Attachment 1_1 TAKREER LPG - Cross Section - Flat Foundation

Tank design description

Takreer Propylene Storage Tank design description_00_flat.doc Page 1 of 40

Tank Design Description

Ruwais Refinery Expansion Project

Takreer

Propylene Storage Tank

(47.000m³)

Alternative: Flat Foundation

revision date prepared checked approved changes

0 09.09.2009 Schiebel Salvatore Dr. Roetzer First internal revision

signature el. el. el.



0 Contents

0 CONTENTS ................................................................................................................. 2

1 APPLICABLE DOCUMENTS....................................................................................... 4

2 DESCRIPTION OF THE TANK SYSTEM..................................................................... 5

2.1 TANK SYSTEM ........................................................................................................ 5

2.2 TANK DATA.............................................................................................................. 6

2.3 DESCRIPTION OF THE CONCRETE TANK STRUCTURE ..................................... 8

2.3.1 GENERAL........................................................................................................ 8

2.3.2 TANK BASE SLAB........................................................................................... 8

2.3.3 WALL ............................................................................................................... 8

2.3.4 RINGBEAM...................................................................................................... 8

2.3.5 ROOF .............................................................................................................. 9

2.3.6 MISCELLANEOUS........................................................................................... 9

2.3.7 TANK TEMPORARY ACCESS OPENINGS....................................................10

2.4 BOTTOM HEATING.................................................................................................10

2.5 TANK SETTLEMENT MONITORING.......................................................................10

2.5.1 REFERENCE POINTS....................................................................................10

2.5.2 INCLINOMETER SYSTEM..............................................................................10

2.6 PRE-STRESSING SYSTEM....................................................................................11

2.6.1 TENDON LAYOUT..........................................................................................11

2.6.2 PRE-STRESSING OPERATION .....................................................................12

3 BASIS FOR ANALYSIS..............................................................................................14

3.1 DESIGN CRITERIA .................................................................................................14

3.1.1 ULTIMATE LIMIT STATE (ULS)......................................................................15

3.1.2 SERVICEABILITY LIMIT STATE (SLS)...........................................................15

3.2 DESIGN OF PRE-STRESSING ...............................................................................17

3.3 DESIGN CODES .....................................................................................................18

3.3.1 MATERIAL AND LOAD PARTIAL SAFETY FACTORS...................................18

3.3.2 SERVICEABILITY LIMIT STATE (SLS)...........................................................18

3.3.3 ULTIMATE LIMIT STATE (ULS)......................................................................18

3.4 MATERIALS ............................................................................................................19

3.4.1 CONCRETE....................................................................................................19

3.4.2 REINFORCEMENT.........................................................................................19

3.4.2.1 LOW TEMPERATURE (CRYOGENIC) REINFORCEMENT....................19

3.4.2.2 NON CRYOGENIC REINFORCEMENT ..................................................19

3.4.2.3 PRE-STRESSING REINFORCEMENT ...................................................20

3.4.2.4 USE FOR CRYOGENIC REBAR.............................................................20



3.5 DESIGN PROCEDURE ...........................................................................................21

3.5.1 CALCULATIONS.............................................................................................21

3.5.2 ANALYSIS METHODS....................................................................................24

3.5.2.1 SOFTWARE............................................................................................24

3.5.2.2 LINEAR ELASTIC ANALYSIS .................................................................24

3.5.2.3 NON-LINEAR ANALYSES.......................................................................25

3.5.2.4 SEISMIC ANALYSIS ...............................................................................26

3.5.2.5 THERMAL MODELS ...............................................................................29

3.5.2.6 CRACK WIDTH CALCULATION .............................................................30

3.5.3 NORMAL SITUATIONS: .................................................................................31

3.5.4 EMERGENCY SITUATIONS:..........................................................................31

3.5.5 LOAD COMBINATIONS..................................................................................33

4 FOUNDATION ............................................................................................................36

4.1 APPLICABLE DOCUMENTS ...................................................................................36

4.2 GENERAL INFORMATION......................................................................................36

4.3 FLAT FOUNDATION CONCEPT .............................................................................37

4.3.1 SETTLEMENTS..............................................................................................38

4.4 SETTLEMENT REQUIREMENTS............................................................................40



1 Applicable Documents

Following documents are applicable or will be referred to:

/1.1/ Geotechnical Investigation for Ruwais Refinery Expansion

Project, NO.5578 Agreement NO.07-5578-F-1

Ruwais, Abu Dhabi, UAE S08000288 Factual Report Revision 2

/1.2/ Geotechnical Investigation for Ruwais Refinery Expansion

Project, NO.5578 Agreement NO.07-5578-F-1

Ruwais, Abu Dhabi, UAE S08000288 Recommendation Report Revision 3

/1.3/ Ruwais Refinery Expansion Project Project Specification – Addendum –

Design General Specification - Rotating Equipment-Minimum General Requirements

Bechtel Document Number 25418-1000-3PS-M000-M0004 Rev. 1

/1.4/ Ruwais Refinery Expansion Project

Project Specification – Earthworks and Reclamation

Bechtel Document Number 5418-1000-3PS-CG00-C0002 Rev. 3



2 Description of the Tank System

2.1 Tank system

The tank system will be designed and constructed as a full containment type LPG storage

tank with a concrete roof and a flat foundation on tank pad of selected fill material.

The typical cross section of the concrete outer tank is shown in figure 2.1.

The tank consists of the following main components:

- a flat foundation

- a monolithic concrete outer tank, comprising a reinforced concrete base slab and a

pre-stressed circular wall and a spherical concrete roof. The wall has a constant

thickness.

- a ring beam on top of the wall

- a steel frame roof platform

- a self supporting, open top steel inner tank

- a suspended ceiling fastened to the roof

- insulation system mainly comprising of foamglas blocks on top of the base slab, per-

lite within the annular space between inner and outer tank together with a resilient

blanket at the outer surface of the inner steel tank and fiberglass blankets on top of

the suspended ceiling

- steel liner (vapor barrier) at the inner surface of the concrete tank

- a corner and bottom protection system (TPS) connected to the outer tank wall and

extended between the foamglas layers of the tank bottom

- a settlement monitoring system

- a bottom heating system



2.2 Tank Data

gross capacity Vbr 56,411 m³

net capacity Vnet 47,000 m³

inner tank diameter Di 65,00 m

inner tank wall height Hi 17,00 m

minimum width of annular space 1,00 m

inner diameter of outer tank Da 67,00 m

wall height of outer tank Ha 18,00 m

height of ring beam 2,50 m

outer diameter of base slab DB 71,60 m

thickness of base slab hB 1,20/0,50 m



Fig. 2.1 Cross section of tank system



2.3 Description of the Concrete Tank Structure

2.3.1 General

The outer tank consists of a concrete structure with concrete roof resting on a flat founda-

tion. Base slab, wall and roof are connected monolithically. The connection wall-to-slab will

be protected against low temperatures in extreme situations – leakage of inner tank – by a

thermal protection system (TPS) min. 5,00 m above the secondary bottom.

The water vapour ingress will be prevented by a carbon steel liner on the inner surfaces of

the concrete tank. For the wall liner vertical anchor rails are provided in a distance of

approx. 2 m, on which the liner plates are welded. The liner on top of the base slab is unan-

chored.

2.3.2 Tank Base Slab

The circular base slab made of reinforced concrete has a diameter of 71,60 m with a thick-

ness of 1,2 m in the rim area and of 0,5 m in the centre area. Temporary drainpipes will be

installed in the concrete base slab in order to drain e.g. rainwater during construction.

These pipes will be closed with concrete after installation of the roof.

In the rim area of the base slab horizontal pre-stressing tendons – with 19 strands - will be

placed in hoop direction in order to create a smooth transition between the pre-stressed wall

and the reinforced base slab.

2.3.3 Wall

The outer cylindrical tank wall is made of pre-stressed concrete. The wall has a constant

thickness of 0,80 m. The ring beam above the wall has a constant thickness of 1,20 m and

a height of 2,50 m. The inner diameter of the cylindrical concrete tank is 67,00 m. The wall

and ring beam are pre-stressed in vertical- and horizontal direction, see section 2.6.

2.3.4 Ringbeam

A roof ring beam of 2,50 m height and a thickness of 1.20 m completes the wall. The ring

beam is made of pre-stressed concrete and of the same concrete quality as the wall. The

function of the roof ring beam is to pick up the membrane forces of the domed roof struc-

ture. Therefore, the roof ring beam is horizontally pre-stressed.

A walkway is located on top of the ring beam.



2.3.5 Roof

The spherical roof is a concrete dome with an inner sphere radius of 67,00 m. Due to the

given diameter of the cylindrical wall of 67,00 m the inner height of the sphere segment will

be approx. 9,0m.

All loads hanging above the inner steel tank - resulting e.g. from the suspended deck and its

insulation - have to be supported by the roof structure. In addition, the pump wells will be

suspended from the roof.

The piping and pump platform consists of a steel frame structure with a steel grating floor

on top. The platform is arranged on the outer part of the roof and supported by the roof shell

and roof ring beam.

2.3.6 Miscellaneous

An inner pressure of maximum 105 mbarg will be applied during service of the tank (= de-

sign pressure). Between the concrete wall and the inner steel tank there is an annular

space of 1,00 m.

The reinforcement at the inner surface of the wall above the corner protection system,

which is affected by cryogenic design temperatures of -48°C, shall be suitable for the ap-

plied temperature.

The reinforcement at the outer surface of the wall, as well as for the base slab and ring-

beam will be normal hot rolled high yield steel.

The reinforced and pre-stressed concrete elements of the outer tank will be made of con-

crete with a minimum required 28 day characteristic strength acc. to section 3.4



2.3.7 Tank Temporary Access Openings

Based on our experience, two access openings in the wall of the outer concrete tank during

construction are foreseen:

- a large opening for transport of material into the tank

- a smaller opening as an access and escape route for personnel and for ventilation

The location of the openings in the circumferential direction depends on the site installation

and will be fixed at a later stage. It is intended to arrange the openings as far as possible

opposite to each other. It is also possible to arrange two large openings.

In vertical direction, both openings are in alignment with each other with a bottom level of

about 0,70 m above the top of the concrete base slab and a top level at least 1,0 m below

TCP elevation (height of opening: approx. 3,00 m).

2.4 Bottom Heating

A bottom heating system will be installed to prevent freezing of the subsoil.

2.5 Tank Settlement Monitoring

2.5.1 Reference Points

Along the perimeter of the base slab of the outer concrete tank, 18 survey/reference points

will be installed for monitoring the settlements of the outer tank. The levels of these points

will be measured using precise leveling instruments, e.g. theodolites.

2.5.2 Inclinometer system

A horizontal inclinometer system is applied in the base slab.

A zero leveling will be carried out after completion of the base slab. Further measurements

will be conducted during construction of the wall, after completion of the dome, during the

hydro test and the pre-commissioning phase.



2.6 Pre-stressing System

The DYWIDAG Pre-stressing System will be used in order to pre-stress the rim area of the

base slab, the wall and the ring beam of the concrete tank in horizontal and vertical direc-

tion.

The design of the pre-stressing will be based on bundled strand tendons consisting of

seven-wire strands of 0,60'' (15,2 mm) diameter.

The strands have a very low relaxation. The post-tensioning system shall be qualified by

testing at cryogenic temperatures.

Impermeable PP/PE sheathing for tendon installation will be used, providing a secondary

corrosion protection whilst the primary corrosion protection is provided by the alkalinity of

grout and concrete.

2.6.1 Tendon Layout

In the DYWIDAG pre-stressing system the strand tendons are post-tensioned and injected

with cement grout to achieve bond with concrete structure.

The sheating is installed in the formwork prior to concreting the structural member. After

concreting, the strands are pulled or pushed one by one into the ducts. The horizontal ten-

dons are equipped with stressable live-end anchors on both ends.

The horizontal tendons extend over 180° of the tank perimeter so that two tendons are nec-

essary to form a complete ring. They are anchored at buttresses. Neighbouring rings are

rotated progressively by 90° against each other in order to get an uniform stresses in the

wall, see Fig. 2.2

In the wall/ringbeam and in the base slab 4 buttresses are arranged.

The vertical tendons are straight and run from top of the ring-beam to the base slab.

They are equipped with live-end anchors at top of the ring-beam and with loops in the

base slab. They will be stressed from top of the ring-beam see Fig. 2.3



2.6.2 Pre-stressing operation

After the concrete is sufficiently hardened, the individual horizontal tendons are tensioned

with hydraulic jacks from both sides. The pre-stressing instructions, which are part of the

structural analysis, provide the basis of the pre-stressing operations. The instructions pro-

vide the specified forces and the sequence of pre-stressing. The jacking stations are num-

bered in accordance with the pre-stressing drawings.

Fig. 2.2 Layout of horizontal pre-stressing tendons (schematically)



Fig. 2.3 Layout of vertical tendons with loop anchors (schematically)



3 Basis for Analysis

The concrete containment shall be designed for all possible combinations of normal and

emergency loads, which may occur during construction, testing, commissioning, operating,

decommissioning and maintenance of the tank. Design load combinations include the most

severe combinations of loads. Emergency load situations are considered separately, i.e.

only one emergency load is considered to prevail at any one time.

3.1 Design Criteria

The LPG storage tank will be designed on Ultimate Limit State (ULS) and Serviceability

Limit State (SLS) for construction, all normal operation situations and for the emergency

situations defined in this section. For all other emergency situations the concrete structure

will be designed on ULS. The design will be performed according to the partial safety-

factored design method following.

For reinforcing steel bars exposed to LPG temperatures at the inner face of the wall, rebars

suitable to cryogenic temperatures (Krybar 50) will be used. Therefore a limitation of steel

stresses other than yield stress does not apply in this case. Such limitations refer only to

normal carbon steel reinforcement in case of use at cryogenic temperatures.



3.1.1 Ultimate Limit State (ULS)

Ultimate Limit State

Stage Performance

Criteria Design Criteria

- Construction phases - Hydro test and pneumatic test

pressure - Operation - Earthquake OBE

Stability

- Ultimate steel strain: 1 % (pre-stressing and reinforcement steel)

- Ultimate concrete strain: 0.35 % - consideration of the reduced stiff-

ness due to crack formation

- Earthquake SSE Stability




- Liquid spill inner tank Stability




- Liquid spill inner tank + OBE Stability




- Pressure relief fire - Adjacent fire

Stability

- steel strain < yield strain (pre-stressing and reinforcement steel)



- Impact of projectiles on tank shell No perforation only local effect

Fig. 3.1 Ultimate Limit State Scenarios (ULS)

3.1.2 Serviceability Limit State (SLS)

For durability reasons, during construction and normal conditions, the maximum crack width

will be limited to wlim = 0.30 mm for base slab and roof, to wlim = 0.20 mm for wall and ring-

beam. This will apply for load conditions as described in the table below.

The corner protection system at the inner surface of the lower concrete tank wall, as well as

the steel liner as an extension of the corner protection system and located within the cellular

glass blocks of the bottom insulation, ensures liquid-tightness during the emergency situa-

tions of liquid spill in order to protect the outer tank from direct contact with LPG in these

areas.



Serviceability Limit State

Stage Performance Criteria

Design Criteria

- Construction phases Durability

maximum crack width: - overall structure: wlim = 0.30 mm - consideration of the reduced stiffness due to crack formation

- Hydrotest and pneu-matic test pressure

- Operation - Earthquake OBE

Durability

maximum crack width: - prestressed concrete wall sections: wlim = 0.20 mm - reinforced concrete sections of base slab and roof:

wlim = 0.30 mm

- consideration of the reduced stiffness due to crack formation

- Liquid spill

Liquid tightness (liquid tightness of the base slab and lower part of the wall by means of a corner protection system)

pre-stressed concrete wall: remaining compression zone: - 10% of wall thickness, ≥ 100 mm - average compressive stress of 1 MPa within the residual compression zone

- consideration of the reduced stiffness due to crack formation

Fig. 3.2 Serviceability Limit State Scenarios (SLS)

In case of a liquid spill it can be demonstrated that a residual compression zone in the wall

of at least 100 mm and an average concrete compressive stress of about 1 N/mm2 within

the compression zone can generally be maintained in the principle direction of pre-stress

above the corner protection system.

The crack width limitation and the residual compressive zone requirements are considered

not to be applied to the worst-case consideration of inner tank spill in addition to OBE.



3.2 Design of Pre-stressing

Horizontal:

The load cases governing the design of the horizontal pre-stressing (principle direction)

force are as follows:

- hydrostatic pressure due to liquid spill

- internal overpressure

- creep, shrinkage and relaxation

Vertical:

The vertical pre-stressing force will be designed in such a way, that there are no axial ten-

sile stresses in vertical direction due to operation situation. However, tensile stresses at the

edge of a cross section will not be limited.

Cracking of concrete sections will be controlled, too, by vertical pre-stressing, by the

amount and distribution of bonded reinforcement bars and by measurements; the crack

width will be limited as stated in table Fig. 3.2

Early age cracking is considered by means of concrete technology reducing the required

crack reinforcement (i.e. acc. to CIRIA - Construction Industry Research and Information

Association, Report C660).



3.3 Design Codes

Governing design code for concrete structure is BS8110.

3.3.1 Material and Load Partial Safety Factors

The following Limit States shall be investigated:

(i) Serviceability Limit State (SLS)

(ii) Ultimate Limit State (ULS)

3.3.2 Serviceability Limit State (SLS)

Serviceability Limit State (SLS) includes different scenarios as described in Fig. 3.2 This

design state shall be utilized to determine crack width, strains, stresses and liquid tightness

in different conditions.

All material factors are taken as 1.0. The load safety factors are taken acc. to chapter 3.5.5

3.3.3 Ultimate Limit State (ULS)

Ultimate Limit State (ULS) includes all loading conditions. This design state shall be utilized

to determine concrete section adequacy per the strength requirements of governing design

code using material partial safety factors according to Fig. 3.3 and load partial safety factors

according to chapter 3.5.5

Strength Parameter Operating, Test, and OBE

conditions

Emergency

condition

Reinforcement 1,15 1,00

Concrete in flexure or axial load 1,50 1,30

Fig. 3.3 Material partial safety factors for the ULS



3.4 Materials

3.4.1 Concrete

The following concrete qualities are proposed in accordance with project specifications. The

characteristic strength is defined as 28-day concrete strength acc. to BS 8110

member cube strength (BS 8110)

Blinding 20,0 N/mm2

Base slab 40,0 N/mm2

Wall / Ringbeam 40,0 N/mm2

Roof 40,0 N/mm2

3.4.2 Reinforcement

3.4.2.1 Low temperature (cryogenic) reinforcement

Reinforcement at the inner face of the wall, which is subject to cryogenic temperatures,

shall be suitable for use at design temperature according to BS 7777-3:1993 § 6.3.4 at

-50.0°C (Krybar -50°C).

Characteristic strength (yield strength): 500 MN/m² - Krybar -50°C (500 B acc. to BS 4449)

3.4.2.2 Non cryogenic reinforcement

All other reinforcement is made of hot rolled high yield steel bars according to BS 4449

Characteristic strength (yield strength): Grade 500 (acc. to BS 4449 - 2005)



3.4.2.3 Pre-stressing reinforcement

Bundled strand tendons made of 7-wire super strands (0.6”) according to DYWIDAG Pre-

stressing System and ETAG 013 (European Technical Approval Guideline) with low relaxa-

tion shall be used. The system incl. strands and anchorages shall be suitable for cryogenic

applications acc. to FIP reports 904/128:1982 and SR 88/2, June 1988. The steel for post-

tensioning tendons shall comply with ASTM A 416.

Characteristic strength (yield strength): 1860 MN/m²

Nominal size: 140 mm²

3.4.2.4 Use for Cryogenic Rebar

The tank is equipped with a corner protection system. The corner protection system made

of steel is located at the inner face of the lower part of the concrete tank wall min. 5,0 m

above the secondary base slab and further within the foam glass blocks of the bottom insu-

lation. It ensures the liquid-tightness during the emergency situations of liquid spill and thus

protects the outer tank concrete wall from direct contact with LPG in these areas.

However, the inner face of the concrete wall above the corner protection is unprotected,

thus in the case of liquid spill in direct contact with LPG. In order to ensure the structural

integrity of the tank in this case, special precautions are required.



3.5 Design Procedure

The main design procedure is shown in Fig. 3.4

3.5.1 Calculations

In Fig. 3.5 a brief overview is given of the software to be used and of the results that will be

obtained. Most of this software has been developed to analyze large and sophisticated

structures and has been used for the design of LNG/LPG tanks constructed by DYWIDAG,

e.g. LNG Tanks Brunei, LNG Tanks Inchon South Korea, LPG Tanks Abu Dhabi, LNG

Tanks Oman, LNG Tanks Tongyoung South Korea, ALNG Train 4 Trinidad, LNG Tanks

Sagunto Spain, LNG Tanks Bal Haf Yemen, Tombak LNG Project and LNG Tank

Nynäshamn Sweden.

The software SOFISTIK will be applied for the design calculations, which have been used

for previous LNG projects.

NAFEMS benchmark tests have been carried out for the SOFISTIK software and are avail-

able.



Fig. 3.4 Principle Design Procedure



SOFISTIK

dynamic analyses - earthquake

Results: - global forces - accelerations (periods) - displacements

Determination of quasi-statical loadings based on the accelerations and tank masses

SOFISTIK

non linear analysis

SOFISTIK

linear structural analysis of single load cases

Results (due to single load cases): axis- and non-axis-symmetrical settlement, deflections and linear sectional forces (based on axis-symmetrical geometry

Construction- drawings

SOFISTIK

superposition of linear sectional forces

Results (due to load combinations): superposed axis- and non-axis-symmetrical, settlement, deflections and linear sectional forces (based on axis-symmetrical geometry)

Results: axis-symmetrical deflections and sectional forces due to reduced stiffness, crack width, check of reinforcement temperature progress, strain, stress

Results: reinforcement, crack width strain, stress

SOFISTIK

design of concrete sections

Results: Check of reinforcement

CALCULATION BY FORMULA

Local impact by a flying valve

Fig. 3.5 Calculation Methods



3.5.2 Analysis Methods

3.5.2.1 Software

The analysis of linear sectional forces, moments and displacements, the seismic analysis of

the tank structure and the calculation of the required percentage of reinforcement will be

performed using the NAFEMS benchmarked computer program SOFISTIK. SOFISTIK is a

commercial 3D-finite element program developed for all types of structures and used in our

company over a period of more than 15 years. The program is provided with pre-

processing, processing, post-processing and graphical presentation of the input and output

data and results of the static and dynamic analysis.

In cases in which the concrete is exposed to extreme temperature, i.e. liquid spill or valve

fire, non-linear effects of the concrete behaviour by reduced stiffness due to concrete crack-

ing will be taken into account for the stress analysis of the wall. The temperature distribution

in the wall due to the various spill pool levels will be also analyzed with this software and

introduced in the model.

SOFISTIK will be used for all other non-linear calculations, in which cracked concrete sec-

tions will be taken into account.

3.5.2.2 Linear Elastic Analysis

For the elastic analysis of linear sectional forces of the various operation and emergency

loads, the main concrete tank structure will be modeled using a 3D-Finite Element computer

program. The model comprises the base slab, the wall, the roof ring beam and roof.

Loading, sectional forces and bending moments are graphically presented in relation to the

line through the center of gravity.

Spring elements (elastic bedding values) will be used to model the sub-soil taking into ac-

count the interaction between the tank structure and the sub-soil.

The various load component results are superimposed in order to develop load combina-

tions for the SLS and ULS design of the concrete components.

In cases where cracked concrete sections will be taken into account in the design, a non-

linear analysis will be performed, see next section.



3.5.2.3 Non-Linear Analyses

In operation and emergency cases in which the concrete is exposed to high tensile stresses

e.g. due to extreme temperatures due to liquid spill or in emergency cases, non-linear ef-

fects of the concrete behavior caused by the reduced stiffness due to crack formation have

to be taken into account.

Contrarily to the linear elastic analysis, where the individual single load cases can be su-

perposed, a non-linear analysis must be carried out for load combinations determined be-

fore. For non-linear calculations the reinforcement is an input and will be determined by the

results of the linear calculation. If this quantity isn’t sufficient to fulfill the requirements

(stress, strain, crack width etc.), it has to be adjusted.

The calculation of non-linear sectional forces is an iteration process, which will be per-

formed by the selected computer program SOFISTIK. The FE-model corresponds to the

one used for the linear elastic calculation.

Fig. 3.6 Tank shell model



3.5.2.4 Seismic Analysis

The model for the seismic analysis consists of an axis-symmetrical lumped mass system

using acceleration response spectra as excitation input. The whole system is required to

remain within the elastic range, no physical or geometrical non-linearity shall occur.

The system considering the interaction of the outer concrete tank, the inner steel tank and

the liquid will be modeled using a FE-model, called ”tuning-fork-system”, consisting of beam

elements and lumped masses. For this analysis also the software SOFISTK is used. The

liquid will be assigned as lumped masses to the nodes of the inner tank. The distribution of

the liquid masses will be done in a parabolic form. The impulsive and sloshing portions of

the liquid mass are calculated according to API 620, Appendix L.

The results of a response analysis are not depending on time, because overall results (i.e.

maximum sectional forces) will be calculated using the SRSS (square root of the sum of the

squares) combination method.

Superposition with other (statical) loadings:

The dynamic models provide global bending moments, shear and normal forces of two-

dimensional beams or one-dimensional springs. These sectional forces will be expanded to

the three-dimensional shell model for superimposing with the statical loadings.

The overall bending moments (due to horizontal excitation) are distributed acc. to a cos-

type shape along the tank wall.

From the overall shear forces (due to horizontal excitation) and normal forces (due to verti-

cal excitation) individual accelerations for base slab, wall and dome are calculated corre-

sponding to their ideal unit weights.

The modal analyses are performed for the horizontal and vertical directions separately.

The superposition of the maximum values shall be done by considering the more unfavour-

able of the following two combinations:

(1) 1.0 Fx + 0.3 Fz

(2) 0.3 Fx + 1.0 Fz

Fx (horizontal direction), Fz (vertical direction)



Fig. 3.7 Tuning fork system (lumped mass model) for horizontal excitation

Fig. 3.8 Lumped mass model for vertical excitation



Following site specific response spectrum is defined for SSE conditions acc. to project

specification “Development of Preliminary 20006 IBC Design Ground Motion Estimates for

the Tekreer Refinery Project, Ruwais, Abu Dhabi”. It is developed for site class D and a

return period of 2475 years.

0,000

0,010

0,020

0,030

0,040

0,050

0,060

0,070

0,080

0,090

0,100

0 1 2 3 4 5 6 7 8 9 10Period [sec]

Vertical Acceleration Spectra = 2/3 * Horizontal Acceleration Spectra

SS

E (

g)

2006 IBC

Period SSE

[sec] [g]

0,00 0,038

0,01 0,041

0,10 0,070

0,18 0,094

0,20 0,094

0,30 0,094

0,88 0,094

1,00 0,083

1,50 0,055

2,00 0,041

4,00 0,021

6,00 0,009

8,00 0,005

10,00 0,003

Fig. 3.9 Spectrum acc. to 2006 IBC for site class D and return period of 2475 years

The shown spectrum is assumed to correspond with SSE. The OBE spectrum is scaled

down by a factor of 1,5. Consequently, the horizontal PGA values are considered with 0,038

g for SSE and 0,025 g for OBE. The vertical PGA values are defined by project specification

as 2/3*0,038 = 0,025 g for SSE and 2/3*0,025 = 0,017 g for OBE.

For the preliminary design the following percentages of the critical damping are considered.

The values are based on previous design experience and literature.

OBE SSE

sloshing mass 0,5% 0,5%

inner tank + impulsive mass 2,0% 4,0%

outer tank 2,0% 5,0%

soil 15,0% 20,0%

Fig. 3.10 Critical damping

Note: Uplift during OBE/SSE is permitted if further performance and acceptance require-

ments specified for the project are met and provided that the foundation can with-

stand the resultant actions.



3.5.2.5 Thermal models

In principle two situations will be taken into account for the temperature analysis of the con-

crete tank: operation respectively spill situations and fire scenarios.

Maximum and minimum ambient temperature profiles are considered as basis for the de-

sign for both situations. Besides the area of the base slab to wall connection one-

dimensional heat transfer dominates in wall as well as in base slab sections.

In other areas than the corner protection system, a “conventional” calculation will therefore

be performed using formulas published in the literature. In the wall to base slab connection

area and on top of the corner protection system the influence of the two-dimensional heat

transfer will be analyzed under spill condition using thermal finite element analysis in order

to study the transition of the one-dimensional temperature gradient from the base slab to

the wall sections and from the corner protection system to the unprotected wall. The struc-

ture is axis-symmetric. It is therefore sufficient to study the temperature distribution of a

segment of the structure. The resulting temperature profiles will afterwards be transformed

to the design models used for the operation and spill design calculations.

The concrete outer tank and all insulation material layers located between the outer tank

and the inner tank are considered for the determination of the temperature profiles. The

steel plates (inner tank, secondary bottom and liners at the inner face of the concrete tank),

however, will be neglected due to their high thermal conductivity.

A constant LPG design temperature is considered at the inner face of the steel tank wall

and of the steel tank bottom for the operations situations. In case of an LPG spill the LPG

penetrates the perlite in the annular space and the cellular glass and sand layers above the

secondary bottom plates. A constant LPG temperature is therefore taken into account at the

inner face of the concrete wall, at the inner face of the corner protection system and on top

of the secondary bottom plates for various spill conditions.

Convection film coefficients are used to model the convective heat transfer between the

outer face of the concrete wall and the surrounding air. The film coefficient depends on the

air movement at the concrete surface. A film coefficient will be therefore not applied be-

tween the base slab and the soil. It will be assumed that an air movement will not occur

there.



3.5.2.6 Crack width calculation

Control of cracking in flexural/tension members will be carried out acc. to BS 8110, part 2,

section 3.8.

Early age cracking is considered also acc. to BS 8110, part 2, section 3.8.



Design Loading Summary Table

The design will be prepared for the following situations:

3.5.3 Normal situations:

- Construction phases

- Hydro test and pneumatic test

- Operation phases

- Earthquake OBE

3.5.4 Emergency situations:

- Earthquake SSE

- LPG spill

- LPG spill + OBE

- Pressure relief valve fire

- Missile impact

The actions listed below are considered for the tank design



Operation and Test Situation:

dc, de

dead weight of the tank structure concrete (den-sity 2500 kg/m³), inner steel tank, steel liners, sus-pended ceiling, steel roof and platform, insulation etc. horizontal pressure due to perlite fill

lcons temporary loads during construction phases and stress

history where appropriate

ss effects of predicted differential centre to edge soil set-

tlements will be considered by the soil-structure inter-action (spring elements in the static model)

lpre pre-stressing incl. losses due to creep, shrinkage and

relaxation

top ambient temperature operation :

max. ambient temperature min. ambient temperature

50,0°C 5,0°C

A A

lw Basic Wind Speed for use with ASCE 7 160 km/h D lr live load on roof:

uniform distributed load 1,5 kN/m2

C

lp live load on platform and access ways : 2,4 kN/m2 C ftest hydro test of inner tank with water, test level: 16,0 m ρ = 1000 kg/m3

ptest pneumatic test pressure: 1,25 x 105 mbarg

according to API 620, app G 13,125 kN/m2

fLPG LPG filling inner tank: H = 16,0 m

design density minimum design temperature

6,074 kN/m³ -48,0°C

B A

pmax design max. internal pressure: +105 mbarg +10,5 kN/m2 B



Emergency Situations

eOBE operating base earthquake, pending depending on detailed site survey

PGA: 0,025 g (hor.) PGA: 0,017 g (vert.)

E E

eSSE safe shut down earthquake,

pending depending on detailed site survey PGA: 0,038 g (hor.) PGA: 0,025 g (vert.)

EE

fsp leakage of inner tank at intermediate levels fsp liquid spill of inner tank, density tsp temperature liquid spill psp internal pressure due to liquid spill – 125%

6,074 kN/m³ -48°C 13,125 kN/m2

B

limp missile impact (local effect): mass

velocity impact diameter

50 kg 45,0 m/sec 100 mm

lvf PRV- fire (acting on roof)

maximum incident heat flux (concrete part) duration

32,0 kW/m2

1 hour*

A

Fig. 3.11 Main loading values

A According to Project Specification, Doc. No. 25418-1000-3PS-MT00-M0004

B According to Datasheet No. 25418-1041-MTD-MTD0-B0065 REV1

C According to EN 14620-1

D According to STRUCTURAL ENGINEERING DESIGN CRITERIA,

25418-1000-3PS-S000-C0001

E Development of Preliminary 2006 IBC Design Ground Motion Estimates for the Tak-

reer Refinery Project, Ruwais, Abu Dhabi

3.5.5 Load combinations

Typical load combinations for the design of the concrete structure of the tank system are

shown in Fig. 3.12 for ULS and in Fig. 3.13 for SLS.

Emergency loading situations are considered separately (i.e. only one emergency load shall

be considered to prevail at any one time) except the situation liquid spill in combination with

OBE.



ULS LPG Spill

Load Combination d lpre lshr ss lcons fLPG pma

ftest ptes

lp, l

lw top eOBE eSSE fsp tsp psp tvf taf lblast lim

kind of loading *) PE PR3)

PE PE2)

PE V V V V V V V V V E E E E E E E E

Construction phases 1,4 0,9

1,2 1,0

1,0 0,0

1,6 0,0

1,6 0,0

Hydro test and pneumatic test 1,4 0,9

1,2 1,0

1,0 0,0

1,2 0,0

1,2 0,0

1,6 0,0

Operation phases + imposed load + wind

1,4 0,9

1,2 1,0

1,2 0,0

1,0 0,0

1,2 0,0

1,2 0,0

1,6 0,0

1,6 0,0

1,2 0,0

Operation + OBE 1,4 0,9

1,2 1,0

1,2 0,0

1,0 0,0

1,2 1,2 0,0

1,6 0,0

1,2 0,0

1,3

ULS

N

orm

al

Operation + SSE 1,05 1,0

1,05 1,0

1,05 0,0

1,0 0,0

1,05 1,05 0,0

1,05 0,0

1,05 0,0

1,05

Inner tank liquid spill 1,05 1,0

1,05 1,0

1,05 0,0

1,0 0,0

1,05 0,0

1,05 1,05 1,05

Spill + OBE 1,0 1,0

1,0 1,0

1,0 0,0

1,0 0,0

1,0 0,0

1,0 1,0 1,0 1,0

Blast wave 1,05 1,0

1,05 1,0

1,05 0,0

1,0 0,0

1,05 0,0

1,05 0,0

1,05 0,0

1,05 1,05

Pressure relief fire 1,05 1,0

1,05 1,0

1,05 0,0

1,0 0,0

1,05 0,0

1,05 0,0

1,05 0,0

1,05

Adjacent fire 1,05 1,0

1,05 1,0

1,05 0,0

1,0 0,0

1,05 0,0

1,05 0,0

1,05 0,0

1,05

Impact of projectiles Only local effect

1,05

ULS

A

bnorm

al

1) PE = Permanent Load, V = Live Load, E = Emergency Load 2) the soil settlements will be considered by the interaction of the structure and the soil (spring elements in the static model)

3) Ptso and Pts∞ will be applied

Cool down and maintenance is covered by the operation situation Fig. 3.12 Typical load combinations with load partial safety factors



SLS LPG Spill

Load Combination d lpre lshr ss lcons fLPG pma

ftest ptes

lp, l

lw top eOBE eSSE fsp tsp psp tvf taf lblast lim

kind of loading *) PE PR3)

PE PE2)

PE V V V V V V V V V E E E E E E E E

Construction phases 1,0 1,0 1,0 1,0 0,0

1,0 0,0

1,0 0,0

Hydro test and pneumatic test 1,0 1,0 1,0 1,0 0,0

1,0 0,0

1,0 0,0

1,0 0,0

Operation phases + imposed load + wind

1,0 1,0 1,0 0,0

1,0 1,0 0,0

1,0 0,0

1,0 0,0

1,0 0,0

1,0 0,0

Operation + OBE 1,0 1,0 1,0 0,0

1,0 1,0 1,0 0,0

1,0 0,0

1,0 0,0

1,0 0,0

1,0

ULS

N

orm

al

Inner tank liquid spill 1,0 1,0 1,0 0,0

1,0 1,0 0,0

1,0 1,0 1,0

ULS

A

bnorm

al

1) PE = Permanent Load, V = Live Load, E = Emergency Load 2) the soil settlements will be considered by the interaction of the structure and the soil (spring elements in the static model)

3) Ptso and Pts∞ will be applied

Cool down and maintenance is covered by the operation situation

Fig. 3.13 Typical load combinations with load partial safety factors



4 Foundation

4.1 Applicable Documents

Following documents are applicable or will be referred to:

Following geotechnical reports are available:

/1.1/ Geotechnical investigation for Ruwais Refinery Expansion

Project, No.5578 Agreement No.07-5578-F-1

Ruwais, Abu Dhabi, UAE S08000288 Factual Report Revision 2

/1.2/ Geotechnical investigation for Ruwais Refinery Expansion

Project, NO.5578 Agreement No 07-5578-F-1

Ruwais, Abu Dhabi, UAE S08000288 Recommendations Report Revision 3

/1.3/ Ruwais Refinery Expansion Project Project Specification – Addendum –

Design General Specification - Rotating Equipment-Minimum General Requirements

Bechtel Document Number 25418-1000-3PS-M000-M0004 Rev. 1

A factual geotechnical report describing the project area is available. An engineering geo-

technical report is not available at present stage.

A final engineering report for the tank area is required to finalize the foundation concept,

especially a soil data report and a recommendation for the foundation by the geotechnical

expert.

4.2 General information

The site preparation rough grading plan

(Bechtel drawing no. 25418-1000-CG0-0000-C0111)

Revision 5 indicates the proposed future rough grade level at +7.60 m.

Plant plan – overall site plan (Bechtel drawing no. 25418-1000-P10-0000-P0001)

shows the propylene tanks in the range of approx. E = 670,500 N = 2,669,000.

At this position the drilling of borehole BH-A16 has been carried out.

The borehole data sheet of BH-A16 defines the existing ground level at +3.10 m and the

ground water level at +1.80m.



4.3 Flat foundation Concept

Acc. to the mentioned geotechnical information a flat foundation is envisaged, which is

schematically displayed in the following figure.

The tank area is handed over at + 7,60 m, which shall also be the final grade of the tank

area. Groundwater is encountered at + 1,8 m.

A tank pad varying from 80 cm to 150 cm, below the rim area respectively the centre area,

is foreseen to accommodate in-homogeneity of the subsoil.

Fig. 4.1 Foundation Layers



4.3.1 Settlements

The subsoil described in the factual geotechnical report consists basically of an upper

weaker part (medium dense to very dense silts SAND) and a lower stiffer part (alternating

SILTSTONE and SANDSTONE). Overhead the natural soil is a 4,50m thick soil layer; this

layer - called DRY FILL - should have a compressive strength higher than Es = 20 Mpa in

the area of the tank.

Following soil layers and related stiffness have been assumed for preliminary settlement

calculations and related bedding definitions.

The detailed subsoil layers used for preliminary settlement investigations and the related

E-Moduli acc. to the geotechnical reports mentioned in section 4.1 are shown in the follow-

ing table.

The definition of the soil layers and their thickness is based on the soil report. The following

tables show an average of the soil layers resulting from borehole BH A32 and BH A 33.

The expected Maximum settlements on this basis amount to approx. 132 - 171 mm. The

differential settlements are within the limits specified in BS 7777.



layer definition absolut

level thickness

relative level

Es

[m] [m] [m] [kN/m²]

6,90 0,0

0 Tank Pad (average thickness) 0,80 70000

6,10 -0,8

1 DRY FILL 3,00 20000

3,10 -3,8

2 silty SAND, medium dense 2,00 20000

1,10 -5,8


-0,90 -7,8


-2,90 -9,8


-4,90 -11,8

6 silty SAND, very dense 1,50 60000

-6,40 -13,3

7 silty SAND, very dense 1,50 60000

-7,90 -14,8

8 Very weathered, SANDSTONE 3,10 100000

-11,00 -17,9

9 Very weathered, SANDSTONE 5,00 100000

-16,00 -22,9

10 slightly weathered, MUDSTONE 1,00 80000

-17,00 -23,9

11 Moderatly weathered, GYPSUM 1,00 10000

-18,00 -24,9

12 slightly weathered, MUDSTONE 1,00 80000

-19,00 -25,9

13 Very weathered, SILTSTONE 61,00 100000

-80,00 -86,9 Fig. 4.2 Soil layers



4.4 Settlement requirements

The tank foundation shall be designed in order to fulfil following limits:

Type of Settlement Differential Settlement Limits

Tilt of the tank 1 : 500 Tank floor settlement along a radial line from the periphery to the tank center

1 : 300

Settlement around the periphery of the tank 1 : 500 but not exceeding the maximum settlement limit calculated for tilt of the tank

Fig. 4.3 Differential settlements limits

The final design will be adjusted to the final engineering geotechnical report, which may

lead to changes.

If the above mentioned is confirmed by the final, still outstanding engineering report for tank

area, the subsoil for the Tank foundation will be suitable for a flat foundation supported on

engineering fill (tank pad) and keep the settlement requirements.