Challenge 7

1) 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.

Ans

Data Given:-

• Dead Load= 100kN
• SIDL = 80kN
• Live Load = 120kN
• Length of cantilever portion from pier face = 4.5m
• Impact (I) = 1.3

• 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
• So eccentricity = ( 4.5 - 0.250)

= 4.250 M

• Overall Moment = 367.6 x 4.250

= 1562.3 kN-m

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

Ans:

RCC Pier Cap		PSC pier Cap
1.	Reinforced concrete or RCC is a composite concrete having ordinary steel or deformed bars to protect itself from loading.	1.	Prestressed concrete as the name suggests contains prestressed high tensile tendons.
2.	The product price to manufacture RCC concrete is low.	2.	The product price to manufacture prestressed concrete is high.
3.	Fatigue limit is low & deformation is more than PSC.	3.	Fatigue limit is high & deformation is less than RCC.
4.	Deformed bars and mild steels are used.	4.	High-quality tendons are used.
5.	Tensile cracks permitted.	5.	Tensile cracks not permitted.
6.	Shear reinforcement is required.	6.	Tendons help to resist the shear reinforcement.
7.	Consumes more time.	7.	Consumes less time.

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

Ans

• 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

Exposure conditions defined in Clause 5.4.1

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

Ans:

• A metropolitan area or metro is a region that consists of a densely populated urban agglomeration and its surrounding territories sharing industries, commercial areas , transport network, infrestructure and housing.A metro area usually comprises multiple main cities , jurisdiction, municipalities, township, cities etc.
• So in most of the cases the designer has to face space issue for the structures.
• There might be many hindrances like
  • may be an existing road below the metro alignment.
  • any permanent structure which couldnt be dismantled.
  • any sensitive restricted area corriodor etc.
• In this type of cases the both the cases has to be considered in the vies of construction of metro as well as without affecting the structure beneath. So to solve this type of things in most of the cases cantilever pier caps has been proposed.

Limitation:

• The eccenticity of the structure should not be more than 3m in any case. (Wheather RCC & PSC).
• The cross section of the cantilever portion is higher compairing to the normal case.