Advantages:

• Good for short spans
• Wide distances can be spanned by resting beams on piers

Disadvantages:

• Can be expensive, even for fairly short spans, because of the need to use steel. A cheap material for beam bridges is concrete, but concrete on its own, is not strong enough to stand up to high forces of tension (pulling), so concrete needs to be reinforced with steel mesh.
• Very expensive for long spans, because of the need for piers to support the long beams
• It is not always possible to build support piers.

BEAM SYSTEM

Beam bridges are the simplest type of bridge, with the earliest beam bridges being just fallen tree trunks. Single slabs of stone are also early simple beam bridges. Abutments on the ends of the bridge or piers in the center of a beam bridge support the weight.

Materials

As long as the forces stay balanced, a beam bridge will support the load. Simple deck beam bridges are usually metal or reinforced concrete. The bridge will fail if the forces within it become too great. Some building materials, such as concrete, can stand very high squashing (compression) forces, but not stretching (tension) forces. Other materials are better in tension than compression. Larger beam bridges consist of great steel girders or massive concrete structures.

Construction

A beam bridge is usually straight, flat, and simple in appearance. There is great variety not only in the materials used but in the shape needed to cope with particular types of load and the places where they are built.
Some bridges, instead of going straight across a road or river at right angles, have to go over at some other angle. These are called skew bridges.

Y.M.D. BRIDGE

Built: 1888

The Y.M.D. Bridge in Hilltown Township no longer is used for traffic. A new bridge was built next to this bridge at Forest Road just off Route 113.		A metal framework extends up the sides and over the top of this bridge.
The structures are held together with rivets.		Small trusses create triangulation on the vertical posts for extra support.

Callowhill Beam Bridge

Location: Callowhill Road - Perkasie, PA

Stream: East Branch of the Perkiomen Creek

This triple span bridge is made of reinforced concrete.		This bridge is on a well traveled road that can be very busy at rush hour. The width of this bridge can handle two lanes of traffic.
The piers are extended for a buttressing effect.		Note the worn buttresses on this side of the bridge.

Kellers Church Road Beam Bridge

Location: Kellers Church Road (near Meadow Lane) - Bedminster, PA

This bridge is a triple span beam bridge.		It has large stone abutments and stone piers.