The UK Network of Building Surveyors and Structural Engineers

www.surveyorsreports.co.uk www.engineersreports.co.uk ER 82266\110921 July 2012 The Stables Rear of 60 the Avenue SOUTHAMPTON SO17 1XS tel: 023 8072 0780 fax: 023 8072 0788 [email protected]

STRUCTURAL CALCULATIONS for 1.8m high balcony screens not exceeding 5.4m long with posts at 1.0m centres by

Balcony Systems Limited

page 1

Prepared by : WRD Engineers Limited Registered in England: No. 07977613 : The Stables, Rear of 60 The Avenue, SOUTHAMPTON, SO17 1XS T D White CEng MICE MIHT MCIArb * M D Royall ACGI BSc CEng MICE MCIArb * Philippa Dixon BSc CEng MICE

The UK Network of Building Surveyors and Structural Engineers

www.surveyorsreports.co.uk www.engineersreports.co.uk ER 82266\110921 July 2012 DESIGN NOTES 1. The structural design of 1.8m high screens is governed by wind loading. 2. For sites in the UK wind loading is calculated in accordance with British Standard 6399-2: 1997 Code of practice for wind loads. 3. The basic wind speed for different geographical locations is obtained from Figure 6 of BS 6399. The basic wind speed varies from 20m/sec in an area around Oxford to 30m/sec in the North Scottish Islands. 4. The basic wind speed is adjusted by various factors to allow for differences in site conditions. These include the site altitude and topography, whether the site is in a town or in the country, distance from the sea, and height of the building. 5. A net pressure coefficient Cp is specified for free standing walls and parapets. This coefficient is obtained from Table 21 of BS 6399. For the purposes of calculating wind loading the 1.8m screens are considered to be similar to free standing walls and parapets. Therefore the net pressure coefficient Cp is considered to apply to the 1.8m high screens. The coefficient varies from 1.2 to 3.4 and therefore significantly increases the design wind loading to be resisted by the screens. A value of 2.1 is selected to cover the majority of different conditions. 6. A reduction factor к is applied to wind loads on free standing walls and parapets where the length to height ratio L/h is equal to or less than 15. These calculations are based upon an L/h ratio of 3 or less, for which к = 0.60. Different values of к will apply where the length of the screen exceeds 5.4 metres. 7. The wind loading calculated in accordance with items 1 to 6 above is known as a ‘service load’. This load is multiplied by a ‘load factor’ to give a ‘limit state’ or ‘factored’ wind load that is used in checking the factored resistance capacity of the screen’s structural members, and also the factored resistance capacity of fixings to the main building structure. 8. For the design of aluminium members the load factor for wind loads specified in BS 8118:part1:1991 ‘Code of practice for the structural use of aluminium’ is 1.2. 9. For the design of steel members the load factor for wind loads specified in BS 5950 ‘Code of practice for the structural use of steel’ is 1.4. 10. The 1.8m screen system has standard base plates and posts. The spacing of the posts is varied to suit different wind load conditions. Should a site fall outside the standard design criteria, individual site specific designs can be prepared as required. 11. The glass used in the screens is 10mm thick thermally toughened soda lime silicate glass having a strength designation of 120 N/mm2.

page 2

Prepared by : WRD Engineers Limited Registered in England: No. 07977613 : The Stables, Rear of 60 The Avenue, SOUTHAMPTON, SO17 1XS T D White CEng MICE MIHT MCIArb * M D Royall ACGI BSc CEng MICE MCIArb * Philippa Dixon BSc CEng MICE

The UK Network of Building Surveyors and Structural Engineers

www.surveyorsreports.co.uk www.engineersreports.co.uk ER 82266\110921 July 2012 1.8m screens ≤ 5.4m long – posts @ 1.0m centres

(continued)

BASIC WIND SPEEDS FOR THE UK page 3

Prepared by : WRD Engineers Limited Registered in England: No. 07977613 : The Stables, Rear of 60 The Avenue, SOUTHAMPTON, SO17 1XS T D White CEng MICE MIHT MCIArb * M D Royall ACGI BSc CEng MICE MCIArb * Philippa Dixon BSc CEng MICE

The UK Network of Building Surveyors and Structural Engineers

www.surveyorsreports.co.uk www.engineersreports.co.uk ER 82266\110921 July 2012 1.8m screens ≤ 5.4m long – posts @ 1.0m centres 1.0

Base plates:

(continued)

300 x 225 x 20

Plan second moment of area of base plate

Elevation =

Z

=

225 x (20)2 6 15000mm3

=

steel design strength

=

fy

=

265 N/mm2

factored moment capacity of base plate

=

Mc

= = =

1.2 x fy x Z 1.2 x 265 x 0.015 4.77 kNm

Posts: (60 x 60 x 5 SHS in steel grade S275) factored moment capacity = 5.27 kNm > 4.77 kNm of 60 x 60 x 5 SHS therefore base plate governs HD bolts: (16mm diameter) maximum factored tension on HD bolts

say

=

factored moment capacity of base plate distance from centre of bolts to face of SHS weld x 2 No.

=

4.77 0.164 x 2

=

14.54 kN/bolt

=

10.39 kN/bolt (unfactored)

=

10.50 kN/bolt page 4

Prepared by : WRD Engineers Limited Registered in England: No. 07977613 : The Stables, Rear of 60 The Avenue, SOUTHAMPTON, SO17 1XS T D White CEng MICE MIHT MCIArb * M D Royall ACGI BSc CEng MICE MCIArb * Philippa Dixon BSc CEng MICE

The UK Network of Building Surveyors and Structural Engineers

www.surveyorsreports.co.uk www.engineersreports.co.uk ER 82266\110921 July 2012 1.8m screens ≤ 5.4m long – posts @ 1.0m centres

(continued)

Elevation

Aluminiun properties: design standard

=

BS 8118@part1:1991 “The structural use of aluminium”

material type

=

extruded aluminium type 6063 T5

limiting stresses

=

(table 4.1 of BS 8118)

a)

bending

=

Po

=

110 N/mm2

b)

compression

=

Ps

=

130 N/mm2

c)

shear

=

Py

=

65 N/mm2

factored resistance capacity of a member

=

calculated member capacity based upon the stresses Po Ps & Py divided by the material factor Ym

material factor

=

Ym

E Value

=

70,000 N/mm2

=

1.2

page 5

Prepared by : WRD Engineers Limited Registered in England: No. 07977613 : The Stables, Rear of 60 The Avenue, SOUTHAMPTON, SO17 1XS T D White CEng MICE MIHT MCIArb * M D Royall ACGI BSc CEng MICE MCIArb * Philippa Dixon BSc CEng MICE

The UK Network of Building Surveyors and Structural Engineers

www.surveyorsreports.co.uk www.engineersreports.co.uk ER 82266\110921 July 2012 1.8m screens ≤ 5.4m long – posts @ 1.0m centres

(continued)

Glass: The glass is supported on all 4 sides. It spans 2 ways and will distribute wind loading onto the posts and top rail as shown below.

distribution of wind pressure on glass

wind pressure on posts

Equating the allowable factored wind pressure to the moment capacity of the posts/base plates:

supporting

factored loads/moments on posts from wind force p: BM due to P1

=

p x 0.50 x 0.50 x (1.8)

=

0.450 p

BM due to P2

=

p x 0.50 x 0.50 x (1.467)

=

0.367 p

BM due to P3

=

p x 1.0 x 0.80 x (0.9)

=

0.720 p

BM due to P4

=

p x 0.50 x 0.50 x (0.333)

=

0.083 p 1.620 p moment capacity of base plate 1.62 4.77 1.62 = 2.944 kN/m2

allowable factored wind force p

=

p

=

pressure coefficient Cp

=

2.10

L/h reduction factor к

=

0.60

therefore allowable wind pressure (factored)

=

2.944 2.10 x 0.60

qs

for

L

≤

5.4m

=

2.336 kN/m2

page 6

Prepared by : WRD Engineers Limited Registered in England: No. 07977613 : The Stables, Rear of 60 The Avenue, SOUTHAMPTON, SO17 1XS T D White CEng MICE MIHT MCIArb * M D Royall ACGI BSc CEng MICE MCIArb * Philippa Dixon BSc CEng MICE

The UK Network of Building Surveyors and Structural Engineers

www.surveyorsreports.co.uk www.engineersreports.co.uk ER 82266\110921 July 2012 1.8m screens ≤ 5.4m long – posts @ 1.0m centres

(continued)

load factor for steel

=

1.4

therefore allowable unfactored wind pressure

=

qs

qs

=

0.613 (Ve)2

(Ve)2

=

1.669 x (10)3 0.613

=

2723

Ve

=

(2723)0.5

=

52.18m/sec

Ve

=

Vs x Sb

=

2.336/1.4

=

1.669 kN/m2

where Ve is the effective wind speed

where

Vs Sb

= =

site wind speed terrain & building factor

site wind speed

Vs

=

Vb x Sa x Ss x Sd x Sp

where

Vb Sa Ss Sd Sp

= = = = =

basic site wind speed = altitude factor(assume 100m) = seasonal factor = directional factor = probability factor =

25m/sec say 1.10 1.0 1.0 1.0

therefore

Vs

=

25 x 1.10

=

27.50 m/sec

and

Sb

=

can be ≤ 52.18/27.50

=

1.897

For sites within the 25m/sec basic wind speed area on the map on page 3 (which is virtually the whole of Great Britain except the extreme North and West of Scotland) at an altitude of 100 metres or less above sea level, examples of the different types of terrain & height of buildings that this covers are as follows: a.

Any location where the effective building height is 19 metres or less.

b.

Sites in town or country areas 10 km or more from the sea with an effective building height of 20 metres or less.

c.

Town sites 100 km or more from the sea with an effective building height of 30 metres or less.

page 7

Prepared by : WRD Engineers Limited Registered in England: No. 07977613 : The Stables, Rear of 60 The Avenue, SOUTHAMPTON, SO17 1XS T D White CEng MICE MIHT MCIArb * M D Royall ACGI BSc CEng MICE MCIArb * Philippa Dixon BSc CEng MICE

The UK Network of Building Surveyors and Structural Engineers

www.surveyorsreports.co.uk www.engineersreports.co.uk ER 82266\110921 July 2012 1.8m screens ≤ 5.4m long – posts @ 1.0m centres aluminium sleeve: section modulus

=

Z

(continued)

=

66 x 66 o/a x 2mm thick

=

(66)3 6 8195 mm3

=

(62)3 6

=

110 N/mm2 x 8195mm3 x (10)-6 1.2

=

0.75 kNm

unfactored allowable wind pressure

=

1.669 kN/m2

load factor for wind loads on aluminium members

=

1.20

factored allowable wind pressure

=

1.669 x 1.2

= =

2.00 x 1.0 x (0.80)2 2 0.64 kNm

=

< moment capacity

moment capacity

=

Po x Z Ym

(page 7)

=

2.00 kN/m2

considering the wind force as a UDL: wind moment on aluminium section 0.8m down from top of screen

OK

The 60 x 60 x 5 SHS steel posts need to extend 1.0m above the base plates. The 66 x 66 x 2 aluminium sleeves are adequate above this level.

CORNER POST/BASE PLATE DETAIL page 8

Prepared by : WRD Engineers Limited Registered in England: No. 07977613 : The Stables, Rear of 60 The Avenue, SOUTHAMPTON, SO17 1XS T D White CEng MICE MIHT MCIArb * M D Royall ACGI BSc CEng MICE MCIArb * Philippa Dixon BSc CEng MICE

The UK Network of Building Surveyors and Structural Engineers

www.surveyorsreports.co.uk www.engineersreports.co.uk ER 82266\110921 July 2012 1.8m screens ≤ 5.4m long – posts @ 1.0m centres

(continued)

Check that deflection of the posts under service load conditions does not exceed 25mm at a height of 1100mm above balcony floor level. posts

=

60 x 60 x 5 SHS x 1.0m high with 66 x 66 x 2mm aluminium sleeves extending to the full height of 1.8m.

second moment of area of posts (‘I’)

=

53.3cm4

service load

=

unfactored wind load on page 7 = 1.669 kN/m2

pattern of wind loads

=

as shown on page 6.

Wind loads on the upper part of the screen are transferred to the SHS post via the aluminium sleeve. Service load deflection is limited to 25mm at a height of 1100mm above the base. For the purposes of this design check, the pattern of wind loading on sheet 6 is simplified to an equivalent concentrated load applied to the post 900mm above the base. This is considered to provide a reasonable approximation of loading sufficient for an assessment of post deflection. The calculated deflection at this level due to the equivalent concentrated load is then extrapolated to give the deflection at the reference height of 1800mm above the base. From page 6: P1 P2 P3 P4

= = = =

service load deflection of post 900mm above base

service load deflection of post 1800mm above base

equivalent concentrated load P: 1.669 kN/m2 x 0.45 x 1800/900 1.669 kN/m2 x 0.367 x 1487/900 1.669 kN/m2 x 0.72 1.669 kN/m2 x 0.083 x 330/900 =

PL3 3EI

=

3768 x (900)3 3 x 205000 x 53.3 x (10)4

=

8.38mm

= =

8.38 x (1 + 3 x 900) 2 x 900 20.95mm

=

≤ 25mm

=

= = = =

1.502 kN 1.013 kN 1.202 kN 0.051 kN 3.768 kN

OK

page 9

Prepared by : WRD Engineers Limited Registered in England: No. 07977613 : The Stables, Rear of 60 The Avenue, SOUTHAMPTON, SO17 1XS T D White CEng MICE MIHT MCIArb * M D Royall ACGI BSc CEng MICE MCIArb * Philippa Dixon BSc CEng MICE

The UK Network of Building Surveyors and Structural Engineers

www.surveyorsreports.co.uk www.engineersreports.co.uk ER 82266\110921 July 2012 1.8m screens ≤ 5.4m long – posts @ 1.0m centres

(continued)

Glass: type

=

10mm thick thermally toughened soda lime silicate safety glass. Designated mechanical strength = 120 N/mm2

design standard

=

BS EN 12150 Parts 1 and 2 ‘Glass in building’

short term working load stress

=

59 N/mm2

long term stress

=

35 N/mm2

E value

=

70 x (10)3 N/m2

design unfactored wind force

=

1.669 kN/m2

(page 7)

The glass will actually span 2 ways, however as a worst case scenario assume that it spans 1.0m one way between the posts. wind moment on glass

=

1.669 x (1.00)2 8

=

0.209 kNm/m

section modulus of glass

=

Z

=

1000 x (10)2 6

=

16667 mm3/m

=

0.209 0.0167

=

12.52 N/mm2

=

< 59 N/mm2

bending stress

=

M Z

OK

The 10mm thick thermally toughened glass is adequate.

page 10

Prepared by : WRD Engineers Limited Registered in England: No. 07977613 : The Stables, Rear of 60 The Avenue, SOUTHAMPTON, SO17 1XS T D White CEng MICE MIHT MCIArb * M D Royall ACGI BSc CEng MICE MCIArb * Philippa Dixon BSc CEng MICE

The UK Network of Building Surveyors and Structural Engineers

www.surveyorsreports.co.uk www.engineersreports.co.uk ER 82266\110921 July 2012 1.8m screens ≤ 5.4m long – posts @ 1.0m centres

(continued)

SUMMARY 1.0

The 1.8 metre high screen system by Balcony Systems Limited consists of 10mm thick thermally toughened safety glass supported in an aluminium frame comprising standard Balcony 1 System top and bottom rails and vertical posts at 1.0 metre centres. The posts consist of 60 x 60 x 5mm structural hollow sections (SHS) in steel grade S275. The steel posts extend 1.0 metre above the base and are sheathed in 66 x 66 x 2mm SHS aluminium tubes that extend the full height of the screen.

2.0

For screens up to 5.4 metres long the system is adequate to withstand wind loads calculated in accordance with BS 6399-2: 1997 for most sites in Great Britain except the extreme North and West of Scotland.

3.0

The calculation of wind loads in accordance with the British Standard depends upon a number of variable factors, such as the site altitude, topography, distance from the sea, height of the building, and whether it is located in the country or in a town.

4.0

For sites at an altitude of 100 metres or less above sea level within the 25 m/sec basic wind speed area, examples of the different types of terrain and height of buildings for which this system is suitable are as follows: a

Any coastal, country, or town location where the effective building height is 19 metres or less.

b

Sites in town or country areas 10 km or more from the sea where the effective building height is 20 metres or less.

c

Town sites 100 km or more from the sea, with an effective building height of 30m or less.

Site specific designs can be prepared for screens that are longer than 5.4 metres; and for sites/buildings that fall outside of the above categories. 5.0

Base plates for the standard posts are 300 x 225 x 20mm thick in steel grade S 275. These have provision for 4 No. 16mm diameter holding down bolts. Base plates for the corner posts are 300 x 300 x 20mm thick in steel grade S275. These have provision for 5 No. 16mm diameter holding down bolts. All bolts are subject to a working load tension (pull-out force) of 10.50 kN. It is the responsibility of the installer to establish that the bolts chosen, and the structure into which they are fixed, are adequate to safely support this load. End

page 11

Prepared by : WRD Engineers Limited Registered in England: No. 07977613 : The Stables, Rear of 60 The Avenue, SOUTHAMPTON, SO17 1XS T D White CEng MICE MIHT MCIArb * M D Royall ACGI BSc CEng MICE MCIArb * Philippa Dixon BSc CEng MICE