In The Name Of Allah

Mansoura University.Faculty Of

Engineering.Civil Eng . Dept.

Report No ( 1)

Arch Bridge

Contents1 -Overview.

2 -How do the abutments support an arch bridge.?

3 -Stone Arch Bridge.

4 -Concrete Arch Bridge.

5 -Precast Concrete Construction.

6 -THE STONE ARCH BRIDGE.

7 -THE KEYSTONE.

8 -HOW TO BUILD AN ARCH.

9 -Skew Arch Bridge.

10 -THE END.

Arch Bridge

Overview

Arch bridges are one of the oldest types of bridges and have great natural strength. Instead of pushing straight down, the weight of an arch bridge is carried outward along the curve of the arch to the supports at each end. These supports, called the abutments, carry the load and keep the

ends of the bridge from spreading out .

The Romans developed considerable skill in constructing arches and many of their structures remain intact today. However, they were not able to calculate the strength of their-arches although their knowledge of geometry inherited from the Greeks led them to adopt semicircular spans. Their arches were constructed

of stone made into the form of wedge shaped segments, or voussoirs, built up side by side on temporary timber supports until the top piece at the crown of the arch is pushed hom(keystone). One of the most famous examples of their handiwork is the Pont du Gard aqueduct near Nîmes, France. Built before the birth of Christ, the bridge is held together by mortar only in its top tier; the stones in the rest of the structure stay together by the sheer force of their own

weight.

Modem arch bridges are built of concrete. It is an effective way to transfer loads to the ground where foundation conditions are adequate to resist horizontal loads. A large nurnber of concrete arch bridges have been constructed in the 20th century in both in-situ reinforced

concrete and precast concrete .

Today materials like steel and pre-stressed concrete have made it possible to build longer and more elegant arches, including a spectacular 1700 foot span in New River Gorge, West Virginia. (More typically, modern arch bridges span between 200-800 feet.)

A prime consideration in the erection of an arch bridge is the method of supporting the voussoirs during construction. The cost of staging required to support the arch centering during the placing of the voussoirs represents a substantial proportion of the cost of construction. Their design and construction therefore requires

detail investigation .

How do the abutments support an arch bridge?

Cut a strip of cardboard that's about one inch by 11 inches. Gently bend the strip so that it has a curve. Position the cardboard on a table so that it resembles an arch. Press down on the center of the arch. What happens to the ends of the

cardboard?

Next, place a stack of books at each end of the arch. Press again. Now what happens? Notice how the stacks of books act as abutments, keeping the

ends of the arch from spreading apart.

When supporting its own weight and the weight of crossing traffic, every part of the arch is under compression. For this reason, arch bridges must be made of materials that are strong

under compression .

Stone arch bridge

Concrete arch bridge

Constructing an arch bridge can be tricky, since the structure is completely unstable until the two spans meet in the middle. The method of construction of precast concrete arches is similar to the method of construction used

during the Roman period.

Wedge shaped precast concrete segments are used as voussoirs and these are built up side by side on temporary supports. There are two basic methods of providing the temporary support system: the provision of a supporting system below the bridge and the use of a tower and stay system. Gladesville Bridge in Sidney, Australia was constructed using

hollow precast concrete segments .

They were placed on falsework supported from the ground. The false work was designed to accommodate a 80-foot 200-foot navigation channel. A diagrammatic representation of the construction of an arch using a tower and a stay system is shown in the figure below.

Precast Concrete ConstructionThe most common form of precast concrete bridge construction is with the use of the conventional precast bridge beams. Different types of precast concrete decks and their structural advantages have been dealt with other speakers on this course. The construction of these types does not in general require special techniques. Their construction will therefore not be

considered.

Precast segmental construction is widely used for the construction of long bridges and viaducts with medium to long spans. In this form of construction, segments are manufactured in a casting yard near the site and then transported to their final position for assembly. During the early stages of development of segmental precast construction, the joints between the segments were wet poured grout or dry mortar pack.

These type of joints enabled the segments to be adjusted ensure that the bridge follows the correct alignment. Modem segmental construction uses the match casting technique. In this method the segments are cast against each other in the same relative order they will have in the final structure. No adjustment is therefore necessary between the segments at assembly. The joints are either left dry or

skimmed with a layer of epoxy resin.

Remember That!!

Arch bridges are one of the oldest types of bridges and have been arounded for thousands of years. Arch bridges have

great natural strength.

They were originally built of stone or brick but these days are built of reinforced concrete or steel. The introduction of these new materials allow arch bridges to be

longer with lower spans .

Instead of pushing straight down, the load of an arch bridge is carried outward along the curve of the arch to the supports at each end. The weight is transferred to the supports at either

end.

These supports, called the abutments, carry the load and keep the ends of

the bridge from spreading out.

The load at the top of the key stone makes each stone on the arch of the bridge press on the one next to it. This happens until the push is applied to the end supports or abutments which

are enbedded in the ground.

The ground around the abutments is squeezed and pushes back on the

abutments.

THE STONE ARCH BRIDGE

The Arch Bridge is very common. They were built with stone before iron and steel bridges were introduced. A good example is seen in the picture below. The Romans used arch bridges throughout Europe and many of them are still standing today as

they are very strong .

THE KEYSTONE The keystone is the most important stone in an arch bridge, without this stone the arch would collapse. The keystone holds the arch

together .Draw a stone arch and label the keystone. Explain why the Keystone is very important.

HOW TO BUILD AN ARCH

Before an arch can be built a wooden frame is built. This allows the stones to be put in position. The frame is removed after the stones are in

position.

EXAMPLES OF STONE ARCH BRIDGES

Skew Arch Bridge

THE END