To clearly understand the bar bending schedule of a pile foundation, it is necessary to be familiar about the typical reinforcement details of a pile foundation. Pile foundation is a common type of deep foundation, used for supporting heavy loaded structures when the site under consideration have a very weak soil that is compressible in nature.
- Layout of a Typical Pile Foundation
- Structural Specification and Reinforcement Details of a Pile Foundation
- Calculation for Bar Bending Schedule of Pile Foundation
Layout of a Typical Pile FoundationA typical pile foundation arrangement have the load structure supported by a pile cap, which is in turn supported by several piles as shown in the plan and front view arrangement in the below figures.
Fig.1: Pile Foundation Arrangement – Superstructure, Pile Cap and Piles
Structural Specification and Reinforcement Details of a Pile FoundationThe figure-2 shows the typical reinforcement details and drawing of a pile foundation. The details of pile cap are not explained in this article.
Fig.2: Pile Foundation DetailsThe whole arrangement is clearly understood from the figure-2. The pile cage has vertical reinforcement held together by outer and inner rings. The Reinforcement in pile construction include:
- Vertical Reinforcement
- Outer Ring Reinforcement
- Inner Ring Reinforcement
Fig.3: Cross-section details in section A-A of figure-2The development length ‘Ld’ is provided outside of the column piercing into the pile cap. The anchorage length to the recommended amount is provided to the bottom of the column as shown in figure-2. From the Figure:
- Length of Pile = 20m
- Diameter of Pile = 0.6m
- Diameter of:
- Vertical Reinforcement = 20mm – 12nos
- Outer Helical Ring = 8mm @ 200mm c/c
- Inner spiral ties = 16mm @ 2000mm c/c
- Bottom Length of Anchorage = 300mm
- Development Length = 40d
- Clear Cover = 75mm
Calculation for Bar Bending Schedule of Pile Foundation
Step 1: Length of Vertical ReinforcementIn the case of bar bending schedule of a column or a pile, there comes need for lapping the rods so that the length of pile (20m) is attained. Hence, a lapping length equal to 5Dd is provided in extra. Therefore, Total Cutting Length for Vertical Reinforcement = Anchorage Length at the bottom of the pile + the height of the pile + development length (40d) + Lap length (50d) – clear cover provided at the bottom. i.e. Lv = 300 + 20000 + 40d +50d -75 = 300 + 20000+ (40 x 12) + (50 x 12) – 75 Total length of vertical reinforcement, Lv = 21.3m Note: During tying the bar, it is recommended to tie at the middle, as tying at the ends of the bars will be subjected to higher stress values.
Step 2: Inner Spacing Ring – Number and Length of each RingHere, we have to determine the length of each inner ring along with their numbers arranged. The number of rings (Nr) = [Length of the Pile / Spacing] + 1 = [20000/2000] +1 = 11 No’s The circumference of the ring gives the length of each ring. For this the radius of the ring has to be determined. Given the radius of the pile, the clear cover, outer ring radius: The radius of the ring = [Radius of the pile – clear cover – diameter: of outer ring – diameter: of vertical reinforcement:]/2 = [600 – 75 – 8 - 12]/2= 252.5mm Hence, Length of ring = 2xpixr = 2 x 3.147 x 252.3 = 1584.4mm = 1.58m
Step 3: Outer Helical Ring – Number and Length of each ringFor every specification of outer helical ring, the radius of the same have to be determined. Radius of Helical Ring Outer = [Diameter of Pile – Clear Cover]/2 = [600 -75]/2 = 262.5mm Length of ring = 2xpixr = 2 x 3.147 x 262.5 = 1648.5mm = 1.65m The number of rings (Nr) = [Length of the Pile / Spacing] + 1 = [20000/200] +1 = 101 No’s
Step 4: Bar Bending Schedule
|Specification||Diameter of Bars (m)||No. of Bars (m)||Length of rods (m)||Total Length (m)|
|Inner Ring bar||16||11||1.58||17.4|
|Outer ring bar||8||101||1.65||166.65|