Challenge 7

Aim:-

Question (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

Question (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 brittle	More brittle

Question (3):- Provide the codal provisions for design crack width depending on the various exposure conditions.

Answer:-

As per the IRS CBC code

Question (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 it is not always possible for the pier to be placed directly below. Below the tracking of the elevated metro, there may be a road that could be running below the metro & if the metro is taking a turn it may go beyond the boundary or ROW of the road. Under such condition, we try to find an alternative such as a cantilever pier cap, where pier remains on the centre of the road but cantilever arm is adjusted lengthwise.

Limitation

If the eccentricity is 2 meters then we go for the RCC pier cap, and if above 2 meters up to 3 meters, we prefer as PSC pier cap but above 3 meters we have to give provide portal frame.