# Document 430922

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PVSOL LTD
STRUCTURAL CALCULATIONS REPORT
In accordance with
Guide to the Installation of Photovoltaic Systems 2nd Edition
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Page 1 of 9
ISSUE No.
DATE
PREPARED BY
18/06/2014
DN
CHECKED BY
APPROVED BY
DN
DISTRIBUTION
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Page 2 of 9
1.0
2.0
JUSTIFICATION OF PANELS FOR GRAVITY LOADS
3.0
JUSTIFICATION OF PANELS FOR UPLIFT LOADS
4.0
CONCLUSIONS
NOTE: This report has been carried out in accordance with BRE Digest 489 & section 4.3.8 to 4.3.11 of
the Guide to the Installation of Photovoltaic Systems as required.
Disclaimer:
The Desk Top Appraisal Report has been produced from information supplied by client. SRS cannot
be held responsible for any damage caused from the supply of limited information or damage caused
due to inaccuracies within the information supplied.
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Dead loads are based on the actual specified make up for the existing roof.
Wind & snow loads to procedures within Eurocode- 1 (BS EN 1991-1).
This applies to roof mounted systems as opposed to integrated “ tile systems”
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EXISTING ROOF MAKE UP:
Existing Tiles
Existing Felt
Existing Trusses
= 0.55kN/m2
= 0.02kN/m2
= 0.15kN/m2
Total DL
= 0.72kN/m2
BS 6399:PT3:4.2 & Eurocode- 1 (BS EN 1991-1)
Calculated using TEDDS design software for both positive and negative internal pressure and for wind acting
both perpendicular and parallel to the front elevation of the building.
Calculated using TEDDS design software for both basic and where appropriate complex snow loadings.
CALCULATIONS:
Building data (duo-pitch roof)
Longer horizontal dimension of the building
L = 7.5 m
Shorter horizontal dimension of the building
W = 5.9 m
Maximum height of the building
H = 5.8 m
Roof pitch angle (-ve for a valley roof)
α = 35.0 deg
Reference height for roof pressure
Hrr = H = 5.8 m
Reference height for wall pressure
Hrw = 3.9 m
Dynamic classification
Building type factor (table 1);
Kb = 0.5
Maximum height of the building
H = 5.8 m
Dynamic augmentation factor (1.6.1);
Cr = [Kb × ( H / (0.1 m) )
0.75
] / ( 800 × log( H / (0.1 m) ) ) = 0.01
Calcs valid - Standard/Hybrid method is applicable
Orthogonal dimensions D = W = 5.9 m B = L = 7.5 m
Site wind speed
NB Calcs suitable only where topography is not significant (cl. 2.2.2.2.1 & fig. 7)
Reference height for wall pressure
Hrr = 5.8 m
Reference height for wall design
Hrw = 3.9 m
Basic wind speed (Figure 6 BS6399:Pt 2)
Vb = 24.0 m/s
Site altitude
∆S = 45 m
Upwind distance from sea to site
dsea = 7 km
Altitude factor
Sa = 1 + (0.001 m ) × ∆S = 1.05
Direction factor
Sd =1.00
-1
Seasonal factor
Ss = 1.00
Probability factor
Sp = 1.00
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Site wind speed
Vs = Vb × Sa × Sd × Ss × Sp = 25.1 m/s
Dynamic pressure - roof
Effective height
He = Hrr = 5.8 m
Factor Sb From BS 6399 : Part 2 : 1997 ..... Table 4
For "country" terrain 7 km from sea with He = 5.8 m and Sb = 1.61
Effective wind speed;
Ve = Vs × Sb = 40.5 m/s
Dynamic pressure;
qs = (0.613 kg/m ) × Ve = 1.00 kN/m
2
3
2
Dynamic pressure - walls
Effective height
He1 = Hrw = 3.9 m
Closest distance from the site to sea;
dsea1 = dsea
Factor Sb From BS 6399 : Part 2 : 1997 ..... Table 4
For "country" terrain 7 km from sea with He1 = 3.9 m and; Sb1 = 1.51
Effective wind speed;
Ve1 = Vs × Sb1 = 37.8 m/s
Dynamic pressure;
qs1 = (0.613 kg/m ) × Ve1 = 0.88 kN/m
3
2
2
Wall pressures (standard method, table 5, D < b )
Reference height for wall pressures;
Hrw = 3.9 m
Scaling length;
b = min( B, 2 × Hrw ) = 7.5 m
Critcal gap width to adjacent buildings;
g = 4.0 m
External pressure coefficients, Cpe From BS 6399 : Part 2 : 1997 ..... Table 5
for D_upon_H = 1.51 and g_upon_b = 0.53
External pressure coeff w;
Cpew = 0.81
External pressure coeff l;
Cpel = -0.50
External pressure coeff side A;
CpesA = -1.58
External pressure coeff side B;
CpesB = -0.89
Internal pressure coeff;
Cpi = -0.3
Room/storey volume for internal size effect factor;
Vi = 55.8 m
Diagonal dimension for internal size effect factors;
ai = 10 × ( Vi )
3
1/3
= 38.2 m
Diagonal dimension for external size effect factors; ae = 8.5 m
Cae = 0.97
Using fig. 4 Curve = "A"External pressure coefficients;
External pressure coefficients;
Cai = 0.88
Dynamic pressure;
qs1 = 0.88 kN/m
Internal surface pressure;
pi = qs1 × Cpi × Cai= -0.23 kN/m
2
2
cl. 2.1.3.2
Net wall pressures
Windward face
2
pw = qs1 × Cpew × Cae - pi = 0.92 kN/m
2
Leeward face
pl = qs1 × Cpel × Cae - pi = -0.19 kN/m
Zone A
pa = qs1 × CpesA × Cae - pi = -1.11 kN/m over length 1.5 m
Zone B
pb = qs1 × CpesB × Cae - pi = -0.53 kN/m over length 4.4 m
2
2
cl. 2.1.3.3
Apex duopitch roof pressures (standard method, 0 degrees)
Roof pressure coefficients From BS 6399 : Part 2 : 1997 ..... Table 10 for α = 35 deg & θ = 0 deg
Roof pressure coefficient A1
CperA1 = 0.80
Roof pressure coefficient A2
CperA2 = -0.33
Roof pressure coefficient B1
CperB1 = 0.53
Roof pressure coefficient B2
CperB2 = -0.33
Roof pressure coefficient C1
CperC1 = 0.50
Roof pressure coefficient C2
CperC2 = -0.13
Roof pressure coefficient E1
CperE1 = -0.73
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Roof pressure coefficient E2
CperE2 = -0.73
Roof pressure coefficient F1
CperF1 = -0.4
Roof pressure coefficient F2
CperF2 = -0.4
Roof pressure coefficient G1
CperG1 = -0.43
Roof pressure coefficient G2
CperG2 = -0.43
Diagonal dim for external pressures size effect fact aer = 8.3 m
3
Room/storey volume for internal size effect factor
Vir = 42.0 m
Diagonal dimension for internal size effect factors
air = 10× ( Vir )
1/3
= 34.8 m
Using fig. 4 Curve = "A"
External size effect factor
Caer = min(1.0, ka + kb × log( aer / ( 1 m ) ) ) = 0.97
Internal size effect factor
Cair = min(1.0, ka + kb × log( air /( 1m ) ) ) = 0.88
Dynamic pressure
qs = 1.00 kN/m
Internal pressure coeff
Cpi = -0.3
Internal surface pressure
pir = qs × Cpi × Cair =-0.27 kN/m
2
2
Net roof pressures
2
Zone A+
prA1 = qs × CperA1 × Caer - pir = 1.05 kN/m
Zone A
prA2 = qs × CperA2 × Caer - pir = -0.06 kN/m
2
2
Zone B+
prB1 = qs × CperB1 × Caer - pir = 0.79 kN/m
Zone B
prB2 = qs × CperB2 × Caer - pir = -0.06 kN/m
Zone C+
prC1 = qs × CperC1 × Caer - pir = 0.75 kN/m
2
Zone C
prC2 = qs × CperC2 × Caer - pir = 0.14 kN/m
2
Zone E+
prE1 = qs × CperE1 × Caer - pir = -0.45 kN/m
2
Zone E
prE2 = qs × CperE2 × Caer - pir = -0.45 kN/m
2
Zone F+
prF1 = qs × CperF1 × Caer - pir = -0.16 kN/m
2
Zone F
prF2 = qs × CperF2 × Caer - pir = -0.16 kN/m
2
Zone G+
prG1 = qs × CperG1 × Caer - pir = -0.16 kN/m
2
Zone G
prG2 = qs × CperG2 × Caer - pir = -0.16 kN/m
2
2
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From the calculated loads we see that each panel weighs 18kg and is 1640mm by 1000mm.
Therefore the weight per m2 = 10.97kg/m2.
The support frame weighs 2kg/m2
The allowable vertical imposed load is 0.6kN/m2 or 60kg/m2 which is far more than the weight of the panel
being placed on the roof.
Once the panel is in situ this area of roof will not be trafficked and so there is no need to consider the actual
weight of the panel as being an additional imposed load on the roof. Should anyone stand on the panel it will
destroyed, the owner of the property will therefore take strict steps to ensure that no one at any time stands
on the panel. Therefore this area of roof can be considered as carrying less than the design imposed load
indicated in BS 6399. Therefore there is no requirement for strengthening as a result of combined imposed
of the panel. However with the panel and frame weighing 12.97kg/m2 this combined loading is equal to or less
than the design imposed load of 0.6kN/m2.
The combined snow and panel load would therefore require no additional strengthening works in order to
carry this increase in load. The existing roof structure is therefore adequate as it stands at present.
Site location
Location of site;
Site altitude;
Carnoustie
A = 45 m
From BS6399:Part 3: 1988 - Figure 1. Basic snow load on the ground
2
sb = 0.55 kN/m
2
salt = 0.1 × sb + (0.09 kN/m ) = 0.14 kN/m
2
s0 = sb + salt × (A - (100 m)) / 100 m = 0.47 kN/m
2
BS6399:Part3:1988 Cl.6.2
α
α
µ1
µ1
Roof geometry
Roof type;
Pitched
Distance on plan from gutter to ridge;
b = 3.600 m
Angle of pitch of roof;
α = 35.0 deg
From BS6399:Part 3: 1988 - Figure 3. Snow load shape coefficients for pitched roofs
µ1 = 0.8 × [(60 deg - α) / 30 deg] = 0.67
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sd1 = µ1 × s0 = 0.31 kN/m
2
BS6399:Part3:1988 Cl.5
From BS6399:Part 3: 1988 - Figure 3. Snow load shape coefficients for pitched roofs
µ1 = 1.2 × [(60 deg - α) / 30 deg] = 1.00
sd1 = µ1 × s0 = 0.43 kN/m
2
BS6399:Part3:1988 Cl.5
Snow sliding down roof
2
Maximum uniform snow load on roof;
sd_max = 0.43 kN/m
Fs = sd_max × b × sin(α) = 0.97 kN/m
BS6399:Part3:1988 Cl.8
3.0
From the TEDDS calcs we see that the panels should ideally be placed within Zone C where there is little or
no wind uplift.
Given that the panel fixings will transfer the load into the existing roof and the roof was originally designed for
this wind load, no strengthening works will be required to the roof structure.
The applied wind load in Zone C is 0.75kN/m2
To calculate the actual wind uplift on the PV Array we refer to BRE Digest 489.
From our calculations above we know that q = 1.00kN/m2 and where a module is less than 0.3m from the roof
surface the Wind Uplift Net Pressure Coefficients for the panels in the centre of the roof is -1.3
-1.00 x -1.3 = -1.300kN/m2 (All roof fixings have to be able to withstand this wind uplift load.)
4.0
CONCLUSIONS
From the TEDDS calcs and the fixing calculations we see that the proposed solar panels can safely be fixed
to the existing roof structure with no strengthening works being required.
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