check sail effect network on a scaffolding

[Giovannino60]

to verify the sail effect of the nets on a scaffold I found these two calculation systems, I ask what is the most correct to apply:

1) Wind actions are assessed in accordance with the following expression:
♪
where:
s= surface of a scaffolding module hit by the wind (s=0.25xh*i sqm)
c= shape coefficient of 1.2
kinetic pressure has the following expression:
pv= (alpha t *alfa r *alfa z *vr )2/16 kg/mq
alpha t =1; alpha r =0.93; alphaz =0.69 for heights up to 5 m
vr is the reference speed of the fixed wind as follows:
- 16 m/s for the operating condition
- 30 m/s for outside exercise condition
g= coefficient of flux given by the report :
g = 1+1.12 / alpha z
2) fv= surface x percentage of full parts of the network (from 30% to 90%) x wind speed.

 

[Betoniera]

to verify the sail effect of the nets on a scaffold I found these two calculation systems, I ask what is the most correct to apply:
.

I repeat this old question, which, however, did not find an answer, to talk about how to calculate the pressures of the wind on the objects (in this case on the roofs of a scaffold). this because it can always interest those who care about structures. later you will also provide an example developed step, step to make understand the procedure.

legislation:
a standard can not replace the rule of law that in this case is dm 14-01-2008 (technical standards on construction) and the circular explanatory 02-02-2009 n. 617.
the calculation of the actions of the wind, must therefore be done according to the ntc 2008 and is indicated in point 3.3
Form coefficients (cp) are indicated in the circular at point c3.3.

the following parameters must be kept in mind:
- the speed of the wind: it is fixed according to the regional zone of belonging (vary from 25 to 28 m/sec).
- the distance from the coast: the wind is stronger near the sea resorts.
- class of soil roughness: that is, if there are buildings that hinder the flow of the wind
- height of construction: the wind is constant up to a certain height (4-8 m) then increases with logarithmic trend. the higher the construction, the more the wind becomes strong.
- form of the object: at equal pressure of the wind, the pressure on the object depends on its shape. a cylinder has cp=0,7 shape coefficient, a building has a cp of 0.8 on the pressure side and a cp=-0,4 on the depression side for a total of 1.2.
- another parameter to keep in mind is the return period. normally is 50 years. but in the case of a scaffolding lasting less than 2 years, we can multiply the pressure by a coefficient of 0.9.

in the case of a scaffolding:
- you can believe the temporary construction.
- the shape coefficient can be considered as 1,2 (such as the walls of a building).
attention: in the presence of micro perforated sheets for example (at 50%) it is absolutely wrong to reduce the pressure by 50%.
I participated in the experimental test, through wind tunnel, of a micro-perforated cloth.
for high turbulence (i.e. for wind speeds of 100 km/h), the resistance of the micro-perforated wind cloth is almost equal to that of a closed cloth.
It follows that the microforated cloth must be treated as a closed cloth.
below an example of the calculation of the wind's actions on a 10 m high scaffold.
If there were doubts about the passages of the calculation, express them as well, I will try to explain them.
in zone 1 that the wind at 25 m/sec (90 km/h) produces a pressure of 51 kg/m2 at the base and 56 kg/m2 at the altitude of 10 m.
a pressure of 41 kg/m2 (cp=0,8) and a depression of 20 kg/m2 (cp=-0,4)
a pressure of 45 kg/m2 (cp=0,8) and a depression of 22 kg/m2 (cp=-0,4),
for a total pressure of 65 kg/m2

the calculation may appear complicated, but it is what prescribes the legislation. However, once understood, it is applicable to any object (walls, roofs, chimneys, billboards, bridges, etc.).

Hello everyone, next

calculation example:
action of the wind (d.m. 14/01/2008) 3.3.5
wind load
property of temporary construction
return period tr = years 10
return coefficient cr = 0.9
wind pressure p = qb*ce*cp*cd
Regional area 1
altitude on sea level as = m 250
class roughness soil class b
distance from coast > 30 km
height of construction as = m 10
reference wind pressure qb=0,1*ro*vb^2/2
air density ro = kg/m3 1,25
reference altitude a0 = m 1000
reference wind speed ( 90 km/h) vb0 = m/sec 25
reference wind speed as<=a0, vb=vb0*cr vb = m/sec 22,57
wind pressure reference qb = kg/mq 31,86
category of exposure iv
exposure coefficient 0 ce0 = 1,62
height with coefficient ce0 zmin = m 8
coefficient of exposure to altitude zc ce = 1,78
dynamic coefficient cd = 1
wind pressure from 0 to 8 qb = kg/mq 51,93
wind pressure at altitude m 10 pv = kg/mq 56,81

wind pressure on walls of pond buildings
shape coefficient surfaces overwind cp = 0.8
pressure walls overwind from 0 to 8 pv = kg/mq 41,54
pressure overwind walls at altitude m 10 pv = kg/mq 45,45
shape coefficient surfaces underwind cp = -0,4
pressure walls underwind from 0 to 8 pv = kg/mq -20,78
pressure walls at altitude m 10 pv = kg/mq -22,73
average total wind pressure pv = kg/mq 65,24

 

[gfrank]

thanks to the "treatment" ...

 

[Nik.spa]

Good morning, young man 60, interesting your treatment. I would now like to know what changes for the calculation of the wind on the scaffolding with the new ntc 2018.