Seismic Analysis for Mechanical Equipment

[Yoga Arviansyah]

Hi currently, I am in process for designing mechanical components for shiplift and transfer system operation. And, the standard itself (which is code for lifting appliance in a marine environment by LLoyd' Register) state that we should analyze seismic event. What I want to know, is this enough for me only finding base shear forces (from ASCE documents and other data) then analyze it in finite element analysis software (such as ansys) to make sure that the structure is safe? or is there any consideration that I should take on it?

Example of the structure is "trestle" in shiplift

Thank You

 

[JStephen]

In some cases, the ASCE base shears assume plastic deformation in the connections, so certain items will be subject to overstrength requirements. IE, you may need more input that just base shears.

 

[driftLimiter]

First input is based on the site location geographically, and geologically. The site hazard is based on location and soil type.

Next as JStephen mentions, you have accounting for permanent plastic deformation. Building structures, and many components within them are designed for consequential damage during an earthquake as a default by the building code. The minimum level in the code allows for damage so much that a building (or component) may no longer be occupiable or usable after the design level earthquake. The design goal in this minimum standard is to avoid collapse an injury.

The ASCE 7 code expresses this plastic deformation in combination of 3 factors, R, Ωo, Cd. Basically if you want to use ASCE 7 you need to determine appropriate values for your specific structure for each of these factors.

You could look towards a more robust specification such as UFC RC V buildings and MC I level components that are designed to be completely elastic during an earthquake.

Usually for such specialty structures, there are additional specs, codes, technical documents etc that specify seismic design method and values. For example in Electrical Substations IEEE 693, Nuclear ASCE 43. To me I would be looking for one of these because you have a structure that likely is not well represented by ASCE 7.

 

[geesaman.d]

I don't have a direct answer to your question, but I suggest you consider (and declare in your report) whether the expectation is for the machinery to survive the seismic event without a catastrophic failure that doesn't endanger surrounding personnel (aka it doesn't topple over) vs. be suitable for operation immediately following the seismic event.

I know my company produces seismic calcs and the basic premise is we confirm the anchors do not extract or loosen during a seismic event and that nothing fails in a way that would make it fall over or come apart. We don't test or offer anything to say the equipment will be safe for long-term operation as a result of the seismic event.