Revisions to ASCE 7-10
In 2010 a major revision to ASCE 7 Minimum Design
Loads for Buildings and Other Structures, commonly
referred to as ASCE 7-10, was published. This revision
supersedes ASCE 7-05, ASCE 7-02 and ASCE 7-98. With
respect to wind loads, ASCE 7-05, ASCE 7-02 and ASCE
7-98 were very similar, and have been the reference
standards for all major building codes for almost a
decade. ASCE 7-10, on the other hand, incorporates
numerous editorial and fundamental changes that
demand attention. ASCE 7-10, has already been
adopted by the 2012 International Building Code and
2010 Florida Building Code
leaving little time for the
fenestration and building
products industry to plan
for its implementation. This
Information Bulletin will
explain the major changes
to ASCE 7-10 and offer
guidance on using ASCE
7-10 in conjunction with
product testing programs.
Major Changes to ASCE 7-10
Wind Load Provisions
There are three obvious and significant changes in ASCE
7-10. First, editorially, ASCE 7-10 was reorganized to a
multiple-chapter format. The wind load provisions have
been moved and expanded from Chapter 6 to Chapter
26 to Chapter 31. The change was implemented to
present a better organized wind load methodology for
the structural design community. Provisions for the
main wind force resisting system (MWFRS), other structures,
and components and cladding (C&C) are presented in
separate chapters dedicated to each topic.
Furthermore, the provisions for both MWFRS and C&C
have been expanded to include new optional analyses
techniques. Each analysis type now includes tables
showing step-by-step procedures for conducting an
analysis.
Second, previous versions of ASCE 7 used a single
wind speed map with importance factors for each
building risk category. ASCE 7-10 now incorporates
three wind speed maps that vary by risk category
(separate maps are provided for the following risk
categories: I, II, and III & IV). Additionally, the wind
speeds are now based on strength design/load and
resistance factor design in place of previously used
allowable stress design. While at first glance, the wind
speed maps in ASCE 7-10 suggest the design
pressures required are much higher than the previous
edition, a 0.6 factor is applied to correlate strength
design to allowable stress design of ASCE 7-05.
August 2012
Finally, ASCE 7-10 has subtly shifted the Exposure
Category for hurricane prone regions from Exposure C to
Exposure D. In ASCE 7-05, Exposure D specifically
excluded hurricane prone regions, but now that exclusion
has been removed. ASCE 7-10 advises that Exposure D
continues 600 feet or 20 times the building height into
Exposure B and Exposure C conditions. This is generally
interpreted that Exposure D is to be applied within 600
feet of the shoreline in coastal regions.
ASCE 7-10 continues to employ the Wind Directionality
Factor, Kd. This factor provides a minor adjustment to
wind loads when they are combined with other load
types (i.e. dead load, live load, snow load). It is not
appropriate to use this factor with calculated wind loads
for most door, window and cladding products as the only
load they are subjected to is wind load. Exceptions would
be curtain wall mullions with axial dead load or sloped
glazing with snow load and dead load.
Strength Design vs.
Allowable Stress Design
Strength design and allowable stress design have both
been recognized by ASCE 7 as long as the two design
philosophies have been prevalent. Traditionally, loads
established by the standard as nominal loads are
factored based on their certainty of occurring to be used
for strength design. For example, dead loads which can
be established with high confidence have a strength
design load factor of 1.2 and live loads which can be
established with less confidence have a strength design
load factor of 1.6. Prior to ASCE 7-10 the wind speed
maps provided nominal wind loads and a strength
design load factor of 1.6 was prescribed for wind loads.
ASCE 7-10 wind speed maps now produce ultimate
design loads that are directly applicable to the strength
design method and the strength design load factor for
wind is 1.0. To use ASCE 7-10 calculated pressures for
the allowable stress design method, the calculated
pressures are factored by 0.6 to convert the ultimate
wind load to a nominal wind load. Note that 0.6 = 1/1.6.
Straightforwardly, the major change in wind load
determination between ASCE 7-10 and ASCE 7-05 is the
order in which strength design wind loads are determined.
Product Testing and
Windborne Debris Requirements
Physical testing of most building components and
assemblies, including windows, has traditionally and
continues to use an allowable stress design methodology.
Typically, products are tested to a design pressure
where serviceability limits (deflection, operability, etc.)
are checked and then to a test load with a specific
factor of safety where elastic behavior is verified. The
factor of safety for allowable stress design testing must
not be confused with the 1.6 strength design load
factor as different product responses are expected at
the respective test loads. That is, elastic behavior is
expected at allowable stress design test load whereas
component failure would be expected at the strength
design test load. Thus, in comparing wind pressures
established by ASCE 7-10 to product performance, one
must verify which design philosophy was used to
establish the wind pressures and convert those design
wind pressures to allowable stress design pressures, if
necessary.
For impact resistant products, the pressures prescribed
for the cyclic loading program should match the product
design pressures established by allowable stress
design. However, the actual definition of wind-borne
debris regions and missile levels are still based on the
Basic Wind Speed. With the new Basic Wind Speed
maps of ASCE 7-10, the definition of wind-borne debris
was modified as shown in Table 1 and Table 2. And, it is
stipulated that the Building Category II Basic Wind
Speed map shall be used for all Building Category III
buildings except health care facilities.
An impacted test unit
August 2012
The wind zones that establish the particular missile level have been adjusted as shown in Table 1 and Table 2. Currently,
there is a significant disconnect between ASCE 7-10 and ASTM E1996. ASTM Task Group E06.51 on Impact Resistance
is currently revising ASTM E1996 and changes addressing both ASCE 7-10 and ASCE 7-05 are expected in the next
published version of the standard.
Table 1. Wind-borne Debris Region and ASTM Wind Zone within 1 Mile of Coast
Standard
Wind-borne Debris Region
ASTM E1996
Wind Zones
ASTM E1996
Wind Zones
ASCE 7-05
Vasd ≥ 110 MPH
Wind Zone 1: 110 MPH ≤ Vasd < 120 MPH
Wind Zone 3: 120 MPH ≤ Vasd ≤ 140 MPH
Wind Zone 4: Vasd > 140 MPH
ASCE 7-10
Vult ≥ 130 MPH
Wind Zone 1: 130 MPH ≤ Vult < 140 MPH
Wind Zone 3: Vult ≥ 140 MPH
2010 FBC /2012 IBC
Vult ≥ 130 MPH
Wind Zone 1: 130 MPH ≤ Vult < 140 MPH
Wind Zone 3: 140 MPH ≤ Vult ≤ 160 MPH
Wind Zone 4: Vult > 160 MPH
Table 2. Wind-borne Debris Region and ASTM Wind Zone more than 1 Mile of Coast
Standard
Wind-borne Debris Region
ASTM E1996
Wind Zones
ASTM E1996
Wind Zones
ASCE 7-05
Vasd ≥ 120 MPH
Wind Zone 1: 110 MPH ≤ Vasd < 120 MPH
Wind Zone 2: 120 MPH ≤ Vasd < 130 MPH
Wind Zone 3: 130 MPH ≤ Vasd ≤ 140 MPH
Wind Zone 4: Vasd > 140 MPH
ASCE 7-10
Vult ≥ 140 MPH
Wind Zone 1: 130 MPH ≤ Vult < 140 MPH
Wind Zone 2: 140 MPH ≤ Vult < 150 MPH
Wind Zone 3: Vult ≥ 150 MPH
Vult ≥ 140 MPH
Wind Zone 1: 130 MPH ≤ Vult < 140 MPH
Wind Zone 2: 140 MPH ≤ Vult < 150 MPH
Wind Zone 3: 150 MPH ≤ Vult ≤ 160 MPH
Wind Zone 4: Vult > 160 MPH
2010 FBC /2012 IBC
August 2012
Sample Calculations
Some practical calculated wind pressures are presented to show
how ASCE 7-10 affects wind loads for components and cladding.
In all cases a mean roof height of 30 feet, component area of 15
ft2 and corner zone (Zone 5) was assumed. ASCE 7-10 allowable
stress design values are calculated by multiplying the strength
values by 0.6.
Table 3. Sample Calculations
Allowable Stress Design: a method of
proportioning structural members such that
elastically computed stresses produced in
the members by nominal loads do not
exceed specified allowable stresses. Also
commonly referred to as Working Stress
Design.
Strength Design: a method of proportioning
structural members such that the computed
forces produced in the members by the
factored loads do not exceed the member
design strength. Also commonly referred to
as Load and Resistance Factor Design.
Nominal Load: The magnitude of the
loads specified in ASCE 7-05 for dead, live,
soil, wind, snow, rain, flood and earthquake.
Basic Wind
Speed
Design
Pressures
Vasd=90 MPH
+16.7/-22.0 psf
+ 27.3/-36.0 psf
+16.4/-21.6 psf
Main Wind Force Resisting System
(MWFRS): an assemblage of structural
elements assigned to provide support and
stability for the overall structure.
+19.2/-25.4 psf
+ 29.7/-39.2 psf
+17.8/-23.5 psf
Components and Cladding (C&C):
elements of the building envelope that do
not qualify as part of the MWFRS.
+61.6/-81.4 psf
+ 88.5/-116.9 psf
+53.1/-70.1 psf
Basic Wind Speed, V: Three-second gust
speed at 33 ft (10 m) above the ground in
Exposure C.
N/A
+104.7/-138.3 psf
+62.8/-83.0 psf
Vasd: Basic Wind Speed used for allowable
stress design.
Building
Method
York, PA
Exposure B
Category II
ASCE 7-05
ASCE 7-10, Strength
ASCE 7-10, ASD
York, PA
Exposure B
Category III
ASCE 7-05
ASCE 7-10, Strength
ASCE 7-10, ASD
Miami, FL
Exposure C
Category II
ASCE 7-05
ASCE 7-10, Strength
ASCE 7-10, ASD
Vasd=146 MPH
Miami, FL
Exposure D
Category II
ASCE 7-05
ASCE 7-10, Strength
ASCE 7-10, ASD
Vasd=146 MPH
Vult=115 MPH
Vasd=90 MPH
Vult=120 MPH
Vult=175 MPH
Vult=175 MPH
Vult: Basic Wind Speed used for strength
design
Conclusion
ASCE 7-10 is a significant update and reorganization of the ASCE 7 standard. The wind speed maps and calculation
methods have been revised to make strength design the primary design philosophy. Design pressures calculated by
strength design should be converted to allowable stress design pressures for comparison to product testing and
certification design pressures. Existing product test reports or product certifications are valid for use with ASCE 7-10
determined pressures. Requirements for ASTM E1996 Wind Zones with respect to ASCE 7-10, 2010 Florida Building Code and
2012 International Building Code are specified within the documents while ASTM E1996 is being revised.
About The Author
Joe Reed , P.E.
Director - Engineering Services
Mr. Joseph Reed has continual engineering experience since 1988 and joined Architectural
Testing in 2002. He is a Professional Engineer licensed in seven states. He has Master of Science
in Civil Engineering from Lehigh University.
717.764.7700 . jreed@archtest.com . www.archtest.com
August 2012