HIGH MAST FOUNDATION

This spreadsheet will help you design high mast foundation for lighting, CCTV cameras and other accessories. This design involves step by step process to arrive at economical, safe and efficient foundation design using NSCP Code 2010, 6 Ed. and ASCE 7.

1.0 Materials/Design Data:
Specified compressive strength of concrete @ 28 days, f'c
Specified yield strength of reinforcement, fy
Strength reduction factor for flexure (tension controlled section), Φt
Factor of safety against overturning, SF
2.0 Properties:
Height, Hp
Base diameter, DB
Top diameter, DT
 @ H = 0-9m:
Average diameter, D1
Thickness. t1
 @ H = 9-18m:
Average diameter. D2
Thickness, t2
 @ H = 18-24m:
Average diameter, D3
Thickness, t2
Foundation
Height, HF
Width, BF
Length, LF
Reinforcement size, Φst
3.0 Loads
3.1 Dead Load
Unit Weight of Concrete, γc
Unit Weight of Structural Steel, γst
3.2 Wind Load (ASCE 7-05 & NSCP 2010)
Velocity pressure, q  (Eq. 6-15, ASCE 7-05)
Basic Wind Speed, V (200 kph), Table 207-1 NSCP 2010, 6th Edition
Basic Wind Speed, V
Velocity pressure coefficient:
 @ H = 9m, Kz1 (Table 207-4 NSCP 2010, 6th Edition)
 @ H =18m, Kz2 (Table 207-4 NSCP 2010, 6th Edition)
 @ H =24m, Kz3 (Table 207-4 NSCP 2010, 6th Edition)
Directional factor, Kd
Topographic factor, Kzt
Importance factor, I
Design pressure, p
Pressure coefficient, Cp
Gust factor, G
4.0 Soil:
Unit weight of soil, γs
Allowable soil bearing capacity, qs
5.0 Design Calculation
Deadload
Weight of pole, Wp = 1.05π(Hp/3)(D1t1+D2t2+D3t3)Yst plus accessories
Weight of foundation, WF = BFLFHFYc
Wind load:
Velocity pressure:
 @ H = 0-9m, qz1= 0.613Kz1KdKztV²l/1000
 @ H = 9-18m,  qz2= 0.613Kz2KdKztV²l/1000
 @ H = 18-24m,  qz3= 0.613Kz3KdKztV²l/1000
Design Pressure:
 @ H = 0-9m, pz1= qz1CpG
 @ H = 9-18m,  pz2=qz2CpG
 @ H = 18-24m,  pz3= qz3CpG
Horizontal Uniform Load:
 @ H = 0-9m, w1= pz1D1
 @ H = 9-18m,  w2=pz2D2
 @ H = 18-24m,  w3= pz3D3
Horizontal Force
 @ H = 0-9m, F1= w1Hp/3
 @ H = 9-18m,  F2=w2Hp/3
 @ H = 18-24m,  F3= w3Hp/3
Reactions (unfactored)
Vertical Load, RV = WP + WF
Horizontal Load, RH = F1+F2+F3
Bending Moment, M = Hp (F1/6+ F2/2 +5F3/6)
Stability Check:
Overturning Moment, Mo= M +RHHF
Actual soil bearing pressure, qact = RV/BFLF + 6Mo/BFLF²
Actual soil bearing pressure, qact
Resisting moment, MR= WFLF/2
Factor of safety against overturning, SFo = MR/Mo
Factor of safety against overturning, SFo
Ultimate Moment
Mu= 1.6qact [(LF-DB)/2] BF [(LF-DB/4)]
Reinforcement:
Use effective depth, d= HF/2
Reinforcement index, ω = [1.695-(1.695²-4Mu/0.59Φt f'c BF d²)^(1/2)/2
Reinforcement Ratio, ρ = ωf'c/fy
Area of Reinforcement, Ast = ρBFd
Spacing of reinforcement, S = BF π Φst²/4Ast
Use reinforcement:
 

Calculation Reference
Design for Wind Loads
Mast Design
Mast Calcultions