Gangway Tower Dead Weight

7/30/2019 Gangway Tower Dead Weight

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Date docume 24/06/08

Client

Author

A DRAFT MMU 06-09-08 06-09-08 LGR

Revision Status Author Date Verified Date Released DMC Date


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revision A18 November 2008 2 / 71

Index

1 Introduction .............................................................................................. 52 3-D Modelling ........................................................................................... 62.1 TRESTLE ............................................................................................................ 62.1.1 Substructure ...................................................................................................................... 72.1.2 Superstructure .................................................................................................................. 92.1.3 Jacket @ Bent 35 ............................................................................................................ 102.2 LOADING PLATFORMS ................................................................................... 122.2.1 Substructure parking area platform A .......................................................................... 122.2.2 Substructure parking area platform B .......................................................................... 132.2.3 Substructure platforms .................................................................................................. 132.2.4 Superstructure ................................................................................................................ 163 Loads ...................................................................................................... 173.1 TRESTLE LOADS ............................................................................................. 173.1.1 Self weight construction ................................................................................................ 173.1.2 Deadweight concrete roadway ...................................................................................... 173.1.3 Dead load existing piping............................................................................................... 183.1.4 Dead load new piping ..................................................................................................... 193.1.5 Horizontal pipe load (Anchor forces) ............................................................................ 203.1.6 Horizontal pipe loads (Friction forces .......................................................................... 213.1.7 Vertical truckload ............................................................................................................ 223.1.8 Wind load east west ........................................................................................................ 223.1.9 Wind load north south .................................................................................................... 233.1.10 Live load ........................................................................................................................... 243.1.11 Wave forces extreme condition ..................................................................................... 253.1.12 Wave forces normal condition ....................................................................................... 263.1.13 Temperature load ............................................................................................................ 273.1.14 Seismic load .................................................................................................................... 283.1.15 Dead weight concrete collar on piles ............................................................................ 283.1.16 Vehicle loading ................................................................................................................ 293.2 LOADING PLATFORMS ................................................................................... 313.2.1 Self weight construction ................................................................................................ 313.2.2 Deadweight concrete roadway ...................................................................................... 313.2.3 Dead load existing piping............................................................................................... 323.2.4 Dead load new piping ..................................................................................................... 333.2.5 Horizontal pipe load (Anchor forces) ............................................................................ 34


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3.2.6 Horizontal pipe loads (Friction forces .......................................................................... 343.2.7 Vertical truckload ............................................................................................................ 343.2.8

Wind load east west ........................................................................................................ 36

3.2.9 Wind load north south .................................................................................................... 373.2.10 Live load parking area 50 LBS per square foot ........................................................... 383.2.11 Wave forces extreme condition ..................................................................................... 393.2.12 Wave forces normal condition (Xdir) ............................................................................ 403.2.13 Loading arms dead weight ............................................................................................. 413.2.14 Loading arms wind force................................................................................................ 423.2.15 Gangway tower dead weight .......................................................................................... 433.2.16 Gangway tower wind force............................................................................................. 443.2.17 Uniform distributed load ................................................................................................ 453.2.18 Hawser pull ...................................................................................................................... 453.2.19 Breasting forces; ship impact load ............................................................................... 463.2.20 Temperature load ............................................................................................................ 473.2.21 Seismic load .................................................................................................................... 483.2.22 Self weight concrete collar ............................................................................................ 483.2.23 Self weight omitted concrete deck ................................................................................ 493.2.24 Seismic moment loading arms ...................................................................................... 503.2.25

Vehicle loading ................................................................................................................ 51

4 Load combinations ................................................................................ 535 Results .................................................................................................... 565.1 TRESTLE .......................................................................................................... 565.1.1 Design results ................................................................................................................. 565.1.2 Beam end forces summary ............................................................................................ 575.1.3 Maximum compression per pile .................................................................................... 595.2 LOADING PLATFORM A .................................................................................. 635.2.1 Beam end forces summary ............................................................................................ 635.2.2 Minimum compression/ tension per pile ...................................................................... 655.2.3 Design results ................................................................................................................. 665.3 LOADING PLATFORM B .................................................................................. 675.3.1 Beam end forces summary ............................................................................................ 675.3.2 Maximum compression per pile .................................................................................... 685.3.3 Minimum compression/ tension per pile ...................................................................... 695.3.4 Design results ................................................................................................................. 706 References ............................................................................................. 716.1 Reports ............................................................................................................. 71


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6.2 Drawings .......................................................................................................... 71Enclosures .................................................................Error! Bookmark not defined.


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1 Introduction

XXXX XXXXXX XXXXXXXXXXX (XXX)was requested by XXXX to prepare a fit for purpose analysis of theexisting gas jetty at XXXXX el XXXXX.

The gas jetty in the port of XXXXX el XXXXX comprises two berths for the export of gas [LPG/LNG]. Theobjective of the project is to upgrade these jetties in line with a full rejuvenation scheme to enable anincrease in terminal throughput and the receipt of LNG-carriers up to 75,000 m

3as per 1 January 2009.

This rejuvenation scheme is based on the following activities:

temporary upgrading of a berth to meet the Jan-2009 milestone;

define and implement modifications to the jetty to guarantee safe loading operations for LPG andLNG carriers up to 7,000 m

3and 75,000 m

3capacity respectively.

The objective of the overall study is to: Carry out a structural fit for purpose analysis of the existing jetty component;

Confirm design loads for the dolphins based on TERMSIM simulations and XXXX designphilosophy;

Structural analysis of new mooring and breasting dolphins.

This report presents the structural fit for purpose analyses. For this study Scenario A is considered (thepresent situation). The layout of the two berths is outlined in Figure 1-1.

Figure 1-1 Berths locations Port XXXXX El XXXXX

The fit for purpose analysis is carried out using the 3-D model STAAD. Separate models are made for thetrestle, loading platform A and B and for all the dolphins. Secondly an analysis is done of the load factors of

the construction determining the residual strength.

In the following section first the setting up of the model is described in three parts: trestle, platform A, andplatform B. The modelling of the dolphins is described in a different report [201].

Berth A

Berth B


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2 3-D Modelling

As stated above, in this section the set up of the 3-D STAAD models is discussed. STAAD.PRO is a stateof the art software model for 3-D model generation, finite element analysis and multi material design. Eachof the three models is discussed separately in the sub sections: TRESTLE, PLATFORM A andPLATFORM B. In these sections the 3-D schematisation of the construction is discussed. Theschematisation of the loads and the determination of the residual strength of the construction arediscussed in sections 3 and 4 respectively.

2.1 TRESTLE

The modelling of the trestle is split in two parts, the substructure consisting of steel tubular pipes and steelbeam pile caps, and the superstructure consisting of steel beam stringers interconnected with steel beams

bracing. A figure of the framing of the superstructure can be found in APPENDIX A.

The superstructure is laid on the pile cap in the model by using new nodes (A, B, etc). These nodes havethe same X and Z coordinate as the underlying nodes (A, B, C, etc.). The Y coordinate has beenincreased. To position the stringer directly on top of the pile cap the elevation has to be increased by halfthe pile cap height and half the stringer height. The pile cap typically has a height of 590 mm and thestringer 640 mm. The elevation is (590+640)/2 = 615 mm.

In Figure 2-1 an example of the elevation between the substructure and the superstructure is shown. Toensure a connection between the substructure and the superstructure in the model, the new nodes (A, B,etc.) have been made slave nodes to the nodes of the pile cap (A, B, etc), rigid in all directions.

Figure 2-1 Elevation between substructure and superstructure

PILE CAP

BRACING

ELEVATION

STRINGER

A

B

B

A

X

Y

Z


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2.1.1 Substructure

BentsThe substructure is made of 45 bents at 14 m spacing. Each bent consists of a set of piles and a pile cap.Depending of the function of the bent (being anchor bent or expansion joint) the piles are placed at a 1:3angle or vertical. 4 types of pile caps can be identified being:Type 1: HE 600 A beam;Type 2: Box beam, assumed 600 mm by 600 mm with 20 mm wall thickness;Type 3: IPE 550 beam;Type 4: At bent 35 a jacket is placed; the construction and modelling of the jacket is discussed separatelyin section 2.1.3.

In the following table, Table 2-1, a summary is given of the specifics for every bent. All bents areschematized accordingly. The bent types can be found in Error! Reference source not found.. The captype is described above and can also be found in Error! Reference source not found..

bent no Type No of vertical piles No of batter piles cap elevation Seabed level Cap type

1 A 2 0 4120 1200 1

2 S 2 1 4150 0 2

3 A 2 0 4180 -300 1

4 Q 2 1 4210 -450 1

5 Q 2 1 4210 -600 1

6 A 2 0 4270 -800 1

7 E 0 10 4300 -100 2

8 Q 2 1 4330 -1200 1

9 Q 2 1 4360 -1400 1

10 Q 2 1 4390 -1600 1

11 A 2 0 4420 -1800 1

12 A 2 0 4450 -3000 1

13 L 1 6 4450 -4000 2

14 A 2 0 4450 -5000 1

15 A 2 0 4530 -6000 1

16 Q 2 1 4560 -6000 1

17 Q 2 1 4590 -6000 1

18 A 2 0 4620 -6000 1

19 A 2 0 4650 -6000 1

20 E 0 10 4680 -6000 2

21 A 2 0 4710 -6000 1

22 A 2 0 4740 -6000 1

23 M 2 2 4770 -6000 1

24 M 2 2 4800 -6000 1

25 A 2 0 4830 -6000 1

26 A 2 0 4860 -6000 1

27 G 0 6 4832 -6000 2

28 R 3 0 4832 -6000 1

29 B 2 0 4800 -6000 3

30 F 2 2 4770 -6000 1

31 F 2 2 4740 -6000 1

32 B 2 0 4710 -6000 3

33 K 1 3 4680 -6000 234 B 2 0 4650 -6000 3

35 JACK 3 0 4620 -6000 4

36 D 2 1 4590 -6000 1


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37 B 2 0 4560 -6000 3

38 B 2 0 4530 -6000 3

39 J 0 8 4500 -6000 2

40 B 2 0 4470 -6000 3

41 B 2 0 4440 -6000 3

42 D 2 1 4410 -6000 1

43 D 2 1 4380 -6000 1

44 R 3 0 4322 -6000 1

45 G 0 6 4322 -6000 2

Table 2-1 summary of bents

Virtual fixitySince the pile end depth is not known with any certainty the pile end is schematized as a fixed support at avirtual depth. This depth (point of fixity, zf) can be determined using a stiffness factor T according to [101].

The stiffness factor T is 1651 mm, and the point of fixity (Zf) is 3000 mm. [See APPENDIX B1]. Accordinglythe piles are assumed to be fixed at a distance of 3.0 m below the seabed.

PilesAll piles used are 16 steel piles with a 3/8 wall thickness. Expressed in millimetres this is an outsidediameter of 406.4 mm and an inside diameter of 387.4 mm.

Around the water level the piles are wrapped with a concrete layer with an outside diameter of 610 mm.The combined cross section of the concrete and steel pile is schematized as a steel pile with the samestiffness as the combined pile. In APPENDIX B2 the calculation is given which determines the outsidediameter for the combined section. The dimensions of the collared pile are schematized as follows:Inside diameter (Di) = 387.9 mm

Outside diameter (Do) = 456 mm.

According to Error! Reference source not found. the collar is located between +2.5 m and -2.5 m aroundMSL (el. + 0.00m). In the model the combined cross section is applied on the piles between el 2.5 m and+ 2.5 m. See Figure 2-2 for the schematisation of a bent.

To account for the additional weight of the concrete collar a uniform distributed load is added on thesection. The weight difference between the actual section and the model section is calculated in

APPENDIX B4. In this calculation the different gravitational force above and below water is taken intoaccount.

The weight difference between the actual cross section and the modelled cross section is 3.08 kN. Thisdifference acts on the total length of the pile, which is 5 m. The distributed load added in the model

therefore is 3.08/5 = 0.61 kN/m.


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Figure 2-2 Schematisation of steel piles

2.1.2 Superstructure

The trestle superstructure consists of a series of stringers and braces. The stringers span 14 meterbetween each bent and are all HE 650 A members. Connecting the stringers are 3 meter long IPE 400beams at the location of the bents and IPE 330 beams at 3.5 meter intervals between the bents. Thebraces in diagonal direction are also IPE 330 beams.

In the model the IPE 330 beams are replaced by full IPE 330s in order to correctly model the stiffness ofthe structure. The IPE 330 beams are connected to the stringers in such a way that they can not takemoment forces and high compression loads. Part of the compression forces will be taken by the concretedeck. Since the deck is not part of the model this force should be taken by the braces. To make sure thebraces are able to take the load full IPE beams in stead of IPE beams are assumed. All the braces aremodelled with moment releases at each end indicating that they can take forces but no moments.

Expansion jointsThe expansion joints in the superstructure are schematized as releases in the stringers. When the beamsare released completely in X direction (normal to the beam) deflections can occur in the model that arelarger than possible in reality. As can be seen from Figure 2-3 the expansion joint exists of a slot of 60 mmwide. This indicates that only 30 mm in each direction is possible. This effect is initially neglected in themodel and the releases are released fully in x direction. In section 5 the result of this assumption isdiscussed in more detail.

Reference is made to Error! Reference source not found. for an overview of the location of theexpansion joints.

BATTER PILE

VERTICALPILE

EL + 2.5 m

EL. 2.5 m

COLLAR

POINT OFFIXITY


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Figure 2-3 Expansion joint detail Error! Reference source not found.

Concrete walkwayThe concrete walkway on top of the stringers is schematized as a superimposed dead load and will bediscussed in the loads section.

All other constructional elements are considered negligible

2.1.3 Jacket @ Bent 35

At bent 35 a jacket is located. The jacket consists of three steel piles with 18 and 20 piles and 219mm bracing. Around the water level the 18 piles are wrapped with a 660 mm concrete collar rangingfrom el -1.0 m to el. + 1.3 m. The 20 pile is also wrapped with a 660 mm concrete collar ranging from el -1.0 m to el. + 3.5 m. No wrapping is assumed round the bracing Error! Reference source not found..

The jacket is held in place by the same 18 steel pipes that support the trestle. These pipes are driventhrough the piles of the jacket and fixated with a filling of concrete. The combined cross-section of the

jacket piles therefore consists of steel pile, concrete filling and outer steel pile.

The combined cross section of the concrete and steel pile is schematized as a steel pile with the samestiffness as the combined pile. In APPENDIX B3 the calculation is given which determines the outside

diameter for the combined section. The dimensions of the steel jacket piles are schematized as follows:

18 pile Inside diameter (Di) = 387.9 mmOutside diameter (Do) = 433.5 mm


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As described these piles are wrapped with a concrete collar around the waterline. The combined crosssection of the concrete and steel pile is schematized as a steel pile with the same stiffness as thecombined pile. In APPENDIX B.4 the calculation is given which determines the outside diameter for thecombined section. The dimensions of the collared pile are schematized as follows:


20 pile Inside diameter (Di) = 387.9 mmOutside diameter (Do) = 491.9 mm.

The 219 mm bracing is assumed to have an inside diameter of 210 mm (wall thickness is 4.5 mm). For

more detail on the dimensions of the jacket reference is made to drawing Error! Reference source notfound.. In Figure 2-4 the model schematisation of the substructure of bent 35 is shown.

Figure 2-4 Model schematisation of Jacket @ bent 35


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2.2 LOADING PLATFORMS

Since an expansion joint is located at bent 46 as well as bent 49 [see APPENDIX A] the loading platformscan be schematized separately from the trestle. In this section loading platform A is discussed.

In the schematisation of the platform the parking area is included in the model. The parking area issupported by three bents with similar construction as the trestle bents. The loading platform itself issupported by vertical and batter piles capped with steel beams (both standard and manufactured beams).The superstructure consists of a series of stringers and braces with a concrete surface on top. In thefollowing subsections the sub- and superstructure are described in more detail.

The superstructure is laid on the pile cap in the model by using new nodes (A, B, etc). These nodes havethe same X and Z coordinate as the underlying nodes (A, B, C, etc.). The Y coordinate has beenincreased. To position the stringer directly on top of the pile cap the elevation has to be increased by half

the pile cap height and half the stringer height. The pile cap has varying heights between 550 mm and 836mm. The stringers typically have a height of 500 mm. The elevation is (836+500)/2 = 669 mm.

Figure 2-5 Elevation of superstructure above substructure

In Figure 2-5 an example of the elevation between the substructure and the superstructure is shown. Toensure a connection between the substructure and the superstructure in the model, the new nodes (A, B,etc.) have been made slave nodes to the nodes of the pile cap (A, B, etc), rigid in all directions.

2.2.1 Substructure parking area platform A

As described above the substructure of the parking area and the platform differs slightly. The substructure

A

A

ELEVATION

STRINGER

PILE CAP


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of the parking area consists of 3 bents with the following specifics, Table 2-2.

bent no bent type No of vertical piles No of batter piles cap elevation Bottom elevation Cap type

46 N 3 1 4286 -6000 1

47 T 3 0 3825 -7500 1

48 T 3 0 3364 -8100 1

Table 2-2 substructure parking area platform A

The cap elevation of the loading platform is assumed to be at the same level as bent 48. The bottom levelis assumed to be at el 9.00 m.

2.2.2 Substructure parking area platform B

Platform B is very similar to platform A. Differences can be found in the structure of the parking area. Thesupporting bents are of a different type and also the surface of the parking area is different. The loadingplatform itself however is exactly the same, although shifted slightly in the longitudinal direction. Thesubstructure of the parking area consists of 3 bents with the following specifics, Table 2-3.

bent no Type No of vertical piles No of batter piles cap elevation Bottom elevation Cap type

49 P 3 1 4834 -6000 1

50 C 3 0 4869 -9000 1

51 U 2 0 4904 -11400 1

Table 2-3 Summary of bent characteristics

The cap elevation of the loading platform is assumed to be at the same level as bent 51. The bottom levelis assumed to be at el 11.40 m.

2.2.3 Substructure platforms

The substructure of the platform also consists of a series of vertical and batter piles but in a differentscheme. The vertical piles are placed in rows of 5 piles with 4.6 and 6.0 m spacing [Figure 2-6]. The batterpiles are placed in the centreline of the platform as shown in Figure 2-6. Capping the longitudinal series ofbatter piles is a combined member designated member B (highlighted inFigure 2-6 by the orange colour)and connecting with the vertical piles member C (highlighted by the yellow colour). The transverse batterpiles and the four vertical piles in the transverse centreline are capped by a combined member designated

member A, highlighted by the green colour.


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Figure 2-6 Framing plan Loading platform

The pile cap of the remaining vertical piles consists of IPE 550 beams.The point of fixity of the piles is taken at the same depth as for the piles of the trestle (3.00 m belowseabed)

MEMBER AMember A is a combined member consisting of an IPE 550 beam supported by a welded I beam with aweb of 1200 mm by 13 mm and flanges of 300 by 20 mm. In APPENDIX B5 figures as well as thecombined beam characteristics are given. In STAAD the member is schematized as an IPE 550 beam witha rectangular bottom plate. The bottom plate is calculated to have the same stiffness in Y and Z directionas the I-beam which it replaces. In APPENDIX B5 the calculation of the stiffness of the bottom plate can befound. A bottom plate is used in the model with a width of 893.7 mm and a thickness of 106.55 mm. Sincethe area of the plate is 4 times larger than the I-beam it replaces, the stiffness of the beam is exaggerated.

However, analysis with the IPE beam only (without bottom plate) indicated that the beam had sufficientstrength; therefore the above described schematisation is assumed acceptable.

In Figure 2-7 the modelled schematisation of member A is shown.


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Figure 2-7 Schematisation of Member A

MEMBER BMember B consists of a HE A 400 beam supported by a welded I beam with a web of 1200 mm by 13 mmand flanges of 300 mm by 18 mm. In APPENDIX B5 figures as well as the combined beam characteristicsare given. Similar to Member A the welded I beam is replaced by a rectangular bottom plate in the model.Since the I-beam has the same dimensions as Member A the bottom plate also has the same dimensions.For this schematisation the same limitation holds as for Member A. In this case analysis also showed thatthe single HE 400 A beam had sufficient strength to bear the loads. Therefore the above describedschematisation is used since it leads to a safe estimate of the forces on the piles.

MEMBER CMember C is a welded I beam with a web of 800 mm by 13 mm and flanges of 210 mm by 18 mm. In

APPENDIX B5 pictures as well as the beam characteristics are given. In STAAD the member isschematized as a wide flanged member with the following specifics, see Figure 2-8.

Figure 2-8 Input screen MEMBER C


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2.2.4 Superstructure

The platforms superstructure consists of a series of stringers and braces. Stringers can be both HE A 500or IPE 450 beams, whereas braces are HE B 220 beams. All braces are modelled as tension onlymembers.

The parking areas superstructure also consists of a series of stringers and braces. The stringers span 14meter between each bent and are all HE 650 A members. Connecting the stringers are IPE 400 beams atthe location of the bents and IPE 330 beams at 3.5 meter intervals between the bents. The braces indiagonal direction are also IPE 330 beams. The braces are schematized in the model as normal full IPE330 members with moment releases at each end. In Figure 2-9 an aerial view of the structure of theparking area is shown. Indicated in red are the stringers. Between the stringers are braces and below the

stringers are the pile caps.

The braces in the parking area and platform area are modelled with releases. The members can only takeaxial and shear forces and are not loaded with moments.

Figure 2-9 Arial view of steel structure parking area

Concrete walkwayThe concrete walkway on top of the parking area is schematized as a superimposed dead load and will bediscussed in the loads section. The concrete roadway on top of the platform itself is schematized as a

series of plates connected with the underlying beams. On top of the concrete planks an overlay of 65 mmis assumed. The concrete is modelled as a slab with a thickness of 165 mm + 65 mm = 230 mm.

The concrete slab on the loading platform is 0.80 m smaller in transverse direction and 0.30 m shorter inlongitudinal direction in the model than in reality, see Figure 2-6 where platform extends 0.40m and 0.15 mon the front and side of the framing of the platform. To accommodate for the difference in dead weight ofthe omitted concrete an extra load is added on the platform models. Reference is made to 3.2.23 for adescription of the load.

All remaining superstructure is not modelled as construction element. The loading arms are schematizedas forces, discussed in the forces section. All other construction elements are schematized as asuperimposed uniform distributed load, also discussed in the loads section.


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3.1.3 Dead load existing piping

The deadweight of the gas and water pipes (including contents) located on the trestle and platforms is alsoadded as a superimposed load. The existing piping is schematised as 3 pipes of different diameter:1. 22 LNG pipe2. 16 LNG return pipe3. 6 LPG + 3 LPG return + 8 Firewater

The pipes are assumed to be schedule 40 pipes [104] with the following characteristics, see Table 3-1.

Diameter [inch] Outside diameter [mm] Wall thickness [mm] Weight [kg/m]

3 88.9 4.78 9.91

6 168.3 7.11 28.26

8 291 8.18 42.53

16 406.4 12.70 123.29

22 558.8 15.88 212.52

Table 3-1 schedule 40 existing pipe characteristics

The pipes are assumed to be either filled with LNG [5 kN/m3], LPG [6.5 kN/m

3], water [10 kN/m

3] or air/gas

[0 kN/m3]. The pipes are supported every 14 m by the bents. Every bent therefore carries 14 m of pipe. On

every bent the following pipe loads are modelled as concentrated loads for the existing pipelines. The LNGand LPG pipes are assumed filled with liquid gas with the specific weights as given above. The returnpipes are assumed to be filled with gas and or air and the specific weight is assumed to be zero (0 kN/m

3).

1. 22 LNG pipe, filled with liquid gas, F = 44.4 kN;2. 16LNG gas return pipe filled with gas and air, F = 16.9 kN;3. 6 LPG filled with liquid gas, 3 LPG filled with gas + 8 Firewater filled with water, F = 15. 2 kN.

In Figure 3-3 the general position of the pipelines on the trestle is shown. The existing pipelines are alllocated on the landward side of the trestle. From bent 1 to bent 45 the position of the pipelines on thetrestle is constant. At bent 28 and onward the pile cap is 200 mm smaller than before. Therefore thedistance of the centreline of the pipe to the end of the pile cap is also smaller. In Table 3-2 and Table 3-3summations of the locations of the pipelines on the pile caps are given. The starting location is at the mostleft part of the pile cap, so the first pipe is located at 1300 mm to the right of the leftmost end of the pilecap. In Figure 3-2 a part of the trestle is shown with the dead load of the existing piping acting on themodel. These loads are acting on all the bents of the trestle.

Figure 3-2 Schematisation of dead load existing piping


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Figure 3-3 cross section of trestle with existing and new Pipelines [202]

Pipe Distance to start point Distance to previous pipe Distance to next pipe

1 1300 mm - 1300 mm2 2600 mm 1300 mm 1100 mm

3 3700 mm 1100 mm -

Table 3-2 location of existing pipelines on bents 1 to 27


1 1100 mm - 1300 mm

2 2400 mm 1300 mm 1100 mm

3 3500 mm 1100 mm -

Table 3-3 location of existing pipelines on bents 28 to 46

The above given positions are used in the model for the position of the concentrated loads schematizingthe dead weight of the existing pipelines.

3.1.4 Dead load new piping

In APPENDIX C the position of the existing pipelines and the new pipelines is given. In the future situationthe LNG pipelines at the trestle between platforms A and B will be removed and replaced by a muchsmaller series of LPG pipelines. Since the dead weight of the existing pipelines is normative for thestrength calculation of the trestle, in the new situation the removal of the LNG pipelines is neglected.Between platform A and the shore however, a new series of LNG and LPG pipelines is added on theseaward side of the trestle. This load will be schematised as extra concentrated loads for the new situation.

The new pipelines are schematized as follows4. 20LNG pipe5. 12 LPG pipe6. 6 LPG return + 8 firewater


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The pipes are assumed to be schedule 40 pipes [202] with the following characteristics, see Table 3-4

Diameter [inch] Outside diameter [mm] Wall thickness [mm] Weight [kN/m]

6 168.3 7.11 28.268 291 8.18 42.53

12 323.8 10.31 79.72

20 508 15.06 183.05

Table 3-4 schedule 40 new pipe characteristics


3], water [10 kN/m

3] or air/gas


every bent the following pipe loads are modelled as concentrated loads for the new pipelines4. 20 LNG pipe, filled with liquid gas, F = 37.9 kN;5. 12LPG pipe filled with liquid gas, F = 11.872 kN;6. 6 LPG filled with gas and air + 8 Firewater filled with water, F = 15. 2 kN.

In Figure 3-3 the general position of the pipelines on the trestle is shown. The new pipelines are located onthe seaward side of the trestle. From bent 1 to bent 27 the position of the new pipelines on the trestle isconstant. At bent 28 and onward the existing pipe load is assumed. In Table 3-5 a summation of thelocations of the pipelines on the pile caps is given.


4 1300 mm - 1300 mm

5 2600 mm 1300 mm 1100 mm

6 3700 mm 1100 mm -

Table 3-5 location of new pipelines on bents 1 to 27

In Figure 3-4 the dead load of the piping is shown acting on the model.

Figure 3-4Schematisation of dead load new piping

3.1.5 Horizontal pipe load (Anchor forces)

The piping can exert horizontal forces on the bents as a result of pressure built up inside the piping. The

pipes are fixed at the anchor bents and are able to expand at the expansion loops, the bend in the trestleat bent 13 and the loop crossing the trestle at bent 27. Anchor bents are located at bents 7, 20 and 39.

At the anchor bents the piping exerts a force at the bent. It is assumed that the force acts on the bents inone direction. This force is schematised as a concentrated load acting at the same place as the


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deadweight of the 22 LNG pipeline working perpendicular to the bent as shown inFigure 3-5.

The magnitude of the force is described in Error! Reference source not found. as 70 KIPS, which

corresponds to 311 kN. It is assumed that this load includes temperature loads in the piping, since thepiping is not a part of the model no further temperature load will be added.

Figure 3-5 Schematisation of pipeline anchor forces on trestle

3.1.6 Horizontal pipe loads (Friction forces

At the non anchor bents the pipeline exerts a friction force at the bents as the pipeline slides over thesupport. This force is assumed to act towards the anchor bents from both sides. This force is schematisedas a concentrated load acting at the same place as the deadweight of the 22 LNG pipeline workingperpendicular to the bent. In Figure 3-6 part of the trestle is shown with the pipeline friction forces indicatedby the arrows.

Figure 3-6 Schematisation of friction forces on trestle

The magnitude of this load is described in Error! Reference source not found. as 2.4 KIPS, which


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corresponds with 10.7 kN. This force is applied on all bents except bents 7, 13, 20, 27 and 38. It isassumed that this load includes temperature loads in the piping, since the piping is not a part of the modelno further temperature load will be added.

3.1.7 Vertical truckload

In Error! Reference source not found. it is indicated that the trestle is designed for a truckload: AASHOH20 S44. It is assumed that the truck load HS 20-44, according to AASHTO [102] is indicated here. Thisloading incorporates a 20 tons tractor truck with semitrailer. The axel loads are given according to

APPENDIX E. This load acts on the concrete roadway on top of the trestle. Since the roadway is notincorporated into the model the load has to be transferred to the stringers which support the roadway. Theroadway is made out of 1 m wide sections and it is tentatively assumed that the concrete spreads the axelloads over its full width, see Figure 3-7

The load acting on the stringers is therefore schematized as three distributed loads acting on 1 m sectionsof the beam. Over a 14 meter long section of the stringer (the span between two bents) the loads areapplied as follows:

F1 = 35.6 kN/m location 2000 mm to 3000 mm of beam starting pointF2 = 142.4 kN/m location 7000 mm to 8000 mm of beam starting pointF3 = 142.4 kN/m location 12000 mm to 13000 mm of beam starting point

(1 LBS = 4.45 N)

Figure 3-7 Schematisation truck load on trestle

3.1.8 Wind load east west

In Error! Reference source not found. it is indicated that the design of the trestle should be able towithstand a wind load of 12 LBS/ft

2in the east west direction. This load should be applied to the


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superstructure of the trestle. The superstructure of the trestle consists of the stringers and the concreteroadway. On top of the roadway a handrail and piping are situated. Combined they have a height of 2255mm (640 mm for the stringers, 1200 for the handrail and pipe rack and 165 + 250 mm for the roadway).

It is assumed that the wind load acts perpendicular to the first part of the trestle (bent 1 to 13, which has amore or less north to south orientation) and has no effect on the second part (Bent 14 to 45), see Figure3-8. The wind load is schematized as a uniform distributed load acting on the stringers.

The magnitude of the load can be calculated as follows:

12 LBS/ft2

equals 574 N/m2

Area equals 2255 mm2/mm

Load equals 574 n/m2

* 2255 mm2/mm = 1.29 N/mm

1

Figure 3-8 schematisation wind load east west on trestle

3.1.9 Wind load north south


2in the north south direction acting on the superstructure and 40 LBS/ft

2

in the north south direction acting on the substructure.

The first load should be applied to the superstructure of the trestle. The superstructure of the trestleconsists of the stringers and the concrete roadway. Combined they have a height of 1055 mm (640 mm forthe stringers and 165 + 250 mm for the roadway).

The second load should be applied to the substructure of the trestle, which consists of steel piles with aconcrete collar. The piles have width of 610 mm at the concrete collar and a width of 406 mm above that. Itis assumed that both sections have a height of 2500 mm. The combined surface is therefore 2.54 * 10

6

mm2.

It is assumed that the wind load acts perpendicular to the second part of the trestle (bent 14 to 45, whichhas a more or less east to west orientation) and has no effect on the first part (Bent 1 to 13). The wind loadon the superstructure is schematized as a uniform distributed load acting on the stringers (blue arrows inFigure 3-9) and the wind load on the substructure is schematized as concentrated forces acting on thenode between the pile and the pile cap shown by the green arrows in Figure 3-9.


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The magnitude of the load on the superstructure can be calculated as follows:

50 LBS/ft2

equals 2394 N/m2

Area equals 1055mm2/mm


* 1055 mm2

/mm = 2.42 N/mm1

The magnitude of the load acting on the substructure can be calculated as follows:

40 LBS/ft2

equals 1915 N/m2

Area equals 2,541,000 mm2


* 2,541,000 mm2

= 4866 N

.

Figure 3-9 Schematisation of wind load north south on trestle

3.1.10 Live load

According to Error! Reference source not found. a live load of 50 LBS per square feet should be appliedon the trestle. This load is applied in the model at an arbitrary part of the trestle between two bents. A loadof 50 LBS/ft

2corresponds with a load of 2.39 kN/m

2. The area the load works on is the full with of the

walkway (3.6 m) the walkway exerts the same load onto the underlying Stringers. Hence this load isapplied on the stringers as a uniform distributed load of 2.39 kN/m

2* 0.5 * 3.6 m

2/m

1= 4.3 kn/m

1as shown

in Figure 3-10.


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Figure 3-10 Schematisation of live load on trestle

3.1.11 Wave forces extreme condition

The trestle is located more or less perpendicular to the harbour entrance. It is therefore assumed thatwaves encounter the trestle at a 90 (perpendicular) angle. This holds for the second part (bents 14 to 45)of the trestle. The first part (shore to bent 13) is assumed to be sheltered from waves by the second partand the platforms.

Based on [203] an extreme wave height (Hs) just in front of the trestle of 1.84 m is to be expected. This issimilar to the wave height indicated in Error! Reference source not found.. With a depth at the trestle of6 m and a wave period of 10 s the wave load on the piles can be calculated. This is done using RFWAVEand RF force, APPENDIX F. RFWAVE uses the Hmax which is equal to 1.8 times the Hs.

Since the piles have two dimensions, 406 mm for the first 3.5 m and 610 mm for the part above that (withcollar) two different runs of RF Force have been done (APPENDIX F). The applied wave load on the pilesis combined using the wave load on the 406 mm pile for the first 3.5 m and the wave load on the widersection on the upper part. This leads to the following load distribution on the pile, see Table 3-6:

level total Force

mm kN/m-6000 0.87

-2500 1.08

-2500 1.63

2640 5.01

Table 3-6 Wave forces Trestle extreme condition, hmax = 3.31 m

The same force is applied on all the trestle piles, including the batter piles. The batter piles have a longershaft length but because the applied force acts over a specified length the force is equal in size as on thevertical piles. The only exception is bent 14, where the depth is only 5.5 m. Here the same load is appliedonly over a shorter length of the pile, compensating for its shorter length.

In Figure 3-11 a typical part of the trestle is shown with the wave forces acting on the piles in the global Xdirection.


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Figure 3-11 Schematisation of wave forces

Although wave crests can come in close proximity of the trestle underside no wave uplifting force isassumed on the superstructure.

3.1.12 Wave forces normal condition

In the normal case a wave height just in front of the trestle of 1.01 m (HS) is assumed, [203]. This is largerthan the wave height indicated in Error! Reference source not found.. With a depth at the trestle of 6 mand a wave period of 10 s the wave load on the piles can be calculated. This is done using RFWAVE andRF force [APPENDIX F]. RFWAVE uses the Hmax which is equal to 1.8 times the Hs.

Since the piles have two dimensions, 406 mm for the first 3.5 m and 610 mm for the part above that (with

collar) two different runs of RF Force have been done (APPENDIX F). The applied wave load on the pilesis combined using the wave load on the 406 mm pile for the first 3.5 m and the wave load on the widersection on the upper part. This leads to the following load distribution on the pile, see Table 3-7:

level total Force

mm kN/m

-6000 0.36

-2500 0.43

-2500 0.71

1220 1.22

Table 3-7 Wave forces Trestle normal condition, hmax = 1.82 m

The same force is applied on all the trestle piles, including the batter piles. The batter piles have a longershaft length but because the applied force acts over a specified length the force is equal in size as on thevertical piles. The only exception is bent 14, where the depth is only 5.5 m. Here the same load is applied


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only over a shorter length of the pile, compensating for its shorter length.

3.1.13 Temperature load

As a result of temperature variation loads can occur within the construction. To model this load atemperature load is added to the model. In Error! Reference source not found. temperature variationsare stated to be between 35 F and 110 F. This corresponds to 274 K and 316 K.

Since it is unclear whether the ambient temperature or the construction temperature is described hereengineering practice is used to determine the temperature variations that can occur. The temperature loadis added only to the upper part of the model (the piles are almost completely below water level wheretemperature fluctuations are significantly smaller).

Assuming that the construction is build in winter (average temperature is 15C) and heats up in summer(60C) a positive temperature variation of 45 can occur

Assuming that the construction is build in moderate temperatures (36C) and cools down in winter (15C) anegative temperature variation of 21 can occur.

In Figure 3-12 part of the trestle is shown with the temperature load indicated by blue arrows. Thetemperature load is only added to the part of the structure that is expected to take part in the distribution ofthe load.

Figure 3-12 Schematisation of temperature load on trestle


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3.1.14 Seismic load

Since Libya is a seismically active area the model should include Seismic loads. Seismic load can bedefined using the UBC 1997 [103].

UBC 1997 load definitions requires the following input parameter:1. Seismic zone coefficient, Libya is in zone 2A, Zone is 0.15;2. Importance factor, we are dealing with hazardous facilities, I = 1.25;3. Numerical coefficient R for lateral load in X: jetty is a non building structure, R = 2.9;4. Numerical coefficient R for lateral load in Z: jetty is a non building structure, R = 2.9;5. Soil profile type: assumed is a stiff soil profile, type SD, STYP = 4;6. Near source factor Na, Na = 17. Near source factor Nv, Nv = 1

The seismic calculation uses the weight loads to calculate the resulting seismic force on the structure. The

weights used in this trestle model are:1. self weight of trestle construction2. self weight concrete roadway3. self weight piping

With these parameters entered into the model, STAAD calculates a seismic load in both the X and the Zdirection. These loads are used in several load combinations to determine the residual strength of theTrestle. Besides horizontal seismic forces also a vertical seismic force should be taken into account.

According to [103] the vertical component of the seismic load can be calculated as follows:EQ (Y) = 0.5 *Ca * I * D, where:- Ca (seismic coefficient of soil type and zone) = 0.22- I (importance factor) = 1.25- D = dead weight of construction in kN

It follows that the horizontal component of the seismic force can be calculated by multiplying the dead loadby 0.1375, see Table 3-8 for the input parameters for the vertical seismic component.

Dead weight type: Force (Y) Seismic force (Y)

Concrete roadway 8.8 kN/m 1.21

Concrete collar 0.61 kN/m 0.08

Existing 22 LNG pipe 44.4 kN 6.11

Existing 16 LNG return pipe 16.93 kN 2.33

Existing smaller pipes 15.92 kN 2.09

New 20 LNG pipe 37.89 kN 5.21

New 12 LPG pipe 11.87 kN 1.63

Table 3-8 Seismic forces related to dead weights

3.1.15 Dead weight concrete collar on piles

As is already explained in section 2.1.1 the modelled cross section of the piles, in combination with theconcrete collar neglects the dead weight difference. This difference in dead load is remedied in the modelby adding a uniform distributed load of 0.61 kN/m. This load is added to the piles as shown in Figure 3-13.


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Figure 3-13 Schematisation dead load of concrete collars on piles

3.1.16 Vehicle loading

Vehicle loading is assumed according to BS 5400. A nominal HB loading is analysed to be acting ondifferent parts of the trestle. The shortest wheelbase is assumed to give the most severe effect. Analysesshowed that the vehicle load had the greatest effect on pressure and tension in the platform piles as shownin the following figures. Figure 3-14 show the location of the vehicle load on the trestle for maximumtension in the piles, Figure 3-15 shows the position of the vehicle load for maximum pressure.

Figure 3-14 Vehicle load for maximum tension

Tension


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3.2 LOADING PLATFORMS

In this section the loads on the loading platforms are discussed. These loads are implemented in themodels in order to assess the residual strength of the structure. With respect to the trestle extra loads havebeen applied due to the loading arms and gangway tower. Most of the forces acting upon the model aresimilar for platform A and platform B. Wave forces however, have different magnitudes for either location.This will be discussed in section 3.1.11 and 3.2.12. the same goes for the loading arms. On platform A theexisting loading arms will be taken into account. On platform B the loading arms will be replaced. This isdiscussed in 3.2.13 and 3.2.14.

3.2.1 Self weight construction

The self weight of the Platform construction is calculated by the model itself based on the modelledelements. Elements not in the model will be added as a superimposed dead weight (3.2.2) or as a uniformdistributed Load (3.2.17).

3.2.2 Deadweight concrete roadway

The deadweight of the concrete roadway on the parking area can not be calculated by the model as it isnot part of the model. Therefore an extra superimposed deadweight will be added. The concrete deck isassumed to be 3.00 m wide with 250 mm curbs and a thickness of 165 mm (on the trestle and parkingareas of the platforms, no overlay is assumed). The corresponding load acting on each of the stringers is7.3 kN/m

1, see 3.1.2. Since the parking area spans on two sides of the middle stringers, they bear double

the load; 14.6 kN/m1. In Figure 3-16 the schematised load is shown added to the model of platform B. Thegreen arrows represent the load on the middle stringers which is double.

Figure 3-16 Load due to dead weight of concrete roadway and parking area on platform B


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3.2.3 Dead load existing piping

The deadweight of the gas and water pipes (including contents) located on the trestle and platforms is alsoadded as a superimposed load. The existing piping is schematised as 3 pipes of different diameter:

1. 22 LNG pipe2. 16 LNG return pipe3. 18RLPG pipe4. 6 LPG + 3 LPG return + 8 Firewater

The pipes are assumed to be schedule 40 pipes [104] with the following characteristics, see Table 3-1

Diameter [inch] Outside diameter [mm] Wall thickness [mm] Weight [kg/m]

3 88.9 4.78 9.91

6 168.3 7.11 28.268 291 8.18 42.53

16 406.4 12.70 123.29

18 457.2 14.27 155.91

22 558.8 15.88 212.52

Table 3-9 schedule 40 existing pipe characteristics


3], water [10 kN/m

3] or air/gas


every bent the following pipe loads are modelled as concentrated loads for the existing pipelines1. 22 LNG pipe, filled with liquid gas, F = 44.4 kN;

2. 16LNG gas return pipe filled with gas and air, F = 16.9 kN;3. 18RLPG filled with liquid gas, F = 34.5 kN;4. 6 LPG filled with liquid gas, 3 LPG filled with gas + 8 Firewater filled with water, F = 15.2 kN.

In Figure 3-17 the general position of the pipelines on the trestle is shown. The existing pipelines are alllocated on the western side of the parking area. In Table 3-10 a summation of the locations of the pipelineson the pile caps are given. The 18RLNG pipeline is assumed at the same position of the smaller LPG andservice pipes.


1 1300 mm - 1300 mm

2 2600 mm 1300 mm 1100 mm

3 & 4 3700 mm 1100 mm -

Table 3-10 Location of existing pipeline on parking area bents

The above given positions are used in the model for the position of the concentrated loads schematizingthe dead weight of the existing pipelines. In Figure 3-18 a schematisation is shown of the vertical pipeloads in the model.


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Figure 3-17 cross section of trestle with existing and new Pipelines [202]

Figure 3-18 Schematisation of pipe loads on the model of platform B

3.2.4 Dead load new piping

On the platforms no new piping is modelled since the current situation is normative.


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3.2.5 Horizontal pipe load (Anchor forces)

The piping can exert horizontal forces on the bents as a result of pressure built up inside the piping. Thepipes are fixed at the anchor bents and are able to expand at the expansion loops, the bend in the trestleat bent 13 and the loop crossing the trestle at bent 27. Anchor bents are located at bents 7, 20 and 39.

Since the bents under the parking area as well as the platform are not anchor bents, no anchor force ismodelled on the platform.

3.2.6 Horizontal pipe loads (Friction forces

At the non anchor bents the pipeline exerts a friction force at the bents as the pipeline slides over thesupport. This force is assumed to act towards the anchor bents from both sides. This force is schematisedas a concentrated load acting at the same place as the deadweight of the 22 LNG pipeline working

perpendicular to the bent.

The magnitude of this load is described in Error! Reference source not found. as 2.4 KIPS, whichcorresponds with 10.7 kN. This force is applied on all bents underneath the parking area of both platforms.In Figure 3-19 a schematisation is shown of the horizontal pipe forces in the model of platform B.

Figure 3-19 schematisation of horizontal pipe forces on platform B

3.2.7 Vertical truckload

In Error! Reference source not found. it is indicated that the governing load for the loading platformshould be determined between a truckload: AASHO H20 S44 and a 400 LBS per square foot live load. It is


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assumed that the truck load HS 20-44, according to AASHTO [102] is indicated here. This loadingincorporates a 20 tons tractor truck with semitrailer. The axel loads are given according to APPENDIX E.

To determine the normative loads, the total load of the truck is determined as well as the total load of thelive load acting the concrete deck between two bents.

The truck load measures: 35.6 kN + 142.4 kN + 142.4 kN = 320.4 kN per side is 641 kN in total.

The live load acts on an area of 3.60 m by 14 m and has a load of 400 lbs/ft2

(19.152 kN/m2. the

total live load equals 965 kN

The live load of 400 LBS is the governing load. It is assumed that this loads acts on the parking area of theplatform, see Figure 3-20 for the schematisation of the load on platform B and Figure 3-21 for theschematisation on platform A.

Figure 3-20 Schematisation of truck/live load on parking area of platform B


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Figure 3-21 Schematisation of truck/live load on parking area of platform A

3.2.8 Wind load east west


2in the east west direction. This load should be applied to the

superstructure parking area of platform A. The superstructure of the parking area consists of the stringers,hand rail and pipe rack and the concrete roadway. Combined they have a height of 2255 mm (640 mm forthe stringers, 1200 for the hand rail and pipe rack and 165 + 250 mm for the roadway). The platformsuperstructure consists of stringers, high members and a concrete roadway. On the outside they have aheight of 1465 mm (550 mm + 500 mm + 165 mm + 250 mm. The middle part of the platform has acombined height of 1751 mm (836 mm +500 mm + 165 mm + 250 mm).

It is assumed that the wind load acts perpendicular to parking area (bent 49 to 51), which has a more orless north to south orientation) and also on the loading platform itself. The wind load is schematized as auniform distributed load acting on the stringers as shown in Figure 3-22.

The magnitude of the load on the parking area can be calculated as follows:

12 LBS/ft2

equals 574 N/m2

Area equals 2255 mm2/mm


* 2255 mm2/mm = 1.29 N/mm

1

The magnitude of the load on the loading platform can be calculated as follows:

12 LBS/ft2

equals 574 N/m2

Outer area equals 1465 mm2/mm

Outer load equals 574 n/m2

* 1465 mm2/mm = 0.841 N/mm

1

Middle area equals 1751 mm2/mm

Middle load equals 574 n/m2 * 1751 mm2/mm = 1.005 N/mm1


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Figure 3-22 Schematisation of wind load east west

3.2.9 Wind load north south

In Error! Reference source not found. it is indicated that the entire structure should be able to withstanda wind load of 50 LBS/ft

2in the north south direction acting on the superstructure and 40 LBS/ft

2in the

north south direction acting on the substructure.

The first load should be applied to the superstructure of the loading platform. The platform superstructureconsists of stringers, combined members and a concrete roadway. On the outside they have a height of915 mm (500 mm + 165 mm + 250 mm. The middle part of the platform has a combined height of 1715mm (800 mm +500 mm + 165 mm + 250 mm).

The second load should be applied to the substructure of the platform, which consists of steel piles with aconcrete collar. The piles have width of 610 mm at the concrete collar and a width of 406 mm above that. Itis assumed that the bottom section has a height of 2500 mm and the top section a height of 1400mm. Thecombined surface is therefore 2.09 * 106 mm2.

It is assumed that the wind load acts perpendicular to the north side of the loading platform, which has amore or less north to south orientation) and has no effect on the parking area. The wind load on thesuperstructure is schematized as a uniform distributed load acting on the stringers and the wind load onthe substructure is schematized as concentrated forces acting on the node between the pile and the pilecap, see Figure 3-23. In this figure the load on the piles is schematised by the blue arrows acting on thetop of the piles.

The magnitude of the load on the superstructure can be calculated as follows:

50 LBS/ft2

equals 2394 N/m2

Middle area equals 915 mm2/mm

Middle Load equals 2394 n/m

2

* 915 mm

2

/mm = 2.19 N/mm

1

Outer area equals 1715 mm

2/mm

Outer Load equals 2394 n/m2

* 1715 mm2/mm = 4.11 N/mm

1


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The magnitude of the load acting on the substructure can be calculated as follows:

40 LBS/ft2

equals 1915 N/m2

Area equals 2,090,000 mm2


* 2,090,000 mm2

= 4,009 N per pile

It is tentatively assumed that no sheltering occurs due to the piles. Therefore the wind load on thesubstructure is assumed to act on all the piles of the platform as can be seen in Figure 3-23.

Figure 3-23 schematisation of wind load north south

3.2.10 Live load parking area 50 LBS per square foot

On the parking area of the platform an additional live load of 50 LBS/ft2

is projected similar to the live loadprojected on the trestle. A load of 50 LBS/ft

2corresponds with a load of 2.39 kN/m

2. This load is added to

the model as a uniform distributed load. Since the roadway of the parking area is not a part of the model,this load has to be added to the stringers supporting the roadway, as shown in Figure 3-24. The distancebetween the stringers is 3.00 m. The load on the stringers is therefore 2.39 kN/m

2* 3m * 0.5 = 3.55 kN/m

1.

In Figure 3-24 the load on the middle stringers is shown in green. Here a double loads acts on the stringerssince the concrete parking area extends on two sides of the stringer. The load in this case is 7.1 kN/m

1.


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Figure 3-24 schematisation of live load on parking area and roadway

3.2.11 Wave forces extreme condition

The platform is located more or less perpendicular to the harbour entrance. It is therefore assumed thatwaves encounter the trestle at a 90 (perpendicular) angle. This also holds for the platforms.

Based on [202] an extreme wave height (Hs) just in front of platform A of 1.23 m is to be expected. This issmaller than the wave height indicated in Error! Reference source not found.. In front of platform B an

extreme wave height (Hs) of 1.84 is to be expected. With a depth at the platform of 9 m and a wave periodof 10 s the wave load on the piles can be calculated. This is done using RFWAVE and RF force. RFWAVEuses the Hmax which is equal to 1.8 times the Hs.

Since the piles have two dimensions, 406 mm for the first 5.5 m and 610 mm for the part above that (with

collar) two different runs of RF Force have been done (APPENDIX F). The applied wave load on the pilesis combined using the wave load on the 406 mm pile for the first 5.5 m and the wave load on the widersection on the upper part. This leads to the following load distribution on the piles of platform A, see Table3-11:

Level Total Force

Mm KN/m

-9000 0.29

-2500 0.38

2500 0.64

460 0.99

Table 3-11 Wave forces Platform A extreme condition, hmax = 2.21 m

And the load distribution as shown in Table 3-11 for the wave loads on the piles of platform B:


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Level Total Force

Mm KN/m

-9000 0.60-2500 0.86

2500 1.38

460 2.51

Table 3-12 Wave forces Platform B extreme condition, hmax = 3.32 m

The same force is applied on all the platform piles, including the batter piles. The batter piles have a longershaft length but because the applied force acts over a specified length the force is equal in size as on thevertical piles. The piles of the parking area are assumed to be sheltered by the platform piles. In Figure3-25 the schematisation of the wave load in the model is shown. The wave forces are acting in thenegative X direction.

Figure 3-25 Schematisation of wave load on platform

3.2.12 Wave forces normal condition (Xdir)

In the normal case a wave height just in front of platform A of 0.67 m (HS) is assumed, [203]. This is similarto the wave height indicated in Error! Reference source not found.. In front of platform B a wave height

of 1.01 m is obtained. With a depth at the platform of 9 m and a wave period of 10 s the wave load on thepiles can be calculated. This is done using RFWAVE and RF force [APPENDIX F]. RFWAVE uses the Hmaxwhich is equal to 1.8 times the Hs.

Since the piles have two dimensions, 406 mm for the first 3.5 m and 610 mm for the part above that (withcollar) two different runs of RF Force have been done (APPENDIX F). The applied wave load on the pilesis combined using the wave load on the 406 mm pile for the first 3.5 m and the wave load on the widersection on the upper part. This leads to the following load distribution on the pile, see Table 3-13


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Level Total Force

Mm KN/m

-9000 0.11-2500 0.14

2500 0.27

460 0.33

Table 3-13 Wave forces Platform A normal condition, hmax = 1.21 m

And the following load distribution for the piles of platform B, see Table 3-14

Level Total Force

Mm KN/m

-9000 0.21

-2500 0.272500 0.48

460 0.67

Table 3-14 Wave forces Platform B normal condition, hmax = 1.82 m

The same force is applied on all the platform piles, including the batter piles. The batter piles have a longershaft length but because the applied force acts over a specified length the force is equal in size as on thevertical piles. The piles of the parking area are assumed to be sheltered by the platform piles.

3.2.13 Loading arms dead weight

The loading arms on the platforms are not part of the models and are therefore modelled as loads. theloading arms on platform A will remain intact, whereas the loading arms on platform B will be renewed. Inthe following sections the modelling of the loading arms for both platforms is discussed.

Platform A

The loading arms on platform A are placed upon a steel structure which is supported by the concrete deck.This structure is not in the model; therefore the forces of the loading arm acting upon the steelsuperstructure will have to be tranversed to the supports. This is done schematising the structure as portalframe with the loading arm on top of it, see APPENDIX D. The load of the wind force and the dead load aretranslated into support reactions that counteract the loads. These support loads will be entered in themodel as the loading arm loads in the opposite reactions. This leads to the following loads, Table 3-15. In

APPENDIX D the base load diagram is shown for the existing loading arms.

LOAD FORCE [kN] R1,V R1,H R2,V R2,H

Dead load (P) -145 75 kN 0 70 kN 0

Wind load (Fv) 24 -102.4 kN -10 kN 102.4 -14

Table 3-15 Reaction loads loading arms platform A

Platform BThe loading arms for platform B are placed directly onto the concrete deck. They are also schematized asa dead weight load. The dead weight acts not in the centre line of the arm; therefore the dead weightexerts both a force on the underlying concrete plate as well as a moment. In APPENDIX D aschematisation of the loading arms can be found, the dead weight load is summarised in the table below,Table 3-16


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LOAD TYPE FORCE ARM MOMENT

Dead weight (P) - 389 kN 900 mm 350 kNm

Torque force (T+) - 175 kN 1000 mm 175 kNmTorque force (T-) +175 kN 1000 mm 175 kNm

Table 3-16 Dead weight forces caused by loading arm

The moment created by the dead weight will be schematised as two torque loads at the edges of the footplate. The moment arm of the torque forces is therefore equal to half the width of the foot plate, which is2.0 m (the arm is 1.0 m). The size of the torque forces can be calculated by dividing the dead weightmoment in two and again dividing by the arm (350 knm/2/1.0 m = 175 kN). The torque forces will be addedto the model creating a moment in the longitudinal axis of the platform.

Three loading arms will be placed on top of the platform. APPENDIX D shows the location of the loadingarms on the platforms, the schematisation of the dead load and torque forces is shown in Figure 3-26.

Figure 3-26 schematisation of dead load of loading arms

3.2.14 Loading arms wind force

The wind force acting on the loading arms of platform B is also schematised as a force combined with amoment. The force acts in the horizontal direction. In this case it is assumed that the wind encounters theplatform at a perpendicular angle coming from the west side. The force is schematised at the centre pointof the loading arm. The wind force on the loading arms for platform A is already described in the previoussection.

In APPENDIX D a schematisation of the loading arms can be found, the wind load is summarised in thetable below, Table 3-17


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Wind force (Fv) 98 kN 10,450 mm 1024 kNm

Torque force (T+) - 512 kN 1000 mm 512 kNmTorque force (T-) +512 kN 1000 mm 512 kNm

Table 3-17 wind load forces caused by loading arm

The moment created by the dead weight will be schematised as two torque loads at the edges of the footplate. The moment arm of the torque forces is therefore equal to half the width of the foot plate, which is2.0 m (the arm is 1.0 m). The size of the torque forces can be calculated by dividing the wind force momentin two and again dividing by the arm (1024 knm/2/1.0 m = 512 kN). The torque forces will be added to themodel creating a moment in the longitudinal axis of the platform, see Figure 3-27 for the schematisation ofthe loads. The forces are acting in the same direction as the extreme wind forces.

Figure 3-27 Schematisation of wind forces loading arm

3.2.15 Gangway tower dead weight

The gangway tower on the platform is not part of the model and schematized as a dead weight load. Thedead weight acts not in the centre line of the tower; therefore the dead weight exerts both a force on theunderlying concrete plate as well as a moment. In APPENDIX D a schematisation of the gangway towercan be found, the dead weight load is summarised in the table below, Table 3-18. The dead weight of thetower is assumed to be 185 kN. For the wind loads the same forces as for the loading arms is assumed.


Dead weight (P) - 185 kN 900 mm 167 kNm

Torque force (T+) - 84 kN 1000 mm 175 knm

Torque force (T-) +84 kN 1000 mm 175 knm

Table 3-18 Dead weight forces caused by gangway tower

The moment created by the dead weight will be schematised as two torque loads at the edges of the foot


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plate. It is assumed that the loading tower has the same foot plate as the loading arms. The moment armof the torque forces is therefore equal to half the width of the foot plate, which is 2.0 m (the arm is 1.0 m).The size of the torque forces can be calculated by dividing the dead weight moment in two and again

dividing by the arm (167 knm/2/1.0 m = 84 kN). The torque forces will be added to the model creating amoment in the longitudinal axis of the platform.

One gangway tower will be placed on top of the platform. The location of the gangway tower is shown inAPPENDIX D; see Figure 3-28 for the schematisation of the dead load.

Figure 3-28 schematisation of dead load gangway tower

3.2.16 Gangway tower wind force

The wind force acting on the gangway tower is also schematised as a force combined with a moment. Theforce acts in the horizontal direction. In this case it is assumed that the wind encounters the platform at aperpendicular angle coming from the west side. The force is schematised at the centre point of thegangway tower.

In APPENDIX D a schematisation of the gangway tower can be found, the wind load is summarised in thetable below, Table 3-19


Wind force (Fv) 98 kN 10,450 mm 1024 kNm

Torque force (T+) - 512 kN 1000 mm 512 kNm

Torque force (T-) +512 kN 1000 mm 512 kNm

Table 3-19 wind load forces caused by gangway tower

The moment created by the wind load will be schematised as two torque loads at the edges of the footplate. The moment arm of the torque forces is therefore equal to half the width of the foot plate, which is2.0 m (the arm is 1.0 m). The size of the torque forces can be calculated by dividing the wind force momentin two and again dividing by the arm (1024 knm/2/1.0 m = 512 kN). The torque forces will be added to the

model creating a moment in the longitudinal axis of the platform, see Figure 3-29.


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Figure 3-29 schematisation of wind load gangway tower

3.2.17 Uniform distributed load

To compensate for the absence in the model of the constructions on top of the concrete deck of the loading

platform a uniform distributed load will be taken acting upon this deck. A load of 4 kN/m

2

is assumed.

3.2.18 Hawser pull

On top of the loading platform two bollards are situated. According to Error! Reference source not found.

on these bollards a hawser pull of 50 kips should be applied. 50 kips corresponds with a force of 222.4 kN.This force acts at the bollard in a direction that is not specified. It is assumed here that the force acts onone bollard in the positive Z direction as shown in Figure 3-30.

Since there is a vertical distance between the point at which the line exerts its force on the bollard and thebeam that the bollard eventually passes this load onto, a moment needs to be added to the model.

The elevation of the line bollard connection point above the substructure is estimated to be 500

mm. The forces acting in the Z-direction = 222.4 kN.

The corresponding moment is 222.4 kN * 500 mm = 111.2 kNm

The width of the footplate in the direction perpendicular to the berthing face is 500 mm, the torquearm is 500/2 = 250 mm.

The corresponding torque force is 222.4 kN

The torque forces will be added to the model at a distance of 250 mm on the berth side and the back sideof the centre point of the bollard, see for the schematisation of the load.


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Figure 3-30 Schematisation of bollard load

3.2.19 Breasting forces; ship impact load

Ships mooring at the platform can exert a breasting force at the platform due to ship impact. In Error!Reference source not found. a ship impact force of 20 tons over a fender length of 10 foot is prescribed.This corresponds with a force of 196 kN over 3 m. In front of the loading platform a fender system islocated. It is assumed that the indicated 196 kN ship impact force transverses through the fenders unto theplatform as shown in APPENDIX G. The ship impact load is modelled on the platform as concentratedloads acting on the outer two pile caps of the platform as shown in Figure 3-31.


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Figure 3-31 schematisation of ship impact load

3.2.20 Temperature load

As a result of temperature variation loads can occur within the construction. To model this load atemperature load is added to the model. In Error! Reference source not found. temperature variationsare stated to be between 35 F and 110 F. This corresponds to 274 K and 316 K.

Since it is unclear whether the ambient temperature or the construction temperature is described hereengineering practice is used to determine the temperature variations that can occur. The temperature loadis added to the upper part of the model. The steel piles are mostly below water level and are therefore

subjected to much smaller temperature fluctuations. Hence the temperature load is only added to thesuperstructure and pile caps of the platform model, see Figure 3-32.

Assuming that the construction is build in winter (average temperature is 15C) and heats up in summer(60C) a positive temperature variation of 45 can occur

Assuming that the construction is build in moderate temperatures (36C) and cools down in winter (15C) anegative temperature variation of 21 can occur.


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Figure 3-32 Schematisation of temperature load

3.2.21 Seismic load

Similar tot the trestle seismic load is added to the platforms acting in three main directions, (X,Y and Z).

The seismic calculation uses the weight loads to calculate the resulting seismic force on the structure. Theweights used in this platform model are:

1. self weight of platform and parking area construction2. self weight concrete roadway3. self weight piping4. self weight loading arms5. self weight gangway tower6. self weight concrete collar7. self weight represented by UDL = 4 kN/m

2

With these parameters entered into the model, STAAD calculates a seismic load in both the X, Y and the Zdirection. These loads are used in several load combinations to determine the residual strength of theTrestle.

3.2.22 Self weight concrete collar

As is already explained in section 2.1.1 the modelled cross section of the piles, in combination with theconcrete collar neglects the dead weight difference. This difference in dead load is remedied in the modelby acting a uniform distributed load of 0.61 kN/m. This load is added to the piles as shown in Figure 3-33.


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Figure 3-33 Schematisation of self weight concrete collar on piles

3.2.23 Self weight omitted concrete deck

In section 2.2.4 already reference is made about the size of the concrete deck on the loading platform thatis smaller in the model than in reality. To accommodate for the accompanying weight difference a uniformdistributed load is added to the sides of the platform as shown in Figure 3-34. The magnitude of the forcesto be added to the platform is determined as follows.

Volume of concrete is calculated by the overhang (0.15 and 0.40m) multiplied by the thickness of theconcrete. Assumed is 250 mm + 165 since concrete curbs run along the edges of the platform. Theconcrete weight is assumed to be 24.5 kN/m

In total this leads the following loads:- berth edge and backside: 0.40 * 0.415 * 24.5 = 4.07 kN/m

- sides: 0.15 * 0.415 * 24.5 = 1.53 kN/m


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Figure 3-34 Schematisation of dead load omitted part of the concrete deck

3.2.24 Seismic moment loading arms

The loading arms are not part of the model but are schematised as loads acting on the concrete deck.Since the mass of the loading arms is concentrated at a certain height above the platform in case ofseismic motion an additional moment has to be modelled. According to APPENDIX X, the force and arm ofthe seismic motion of the loading arms on platform B are as follows:

- Fsh = 99.25 kN, arm As = 9650 mm- Fsv = 66.30 kN, arm B = 900mm

From these forces and arms two moments can be derived:- Msh = 957.76 kNm- Msv = 59.67 kNm

The horizontal moment is assumed to act in both X and Z direction occurring simultaneously with seismicforces in the corresponding direction. The vertical moment is assumed to act simultaneously with verticalseismic forces and has an orientation along the X axis. Figure 3-35 shows a schematisation of the seismicforces acting in the Z direction.

For platform A no such values are obtained. Therefore this mechanism is ignored.


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Figure 3-35 schematisation of seismic forces loading arms on platform A

3.2.25 Vehicle loading

Vehicle loading is assumed according to BS 5400. A nominal HB loading is analysed to be acting ondifferent parts of the trestle. The shortest wheelbase is assumed to give the most severe effect. Analysesshowed that the vehicle load had the greatest effect on pressure and tension in the platform piles as shownin the following figures. Vehicle loading located as shown in Figure 3-36 leads to the highest tension forcesin the piles of the platform whereas vehicle loading as shown in Figure 3-37 leads to the highestcompression forces in the platform piles.


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Figure 3-36 Schematisation of vehicle loading for maximum tension

Figure 3-37 schematisation of vehicle loading for maximum pressure


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4 Load combinations

The STAAD models will be tested for 5 basic loading combinations. The loading cases are assembledaccording to [106], and consist of a normal case, extreme metocean case, extreme mooring case, extremeberthing case and a Seismic case. Since no mooring facilities exist in the vicinity of the trestle, in themooring case only the anchor force can be applied to this model. The loading combinations are chosen insuch a way as to maximise the pressure and tension in the piles. In directional cases, pressure ismaximised by adding live loads and applying a load factor of 1.2 for dead loads and tension is maximisedby omitting live loads and applying a load factor of 0.9 for dead loads.

The seismic cases are determined according to UBC 1997 [103]. The UBC states that In the case of bothhorizontal and vertical components, the horizontal components should alternatively be multiplied by 0.3while the other components are multiplied by 1. For the 105 cases the X direction is assumed normativeand the Z component is multiplied by 0.3, whereas the 107 cases assume the Z direction normative and

multiply the X direction by 0.3. Within these cases the directions are alternatively varied. The cases with anegative direction for the Z component are optimised for tension by multiplying the dead load factors by0.9.

Special attention is given to the piles of the loading platforms.

The following cases were defined:

101 Load combination normal condition;

1011 normal condition with positive temperature difference (+45K)

1012 Normal condition with negative temperature difference (-20)

102 Load combination extreme metocean1021 Extreme metocean with live loads applied

1022 Extreme metocean without live loads

103 Load combination extreme mooring

1031 mooring with live loads applied

1032 mooring without live loads applied

104 Load combination extreme berthing1

1041 berthing with live loads applied

1042 berthing without live loads applied

105 Load combination seismic

8 load combinations have been derived for the seismic loads, alternating positive and

negative directions. X is the predominant direction.

107 Load combination seismic

8 load combinations have been derived for the seismic load, alternating positive and

negative directions. Z is the predominant direction.

In Figure 4-1 and Figure 4-2 overviews are given of all the determined load cases.

1Berthing load is only applied on the platform models


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Figure 4-1 Load combinations ULS


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Figure 4-2 Load combinations SLS


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5 Results

In this section the results of the STAAD models are discussed. For the loading platform focus of thediscussion is on the normal forces in the piles. Tabulation of the results can be found in the appendices.

All the steel members are checked according tot the British Standard 5950 [105]. The indicated steel gradeis A36 with a yield-strength of 248 kN/m

2.

5.1 TRESTLE

5.1.1 Design results

In APPENDIX O a table of the design results of the STAAD model can be found. STAAD checks thebeams according to BS 5950. This table shows that for three members, the piles of bents 3 and 4, theloads exceed the capacity according to BS 5950. The cause of this failure can be found in the modelling ofthe expansion joints as releases. In Figure 5-1 can be seen that the section of the trestle of which the failedmember is a part is placed between two releases and contains no transverse fortification in the form ofbatter piles. The section on itself is therefore not strong enough to take the load.

Figure 5-1 Deflection of tres

Gangway Tower Dead Weight

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