243 14TH CANADIAN CONFERENCE ON BUILDING SCIENCE AND TECHNOLOGY GUARDS IN BUILDINGS – THE CANADIAN CHALLENGE G. Hildebrand and P. Vegh ABSTRACT Several tempered glass balconies from more than twenty buildings have shattered since the summer of 2011 and incidents of glazed balcony glass breakage continue to be reported. These incidents attracted public and media attention to the issue of the safety of existing balcony guards. This in turn prompted a high level of technical scrutiny relating to the design and regulatory requirements for guards. In Ontario the Ministry of Municipal Affairs and Housing formed a committee of stakeholders to address the issue and recommend interim revisions to the Ontario Building Code to ensure public safety. The stakeholders comprised developers, engineers, architects, regulators and building code officials. The new Code amendments were released and took effect in July 2012 and apply to new construction after July 2012. Concurrently a Canada wide CSA Committee has been formed and has begun working on the preparation of a new CSA Standard for guards. This paper, provides background insight regarding the issues associated with building guards including: guard failure mechanisms, inadequacy of existing regulation relating to their design and installation, interim measures to mitigate the risks associated with guard failures and, the current approach and variables being considered by the new CSA A500 “Building Guards: standard.” This paper will outline the basic structure of the CSA approach, which has identified the key areas such as; Categories and Locations of Guards, Durability, Safety and Risk Assessment, Design Criteria (e.g., loads), Materials and Component Requirements, Testing Procedures, Installation and Inspection and Repair and Maintenance, that the standard will address. The intent of this paper is to alert architects, engineers, specification writers, developers and building professionals about some of the problems associated with building guards, educate them regarding the variables that must be considered in their design and inform them about the potential effects of the expected changes the new Standard will have on the industry. The authors were members of the Ministry of Municipal Affairs and Housing expert panel and have spearheaded the development of the CSA A500 Guard Standard, currently under development. BACKGROUND In the not too distant past, most balcony guardrail systems for residential high-rise buildings were not light- weight assemblies. Early high-rise balcony guardrail systems employed materials such as steel, cast in place or precast concrete, masonry, or combinations of these materials. In addition, the most common method of construction was to fully support the entire railing assembly on top of the balcony slab and inboard from its outer edge. The first versions of “by-pass” guard assemblies, in which the railing assembly is supported outboard from the balcony slab edge, were mostly constructed of precast concrete panels or steel posts with steel panels. These were typically secured to the building using cast-in-place anchors and plates. Failure of any of the guard components was rare, within their useful service life, often governed by corrosion of the guard assembly itself or corrosion of the embedded anchors and/or reinforcing steel with the resulting damage of the surrounding concrete. In more recent years, (i.e., ≈ 15 years) the architectural community has gradually incorporated much lighter guard designs comprising materials such as glass and aluminum (or dimensionally reduced steel), citing the fact that these lighter-weight designs offer several desirable characteristics, particularly in the use of glass as a baluster or infill component.
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14TH CANAD IAN CONFERENCE ON BU I LD ING S C I ENCE AND T E CHNOLOGY
GUARDS IN BUILDINGS – THE CANADIAN CHALLENGE
G. Hildebrand and P. Vegh
ABSTRACT
Several tempered glass balconies from more than twenty buildings have shattered since the summer of 2011
and incidents of glazed balcony glass breakage continue to be reported. These incidents attracted public and
media attention to the issue of the safety of existing balcony guards. This in turn prompted a high level of
technical scrutiny relating to the design and regulatory requirements for guards. In Ontario the Ministry of
Municipal Affairs and Housing formed a committee of stakeholders to address the issue and recommend
interim revisions to the Ontario Building Code to ensure public safety. The stakeholders comprised
developers, engineers, architects, regulators and building code officials. The new Code amendments were
released and took effect in July 2012 and apply to new construction after July 2012. Concurrently a Canada
wide CSA Committee has been formed and has begun working on the preparation of a new CSA Standard
for guards. This paper, provides background insight regarding the issues associated with building guards
including: guard failure mechanisms, inadequacy of existing regulation relating to their design and
installation, interim measures to mitigate the risks associated with guard failures and, the current approach
and variables being considered by the new CSA A500 “Building Guards: standard.” This paper will outline
the basic structure of the CSA approach, which has identified the key areas such as; Categories and Locations
of Guards, Durability, Safety and Risk Assessment, Design Criteria (e.g., loads), Materials and Component
Requirements, Testing Procedures, Installation and Inspection and Repair and Maintenance, that the standard
will address.
The intent of this paper is to alert architects, engineers, specification writers, developers and building
professionals about some of the problems associated with building guards, educate them regarding the
variables that must be considered in their design and inform them about the potential effects of the expected
changes the new Standard will have on the industry. The authors were members of the Ministry of Municipal
Affairs and Housing expert panel and have spearheaded the development of the CSA A500 Guard Standard,
currently under development.
BACKGROUND
In the not too distant past, most balcony guardrail systems for residential high-rise buildings were not light-
weight assemblies. Early high-rise balcony guardrail systems employed materials such as steel, cast in place
or precast concrete, masonry, or combinations of these materials. In addition, the most common method of
construction was to fully support the entire railing assembly on top of the balcony slab and inboard from its
outer edge. The first versions of “by-pass” guard assemblies, in which the railing assembly is supported
outboard from the balcony slab edge, were mostly constructed of precast concrete panels or steel posts with
steel panels. These were typically secured to the building using cast-in-place anchors and plates. Failure of
any of the guard components was rare, within their useful service life, often governed by corrosion of the
guard assembly itself or corrosion of the embedded anchors and/or reinforcing steel with the resulting
damage of the surrounding concrete. In more recent years, (i.e., ≈ 15 years) the architectural community
has gradually incorporated much lighter guard designs comprising materials such as glass and aluminum
(or dimensionally reduced steel), citing the fact that these lighter-weight designs offer several desirable
characteristics, particularly in the use of glass as a baluster or infill component.
14TH CANAD IAN CONFERENCE ON BU I LD ING S C I ENCE AND T E CHNOLOGY
although the British standards (and many others) also prescriptively specify minimum glass thickness for
various glass infill and balustrades, based on the size of the panel or their proximity to their surrounding
building components. Similar to the Canadian references, most of the other standards reviewed, consider
tempered or laminated glasses as “safety glass” and allow either to be used for a balcony railing application.
It is interesting to note that other standards, such as the Australian standard, AS1288 explicitly divide glass
for use in guardrails into two distinct categories; 1) structural balustrade panels; or 2) infill balustradepanels.
This is an important distinction in that, where the glazing is acting as a balustrade, it is considered part of
the main live load bearing assembly and a number of restrictions come into play. These include line loading
and the requirement for a continuous capping and adequate load transfer to adjacent panels. This latter
requirement is also provided for in the Canadian Standard CAN/CGSB 12.20 document.
One exception to the directive allowing either tempered or laminated glass for use on balconies, is the
requirement for laminated glass given in the, “Guidelines on the use of Glass in Buildings – Human Safety”2
published by the Confederation of Construction Products and Services (CCPS). This document is a consensus
document, written by a number of industry and regulatory stakeholders and is intended to be mandated by
code within the various jurisdictions in India. With respect to guardrail glazing, the document offers a lucid
set of prescriptive instructions based on end use, with five classifications given in a table and supported by
pictorial examples to ensure non-ambiguity. For guard glass in residential high-rise buildings, the glass falls
under a, “Case 5; Glass acting as a balustrade, parapet or a railing (Human Impact and risk of fall)”category and laminated safety glass would be required.
This guideline specifically addressed two issues, one relating to the issue of retention of the occupant and
the second, the issue of managing the glass after it is broken. Once again, the only issue associated with this
approach is the fact that, in order to satisfy its safety intent, the broken glass must remain in place and not
fall as a single large piece of broken glass.
LOAD CONSIDERATIONS
With respect to the general issue of loads, supplemental to previous comments, the anticipated loads imposed
on guards and their subject component mainly consist of:
1) Live loads are loads imposed either intentionally or accidentally. Intentional loads are service occupant
loads applied in the course of the service life of the guardrail. Live Accidental loads are unintentional live
loads related to impact. These loads are those associated with objects such as a human striking the glass
infill, either with their body, in the case of an accidental fall or, by throwing or hitting the glass with an
object. Accidental human falls have been extensively studied and resultant safety standards, such as the
American National Standards Institute Inc. (ANSI) Standard Z97.1 – 2004. “American National Standard
for safety glazing materials safety performance specifications and methods of test” provide the appropriate
loads and methods of calculating the additional loads based on a study of accidental falls.
2) Wind loads are the forces exerted on the guardrail glazing from the prevailing winds. Establishing the
actual loads acting on balcony guardrails from wind is quite difficult and whether, determined through a
wind tunnel study, or calculation using the methods provided in the building codes, the actual loads will
vary throughout the building and are largely indeterminate. For this reason, the basic wind loads on cladding
(and guardrail) assemblies are usually subject to a number of safety factors to account for this uncertainty.
The current Canadian building code prescribes that both live and wind loads be combined in a prescribed
14TH CANAD IAN CONFERENCE ON BU I LD ING S C I ENCE AND T E CHNOLOGY
REFERENCES
1 Tim Morgan CEng MIMechE, Technical Manager, Pilkington Architectural “Aspects of Structural Glass”presentation to the Institute of Structural Engineers, SE Counties Branch, England, 2010Source: GlassAssociation of North America (GANA) Guide to Architectural Glass 2010 Edition2 Confederation of Construction Products and Services (CCPS) (2013), “Guidelines on use of Glass inBuildings - Human Safety” 3 Ontario Ministry of Municipal Affairs and Housing, “Report of the expert panel on glass panels inbalcony guards.”, March 30, 2012, Toronto Ontario.