Bridge construction has been
improved tremendously with the advancement in science and technology. Better
and lighter materials are now available that can endure greater loads. The
construction is now much faster due to the introduction of a variety of heavy
construction equipment.
Bridge construction tends to
involve huge projects that encompass the utilization of skills related to
several engineering disciplines including geology, civil, electrical, mechanical,
and computer sciences. Therefore, integrating the efforts of all involved must
be meticulous. The initial plans are prepared regarding the project, including
the characteristics of the desired bridge, the site details, and the
requirement of resources. The bridge design will be determined by the type of
bridge being constructed. The main types of the bridges are beam, arch, truss,
cantilever, and suspension. The beam bridge is one of the popular types.
Bridges can also be categorized by the planned use, like road and rail bridge, pedestrian pavement, material to be used like
steel or concrete, and fixed or moveable. Moveable bridges are constructed when
the ship height may be more than the bridge floor. In such situations, the road
has the capability to be lifted or pivoted, to permit marine traffic movement
under it.
Construction of the
foundations is the first step toward building a bridge. This process involves
detailed geotechnical investigations of the bridge site. The type of bridge
foundation has to be selected, such as the well foundation, pile foundation,
and the opened foundation. Each foundation is suitable for specific soil
strata, and the desired bridge characteristics. The soil characteristics will
determine the load bearing capacity, and other important parameters. The superstructure
is basically designed in accordance with the technical requirements, aesthetic
reasons, and the construction methodology. Excavation required for the
foundations may need to be executed to sizeable depths, involving hard ground,
before the solid rocks are reached. Engineering feats will be involved to avoid
water, and prevent collapse of the diggings. Tunnels specifically may be
subjected to sudden failures.
Heavy equipment will be used
extensively during the bridge construction including bulldozers, excavators,
asphalt mixers, formworks, and fabrication equipment. The construction and
other equipment needs to be identified thoroughly, according to their
capability and other desired functions. The foundation and the superstructure
design will need to be considered. This expensive equipment should not remain
idle, and must be used cautiously to obtain optimum advantage.
Several loads act on a bridge,
and the bridge is designed accordingly. Dynamic loads are particularly of prime
significance. A bridge is designed to endure the normal vehicle loads, and
other forces created due to winds and earthquakes. Several bridges have
collapsed due to high speed winds. Even if the wind speeds are reasonably low,
the dynamic forces can become excessive for the bridge to resist. Initially,
the bridge may vibrate violently, causing the bridge structure to fail at a few
weak elements, or even damage the major components. Investigations conducted
after bridge failures have revealed that the real forces on bridges that
collapsed were significantly less compared to the loads for which the bridge
was designed. However, the oscillations created due to the winds were enough to
cause the failure. Therefore, special reinforcement may be necessary for
prevention against high speed winds and earthquakes. Thus, lighter materials
are used that are arranged in suitable geometric structures, and it is ensured
that the configuration is aerodynamically stable.
Since bridge construction is
an expensive project, it is essential that all necessary tests may be conducted
prior to the actual construction. These tests and investigations can reveal the
bridge behavior under different dynamic
loads. Computer aided design and testing are powerful tools that must be used
to assist in the bridge design. Bridge design has benefited considerably due to
the growth of computer programs. Such computer programs reveal immense
information concerning the effect of different forces being applied on a
bridge. Wind tunnels are being used extensively for the analysis of aircraft
designs. Now these techniques are also being applied for bridge design
examination. A wind tunnel is basically a space that is enclosed. Air at a fast
speed is moved through the bridge model. Likely design and structural defects
can be discovered by photography and study of the air movement pattern over the
model.