357
Chapter 17 Constructing Structures
Cantilever bridges
Cantilever bridges use trusses extend-
ing out in both directions from the sup-
port beams, similar to arms. The ends of
the arms can intersect with the road lead-
ing up to the bridge or hook up to another
truss unit to form a longer span. The arms
transmit the load to the center.
Suspension bridges
Suspension bridges use cables to carry
the loads. A large cable is suspended from
towers. From the large cable, smaller cables
drop down to support the deck. Suspen-
sion bridges can span distances as great as
4000′ (1220 m) and longer.
Communication
Structures
Most telecommunication technology
relies on constructed towers to support
antennas. These towers are usually placed
on a concrete foundation. A steel tower is
built on top of the foundation. Once the
tower is complete, the signal wiring can be
installed. Similar techniques are used to
construct towers for power-transmission
lines. See Figure 17-26.
Truss
Cantilever
Suspension
Arch
Figure 17-25. Four of the five types of
bridges are the truss, the cantilever, the
suspension, and the arch. The fifth is the
beam bridge.
Figure 17-26. This helicopter is helping
to construct a tower for an electricity-
transmission line.
American Electric Power Co.