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Re: structures & ethics

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Fellow engineers,

In Canada we have a component of our codes (Commentary K of the Structural Supplements) which deals with this situation. Two of the topics it deals with are: there is a lower standard of acceptability for strength, use and occupancy loading, etc.; and it waves serviceability considerations on the basis that if it has been in satisfactory service for many years it has proven that it is serviceable. One other stipulation is that if the structure requires upgrade by the standard presented in the commentary the upgrades must meet current code, not the reduced standard.

This seems to me to be similar to what I read into the list discussions on requirements for seismic upgrade. Is there not something in your own codes that might cover this situation? Nels Roselund would seem to be one of the best people on the list to answer this question because of his work with older buildings.

Respectfully submitted,

H. Daryl Richardson


----- Original Message ----- From: "Gautam MANANDHAR" <GMANANDH(--nospam--at)ci.alameda.ca.us>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, November 23, 2004 8:35 PM
Subject: RE: structures & ethics


Dennis:

I agree with you that the code is minimum.  I also agree that providing
a repair that last long is recommended.    However, I believe that one
has to consider economics when you work with an existing building.  If
the client is willing to spend the money, bless is his soul.

So far,the discussion has been related to gravity load; what about
seismic? Or wind?  I am sure few of the exisitng   houses have shear
transfer mechanism we now consider standard (clip angles, collector
straps, etc). In the process of doing what  is in the best interest of
the occupant, do you then recommend tearing up exisiting construction to
install shear walls, holddowns, etc.  - the original scope was to fix
the damage caused by the vehicle.  By all means, repair the damage to
meet current standards.  But I would limit the work to just that unless
the owner wanted more.

Happy thanksgiving.  I will see you guys Monday.

Gautam

dennis.wish(--nospam--at)verizon.net 11/23/2004 6:15:40 PM >>>
Gautam,
Not to argue the point but the original message stated "Some of the
purlins
are visibly sagging. The glulams look OK." This is a deflection problem
that
is a function of bending.
The real question is not just to satisfy your interpretation of the
code to
make your soul feel at rest, but to do what you believe is in the best
interest occupants of the building. As an argument, we can agree that
the
code allows in section 2320 for conventional construction, but few
engineers
would use this provision to design a home when full compliance
engineering
is a better approach.
There is often times when obligation has nothing to do with making
repairs
that are long lasting. We can keep patching but what the client appears
to
want is a fix so why not give them something we feel confident will
last?
Remember, the code is only the minimum requirement - you can do
better.

Dennis

-----Original Message-----
From: Gautam MANANDHAR [mailto:GMANANDH(--nospam--at)ci.alameda.ca.us]
Sent: Tuesday, November 23, 2004 10:12 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: structures & ethics

Dennis:

I agree with you that one cannot neglect the effect of creep.
However, the original post was regarding the overstress and not the
deflection.  I am assuming that except for the vehicular damage, the
building is in good shape.

Section 3403.2 of CBC allows repairs/addition to a existing structure
without requiring the rest of the structure to meet current code
provided the repair/addition does not overload the existing structure.

In Steve's case, replacing the damaged purlin will not add additional
load to the structure.  Therefore, by code, the project
engineer/building owner is not obligated to upgrade the building in
spite of the existing calculated overstress. This makes sense -
otherwise, we would end up upgrading any building we touch -if not for
gravity loads, for seismic loads.

Gautam Manandhar

dennis.wish(--nospam--at)verizon.net 11/22/2004 11:58:33 PM >>>
Gautam,
You disregard 30 years over which creep has an effect on the original
deflection and framing. Not only may a camber have been considered in
the
original design, but wood is not perfect and a framer will most often
install the sub-purlins with the crown side up to accommodate the
weight of
the materials. Furthermore, water damage from roof leaks, drying of
lumber
depending on its location and original moisture content is an
important
consideration.
This is not a steel roof but one based on materials that are fibrous
and
originally a living thing. 30 years later the installation of roofing
materials can make a big different.
I am looking at deflection problems in the overhang of buildings that
are at
least 30 years old and which have been fixed a number of times to
compensate
for the cantilevered deflection. This is not uncommon - especially in
older
condominium (single or dual family units) where the roof was
cantilevered
out five feet or more and has, over the years, deflected to an
unsightly
dimension based on the weight of a tile roof originally calculated to
work.
I almost always try and get the HOA to allow me to cut back the
overhang
even if it is a good selling point. My argument is that it is
unsightly
and
will continue to pose a problem when a layperson assumes it is a
structural
defect.
Dennis

-----Original Message-----
From: Gautam MANANDHAR [mailto:GMANANDH(--nospam--at)ci.alameda.ca.us]
Sent: Monday, November 22, 2004 12:50 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: structures & ethics

Steve:

You mentioned about re-roofing. The live load was defiantly on the
structure when the roof was initially installed.  I am presuming
nothing
happened then; why should anything happen now?  If you feel that
adding
an extra layer of roofing could cause problems gravity wise, you could
instruct the owner to make sure he removes the current layer- although
I
have seen houses with more than one layer of roofing.

You stated:
"My problem is - can we allow the building to stand without
strengthening, even in the "repaired to preexisting" condition, while
knowing that it is not code-compliant?"

My question to you is - where do you draw the line.  What about
seismic
- does the building meet seismic requirements - collectors,
deflection,
hold down, etc.  I would presume not.  Do we limit ourselves to
gravity
design only or also include sesimc.

There are many buildings that do not meet code and , based on
engineering principles as we know it,  should not even be standing up.


Consider a 1930-40 (??) era stick frame building.  The roof rafter
consists of 2x4, 2x6 spanning 14-16 feet; the ridge consists of a 1x
board; the hip beam are nailed to the 1x board; collar ties are
non-existent.   Based on wl^2/8 we use for wood frame design, there is
no way the roof should even be exsiting.  If one argues that the
moment
and deflection in the roof rafter are reduced due to a horizontal kick
at the sill plate level, one would expect to see damage in the plaster
at the sill plate level; you would be hard pressed to find one.
Moreover, the vertical studs have hinges at the top and bottom -
another
no-no per code.  Now, if the owner comes to you to design a new
skylight
that fits in right between the rafters, would you recommend that the
owner replace the roof rafters because there is no way one can justify
the rafter design with the engineering principles we commonly use for
wood design.

I do understand your dilemma - especially considering the fact that
this is litigation loving nation.  However, you my find solace under
section 3403.2 of California Building Code.

Gautam

mailbox(--nospam--at)sgeconsulting.com 11/22/2004 11:32:39 AM >>>
Gautam,

I hope I did not mentioned anywhere that the building is, or was
supposed to, "come tumbling down."  I do not believe in that
happening.

The building survived at least two good-size earthquakes (1971 and
1994), and is not going anywhere any time soon.  After all, the safety
factors in wood design are in the order of 4-to-6, which, obvioulsy,
quite safely covers the noted overstress.

My problem is - can we allow the building to stand without
strengthening, even in the "repaired to preexisting" condition, while
knowing that it is not code-compliant?

Example: based upon my observation, I would assume that the building
had not been re-roofed.   What will happen when the reroofing start?
Probably, nothing.  But at a 12' height, something may happen.  Then
what?

I do not really care what my client would THINK about my degree.  I do
care about what he will be willing to DO about my license in case of
any
problem - no matter how much he wants to save money now.

Along with my professional and personal ethical considerations, this
is
my main concern.

Thanks,

V. Steve Gordin, PhD
Registered Structural Engineer
Irvine CA



----- Original Message ----- From: Gautam MANANDHAR
 To: seaint(--nospam--at)seaint.org
 Sent: Monday, November 22, 2004 10:58 AM
 Subject: Re: structures & ethics


 Steve:

 Since the building has been standing up for the last thirty years in
 spite of the 70-100% overstress for DL +LL and 15%  for DL,  I would
 guess it will stand another 30 years without any problem (you did
not
 say that the members were sagging & assumming no major earthquak
hits
 it).   Either the loading is being overestimated or the strength
 underestimated.

 Even though the code requires a Live Load on the roof members, the
 members  very seldom see that load - that could explain the high
 overstress for DL+LL combinations without any detrimental effects to
the
 building integrity. (Some time ago, there was a discussion in this
forum
 about metal connectors in modern day pre-manufactured wood trusses
that
 failed when subjected to full design dead + live load.)

 The factor of safety probably explains the 15% overstress for DL
 without any detrimental effect.

 If you tell your client that he has to replace the undamaged roof
 framing because your calc shows that they are highly overstressed
and
 should have come tumbling down 30 years long ago, he will wonder if
you
 did earn your PhD the old fashioned way.  I think you should tell
your
 client what you found based on your calc and let him make the
decision.
 You should clarlify the scope of work  in your contract and limited
to
 the new work with the assumption that the existing framing is
adequate
 based on the fact that it is still standing.  After all, gravity is
very
 "unforgiving".

 Gautam


 >>> mailbox(--nospam--at)sgeconsulting.com 11/22/2004 9:40:06 AM >>>
 Good morning.

 I was asked to provide repair plans and specifications for an
existing
 roof damaged by a vehicle (sic).  The problem now became not only
 structural, but ethical, too.

 THE LAYOUT

 The building is apparently a former post office (1970s?), with 5
1/8"x
 24-3/8"glulam beams @26' o.c. cantilevering 16' off brick wall along
one
 side.   Further into the building, the glulams also bear on wood
 columns, and then cantilever and support other glulams spanning
toward
 the opposite brick wall.

 Sawn purlins span about 26' between the glulams at 8-to-9 feet
 on-center, supporting 2x4 @24", some insulation, lots of electrical
 conduits and ducts, plywood diaphragm, and the composition roofing.

 The "fascia" (still 6x12, nominal/typical) purlin of the overhang
was
 apparently hit and broken by the u-turning big rig, with subsequent
 damage (delamination with lateral offset) to one of the
cantilevering
 glulams.

 THE PROBLEM

 I ran the analysis based upon the current codes as well as upon the
 1960s and 1970s codes (UBC).  The analysis shows that the undamaged
 subpurlins, purlins, glulams, and columns are inadequate against
DL+LL
 (70-to-100% overstressed), and even against DL only (with 0.9
factor,
 overstressed 15%).

 For the sawn lumber, I tried even select structural (dense select
 structural) - did not help...

 Some of the purlins are visibly sagging.  The glulams look OK.

 I can just replace the damaged purlin (these are the only ones that
are
 adequate
 due to 50% tributary area) and to repair only the damaged glulam to
the
 "preexisting condition" (I can do it with lag screws etc.).  After
all,
 the building may be OK solely by the fact of it existing like that
for
 about 30 years, right?

 THE QUESTIONS

 If I am right in my assumptions - how that could happen (don't
answer
 that)?

 If I am wrong in my assumptions - what am I missing?

 What should I do within the limitations of common sense, structural
 analysis, and professional ethics?

 Thank you.

 V. Steve Gordin, PhD
 Registered Structural Engineer
 Irvine CA





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