Week 4 Challenge

Aim and Introduction :

• To calculate the Earth pressure acting on the abutment wall, for the given dimensions and to apply the calculated pressure loads on the staadpro, and perform structural analysis. 
•  Earth pressure is the Horizontal thrust exerted by retained earth on the vertical structure like wall, pier, abutment,

Based on the pressure exertion it is classified as,

                    

                                                     

• Earth pressure at Rest :

        Earth pressure at rest occurs when the structure is stationary without any lateral displacement or movement.

• Active Earth pressure :

        Active earth pressure occurs when the retaining wall moves away from the backfill, which means the soil pushes

the wall

• Passive Earth pressure :

        Passive Earth pressure occurs when the wall moved towards the backfill, which means the soil

pushes the wall

PROCEDURE :

• Here, we need to calculate earth pressure for inner and outer fill, the ground level is at 3 metres that is outer filling and the backfill is at a level of 7 metres take it as inner filling.
• let us assume outer and inner fill as K1 and K2.
• The formula to find out, Earth pressure(k)= coefficient of earth pressure (k0 or ka or kp) * density * height 

• The water table is at ground level so in this case, we need to calculate submerged unit weight, submerged unit weight = saturated unit weight - unit weight of water. 
• k1 = ka * submerged unit weight * height
• the coefficient value of ka and kp value is taken as 0.35

    => k1 = 0.35 * (19-10) * 3

    => k1= 9.45 KN/m2

• k2 value calculated for two condition total height is 7 metre for up to ground level it is calculated for submerged condition , for the remaining 4 metre it is calculated for normal condition

   => k2 = [0.5 * (19 -10) * 3 ] + [0.5 * 18 * 4]

   =>k2 = 49.5 KN/m2

In this staad pro modelling we need to design a wall and apply the calculated earth pressure loads on it.

     

• first enter the node coordinates as (0, 0,0) and (0,0,5)  z-direction  5 metres represents the length of the wall. 
• 

      

• After entering the node values for the length of wall , add a plate element of 0.5 spacing on y direction , then use translational repeat command at 0.5 spacing for 15 no of steps, thus gives height of the wall of 8 metres.

     

•   Then repeat the translational repeat command to create plate along its length of 5m.

     

• Provide footing for the wall by creating a nodes on the either side of the wall , and specify the dimension.

     

• The above is the sectional view of the wall and the height and length of wall as per given diemsions.

      

• specify the foundation as plate mate and enter the sub grade modulus  values, and also click on the y direction and then click add ,then assign these support to selected plates.

     

• The cross sectional view of the wall along is shown above in 3 dimensional view.

     

• so the height at which the earth pressure loads to be applied is shown, by using the node to node distance command in utilities tab.
• The height of 3m and 7m is marked where the pressure due to outer and inner fill will be applied 

            

     

• Loading is to be applied for the designed wall, add plate loads use hydrostatic load so and the select the plate on which the load will acts.
• enter the load values as 9.45kn/m2 and select plates up to 3 metres then click on y axis and click add.

    

• The staad pro will split the load accordingly when we use hydrostatic condition in the plate loads tab which shows the earth pressure loading condition.
• the load is applied up to 3 metres shows the earth pressure due to outer fill.

    

• select the remaining plates along its row and then apply the load accordingly with its height.

    

• Add an another loading of 49.5 kn/m2 which is due to inner fill, for the height of 7m, select the plate up to 7m height and apply the loads on the opposite direction of previous load.
• using the hydrostatic load condition the staad pro will split the load accordingly with its height .
• and select the remaining plates along its row and apply the load
• after loading save the file and click run analysis command for the analysing  structure.

RESULT :

After analysis, click on the post processing command to check for plate stresses.

• The above contour image shows the maximum and minimum of moment and shear values along x direction, the maximum earth pressure acts on the bottom part, where at top minimal amount of pressure acts.
• The wall has been designed for given dimension, loads due to earth pressure were calculated and applied on the structure using the staad pro, and their