Nov. 07, 2022

Multi-tiered bracing systems design

  • Article
  • Multi-tiered bracing systems
  • Seismic design

Steel multi-tiered bracing frames are a configuration of two or more bracing panels that are stacked between the ground and roof levels in tall single-storey buildings. This type of building is currently used in industrial and power plant projects.

  1. Types of bracing

    The lateral load resisting system for these buildings generally consists of steel chevron bracing (diagonal V or inverted V) or X-bracing, similar to the examples shown in Figures 1 and 2.

  2. These types of bracing are used to provide adequate structural behaviour and are suitable for tall, single-storey buildings. For ductile seismic design, it’s more convenient to use shorter bracing lengths to meet slenderness criteria. The design approach by capacity for structural elements may or may not be applied, depending on the criteria for classifying a building’s civil protection level.

    Mining buildings with a limited life cycle could often be considered with a lower civil protection risk level.

    Then how must structural engineers go about deciding which methodology to use for the seismic design of these systems?

  3. Overview of standards

    Multi-tiered bracing systems are not addressed in the CSA-S16-14 standard. In Canada, structural engineers who design these systems rely on scientific papers published by researchers or on American standards to compensate for this lack of requirements.

    The good news is that the new version of the CSA S16 standard, released in 2019, addresses the design of multi-tiered bracing systems, which finally provides structural engineers with better guidance in designing these elements.

    In fact, Clause 27.5.2.6 guides us in the design of multi-tiered bracing. This clause specifies restrictions when designing multi-tiered bracing. It also describes requirements for other structural elements, like the building’s struts and columns.

    For example, according to Clause 27.5.2.6.2, chevron bracing must have out-of-bracing lateral struts at the brace-to-strut connections to stabilize it.

    However, in most industrial buildings, clearance to install the major equipment is required, eliminating the out-of-plane bracing structural element. To address this issue, Clause 27.5.2.6.3 explains how to overcome the lack of such lateral support when designing structural elements, ensuring the system will resist the lateral loads.

    These new clauses indicate that structures can be optimized while remaining safe and cost-effective.

    Do you have design examples to share? Interpretations to confirm? If your work involves industrial building design, and you have constraints to consider when choosing a structural system, we would be happy to talk to you about them.

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