Eng. Arshad Khan was born in Nairobi and did his early schooling there. He then went to Bath University
where he graduated with a 1st Class Honours BSc degree in building engineering. After a year working in
London he went to Imperial College and graduated with an MSc in Concrete Structures & Technology.
After two years working on site in Southern Somalia, Arshad spent his early career in Kenya, rising up to
director of Howard Humphreys, and was responsible for iconic projects such as Times Tower, Riverside
Park, CFC Tower and AmBank House.
After 18 years working in Kenya, he moved to Vienna in 1998 where he operated as an independent
engineer. In 2004 he moved to Dubai, where he was appointed as the Lead Structural Engineer for the Palm
Jumeirah. From 2006 to 2009 he was the Director of Structures for Atkins Middle East, covering Bahrain,
Qatar, Abu Dhabi and Kuwait, where he designed numerous high-rise buildings of up to 100 stories. His
specialisation is in the analysis and design of earthquake resistant tall buildings, with particular expertise in
achieving significant economy by means of innovation, optimisation and value engineering.
Eng. Arshad has published and presented papers in international conferences in Abu Dhabi, Singapore and
London, including one on AmBank House and one on Times Tower. He presented this paper, on the Al-S
Tower, to the client in Kuwait in February 2009. Arshad returned home to Kenya in late 2010, after an
absence of 12 years, and operates on a freelance basis. His email contact is arshaddotkhan@gmail.com.
Innovative Design of a 100 Story RC Skyscraper using Modern Techniques
by
Eng. Arshad Khan, MSc, BSc, DIC, CEng, FIStructE, FICE, MIEK, MAAK (E), REng.
Al-S Tower, Kuwait
1.0
Introduction
This paper describes the structural concepts proposed for the Al-S Tower Development in Kuwait. The
project comprises a very slender high-rise tower with a maximum height of approximately 430 m above the
ground located in the Megwaa area of Kuwait City. The podium of the building comprises two retail floors,
four floors for hotel facilities, three parking floors and four basement levels.
Several structural systems have been investigated with priority given to the following factors:








Economy of construction
Buildability
Speed of construction
Accommodation of architectural requirements
Adaptability for the provision of building services
Availability of local resources and experience
Maximising prefabrication and repetition
Minimising long lead-in items


2.0
Site access and storage restrictions
Fire resistance
Structural Materials
Consideration has been given to structural solutions using reinforced concrete and structural steel as the
primary materials. The advantages and disadvantages of each of them are summarised as follows.
For a reinforced concrete structure, the positive points are:








Traditional well-proven method of construction in Kuwait resulting in competitive price and
availability.
Use of local materials
No lead-time as in steelwork for ordering, delivery and fabrication
Suitability for cladding fixtures
Inherent fire resistance
Better acoustic performance
More flexible for building services requirements
Higher inherent damping compared to steel structures
The negative points of a reinforced concrete system are:



Heavier self-weight of the structure
Larger member sizes compared to steel system
Longer construction time
Benefits of a steel structure are:





Lighter structural self-weight
Smaller member sizes compared to reinforced concrete
Speed of construction because most of the framework is fabricated in the workshop.
More efficient for larger spans or for open spaces than concrete structures.
Recyclable or re-usable material.
The negative aspects of steelwork are as follows:





Higher material cost
Longer lead time
Additional fire and corrosion protection
Additional structural depth required for steel beams, which may potentially conflict with the building
services requirements
Lack of local experience in fabrication of heavy sections
Based on the above considerations, the structural steel option is discounted.
3.0
Proposed Structural Systems
3.1
Floor Systems for the Tower
In the typical floor plans, there are two zones that will have different floor systems. These are the zones
within the cores, which include corridors, service areas and lift shafts, and the zones beyond the cores,
which includes regular hotel/residential, office and retail areas. The zones within the cores will generally be
conventional reinforced concrete slabs (150 to 200mm thick) with beams where required. For the remaining
zones four floor system options have been considered (with one sub-option), as described below.
Option 1 - Hollow Core Pre-tensioned pre-cast slabs (HCS) on RC beams
This product is available in Kuwait and is extensively used in buildings. A cast in-situ structural concrete
screed will be provided for levelling and to ensure diaphragm action
The advantages of this system are:





Lighter floor than a PT slab or 2-way RC slab
Reduced sizes of columns and foundations
Faster construction
Elimination of floor formwork
Good sound insulation
The disadvantages of this system are:




Reduced flexibility in penetrations in slab
Visible joints and nibs under soffit- aesthetics
More crane works and coordination required
Requires coordination with specialist sub-contractor on site
Option 2– Solid Reinforced Concrete 2-way spanning Slab
This is traditional construction, with the slab thickness controlled by deflection criteria.
The advantages of this system are:




Simple method of construction not needing specialist
capabilities
Simple traditional formwork
Minimal site coordination
Flexibility for the passage of horizontal services and
cutting small openings
The disadvantages are:



Heavier than most if the other options, leading to larger
columns and foundations.
Aesthetics- down stand beams in both directions, visible
in non-ceiling areas.
In-situ placement of large amount of rebar which takes
longer than for pre-cast or post-tensioned slabs
Option 2A– Solid Reinforced Concrete Slab with Secondary RC Beams
This is traditional construction, with the slab thickness minimised by use of secondary beams.
The advantages of this system are:




Simple method of construction not needing
specialist capabilities
As light as ribbed slab floor system if 2 secondary
beams are used per bay
Minimal site coordination
Flexibility for the passage of horizontal services
and cutting small openings
The disadvantages are:



Larger amounts of shuttering which may result in
higher cost and longer construction time
Aesthetics- down stand beams will be visible in
non-ceiling areas.
In-situ placement of large amount of rebar which
takes longer than for pre-cast or post-tensioned slabs
Option 3 – One Way Spanning Ribbed Slab
This is a very efficient and light construction, with the slab thickness minimised by use of ribs at 900mm
centres.
The advantages of this system are:






Simple method of construction not needing
specialist capabilities
Lightest overall floor system (similar to option 2A)
Minimal site coordination
Easy to incorporate fairly large vertical riser
penetrations
Flexibility for the passage of horizontal services
and cutting small openings
Possibility of pre-casting double-tee units, hence
sharing advantages of off-site fabrication
The disadvantages are:



Larger amounts of special shuttering (moulds) which
may result in higher cost and longer construction time
Aesthetics- ribs will be visible in non-ceiling areas.
Lower acoustical insulation than the other options
Option 4 - Post – Tensioned (PT) Concrete Slab
A solid post-tensioned one-way spanning slab supported on main RC beams. (Note: 2-way PT slabs are not
possible for the tower due to the restraints imposed by the external “pierced tube” framework.
The advantages of this system are:


Shallower structural depth compared to solid RC slab, option 2
Fastest in-situ concrete option
The disadvantages of this system are:





Limitation on fixing services and cutting openings after the
slab has been cast
More coordination with a specialist sub-contractor on site
Heavier than the many of the other options
Not commonly used in Kuwait
Restraint of external tube structure of tower will require
special gap-strips
Cost Comparison
At this stage cost comparisons can only be made on the basis of materials usage and overall weight as that
has considerable impact on the sizes of columns and foundations. The system can be further refined and
priced during the preliminary design stage, taking account of rebar consumption as well as
shuttering/formwork costs. The conceptual sizes of floor framing members and volumes of concrete utilized
for the different floor options have been worked out in order to make an appropriate recommendation.
Recommendations
For high-rise towers, as the floor system has a big impact on the sizes of beams, columns and foundations,
the best system to adopt should be the lightest system. Based on that consideration and taking all other
pros/cons into account, the recommended option at this stage is the one-way ribbed slab system (option 3),
although the options will be further studied for the final selection during the preliminary design stage. The
ribbed slab depth can be further reduced to 400mm for the shorter spans.
The conceptual framing system used for the ETABS model for the tower is shown in the screen shots in the
next page, for the reducing floor plates up the tower. The 3-D image shows Level 34 from underneath.
It is important to highlight that the choice of this floor system does not preclude the contractor from
proposing traditional RC slab system with secondary beams (option 2A) as this is equivalent in weight to the
ribbed slab system. Some local areas within the lift lobby shall be conventional reinforced concrete due to
short spans, presence of a large number of openings and heavy loading.
The mechanical floors and the roof slab will likely be conventional reinforced concrete slab, which will be
thicker than normal floors to account for vibration and noise controls.
3.2
Floor System for the Car Parking Levels
At this stage the proposed car parking is planned to be by automated delivery system, which will rely on
steelwork framing fitted within the concrete walls/columns. Where necessary, in order to reduce the
slenderness of columns, RC beams may need to be provided at some of the floor levels. In addition, certain
parts of the parking floors may require traditional RC floor slabs, for which provision has been made during
the conceptual design.
The column grid spacing for the car parking outside the footprints of the towers is fairly regular which
permits the possibility of considering two-way spanning flat slabs in addition to the other options considered
for the tower. Due to headroom restrictions, the option of using HCS is only possible by use of shallow
depth band beams.
Levels M1-9 and 10-18 Framing Plans
Levels 22-30 and Level 42 Framing Plans
Levels 58 and 70 Framing Plans
Level 34 Framing in 3-D
3.3
Floor System for the Retail, Restaurant and Gymnasium Areas
The column grid spacing for the retail area follows either the regular grid outside the footprints of the towers
or it follows the same grid as the towers under their footprints without the need for any transfer structures.
The recommended floor option for this zone, under the footprint of the tower, is also Option 3, using 400mm
and 500mm deep ribbed slabs depending on the spans and the loading.
In the podium floors the column grid spacing is fairly regular and has fewer number floors compared to the
tower, so self-weight is not so critical. Hence the recommended slab system at this stage is a flat slab of
300mm thickness with drop panels of 450 thick where ever required. Perimeter beams of size 400X800 are
provided where ever possible to avoid drop panels.
3.4
Floor System for the Mechanical Areas in Podium
The recommended floor system for the mechanical floors is 350mm thick flat slab with 500mm thick drop
panels wherever required. The thicker than normal floor is to account for vibration, noise controls and higher
live load due to mechanical equipment. The floor system for the third floor is 300 thick solid slab supported
on 600X800mm beams.
3.5
Floor System for the Ballroom
The recommended slab system at this stage is a flat slab 300mm thick with drop panels of 450 thickness
wherever required.
3.6
Floor System for the Fourth floor
Some of the columns along grids R and S have to be stopped at second floor to permit an open floor area for
the ballroom. This necessitates the use of trusses for the span of 27m to support the floors above. The depth
of the trusses is 3.8m using structural steel sections. The remaining area with smaller spans is to be
conventional one way solid slab of 300 thickness supported on beams of sizes 600 x 900mm.
3.7
Podium Roof
A steelwork retractable roof supported on steel beams/trusses will be provided for the podium roof.
4.0
Lateral Stability and Gravity Support Systems
Lateral forces due to wind and notional loads need to be safely transferred from individual floors down to
the foundation without excessive deflections in the structure.
Al -S Tower is very slender indeed, with an aspect ratio of about 12:1 in one direction and about 9:1 in the
other and therefore is a very challenging building to design. Compared to this other tall buildings in the
world have a maximum aspect ratio of around 8:1 (such as Burj Dubai, Taipei 101, Petronas Towers, etc).
This tower is about the same height as the latter two towers quoted above.
Having considered other options, such as shear /core wall systems, dual system with moment-resisting
frames, braced systems, etc, the best one that suited the architectural/functional requirements and the
exacting performance required for lateral sway and acceleration, is the system described below as being the
most appropriate.
The lateral stability is provided primarily by the external “pierced-tube” system (also referred to as a
punched-tube system), in conjunction with the lift and stairway cores, coupled with shear walls and
moment-resisting frames in certain locations. Outrigger and Belt Truss systems have been incorporated at
service floors at this stage but these may not be necessary after wind tunnel loading has been assessed,
unless additional stiffness is required for the acceleration control. Preliminary wind loads for the tower
portion, as per the ASCE wind code, have been assessed and the tower is sufficiently stiff to resist these. It is
expected that the final wind loads from the wind tunnel tests will be less than these code values.
Levels 30 to 34 Showing Planted Column
The main advantages of this structural system are:



Very stiff and efficient for lateral stability as the members are at the perimeter of the tower.
Torsionally stiff.
Little reliance for lateral stability on the internal lift shaft cores, so that they remain relatively thin300mm even at the base.







Freedom to plan the internal layout and column/core positions without compromising the overall
lateral stability.
Ability to remove alternative tube columns to suit architectural/functional requirements
Repetitive use of standard size formwork for the punched rectangles in the tube.
Suited for fast slip-forming.
Efficient usage of materials; current design consumes only about 0.6 m3 of concrete per m2 of gross
floor area, which is very good for a building of this height and slenderness.
Minimises requirement for external blockwalls, as all the openings will be glazed.
Provides very good thermal mass to the exterior, hence minimising solar gain into the building.
ETABS Model and Wall Stresses along Gridlines 11 and N
Images from the conceptual ETABS models for the tower are shown in the above screen shots.
The lateral stability for the podium is provided primarily by lift and stairway cores, coupled with shear walls
and moment-resisting frames in certain directions.
As far as possible, all gravity load paths have been kept simple and vertical, but in three locations in the
tower this was not possible and the transfer structures are described below.
4.1 Sloping Set-backs
In order to find the most optimal solution, the sloping beams have been used as raking columns to pick up
gravity loading from the edges of the set-back floor slabs. This forms a very efficient triangulated system
which will reduce the beam sizes (as they will not need to be cantilevers) and also results in the raking
columns acting as bracing against lateral sway of the tower.
The screen shot below shows the axial forces in the raking columns as well as in the mullions which will be
spaced at 4.2m centres to coincide with the intersection of the raking column with each floor plate.
Levels 36 to 53 Raking Columns and Mullions
4.2 Gravity Transfer at Gridline D
The 5m setback at Levels 9-10 does not coincide with any columns below, so between Levels 8 and 9 there
are floor-height transfer walls which efficiently transfer the gravity loading on to the external tube and the
columns on gridline E.
4.3 Gravity Transfer at Gridline E
Column 9E stops at Level 21 and then continues at Level 32. Therefore this column is supported on a
transfer wall within the double height MEP floor at Level 31. Due to the geometry of this structure it is
economical in terms of materials usage, as it also assists in the tower’s lateral stability as a belt truss/wall.
The image on the next page shows the gridlines and plan at Mezzanine Level.
ETABS Model Gridlines and Layout at Mezzanine 1 Level
4.4 Viewing Deck/Spire Structure
At this stage the top floors framing around the triangular cut-out have been modelled and analysed as a
traditional RC structure, with framed floors and columns/shear walls. During the next stage this may be
changed to structural steelwork in order to make it more buildable and at the same time make it lighter so
that the global dynamic response would improve.
4.5
Differential Column Shortening
For tall concrete structures (more than about 30 storeys), the effects of elastic column shortening as well as
long term shortening due to creep and shrinkage become significant. This happens mainly due to the fact
that columns are usually much more heavily stressed than the shear/core walls. This then leads to
increasingly differential “settlement” between the columns and the walls, with beams and slabs ending up at
a slope. The best way to mitigate this effect is by stress balancing between columns and adjacent wallshowever this is not always possible (due to lateral stability requirements), so a detailed and complex analysis
is normally required during the PD and DD stages in order to work out and specify “super-elevations” at
every 5-10 floors.
With this, the floors/beams are deliberately cast at a negative/reverse slope, with the idea that in due time
they would revert to the horizontal.
4.6
Differential Temperature Effects
In tall structures (more than about 30-40 storeys), the effects of differential temperature gain/loss between
the external envelope and the internal structure become significant, as this leads to secondary stresses within
the connecting members (beams, floors, etc). This aspect will need to be carefully assessed and catered for
during the PD and DD stages.
5.0
Design codes
The design will be done in accordance with the following main codes and standards:
BS 8110
Part 1:
Part 2:
BS 5950
Part 1:
S 6399
Part 1:
Part 3:
Structural use of concrete
Code of practice for design and construction
Code of practice for special circumstances
Structural use of steelwork in building
Code of practice for design in simple and continuous construction:
hot rolled sections
Loadings for Buildings
Code of practice for dead and imposed loads
Code of practice for imposed roof loads
Foundations
Protection of structures against water from the ground
Design of concrete structures for retaining Aqueous Liquid
The structural use of masonry
Wind loads in concept design phase
Report on High Strength Concrete
High Strength Concrete
Seismic design
BS 8004:
BS 8102:
BS 8007:
BS 5628:
ASCE 7-05
ACI 363R-92
ACI 441-R96
UBC Code 1997 &
ACI 318-05
NFPA 5000
Fire Resistance
Note: All current Kuwait Regulations will be complied with and will take precedence should they conflict,
unless specifically waived by the Municipal engineers
6.0
Dead and Imposed Loads
6.1 Dead Loads
Screed
Concrete + in-situ topping
Lightweight concrete
Service and suspended ceiling
200mm light weight block work partitions
100m light weight block work partitions
Dry wall partition
Cladding (glass and aluminium)
Density = 20 kN/m3
Density = 24 kN/m3
Density = 13 kN/m3
Density = 0.3 kN/m2
1.8 kN/m2 (on elevation)
1.2 kN/m2 (on elevation)
0.9 kN/m2 (on elevation)
1.0 kN/m2 (on elevation)
6.2 Imposed loads
Residential areas
Office areas (including movable partitions)
Plant, mechanical/electrical room areas
Stores, corridors, lift lobbies and staircase
Car park areas
Retail areas
Balconies
Transformer rooms
Roofs (unless noted otherwise)
Landscaping (to be confirmed)
2.0 kN/m2
3.5 kN/m2
7.5 kN/m2
4.0 kN/m2
3.0 kN/m2
5.0 kN/m2
3.0 kN/m2
10.0 kN/m2
1.5 kN/m2
16.0 kN/m2
Note: Codified live load reduction factors will be used where applicable.
7.0
Wind Loads
The basic wind speed will be established by the wind specialist based on the meteorological data for Kuwait.
For the concept stage designs, following data, per ASCE 7-05 will be used to estimate the wind load on
structure. The wind tunnel test results will be used for the preliminary and detailed design stages.
Basic wind speed
V = 40 m/s
3 second gust wind speed for Kuwait
Velocity Pressure
Exposure Coefficient.
Exposure D
Open area (for a tall building located at sea
shore) outside hurricane prone regions
Topographic Factor
Kzt = 1.0
Flat coastal fringe.
Wind Directionality
Kd = 0.85
Main Wind Force Resisting System
Importance Factor
I = 1.0
Category II building
8.0
Seismic Loads
Load factors for seismic design shall be in accordance with UBC 1997 Ch.16
Seismic Zone
Soil profile factor
Occupancy category
Ductility factor
9.0
1
Sc
Z = 0.075
I = 1.0
R=5.5 for concrete frame system
Load Combinations
The following combinations will be used in design:
9.1 Serviceability Limit State
-
1.0 DL + 1.0 LL
1.0 DL +/- 1.0W
0.8 (DL + LL +/- W)
0.9 DL + UPL
9.2
Ultimate Limit State
-
1.4 DL + 1.6LL
1.2 DL + LL +/- E
0.9 DL +/- E
1.2 DL + 1.2LL +/- 1.2W
1.4 DL +/- 1.4W
0.9 DL +/- 1.4W
9.3
Piles and Foundations
-
1.0 DL + 1.0LL
0.8 (DL + LL +/- W)
0.75 (DL + LL +/- E/1.4)
0.9D +/- E/1.4
Where:
10.0
DL: Dead Load.
LL: Live Load.
E: SRSS Seismic load from Response spectrum analysis.
W: Wind Load in any direction.
UPL: Uplift Load.
Robustness
Disproportionate and progressive collapses are important considerations for a building such as this. The
structural system adopted has inherent robustness and redundancy, as evident from the removal of one
column at ground level (on gridline 11, at the main hotel entrance) without the need for a heavy transfer
structure.
The provisions of BS 8110 for structural robustness will be met by providing vertical and horizontal ties and
careful attention to rebar detailing.
11.0
Damping Values
2% damping value will be considered appropriate for serviceability and ultimate limit states under 50 year
return period wind loads. The estimation of the occupant comfort (10 year return period wind) will be
performed with a structural damping ratio of 1.5% for the concrete structures. A 5% damping value will be
used for seismic loads in ultimate limit state.
12.0
Occupants Comfort
Wind tunnel test studies will be carried out to assess the occupancy comfort. The maximum peak
acceleration for 10 year return period wind shall not exceed 15 mg at the top occupied floor for residential
units and 20 mg for the top office floor. An assessment as to whether the tower is stiff enough to obviate
such problems is to study the first 3 or 4 natural modes of vibration. If the first and second modes are within
the limits of n/10 seconds or H/60, where n= number of storeys and H= overall height of tower, then this is
sufficient evidence at this stage of the design. The images and table below shows the mode shapes and the
time periods for the first 4 modes and they are all within expected limits.
ETABS Natural Modes of Vibration 1st, 2nd, 3rd and 4th
However, the shape of the tower makes it susceptible to cross-wind excitement and this aspect will be
studied in more detail after receipt of the wind tunnel test results.
13.0
Wind Drifts
A normally acceptable wind drift ratio is H/400 to H/500 for a 50 year return period of wind. This wind drift
will be calculated for service load combinations with wind loads from the wind tunnel tests. Based on the
code wind loads, the preliminary analysis shows that the tower is stiff enough to fall within the above limits.
14.0
P-delta Effects
P-Delta analysis requirement for the seismic analysis will be verified and included, as per clause 1630.1.3 of
UBC-97.
P-Delta analysis requirement for the wind analysis will be verified and included, if necessary, at the detailed
design stage, as per Clause 12.8.7 ASCE 7-05.
15.0
Foundations
15.1
Tower Foundation
Although no soil investigation report is available for the project site yet, it is envisaged that a piled raft
foundation will be required to carry column and wall loads of the towers. The raft thickness is expected to be
about 4m under the tower at one end, reducing to about 3m at the other end.
15.2
Podium Foundation
The excavation for foundation and basement construction will be carried out either by an open excavation or
by a temporary soil retention system such as diaphragm wall or contiguous wall systems, depending on the
ground water condition at the reclamation land. As the whole site is covered by basements, the foundation
for the Podium will also be a raft (1.5-2.0m thickness) on piles. The selection of the final systems will be
made after a detailed review on the information provided by the soil investigation report.
15.3
Basement Walls
The basement walls will be designed as water retaining and in addition there will be external
waterproofing/tanking. The walls will be 600mm thick for B4 and B3 and can reduce to 400mm thick for B2
and B1.
16.0
Movement Joints
As the site is quite large, joints will be required in order to accommodate temperature movements during
construction and during service. The normal criterion is to space these at between 50-75m but, with suitable
design and detailing, the joint spacing can be extended up to 100-120m, especially in those floors that are
below ground or subject to little temperature change during service due to a controlled environment.
Due to expected differential settlement between the tower and the podium, a movement joint adjacent to
gridline P will be provided to separate the tower from the podium. However, this will result in potential
pounding problems from seismic sway, so the width of the joint will need to be carefully assessed during the
preliminary design stage.
17.0
Materials
Concrete will typically be Grade C45 to C80 depending on the strength requirements. The high strength
concrete will be used for the walls and columns at the lower levels of the towers. High strength concrete will
be achieved by the addition of silica fume to the mix and use of super-plasticizer to achieve a low free water
to cement ratio, typically below 0.40. A durable low heat of hydration concrete for the raft slabs and
basement walls will be achieved using a mix of OPC and GGBFS.
Concrete for piling may be triple blend comprising the ordinary Portland cement (OPC), the ground
granulated blast furnace slag (GGFBS) and the micro-silica.
Reinforcement will be high yield deformed bars fy = 460N/mm2
Block work walls will generally be constructed using lightweight concrete blocks with a density not
exceeding 600 kg/m3. A study was conducted to compare 3 different types of blocks available in Kuwait
and from this it is clear that the lighter blocks have an advantage as they can reduce the overall dead loading
per floor by as much as 10%, which will have a significant affect on the sizing of columns and foundations.
Structural steelwork will comply with BS5950 and will be Grade S275, S355, or S460 as required.
18.0
Durability
The design life for the concrete is 50 years. The extreme climate and presence of chlorides and sulphates in
the ground and the atmosphere create an onerous requirement for concrete durability which will be achieved
by adopting a combination of the following measures:



Specifying high quality, dense, low permeability concrete.
Specifying adequate cover to reinforcement.
Application of external tanking below ground and external protection above ground.
The following concert covers for rebar will be specified to achieve the more onerous requirement for either
durability or fire protection:




35 to 60mm for internal surfaces
50 to 60mm for external/exposed elements
75mm for pile caps
100mm for piles
Concrete below ground will be designed as water excluding, both to prevent ingress of water and also to
prevent aggressive ground water penetrating the concrete, causing corrosion of the reinforcement. The
design shall be to BS 8102 Type B using BS 8007 with a 0.2 mm crack width for the inner faces of raft and
retaining walls & 0.3 mm for the other faces. This should provide a Grade 3 environment within the
building (dry environment).
External water bars will be provided at all construction joints in concrete below ground (‘ground’ defined as
the level of backfilling behind the external walls of the building on completion).
The waterproofing system (membranes, protection boards, water bars, joint fillers, sealants etc) will be
specified to be from a single manufacturer’s product range to ensure compatibility and to be applied strictly
in accordance with the manufacturer’s instructions. Details will be developed with potential suppliers during
the design stage.
19.0
Fire Resistance
As per the requirements of NFPA 5000, the fire resistance shall be 2 hours for floor plates system and
between 3 and 4 hours for primary framing members, transfer structures, columns and walls, depending on
different levels. For any steel structures the appropriate fire rating will be achieved by providing a spray
applied cementitious, vermiculite or other polyvinyl coats, while the vertical steel elements within
residential or office units would have a dual fire protection system consisting of a thinner spray-on system
boxed out with gypsum board.
During the next phase of design the performance of high strength concrete elements subjected to high
temperatures will be investigated as these are prone to explosive spalling failure which can be overcome by
adding polypropylene fibres to the concrete mix.
20.0
Construction Methods and Sequence
These aspects will be considered during the PD stage, in consultation with buildability experts as well as
with the involvement of the potential main contractor. At this stage, the scheme as proposed does not pose
any undue challenges, apart from the great height, as the construction materials and structural system
selected are appropriate for Kuwait.
21.0
The Next Step- the Preliminary Design Stage
During the preliminary design stage, all structural members will be optimised for gravity loading and the
lateral stability systems will be optimised based on wind tunnel test results. The foundations will be
optimised based on results of the GI results and the ultimate aim of this activity will be to minimise concrete
and rebar quantities but at the same time to ensure buildability for fast construction and a quick floor-tofloor cycle for the tower. Key issues that will require attention are:







22.0
Ground Investigations
Enabling works package
Consultation with contractors and buildability experts
Detailed Wind Tunnel Tests after the structure has been optimised and fully coordinated with the
other disciplines (architecture, MEP, landscape, etc)
Second order effects (elastic, creep, temperature, shrinkage and p-delta).
Foundation design after receipt of the GI factual and Engineering report
Piling package
Acknowledgements
The author would like to acknowledge the engineering and architectural teams at Atkins Bahrain office for
their contribution to the design of this iconic building, and also notes that the artist’s image of the tower is
Atkins Copyright. All ETABS images were generated by the author during the concept design stage.
Compiled by Eng Arshad Khan, Nairobi, April 2013-(adapted from the Concept Design Report dated January 2009)