wind load design

1. Group Name ID NO
• 1. Behailu haile 422/09
• 2. Asefa Hadush 433/09
• 3. Abreham Atsbeha 370/09
• 4. Agazi G/Yesuse 376/09
• 5. Alemsegd Megrsa 273/09
• 6. Almaz Germa 374/09

2. ADDIS COLLEGE
FACULTY OF CIVIL ENGINEERING &
CONSTRUCTION MANAGEMENT
DEPARTMENT OF CIVIL
ENGINEERING
Analysis and comparison of
wind effect on different types
of the roof structure

3. INTRODUCTION
Wind forces are variable loads which act directly
on the internal and external surface of
structures
The response of a structure to the variable
action of wind can be separated in to two
components,
1. Background component which involves static
deflection of the structure under the wind
pressure
2. Resonant component , on the other hand,
involves dynamic vibration of the structure in
response to changes in wind pressure.

4. INTRODUCTION
In most structures the resonant
component is relatively small and
structural response to wind forces is
treated using static methods of
analysis alone.

5. INTRODUCTION
• Choosing the most appropriate type of roofs depends
immense on the conditions of the place where the
buildings are constructed is important.
• But buildings’ functions have also produced typical roof
shapes.
• Different roof types can be combined, but this often
produces a complicated geometry of details.
• Simple structures are therefore preferable, to avoid
leakage.
• The main distinction in roof types is between pitched
and flat roofs;

6. INTRODUCTION
• A flat roof:-has a pitch of zero in either instance;
all other roofs are pitched.
• Pitched roof:- pitch is the steepness of a roof
expressed as a ratio of pinch rise per horizontal
foot, or as the angle in degrees,
• Mono pitch roofs:- has a single rafter and is a
right angle truss used to form lean-to roofs or
single pitched roofs.

7. INTRODUCTION
• Dou pitch roof:- just as the name suggests,
have two different pitches on each side of the
roof.
• Hipped roof:- is a type of roof where all sides
slope downwards to the walls,
by definition (hipped roof is with steeply
pitched slopes rising to a peak).

8. RESEARCH METHODOLOGY
• Method of analysis is conducted using
software analysis, Ethiopian and Euro codes
are the main guides for our research.
• Most commonly applicable roof types are
compared.
• The roof types are analyzed independently
then each output is compared.
• Similar material and literatures are used for
roofs under analysis.

9. RESEARCH METHODOLOGY
•The thesis help us to practice some software

10. Study Area Description
• The study area is Adama town and the
analysis used to other towns(places) having
similar character.
• Adama varies from ground elevations of
1,595masl to 1,740m asl.
• Areas with higher altitudes are found from the
central to the northern and on the southern
verges of the town.
• Therefore the average altitude is 1712m asl.

11. location map of Adama town

12. 1.4.1 General Objective
• The general objective of this study is to
examine the extent of wind load on roofs
structure and evaluate its impact on different
types of roofs in the study area, having
altitude of 1712m, Ethiopia like Adama.

13. Specific Objective
 To analyze wind load effects on
various roof types;
 To compare and contrast wind load
effect on different roof types ;
 To identify safe and economical roof
structures.

14. Reference wind velocity
• The reference wind velocity for a locality is
defined as the mean wind velocity at 10m
above farmland averaged over a period of 10
minutes with a return period of 50 years
• Vref = CDIRCTEMCALTVref, 0
• Where Vref,0 is the basic reference wind
velocity 10m above sea level

15. • CDIR
Direction factor Allows for the orientation of the
structure in relation to the direction of the
prevailing wind
• CTEM
Seasonal variations in temporary structures The
seasonal variation factor, CTEM, may be applied to
structures of a temporary nature which are exposed
to wind for only part of a given year
• CALT
Altitude factor allows for the altitude of the site on
which the structure is located. Wind speeds tend to
be greater in sites located at high altitudes.

16. Reference wind velocity
• Vref=Cdir*Ctemp*Calt*Vref=22m/s for Ethiopia as
per ECS 145 2015
• Assuming Adama altitude in Ethiopia at
1712m Altitude above MSL => ρ=0.98kg/m3.
@ 20 0C By interpolation
• qp = ρ/2* Vref
2 The basic velocit preasure
in our case it is 0.237KPa
• The wind pressure acting on the external
surface of a structure is function of the
reference wind pressure which is given by:

17. Exposure coefficient
• The exposure coefficient takes account of
the variation from the reference wind
velocity due to the roughness around the
structure,
• the local topography and the height of
the structure above ground level is
considered
• In our case the height of the building is
35.5m

18. Exposure coefficient
• Where Cr and Ct are roughness and
topography coefficients respectively and kT is
a terrain factor(find in table 3.2 EBCS 1)
•Our site is categorized under Category 3 as
per The terrain categories are illustrated in Annex
A.1. ..CES 145
•Which regular cover of vegetation or
buildings or with isolated obstacles with
separations of maximum 20 obstacle eights
(such as villages, suburban terrain, permanent
forest)
• KT[Terrain Factor]=0.22, Zo=0.3m , Zmin=5m

19. Wind pressure
• Wi=qp(z ) * cpi Internal Wind
preasure
•Where: Cpi = 0.8 or -0.5 for closed
buildings with partition wall and
openings) ss per ECS 145
• In our case 20150.711*0.8=
0.57KN/m2

20. • we=qp(z ) * cpe External Wind presure
• In our case 0.711Cpe
•We take Maximum Cpe from Roof zoning
therefore we =2.183KN/m2

21. compare and contrast wind load
effect on different roof types
1. Flat slab roof
• Reinforced concrete slab is analysis using
wind load and its dead load
• The slab is divided in to panels As per ECS
2015 the support conditions are taken in to
consideration
• Depth of slab and span of slab are
determined.
• Minimum reinforcement is analyzed

22. • We use Excel template for slab analysis
• Diameter 8 bar average spacing 150 mm and
200mm
• Slab thickness 150mm with concrete cover
25mm both sides is Effective and safe

23. 2. Hipped roof @ 35.5 m

24. • The topography coefficient, Ct, accounts for the
increase in mean wind speed over isolated hills and
escarpments. Details for its calculation in such cases
are given in EBCS1 (Figure 3.6 and 3.7). For all other
situations, Ct may be taken as unity.

25. External wind pressure
• The wind pressure acting on the external surface
of a structure is function of the reference wind
pressure which is given by:
•
• Where  = air density (kg/m3)
• ref = reference wind velocity (m/s)
• The density of air varies with temperature,
elevation and the expected atmospheric pressure
in the region during a storm. EBCS1 gives a
recommended design value of  at 200 C for
different altitudes. Table 3.15 EBCS 1

26. Cont…….
• We = ce(ze)cpeqref
• cpe(external pressure coefficient) find in
EBCS 1 Appendix A

27. Internal wind pressure
• Internal pressure arises due to openings, such as
windows, doors and vents, in the cladding. In
general, if the windward pane has a greater
proportion of opening than the leeward panel,
then the interior of the structure is subjected to
positive (outward) pressure
• wi =ce(zi)cpiqref
• Cpi ((internal pressure coefficient) find in EBCS 1
Appendix A)
• For buildings with internal partitions the extreme
values, cpi = 0.8 and cpi = -0.5, may be used.

29. • Wind force on structures
• The total wind force action on individual zones
of clad structures is proportional to the
difference in pressure between the external
and internal faces. That is:
• Fw = (we – wi) Aref

30. Example 1
• Site
altitude 2000
• Suburban
or industrial
area

31. • According to EBCS1, Art 3.5.2
• External pressure (We)
• We=qrefce(ze)cpe
• Where Cpe is the external pressure coefficient
derived from Appendix A.
• Internal pressure (Wi)
• Wi= qref Ce (zi) Cpi
• Where
• qref =reference mean wind velocity
• Ce (ze) =exposure coefficient
• z= reference height
• Cpe= external pressure coefficient
• Cpi= internal pressure coefficient

32. • Vref=CDIR CTEM CALT Vref,o
• According to Section 3.7.2 of EBCS 1
• CDIR=CTEM =CALT=1 and Vref,o=22m/s
• Vref=22m/s
• According to table 3.15 of EBCS 1
• For altitude 2000 p=0.94Kg/m3
• Table 3.2 EBCS 1 i take terrain categories
III(suburban or industrial areas and
permanent forests)
• KT=0.22 Zo(m)=0.3 Zmin(m)=8

33. • Z=35m
• Form table 3.3 of EBCS 1, the roughness coefficient Cr
• 30------1.01
• 35-------? Using liner interpolation
• 50------1.13
• Cr=1.042
•
• Take the Topography coefficient Ct(z)=1 the area is topographically
unaffected
• The exposure coefficients Ce(Z) can be simply read from table 3.5 of
EBCS 1.
•
• 30---------------2.29
• 35----------------? Using liner interpolation
• 50---------------3
• Ce(Z)= 2.47

34. • Calculation of Cpe and Cpi
• Using Appendix A of section A.2.4 of EBCS 1
h=35m
α=tan-(5/24)= 11.770