STRUCTURES

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25 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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STRUCTURES

By Mr. V. Shaikh

Why learn about structures


It all started in the caves


Na it is too boring, dark and wet.
Animals share it.


Lets move outside. It is bright and
colourful



What about the rain and wind?


Cut some trees and branches and big
leaves and fashion a …………

What next


This does not protect us much from the wind
and rain.


Hey, I have an idea!! Lets collect stones and
mix some mud to build a wall.


That’s better, but what about the roof?


Should we put branches and dried leaves.


Works but not that great


The designer bug has got into me. I will
research some new material called iron


Types of structures


Buildings


Towers


Dams


Domes


Tunnels


Bridges

Bridges


Why learn about bridges?


You see and use them all the time.


Easy to understand the principles of
design and build models.


Lots of resources available.

Types of Bridges


Girder Bridge



Truss



Rigid Frame


Arch



Cable Stayed



Suspension

Girder Bridge


Typical Span Lengths


10m
-

200m


Most common and most basic bridge.


I
-
beam girders and box
-
girders.


I



Beam girders easy to construct


but unstable for curves.


Not suitable for torsion


Box Girders are more stable


but difficult to weld from inside.

Truss Bridge


Typical Span Lengths


40m
-

500m


In most cases the design, fabrication, and
erection of trusses is relatively simple


The small size of individual parts of a truss
make it the ideal bridge for places where large
parts or sections cannot be shipped or where
large cranes and heavy equipment cannot be
used during erection.


Common types are:

Warren truss, the Pratt truss,

and the Howe truss.








Questions


Rigid Frame


Rigid frame bridge is one in which the piers
and girder are one solid structure.


The three main types are: Batter Post, ‘V’
Shaped and Pi Shaped

Arch


Typical Span Lengths


40m
-

150m


Arches use a curved structure which provides a
high resistance to bending forces.


Arches are well suited to the use of stone.
Many ancient and well know examples of stone
arches still stand to this day


Good choices for crossing valleys and rivers




Types of Arch Bridges


Structurally there are four basic arch types:



hinge
-
less
-

very rigid, no deflection


two
-
hinged


most common, economical


three hinged


more flexible, difficult to make


tied arches


bottom ends tied, used when
foundation is soft


Cable Stayed


Typical Span Lengths


110m
-

480m


A typical cable stayed bridge is a continuous girder
with one or more towers erected above piers in the
middle of the span. From these towers, cables
stretch down diagonally (usually to both sides) and
support the girder.


Steel cables are extremely strong but very flexible.


Economical, slender and lighter structure which is
still able to span great distances.


Bad in high winds great in earthquake prone areas

Types of Cable Stayed Bridges


Can be classified by number of spans, number
of towers, girder type, number of cables.








Suspension


Typical Span Lengths


110m
-

480m


It was the introduction of steel wire ropes that
allowed spans of over 500m to become a reality.


It is a continuous girder with one or more towers
erected above piers in the middle of the span. At
both ends of the bridge large anchors or counter
weights are placed to hold the ends of the
cables.


Long span suspension bridges, though strong
under normal traffic loads, are vulnerable to the
forces of winds.



Questions