Forces exerted on NSE’s during Earthquakes

Forces exerted on NSE’s during Earthquake

An NSE in a building experiences two types of challenges during the shaking caused by an earthquake, namely :

1. Inertial force induced by the mass of the NSE which is caused by the acceleration at the base of the structural element on which the NSE is installed.
2. Deformation of the NSE on its support points to the structural element as a result of different movements which the support points undergo. The deformation can be either in the form of ‘displacement’ or ‘rotation’.

 

Inertial failures are failures caused by:

1. Excessive shaking of the component
2. Component rocking due to unanchored or marginally anchored conditions
3. Component sliding due to unanchored conditions

Displacement / Deformation failures are failures caused by:

1. Excessive building inter-story displacements or drift
2. Incompatible stiffness between the building structure and component
3. Interaction between adjacent structural systems and nonstructural systems
4. Multiple structure connection points

Based on the strength of the above forces (Inertial forces and Displacement) experienced by an NSE, they can be classified into Primary effect and Secondary effect. For example, water supply pipelines, air conditioning ducts and electrical cables experience displacement during an earthquake whereas other HVAC equipment experience inertial force.

Force-sensitive NSE’s such as generators and pumps can rock, slide and topple over if not anchored properly to the structural elements. On the other hand, a displacement sensitive NSE such as a water main pipeline can pull, compress and shear during an earthquake.

Interaction between Structural and Non-Structural Elements

The shaking effect of earthquake on lightweight NSE’s does not heavily impact the shaking of the building in most circumstances. However, in the case of heavy NSE’s, the oscillating effect of earthquakes on them does affect the response of the structural elements as well. In such a case, the building response to the earthquake must be modelled considering both NSE’s and SE’s. This can be done by combining the independent dynamic response properties of both these systems.

Evaluation of Earthquake Response of NSE’s

The Earthquake performance of NSE’s may be assessed from:

1. Performance evaluation of NSE’s employed in buildings and structures through post-earthquake investigations.
2. Detailed experimental investigations of NSE’s on shake tables, under different ground motions and performance parameters.
3. Rigorous analytical investigation of NSE’s under earthquake ground motion at the base of the structure or building on which the NSE is housed, based on concepts of structural dynamics and through accurate modelling of interiors of NSEs along with that of the building and its SEs.