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TOWER CRANE FOUNDATION DESIGN Structural Design Report
Prepared by Edifice Consultants Pvt.Ltd
Tower Crane Foundation Design
1.0.0
GENERAL
1.1.0
Scope
This report is prepared to highlight the design calculations for a Tower Crane Foundation. 1.2.0
Brief Structural Description
The dimensions of the Foundation is 6000mmx6000mmx1500mm. The geometric centre of Tower Crane is placed at a eccentricity of 1350mm to the geometric centre of the foundation. (Refer to Annex 1). 2.0.0
DESIGN DATA
2.1.0
Material Properties
2.1.1
Soil
Bearing capacity of soil is 150 kN/m2 Friction angle is 30 2.1.2
Concrete
Density of the Concrete is 24kN/m3
2 Characteristic strength of concrete for columns, beams and slabs is fcu = 25N/mm 2.1.3
Reinforcement Steel
Characteristic strength of reinforcement steel is (Deform bars Type 2) fy = 460N/mm2
2.2.0
Loads
The Foundation reactions (Working loads) given by the ICC are as follows. Moment (M)
= 1598.5 kNm
Axial Force (P)
= 774.4 kN
Horizontal Reaction (H)
=25.2 kN
Edifice Consultants Pvt.Ltd
Page 1
Tower Crane Foundation Design
3.0.0
STANDARDS REFERRED
3.1.0
Design codes of practices
Structural use of concrete
BS 8110-Part I: 1997
Structural use of concrete
BS 8110-Part 2: 1985
3.2.0
Manuals and Hand books
Structural Foundation Designer's Manual by W.G Curtin, G.Shaw, G.I Parkinson & J.M Golding.
Edifice Consultants Pvt.Ltd
Page 2
Tower Crane Foundation Design
4.0.0
SLS Checks
4.1.0
Checks for bearing
The bearing capacity of the soil is = 150 kN/m2 Base size
= 6mx6mx1.5m
Weight of the base
= 6 × 6 × 1.5 × 24 = 1296kN
Axial Force-P (from the Tower)
= 774.4kN
Eccentricity of to the Axial Force- e p
= 1.350m
Moment -M (from the Tower)
= 1598.5kNm
Horizontal Reaction-H (from the Tower)
= 25.2kN
Hence total axial load on the footing at SLS
= 774.4 + 1296 = 2070.4kN
Hence total Moment on the footing at SLS
= 1598.5 + 774.4 × 1.350 + 25.2 × 1.5 = 2681.74kN
Maximum pressure beneath the footing can be evaluated as below. σmax =
Hence Tensile Stress develops beneath the footing. Hence Pressure distribution beneath the footing needs to be readjusted . Assume the Length of the Foundation under compression is Lb
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Page 3
Tower Crane Foundation Design
Figure 4.1 : Extract from Structural Foundation Designer's Manual
As per Figure 4.1,
Pe + M + Hh 774.4 × 1.350 + 1598.5 + 25.2 × 1.5 p et = = = 1.30m T 2070.4
Lb = 3 ×
L − e = 3 × 6 − 1.3 = 5.1m 2 T 2
Assume a F.O.S of 1.5 at Ultimate Limit Stare. 5.1.0
Checks for the Bending
The maximum bending moment at tower face can be found as follows. The Ultimate Pressure at the tower face
= 1.5
135.32 × 2.475 = 98.50kN/m2 5.1
1 2.475 M = × 98.50 × 2.475 × = 100.56kNm/m 2 3 (Please note that the moment is calculated for a 1m width strip of the footing) T16 bars to be used as reinforcement. Cover to reinforcement is 50mm.
d = 1500 − 50 − 16 −
16 2
= 1426mm
Consider a Unit Width of the footing (Clause 3.4.4.4 of BS 8110-1:1997)
k=
M f bd2 cu
=
100.56 × 106 25 × 1000 × 14262
k
0.9
0.002
0.9
z = d0.5 + 0.25 −
z = d0.5 + 0.25 −
= 0.002 < 0.156,Hence compressio n r/f not required.
= 0.99d > 0.95d
z = 0.95d
As =
M 0.95fy z
=
100.56 × 106 0.95 × 460 × 0.95 × 1426
Edifice Consultants Pvt.Ltd
= 170mm2 /m
Page 6
Tower Crane Foundation Design
Checks for the minimum amount of reinforcement (As per Table 3.25 of BS 8110-1:1997) A 100 s = 0.13 A c
A s,min =
0.13 × 1000 × 1500 100
= 1950mm2
Provide T16 @ 100 mm C/C Both Ways.
A s ,provided = 2010mm2 /m A s ,provided = 2010mm2 /m Hence the requirement for the minimum reinforcement is satisfactory. ,
Edifice Consultants Pvt.Ltd
Page 7
Tower Crane Foundation Design
6.0.0
Checks for shear
6.1.0
Maximum shear stress at Tower face
The Maximum Shear Force at Tower Face, 1 V = × 98.50 × 2.475 = 121.90kN 2
Hence shear stress at column face, v=
121.90 × 103 = 0.09N/mm2 1000 × 1426
Maximum possible shear 0.8 fcu or 5N/mm2 which is lesser
Tower Crane Consists of 4 Tower Legs and each Leg is connected to the Foundation through a Base Plate and Anchor Bolts. Assume the dimensions of the Base Plate is 350mmx350mm. Assume the Tower Moment (1598.5 kNm) is applying from a Diagonal Direction. Hence Maximum Compression force on a Tower Leg due to Moment (diagonal direction) is N = moment
1598.5 = 580kN 2 2 1.95 + 1.95
Assume Tower Axial Force (774.4 kN) is equally carried by the 4 Tower Legs. Hence Axial Force per Leg, N = axial
774.4 4
= 193.6kN
Hence Maximum Tower Leg Reaction is, N = 580 + 193.6 = 773.6kN Leg, max
