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BCC Ruling No. 95-08-428

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BUILDING CODE COMMISSION DECISION ON B.C.C. #95-08-428

IN THE MATTER OF Subsection 24(1) of the Building Code Act, 1992.

AND IN THE MATTER OF Article 4.1.1.4., Sentences 4.1.10.5.(1) and 4.1.10.5.(2) of the Revised Regulation of Ontario 1990, Regulation 61, as amended by O.Regs. 400/91, 158/93, 160/93 and 355/94 (the "Building Code").

AND IN THE MATTER OF an application by Mr. Robert Fallowfield, Aluma Systems Canada Inc. for the resolution of a dispute with Mr. Michael Nixon, Chief Building Official, City of Toronto, concerning whether horizontal bracing members are required to resist horizontal live loads for temporary grandstand structures at the Exhibition Grounds, Toronto, Ontario.

APPLICANT

Aluma Systems Canada Inc.
Concord, Ontario

RESPONDENT

Mr. Michael Nixon
Chief Building Official
City of Toronto

PANEL

Mr. Demir Delen, Panel Chair
Mr. Remus Tsang
Mr. Sang Shim

PLACE

Toronto, Ontario

DATE OF RULING

February 28th, 1995

APPEARANCES

Mr. Robert Fallowfield
Aluma Systems Canada Inc.
For the Applicant

Mr. Bill Chiang
Building Engineer
AND
Mr. Lance Cumberbatch
Zoning Building Plan Examiner
City of Toronto
For the Respondent

RULING

  1. The Applicant

Mr. Robert Fallowfield, Aluma Systems Canada Inc. is the applicant for a permit under the Building Code Act, 1992 to erect temporary grandstand structures for the Molson Indy at the Exhibition Grounds, Toronto, Ontario.

  1. Description of Constrution

The subject structure is a modular steel temporary grandstand to be erected on the Exhibition Grounds in the City of Toronto for the viewing of the annual Molson Indy Races. The grandstand is approximately 82.3 m (270 ft) long by 20.9 m (68.7 ft) wide. It has 33 rows of bleachers and seating capacity for 5044 people.

  1. Dispute

The dispute between the Applicant and Respondent concerns the technical interpretation of Article 4.1.1.4., Sentences 4.1.10.5.(1) & 4.1.10.5.(2) of the Building Code. At issue is whether horizontal bracing members are required to resist horizontal live loads for temporary grandstand structures at the Exhibition Grounds, Toronto, Ontario.

  1. Provision of the Building Code

Article 4.1.1.4. Design Basis

1. Buildings and their structural members shall be designed by one of the following methods,

a. standard design procedures and practices provided by this Part and any standards and specifications referred to therein, except in cases of conflict the provisions of the Building Code shall govern; or

b. one of the following three bases of design,

i. analysis based on generally established theory,

ii. evaluation of a given full-scale structure or a prototype by a loading test,

iii. studies of model analogues, provided the design is carried out by a person qualified in the specific method applied and provided the design ensures a level of safety and performance at least equivalent to that provided for or implicit in design carried out by the methods referred to in Clause (a).

2. Communications towers, dish antennas and their supporting structures shall conform to CAN3-S37, "Antennas, Towers, and Antenna Supporting Structures".

Sentences 4.1.10.5.(1) & 4.1.10.5.(2)Resonances and Sway Forces

1. Where the fundamental vibration frequency of a structural system supporting an assembly occupancy used for rhythmic activities, such as dancing, concerts, jumping exercises or gymnastics, is less than 6 Hz, the effects of resonance shall be investigated by means of a dynamic analysis.

2. The floor assembly and other structural elements that support fixed seats in any building used for assembly occupancies to accommodate large numbers of people at one time, such as grandstands, stadia and theatre balconies, shall be designed to resist a horizontal force equal to at least 0.3 kN ( 70 lb) for each metre length of seats acting parallel to each row of seats, and at least 0.15 kN (35 lb) for each metre length of seat acting at right angles to each row of seats, assuming such forces to be acting independently of each other.

  1. Applicant's Position

The applicant submitted that all vertical bays of the grandstand are designed independently to resist the sway and wind loads identified in the Building Code.

The Building Code specifies the vertical and lateral loads for which these grandstand structures must be capable of resisting. Those loads are dead load of the structure, 100 psf vertical live load due to people, horizontal wind load and horizontal sway load.

The vertical legs of the grandstands are braced with vertical diagonal bracing in every bay, eliminating the need to carry load horizontally across a bay.

The grandstand structures will be erected with sufficient vertical bracing in every bay to meet the Building Code. Therefore, the bracing required by the City of Toronto Building Department is not necessary.

  1. Chief Building Officials Position

The respondent submitted that the proposed bleacher/grandstand structure has a natural frequency in the sway mode of 1HZ to 3HZ, therefore the dynamic behaviour of the proposed structure is a factor in its design. Dynamic behaviour is influenced by the stiffness rather than the strength of the structure. The applicant's structural analysis does not address this issue of dynamic behaviour as required in Sentence 4.1.10.5.(1) of the Building Code.

Inadequate horizontal bracing is proposed. This could result in the deterioration of the bleacher/grandstand structure due to the severe forces created through the dynamic sway when people begin to move. Research by Professor Jim Dickie of the University of Manchester found that the sway characteristic of the rear frames deteriorates as the height of the bleachers/grandstand increases.

An alternative to this is to make the frames sufficiently rigid through the use of vertical bracing. This however causes uneven loading in the supporting legs which in turn brings a risk of differential settlement. The settlement problem can be avoided through the use of foundations that have been designed for these forces but due to the temporary nature of the structure the owners of the site may not permit such a large undertaking.

In addition to the question of dynamic behaviour, it was found that the applicant failed to submit with their computer analysis sufficient supporting documentation. The documentation is required to explain the concept/theory behind both the software and modelling used in analysing the frames. This information is required to see if the requirements of Article 4.1.1.4. of the Building Code are met.

  1. Commission Ruling:

In favour of the Applicant. It is the decision of the Building Code Commission that appropriately designed diagonal vertical bracing at every bent in both directions to resist the loads identified in Article 4.1.10.5., complies with the Building Code requirements provided proper foundations are designed as per Part 4.

  1. Reason:

Horizontal bracing is not specifically required by the Building Code as long as the structure is shown to resist the applicable loading by analysis based on generally established theory.

Dated at Toronto, this 28th day, in the month of February, in the year 1995, for application number 1995-03.

Demir Delen

Remus Tsang

Sang Shim