Week 1 Challenge

Week 1 Challenge On Dead Load Calculations

Aim

This report is about the analysis of a girder using Staad Pro with the primary aim is to findout the dead loads on the given box girder.

Data Provided

Box Girder Details:-

Width of the bridge deck = 10.2m

Span of the bridge = 12.0m

Pier Size = 2.5m

Unit Weight of soil(Y) = 19.0 KN/cub.metre

Methodology

To evaluate this Moment Of Inertia of the girder has to be found.

For the dead loads, only total area calculation of the box girder has been shown in this report.

The box girder has been divided into different sections for the handy calculations as shown below:

Area Calculation:

A1 = Area of rectangle = l*b=(0.9*2.175)*2= 3.915 sq.m ( since the other side is symmetric)

A2 = Area of rectangle = l*b=(1.37*1.825)*2= 5.0005 sq.m ( since the other side is symmetric)

A3 = Area of triangle = 0.5*b*h= 0.5*(1.37*0.125)*2= 0.171 sq.m ( since the other side is symmetric)

A4 = Area of triangle = 0.5*b*h= 0.5*(0.82*1.825)*2= 1.496 sq.m (since the other side is symmetric)

A5 = Area of rectangle = l*b = 2.722*2.175= 5.92 sq.m

A6 = Area of triangle = 0.5*b*h= 0.5*(1.2*0.125)*2= 0.15 sq.m ( since the other side is symmetric)

A7 = Area of triangle = 0.5*b*h= 0.5*(0.6*1.825)*2= 1.095 sq.m (since the other side is symmetric)

A8 = Area of rectangle = l*b= (0.6*1.825)*2= 2.190sq.m ( since the other side is symmetric)

Area of the whole rectangle = 2.4*10.2= 24.48 sq.m

Area of the box girder = Area of whole rectangle - (Area of section 1,2,3,4,5,6,7,8)

= 24.48 - ( 3.915+5.0005+0.171+1.496+5.92+0.15+1.095+2.190)

= 24.48 - 19.9375 = 4.54 sq.m

We know that load can be evaluated by multiplying the area with unit weight of concrete.

i.e. uniform dead load = Area * unit weight = 4.54*25= 113.5 KN/m

This load is applied along the length of the girder.

Now, we assume the load as point load and reactions can be known using the formula wl/2 as the deck slab is a simply supported structure.

Ra+Rb= wl

For simply supported beam, pinned supports shall be defined.

Ra=Rb=wl/2= 113.5*12/2= 681 KN ( approximately).

To check the results , a staad pro analysis was done without including the piers. The supports were defined at the centre of the girder with pinned supports.

Following are the results obtained from staad pro. The result varies a little, this might be due to the approximation of the numbers calculated manually.

The staad pro results are accurate . One can design the girder from the above results.