This document discusses bridges and provides information on their history, components, design considerations, and calculations. It notes that the oldest known bridge was a wooden bridge built in England in 3306 BC. It then outlines the various components of bridges, including foundations, substructures, and superstructures. The document discusses factors to consider in bridge design, such as waterway size, terrain, and stream characteristics. It provides empirical formulas for estimating design flood levels. Finally, it shows calculations for determining waterway size and afflux based on given flood discharge, velocity, and flow width values.

1. Presented by:
T B Banerjee

2. Preamble
The earliest reference available is of a bridge across Nile
built in about 2650 B.C. However according to Swedish
institute of construction the oldest bridge built was an 1100
M by long wooden bridge built in England in 3306 B.C. The
oldest pedestrian bridge still standing in a stone slab bridge
across river miles. Smyrna, Asia Minor (Turkey) said to be
2500 years old. In known history, the Chinese appear to be
the earliest to built store bridges.

3. Subjects to be covered
Types of bridges
Various components of bridges
Preparation of General Arrangements Drawing (GAD)
Siting of bridges
Survey
Hydraulic Analysis
Calculation of Discharge
Watering and scour depth

4. Various components of bridge
Foundation Sub Structure Super Structure
RCC Sab T beam-cum-shab PSC givdiv stal girder
Shallow
Foundation Deep foundation
Open
foundation
Well foundation
Pile foundation
Well curb
Well Staining
Well Cap
Pier Abutment
Rectangular
Pier
Circular
Pier
Abutment shaft Abutment Cap
Dirt wall
Circular Rectangular
individual
columns
Pier Cap
Return Walls and/or Wing
Walls
Cantilever
Bridge

5. Since flood discharge of a higher magnitude than the design discharge can occur during the life time often
bridge (assumed 100 years), the committee considered it prudent to provide for an adequate margin of safety
while designing the foundation and protection works. An empirical approach to this is to add 30% for small catch
out.
The most important factor to be decided in the design of the bridge is the determination of the waterway required
for passing the normally expected highest flood discharge. There are a number of factors which affect the
runoff and then the floor discharge from a catchment area served by the bridge. They can be broadly divided
into the following.
Rainfall and whether characteristic
Terrain characteristic
Stream characteristic
 Simplest and the oldest method for estimation of the design flood has been the use of suitable empirical
formula. Most important and extensively used in India are
Design formula Q = CA ¾ c variable between 825 to 1400
Inglis formula Q = 7000 √A applicable only in Bombay Region
Ryves formula Q = CA 2/3 varies from 450-2700
Apart from the above there are two rational method also one of which is area vel. Method and the other is unit
hydrograph method..

8. Silt Factors
Soil Type Gradation Mean size of grain
mm
F (silt factor)
Silt Fine 00.120 00.600
Medium 00.233 00.850
Standard 00.323 01.000
Sand Medium 00.505 01.250
Coarse 00.725 01.500
Bajri (Pebbles) Fine 00.988 01.750
Medium 01.290 02.000
Coarse 02.422 02.750
Gravel Medium 07.280 04.750
Heavy 26.100 09.000
Boulders Small 50.100 12.000
Medium
Large
72.500 15.000
188.800 24.000
The wetted perimeter is equal to the width of the stream. In such cases, the following relationship
W= 8 x Q ⅟2
3

9. Determine the water way for a bridge across a stream with flood discharge of 225 𝑚3/sec; velocity
1.5m/s and width of flow at high flood level is 60 m. Often allowable velocity under the bridge is 1.8
m/sec
Solution: Area of Natural Waterway
A =
𝑄
𝑉
=
225
1.5
= 150 𝑚2
Mean depth of flow d =
𝐴
𝐿
=
150
60
= 2.5 m
Safe velocity (assumed) =
90
100
x allowable vel.
= 0.9 x1.8 = 1.62 m /se
Afflux : 𝑥 = { 𝑣2
17.9
+ 0.015}{𝐴2
𝑎2 - 1}a = area of artitifical waterway=
225
1.62
= {1.52
17.9
+ 0.015}{1502
138.9
-1}=138.9 𝑚2
{0.126 + 0.015} {1.166-1}
= 0.141 x 0.166 = 0.023 m
= L1=
𝑎
𝑑+𝑥
=
138.9
2.5+.023
= 55.03 m