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Vision Industrial Park Namibia

Pre-Feasibility Study

Bulk Terminal

Appendix D - Structural Report

Prepared for

GECKO HOLDINGS

Prepared by

WML Coast (Pty) Ltd

VISION INDUSTRIAL PARK Pre-feasibility Study on Bulk Terminal APPENDIX D - STRUCTURAL REPORT 22 July 2011

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Vision Industrial Park Namibia

Pre-feasibility Study

Bulk Terminal Appendix D - Structural Report

Contents

1 Introduction ................................................................................... 3

2 Design Concept ............................................................................. 3

3 Design Pararmeters ...................................................................... 4

3.1 Design Methods and Standards ..................................................................... 4

3.2 Design Loads .................................................................................................... 5 3.2.1 Design Vessel ............................................................................................................ 5 3.2.2 Live Loads .................................................................................................................. 5 3.2.3 Dead Load .................................................................................................................. 5 3.2.4 Berthing Loads .......................................................................................................... 5 3.2.5 Mooring/Bollard Loads ............................................................................................... 6 3.2.7 Other Loads ................................................................................................................. 6

4 Piling Aspects ................................................................................ 7

4.1 Piling at Swakopmund Location ..................................................................... 7 4.1.1 Open Piled Access Causeway Piling ........................................................................ 7 4.1.2 Quay Structure Piles .................................................................................................. 7 4.1.3 Mooring Dolphin Piles ................................................................................................ 8

4.2 Piling Walvis Bay Location .......................................................................... 11

5 Concrete Deck Structure ............................................................ 14

6 Crack Control ............................................................................... 15


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1 Introduction

This report has been compiled to describe the preliminary design process for the various structural aspects of the bulk terminal options at Swakopmund and Walvis Bay. It should be noted that design is limited to development of concept structural options and sizing of structural elements towards cost estimation.

This report is an Appendix to the main report “Vision Industrial Park – Pre-feasibility Study on Bulk Terminal – Final Report” dated 22 July 2011 which should be read in conjunction with this report.

2 Design Concept

The proposed protective structures and bulk terminal concepts can all be divided into different sections sharing the similar characteristics, namely: open piled access causeway, armoured rock access causeway, armoured rock breakwater, quay structure for bulk terminal, quay bridge structures and mooring dolphins.

This report will look at the design process followed in determining material quantities for all parts of the proposed structural concepts, except for the armoured rock access causeway and breakwater (which are dealt with in the breakwater design report).

The two locations considered for the bulk terminal (the Port of Walvis Bay and Swakopmund) vary greatly with regards to the exposure conditions and sea floor. Walvis Bay offers protection from severe wave action and the sea floor consist of sand. The location in Swakopmund is totally exposed and the sea bed consists of rock.

Various different configurations were considered in order to allow the client to choose an optimum configuration of the structures as well as the best location for the project.

The desired location for the project is along the coast at Swakopmund at a location between Mile 6 and Mile 17. In this location the land onshore is potentially available for development directly along the shore. It is also favoured due to its close proximity to the mines (where the products from the industrial park are required). The two biggest drawbacks of building in this location are the rocky sea floor and the exposed conditions. This negates the possibility of dredging and necessitates the building of very long access structure in order to reach the required depth necessary for the design vessels to be able to berth safely. Construction time at this location is also greatly increased when compared to the location at Walvis Bay, due to the difficulty of socketing piles into bed rock.

The exposed nature of the structure at Swakopmund has led to the design concept of seperating the mooring structures from the quay structure. This is to protect the quay structure in case approach velocities are exceeded.


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Mooring dolphins with fenders are provided underneath the quay structure at intervals of 36m. Any damage caused by high energy impacts during berthing will thus only affect the mooring dolphins and not the quay super structure.

The alternate location is in the Port of Walvis Bay. Here there is significant protection from oceanic conditions as well as a sandy sea bed. This results in a smaller, cheaper structure that will take less time to construct than the options at Swakopmund. The disadvantage of building the structure here is that the land for development is behind the dunes, i.e. far from shore. Therefore extra costs will be incurred in order to secure space for the development. Another consideration is that this location is further away from the mines, this leads to an increase in haulage distance and hence increases the cost of importing/exporting materials at the terminal.

Furthermore, the layout of the quay structure differs significantly between the proposals for Swakopmund and Walvis Bay. At Swakopmund berthing and mooring can only take place on one side of the quay structure. This is neccessary due to the fact that the quay structure needs to be in close proximity to the breakwater in order to be sufficiently protected. Another reason is that dredging is not possible due to the rock formations on the sea floor, thus to provide berthing/mooring facilities for larger vessels it is neccessary to extend the quay further into the sea.At Walvis Bay berthing is possible on both sides of the quay structure due to the protected nature of the location and the possibility of dredging to cater for vessels of a larger size.

3 Design Pararmeters

3.1 Design Methods and Standards

The design codes used are listed below:

• Design of Steel Piling: SANS 10162-1: 2005 (The structural use of steel, Part 1: Limit-state design of hot-rolled steelwork).

• Design of Reinforced Concrete (including stressing tendons): SABS 0100-1 (The structural use of concrete, Part 1: Design)

• Determination berthing loads: PIANC 2002 (Guidelines for the Design of Fender Systems: 2002 Marcom Report of WG330)

• Determination of Live Loads: Technical Manual for Highways 7 • Load Combinations: SANS 10160 (Basis of structural design and actions for

buildings and industrial structures).

Due to the fact that the design process was preliminary only, many detail calculations were omitted due to being insignificant in respect to the material quantities they represent. In other cases certain assumptions were made by the design engineer in order to simplify the design/costing process. What follows is a look at the procedures followed to determine necessary material quantities for each option.


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3.2 Design Loads

3.2.1 Design Vessel

The design vessel for the final stage of the project was used as the standard for all calculations. This vessel has a mass of 80,000t. Due to the exposed nature of the structure a relatively high approach speed of 0, 2m.s-1was assumed.

3.2.2 Live Loads

The access structure as well as the quay structure was assumed to be subjected to a uniformly distributed load of 30kPa. This was determined through the adaptation of the criteria set forth in the Technical Manual for Highways 7. This load was further multiplied by a factor of 1.6 to get the ultimate limit state (ULS) design loads.

Initially the quay crane was included as its own load case, but it became apparent that the assumed live load was always going to be the critical loading case when compared to the specified crane. A separate load case for the crane was therefore discontinued.

3.2.3 Dead Load

Due to the fact that initial design was preliminary only and to be used for costing purposes it was assumed that it is sufficient to consider the dead load as an evenly distributed load across the deck. The value of this load was determined to be 18kPa by taking the total weight of concrete in the deck and dividing it by the surface area. This value was multiplied by a factor of 1.2 to get the ULS design loads.

3.2.4 Berthing Loads

Berthing loads were determines in accordance with PIANC 2002.

The energy required to be dissipated by the fenders was determined as follows.

0.5

Where:


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1.8

0.667

1

1

Therefore:

0.5 80000 0.2 1.8 0.667 1 1

1920

Using a safety factor of 1.5 as suggested by the Trelleborg (Safe Berthing and Mooring) product catalogue, the design energy that needs to be dissipated comes to 2880kJ. Assuming that two fenders will be placed next to each other and that energy will be uniformly dissipated between the two fenders, we obtain design energy of 1440kJ per fender.

Using this value and the Trelleborg Marine Fender Catalogue, a SCN 1600 fender was chosen. Therefore the required force that needs to be resisted by the berthing structure (the quay structure in the case of Walvis Bay, and the berthing dolphin in the case of Swakopmund) is 1855kN per fender (from the Energy-Reaction force diagrams supplied by Trelleborg Marine) or a total of 3710kN per dolphin/contact point. Applying a live load safety factor of 1.5, the final design force comes to 5565kN.

3.2.5 Mooring/Bollard Loads

In the design of the quay structure for Walvis Bay (Option 4) it was necessary to apply berthing and mooring loads simultaneously, due to the fact the mooring takes place on both sides of the structure. Thus, one ship could be moored while another berths on the other side. It was assumed that mooring would be facilitated by four mooring lines each carrying a load of 1000kN.

For the dolphin design, in the case of the Swakopmund locations, Berthing and mooring loads were applied alternately. The reasoning behind this was that a ship cannot berth and be moored to the same dolphin at the same time.

3.2.7 Other Loads

Due to the open nature of the trestle structure, the limited time available for the design of the structures and the magnitude of the other design forces it was decided to ignore the effect of


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wind, wave and current loads as well as temperature. Provision was made for expansion/contraction joints at the discretion of the engineer.

4 Piling Aspects

4.1 Piling at Swakopmund Location

The fact that it is necessary to socket the piles into bedrock at this location makes it impractical to use steel piles. The use of concrete piles cast in a steel tubing allows for greater connectivity between the socketed base and the pile. The forces required to be resisted by the piles was determined with the help of a finite element model. The final reinforced pile design was done with the reinforced concrete design modules in the Prokon design package and the structural effect of the steel pile casing was ignored (it effectively acts as corrosion protection for the reinforced concrete core).

4.1.1 Open Piled Access Causeway Piling

The access trestle piling was designed with a distributed transverse load equal to 10% of the deck live load. This force was further multiplied by a safety factor of 1.6 to give a total lateral force of 96kN/m.

4.1.2 Quay Structure Piles

The loading combination used to design this quay structure is shown in figure 1 below. No berthing loads were applied as mooring dolphins are provided at regular intervals and a high energy collision with the quay structure is unlikely. Instead the structure was designed to take all the live/dead loads described under loading conditions as well as a lateral force of 120kN/m. This force is equal to 10% of the deck live load and has been multiplied by a safety fact of 1.6. It assumed to be sufficient to simulate wind and current loads as well as any lateral loads caused by movement on top of the deck.


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Figure 1: Critical Loading Case for Quay Structure at Swakopmund

The critical piles loads were identified and all quay structure piles were designed according to these loads. The procedure followed is described at the end of the section on piles.

4.1.3 Mooring Dolphin Piles

Due to the positioning of the mooring dolphins underneath the quay structure, they are not subjected to any loads except the berthing impact load and mooring loads. The forces in the piles were determined through the use of the finite element model that was loaded either with the berthing or the mooring loads. The two different load cases are shown in figures 2 and 3.


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Figure 2: Load Case 1 for Mooring Dolphin Design


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Figure 3: Load Case 2 for Mooring Dolphin Design

From these models the maximum forces required to be resisted by the piles was determined for each load case, and the critical load case for each pile was identified. The reinforced concrete design modules of Prokon were then used to determine the required reinforcing in each pile. The procedure used to determine the required reinforcing in a circular concrete pile is described below.

The forces required to be resisted by the back piles in the ULS are as follows:

2859

, 320

, 323

, 3


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, 55

The pile was assumed to be fully fixed at the socket and connected monolithically connected to the pile capping beam. Thus the column has end conditions of type one on both ends and the effective length factor is equal to 0.75. The column is also assumed to be braced in both X and Y directions.

This data is input into the circular concrete column design module in the Prokon analysis software. The design process followed by the module is as follows:

(1) The column design charts are constructed.

(2) The design axis and design ultimate moment is determined.

(3) The steel required for the design axial force and moment is read from the relevant design chart.

(4) The area steel perpendicular to the design axis is read from the relevant design chart.

For this pile:

, 10797

, 12566 10 40

The shear reinforcing required is nominal and equates to R10 bars spaced at 300mm.

All other reinforced piles (including quay and access trestle piles in Swakopmund) were designed according to the same methods.

4.2 Piling at Walvis Bay Location

The protection offered by the Port of Walvis Bay makes approach and berthing velocities easier to controland predict, and thus the risk of damage to the structure is much lower than in the exposed areas at Swakopmund. This negates the need for mooring dolphins as the fenders can be attached to the quay structure. Raker piles are used in the quay structure to counter the lateral berthing forces (see drawing 100610/433).

The sandy nature of the sea floor in the Port of Walvis Bay makes driving piles to depths possible. In order to reduce construction time the piles for the proposed structure in this location were designed as hollow circular sections. The required pile size was determined using a finite element model (shown below) and applying the berthing loads, mooring loads, live deck loads and dead loads in different combinations until a critical state was reached. The critical combination is shown below in figure 4. It consists of the berthing force of one vessel, a vessel moored with four lines, each carrying a load of 1000kN, and a full live and dead load.


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Figure 4: Critical Loading Case for Quay Structure at Walvis Bay

The pile size was chosen through trial and error with the help of the Prokon design calculations. The interaction requirements that need to be met are expressed by the following formulas as found in SANS 10162-1:2005.

a) Cross Sectional Strength

1

b) Overall Member Strength

1

c) Lateral Torsional Buckling Strength

1


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Where:

,

When using a 1500x19mm steel pipe, and making use of the Prokon Design calculations module, the interaction diagrams for the critical piles are as follows:

a)

1100024000

21708640

49

8640 0.73

b)

1100020000

9718640

238640 0.67

c)

1100021000

21708640

23

8640 0.78

Therefore we can deduce that 1500x19mm piles will be sufficient.

The rigidity of the deck/pile capping beams cause forces to be relatively evenly distributed between the piles, this coupled with the fact that the berthing impact could happen at various points along the structure lead to a design specification of 1500x19mm piles throughout. It is necessary to treat these piles with a form of corrosion protection before installation in order


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to ensure the longevity of the structure. Cathodic protection has been provided for in the quantity calculations to allow for corrosion protection.

The same piles were specified for the access structure without further calculations. It was assumed that, due to the decreasing lengths of the piles and the loading conditions at this location, the actual pile sizes derived from a detailed design of the situation would not differ enough to create a significant change in the cost of the overall structure.

5 Concrete Deck Structure

The suspended deck was designed to consist of 18m precast concrete beams. These beams span the gap between portals and tie in to the pile capping beams. There are two different types of beams that form the deck of the structure: “small T-beams” and “crane rail beams” (refer to attached drawings for cross sections of each particular option). The small T-beams are used to form the entire deck of the access structure and a large part of the quay structure deck. Two (four in the case of Walvis Bay) crane rail beams are provided per span on the quay structure. Sections of the respective quay structures are shown in figures 5 & 6 below:

Figure 5: Section of proposed quay structure for Swakopmund


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Figure 6: Section of proposed quay structure for Walvis Bay

It is envisaged that the pile capping beams be constructed as precast trough units to be filled on-site with an in-situ cast. This will make the handling and placing of these beams easier as well as allowing space for steel from the precast deck beams to tie into the beam and create a rigid deck once the final in-situ casts have set.

6 Crack Control

Due to the exposed nature of the structure it is neccessary to limit crack control in order to protect the steel reinforcement. The standard design limitation on crack controlin reinforced concrete is 0.3mm.This is often adjusted in marine environments and limited to 0.15mm for the ultimate limit state and 0.1mm for the serviceability limit state in order to offer greater corosion protection for the reinforcing steel.

Due to the conservative approach taken in determining the design live loads, it becomes impractical to limit the cracks to 0.15mm. The deck structure was therefore designed to allow cracking up to 0.2mm under full live load (30kPa). It is highly unlikely that the structures will ever be loaded in such a way that this load is acheived. This coupled with the fact that the loads are mainly made up of moving vehichles makes it very unlikely that a crack width of 0.15mm willbe exceeded for any siginificant period of time.


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In order to control crack width the reinforcing for ULS was determined as if crack width was not a limitation. Calculations were then performed to determine the maximum bending moment experienced before the crack width exceeds the allowable size. Prestressing tendons were designed to counter the maximum moment to which the beam is subjected and bring the resultant moment experienced under ULS to within an acceptable range. Provision has been made for hogging steel in order to resist the moment created by the tendons in case no live load is present.

An example of the spreadsheet used to determine crack widths and critical moments is shown below. The precedure followed is detailed in Annexure A of SABS 0100-1, Edition 2.2.

Properties Equivalent Concrete Properties Crack Width d (to centre of reinforcement) 2374.00 Area 100533.3333 h‐x 1703.524

cover to reinforcing 126 Chosen depth 252 a' 2500.000b 1000 Eq Concrete b 398.9417989 x 796.476

h 2500Same as bar diameter 40 bt 1000.000

As 15080 Eq Concrete b 2513.333333 h 2500.000Es 200 E1 0.000730Ec 30 Ets 0.000203Rebar Diameter 40 Em 0.000527

Neutral axis depth (Ec/2) 796.4764842 acr 131.894ae 13.33333333 cmin 106.000q 0.006352148x/d 0.335499783 w 0.202323x 796.4764842Eeff 15

Strain calcs Mmax 4300Ic/bd^3 0.04998607Ic 6.68792E+11Es 0.000676179Strain (E1) 0.000730187

Compiled by Coenraad Coetzer

WML Coast (Pty) Ltd

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