THE FOUNDATION DESIGN OF CBSS 6M RADIO TELESCOPE.

ONUIGBO, KEN and OMOWA E.

ICT DIVISION

BY

OCTOBER, 2015.

ABSTRACTFoundation of structures are salient but very important as it determines the life of the

structure. Our 6m Radio Telescope therefore requires a stable foundation so as to

achieve its optimum life span. In this work, the foundation design of CBSS 6m Radio

Telescope was carried out. The bearing capacity of the sub-soil in Nsukka area, which is

one of the basic considerations in foundation design, was used to calculate the required

size of the foundation trench. The sizes and distribution of steel reinforcements were

also computed using the Civil Engineering Design Code BS 8110. Based on the above,

the Bill of Engineering Measurements and Evaluations (BEME) were prepared to serve

as a guide to the Management of CBSS in the successful execution of the project.

Keywords: 6m Radio Telescope, Bearing Capacity, Steel Reinforcements, Design

Code , BEME.

Introduction. Purpose of the study. Determinants of the type of a foundation Load analysis. Design of the foundation trench. Design of the reinforcements. The bill of Engineering measurement and Evaluation. Conclusion.

OUTLINE:

INTRODUCTION

The foundation is the lowest part of a structure that transfers the load of the super structure to the soil on which it rests.

This part of the structure is somewhat unseen hence often neglected despite the fact that it is the most important part of the structure.

A properly designed foundation is that which transfers the structural load through out the soil without over stressing of the soil.

INTRODUCTION CONTD.

Such stress could result in excessive settlement or shear failure, both of which can damage the structure.

Our 6m radio telescope is never completed until it is mounted on a solid foundation, designed and constructed to counter the forces that will be acting on the it through out its entire life.

Such foundation must be designed and constructed based on a sound engineering economy.

PURPOSE OF THE STUDY

To provide a real time working drawings and

specifications for the completion of the 6m radio

telescope, putting cost into consideration.

To provide a consultancy service to CBSS on the civil

engineering aspect of the foundation to the 6m radio

telescope.

DETERMINANTS OF THE FOUNDATION OF A STRUCTURE.

Functions of the intending structure.

Its structural load.

The geological type of soil.

The bearing capacity of the sub soil.

The settlement criteria of the soil.

The cost available for the project.

Dia.30cmCounter balance

weight (Mc/2)Kg

Motor Assem

bly

Dish (400Kg)

U-Channel

Web Support

Cylindrical pipe

12

cm

50

cm

4m

12mm

ASSEMBLY DRAWING

Concrete core

LOAD ANALYSIS

No of sectors in the dish 6 No of ribs in a sector 11 Weight of a rib 4Kg Weight of 11 ribs in 1 sector 44Kg Trusses 5Kg Bolds and Nuts 1Kg Sub-total 50Kg

Weight of 6 sectors 300Kg Top ring plate 15Kg Bottom plate 20Kg Sheet 50Kg Miscellaneous 15Kg

Approx. Total weight of Antenna 400Kg

COUNTER WEIGHT: CALCULATEDRecall,

Mc = 400*x/y ……………… (1)

Where x = 12cm, y = 50cm

Therefore,

Mc = 400*12/50

Mc = 4800/50 = 96Kg

But, M’c = Mc/2

M’c= 96/2 = 48Kg.

Hence the total weight of dish is 400+96Kg.

=496Kg

Mc(Kg) 400Kg

o

12cm50cm

DESIGN OF THE FOUNDATION TRENCH DESIGN CODE BS 8110

P = N/A …………………………………….. (2)

Where

N = Axial load

A = Base Area of footing

P = Bearing capacity of the soil.

Axial load(N) = weight of the dish * acceleration due to gravity. ….(3)

= 496Kg*9.81m/s2

= 4865.76KN

Assume self weight of concrete footing to be 150KN.

Total design load = 1.0gk + 1.0qk

= 4865.76 +150.

= 5015.76KN.

Assuming the bearing capacity to be 200KN/m2, and substituting for N,

Base Area = 5015.76/200

= 25.079m2.

Hence, provide a base of 5m by 5m.`

DESIGN OF THE FOUNDATION TRENCH DESIGN CODE BS 8110 CONTD.

5.0m

SECTION A-A

5.0m

1.2m

A A

5.0m

FOUNDATION PLAN

DESIGN OF THE REINFORCEMENTS

Taking 50% and 35% factors of safety respectively for dead load (gk) and

live load( qk),

Axial load = 1.5gk+ 1.35qk

= 1.5*4868.761+1.35*150

= 7505.642KN/m

Earth pressure = Axial load/Area2

= 7505.642/(25.079)2

=11.934KN/m2

Assume a 600mm concrete footing with effective depth, K = 520mm

DESIGN OF THE REINFORCEMENTS CONTD.

2m 1m

5m

Bending moment as a result of axial load:

At the column face, moment is critical Hence, M = (11.934*5*2)2/2 =119.34KN/m2

Bending moment as a result of wind force:

Moment = area of dish*wind speed *height

Area of dish =πd2

= 3.142*6*6 =113.112m2

Assuming wind speed to be 48m/s at 5m height,

Moment = 113.112*48*5 = 27.15KN/m2

Total moment on the foundation= axial load moment+ wind speed moment.

=119.34+27.15 =146.49KN/m2

As=M/0.87fykz

Where As= Area of required steel fy= Characteristic strength of steel

k = effective depth z = lever arm(0.95) As= 146.49 *106/0.87*500*0.95*520 =681.70mmHence provide Y16@200mm c/cAlso provide 6nos of Y25 as bolted nuts.

Courtesy:R.C.D. Table A.3R.C.D. Table A.1

25nos Y16 @ 200c/c bottom

25nos Y16 @ 200c/c top

5m

5m

BB

BASE PLAN

SECTION B - B

dd

dd

dd

900mm

90

0m

m C C

Column Plan

6 Nos. of Y25 as threaded bolts

900mm

1.9

mm

8 Nos. of Y10 @ 225mm as stirrups

Section C-C

BILL OF ENGINEERING MEASUREMENT AND EVALUATION (BEME)

S/N DESCRIPTION QUANTITY UNIT RATE(N) AMOUNT(N)

1Excavation of the foundation trench upto 1.2m depth 32.5 m3 950 35,635.00

2Preparation and casting of concrete mix of grade 1:2:4 16.73 m3 28000 468,400.00

325mm high yield steel reinforcement 12 m 300 3,600.00

416mm high yield steel rienforcement 345 m 250 86,250.00

510mm high yield steel rienforcement 38 m 100 3,800.00

6

Backfilling of foundation with dug out laterite materials and

compaction 21.64 m3 400 8,656.00

7carting away excess laterite materials away from site 15.86 m3 600 9,516.00

82 working days each for mason, carpenter and iron bender 6 # 4000 24,000.00

9 25mm marine plywood 1 sheet 3,500 3,500.00

10 Transportation, logistic and misc 50,000.00

TOTAL    693,347.00

Most projects are often times delayed, while some

are abandoned mid way due to poor planning.

Hence it is better not to start a fence until you

know what you are walling in and what you are

walling out. This study is a sort of a proactive

measure to executing the foundation of our 6m

Radio Telescope. In addition to the design, it offers

an Engineering over view of what to expect in

terms of materials and resources.

CONCLUSION

REFERENCES:

Reynolds and Steadman, (2001), Reinforced Concrete Designers Manual.

Bill Mosley, et al, (2007), Reinforced Concrete Design.

Anthony O. A. et al, (2011), Proctor Cone Penetrometer for In-situ Soil Strength Studies in Nigeria.

Chukwunyere K. E., 6m Radio Telescope Mount Design

THANK YOU ALL