8/14/2013 1 WIND LOADS ON BUILDINGS IN ACCORDANCE WITH NSCP 2010 SECTION 207 Lecturer ENGR. ADAM C. ABINALES, M.ENG, F.ASEP Course STRUCTURAL ENGINEERING Introduction/Course Description Introduction One of the major and significant revisions of the NSCP Vol. I Sixth Edition 2010 is Chapter 2 which stipulates provisions on the minimum design loads to be applied on buildings, towers and other vertical structures. Section 207 of the NSCP Vol. I Sixth Edition2010 which discusses the wind load provisions of Chapter 2 Minimum Design Requirements is one of the major and significant changes. Wind load provisions of the NSCP Vol. I 2010 are generally referenced from the wind load criteria of the American Society of Civil Engineers (ASCE) publication, SEI/ASCE Standard 7-05, Minimum Design Loads for Buildings and Other Structures. Objectives and Results Objectives To provide a guide and information on the use of Section 207 of the NSCP Vol. I Sixth Edition 2010 with some illustrative examples for the civil engineering graduates, practicing civil/structural engineers, private and government stakeholders in construction industry and members of the academe community in the Philippines. To present the major and significant provisions of Section 207 Wind Load of Chapter 2 of the NSCP Vol. I Sixth Edition 2010. Results Understand and learn the basic wind load calculation as applied to building using Method 1 or Method 2. Understand and learn the basic wind load calculation as applied to tower structure using Method 2. Skills developed Proficiency on wind load derivation for building Proficiency on wind load derivation for tower structure Vocabulary Basic Wind Speed, denoted by Basic wind speed is a three-second gust speed at 10 m above the ground in Exposure “C” and associated with an annual probability for 2% of being equaled or exceeded (50-year mean recurrence interval). Design Wind Force, denoted by Design wind force is the equivalent static force to be used in the determination of wind loads for open buildings and other structures.
Seminar delivered by Engr. Adam Abinales. The Wind and Earthquake Engineering Seminar was held by ASEP in Cagayan de Oro August 2013 to promote correct interpretation of the Structural Code of the Philippines to reduce risk during calamities (typhoon and earthquake).
Part 1 discusses the applicability of wind loadings on enclosed buildings.
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8/14/2013
1
WIND LOADS ON BUILDINGSIN ACCORDANCE WITH NSCP 2010
SECTION 207
Lecturer ENGR. ADAM C. ABINALES, M.ENG, F.ASEP
Course STRUCTURAL ENGINEERING
Introduction/Course Description
� Introduction� One of the major and significant revisions of the
NSCP Vol. I Sixth Edition 2010 is Chapter 2 which stipulates provisions on the minimum design loads to be applied on buildings, towers and other vertical structures.
� Section 207 of the NSCP Vol. I Sixth Edition2010 which discusses the wind load provisions of Chapter 2 Minimum Design Requirements is one of the major and significant changes. Wind load provisions of the NSCP Vol. I 2010 are generally referenced from the wind load criteria of the American Society of Civil Engineers (ASCE) publication, SEI/ASCE Standard 7-05, Minimum Design Loads for Buildings and Other Structures.
Objectives and Results
� Objectives� To provide a guide and information on the use of Section 207 of the
NSCP Vol. I Sixth Edition 2010 with some illustrative examples for the civil engineering graduates, practicing civil/structural engineers, private and government stakeholders in construction industry and members of the academe community in the Philippines.
� To present the major and significant provisions of Section 207 Wind Load of Chapter 2 of the NSCP Vol. I Sixth Edition 2010.
� Results� Understand and learn the basic wind load calculation as applied to
building using Method 1 or Method 2.
� Understand and learn the basic wind load calculation as applied to tower structure using Method 2.
� Skills developed� Proficiency on wind load derivation for building
� Proficiency on wind load derivation for tower structure
Vocabulary
� Basic Wind Speed, denoted by �
� Basic wind speed is a three-second gust speed at 10 m
above the ground in Exposure “C” and associated with
an annual probability for 2% of being equaled or
exceeded (50-year mean recurrence interval).
� Design Wind Force, denoted by �
� Design wind force is the equivalent static force to be used
in the determination of wind loads for open buildings
and other structures.
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Vocabulary
� Design Wind Pressure, denoted by �
� Design wind pressure is the equivalent static pressure to
be used in the determination of wind loads for buildings
and may be denoted as:
� �� = pressure that varies with height in accordance
with velocity pressure �� evaluated at height �; or
� �� = pressure that is uniform with respect to the
height as determined by the velocity pressure ��evaluated at mean roof height �.
Vocabulary
� Building, Enclosed
� Building, Enclosed is a building that does not comply with
the requirements for open or partially enclosed
buildings.
� Building, Open
� Building, Open is a building having each wall at least 80%
open.
Vocabulary
� Building, Partially Enclosed
� Building, Partially Enclosed is a building that complies
with both of the following conditions:
� the total area of openings in a wall that receives
positive external pressure exceeds the sum of the
areas of openings in the balance of the building
envelope (walls and roof) by more than 10%; and
� the total area of openings in a wall that receives
positive external pressure exceeds 0.5 m2 or 1% of
the area of that wall, whichever is smaller, and the
percentage of openings in the balance of the
building envelope does not exceed 20%.
Vocabulary
� Building, Low-rise
� Building, Low-rise is an enclosed or partially enclosed
building that comply with the following conditions:
� mean roof height � less than or equal to 18 m; and
� mean roof height � does not exceed least horizontal
dimension.
� Building, Envelope
� Building Envelope consists of cladding, roofing, exterior
wall, glazing, door assemblies, window assemblies,
skylight assemblies and other components enclosing the
building.
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Vocabulary
� Building, Flexible
� Building, Flexible is a slender building that has a
fundamental natural frequency less than 1 Hz.
� Building, Rigid
� Building, Rigid is a building or other structure whose
fundamental natural frequency is greater than or equal
to 1 Hz.
Vocabulary
� Components and Cladding (C&C)
� Components and Cladding (C&C) are elements of the
building envelope that do not qualify as part of the main
Design wind pressures for MWFRS of this building can be obtained using Section 207.5.12.2.1 for buildings of all heights or Section 207.5.12.2.2 for low-rise buildings. In this example, pressures are determined using buildings of all heights criteria:
� � ���� & ��������
where
� � �� for windward wall at height � above ground
� � �� for leeward wall, side walls, and roof at height �
�� � �� for enclosed buildings
� = gust effect factor
�� = external pressure coefficient
������ = internal pressure coefficient
� Reference /
Notes
Section
207.5.4.4 or
Table 207-2
Section
207.5.12.2.1
Equation 207-
17
Figure 207-6
Figure 207-5
Solution and Discussion to Example
Problem 1
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Solution and Discussion to Example
Problem 1
Solution and Discussion to Example
Problem 1
� Design Wind
PressureFor this example, when the wind is
normal to the ridge, the windward roof experiences both positive and negative external pressures. Combining these external pressures with positive and negative external pressures will result in four loading cases when wind is normal to the ridge.
When wind is parallel to the ridge, positive and negative internal pressures result in two loading cases. The external pressure coefficients �� for θ = 0° apply in this case.
� Reference /
Notes
Figure 207-6
Solution and Discussion to Example
Problem 1
� External
Pressure
Coefficient
�� on Wall
The pressure coefficients for the windward wall and for the side walls are 0.8 and -0.7, respectively, for all '/(ratios.
The leeward wall pressure coefficient is a function of '/( ratio. For wind normal to the ridge, '/( = 60/75 = 0.8; therefore, the leeward wall pressure coefficient is -0.5.
� Reference /
Notes
Figure 207-6
Solution and Discussion to Example
Problem 1
� External
Pressure
Coefficient
�� on Wall
� Reference /
Notes
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Solution and Discussion to Example
Problem 1
� External
Pressure
Coefficient
�� on Wall
For wind parallel to the ridge, '/( =
75/60 = 1.25; the value of ��,
obtained by linear interpolation, = -
0.45.
In summary, the wall pressure coefficients
are:
� Reference /
Notes
Figure 207-6
Surface Wind direction '/( ��
Windward wall All All 0.80
Leeward wall Normal to
ridge0.8 -0.50
Parallel to
ridge1.25 -0.45
Side wall All All -0.70
Solution and Discussion to Example
Problem 1
� External
Pressure
Coefficient
�� on Roof
The roof pressure coefficients for
the MWFRS are determined
and shown below:
*Values obtained by linear interpolation. For
wind normal to ridge, �/' = 11/60 = 0.186.
� Reference /
Notes
Figure 207-6
Surface 15° 18.4° 20°
Windward
roof-0.5 -0.36* -0.3
0.0 0.14* 0.2
Leeward
roof-0.5 -0.57* -0.6
Solution and Discussion to Example
Problem 1
� External
Pressure
Coefficient
�� on Roof
� Reference /
Notes
Figure 207-6
Solution and Discussion to Example
Problem 1
� Internal
Pressure
Coefficient
����
Values for ���� for buildings are
addressed in:
The openings are evenly distributed in the walls (enclosed building). The reduction factor of Section 207.5.11.1.1 is not applicable for enclosed buildings;
therefore, ���� = ±0.18
� Reference /
Notes
Section
207.5.11.1
Figure 207-5
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Solution and Discussion to Example
Problem 1
� Gust Effect
Factor �For rigid structures (where the ratio of
� to the least width of building = 16/60 = 0.18 < 4), hence, rigid building, � can be calculated using Equation 207-4:
� � 0.9251 * 1.7+,��̅.
1 * 1.7+/��̅where
+, = +/ = 3.4
�̅ � 0.6� = 0.6(11) = 6.6 m or �̅ � �0�1 = 4.5 m
2 = 0.2
ℓ = 150 m
ε5 = 1/5
� Reference /
Notes
Section
207.5.8.1
Table 207-5
Solution and Discussion to Example
Problem 1
� Gust Effect
Factor �
� Reference /
Notes
Table 207-5
Solution and Discussion to Example
Problem 1
� Gust Effect
Factor �Then, compute the other notations
��̅ � 267
�̅
6/�
� 0.267
�.�
6/�
��̅ � 0.214
. �1
1 * 0.63( * �'�̅
7.�8
in which
'�̅ � ℓ�̅
10
9̅
� 1506.6
106/;
'�̅ � 138.04
� Reference /
Notes
Section
207.5.8.1
Equation 207-
5
Equation 207-
6, use ( = 60
m (the smaller
value gives
larger value of
�)
Equation 205-
7
Solution and Discussion to Example
Problem 1
� Gust Effect
Factor � Then,
. �6
6<7.�8=>?@@
@AB.>C
>.=A
. � 0.84
Substituting the computed
values to evaluate �:
� � 0.9251 * 1.7�3.4��0.214��0.84�
1 * 1.7�3.4��0.214�
� � 0.883
� Reference /
Notes
Equation 207-
6
Equation 207-
4
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Solution and Discussion to Example
Problem 1
� Net Wind
Pressures on
MWFRS
Wind pressure on the MWFRS is
determined as
� � ���� & ��������� � ��0.883��� & �1640��D0.18�
On the windward wall from 0 –
4.5 m, wind normal to ridge:
� � 1367�0.883��0.8� & �1640��D0.18�
� � 670 N/m2 with (+) internal pressure
� � 1261 N/m2 with (-) internal pressure
� Reference /
Notes
Equation 207-
17
Solution and Discussion to Example
Problem 1
� Net Wind
Pressures on
MWFRS
In summary, the net pressures
for the MWFRS (wind normal
to ridge) are shown in table:
� Reference /
Notes
Surface � (m) � (N/m2) � ��Net pressure (N/m2) with
(+����) (-����)
Windward
wall4.50 1367 0.883 0.80 670 1261
6.00 1447 0.883 0.80 727 1317
Leeward
wallAll 1640 0.883 -0.50 -1019 -429
Side walls All 1640 0.883 -0.70 -1309 -719
Windward
roof* - 1640 0.883-0.36 -816 -226
0.14 -92 498
Leeward
roof- 1640 0.883 -0.57 -1120 -530
Solution and Discussion to Example
Problem 1
� Net Wind
Pressures on
MWFRS
From previous calculation, note
that �� = 1640 N/m2; ���� =
±0.18; therefore, the quantity
��(����) = ±295 N/m2
*Two loadings on windward roof
and two internal pressures
yield a total of four loading
cases.
� Reference /
Notes
Refer to
Figures 1-1
through 1-2 in
next slides
Solution and Discussion to Example
Problem 1
� Net Wind
Pressures on
MWFRS
Figure 1-1 – Net Design Wind Pressures for MWFRS
when Wind is Normal to Ridge with Negative
Windward External Roof Pressure Coefficient
� Reference /
Notes
Surface � (m) � (N/m2) � ��Net pressure (N/m2) with
(+����) (-����)
Windward
wall4.50 1367 0.883 0.8 670 1261
6.00 1447 0.883 0.8 727 1317
Leeward
wallAll 1640 0.883 -0.5 -1019 -429
Side walls All 1640 0.883 -0.7 -1309 -719
Windward
roof*- 1640 0.883
-0.36 -816 -226
0.14 -92 498
Leeward
roof- 1640 0.883 -0.57 -1120 -530
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Solution and Discussion to Example
Problem 1
� Net Wind
Pressures on
MWFRS
Figure 1-2 – Net Design Wind Pressures for
MWFRS when Wind is Normal to Ridge with
Negative Windward External Roof Pressure
Coefficient
� Reference /
Notes
Surface � (m) � (N/m2) � ��Net pressure (N/m2) with
(+����) (-����)
Windward
wall
4.50 1367 0.883 0.8 670 1261
6.00 1447 0.883 0.8 727 1317
Leeward
wallAll 1640 0.883 -0.5 -1019 -429
Side walls All 1640 0.883 -0.7 -1309 -719
Windward
roof*- 1640 0.883
-0.36 -816 -226
0.14 -92 498
Leeward
roof- 1640 0.883 -0.57 -1120 -530
Solution and Discussion to Example
Problem 1
� Net Wind
Pressures on
MWFRS
Figure 1-3 – Net Design Wind Pressures for
MWFRS when Wind is Normal to Ridge with
Positive Windward External Roof Pressure
Coefficient
� Reference /
Notes
Surface � (m) � (N/m2) � ��Net pressure (N/m2) with
(+����) (-����)
Windward
wall
4.50 1367 0.883 0.8 670 1261
6.00 1447 0.883 0.8 727 1317
Leeward
wallAll 1640 0.883 -0.5 -1019 -429
Side walls All 1640 0.883 -0.7 -1309 -719
Windward
roof*- 1640 0.883
-0.36 -816 -226
0.14 -92 498
Leeward
roof- 1640 0.883 -0.57 -1120 -530
Solution and Discussion to Example
Problem 1
� Net Wind
Pressures on
MWFRS
Figure 1-4 – Net Design Wind Pressures for
MWFRS when Wind is Normal to Ridge with
PositiveWindward External Roof Pressure
Coefficient
� Reference /
Notes
Surface � (m) � (N/m2) � ��Net pressure (N/m2) with
(+����) (-����)
Windward
wall
4.50 1367 0.883 0.8 670 1261
6.00 1447 0.883 0.8 727 1317
Leeward
wallAll 1640 0.883 -0.5 -1019 -429
Side walls All 1640 0.883 -0.7 -1309 -719
Windward
roof*- 1640 0.883
-0.36 -816 -226
0.14 -92 498
Leeward
roof- 1640 0.883 -0.57 -1120 -530
Solution and Discussion to Example
Problem 1
� External
Pressure
Coefficient
�� on Roof
(Wind
Parallel to
Ridge)
� Reference /
Notes
Figure 207-6For wind parallel to ridge, �/' = 11/75 = 0.147 and θ < 10°. The values of
�� for wind parallel to ridge are:
*The values of smaller uplift pressures on the roof can become critical with roof live load; load combinations are given in Sections 203.3 and 203.4.
Surface �/'Distance from
windward edge��
Roof ≤ 0.5 0 to � -0.9, -0.18*
� to 2� -0.5, -0.18*
> 2� -0.3, -0.18*
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Solution and Discussion to Example
Problem 1
� External
Pressure
Coefficient
�� on Roof
(Wind
Parallel to
Ridge)
� Reference /
Notes
Figure 207-6
Solution and Discussion to Example
Problem 1
� External
Pressure
Coefficient
�� on Roof
(Wind
Parallel to
Ridge)
� Reference /
Notes
Refer to
Figures 1-5
through 1-6 in
next slide
The net pressures for the MWFRS (wind parallel to ridge) are:
�� = 1640 N/m2; ���� = ±0.18;
�������� = ±295 N/m2
*Distance from windward edge.
Surface � (m) � (N/m2) � ��Net pressure (N/m2) with
(+����) (-����)
Windward wall 0 - 4.50 1367 0.883 0.80 670 1260
6.00 1447 0.883 0.80 727 1317
9.00 1576 0.883 0.80 818 1408
12.00 1673 0.883 0.80 886 1476
15.00 1753 0.883 0.80 943 1533
16.00 1769 0.883 0.80 954 1544
Leeward wall All 1640 0.883 -0.45 -947 -357
Side walls All 1640 0.883 -0.70 -1309 -719
Roof* 0 to h* 1640 0.883 -0.90 -1598 -1008
h to 2h* 1640 0.883 -0.50 -1019 -429
> 2h* 1640 0.883 -0.30 -729 -139
Solution and Discussion to Example
Problem 1
� External
Pressure
Coefficient
�� on Roof
(Wind
Parallel to
Ridge)
Figure 1-5 –Net Design Wind Pressures for MWFRS when Wind
is Parallel to Ridge with Positive Internal Pressure
� Reference /
Notes
Surface � (m) � (N/m2) � ��Net pressure (N/m2) with
(+����) (-����)
Windward wall 0 - 4.50 1367 0.883 0.80 670 1260
6.00 1447 0.883 0.80 727 1317
9.00 1576 0.883 0.80 818 1408
12.00 1673 0.883 0.80 886 1476
15.00 1753 0.883 0.80 943 1533
16.00 1769 0.883 0.80 954 1544
Leeward wall All 1640 0.883 -0.45 -947 -357
Side walls All 1640 0.883 -0.70 -1309 -719
Roof* 0 to h* 1640 0.883 -0.90 -1598 -1008
h to 2h* 1640 0.883 -0.50 -1019 -429
> 2h* 1640 0.883 -0.30 -729 -139
Solution and Discussion to Example
Problem 1
� External
Pressure
Coefficient
�� on Roof
(Wind
Parallel to
Ridge)
� Reference /
Notes
Surface � (m) � (N/m2) � ��Net pressure (N/m2) with
(+����) (-����)
Windward wall 0 - 4.50 1367 0.883 0.80 670 1260
6.00 1447 0.883 0.80 727 1317
9.00 1576 0.883 0.80 818 1408
12.00 1673 0.883 0.80 886 1476
15.00 1753 0.883 0.80 943 1533
16.00 1769 0.883 0.80 954 1544
Leeward wall All 1640 0.883 -0.45 -947 -357
Side walls All 1640 0.883 -0.70 -1309 -719
Roof* 0 to h* 1640 0.883 -0.90 -1598 -1008
h to 2h* 1640 0.883 -0.50 -1019 -429
> 2h* 1640 0.883 -0.30 -729 -139
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Solution and Discussion to Example
Problem 1
� External
Pressure
Coefficient
�� on Roof
(Wind
Parallel to
Ridge)
Figure 1-6 –Net Design Wind Pressures for MWFRS when Wind
is Parallel to Ridge with Negative Internal Pressure
� Reference /
Notes
Surface � (m) � (N/m2) � ��Net pressure (N/m2) with
(+����) (-����)
Windward wall 0 - 4.50 1367 0.883 0.80 670 1260
6.00 1447 0.883 0.80 727 1317
9.00 1576 0.883 0.80 818 1408
12.00 1673 0.883 0.80 886 1476
15.00 1753 0.883 0.80 943 1533
16.00 1769 0.883 0.80 954 1544
Leeward wall All 1640 0.883 -0.45 -947 -357
Side walls All 1640 0.883 -0.70 -1309 -719
Roof* 0 to h* 1640 0.883 -0.90 -1598 -1008
h to 2h* 1640 0.883 -0.50 -1019 -429
> 2h* 1640 0.883 -0.30 -729 -139
Solution and Discussion to Example
Problem 1
� External
Pressure
Coefficient
�� on Roof
(Wind
Parallel to
Ridge)
Figure 1-6 –Net Design Wind Pressures for MWFRS when Wind
is Parallel to Ridge with Negative Internal Pressure
� Reference /
Notes
Surface � (m) � (N/m2) � ��Net pressure (N/m2) with