Challenge 7
Aim:-
Que (1): - Calculate the moment for the design of the pier cap considering reactions @ 250mm from the tip of the cantilever: D.L. (100kN), SIDL (80kN), & LL (120kN). The total length of the cantilever from the pier face is 4.5m. Consider an impact of 1.3 for live load.
Answer:-
Given Data:-
- Dead Load - 100 kN
- SIDl - 80 kN
- Live load - 120 kN
- I ( Impact Factor) - 1.3
Solution:-
- SLS Load Combination = `DL + 1.2 xx SIDL + 1.1 xx LL xx I`
Moment (M)= ( `100 + 1.2 xx 80 + 1.1 xx 120 xx 1.3` )
= 367.6 kN-m
Reactions from the tip of the cantilever = 0.250 M
Total eccentricity = ( 4.5 - 0.250 )
= 4.250 M
Total Moment = 367.6 x 4.250
= 1562.3 kN-m
Que (2):- Differentiate between RCC and PSC pier caps in all aspects
Answer:-
| Reinforcement Cement Concrete Pier Cap | Prestress Concrete Pier cap |
| Weight of the structure is more | weight of the structure is less |
| In case of deflection it deforms more compare to PSC | Incaseof deflection it deforms less ( 1/4 th of RCC level ) |
| Material cost is the low | Material cost is high |
| Mild Steel and deformation bars is used | High strength tendons are used. Tendons are made from high-tensile steel in the form of a single-wired or multiwire strand |
| Tensile crack will be visible | No tensile crack |
| No quality control required | Required good quality control and skilled labor |
| Time required is more as compared to PSC | Less time required |
| Slow construction | Fast construction |
| Steel corrosion is possible in RCC | Corrosion of steel is negligible in PSC |
| Less Britel | More brittle |
Que (3):- Provide the codal provisions for design crack width depending on the various exposure conditions.
Answer:-
As per the IRS CBC code
Que (4):- At what conditions, the cantilever pier cap is preferred, and state the limitations of the same.
Answer:-
We know that metro alignment is curved in nature there would be curves and bifurcation of the metro line & in that location not always possible for the pier can be placed directly below. the tracking on the elevated metro because there could be a road that would be running below the metro & If the metro is taking a turn it may go outside of the boundary under that condition we tried to find an alternative as a cantilever pier cap where pier remains on its place but cantilever arm slightly move.
Limitation
If the eccentricity is 2 meters then we go for the RCC pier cap, If above 2 meters up to 3 meters we prefer as PSC pier cap but above 3 meters we have to give the portal frame