Challenge 10
1.Explain the design codal provisions for pile cap of metro viaducts in detail.
AIM :
HERE I AM GOING TO EXPLAIN THE DESIGN CODAL PROVISION FOR PILE CAP OF METRO VIADUCTS IN DETAIL.
A reinforced concrete slab or block which interconnects a group of piles and acts
as a medium to transmit the load from wall or column to the Piles is called a Pile
Cap. The Pile cap should normally be rigid so as to distribute the forces equally on
the piles of a group. In general it is designed like a footing on soil but with the
difference that instead of uniform reaction from the soil, the reactions in this case
are concentrated either point loads or distributed.
Codal provisions made in IS 2911(Part 1/sec3)-2010 : 1. The size of the pile cap is fixed in such way that it has clear overhang beyond the outermost pile not less than 100mm, but preferably 150mm. 2. It should be deep enough to allow the necessary overlap of reinforcements from column and piles.
* TABLE 11 CLAUSE 10.2.2 OF IRS CBC STRESS LIMITATIONS FOR THE SERVICELIBLITY LIMIT STATE.
MATERIAL TYPE OF STRESS UNDER DESIGN LOADING TYPE OF CONSTRUCTION
R.C.C PSC
CONCRETE TRIANGULAR OR MEAR TRIANGULAR COMPRESSIVE STRESS 0.50FCK 0.40FCK
UNIFORM OR NEAR UNIFORM COMPRESSIVE STRESS (E.G Y
DUE TO AXIAL LOADING 0.38FCK 0.30FCK
REINFORCEMENT COMPRESSION TENSION 0.75FY NA
PRE-STRESSING TENDONS TENSION NA DEEMED TO SATISFIED BY
16.8.1
- TABLE 10 ( CLAUSE 10.2.1) OF IRS CBC DESIGN CRACK WIDTH THE VARIOUS EXPOSURE CONDITIONS
EXPOSURE CONDITION DESIGN CRACK WIDTH IN MM
- MODERATE _ 0.20
- SERVERE _ 0.10
- EXTREME _ 0.10
2.Explain the design philosophies involved in the design of pile cap
AIM :
HERE I AM GOING TO EXPLAIN THE DESIGN PHILOSOPHIES OF PILE CAP
The allowable pile loads are defined by the user for general piles in the Pile Definitions spreadsheet. For hot rolled steel, concrete, and wood piles, the program calculates the axial capacity based on the pile and material properties. If the piles are part of a pile cap element then, these allowable loads are reduced by the Reduction Factors on the pile cap definition .
The loads developed in the piles within the pile cap elements are found using the equations below. Some things to note on the computation of these forces:
- Loads are only applied to the cap at the pedestal location, which is placed at the centroid of the cap.
- The axial pile stiffness (given in the Pile defination (spreadsheet) is considered the same for both compression and tension and is taken from the comp stiffness.
- The pile cap is assumed rigid.
- The centroid location for force calculations of the piles is from the mid-height of the pile cap.
- Transfer all the load and moment
- Very rigid structure
- Important for positioning piles
- Temporary base for casting of pier