Week 1 Challenge

Aim : To calculate the dead load on a box girder bridge of span 12 m.

Given data :

Width of bridge deck – 10.2 m

Span of the bridge - 12 m

Pier size – 2.5 m dia

The seismic zone – zone 4

Wind speed – 47 km/hr

Location – Bengal

Theory : Dead Load as per IS 875 – Part 1, the unit weight of materials are different from each other. Some of them are listed below.

• Reinforced cement concrete – 25 KN/m^3
• Plain cement concrete – 24 KN/m^3

Self weight of structural elements .

To calculate the load the formula is given by

Self weight (Load) KN/m, = cross section area of structural element x unit weight

The box girder is divided into 11 basic shapes for make easier to calculate the area, By using area we can calculate the dead load.

Note : The area of the different shapes of the geometry are calculated by using area formulas are listed below.

• Area of triangle = 0.5 x base x height
• Area of rectangle = length x breadth
• Area of parallelogram = base x height

Si No	Shape	Length, m	Breadth, m	Height, m	Area, square meters	Unit weight of concrete, KN/m^3	Load, KN/m
1	Rectangle	1.3	0.225	-	0.29	25	7.25
2	Rectangle	1.2	0.225	-	0.27	25	6.75
3	Triangle	-	0.125	1.2	0.075	25	1.875
4	Rectangle	1.3	0.225	-	0.29	25	7.25
5	Triangle	-	0.125	1.3	0.08	25	2
6	Rectangle	1.04	0.225	-	0.234	25	5.85
7	Rectangle	0.350	0.269	-	0.094	25	2.35
8	Parallelogram	-	0.269	2.3	0.61	25	15.25
9	Rectangle	1.8	0.2	-	0.36	25	9
10	Rectangle	0.18	0.2	-	0.036	25	0.9
11	Triangle	-	0.08	0.2	0.008	25	0.2
Total Load							= 58.675

The given structure is symmetrical axis hence the total load is 58.675 x 2 = 117.35 KN.

Aim : To prepare the model in a STAAD Pro and perform the analysis and justify with the results.

Theory : The general steps to be create a STAAD Pro model is given below,

Step 1 : Create the nodes by using the nodes cursor.

Step 2 : Joining the nodes by using the respective beam plate cursor.

Step 3 : Supports given to the nodes whether its pinned or fixed or any other custom supports

Step 4 : specifications given to the respective beams plates

Step 5 : Assign the dead load as per calculation

Step 6 : Save the model and perform the analysis

Step 7 : The results are obtained and discuss with the results

Step 8: Take the print out of report of necessary results.

Creating the nodes by using node cursor.

Open the STAAD Pro window > Select > Node cursor > enter the value with respect to X Y Z axis > click enter.

Join the nodes by using beam cursor.

Select > beam cursor > join by dragging the mouse or enter the node numbers > click enter

Moments released with respect to support which is to the given supports.

Supports are given to the respective nodes.

Specifications > Supports > select the supports > click enter

Assigning the properties to the beam .

Specification > Prismatic > Rectangle > enter dimensions > select the beam > assign the properties to selected beams.

Defining the load cases .

Loading > Load case detail > select load > Add

Add > member load > enter the value > ok

Select the defined load > select the beam > Assign to selected beam > click enter

Run analysis > go to post processing mode > Results

The reactions are generated at the end of the nodes .the reaction value is 704.1 KN

• The shear force is maximum at the end and minimum at the end of the mid span.
• Exactly at 6m the shear force is 0.
• At node 1 the shear force is positive and node 2 the shear force is negative of value 704.1 KN

• The bending moment is maximum at midspan and minimum at the end support.
• The maximum bending moment is at the 6 m, the value is 2112.3 KNm
• The maximum displacement is 5.12mm occurs at the exactly mid span.

• Reports are taken printout which ever is necessary by using report option.
• In the report option we obtain the results of section forces, displacement, reactions, plate stresses.
• The exact report is to be taken further move to design process.