WEEK 1 CHALLENGE ON DEAD LOAD CALCULATIONS

Aim

This report encapsulates the analysis of a girder using staad pro with the primary aim to deduce the dead loads on the given box girder.

Data Provided

Box girder Details-

Width of the bridge deck = 10.2m; Span of the bridge = 12m; Pier size = DN2500;

Unit weight of soil (γ) =19kN/m³

Methodology

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

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

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

Area Calculation

Area of rectangle 1 = l x b = (0.9x 2.175) x 2 = 3.915 m² (since the other side is symmetric)

Area of rectangle 2 = l x b = (1.37 * 1.825) x 2 = 5.009 m² (since the other side is symmetric)

Area of triangle 3 = 0.5 x b x h = ½ x (1.37 x 0.125) x 2 = 0.171 m² (since the other side is symmetric)

Area of triangle 4 = 0.5 x b x h = ½ x (0.82 x 1.825) x 2 = 1.496 m² (since the other side is symmetric)

Area of rectangle 5 = l x b = (2.722 x 2.175) = 5.920 m²

Area of triangle 6 = 0.5 x b x h = ½ x (1.2 x 0.125) x 2 = 0.15 m² (since the other side is symmetric)

Area of triangle 7 = 0.5 x b x h = ½ x (0.6 x 1.825) x 2 = 1.095 m² (since the other side is symmetric)

Area of rectangle 8 = l x b = (0.6 * 1.825) x 2 = 2.190 m² (since the other side is symmetric)

Area of the whole rectangle = 2.4 x 10.2 = 24 m²

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

The total area of the girder = 24 – (3.915-5.009-0.171-1.496-5.920-0.15-1.095-2.190) = 4.067 m²

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

uniform dead load = 4.06 x 25 = 102.5 kN/m

Now, the 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 = = 618 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.

Software Analysis using Staad Pro

The end result of this analysis is finding the stresses in the plate elements. To do so, the following procedure has been carried through step-by-step carefully in staad pro.

• Creating the nodes as shown in Figure 1-

Figure 1 – Node Creation

The Figure 2 illustrates the nodal coordinates of box girder

Figure 2 Nodes indicated in Coordinate System

Once, all the nodes are created, a mesh of 0.5m has been created with the aid of translational command projected in Z-direction (span direction).

Figure 3- Translation with respective Z-direction

The next step was to connect all these nodes selecting “Add Plate” command.

Figure 4 Plates connected to the nodes (top) and front view of the girder (below)

The next step is to Define the plate properties as shown from the “properties whole structure tab”

Each plate thickness was provided as per the girder given and all the above properties were assigned to the model.

Material properties were assigned for the model viewed as Concrete.

The next support is to assign the support to the structure. This was done using the Support tab and the fixed supports were provided to the piers of 2500mm thick in diameter.

Lastly, loading conditions were applied as follows:

Self weight was defined to the whole structure.

Now, the whole structure was projected in Z direction without link steps with a distance of 0.5m and number of steps 23 as shown in the figure.

The figure below shows the whole structure projected by the translational repeat.

A 3D rendering view has also been shown below:

Now, using the analysis tab and perform analysis option has to be added.

Then run analysis command shall be done. The end report shows the following result file.

Go to the Post Processing Tab to find the summary of the structure for the design to be carried.

***END OF THE REPORT***

Note: I have attached my word file as the images are not copied from the original file.