9A STRUCTURAL SYSTEMS FOR BRIDGES AND UNDERPASSES
The Safari Park Project includes several vehicular and pedestrian bridges as well as animal underpass crossings linking the
various safari zones. The following sections present the applicable structural system alternatives for bridges and underpasses,
evaluated in accordance with the same criteria adopted for the building structures in Section 9. The selected system for each
crossing element shall be confirmed during the detailed design stage following review of the approved Master Plan,
geotechnical investigation report, and loading requirements.
9A.1 STRUCTURAL SYSTEM ALTERNATIVES — BRIDGES
The following structural systems have been evaluated for bridge structures within the Safari Park. The primary driving criteria
are span length, clearance requirements, aesthetics, constructability, and durability in the Qatar environment. Load
combinations for bridge structures shall be based on AASHTO LRFD Bridge Design Specifications in addition to the codes
listed in Section 3.
Structural
System
System Description
System Advantages
System Disadvantages
Cast In-Place
RC Box Girder
Bridge
• A monolithic reinforced
or prestressed
concrete box section
spanning between
piers and abutments.
• The hollow
rectangular/trapezoidal
section provides high
torsional and flexural
rigidity.
• Suitable for medium to
long spans (30–200
m). Ideal for curved
alignments.
• Excellent torsional
stiffness — ideal for
curved alignments
• No exposed steel
requiring fire
protection
• Durable in
aggressive Gulf
environment
• Flexible section
geometry (single or
multi-cell)
• Continuity reduces
mid-span moments
• Requires extensive
formwork and
falsework
• Long construction time
• Significant self-weight
• Prestressing requires
specialist
subcontractor
• Higher initial cost than
simple beam
systems
Precast
Prestressed
Concrete I/TGirder Bridge
• Factory-manufactured
prestressed I-beams,
T-beams, or U-beams
placed on pier caps
with a composite castin-place concrete
deck.
• Common spans range
from 15 m to 50 m.
• The most widely used
system in the Gulf
region for highway
bridges.
• Fast erection —
minimal disruption
to traffic below
• Factory quality
control ensures
high durability
• Familiar to local
contractors
• Economical for
typical highway
spans
• Composite deck
adds stiffness and
reduces beam
depth
• Limited span range
compared to box
girder or cablestayed systems
• Requires craneage for
girder placement
• Coordination of
erection sequence
on site
• Connections between
girders require
careful detailing
RC Arch Bridge
• Load is transferred
primarily in
compression along the
arch rib to the
abutments.
• Suitable for spans of
50–300 m. The arch
may be a deck arch,
through-arch, or tied
arch (bowstring).
• Particularly suited to
landmark crossings
within the Safari Park
where aesthetics are a
priority.
• Structurally efficient
— arch works in
compression
• Highly aesthetic —
landmark quality
• Suitable for long
clear spans
• No intermediate piers
required within the
span
• Compatible with
themed
architectural design
• Requires strong
abutments to resist
horizontal thrust
• Complex geometry —
specialist design and
construction required
• Formwork for arch is
expensive and timeconsuming
• Not suitable where
poor founding
conditions limit thrust
capacity
Steel
Composite
• Structural steel plate
girders or I-sections
• Lightweight
superstructure
• Requires fire
protection to
Structural
System
Bridge (Steel
Beams + RC
Deck)
System Description
System Advantages
System Disadvantages
act compositely with a
cast-in-place
reinforced concrete
deck slab.
• Suitable for spans of
20–100 m and multispan continuous
configurations.
• Common for pedestrian
bridges, service
bridges and road-overroad crossings.
reduces
substructure loads
• Rapid erection —
minimises
disruption
• Suitable for tight site
constraints
• Flexible for nonstandard
geometries
• Composite action
reduces steel
section depth
exposed steel
elements
• Susceptible to
corrosion —
galvanising and
protective coatings
required (standard
for Safari Park)
• Regular inspection
and maintenance
needed
• Requires skilled
fabrication and
welding
• Higher material cost
than RC in Gulf
region
9A.1.1 Bridge System Illustrations
Figure 9A-1: Cast In-Place RC Box Girder Bridge — Elevation View
Figure 9A-2: Precast Prestressed I-Girder Bridge — Cross-Section View
Figure 9A-3: RC Arch Bridge — Elevation View
9A.2 STRUCTURAL SYSTEM ALTERNATIVES — UNDERPASSES
The following structural systems have been evaluated for underpass structures within the Safari Park, including animal
crossing tunnels, pedestrian subways, and vehicle underpasses. The design of buried structures shall account for earth
pressure, hydrostatic pressure where applicable, and vehicular surcharge in accordance with ASCE 7-16 and AASHTO LRFD.
Earth pressure coefficients shall be confirmed by the Geotechnical Investigation Report.
Structural
System
System Description
System Advantages
System Disadvantages
RC Box Culvert
(Single/MultiCell)
• A closed rectangular
reinforced concrete
frame buried beneath
earth fill or road
pavement.
• Single-cell or multi-cell
configurations.
Suitable for spans up
to 15 m per cell.
• The dominant
underpass solution for
animal, pedestrian
and vehicle crossings
in Safari Park.
• Simple and economic
to construct
• Suitable for shallow
cover and low fill
heights
• Can be cast-in-place
or precast
• Multi-cell
arrangements
provide wide clear
openings
• Compatible with
surrounding
earthworks
• Limited clear height
without increasing
structural depth
• Requires temporary
excavation and
dewatering
• Not suitable for high
groundwater without
waterproofing design
• Long construction
period for large multicell culverts
RC Portal
Frame
Underpass (UFrame)
• An open-bottom Ushaped reinforced
concrete frame with a
roof slab spanning
between two wall
legs.
• The base invert may be
a separate slab or
native ground
depending on
geotechnical
conditions.
• Used for road vehicle
and pedestrian
underpasses with
flexible foundation
design.
• Open base allows
flexible foundation
design
• Suitable for variable
ground conditions
• Economical for
medium-width
crossings
• Familiar to local
contractors
• Haunches at corners
increase structural
efficiency
• Base slab must be
added where
groundwater or
heave is a risk
• Lateral earth pressure
governs wall
thickness
• Less efficient than box
culvert for very
shallow crossings
• Requires careful
backfill compaction
to control pressures
Precast Buried
Arch / SoilSteel Arch
• Precast concrete arch
segments or
corrugated steel arch
plates are assembled
in a trench.
Compacted granular
fill provides soil-arch
• Very fast installation
— minimal
formwork
• Excellent span-todepth efficiency
• Requires minimum
cover (typically ≥
H/4)
• Fill compaction quality
is critical to
performance
Structural
System
System Description
System Advantages
System Disadvantages
interaction for load
resistance.
• Clear spans up to 20 m
are achievable.
Minimal excavation
and rapid installation.
• Soil-arch interaction
reduces structural
demands
• Suitable for wildlife
and pedestrian
crossings
• Good aesthetic
integration with
landscape
• Not suitable for very
high live loads
without validation
• Requires specialist
supplier and
installation
• Limited flexibility for
irregular geometry
9A.2.1 Underpass System Illustrations
Figure 9A-4: RC Box Culvert Underpass — Cross-Section View
Figure 9A-5: Portal Frame (U-Frame) Underpass — Cross-Section View
Figure 9A-6: Precast Buried Arch Underpass — Cross-Section View
9A.3 QUICK COMPARISON SUMMARY
The table below provides a concise summary of all evaluated systems to assist in system selection at the detailed design
stage.
System
Type
Typical
Span
Key Advantage
Primary Use in Safari
Park
RC Box Girder
Bridge
Bridge
30–200 m
High torsional stiffness;
curved alignments
Main vehicular crossings
Precast I/T-Girder
Bridge
Bridge
15–50 m
Fast, economical, familiar
to local contractors
Road overpasses, short
crossings
RC Arch Bridge
Bridge
50–300 m
Landmark aesthetic;
compression-efficient
Themed gateway and
feature bridges
Steel Composite
Bridge
Bridge
20–100 m
Lightweight, rapid erection
Pedestrian and service
bridges
RC Box Culvert
Underpass
Up to 15
m/cell
Simple, durable, economic
Animal and pedestrian
crossings
Portal Frame (UFrame)
Underpass
Up to 20 m
Flexible base; adaptable to
ground conditions
Vehicle underpasses
Precast Buried
Arch
Underpass
Up to 20 m
Fast installation; landscape
integration
Wildlife crossings,
pedestrian tunnels
Note: The recommended system for each specific bridge and underpass crossing shall be confirmed during the Detailed Design phase
following review of the approved Master Plan, the Geotechnical Investigation Report (GIR), and the project-specific loading requirements.
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