Non-structural Engineering:

Seismic Risk Assessment

A non-structural seismic mitigation program consists of such key elements as; seismic risk assessments, component selection, seismic engineering, retrofit cost estimating, installation, quality assurance, and mitigation tracking and documentation.

Non-structural components, or operational and functional components (OFCs), can be divided into three sub-components: Architectural (external and internal), Building services (mechanical, plumbing, electrical, and telecommunication), and Building contents (common and specialized).

There are three primary risks associated with the failure and/or dislocation of OFCs in a building:

Life safety of the occupants, Functionality and performance of the facility, and Property loss.

Even during low to moderate intensity ground shaking, when there is little or no damage to the structure, failure of non-structural components is common. There are numerous methods for quantifying the risk levels of OFCs. The Canadian Standards Association (CSA) released seismic risk assessment guideline known as CSA S832-06 considers soil conditions, seismic zone, aspect ratio, flexibility, building type, quality of existing seismic restraint, pounding potential, business continuity/resumption, and life safety to occupants. The outcome of this assessment, the total risk, is the product of vulnerability and consequences. Once the non-structural components within a building have been listed, they can be tabulated and sorted by risk level. This methodology aids the owner of the facility in prioritizing his/her seismic mitigation efforts.

The principles that have been developed and refined for structural engineering can be utilized in the engineering of non-structural seismic restraints.

In the risk assessment stage a team of specialists (i.e. a structural engineer or a structural technologist trained by a structural engineer) should participate. The parameters that should be considered vary based on different building codes. For instance, in the most recent CSA S832-01 “Canadian Guideline for Seismic Risk Reduction of Operational and Functional Components (OFCs) of a Building” the parameters are divided into two main categories:

1 Vulnerability: The vulnerability of non-structural components can be defined as the probability of failure of the component during an earthquake. A component’s vulnerability depends on the seismic forces and deformation applied to the equipment by the horizontal and vertical movement of the supporting structure or the structural elements. Table 1 provides the CSA S832-01 methodology for estimating a vulnerability rating score for non-structural components based on eight parameters. The last two columns in the table relate to the resultant risk rating for the example that follows the tables

2 Consequences: The consequence of failure of any non-structural component of a building during an earthquake is subject to the impact on life safety, building functionality and property.

Our risk assessment specialists are familiar with other North American Seismic Risk Assessment methodologies such as FEMA and ASCE … etc as well as CSA S832 in Canada.

We also provide training to other engineering companies to develop their own seismic mitigation division.

Seismic Risk Mitigation

Before designing a new restraint, the existing situation of the equipment with respect to the structure (i.e. the existing connection, or if available, restraint) should be analyzed. This requires the investigation of the capability of the existing attachments and restraint elements. Specifically the structural – non-structural interaction. Each attachment should be studied with respect to the potential for uplift and displacement, as well as taking into account: horizontal forces, and the supporting structure’s behaviour. If there is no restraint and/or attachment to the structure, or there are questionable restraints and/or attachments, new restraints should be designed. For this purpose the design engineer must first obtain the horizontal force applied to the equipment during an earthquake. In order to find the horizontal force (i.e. the base shear for structural analysis) the following parameters are required by most of the available codes:

  1. The seismic zone or spectral response acceleration, where the supporting structure is located, and attenuation parameters.
  2. Site Class or the soil type where the structure is built.
  3. The importance of the building.
  4. The non-structural component’s elevation or its position with respect to the structure’s height.
  5. The flexibility of the equipment or existing attachments (i.e. in NBCC 2005 the equipment with natural time period less than 0.06 sec are considered as rigid equipment).
  6. The components response modification factor.
  7. What type of material the equipment contains (i.e. whether it is considered to be a toxic or explosive material).

Our engineers are expert in designing seismic restraint as well as analyzing the existing restraint to design for upgrade.

We also provide training to other engineering companies to develop their own seismic mitigation division.