Week 6 Challenge
. 1. Summarize your study for the bending moment, shear force and deflection diagrams for the raft foundation in stadd and compare them with manual calculation for different set of loads. Fill of 1 m on top slab.
1) earth pressure 2) self-weight 3) Surcharge 4) 70R load
Ans
Aim of the challenge -
- To Analyze and design the raft foundation by applying earth pressure, self-weight, surcharge loading and 70R vehicle loading and calculating bending moment, shear force & deflection through staad. pro as well as by manual calculation also.
- So first of all the Vehicular underpass is modelled as portal frame structure in Staad.pro and analyzed for a unit length.
- Various load as described applied to the structure and being analyzed.
- Spring foundation assigned to the structue as per the calculated value for diffrent springs as per the length of the nodes considered for the spring foundation.
The Staad model has been created according to the sizes given .
- The 3D render view of the model.
Manual Calculation
1. Self Weight of the bottom Slab
The thickness of the bottom slab = 0.9m
Width of the Underpass = 12.0m
Thickness of wall = 0.9m
Volume of slab = (12+2 x 0.9) x 0.9 x 1 = 12.42 m3
Slf wt of slab = 12.42 x 2.5 = 31.05 t
2. Earth Pressure Calculation
phi = 30 degree
earth pressure co-efficient = 0.5
Density of soil = 20 Kn/m3
| Height from top (m) | Intensity of Earth pressure(KN/m2) | |||
| 1.400 | 1.400 | 0.5 *20*1.4 | = | 14.00 |
| 0.450 | 1.850 | 0.5 *20*1.85 | = | 18.50 |
| 0.150 | 2.000 | 0.5 *20*2 | = | 20.00 |
| 5.175 | 7.175 | 0.5 *20*7.175 | = | 71.75 |
| 0.150 | 7.325 | 0.5 *20*7.325 | = | 73.25 |
| 0.450 | 7.775 | 0.5 *20*7.775 | = | 77.75 |
3. Live load surcharge
| Equivalent height | = | 1.2 | m | |||
| Uniform Intensity of loading | = | 1.2*20*0.5 | = | 12.00 | KN/m2 |
4. 70R load
For 70R loading 70ton of vehicular loading is being applied on the structure.
Applying in staad model
1. Self Weight
Self wt has been applied to the structure by inputing the self wt. as -1 in staad.
2. Earth Pressure
The Earth pressure applied to the structure from top to bottom in trapizoidal format.
3. Live load surcharge
4. 70R load