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
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
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
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
template structure 导管架平台（结构）
fixed offshore structure 固定式近海平台（结构）
jacket structure 导管架平台（结构）
prefabricated steel substructure 预制钢质导管架（底座）
seafloor 海底
deck 甲板（平台）
(pipe)pile （圆管）桩
leg 桩腿，支线
current 潮流
flat topped barge 平顶驳船
derrick barge 起重船
pile driver 打桩船
bracing 撑杆，拉紧连杆
oil drilling and production platform 石油钻井和生产平台
skirt piles 裙桩
hurricane 飓风
base overturning moment 对基倾覆力矩
gravity structures 重力式平台（结构）
soft-soil 软质土壤
cellular base 蜂窝（式）基础
unbraced column 无撑杆立柱
on-site installation 现场安装
hostile area 气候恶劣区域
guyed tower 牵索塔
tension-leg platform 张力腿平台
uniform cross-sectional support structure 等截面支持构件
guy line 牵索
clump weight 水泥块
dual stiffness mooring system 双重刚性系泊系统
lateral excursions 侧向偏移
oscillation 振荡
Additional Terms and Expressions
pile supported platform 桩基式平台
concrete shaft 混泥土柱身
concrete column 混泥土柱身
continental shelf 大陆架
caisson 沉箱
mat 沉垫
drilling derrick 钻井架
free standing derrick 轻便井架
drilling operation 钻井作业
drill stem-test(DST) 钻柱试验
drilling string 钻井管柱
blow out 井喷
blow out preventor (B.O.P) 防喷器
blow out panel 防爆盖板
weather cladding 风暴盖
mast 活动钻塔，桅
guide fixture 导向固定装置
block/crown 天车
cellar deck 井口甲板
casing 套管
carrier 载管
moon pool 月池，船井
Christmas tree 采油树
mode of operation 工况
shallow earthquake 浅表性地震
ground motion 地壳运动
sea-bed 海床
sub-soil 底土
heaving compensator 垂荡补偿器
fire protection coating 防火涂层
surface protection 表面防护
accidental load 偶然性载荷
environmental load 环境载荷
deformation load 变形载荷
collision load 碰撞载荷
punching shear load 冲剪载荷
heat load 热载荷
explosion load 爆炸载荷
live load 活载荷
dead load 固定载荷
Notes to the Text
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”。
By far the most 参见第三课注6。
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
These become significant at water depths of about
(少324及以后)
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
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
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
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
template structure 导管架平台（结构）
fixed offshore structure 固定式近海平台（结构）
jacket structure 导管架平台（结构）
prefabricated steel substructure 预制钢质导管架（底座）
seafloor 海底
deck 甲板（平台）
(pipe)pile （圆管）桩
leg 桩腿，支线
current 潮流
flat topped barge 平顶驳船
derrick barge 起重船
pile driver 打桩船
bracing 撑杆，拉紧连杆
oil drilling and production platform 石油钻井和生产平台
skirt piles 裙桩
hurricane 飓风
base overturning moment 对基倾覆力矩
gravity structures 重力式平台（结构）
soft-soil 软质土壤
cellular base 蜂窝（式）基础
unbraced column 无撑杆立柱
on-site installation 现场安装
hostile area 气候恶劣区域
guyed tower 牵索塔
tension-leg platform 张力腿平台
uniform cross-sectional support structure 等截面支持构件
guy line 牵索
clump weight 水泥块
dual stiffness mooring system 双重刚性系泊系统
lateral excursions 侧向偏移
oscillation 振荡
Additional Terms and Expressions
pile supported platform 桩基式平台
concrete shaft 混泥土柱身
concrete column 混泥土柱身
continental shelf 大陆架
caisson 沉箱
mat 沉垫
drilling derrick 钻井架
free standing derrick 轻便井架
drilling operation 钻井作业
drill stem-test(DST) 钻柱试验
drilling string 钻井管柱
blow out 井喷
blow out preventor (B.O.P) 防喷器
blow out panel 防爆盖板
weather cladding 风暴盖
mast 活动钻塔，桅
guide fixture 导向固定装置
block/crown 天车
cellar deck 井口甲板
casing 套管
carrier 载管
moon pool 月池，船井
Christmas tree 采油树
mode of operation 工况
shallow earthquake 浅表性地震
ground motion 地壳运动
sea-bed 海床
sub-soil 底土
heaving compensator 垂荡补偿器
fire protection coating 防火涂层
surface protection 表面防护
accidental load 偶然性载荷
environmental load 环境载荷
deformation load 变形载荷
collision load 碰撞载荷
punching shear load 冲剪载荷
heat load 热载荷
explosion load 爆炸载荷
live load 活载荷
dead load 固定载荷
Notes to the Text
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”。
By far the most 参见第三课注6。
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
These become significant at water depths of about
(少324及以后)
