ASTM C1401-23

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1401 − 23
Standard Guide for
Structural Sealant Glazing
This standard is issued under the fixed designation C1401; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 Structural sealant glazing, hereinafter referred to as
2.1 ASTM Standards:
SSG, is an application where a sealant not only can function as
B117 Practice for Operating Salt Spray (Fog) Apparatus
a barrier against the passage of air and water through a building
C99 Test Method for Modulus of Rupture of Dimension
envelope, but also primarily provides structural support and
Stone
attachment of glazing or other components to a window,
C119 Terminology Relating to Dimension Stone
curtain wall, or other framing system.
C162 Terminology of Glass and Glass Products
1.2 This guide provides information useful to design
C503 Specification for Marble Dimension Stone
professionals, manufacturers, contractors, and others for the
C509 Specification for Elastomeric Cellular Preformed Gas-
design and installation of a SSG system. This information is
ket and Sealing Material
applicable only to this glazing method when used for a building
C510 Test Method for Staining and Color Change of Single-
wall that is not more than 15° from vertical; however, limited
or Multicomponent Joint Sealants
information is included concerning a sloped SSG application.
C568 Specification for Limestone Dimension Stone
C615 Specification for Granite Dimension Stone
1.3 Only a silicone chemically curing sealant specifically
C717 Terminology of Building Seals and Sealants
formulated, tested, and marketed for structural sealant glazing
is acceptable for a SSG system application. C719 Test Method for Adhesion and Cohesion of Elasto-
meric Joint Sealants Under Cyclic Movement (Hockman
1.4 The committee with jurisdiction for this standard is not
Cycle)
aware of any comparable standard published by other organi-
C794 Test Method for Adhesion-in-Peel of Elastomeric Joint
zations.
Sealants
1.5 The values stated in SI units are to be regarded as
C864 Specification for Dense Elastomeric Compression Seal
standard. The values given in parentheses after SI units are
Gaskets, Setting Blocks, and Spacers
provided for information only and are not considered standard.
C880 Test Method for Flexural Strength of Dimension Stone
SI units in this guide are in conformance with IEEE/ASTM SI
C920 Specification for Elastomeric Joint Sealants
10.
C1036 Specification for Flat Glass
1.6 This standard does not purport to address all of the
C1048 Specification for Heat-Strengthened and Fully Tem-
safety concerns, if any, associated with its use. It is the
pered Flat Glass
responsibility of the user of this standard to establish appro-
C1087 Test Method for Determining Compatibility of
priate safety, health, and environmental practices and deter-
Liquid-Applied Sealants with Accessories Used in Struc-
mine the applicability of regulatory limitations prior to use.
tural Glazing Systems
1.7 This international standard was developed in accor-
C1115 Specification for Dense Elastomeric Silicone Rubber
dance with internationally recognized principles on standard-
Gaskets and Accessories
ization established in the Decision on Principles for the
C1135 Test Method for Determining Tensile Adhesion Prop-
Development of International Standards, Guides and Recom-
erties of Structural Sealants
mendations issued by the World Trade Organization Technical
C1172 Specification for Laminated Architectural Flat Glass
Barriers to Trade (TBT) Committee.
C1184 Specification for Structural Silicone Sealants
C1193 Guide for Use of Joint Sealants
This guide is under the jurisdiction of ASTM Committee C24 on Building Seals
and Sealants and is the direct responsibility of Subcommittee C24.10 on
Specifications, Guides and Practices. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved June 1, 2023. Published June 2023. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1998. Last previous edition approved in 2022 as C1401 – 14 (2022). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/C1401-23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1401 − 23
C1201 Test Method for Structural Performance of Exterior E1424 Test Method for Determining the Rate of Air Leakage
Dimension Stone Cladding Systems by Uniform Static Air Through Exterior Windows, Skylights, Curtain Walls, and
Doors Under Specified Pressure and Temperature Differ-
Pressure Difference
C1248 Test Method for Staining of Porous Substrate by Joint ences Across the Specimen
E1425 Practice for Determining the Acoustical Performance
Sealants
of Windows, Doors, Skylight, and Glazed Wall Systems
C1249 Guide for Secondary Seal for Sealed Insulating Glass
E1825 Guide for Evaluation of Building Exterior Enclosure
Units for Structural Sealant Glazing Applications
Materials, Products, and Systems
C1253 Test Method for Determining the Outgassing Poten-
E1886 Test Method for Performance of Exterior Windows,
tial of Sealant Backing
Curtain Walls, Doors, and Impact Protective Systems
C1265 Test Method for Determining the Tensile Properties
Impacted by Missile(s) and Exposed to Cyclic Pressure
of an Insulating Glass Edge Seal for Structural Glazing
Differentials
Applications
E1996 Specification for Performance of Exterior Windows,
C1294 Test Method for Compatibility of Insulating Glass
Curtain Walls, Doors, and Impact Protective Systems
Edge Sealants with Liquid-Applied Glazing Materials
Impacted by Windborne Debris in Hurricanes
C1330 Specification for Cylindrical Sealant Backing for Use
E2128 Guide for Evaluating Water Leakage of Building
with Cold Liquid-Applied Sealants
Walls
C1369 Specification for Secondary Edge Sealants for Struc-
E2203 Specification for Dense Thermoplastic Elastomers
turally Glazed Insulating Glass Units
Used for Compression Seals, Gaskets, Setting Blocks,
C1392 Guide for Evaluating Failure of Structural Sealant
Spacers and Accessories
Glazing
E2099 Practice for Specification and Evaluation of Pre-
C1394 Guide for In-Situ Structural Silicone Glazing Evalu-
Construction Laboratory Mockups of Exterior Wall Sys-
ation
tems
C1472 Guide for Calculating Movement and Other Effects
E2431 Practice for Determining the Resistance of Single
When Establishing Sealant Joint Width
Glazed Annealed Architectural Flat Glass to Thermal
C1487 Guide for Remedying Structural Silicone Glazing
Loadings
C1521 Practice for Evaluating Adhesion of Installed Weath-
G15 Terminology Relating to Corrosion and Corrosion Test-
erproofing Sealant Joints
ing (Withdrawn 2010)
C1564 Guide for Use of Silicone Sealants for Protective
2.2 IEEE/ASTM Standard:
Glazing Systems
IEEE/ASTM SI 10 Standard for Use of the International
D1566 Terminology Relating to Rubber
System of Units (SI): The Modern Metric System
D2203 Test Method for Staining from Sealants
2.3 Aluminum Association Manual:
D4541 Test Method for Pull-Off Strength of Coatings Using
Aluminum Design Manual
Portable Adhesion Testers
2.4 ANSI/ASCE Standard:
E283 Test Method for Determining Rate of Air Leakage
ANSI/ASCE 7, Minimum Design Loads for Buildings and
Through Exterior Windows, Skylights, Curtain Walls, and
Other Structures
Doors Under Specified Pressure Differences Across the
2.5 AAMA Standards:
Specimen
501.1 Standard Test Method for Metal Curtain Walls for
E330 Test Method for Structural Performance of Exterior
Water Penetration Using Dynamic Pressure
Windows, Doors, Skylights and Curtain Walls by Uniform
501.2 Field Check of Metal Curtain Walls for Water Leak-
Static Air Pressure Difference
age
E331 Test Method for Water Penetration of Exterior
TIR-A11–1996 Maximum Allowable Deflection of Framing
Windows, Skylights, Doors, and Curtain Walls by Uni-
Systems for Building Cladding Components at Design
form Static Air Pressure Difference
Wind Loads
E547 Test Method for Water Penetration of Exterior
2.6 ANSI Standard:
Windows, Skylights, Doors, and Curtain Walls by Cyclic
Z97.1 Safety Performance Specifications and Methods of
Static Air Pressure Difference
Test for Glazing Materials Used in Buildings
E631 Terminology of Building Constructions
2.7 CPSC Standard:
E783 Test Method for Field Measurement of Air Leakage
16 CFR 1201 Standard on Architectural Glazing Materials
Through Installed Exterior Windows and Doors
E1105 Test Method for Field Determination of Water Pen-
etration of Installed Exterior Windows, Skylights, Doors, The last approved version of this historical standard is referenced on
www.astm.org.
and Curtain Walls, by Uniform or Cyclic Static Air
Available from the Aluminum Association, 900 19th St., N.W. Washington, DC
Pressure Difference
20006.
E1233 Test Method for Structural Performance of Exterior
Available from American National Standards Institute, 25 W. 43rd St., 4th
Floor, New York, NY 10036.
Windows, Doors, Skylights, and Curtain Walls by Cyclic
Available from the Architectural Aluminum Manufacturers Association
Air Pressure Differential
(AAMA).
E1300 Practice for Determining Load Resistance of Glass in
Available from the Consumer Product Safety Commission (CPSC),
Buildings Washington, D.C. 20207.
C1401 − 23
3. Terminology 3.2.7 stick system, n—a metal framing system of numerous
elements that is construction site assembled and field glazed,
3.1 Definitions:
usually in-place on the face of a building.
3.1.1 Refer to Terminology C119 for definitions of the
following terms used in this guide: dimension stone, granite, 3.2.8 thermal bridge, n—a method that transfers thermal
hysteresis, limestone, and marble. energy, usually by means of a metallic path from the interior to
3.1.2 Refer to Terminology C162 for definitions of the the exterior of a window or curtain wall system.
following terms used in this guide: chip, chipped glass, double
3.2.9 unitized system, n—a panelized metal framing system
glazing unit, flat glass, glass, heat-strengthened glass, heat-
that is preassembled and usually shop-glazed, with the panels
treated, laminated glass, lite, pyrolitic coating, safety glass,
transported to a construction site for erection on a building.
skylight, spandrel glass, tempered glass, thermal stress, tough-
3.3 Symbols:
ened glass, and wave.
3.1.3 Refer to Terminology C717 for definitions of the
A = solar absorptivity coefficient.
following terms used in this guide: adhesive failure, bicellular
α = coefficient of linear thermal movement mm/mm/°C
sealant backing, bite, bond breaker, butt glazing, cell, chemi-
(in./in./°F).
cally curing sealant, closed cell, closed cell material, closed
B = structural sealant joint bite mm (in.).
cell sealant backing, cohesive failure, compatibility,
C = perpendicular distance between parallel sides m (ft).
compound, cure, durability, durability limit, elastomeric,
elongation, gasket, glazing, glazing construction site, hardness,
ΔL = thermal movement mm (in.).
joint, lite, modulus, open cell, open cell material, open cell
ΔT = summer temperature differential °C (°F).
s
sealant backing, outgassing, premature deterioration, primer,
ΔT = winter temperature differential °C (°F).
w
seal, sealant, sealant backing, secant modulus, service life, F = allowable structural sealant dead load stress kPa
d
setting block, shop glazing, silicone sealant, spacer, standard (psi).
F = allowable structural sealant tension stress kPa (psi).
conditions, structural sealant, substrate, thickness, and tooling.
t
F = allowable structural sealant shear stress kPa (psi).
3.1.4 Refer to Terminology D1566 for the definition of the v
f = computed tensile stress kPa (psi).
following term used in this guide: compression. t
f = computed shear stress kPa (psi).
v
3.1.5 Refer to Terminology E631 for the definitions of the
H = heat capacity constant.
following terms used in this guide: air-leakage, anchorage,
L = side of lite or panel m (ft).
anchorage system, building envelope, cladding system, curtain
L = long side of lite or panel m (ft).
wall, glaze, mechanical connection, mockup, operable, panel,
L = short side of the lite or panel m (ft).
performance standard, sealed insulating glass, shop drawing,
% = shear movement percent.
specification, static load, tolerance, water-vapor retarder,
P = lateral load due to wind kPa (psf).
w
weephole, and working drawing.
R = radius of a lite or panel m (ft).
3.1.6 Refer to Terminology G15 for the definition of the
T = structural sealant joint thickness mm (in.).
following term used in this guide: chemical conversion coat- T = ambient summer temperature °C (°F).
a
T = summer surface temperature °C (°F).
ing.
s
T = ambient winter temperature °C (°F).
w
3.2 Definitions of Terms Specific to This Standard:
2 2
W = unit weight of lite or panel kg/m (lb/ft ).
3.2.1 aspect ratio (AR), n—the ratio of the long dimension
φ = angle in degrees.
of the glass to the short dimension of the glass. AR is always
equal to or greater than 1.0.
4. Summary of Guide
3.2.2 negative pressure, n—an applied load, usually wind
4.1 General—This guide has been subdivided into major
induced, that tends to pull a glass lite or panel away from a
headings. A very brief description of each major heading is
building surface.
provided to assist the reader in locating general areas of
3.2.3 opacifier, n—an opaque material applied to the interior
information. For a more detailed listing of guide topics and
facing surface of a glass spandrel panel, which can include
section headings, refer to Appendix X1 for a complete listing
materials, such as adhesively applied organic films, a liquid-
of the numbered sections and their descriptors.
applied silicone coating, or a fired-on ceramic enamel frit.
4.2 Predesign Considerations (Section 6), in general, the
3.2.4 panel, n—a cladding material other than glass that is
responsibilities and relationships of the various participants in
manufactured or fabricated from solid, laminated or composite
SSG system development and implementation.
assemblies of materials such as dimension stone, metal or
plastic.
4.3 Performance Criteria Considerations (Sections 7 – 14),
SSG system structural loads, movements, construction
3.2.5 positive pressure, n—an applied load, usually wind
tolerances, weather tightness, sound transmission, fire
induced, that tends to push a glass lite or panel inward from a
resistance, and durability.
building surface.
3.2.6 snap time, n—the time in minutes at which a multi- 4.4 System Design Considerations (Sections 15 – 18), infor-
component sealant tears within itself and does not string when mation is provided about the basic types of SSG and related
a spatula is removed from the curing sealant. systems, as well as system weatherproofing concepts.
C1401 − 23
4.5 Component Design Considerations (Sections 19 – 26), and components have a sound knowledge of SSG system
framing systems, framing finishes, glass, panels, structural requirements and become involved in the design and planning
sealants, weather seal sealants, and accessory material infor- for each application. Suppliers of, among others, sealants,
mation. framing finishes, glazing materials and components, and vari-
ous accessories should review and agree with the developed
4.6 Structural Sealant Design Considerations (Sections 27 –
SSG system plans, requirements, and quality control program.
31), structural joint location and configuration, adhesion and
compatibility concerns, theoretical structural design, and other 5.5 The results of not planning for and implementing quality
design and weather seal considerations. control programs during at least the design, testing, fabrication,
and installation phases of a SSG system’s development can
4.7 Testing Considerations (Sections 32 – 37), predesign
result in less than desirable results, which can include nuisance
scale model wind and snow load testing, design and fabrication
air or water leakage or catastrophic failure where life safety of
component testing for quality, adhesion, and compatibility, and
the public can be at risk (1, 2).
full-size assembly mock-up testing information.
4.8 Shop Glazing Considerations (Sections 38 – 42), mate- PREDESIGN CONSIDERATIONS
rials prequalification, quality control programs, and inspection
6. Roles of Major Participants
and testing quality assurance issues.
6.1 General—Responsibility for the design,
4.9 Construction-Site Glazing Considerations (Sections 43
implementation, and maintenance of a SSG system depends
– 47), materials prequalification, quality control programs, and
largely on the contractual relationships between the partici-
inspection and testing quality assurance issues.
pants and their extent of participation. This relationship can
4.10 Post-Installation Considerations (Sections 48 – 51),
vary on individual projects, but it should be established clearly
quality control, maintenance, and periodic monitoring pro-
at the beginning and understood by all concerned parties. The
grams.
following descriptions briefly describe the normal roles and
duties generally ascribed to the participants, which usually is
5. Significance and Use
adequate for the development of a SSG system.
5.1 The old saying “A chain is only as strong as its weakest
6.2 Building Owner—The building owner should review
link” is very applicable to a SSG system. In reality, a SSG
and approve the design concept and budget for the develop-
system, to be successful, must establish and maintain a chain of
ment and implementation of a SSG system. It is the building
adhesion. For example, a factory applied finish must adhere
owner’s responsibility to establish and maintain a realistic
adequately to a metal framing member, a structural glazing
post-construction inspection and testing program to evaluate
sealant to that metal finish, that structural glazing sealant to a
structural sealant integrity. Typically, the building owner also
reflective coating on a glass lite, and lastly, that reflective
should authorize required maintenance, structural repairs, and
coating to a glass surface. This guide will assist in the
replacement of components expeditiously.
identification and development of, among others, performance
criteria, test methods, and industry practices that should be
6.3 Architect—The architect should provide the basic sys-
implemented to obtain the required structural glazing sealant
tem design concept, performance criteria, and a cost estimate
adhesion and compatibility with other system components.
for the owner’s review and approval. The architect also should
provide the owner with an explanation of the SSG system
5.2 Although this guide has been arranged to permit easy
design concept, degree of risk involved, and maintenance and
access to specific areas of interest, it is highly recommended
eventual replacement requirements. The architect has the
that the entire guide is read and understood before establishing
responsibility to conduct a feasibility review of the basic
the requirements for a particular SSG system.
design concept, system features, and material requirements
5.3 This guide should not be the only criteria upon which
with potential manufacturers and contractors. The architect
the design and installation of a SSG system is based. The
also should engage a SSG system consultant, if one is needed,
information herein is provided to assist in the development of
and provide contract documents (working drawings and speci-
a specific program with a goal of achieving a successful SSG
fications) in accordance with the chosen construction method
system installation. Information and guidelines are provided
and the architect’s professional services agreement. Construc-
for the evaluation, design, installation, and maintenance of a
tion administration by the architect usually includes, among
SSG system and many of its various components. Considering
others, shop drawing, product data, sample review, and ap-
the range of properties of structural glazing silicone sealants, as
proval or other appropriate action. The architect also makes
well as the many types of framing system designs, material
on-site visits in accordance with the professional services
combinations that can be used, various material finishes, and
agreement.
the many types and varieties of accessories, the information
6.4 Consultant—A consultant usually is engaged by the
contained herein is general in nature.
architect but also can be engaged by the general contractor,
5.4 Generally, the design, fabrication, and installation of a
curtain wall subcontractor, or the owner. The consultant
SSG system requires more technical knowledge and experience
then is required for a conventionally glazed window or curtain
wall system. To ensure the success of a SSG system, it is
The boldface numbers in parentheses refers to the list of references at the end
important that suppliers, fabricators, and installers of materials of this standard.
C1401 − 23
provides guidance and technical expertise and establishes subcontractor is retained. Coordination between the system
requirements for the design and implementation of the SSG manufacturer and the installer is required.
system, among others.
6.9 Metal Framing Fabricator or Supplier—
6.5 Building Code Authority—All codes accept traditional
Responsibilities include coordinating with the metal supplier
glazing with conventional mechanical glazing retainage;
and the finish applicator; monitoring of metal surface finish
however, some jurisdictions may permit SSG systems only
quality control; and, approval of the product for the specific
with supplementary mechanical retainage. Other code jurisdic-
SSG application. The metal framing fabricator also has the
tion requirements can include, among others, establishment
responsibility to provide representative production run samples
and certification of specific structural sealant material
of metal finishes for adhesion and compatibility evaluation by
properties, controlled inspection of a SSG system installation,
the structural sealant manufacturer.
and post-installation periodic inspection and certification pro-
6.10 Glass Manufacturer or Fabricator—Responsibilities
grams. For example, the ICBO Evaluation Service, Inc., a
include review of the project design requirements; recommen-
subsidiary of the International Conference of Building Officials
dation of glass thickness and type to meet, among others, wind
(ICBO), which publishes the Uniform Building Code (UBC),
load and thermal stress conditions as specified for the SSG
requires fulfillment of certain criteria before a structural sealant
system; quality control of the secondary seal of insulating glass
is acceptable for use in jurisdictions that have adopted the
UBC. Code acceptance criteria may involve testing and con- units and any glass coatings, such as reflective or low-
emissivity; and, approval of the glass product(s) for a specific
ditions of testing that normally are not conducted by structural
SSG application. The glass manufacturer also has the respon-
sealant manufacturers or require conditions of use that will
limit the type and character of a SSG system. Additionally, sibility to provide production run representative samples of the
other code requirements for example impact resistance may glass type(s) for adhesion and compatibility evaluation by the
also have an effect on the design of an SSG system (See 8.6)
structural sealant manufacturer. The glass manufacturer also
The building code and the specific code jurisdiction authorities
has the responsibility to determine with the cooperation of the
should be consulted prior to any SSG system detailed design.
fabricator of the insulating glass units, if a separate party, the
compatibility of at least the structural sealants and accessories
6.6 Contractor—The contractor selects the subcontractors
that may have an effect on the performance of the insulating
and reviews, approves, and submits to the architect submittals,
glass unit edge seal.
such as shop drawings, product data, and samples. The
contractor also performs the construction and other services in
6.11 Panel Manufacturer or Fabricator—Panel types in-
accordance with the contract documents and the approved
clude metal, composite, plastic, and stone among others (See
submittals. Supervision, direction, and coordination of the
Section 23). Responsibilities include: review of the project
construction and other services, to assure compliance with the
design requirements; recommendation of panel type to meet,
contract documents, also is performed by the contractor. Most
among others, wind load and thermal stress conditions as
importantly, the contractor has the responsibility for and
specified for the SSG system; quality control of any panel
control of construction means, methods, techniques, sequences,
finishes or coatings and approval of the panel product(s) for a
and procedures unless the contract documents direct otherwise.
specific SSG application. The panel manufacturer also has the
responsibility to provide production run representative samples
6.7 SSG System Designer—This responsibility often is the
of the panel type(s) for adhesion and compatibility evaluation
architect’s, however, a SSG system consultant or a curtain wall
subcontractor also can perform this work. Responsibilities by the structural sealant manufacturer.
include the design of the SSG system to meet the architect’s
6.12 Structural Sealant Manufacturer—Responsibilities in-
design parameters and performance criteria and development
clude conducting structural sealant compatibility testing with,
of specific material selection criteria for glass, panels, metal
among others, spacers, gaskets, setting blocks and other
finishes, sealants, gaskets, and other SSG system components.
sealants; adhesion testing of the structural sealant(s) to the
Importantly, the system designer also should develop a SSG
panel surface, metal finish and glass substrates; review and
system that can be resealed or reglazed, easily and adequately,
approval of the structural sealant joint dimensions provided by
if glass, sealant, or other component replacement is necessary.
the SSG system designer; recommendation of a sealant(s) for
6.8 SSG System Subcontractor—Responsibilities include
the structural and weather seals, as well as, if necessary, a
obtaining the approval of, among others, panel, metal finish,
primer; and approvals of the sealant products for the specific
glass, and sealant manufacturers for use of their products in a
SSG application.
SSG application; preparation and submittal of shop drawings to
6.13 Accessory Material Suppliers—Accessory material
the general contractor for processing and approval; and,
suppliers have the responsibility to provide spacers, gaskets,
fabrication and installation of the SSG system in accordance
setting blocks and other products of the correct material
with, among others, the contract documents, approved shop
drawings, mock-ups, and component manufacturer’s recom- formulation, hardness, shape, and tolerances as specified by the
mendations. Sometimes a separate SSG system installation architect, consultant, or SSG system designer. The accessory
C1401 − 23
material supplier also has the responsibility to provide produc- building code and the ANSI/ASCE 7 determined wind load
tion run representative samples of the accessories for adhesion values typically apply to buildings of square or rectangular
and compatibility evaluation by the structural sealant manu- shape with vertical walls. The use of a building code or the
facturer. analytical procedure in ANSI/ASCE 7 may not be sufficient for
these buildings, particularly when of other shapes. Often, this
PERFORMANCE CRITERIA CONSIDERATIONS
is the case when a building is in an urban environment; of
unusual configuration; closely related to other buildings as in a
7. General
campus setting; or, in an area of unusual or unpredictable wind
7.1 Typical performance criteria that are applicable to a
patterns. For these and other reasons scale model testing of a
conventional glazing system also apply to a SSG system;
building in a boundary layer wind tunnel (BLWT) may be
however, some of these performance criteria may require
necessary (see 33.1.1).
different treatment, extra care, or additional criteria. The
8.3 Snow—For sloped wall surfaces or skylights, the effect
following typical performance criteria are described where
of snow loading and drifting patterns on a SSG system must be
SSG issues need to be considered. Typically, some combina-
considered. The building code and ANSI/ASCE 7 establish
tion of the following structural loads and movements, depend-
values that can be used for design. Also, the AAMA skylight
ing on an engineering analysis of a particular SSG system’s
and sloped glazing, 501.1 and 501.2, will provide the design
design requirements, may have to be considered. For example,
professional with design information for snow loading and
the effect of wind load and thermal movement is a commonly
control on sloped surfaces. Since the actual pattern and
encountered combination that may have to be evaluated when
velocity of wind flow around a building can have a dramatic
designing a structural sealant joint. Additional general glazing,
impact on drifting and snow load, however, the use of a scale
as well as performance criteria information, is available from
model testing facility to establish these patterns and loads is
industry associations, such as the American Architectural
recommended (see 33.1.3). Snow and ice loads usually cause a
Manufacturers Association (AAMA), the Glass Association of
long-term compressive stress on a structural sealant joint and
North America (GANA) (formerly the Flat Glass Marketing
can become another of the secondary loading conditions that
Association, and the American Society of Civil Engineers
should be evaluated when designing a SSG system. The effect
(ASCE).
of snow load on vertical wall surfaces usually is not a
8. Structural Loads
performance criterion; however, the additional dead load gen-
8.1 Dead—A SSG system, depending on a particular design, erated by hardened snow or ice sheets, which can form on
may require the structural sealant joint to resist a constant dead vertical and other surfaces, may need to be considered.
load stress. This usually occurs when glass or panels are
8.4 Live (Maintenance)—Normally, loads transferred di-
unsupported by setting blocks or other mechanical devices and
rectly to a window or curtain wall framing member by
also at suspended soffit construction. The allowable dead load
maintenance platforms will not have a significant effect on the
stress for design will depend on the modulus of the structural
structural joints in a SSG system; however, the use of continu-
sealant and the dimensions of the structural sealant joint. Some
ous maintenance tracks, as well as intermittent tie-back buttons
structural sealant manufacturers will not permit glass or panels
or other devices, may have an influence on the practical aspects
to be suspended or unsupported by setting blocks or other
of SSG system design, such as adequate access to apply the
means. For those sealant manufacturers who permit dead load
structural sealant in the joint opening and the development of
stressing of the structural sealant, there has been a precedent to
thermal bridges (see 11.4.1).
limit the dead load stress to no more than 7 kPa (1 psi). The
structural sealant manufacturer should be consulted early 8.5 Seismic:
during SSG system design since not all sealant manufacturers
8.5.1 Seismic design largely is based on probability and
will permit a constant dead load stress on the sealant joint or
economics (3). The magnitude and frequency of seismic loads
permit exceeding a 7 kPa (1 psi) limit.
cannot be determined with the same degree of accuracy as
other types of building loads. It is possible the magnitude of
8.2 Wind—The realistic establishment of negative and posi-
loading may vary by a factor of two or more; therefore, due to
tive wind loads is important (3, 4). It is primarily the wind
economic reasons, a commonly accepted earthquake design
loading conditions, except for some seismic zones, which
philosophy is to control major structural damage while allow-
determine the size and shape of a structural sealant joint in a
ing some minor nonstructural damage as a result of an
SSG system. Other secondary loading conditions, such as dead
earthquake.
load and thermal movement also can contribute to the design of
a structural sealant joint. The building code applicable to a SSG 8.5.2 The applicable building code should be consulted for
system will establish minimum requirements for the wind load seismic design guidelines. There are benefits to using a SSG
to be resisted by a curtain wall or window system and therefore system in areas prone to earthquakes. The resilient attachment
a SSG system. Often, cladding wind loads are not adequately of a glass lite or panel to the supporting framework by the
described by those building codes that use a simple table of structural sealant joint has proven to be beneficial in control-
wind load values. The ASCE standard ANSI/ASCE 7, which ling and in some cases eliminating breakage normally experi-
also is referenced in some of the national model building enced during a small to moderate earthquake. Since the lite or
codes, provides a detailed analysis and description of the wind panel is not captured in a metal glazing pocket the opportunity
loads to be resisted by a curtain wall or window system. The for it to impact the metal glazing pocket surfaces is minimized,
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eliminating a primary cause of breakage. Depending on system ANSI/ASCE 7 national wind load standard, which is refer-
design, however, adjacent glass lite or panel edges could enced by building codes, also contains provisions for resistance
contact each other and cause breakage or other effects. Also, to missile impact. Additionally, those that insure buildings in
when a glass lite break does occur, the SSG system, due to coastal areas may also have requirements such as those
continuous attachment of the glass edge, can retain much if not contained in the Building Code for Windstorm Resistant
all of the broken glass, depending on glass type, and provided Construction by the Texas Windstorm Insurance Association.
that the structural joint retains sufficient integrity. Resilient The designer of an SSG system, particularly for coastal
attachment of a glass lite also has proven beneficial in other regions, should consult local code, governmental, and insur-
violent natural occurrences such as hurricanes. ance authorities to determine the requirements for resisting
missile impacts and their effect on the design of an SSG system
8.5.3 The level of performance required of a SSG system
prior to any detailed design.
during and after an earthquake will vary depending on the
system design philosophy. The SSG system should remain
9. Movements
stable after an earthquake. For example, depending on the
magnitude of an earthquake, glass may or may not break.
9.1 Building Motion—Tall buildings will respond to wind
Laminated glass often is used in seismic regions so that it can
pressure and other lateral forces, such as earthquakes, by
remain in the opening if it does break; however, whether or not
swaying laterally or twisting due to torsional moments. The
remedial work is required to regain SSG system functionality,
magnitude of these movements can be determined by a
for example, air or water resistance and structural performance,
structural engineer or by scale model testing in a BLWT (see
is a choice for the designer, depending on building code
33.1.1). These movements usually are expressed as an offset at
requirements, which will affect the design and cost of the SSG
each story relative to adjacent stories (story drift). These
system.
movements can create a shear stress, which may have to be
8.5.4 Racking motion of a building frame in an earthquake
considered with other secondary stresses in the design of the
will cause planar motion of a glass lite or panel, typically structural sealant and other joints of a SSG system.
causing a shear stress in a structural sealant joint. Although
9.2 Thermal Movement—The effect of thermal movement
conventional SSG systems perform well in an earthquake,
always must be considered and provided for in the design of a
consideration should be given to isolating the lite or panel from
SSG system. If not, excessive air leakage and water infiltration,
building frame movement. One method to consider is to
as well as potential structural problems, can occur. The effect
structurally adhere the lite or panel to a subframe, then attach
of thermal movement within the structural sealant joint, due to
the subframe to the primary curtain wall or window framing
differential thermal movement between glass or panels and the
members with mechanical fasteners in slotted holes (5).
supporting framework, should be investigated for any effects
on the structural sealant joint that may have to be considered
8.6 Missile Impact—Windborne debris has been established
along with other structural sealant joint secondary stresses.
as a principal cause of glass breakage during windstorms (6).
The designer of a SSG system may have to make provisions in
9.3 Live Load—Deflection caused by structure or floor live
the system design to resist large and small missile impacts (7).
loading should be considered for SSG system sealant joints,
At lower floors, large objects, such as framing members and
such as expansion joints, that occur usually at each floor level
facade elements from nearby collapsed structures and at lower
in multistory construction. The building structural engineer can
and upper floors windborne gravel from ballasted roofs, the
supply live load deflection criteria for use in designing the SSG
largest source of glass breakage, tend to strike a building
system. Actual live loads can be highly variable (8). A
envelope. If the building envelope does not remain intact
multistory building, with the same design live load for all
during a windstorm, the wind-induced increase to a building’s
floors, will have the actual live load, which can be substantially
internal pressure adds to the wind-induced external suction on
less than a code prescribed value, vary from floor to floor and
leeward walls and roofs, thereby increasing the possibility of a
from one area of a floor to another. Very rarely will the live
structural failure or collapse of facade elements. In addition,
load be uniform everywhere. Where live load, and thus
breaching the envelope allows damage to the building interior
deflection of a structure varies, the relative difference in live
and potential harm to occupants. Guide C1564 can be used to
load deflection between floors should be considered in the
determine the design and installation requirements for the
multistory SSG system expansion joint width design.
missile impact structural sealant in addition to those required
9.4 Dead Load—Deflection caused by structure or floor
for SSG. Test Method E1886 and Specification E1996 can be
dead loading also should be considered for SSG system
used to determine the performance of a window or curtain wall
expansion joints. The building structural engineer can supply
when impacted by a missile and exposed to a cyclic pressure
dead load deflection criteria for SSG system expansion joint
differentials, as is commonly encountered during these storms.
design.
Various building codes and governmental authorities such as
9.5 Framing Effects:
the BOCA National Building Code, South Florida Building
Code, and the International Building Code include require- 9.5.1 Elastic Frame Deformation—Multistory concrete
ments for building envelope resistance to missile impacts. The structures, and to a lessor degree steel, shorten elastically
provisions in these codes are not consistent with each other, almost immediately due to the application of loads (8, 9).
with changes occurring each year, and they vary in required Frame shortening, the degree of which can be estimated by a
test methods, test protocol, and resultant performance. The structural engineer, will cause an irreversible narrowing of
C1401 − 23
SSG system expansion joints that typically occur at each floor glass lites or panels to come into contact with each other. This
level in multistory construction. Frame shortening can be increase also should be evaluated for its impact when, at other
compensated for by building each floor level slightly higher, in
times, the primary lateral load is applied. Depending on the
effect negating most of the short-term shortening that occurs
structural sealant modulus and the structural joint thickness, a
before SSG system installation. Lower floors of multistory
glass lite or panel could be pulled off setting blocks with a
structures will experience greater shortening then upper floors.
sufficiently large negative applied load. Another technique to
For each concrete column, the amount of shortening is depen-
enhance seismic performance is to structurally seal a lite or
dent on, among others, the amount of reinforcement and the
panel to a subframe, usually by shop glazing, which then is
time of application of loads (dead load of additional floors and
mechanically attached to a metal framing system or the
live load). Additionally, joint width narrowing can be consid-
building frame in a manner that permits differential movement,
ered during the design of an SSG system expansion joint. Some
both vertically and horizontally, between the subframe and the
of the frame shortening affect will occur before the cladding is
framing system or building (5). The subframe mechanical
erected and the size of the SSG system expansion joint opening
attachment mechanism then is designed to accommodate the
is established. Presently, the amount of shortening that occurs
expected seismic movement.
before the joint opening is established is determined by an
informed estimate, and therefore, should be conservative.
10. Construction Tolerances
9.5.2 Creep—The time dependent deformation of materials
10.1 General—The SSG system design must respond to
while loaded, in particular for a concrete structure, should be
tolerances likely to effect its fabrication and installation (11).
included in SSG system floor level expansion joint design. This
The SSG system performance criteria should specify the
deformation, which occurs at a decreasing rate as time
allowable material, fabrication, and erection tolerances. Mini-
progresses, can cause a continuing decrease in the width of an
mum and maximum deviation from other performance criteria
expansion joint opening in multistory and other buildings.
also need to be realistically established. Bowed glass, under- or
Creep, in contrast to elastic frame shortening, can occur over a
over-sized glass, straightness of framing members, and gasket
long period of time (8, 9). The building structural engineer can
size variation all must be considered during system design
provide creep deflection criteria for SSG system expansion
joint design. relative to their effect on the dimensions of a structural sealant
joint opening. If affecting the loading or structural performance
9.5.3 Shrinkage—Concrete framed structures will undergo
of any structural sealant joint, tolerances need to be considered
long-term shrinkage for a period of months (8, 9). The rate of
in the performance review. Manufacturing tolerances should be
shrinkage is dependent on the initial amount of concrete mix
communicated and added to the required minimum joint
water present, ambient temperatures, rate of air movement,
relative humidity of the surrounding air, the shape and size of dimensions. It is essential that the effective structural sealant
the concrete section, and the amount and type of aggregate in dimensions are never smaller than the calcula
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