Challenge

Week 8 Challenge

AAkash Singh17 Dec 2022

Aim: To determine the centrifugal load acting on bridge and analyze accordingly in Staad.Pro.

Introduction:

The objective is to calculate centrifugal loads from the given data manually and attempt the same in Staad.Pro for the bridge and analyse the results and effects on the structure.

The Illustrated bridge is 12 m in length having a carriage of width 7m with the camber of 2% on pavements.

Given Data (for calculation):

Span of bridge = 12.0 m

Width of carriage way = 7.0 m

Live load on bridge = Class 70R tracked vehicle.

Design Speed of vehicles = 75 km/hr

Radius of curvature = 3 m

Assumption:

Size of Pier = 1.5 m Diameter

Height of Pier = 10.0 m

Size of Girder beam = 1.0 m x 1.7 m

Size of Cross beam = 0.9 m x 1.5 m

Thickness of deck slab = 0.3 m = 300 mm

Procedure:

All the loads are calculated in such a manner as mentioned below,

According to IRC 6 code, Live load of 70R tracked vehicle is 70KN

So, Live load (W) = 70 KN

Radius of curvature (R) = 3 m

Design speed (V) = 75 km/hr

Centrifugal Load (Fc) = (W x V²) / (127 x R) = (70 x 75²) / (127 x 3) = 1033.5 KN

And,

Number of Load combination for moving loads = (span of bridge + length of vehicle) / increment per combination

= (12+3.6)/1 = 15.6 ≈ 16

Computer Proficiency:

Create a model by putting the necessary inputs as file location, units etc.

Create two nodes (x,y,z) represents as (0,0,0) & (0,10,0) Because the height of pier is assumed to be 10.0 m.

3. Go to Add Beams option and connect the both nodes. And replicate the pier at spacing of 7.0 m in z direction.

Connect the beam at the top of pier by add beams option in order to make cross beam of carriageway.

Go to Properties tab, define the size of piers, cross beam & girder beam as mentioned above and assign all the members accordingly.

Go to supports tab, and create fixed support and assign to end of peirs.

Select the whole assembly and replicate it in 12.0m in x direction and connect top of the piers in order to make the beam girder.

Assign all the missing property element as discussed above. Refer image below.

Divide the outer cross beams into three parts by the insert node tool and replicate the cross beams at spacing of 3.0m. Refer image below.

Go to create mesh, and connect corner node of the panel and create quadrilateral mesh of 0.5 m x 0.5 m.

Assign the thickness of the plate and replicate it into every panel in order to make deck slab.

Go to loading tab, define the vehicle loading as discussed above. Refer image below.

Add load case as Dead Load for self-weight as factor -1.

Go to Load Cases and generate load combination, number of combinations will calculate as discussed above. And provide detail of starting of moving and their ranges as illustrated in images below.

And repeat the same process to generate the load combination for the vehicle in opposite direction.

Then Go to Analysis tab, select Analysis command and add the perform analysis command.

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Analytical Results:

Bridge has been analysed and check for different load combination and different displacement for different scerios has been record.

Maximum node displacements is recorded as 3 mm.

Maximum Base reactions are recorded axial force as 1523.51 KN and moment as 207.26 KN-m.

Maximum shear force recorded in beam in Fy direction is 1023.373 KN.

Maximum Bending Moment recorded in beam in Mz direction is 1539.971 KN-m.

Maximum Shear Force in SQX (local) direction for deck slab is recorded as 199.31 KN/m2.

Maximum Shear Force in SQY (local) direction for deck slab is recorded as 234.614 KN/m2.

Maximum Moment in MX (local) direction for deck slab is recorded as 15.256 KN-m/m.

Maximum Moment in MY (local) direction for deck slab is recorded as 13.9957 KN-m/m.

Conclusion:

Different results have been found under the centrifugal loads,