Challenge 7

Aim:

Q1) Calculate the moment for design of pier cap considering reactions @ 250mm from tip of cantilever: D.L. (100kN), SIDL (80kN), & LL (120kN). Total length of the cantilever from the pier face is 4.5m. Consider an impact of 1.3 for live load.

Given Data:-

• Dead Load= 100kn
• SIDL = 80kn
• Live Load = 120kn
• Impact (I) = 1.3

Solution:-

• SLS Load Combination = DL + 1.2 x SIDL + 1.1 x L.L x I

Moment (M)= (100+1.2 x 80 + 1.1 x 120 x 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

Q2) Differentiate between RCC and PSC pier caps in all aspects.

-->

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 than RCC.
The construction of this piers are slow.	The construction of this piers are fast.
Steel corrosion is possible in RCC.	Corrosion of steel is negligible in PSC.
This type of Pier Cap is less brittle.	This type of Pier Cap is More brittle

Q3) Provide the codal provisions for design crack width depending on the various exposure conditions.

--> As per IRS CBC code Clause 10.2.1(a)

TABLE 10: DESIGN CRACK WIDTHS

Exposure Condition	Design crack width in mm
Moderate	0.20
Severe	0.10
Extreme	0.10

Q4) At what conditions, the cantilever pier cap is preferred, and state the limitations of the same.

--> 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.
• The width should be sufficient enough to accomodate superstructures from both sides. It should range between 3-3.5M.
• Vehicle cleareance should be 5.5m for safe moment of vehicles below metro viaducts.