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Code min. Design requirements

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As a result of recent dialogues that I have been involved in on this
list, I think I would like to open a new topic that has been mentioned,
but not specifically dealt with.

What standard of performance do we expect from structures that are
designed and constructed in conformance with the 1997 UBC?

I believe that most of the engineering design community believes that a
building designed and constructed in accordance with current Code only
provides a minimum Life-Safety level of performance.  The Code itself
states the following:

UBC 1626.1 Purpose.  The purpose of the earthquake provisions herein is
primarily to safeguard against major structural failures and loss of
life, not to limit or maintain function.

This section of the 1997 UBC would indicate that the authors of the Code
also believe that a Code complying building will only provide a minimal
life-safety level of performance.  The underlying message is; if your
design and or construction fall short of the standards in the 1997 UBC,
then the life or safety of the persons occupying the building is in
danger.

There is a problem with this view, in that there are standards put out
in recent years for engineers to use in the evaluation of existing
structures.  The process of evaluation of existing structures is
something that the UBC was not intended for.

These documents are FEMA 273 or the NEHRP guidelines and FEMA 310.  

FEMA 310 defines a life-safety level of performance as follows:

Building performance that includes significant damage to both structural
and non-structural components during a design earthquake, though at
least some margin against either partial or total collapse remains. 
Injuries may occur, but the level of risk for life threatening injury
and entrapment is low.

This sounds somewhat familiar to the wording used in the UBC.  

FEMA 273 gets more detailed, and in fact, in my opinion, starts
confusing the issue.  Among other levels of performance, they have the
following levels of performance that pertain to this discussion:

Life Safety: Structure remains stable and has significant reserve
capacity; hazardous nonstructural damage is controlled.

Limited Safety: Extends between life Safety and Collapse prevention.

Collapse prevention: The building remains standing, but only barely; any
other damage or loss is acceptable.

FEMA 273 collapse prevention sounds like the UBC and FEMA 310 Life
Safety definition.

My main problem is this, FEMA 310 states that wood light framed
structures (residential, commercial, and industrial) designed and
constructed in accordance with the 1976 UBC will provide a Life Safety
level of performance.  This includes multi-story wood framed buildings,
as well as building utilizing shear walls constructed with stucco and
drywall.  As we all know, there is a VAST difference in design
requirements between these two Codes.  Yet the 1997 UBC also seems to
state that design to the current Code standards will only provide a life
safety level of performance.

So which is it?  Whom are we to believe.  Both of these documents are
fairly new, and had major updates to them as a result of the 1994
Northridge earthquake.

I guess there are really 3 questions:
1.  What level of performance should the Code require as a bare minimum
for seismic design?
2.  What is the definition of Life Safety we want to use, UBC and FEMA
310, or FEMA 273, (which I believe will be more in line with the new
year 2000 IBC)?
3.  With the definition of Life Safety being very close for the UBC and
FEMA 310, why are they MILES apart on the level of design that is
required for these buildings?

All input is appreciate, as I am struggling to understand all this
myself.

Lynn