**3.6 Truss bridge**

The truss bridge is a load-bearing structure efficiently incorporating trusses in an array of triangular sections and has been around for centuries. Dynamic loads are accommodated by triangular elements which absorb tension and compression. The combination of tension and compression ensures the structure of the bridge is maintained and the decking area remains uncompromised even in relatively strong winds.

### **3.7 Tied arch bridge**

Incorporating an arch structure supported by vertical ties between the arch and the deck, the tied arch bridge creates downward pressure from the arch structure to the deck of the bridge which translates into tension by the vertical ties. The tips of the arch structure are connected by a bottom chord. The deck strengthening chord connects the tips of each end of the acting like a bowstring which absorbs pressure.

## **4. Bridge components**

Consideration is given to the three primary components of a bridge structure and their subcomponents of which all are subject to elements of deterioration and potential failure.

#### **4.1 Foundation**

A bridge foundation, for all types of bridges, consists of the following components: *Piles:* The initial foundation of a bridge are piles, wood, steel, or concrete, driven into the ground to support the entire weight of a bridge. By distributing p Piles distribute weight and stresses applied by the bridge evenly through the ground making it stable and strong.

*Caps:* To provide additional load transferring capacity pile caps are placed on top of the pile foundation provide additional load transferring capacity to the piles and give maximum strength to the upper part of the bridge.

*Bents:* Forming the foundation for the substructure bents connect piles and caps.

#### **4.2 Substructure**

A bridge substructure consists of the follow components which transfer the bridge load forces to the foundation:

*Abutments:* Capable of withstanding high levels of horizontal force abutments are the vertical support at the ends of the bridge.

*Piers:* Providing support points for the bridge piers are mounted at the end of each span to reduce the effects of forces and vibrations.

*Pier Caps:* Acting as a space for the girders pier caps function to transfer loads on bearings from the superstructure components on the top.

#### **4.3 Superstructure**

The bridge superstructure.

*Girders:* Girders (or beams) join pile caps together and give support to the deck and can be over a single span spans joining all the bents, dependent on the length of the bridge. Girders usually have a truss design to improve stress and load resistibility, passing pressure to the foundation.

*Bearings:* Bearings are structural members capable of transferring loads from the deck to the substructure. These displace stresses and load to the piers through the girders to allow movement between parts of a bridge. The movement can be linear as well as torsional.

*Trusses:* Trusses are made by joining triangular components to divide loads and bending moments through the bridge. Some types are simple trusses, suspension, and also cantilever trusses. The truss network provides a surface for transportation which can be built as a deck truss, pony truss, or through truss. Each truss differs in how the traffic will move on the bridge.

*Decks:* Decks made of concrete or metal direct traffic load and include drainage systems, curbs, expansion components, sidewalks and approach slabs.

*Barriers:* Bridges have barriers on the sides for safety and protection of the decks.

*Arches:* A bridge with arches has a high degree of strength. Arches control the safety and load bearing ability of the bridge. The quantity of arches and materials used for construction is very important.

*Spandrel:* A space connecting the bridge pillars and deck beam is called the spandrel. There can be open or closed spandrels depending on the arch design.
