Seismic Respond Spectrum of Horizontal Members

[struggle66]

It is Me again.

Before I ask, please bear with me I have zero knowledge on seismic design

In one of my EC2 project (PT flat slab system), structural consultant told me that I need to do respond spectrum analysis for my slab under seismic dynamic loads as there is no beams (He is using my slab as equivalent beams)for framing & the natural frequency of the building falls below 0.5 (He can't apply the lateral force to the building). Frankly I have no idea what to do.

Anyway I am going to spend a few months for the seismic design. & I am only doing horizontal PT member design.

But at this moment can anyone please guide me where to start & what to check (ductility? Minimum Capacity?) & what to do step by step for the seismic design of horizontal members?

Thanks

 

[Klitor]

I believe you have 2 independent issues here:

1. You need to include vertical component of seismic acceleration (since you have long spans and/or cantilevers)
2. Your lateral force resisting system is flat slab frame (not explicitly covered in eurocode8)

Is this about that cicular building?

 

[struggle66]

Thanks

Klitor

1. How do I include vertical acceleration. Do I have to use a software that can include dynamic seismic vertical load?

2. I think LFRS should be designed by the main structural consultants. I am doing the PT flat slab.
This isnt about circular building.

 

[Klitor]

1. Pretty much any structural fem software can do it. I suggest you first check local code if you even have to do it (generic ec8 asks for it only in zones with a>0.25g)
Ec8 clause 4.3.3.5.2 has the procedure and acc combinations explained

2. In my area,if i was eor i would be responsible for both lfrs+pt. i would push for wall system and try to avoid flat slab frames.
Maybe rapt or someone more experienced can chime in.

 

[rfrazao]

Not sure if this helps but Quaketek builds seismic dampers and they have an explanation on how to model them in ETABS/SAP [URL unfurl="true"]http://www.quaketek.com/seismic-design[/url]. The company specializes in friction dampers not PT flat slab, but the guide might help give you some ideas as to how other seismic protection technologies are modeled.

 

[JoshPlumSE]

Plate analysis and Response Spectra is a bit of a pain and requires some real experience to interpret the results.

The reason for this is because the result of a single plate element doesn't tell you that much on it's own. But, the response spectra solution is geared towards giving good results only for single elements at a time. When you look at the combined results of multiple force or multiple elements together, the results can often be misleading... Unless you have some experience in how to interpret them.

You might take a look at the below "blog topics" that I wrote on the subject:

https://risa.com/news/why-dont-response-spectra-reactions-satisfy-statics-risa3d/

This blog was written about support reactions. But, the same "loss of relative signage" issue affects plate elements. Now, if you have a truly dominant mode and your analysis program allows you to use this for the RSA signage, then you'll be okay. Otherwise, it can be a bit tricky combining results from multiple plates into something you can effectively use for design.