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RE: UBC 97 - SEISMIC DESIGN GRANULAR SILOS

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Stefan,
Given your constraints, treating the silos as nonstructural components per section 1632 should result in a more conservative design.

I just get nervous when I see the UBC zones being used. There were many significant changes in the transition to the IBC. Studies have shown that you can be very far off with base shear calculations when compared to using seismic specral ordinates.

It might be worth a little extra time and see how your design would look if you used the ASCE 7-05. You don't have to tell your client, but it would be an intersting check.

It is worth noting that the Veletsos paper is about the best document that there is on seismic design of silos and bins containing granular material.

Another good document for reference is Tubular Steel Structures by Troitsky. But the Veletsos paper is what should be used for seismic design.

Regards,
Harold Sprague





From: "Stefan Reumers" <Reumers.S(--nospam--at)ellimetal.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: UBC 97 - SEISMIC DESIGN GRANULAR SILOS
Date: Thu, 16 Feb 2006 09:01:44 +0100

Thanks Harold,

The thing about UBC'97 not being the most appropriate code for
calculating silos is exactly what I told our client but he would not
listen. So I am stuck with this code.

The discussion now is wether or not to use section 1632.

However trying to keep the wall-thicknesses of the silos within
realistic limits, I proposed to apply the Veletsos, Younan and
Bandyopadhyay-report (Dynamics of solid-containing tanks, prepared for
the department of energy, Washington, D.C.).
This report allows for a part of the horizontal force to be transferred
to the bottom (in our case the cone-cylinderjunction of the silo)
through intergranular friction.
For those who are interested in this report, it can be downloaded here :
http://www.osti.gov/bridge/purl.cover.jsp?purl=/453784-sUxqbN/webviewabl
e/

This report also formed the base for parts of the new Eurocode 8 Part 4
(Design of structures for earthquake resistance - Silos, tanks and
pipelines).

If any-one has experience with this method of design please let me know.

Kind regards

Stefan Reumers

-----Original Message-----
From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com]
Sent: woensdag 15 februari 2006 20:31
To: seaint(--nospam--at)seaint.org
Subject: RE: UBC 97 - SEISMIC DESIGN GRANULAR SILOS

It sounds like this is an attempt to use importance factors and the 1997
UBC
to achieve a perceived higher performance.  I would suggest that you use
a
more up to date code like the ASCE 7-05 and perform a more sophisticated

analysis.  Conservatism on loads does not necessarily buy you better
performance.

Applicability of the UBC 97 to properly design granular silos is a
reach.
There were some adjustments made in the NEHRP that have been reflected
in
the ASCE 7-05.  I would urge you to look at the ASCE 7-05 section 15.3.1
and
15.3.2 which had granular silos in mind when it was created.  It was in
the
ASCE 7-02 as well.

Further, there has been coordination between nonstructural components
and
nonbuilding structures in the NEHRP / ASCE / IBC process to try to
account
for this as much as possible.  Not much was included in the UBC 97.
This
was in the early days of the nonbuilding structures effort.

I would look at the relative stiffnesses of the aluminum silos and the
concrete support structure.  I would also treat the contained product as

just an impulsive mass.  We have looked at the potential of a convective

component but there is not enough data.

Regards,
Harold Sprague

>
>-----Original Message-----
>From: Stefan Reumers [mailto:Reumers.S(--nospam--at)ellimetal.com]
>Sent: Wednesday, February 15, 2006 6:58 AM
>To: seaint(--nospam--at)seaint.org
>Subject: UBC 97 - SEISMIC DESIGN GRANULAR SILOS
>
>
>
>I have to design 24 aluminium silos 720 m3 each for the storage of
granular
>Polyethyleen.
>
>These silos are mounted on a 20 m high concrete structure.
>
>
>
>Prescribed earthquake code is UBC '97.
>
>
>
>Does Section 1632 apply or can I use Sections 1634 together with
Section
>1630 ?
>
>This makes quite some difference in the total lateral force.
>
>
>
>In addition, our customer asks for an importance factor of 1,50 as to
my
>opinion granular storage silos would only require an importance factor
of
>1,0.
>
>
>
>
>
>Any help would be much appreciated
>
>
>
>
>
>Stefan Reumers
>
>Engineering Silo Dept.
>
>Ellimetal nv
>


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