The following are the main elements in the design of reaction system for 1500 mm diameter test pile.
- Design of Reaction Anchor.
- Design of Dywidag Bars.
- Design of cross beam.
Anchor Design
The test load = 1.5 x W.L = 1.5 X 21800 = 32700 KN (Comp.)
No. of anchors = 24 Nos.
Load / Anchor = 32700 / 24 = 1362.50 KN
Diameter of anchor strands = 15.20 mm
According to FIP Code
Grade of anchor strand = 1570 /1770 N/mm2
Allowable load/ strand = 1.770 X 130 / 1.60 = 144 KN/ strand
No. of strand/ anchor = 1362.50/144 = 9.46 = 10
Provide 10 Nos. of Strands / anchors
Total No. of strands = 24 x 10 = 240 Nos.
Load on one strand = 32700 / 240 = 136.25 KN < 144 KN (safe)
Total length of anchor ‘L’ = 25.60 m.
Proposed 10 Nos. strands (15.24 mm dia) of 24 anchors located as shown in the sketch.
Design For Grout Body Length
Load per anchor = 32700 / 24 KN = 1362.50 KN
Safety factor = 2
Ultimate anchor load = 1362.50 x 2 = 2725 KN
Required grout length(Lo) = Pu / ( Ao x sigma )
Nominal diameter of strands = 15.20 mm
Perimeter = Ao = 0.0152 x p = 0.048 m
Proposed No. of strands = 10
Lo = 2.725 MN / ( 10 x 0.048 x 1.0 MN/m2) = 5.68 m
Provide grout body of 10.00 m long
GROUT – Ground Interaction
Ultimate anchor load = 2725 KN
Proposed length of grout body = 10.00 m
According to B.S- 8081 – 1989– fig. 60 (conservative).
The skin friction capacity for medium dense sand = 300 – 800 KN/m2
Considering an ultimate skin friction capacity of 600 KN/m2
Use 1500 mm diameter casing for drilling of anchor.
Pult = 0.15 x p x 10.00 x 600 KN/m2 = 2827 KN/anchor >2725 KN (safe)
Elastic Elongation Of Anchor
Max. load / anchor = 1362.50 KN
Elastic elongation = I = (P x L) / ( E x A )
P = Anchor Load = 1362.50 KN
L = Free Length of Anchor = 25.60 – 10 =15.60KN
E = Young’s Modulus = 200 KN
No. of strands = 10 Nos.
Area of strands = (10 x 15.202 x p) / 4 = 1810 mm2
Max. elongation = (1362.50 x 15600 ) / 200 x 1810 = 58.72mm
Dywidag Bar Design
Dywidag bars are used to transfer the load from the anchor to the cross beam.
The Dywidag bars of steel grade 1080/1230 N/mm2
Total Test load = 32700 KN
The working load of 36 mm dia. Bar with a F.O.S. of 1.6 = 783 KN (Data sheet attached)
No. of 36 mm Dywidag bars required = 32700 / 783 = 41.76 = 42 Nos.
No. of Anchors = 24 Nos.
No. of Dywidag Bar / Anchors = 2 Nos.
Total No. of Dywidag bars = 24 x 2 = 48 Nos. > 42 Nos. (safe)
Design of Cross Beam
The cross beam is capable to provide a reaction of 4000 tons to test piles. Since test load is only 3270 tones the cross beam is adequate to provide reaction load to the test pile.