Composites Technology October 2010

Engineering Insights
A MARVEL
IN MAKKAH
Overall tower height: 610m/2,001 ft
Composite cladding: 45,000m2/484,376 ft2
Mosaic tiles: 100 million (13,000 gold)
LEDS (light-emitting diodes): 700,000
Composite design makes possible the world’s largest clock and tallest clock tower.
R
compositesworld.com
Source | Premier Composite Technologies
ising above Islam’s holiest city, the 610m/2001-ft tall Makkah
Clock Royal Tower is the focal point for the nearly complete
Abraj Al-Bait hotel complex opposite the Grand Mosque of
Makkah (Mecca) in Saudi Arabia. A key part of the Development
of King Abdul Aziz Endowment (DOKAAE) project, devised to
upgrade the mosque environs, the clock tower is the world’s largest
— almost five times the size of London’s Big Ben.
When Premier Composite Technologies (PCT, Dubai, United
Arab Emirates) was tasked by lightweight-architecture specialists
SL-Rasch (Leinfelden-Echterdingen, Germany) to build and install
the clock, it came well prepared. Previously, PCT had fabricated
composite protection flaps for mechanized umbrellas (see “Learn
More,” p. 48) and, earlier, 27 fiberglass sliding domes for the Holy
Mosque of the Prophet in Al-Madinah (Medina), Saudi Arabia, as
well as composite domes up to 42m/138-ft in diameter for showpiece buildings elsewhere in the Middle East and Asia.
46
Spire
FINIAL:
Carbon/epoxy
structure
(no steel substructure)
160m/525 ft
Helicopter control tower
Solar panels
PCT’s managing director, Hannes Waimer, credits the failure-free
performance of these structures, in part, to detailed design and testing performed by the SL-Rasch/PCT team. Paired on many projects,
beginning with the sliding domes in 1988, PCT and SL-Rausch nevertheless faced some unusually large challenges in this massive tower.
Because it is rectangular — the east and west faces are slightly more
narrow (38m/125-ft wide by 43m/141-ft tall) than the north and
south faces (43m/141 ft square) — PCT would have to fabricate two
different pairs of clock faces, each assembled from hundreds of differently shaped panels, which would be drilled to accommodate a total of 700,000 light-emitting diodes (LEDs) for night-time illumination. Further, the clock would be crowned with a 22m/72-ft diameter,
160m/525-ft tall, crescent-topped finial (see drawing, p. 47), which
would house a Lunar Observation Center. Compounding the difficulty, the hotel was already under construction when Saudi King Abdul Aziz decided that its main tower should be crowned with a clock
— the original 76-story structure was not designed to
support the 200m/656-ft tall addition. “This is where
composites came into play,” Waimer explains. “Composites offered a very light, yet strong construction as
well as a fast and economical fabrication process.”
Low weight/high function
This close-up of one of
the four massive Makkah
Clock Royal Tower clock
faces (note the man in lower
left corner for scale of
structure).
Crescent
To minimize weight, the team designed a steel spaceframe clad with composite panels strong enough to
resist wind speeds of 53.8 m/sec (131 mph/211 kmh).
Here, PCT enlisted the aid of materials supplier Gurit
UK (Newport, Isle of Wight, U.K.) not only to develop
composite laminate plans, but also to perform finite
element analysis (FEA). The latter confirmed a stiffnessdriven design, which pointed to sandwich construction; final materials selection also was influenced by
the need to meet British Fire Standard BST476-7 Class
I surface flame-spread requirements while maintaining
sufficient laminate stiffness and strength in a structure
compromised by thousands of LED ports.
“We … had to integrate [the] LEDs into this substructure and then extend them through the cladding
to be visible from the exterior,” says Waimer. Gurit’s
FEA determined both the local and global effects that
the through-holes would have, and PCT verified the
predictions via testing.
The clock tower’s scrollwork and other complex, three-dimensional (3-D) ornamentation tested
Composite cladding
panels over steel
spaceframe, with
mosaic-tile overlay
Observation
deck
Lunar
Observation
Center
Comosite
dome and
glass/epoxy-clad
corner tower
43m/141 ft
Lightning arrestor deploys
from each corner of clock face)
Hour hand
(23m/75-ft long by
3m/10-ft wide)
Arcade (glass/epoxy w/
mosaic-tile overlay)
Top of original 76story hotel tower
Illustration | Karl Reque
Engineering Challenge:
Design Solution:
Add a 200m/656-ft tall clock and finial to a hotel tower originally designed to accommodate neither, using materials that minimize added
weight yet can reproduce the complex, sculpted architectural style of
the Middle Eastern locale.
Use steel-spaceframe-supported carbon- and glass-fiber-reinforced,
sandwich-construction cladding panels for the clock and clock hands,
and the corners, and top the structure with a self-supporting, allcarbon composite structure for the finial.
PCT’s ability to keep pace with the client’s construction schedule.
This, and the large number and intricacy of the molds, tipped the
scale toward wet layup. This decision limited PCT’s core choices.
“We looked at using aluminum honeycomb,” Waimer recalls, “but
we were not comfortable that it would meet the significant bonding requirements due to our need to use wet layup.” Instead, PCT
chose Divinycell P100 polyethylene terephthalate (PET) foam, supplied by DIAB International AB (Laholm, Sweden), because it met
mechanical and fire requirements and was compatible with the wet
lay/vacuum bag process.
Used in all of the clock tower cladding, the PET core thickness
varies from 15 mm to 20 mm (0.6 inch to 0.8 inch) for most panels
to as thick as 50 mm/2 inches in the clock tower corners. “We analyzed every part of the building,” says Waimer, “to put in precisely
what material was needed, but no excess, in order to save weight.”
Next, he recounts, “We needed to develop an economical method for attaching the panels, which averaged 20m [66-ft] long and
2.5m [8-ft] wide, to the building.” To meet wind load requirements,
PCT decided to attach the cladding to the spaceframe using a variety of steel brackets. Solid-laminate flanges, 280 mm/11 inches long
were molded into the cladding panels, enabling the cladding to be
through-bolted to the brackets.
Working with Stuttgart University (Stuttgart, Germany), SLRasch engineered and tested a system for incorporating lightning
arrestors into the composite cladding. Further, in each of the tower’s
four corners, 3m/10-ft telescoping steel lightning arrestors deploy
automatically during storms (see drawing, this page).
Sandwich-construction cladding
The cladding panel skins, 2 mm to 3 mm (0.08 inch to 0.12 inch) in
thickness, were mostly 800 g/m2 (23.5 oz/yd2) and 1000 g/m2 (29.4 oz/
yd2), stitched E-glass quadraxials with balanced construction. Small
quantities of unidirectional and stitched 0°/90° reinforcements were
also used locally where additional properties were needed. Suppli-
CT o c t o b e r 2 0 1 0
Besting
Big Ben
MAKKAH CLOCK ROYAL TOWER
Abraj Al-Bait Hotel Complex
47
ers included a mixture of Chinese and European
companies, including Formax UK Ltd. (Leicester,
U.K.) and Saertex (Saerbeck, Germany).
PCT selected Gurit’s Ampreg 21FR epoxy with
Ultra Slow hardener for the wet lamination resin,
which offered structural performance, durability
and compatibility with the epoxy adhesives used
for secondary bonding of structures. Computercontrolled cutting machines from Aeronaut Elektron (Terrey Hills, New South Wales, Australia)
minimized waste in kitting the fabrics and foam,
and the fabrics were wet-out using impregnation
machines designed and built in-house. After layup,
laminates were vacuum-bagged, with some parts
cured at room temperature overnight and others
cured in an oven to shorten overall cycle time. All
cured parts were then placed outside in the sun
to achieve a postcure, as Waimer explains, “Some
panels are very large, 30m2 to 40m2 [323 ft2 to 431
ft2], fabricated in one piece; so everything must be
postcured to ensure the required ... properties.”
compositesworld.com
Lightweighting the hands of time
46
More heavily loaded than the cladding panels and each equipped
with roughly 3,000 LEDs, the clock faces’ minute and hour hands
(3m/10-ft wide, 26m/85 ft and 23m/75 ft long, respectively) needed
to be stiff and lightweight to prevent excessive deflection and vibration during service. Heat generated by the LEDs and absorbed by
the predominantly black tiled finish in the sun demanded a higher
design temperature (85°C/185°F) than the clock faces.
The clock hands are sandwich structures. Skins feature an outer
layer of prepregged glass cloth, backed by three to nine plies of Gurit’s WE91-2 prepreg, made from large-tow carbon fiber manufactured by Zoltek Inc. (St Louis, Mo.) and SGL Technologies GmbH
(Wiesbaden, Germany). The core is Gurit Corecell T-foam, a styrene
acrylonitrile selected because it offers greater rigidity and strength
than PET and resists temperatures up to 100°C/212°F. Core density
varied from 80 kg/m³ to 130 kg/m³ (5 lb/ft3 to 8lb/ft3), and thickness
ranged from 20 mm/0.8-inch to 30 mm/1.2-inch, with another three
to nine plies of prepreg on the inner skin. To connect the hands to
their steel hubs, 26 plies of prepreg were laid to form a solid laminate
up to 21 mm/0.83 inch thick. The clock hands were cured under
vacuum bag at 80°C/176°F.
Designed as a self-supporting structure to minimize weight, the
finial was driven by a high stiffness-to-weight requirement. “The
client wanted to use the inside space, so we could not use a steel
substructure here,” Waimer points out. “It would have occupied too
much room.” The laminate combines unidirectional, biaxial and, to
Read this article and view additional construction photos of the Makkah
clock and PCT’s umbrella project online | http://short.compositesworld.
com/qUD9kZt8.
Source | Premier Composite Technologies
Engineering Insights
To test the design, a quarter clock face
was built near Premier Composite
Technologies’ 21,275m2 (229,000-ft2)
facility. Drilling and LED insertion alone
took eight people more than eight days,
using injection molded 30 percent glass
polybutylene terephthalate tubes bonded
with Gurit’s Spabond 340 LV epoxy
adhesive. Erection of its nearly 50 parts,
including 700m2 (7,535 ft2) of composite
cladding, took six days and a crew of 12
and was the means to train installers.
The section later was shipped to Makkah
for incorporation into a clock face.
speed production, multiaxial fabrics made from Toray Industries’
(Tokyo, Japan) T700 carbon fiber.
“The finial was actually not as difficult to mold because it was
larger with more gentle curves,” Waimer recalls. “The scrollwork and
other decorations on the clock faces required using thinner fabrics
because we could not get the heavier textiles into and around the
corners, so this slowed fabrication.” Because the finial was wet-layed,
the same low-temp Divinycell P100 foam used in the cladding was
sufficient. Ultimately, the finial adds only 12 metric tonnes/26,456
lb to the building load.
Analysis, testing and installation
During the past 18 months, PCT has built more than 18,000m2
(193,750 ft2) of molds and already has fabricated 60 percent of the
project’s 45,000m2 (484,376 ft2) composite cladding. Approximately
100 million Italian mosaic tiles have been epoxy-bonded to the tower
exterior — including 13,000 made from gold. The reflective tiles not
only provide continuity with Middle East architectural styling, but
also reduce panel surface temperature and, reportedly, will provide
100-year protection from UV degradation, under which, Waimer
contends, “no paint will last even 10 years.”
As CT went to press, all clock tower panels and segments had
been fabricated and shipped to the construction site. Waimer hopes
to complete installation by the first quarter of 2011. With the finish
in sight, Waimer says, “This has been an extremely challenging project, but also a once-in-a-lifetime project.” | CT |
Contributing Writer
Ginger Gardiner is a freelance writer
and regular CT contributor based in
Washington, N.C.
[email protected]