48310: Introduction to Civil and Environmental Engineering-Bridge Design Project

Assignment 2

General Information

• This is an individual assignment (only for 1 student).

• The aim is to complete a waterway bridge project including one part: detailed design with required figures and calculations.  

Detailed Design (100%)

A two-lane bridge is going to be constructed in Gundagai over Murrumbidgee River. The length of bridge is 145 m and its deepest point is 7.5 m below the ground surface.

Q 1. 

• The aim is to complete a waterway bridge project including one part: detailed design with required figures and calculations.  
• A two-lane bridge is going to be constructed in Gundagai over Murrumbidgee River. The length of bridge is 145 m and its deepest point is 7 m below the ground surface.

Peak flood discharges were recorded from 1991 to 2020 for Murrumbidgee River in Gundagai, NSW, Australia. The latitude and longitude of the bridge location are as follows:

• Latitude: 35.06° S
• Longitude: 148.10° E

Table 1: Proposed Recorded Peak Flood Discharges for Gundagai Murrumbidgee River (from 1991 to 2020)

Q 1.1.  Based on Flood Frequency Analysis (FFA), find the flood discharge in m³/s (q_max) for the Average Recurrence Interval (ARI) of 100 years.

Q 1.2. Based on Rational Method determine the flood discharge in m³/s (Q_max) for the Average Recurrence Interval (ARI) of 100 years. Assume the area of the catchment is 620 km², the average slope 2% and the mainstream length in the catchment is 5.37 km. The impervious fraction of catchment area is 0.36 (f = 0.36).

Note: For the design purpose, select the flood discharge in the river in the location of the bridge based on the maximum of these two flood discharges, calculated based on FFA and the rational method.

Q 2. 

The width and height of different points of the river at bridge cross section in its centre-line is given in Table 2. The equivalent Manning’s coefficient is 0.036 and the slope of the river in this section is 2%.

Q2.1. Plot the cross section of river without water.

Q2.2. Determine the maximum height of water in the river with the given cross section, when carrying a flood discharge based on the 100 year ARI, found in Q1.

Determine the highest water level achievable in the river, based on the provided cross-section, while accommodating a flood discharge as per the 100-year ARI, as identified in Q1.

Table 2: Width and Height of Different Points of the River at Bridge Cross Section in its Centre-line

Q 3.

For this bridge 3 piers with spread footing are considered. Design data are as follows:

• No of circular piers = 3
• Diameter of each pier = 2.5 m
• Assume the height of middle pier = 10.5m
• Assume the height of side piers = 8 m
• Height of spread foundation = 2 m
• Spread foundation base dimensions = 5m x 5m
• Depth of foundation from the river bed to the base of footing = 4 m

To control the local scour around pier foundations, gravel riprap is used. Close to the location of bridge, the river has a straight reach.

Q3.1. In order to control the local scour around pier foundations, course sand or gravel riprap is used. Close to the location of bridge, the river has a straight reach. Based on your previous calculations, check the depth of local scour for different mean diameter of gravel (1 mm, 2 mm, 5 mm or 10 mm). Which one do you recommend? Explain why? (Use the maximum flow rate found in Q1.)

Q3.2. Based on the maximum flow rate found in Q1:

(a) Find the Area of the river cross section without piers.  

(b) Find the Area of the river cross section with piers.  

(c) Find the average velocity of river during the 100-year flood without bridge piers.

(d) Find the average velocity of river during the 100-year flood with bridge piers.

(e) Accordingly, find the afflux height and the length of backwater.

Q3.3. Consider the pier in the middle of the bridge is submerged to a certain depth during the flood with a return period of 100 years. Calculate the drag force on the middle pier. Assume the drag coefficient (C_D) is 0.36. In drag force equation, use the average velocity of river during the 100-year flood with bridge piers, calculated in Q3.2.

Q3.4. How much concrete (in tonnes) as a minimum amount do we need for construction of piers (without the pier cap) and foundations?  Assume the unit weight of reinforced concrete is 2.5 t/m³.

Q3.5. How much steel rebar (in tonnes), as a minimum, do we need for construction of piers and foundations?  Assume the required mass of deformed bars is approximately 5% of the reinforced concrete mass for columns and 3% for the foundations. Assume the specific gravity of steel is 7.85.

Q 4. 

Evaluate the wind load on the bridge deck with the profile shown in the figure. The bottom of the bridge deck is 7m above the riverbed. Assume design wind speed is 35 m/s.

Q 5.

Assume we are using two lanes for the proposed bridge (one lane in each direction). Based on the following traffic data find the total number of heavy vehicles over design period, which is required for the design of pavement on bridge deck.

• Annual Average Daily Traffic (1^styear) = 5350
• Direction Factor= 0.5
• Percentage of Heavy Vehicles = 5%
• Average number of Axle Groups per Heavy Vehicle= 2.5
• Pavement design period = 30 years
• Annual growth rate of traffic = 6%

Assignment Rubric (Scoring Scheme)

Detailed Design (100%)

1. Title page and table of contents (4%)
2. Q1 (30%)
3. Q2 (30%)
4. Q3 (20%)
5. Q4 (4%)
6. Q5 (4%)
7. Summary (8%)

Note 1: Please show your working out and prepare clear figures, tables and drawings if warranted. You can use MS-Excel for calculations or MS-PowerPoint for drawings. You may also use AutoCAD (but it is not compulsory). Please copy and paste all items in one MS-Word document and then convert it to a PDF file.

Note 2: Although page limit is not enforced, the maximum page is expected not to be more than 30 pages, including all sections, title page and references. There is no limit for the minimum page number.