Week 1 Challenge

Given data:

 The Bridge Construction Site is within a 60 km radius of the Bay of Bengal.

The unit weight of soil is 19 kN/m3.

Width of deck slab= 10.20 m 

Span = 12m 

Pier Size = 2.5m dia

Seismic zone = Zone 4

Wind speed = 47km/h 

To find:

1. We have to assess the various dead loads for the given box girder bridge x-section. 

2. Calculate the various loads and apply them in Staad pro and perform structural analysis.

Solution:

There are two methods of solving this problem for calculating the dead load i.e.

1. Manual method 

2. Calculation of the area of the cross-section by AutoCAD(by drawing the given x-section on Autocad as per the dimensions given and finding the area of cross-section by AREA Command)

Method 1:

it will give inaccurate values of the area, But still can be used.

Area of slab portion= 10.20 x 0.225 = 2.295 sqm

Area of bottom slab of box girder = 4.02 x 0.2 = 0.804 sqm

Area of slanted portions of box girder = 2 x 2.34 x 0.25 = 1.17 sqm 

area of joints of slab and box girder

A1 = 2x0.269x0.350 - 2 x 0.269 x 0.225 = (0.188 - 0.121)= 0.067 sqm 

A2 = (2 x 1.37 x (0.35+0.225)x0.5) - (2 x 1.37 x 0.225)= (0.79- 0.6165)= 0.173 sqm 

A3 = (2 x 1.20 x (0.35+0.225)x0.5) - (2 x 1.20 x 0.225)= (0.69-0.54)= 0.15 sqm  

The total area of cross-section = 2.295+0.804+1.17+0.067+0.173+0.15 = 4.66 sqm

Method 2:

After drawing the cross-section of the given bridge on AutoCAD, Select the x-sectional area and apply the area command to find out the area of the cross-section which comes out to 5 Sqm.

Let's adopt the greater and more accurate value of the area so as to ensure an effective estimate.

Dead load calculations:

Unit weight of RCC= 25 KN/cubic meter

So Dead weight of the given x-section is = 25 x 5 x 12 = 1500 KN

this load of the entire span of box girder will be equally distributed between two piers of dia 2.5 m.

So UDL can be considered for analysis in STAAD pro i.e. 1500/2=750 KN