3.
3 Decks
A bridge deck (or road bed) is the roadway, or the pedestrian walkway, surface of a bridge. The
deck may be of either cast-in-situ or precast concrete, wood which in turn may be covered with
asphalt concrete or other pavement. The concrete deck may be an integral part of the bridge
structure (e.g., T-section beam structure), or it may be supported with I-beams or steel girders, as
so-called composite bridges. The deck may also be of other materials, such as wood or open steel
grating.
Sometimes the deck system is called a floor system, such as for a bridge deck that installed in a
through truss. A suspended bridge deck will be suspended from the main structural elements on a
suspension or arch bridge. On some bridges, such as a tied arch or a cable stayed, the deck is a
primary structural element, carrying tension or compression to support the span. But for girder
beams, the bridge deck system is not the load carrying system. Despite this, they are important
for the bridge serviceability, safety as well as the aesthetics. Thus, deck system deserves special
attention in all bridge design and construction.
The deck system varies with different bridge types and bridge superstructure construction
methods, and particular attention of this chapter will be given to the bridge accessories with
special emphasis on pavement, drainage system and waterproofing system, expansion joint,
sidewalk, lamps post, handrail, and guardrail.
Types of Bridge Decks Photo
In the case of a Tied arch or cable-stayed bridge, the deck is the main structural element that
carries the load and transfers it via cables. Also, the deck has an important role in establishing
the aesthetic appearance of the bridge. So while designing a bridge, it is very important to give
special attention to decks to maintain good serviceability, safety, and appearance, etc. The deck
system varies according to the bridge structure, types of construction methods. Here we discuss
various types of bridge decks;
3.3.1 Purpose of Deck
The purpose of a bridge deck is to provide a flat surface for vehicles, pedestrians, or trains to
travel across a body of water, valley, or other obstacle. It acts as the roadway of the bridge,
supporting the weight of the traffic and transferring it to the bridge's substructure. A strong and
durable bridge deck is essential for the safety and functionality of the entire bridge structure.
The different important purpose of bridge deck are listed below
1. Structural support: Bridge decks provide a solid structure that supports the weight of vehicles,
pedestrians, and other loads crossing the bridge. They transfer these loads to the bridge supports,
such as abutments and piers.
2. Safety: Bridge decks provide a stable and safe surface for vehicles and pedestrians to travel
across. They are designed to withstand various weather conditions and loads, ensuring the safety
of all users.
3. Durability: Bridge decks are designed to be durable and long-lasting, with materials chosen to
withstand the effects of traffic, weather, and other environmental factors. Proper maintenance is
crucial to ensuring the longevity of the bridge deck.
4. Functionality: Bridge decks are designed to accommodate the specific needs of the bridge,
such as the number of lanes, width, and slope. They are also designed to allow for expansion
joints to accommodate changes in temperature and prevent damage to the structure.
3.3.2 Types Deck
Reinforced Concrete Decks
Concrete Decks are most common in bridge construction and this is especially because of the
ease of preparation and placement to various shapes and sizes. Concrete decks have good
durability, are very resistant to wear, and also provide good traction control. Among these design
features the durability of the concrete decks is also very dependent on the drainage system
provide, reinforcement cover, bridge skew, and thickness of the slabs.
The main cause of concrete slab deterioration is due to reinforcement corrosion. The corrosion is
typically due to the chloride attacks (penetration of chloride molecules through the cracks on the
decks). So as said earlier the provision of adequate reinforcement cover is very important in deck
slabs. There are different types of concrete decks are used in bridges and some of them are;
Solid Slab Bridge Decks
Solid rectangular (fig: 1) is not very efficient structural form in bridges as because of the moment
of area is small relative to its area and weight. This type of decks mostly adopted in relatively
small span (upto 20m) and the cost of construction is comparatively low and reinforcement is
simple.
Voided Slab Deck
Voided rectangular slab sections are used when the span range of bridge in between 20-30m. It is
common in some countries to use situ concrete with polystyrene voids as shown in figure. This
can be constructed using ordinary reinforced concrete or can be post tensioned.
The presence of voids may increases the cost of construction and this is because of the voids
adds complexity to the reinforcement particularly the reinforcement in transverse bending
section. But it reduces the self-weight and area of the concrete to be prestressed with affecting
the second moment of area. The diameter of the void most often given 60% less the depth, also
the void must accounted for considering the design to resist transverse bending.
T Slab Sections
T sections are mostly adopted in span range of 20-40m as an alternative to void slabs in bridges.
The beams can be done on either precast or on site construction. The top portion of the T section
called flange which supports the slab work with beam to reduce the compression and deflection
can be controlled to a great extent.
Also it has greater moment of resistance compared to rectangular sections and cast
monolithically with slab. The main challenges in T section bridges are the action of shear force.
Cracks can develop in web and flange due to the changes in cross section.
T sections source: researchgate.com
Box Slab or girder section
Box sections are used when the span more than 40m and box sections are more economical in
constructions of decks in this span range. T section has higher area moment of inertia per unit
weight compared to T sections and voided slab. The box girders can also be constructed as
precast section or composite with precast, pre-tensioned U section and an in situ concrete slab.
The box girders have many advantages like good resistance to torsion and this because of the
deck is in curved plane. Also the girder can be constructed in wider because of the presence of
two webs and strong flanges. The interior of the box girders can be used for service such as gas
lines, pipe lines, cables etc.
Box Girders
Steel Orthotropic Bridge Decks
Steel orthotropic decks are now extensively used in Europe, South America and Asia. The main
advantages of these decks are the weight of the structure can be considerably reduced (due to the
decks are designed integral with girders as a common flange), have a long life and easy to install.
Another feature of steel orthotropic Bridge Decks is that in short span bridge it can be installed
as a single unit. A major drawback in steel bridges is the effect of fatigue. A detailed design is
necessary to overcome fatigue issues in steel bridges.
Steel Orthotropic Bridge Decks
Composite Bridge Decks
Composite Bridge Decks can generally refer to the interaction of structural members of concrete
and steel. This is used in bridge construction is mainly because of the ability to adapt the
geometry and design constraints and also the reliability of steel members. The shear transmission
in composite decks is done through shear connectors which are embedded in concrete and the
other end is welded on the steel beam.
The concrete is good in compression and steel is good in tension and compression. Hence
the deflection can be controlled to a large extent. Also, the steel members can be recycled in the
future during the time of demolition. The steel as the main member is easier to erect when
compared to the concrete girder.
Composite Bridge Decks
Fibre Reinforced Polymer Decks
Fibre Reinforced Polymers are mostly used in the aerospace industry and now it’s also used in
bridge construction. FRP composite materials are made up of fibre aligned within resin materials
and this makes the panels very strong, customizable, and very light. Carbon and glass fibres are
most often adopted for bridge decking. It is installed as full-depth deck panels after molding it
into cellular panels.
Fibre Reinforced Polymer Decks
Fibre Reinforced Polymer Decks are used as an alternative to cast in place concrete Bridge
Decks. These panels are designed to interlock each other with male and female shear keys. To
connect it over the steel frames, pockets are formed over the beam and then welded by shear
connectors.
FRP materials can lose strength when exposed to high heat and result in a vehicle accident.
Asphalt, concrete or polymer materials are given in wearing surfaces as overlays. FRC is very
useful in movable bridges, decks or slabs subjected to the highly corrosive environment
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