DST) 钻柱试验 11. drilling string 钻井管柱 12. blow out 井喷 13. blow out preventor (B.O.P) 防喷器 14. blow out panel 防爆盖板 15. weather cladding 风暴盖 16. mast 活动钻塔，桅 17. guide fixture 导向固定装置 18. block/crown 天车 19. cellar deck 井口甲板 20. casing 套管 21. carrier 载管 22. moon pool 月池，船井 23. Christmas tree 采油树 24. mode of operation 工况 25. shallow earthquake 浅表性地震 26. ground motion 地壳运动 27. sea-bed 海床 28. sub-soil 底土 29. heaving compensator 垂荡补偿器 30. fire protection coating 防火涂层 31. surface protection 表面防护 32. accidental load 偶然性载荷 33. environmental load 环境载荷 34. deformation load 变形载荷 35. collision load 碰撞载荷 36. punching shear load 冲剪载荷 37. heat load 热载荷 38. explosion load 爆炸载荷 39. live load 活载荷 40. dead load 固定载荷 Notes to the Text 1. Offshore structures 原意为“离岸结构”或“近海结构”，这里根据文中的意思译为“固定式 平台”。 2. By far the most 参见第三课注 6。 3. This type of structure consists of a prefabricated steel substructure that extends from the seafloor to above the water surface and a prefabricated steel deck located atop the substructure. 主句为 This type of structure consists of a prefabricated steel substructure and a prefabricated steel deck
that extends from.to.…, surface定语从句,修饰 substructure; located atop the substructure过去分词短语后置,修饰deck. 翻译此类句子时,可先译出主句,然后再分别译出修饰部分。例如,此句可译为:“这 种平台由一个预制的钢质导管架和一个预制的钢质平台甲板组成:导管架从海底一直延伸到 水面上,平台甲板位于导管架顶上。 4. A second modification has been based on the observation that, with taller structures and increased base widths, the interior piles become less effective in resisting overturning moments A second( modification)序数词前加不定冠词,参见第二课注1。 that引出同位语从句,修饰 the observation从句中with引出的介词短语作为插入语,具 有伴随的意思 5. in place of( piles)代替(桩) 6. In their more popular form, gravity structures are constructed with reinforced concrete and consist of a large cellular base surrounding several unbraced columns which extend upward from the base to support a deck and equipment above the water surface A large cellular base为 consist of的宾语, surrounding several unbraced columns现在分词 短语,修饰base. which extend upward from. above the water surface定语从句,修饰 columns 7. These become significant at water depths of about (少324及以后)
that extends from…to…surface 定语从句，修饰 substructure ;located atop the substructure 过去分词短语后置，修饰 deck. 翻译此类句子时，可先译出主句，然后再分别译出修饰部分。例如，此句可译为：“这 种平台由一个预制的钢质导管架和一个预制的钢质平台甲板组成；导管架从海底一直延伸到 水面上，平台甲板位于导管架顶上。” 4．A second modification has been based on the observation that, with taller structures and increased base widths, the interior piles become less effective in resisting overturning moments. A second (modification) 序数词前加不定冠词，参见第二课注 1。 that 引出同位语从句，修饰 the observation.从句中 with 引出的介词短语作为插入语，具 有伴随的意思。 5．in place of (piles) 代替（桩） 6．In their more popular form, gravity structures are constructed with reinforced concrete and consist of a large cellular base surrounding several unbraced columns which extend upward from the base to support a deck and equipment above the water surface. A large cellular base 为 consist of 的宾语，surrounding several unbraced columns 现在分词 短语，修饰 base. which extend upward from…above the water surface 定语从句，修饰 columns 7. These become significant at water depths of about (少 324 及以后)
