Seismic Calculations for Equipment

Seismic load calculations and analysis for MEP and HVAC equipment, to IBC, ASCE 7, Eurocode 8 or the code that applies to your project. Produced as submittal-ready documentation for equipment approval, by overturning calculation, equipment analysis or the shake-table certification route.

Design codes

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Rooftop air handling unit on spring isolators with a colour-mapped seismic analysis result

Three routes

Three ways widely accepted in the MEP / HVAC industry

Each route proves something different. Which one your project needs depends on what your job specification asks for. One thing none of them changes: certified equipment is not a certified installation. Whichever route qualifies the equipment, its anchorage to the structure is still calculated.

01
Overturning Calculations
Proves
The anchorage transfers seismic loads into the structure — the component stays restrained to it.
Starting point
The component is sturdy and will not collapse.
Outcome
The correct type and number of restraints, and installation drawings where the project requires them.
How it works →
02
Equipment Seismic Analysis
Proves
The component will not dismantle or fail — it remains a single piece. It qualifies the equipment, never its restraint to the building.
Starting point
Your 3D model and job specification, with the project's seismic parameters.
Does not prove
That the equipment is fully functional after the event — or that its anchors will hold.
How it works →
03
Shake Table Testing
Proves
The component is fully functional after a seismic event — as long as it stays restrained to the structure, which takes a restraint and anchorage design of its own.
Typical for
Mission-critical facilities — nuclear plants, data centres, military bases.
Trade-off
A handful of facilities worldwide, high cost and long waiting times. For many projects, equipment seismic analysis is the cost-effective alternative.
How it works →

Overturning Calculations: Seismic calculation per equivalent lateral force procedure

IBC, other international building codes and local codes require seismic design for non-structural components.

The starting assumption is that the component is sturdy and would not collapse. Hence the primary concern is to restrain the component to the structure — anchored rigidly, or resiliently mounted on isolators yet seismically restrained. This minimises movement in the event of an earthquake. The anchorage calculation makes sure of transferring seismic loads to the structural element like a slab floor or ceiling.

First thing is to determine the magnitude of the design loads, then apply it in the worst direction possible. Then assume that it acts on the center of gravity of the component. Thus causing overturning that generates moment forces at the restraint points. Based on the restraint type and their ratings, they create tension and shear stress at the anchors.

The design force F_p acts at the centre of gravity. Its overturning moment M is resisted at the restraint points: the anchors on the uplift side go into tension (T), the opposite side into compression (C), and every anchor takes shear (V).

Selecting the correct type and number of restraints to transfer the seismic forces without failure completes the restraint design. Depending on each project requirement our engineers also produce detailed installation drawings that promote correct installation.

This can be achieved either by anchoring the equipment directly to the structure, or by using vibration isolators and seismic snubbers in combination. Seismically restrained isolators combine the two in a single unit, which makes them cost-effective and easier to install on site.

Equipment Seismic Analysis for certification objective

FEA (Finite Element Analysis) is a well known method to investigate the structural integrity of a component. The primary concern is to satisfy the mechanical strength criteria. With the aim to prove that components or sections of the component will not dismantle or fail, and it will remain as single piece. Even so, the analysis does not replace the anchorage calculation: the equipment still has to be restrained to the structure by design.

Colour-coded seismic analysis of packaged HVAC equipment — Seismic analysis of a packaged plant skid — an Acrefine project. Colours show the analysis result across the frame and the mounted components.

To perform a seismic analysis, having a 3D model is the starting point. The equipment base is crucial, as it is where the snubbers or isolators are attached. One can not perform an analysis without it. The 3D model is the input data, along with project specific seismic parameters. They are essential to determine the seismic forces.

Special analysis software is in action to perform the analysis, once all necessary input data are in place. Acrefine can help you qualify your equipment by analysis. All you have to do is to supply the 3D model, along with your job specification.

Note. The aim of seismic analysis is not to prove that your equipment will be in fully functional state after the seismic event. For this aim, shake table testing is the only method.

Shake Table Testing for maximum safety

In some projects, the component is expected to be fully functional after a seismic event. These are typically mission-critical facilities like nuclear plants, data centres, and military bases. Sometimes qualification based on calculations and analysis is not adequate or acceptable. In these cases practical means come into play like a full-scale shake table testing. Even a unit that passes the test still needs its anchorage designed for the project it is installed in.

Packaged rooftop HVAC unit on seismic restraint mounts on the steel platform of a shake table, with hydraulic actuators at the platform edges — Full-scale shake table test set-up: the unit sits on the platform on its own seismic mounts, and the actuators reproduce the specified earthquake motion.

These tests can be single axis or multi-axes. They simulate various past earthquakes or acceleration criteria set by building codes or project specifications.

There are only a handful of testing facilities around the world, where you can have your equipment tested. The challenges are the high costs and extremely long waiting times. Having said that, if you decide to have your equipment tested, Acrefine here can help you.

We offer consultancy services for shake table testing.

Industrial member

As an industrial member of SPONSE (the International Association for the Seismic Performance of Non-Structural Elements), we have close relations with testing facilities in Europe.

Questions

Before you ask for a quotation

Do I need Seismic Calculations?

Review your job specification carefully. If the project is in a seismic region, then most likely the answer is yes. If your project also involves distributed services — ductwork, pipework, cable trays — see our seismic bracing design service.

How much do Seismic Calculations cost?

It depends on how much equipment there is in your project, and on the extent of its building services. Some equipment and suspended items may be exempt, depending on the building code you must comply with.

In many cases, a seismic design pays off greatly over time. You would not want to risk your building, not to mention life safety. Contact us for a quotation.

Our products

Seismic Restraint

The restraints and snubbers our calculations specify — standard ranges through our online store Fixing Smith, heavy-duty units directly from us.

Describe the equipment and where it will be installed.

We will tell you which route your project needs — and if none of them does, we will tell you so.