Structural Engineering: 2008-06-01

Saturday, June 7, 2008

RE: Story Drift - Cracked or Uncracked Section Properties

Depends on what you are after. If you are doing some sort of analysis where
the relative stiffness is important, then it will not matter. If you after
an actual deflection/drift, then it will DEFINITELY matter. In the
situation that you describe, I would agree that the 1.43 value should be
included.

Regards,

Scott
Adrian, MI

-----Original Message-----
From: William Haynes [mailto:gtg740p@gmail.com]
Sent: Friday, June 06, 2008 9:29 PM
To: seaint@seaint.org
Subject: Re: Story Drift - Cracked or Uncracked Section Properties

Yes, the 10.11.1 section values is what I was referring to (lets just assume
we are using these instead of a more detailed analysis method for what I am
about to type). I had someone argue with me before that you should use the
10.11.1 values even for a serviceability drift check for wind. His argument
was that once the members reach this extent of cracking (guideline 10.11.1
factors) under design lateral loads, the building still needs to be
serviceable from this point onward (he disregards the 1.43 increase in the
commentary). But my thought was that a design wind or seismic event happens
once in the lifetime of the structure and some repair is expected after this
event. Therefore, applying the 10.11.1 values is not justified for a typical
occupant discomfort evaluation and the 1.43 increase is justified. What do
you think Scott?

On Fri, Jun 6, 2008 at 8:26 PM, Scott Maxwell <smaxwell@umich.edu> wrote:
> If you mean the approximations for Icr that are given in section
> 10.11.1, then strictly speaking, those are purely use INSTEAD of doing
> a full second-order analysis to determine the effects of "moment
> magnification" (i.e. second order effects). They are meant to
> represent a cracked section at close to failure and have some even
> MORE conservative "fudge" in them.
>
> In reality, many engineers commonly use these values, but they can
> result in an overestimation of the second order deflections...which is
> probably where the 1.43 factor came into play by someone. By default,
> the values in ACI 318 section 10.11.1 are .875 of those in the
> reference document that is the basis for that section.
>
> Point is that this is a commonly accepted way...but it is not strickly
> speaking what those values are for in the code.
>
> Regards,
>
> Scott
> Adrian, MI
>
> -----Original Message-----
> From: William Haynes [mailto:gtg740p@gmail.com]
> Sent: Friday, June 06, 2008 7:42 PM
> To: seaint@seaint.org
> Subject: Re: Story Drift - Cracked or Uncracked Section Properties
>
>
> For the question on when to use cracked vs non-cracked:
>
> If I remember correctly, you can multiply the cracked section factors
> given in ACI by 1.43 when checking service level drift. I don't
> believe you are able to assume the moment frame sections are
> completely uncracked in any case.
>
> WH
>
> On Fri, Jun 6, 2008 at 5:06 PM, Scott Maxwell <smaxwell@umich.edu>
> wrote:
>> Cd is purely the "switch" from an elastic deformation to an assumed
>> inelastic (I say assumed as it is an approprimation...not an exact
>> analysis). When you do you elastic analysis, you should be using
>> cracked section properties.
>>
>> Regards,
>>
>> Scott
>> Adrian, MI
>>
>> -----Original Message-----
>> From: Paul Blomberg [mailto:paul.blomberg@gmail.com]
>> Sent: Friday, June 06, 2008 4:25 PM
>> To: seaint
>> Subject: Story Drift - Cracked or Uncracked Section Properties
>>
>> We are checking some concrete moment frame calcs and debating
>> internally about using the cracked or uncracked concrete section
>> properties for the structural analysis. There is some discussion
>> that Cd (deflection amplification factor) incorporates the loss of
>> stiffness as the concrete cracks while most believe that Cd increases
>> the elastic deflections (using cracked section properties) to to
>> account for inelastic behavior and that the elastic deflection is
>> based on a cracked section. The code is a mix of a north African
>> national code with incorporation of ACI 318-05 and ASCE 7-05 just for
>> fun.
>>
>> So on this fine Friday, anyone want to chime in on this debate. When
>> do you use the uncracked section properties of concrete versus the
>> cracked section properties?
>>
>> Paul.
>>
>
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RE: Tornado Alley construction

Ya...I figured...but then you must have glanced over this part (note my emphasis on part):

"...that or they just happen to drive past the home on the way home if they are like me and don't drink!"

Thus, I won't be stumbling to some random house and passing out anytime soon...at least not do to drinking things of the alcoholic persuasion...might for other reasons. <grin>

BTW, there was supposedly an F1 tornado spotted within about 30 miles of me. Haven't seen confirmation reports, but they did have some reports on the news.

Regards,

Scott

Adrian, MI

-----Original Message-----
From: Jnapd@aol.com [mailto:Jnapd@aol.com]
Sent: Friday, June 06, 2008 10:30 PM
To: seaint@seaint.org
Subject: Re: Tornado Alley construction

stumble to that home on the way back to his/her home in a drunken stuper only to pass out in the front yard of that home being built

I was referring to your self guided trip home by way of the local libations dispenser.

Joe Venuti
Johnson & Nielsen Associates
Palm Springs, CA

Get trade secrets for amazing burgers. Watch "Cooking with Tyler Florence" on AOL Food.

Friday, June 6, 2008

Re: Tornado Alley construction

stumble to that home on the way back to his/her home in a drunken stuper only to pass out in the front yard of that home being built

I was referring to your self guided trip home by way of the local libations dispenser.

Joe Venuti
Johnson & Nielsen Associates
Palm Springs, CA

Get trade secrets for amazing burgers. Watch "Cooking with Tyler Florence" on AOL Food.

Re: Story Drift - Cracked or Uncracked Section Properties

Yes, the 10.11.1 section values is what I was referring to (lets just
assume we are using these instead of a more detailed analysis method
for what I am about to type). I had someone argue with me before that
you should use the 10.11.1 values even for a serviceability drift
check for wind. His argument was that once the members reach this
extent of cracking (guideline 10.11.1 factors) under design lateral
loads, the building still needs to be serviceable from this point
onward (he disregards the 1.43 increase in the commentary). But my
thought was that a design wind or seismic event happens once in the
lifetime of the structure and some repair is expected after this
event. Therefore, applying the 10.11.1 values is not justified for a
typical occupant discomfort evaluation and the 1.43 increase is
justified. What do you think Scott?

On Fri, Jun 6, 2008 at 8:26 PM, Scott Maxwell <smaxwell@umich.edu> wrote:
> If you mean the approximations for Icr that are given in section 10.11.1,
> then strictly speaking, those are purely use INSTEAD of doing a full
> second-order analysis to determine the effects of "moment magnification"
> (i.e. second order effects). They are meant to represent a cracked section
> at close to failure and have some even MORE conservative "fudge" in them.
>
> In reality, many engineers commonly use these values, but they can result in
> an overestimation of the second order deflections...which is probably where
> the 1.43 factor came into play by someone. By default, the values in ACI
> 318 section 10.11.1 are .875 of those in the reference document that is the
> basis for that section.
>
> Point is that this is a commonly accepted way...but it is not strickly
> speaking what those values are for in the code.
>
> Regards,
>
> Scott
> Adrian, MI
>
> -----Original Message-----
> From: William Haynes [mailto:gtg740p@gmail.com]
> Sent: Friday, June 06, 2008 7:42 PM
> To: seaint@seaint.org
> Subject: Re: Story Drift - Cracked or Uncracked Section Properties
>
>
> For the question on when to use cracked vs non-cracked:
>
> If I remember correctly, you can multiply the cracked section factors given
> in ACI by 1.43 when checking service level drift. I don't believe you are
> able to assume the moment frame sections are completely uncracked in any
> case.
>
> WH
>
> On Fri, Jun 6, 2008 at 5:06 PM, Scott Maxwell <smaxwell@umich.edu> wrote:
>> Cd is purely the "switch" from an elastic deformation to an assumed
>> inelastic (I say assumed as it is an approprimation...not an exact
>> analysis). When you do you elastic analysis, you should be using
>> cracked section properties.
>>
>> Regards,
>>
>> Scott
>> Adrian, MI
>>
>> -----Original Message-----
>> From: Paul Blomberg [mailto:paul.blomberg@gmail.com]
>> Sent: Friday, June 06, 2008 4:25 PM
>> To: seaint
>> Subject: Story Drift - Cracked or Uncracked Section Properties
>>
>> We are checking some concrete moment frame calcs and debating
>> internally about using the cracked or uncracked concrete section
>> properties for the structural analysis. There is some discussion that
>> Cd (deflection amplification factor) incorporates the loss of
>> stiffness as the concrete cracks while most believe that Cd increases
>> the elastic deflections (using cracked section properties) to to
>> account for inelastic behavior and that the elastic deflection is
>> based on a cracked section. The code is a mix of a north African
>> national code with incorporation of ACI 318-05 and ASCE 7-05 just for
>> fun.
>>
>> So on this fine Friday, anyone want to chime in on this debate. When
>> do you use the uncracked section properties of concrete versus the
>> cracked section properties?
>>
>> Paul.
>>
>
> ******* ****** ******* ******** ******* ******* ******* ***
> * Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> * This email was sent to you via Structural Engineers
> * Association of Southern California (SEAOSC) server. To
> * subscribe (no fee) or UnSubscribe, please go to:
> *
> *

******* ****** ****** ****** ******* ****** ****** ********

RE: Tornado Alley construction

It is a little gusty around here today! And we are under a tornado watch right now (I am watching but I don't see nothin'!). Looks like Ft. Wayne, IN might be getting hit...there is a LOT of red there. Nothing in my area yet...but we could sure use some rain.

On the plus side, my A/C is now installed in the bedroom (but not the office yet)...so I can get a wee bit more comfortable there.

Regards,

Scott

Adrian, MI

-----Original Message-----
From: Jnapd@aol.com [mailto:Jnapd@aol.com]
Sent: Friday, June 06, 2008 5:54 PM
To: seaint@seaint.org
Subject: Re: Tornado Alley construction

Scott

I hope you make home safely tonight..........

Joe Venuti
Johnson & Nielsen Associates
Palm Springs, CA

Get trade secrets for amazing burgers. Watch "Cooking with Tyler Florence" on AOL Food.

RE: Story Drift - Cracked or Uncracked Section Properties

If you mean the approximations for Icr that are given in section 10.11.1,
then strictly speaking, those are purely use INSTEAD of doing a full
second-order analysis to determine the effects of "moment magnification"
(i.e. second order effects). They are meant to represent a cracked section
at close to failure and have some even MORE conservative "fudge" in them.

In reality, many engineers commonly use these values, but they can result in
an overestimation of the second order deflections...which is probably where
the 1.43 factor came into play by someone. By default, the values in ACI
318 section 10.11.1 are .875 of those in the reference document that is the
basis for that section.

Point is that this is a commonly accepted way...but it is not strickly
speaking what those values are for in the code.

Regards,

Scott
Adrian, MI

-----Original Message-----
From: William Haynes [mailto:gtg740p@gmail.com]
Sent: Friday, June 06, 2008 7:42 PM
To: seaint@seaint.org
Subject: Re: Story Drift - Cracked or Uncracked Section Properties

For the question on when to use cracked vs non-cracked:

If I remember correctly, you can multiply the cracked section factors given
in ACI by 1.43 when checking service level drift. I don't believe you are
able to assume the moment frame sections are completely uncracked in any
case.

On Fri, Jun 6, 2008 at 5:06 PM, Scott Maxwell <smaxwell@umich.edu> wrote:
> Cd is purely the "switch" from an elastic deformation to an assumed
> inelastic (I say assumed as it is an approprimation...not an exact
> analysis). When you do you elastic analysis, you should be using
> cracked section properties.
>
> Regards,
>
> Scott
> Adrian, MI
>
> -----Original Message-----
> From: Paul Blomberg [mailto:paul.blomberg@gmail.com]
> Sent: Friday, June 06, 2008 4:25 PM
> To: seaint
> Subject: Story Drift - Cracked or Uncracked Section Properties
>
> We are checking some concrete moment frame calcs and debating
> internally about using the cracked or uncracked concrete section
> properties for the structural analysis. There is some discussion that
> Cd (deflection amplification factor) incorporates the loss of
> stiffness as the concrete cracks while most believe that Cd increases
> the elastic deflections (using cracked section properties) to to
> account for inelastic behavior and that the elastic deflection is
> based on a cracked section. The code is a mix of a north African
> national code with incorporation of ACI 318-05 and ASCE 7-05 just for
> fun.
>
> So on this fine Friday, anyone want to chime in on this debate. When
> do you use the uncracked section properties of concrete versus the
> cracked section properties?
>
> Paul.
>

******* ****** ****** ****** ******* ****** ****** ********

RE: 2006 IBC partition loads

Per item 2 of section 12.7.2 (Effective Seismic Weight) of ASCE 7-05:

"Where provisions for partitions is required by Section 4.2.2 in the floor load design, the actual partition weight or a minimum weight of 10 psf of floor area, whichever is greater."

Regards,

Scott

Adrian, MI

-----Original Message-----
From: Jordan Denio [mailto:jordan@AshleyVance.com]
Sent: Friday, June 06, 2008 5:25 PM
To: seaint@seaint.org
Subject: 2006 IBC partition loads

List,

The 2006 IBC considers the partition load a live load (1607.5). The UBC treated partition loads as a dead load (1606.2). Is the code implying that the 15 psf blanket partition load does not need to be considered in the seismic weight?

Jordan Denio

Re: Story Drift - Cracked or Uncracked Section Properties

For the question on when to use cracked vs non-cracked:

If I remember correctly, you can multiply the cracked section factors
given in ACI by 1.43 when checking service level drift. I don't
believe you are able to assume the moment frame sections are
completely uncracked in any case.

On Fri, Jun 6, 2008 at 5:06 PM, Scott Maxwell <smaxwell@umich.edu> wrote:
> Cd is purely the "switch" from an elastic deformation to an assumed
> inelastic (I say assumed as it is an approprimation...not an exact
> analysis). When you do you elastic analysis, you should be using cracked
> section properties.
>
> Regards,
>
> Scott
> Adrian, MI
>
> -----Original Message-----
> From: Paul Blomberg [mailto:paul.blomberg@gmail.com]
> Sent: Friday, June 06, 2008 4:25 PM
> To: seaint
> Subject: Story Drift - Cracked or Uncracked Section Properties
>
> We are checking some concrete moment frame calcs and debating internally
> about using the cracked or uncracked concrete section properties for the
> structural analysis. There is some discussion that Cd (deflection
> amplification factor) incorporates the loss of stiffness as the concrete
> cracks while most believe that Cd increases the elastic deflections (using
> cracked section properties) to to account for inelastic behavior and that
> the elastic deflection is based on a cracked section. The code is a mix of
> a north African national code with incorporation of ACI 318-05 and ASCE 7-05
> just for fun.
>
> So on this fine Friday, anyone want to chime in on this debate. When do you
> use the uncracked section properties of concrete versus the cracked section
> properties?
>
> Paul.
>

******* ****** ****** ****** ******* ****** ****** ********

Re: 2006 IBC partition loads

The section specifying the 10 psf Partition DL for seismic is ASCE 12.7.2.2

In a message dated 6/6/2008 2:39:07 P.M. Pacific Daylight Time, gmse4603@gmail.com writes:

No, it's listed as 10 psf for seismic dead load (just like before) in another part of the code.

-gm

On Fri, Jun 6, 2008 at 2:25 PM, Jordan Denio <jordan@ashleyvance.com> wrote:

List,

The 2006 IBC considers the partition load a live load (1607.5). The UBC treated partition loads as a dead load (1606.2). Is the code implying that the 15 psf blanket partition load does not need to be considered in the seismic weight?

Jordan Denio

Get trade secrets for amazing burgers. Watch "Cooking with Tyler Florence" on AOL Food.

Re: Tornado Alley construction

Scott

I hope you make home safely tonight..........

Joe Venuti
Johnson & Nielsen Associates
Palm Springs, CA

Get trade secrets for amazing burgers. Watch "Cooking with Tyler Florence" on AOL Food.

Re: 2006 IBC partition loads

No, it's listed as 10 psf for seismic dead load (just like before) in another part of the code.

-gm

On Fri, Jun 6, 2008 at 2:25 PM, Jordan Denio <jordan@ashleyvance.com> wrote:

List,

The 2006 IBC considers the partition load a live load (1607.5). The UBC treated partition loads as a dead load (1606.2). Is the code implying that the 15 psf blanket partition load does not need to be considered in the seismic weight?

Jordan Denio

RE: Tornado Alley construction

If you are NOT in a hurricane region or serious seismic region (i.e. West Coast), it is NOT basic stuff...not matter how much you or I think that maybe it should be. Granted, anchor bolts (code minimum, which is something like 5/8" diameter at 4 or 6 ft on center) is basic stuff to some degree. But, "hurricane" straps and hold-downs for shearwalls are DEFINITELY not in most of the country. You would be suprised at some of the nasty looks you can get when you start including hold-downs because you had the NERVE to do a lateral analysis which then showed overturning on shearwalls. Keep in mind that in many parts of the country, the only way an engineer might get any where close to a resisdential home being built is he/she is drunk from tasting some fine beers at the local pub on a Friday afternoon after a hard day of dealing with contractors <grin> and had his/her keys taken away and managed to stumble to that home on the way back to his/her home in a drunken stuper only to pass out in the front yard of that home being built...that or they just happen to drive past the home on the way home if they are like me and don't drink! <grin>

Regards,

Scott

Adrian, MI

-----Original Message-----
From: David Topete [mailto:d.topete73@gmail.com]
Sent: Friday, June 06, 2008 5:15 PM
To: seaint@seaint.org
Subject: Re: Tornado Alley construction

i don't disagree with you, Scott. i think the shocking part of the article is that there are some builders that are including straps and J-bolts (embedded 6"-8") into footings, which is not necessarily mandated by the local bldg. code... That stuff seems so basic... Cro-Magnon even knew that(!)....

On Fri, Jun 6, 2008 at 2:06 PM, Scott Maxwell <smaxwell@umich.edu> wrote:

That article kind of glances over the fact that it was an F1 tornado (a baby tornado on the Fujita Scale)...talking wind speeds that are 73 to 112 mph. Now, I am not saying that I would want to be sitting there gawking at it as it headed for me, but in the grand scheme of things it ain't bad at all. Add to that the fact that according to the article it never got closer than 3/4 of mile to "well built houses". Thus, while the straps and anchor bolts (assuming installed properly and such) are a very good thing and I am certainly not suggesting that they are a bad I did, I would argue in the case outlined in the article it is a rather decent stretch to believe that they were the reason why there was no damage...the more likely reason was at the location of those homes, the winds speeds likely did not even get past the standard wind design speed for most of the country (90 mph) as dictated by code.

What the article neglects to mention is that _IF_ you are in the path of a serious tornado (say F3 or higher), there is likely not much one can do to prevent your home from being majorly trashed without doing MAJOR overdesign (i.e. forget wood...we are talking CMU or R/C with a significant amount of reinforcing...and even then there are situations where projectiles in very substantial tornados can still penetrate unreinforced CMU or concrete sections...take a look at the description of an F5 on this page: http://www.tornadoproject.com/fscale/fscale.htm ...note the part that says: "steel reinforced concrete structures badly damaged.") relative to current codes. The current codes in the US don't come any where near designing homes to with stand direct hits of a tornado...and it is not just because tornado alley jurisdictions may not require straps or such. The reality is that if an F3 or greater directly hits your home, all the straps in the world will likely not save it...they might mitigate the damage...it is debateable if they will mitigate the damage enough that the home would be savagable...but then strictly speaking, traditionally codes are not about the financial health or repairability of the structure but rather does the structure survive long enough and well enough so that your tushie is largely unharmed in any significant way.

I will say it again...I am not saying that straps and such are NOT a good idea...they are. But, they should not give someone the false sense of security that if an F3 or greater tornado (maybe even a F2) that directly hits their house that their house will be unscathed or even minimally damaged...if you have a direct hit of an F3 or greater, your house is most likely toast, with or without straps.

Regards,

Scott

Adrian, MI

-----Original Message-----
From: David Topete [mailto:d.topete73@gmail.com]

Sent: Friday, June 06, 2008 3:00 PM
To: SEAINT
Subject: Tornado Alley construction

http://www.journalrecord.com/article.cfm?recid=89512

It's amazing what uplift straps and sill bolts can do to prevent a house from flying away... Granted, I'm out here in eqk country so tornadoes (or hurricanes) are not readily designed for. But, with all the damage from tornadoes each year, especially through "Tornado Alley," wouldn't most building departments want to scrap the IRC and its prescriptive methods (if that is the code in effect) in favor of anchor bolts and roof straps???

--
David Topete, SE

--
David Topete, SE

Re: BIM

When I first went to REVIT training a few years back, this was my initial scary thought too - will take for ever to do all the nuts and bolts. But the transition is happening in a gradual manner. Structural engineers have been working on 3-D models for several years and it is a piece of cake for us but it is a different story for the Architects who normally sketch it (squiggly lines) - now they need to draw every component as though they are building it.

The best way to start is to have just the building schematics developed in REVIT - basic model. From here you can cut floor plan and elevations. Details can still be in AutoCAD.

I hope I answered your questions.

Ashwin Ranga Swamy, P.E.
Los Angeles, California

From: Dave Adams

Sent: Thursday, June 05, 2008 7:06 AM

To: seaint@seaint.org

Subject: RE: BIM

Does it make much sense for simple, one- or two-story buildings?

Dave K. Adams, S.E., P.Eng.

Lane Engineers, Inc.

Tulare, CA

Web: www.training4engineers.com

From: Jim Getaz [mailto:jgetaz@shockeyprecast.com]
Sent: Thursday, June 05, 2008 5:22 AM
To: seaint@seaint.org
Subject: Re: BIM

Casey,

We've done about eight projects with Tekla.

Gerard is correct in that it may take a while to develop templates for drawings that show everything you want as the engineer and everything the GC (architect, subcontractors, other designers) wants to see, too.

Our experience is that it is a much more difficult move than from the drafting board to AutoCAD, so I'd like to know what Ashwin and Jacobs are doing right that we're not. It may be partly that we are trying to produce erection drawings and fabrication drawings from the model and each presents its own challenges. Further, when the model has all the concrete reinforcing and connection information, it is huge. The good thing is that it is a concurrent multi-user system. Many people can be working on the same model at the same time, and when it saves, it flags conflicts in their changes. It is a very powerful program – you probably all know how that works: it makes it so the team can do anything, but it is hard to learn how to do everything because there's so much to learn.

HTH,

Jim Getaz

Precast Concrete Engineer

2006 IBC partition loads

List,

The 2006 IBC considers the partition load a live load (1607.5). The UBC treated partition loads as a dead load (1606.2). Is the code implying that the 15 psf blanket partition load does not need to be considered in the seismic weight?

Jordan Denio

Re: Tornado Alley construction

i don't disagree with you, Scott. i think the shocking part of the article is that there are some builders that are including straps and J-bolts (embedded 6"-8") into footings, which is not necessarily mandated by the local bldg. code... That stuff seems so basic... Cro-Magnon even knew that(!)....

On Fri, Jun 6, 2008 at 2:06 PM, Scott Maxwell <smaxwell@umich.edu> wrote:

That article kind of glances over the fact that it was an F1 tornado (a baby tornado on the Fujita Scale)...talking wind speeds that are 73 to 112 mph. Now, I am not saying that I would want to be sitting there gawking at it as it headed for me, but in the grand scheme of things it ain't bad at all. Add to that the fact that according to the article it never got closer than 3/4 of mile to "well built houses". Thus, while the straps and anchor bolts (assuming installed properly and such) are a very good thing and I am certainly not suggesting that they are a bad I did, I would argue in the case outlined in the article it is a rather decent stretch to believe that they were the reason why there was no damage...the more likely reason was at the location of those homes, the winds speeds likely did not even get past the standard wind design speed for most of the country (90 mph) as dictated by code.

What the article neglects to mention is that _IF_ you are in the path of a serious tornado (say F3 or higher), there is likely not much one can do to prevent your home from being majorly trashed without doing MAJOR overdesign (i.e. forget wood...we are talking CMU or R/C with a significant amount of reinforcing...and even then there are situations where projectiles in very substantial tornados can still penetrate unreinforced CMU or concrete sections...take a look at the description of an F5 on this page: http://www.tornadoproject.com/fscale/fscale.htm ...note the part that says: "steel reinforced concrete structures badly damaged.") relative to current codes. The current codes in the US don't come any where near designing homes to with stand direct hits of a tornado...and it is not just because tornado alley jurisdictions may not require straps or such. The reality is that if an F3 or greater directly hits your home, all the straps in the world will likely not save it...they might mitigate the damage...it is debateable if they will mitigate the damage enough that the home would be savagable...but then strictly speaking, traditionally codes are not about the financial health or repairability of the structure but rather does the structure survive long enough and well enough so that your tushie is largely unharmed in any significant way.

I will say it again...I am not saying that straps and such are NOT a good idea...they are. But, they should not give someone the false sense of security that if an F3 or greater tornado (maybe even a F2) that directly hits their house that their house will be unscathed or even minimally damaged...if you have a direct hit of an F3 or greater, your house is most likely toast, with or without straps.

Regards,

Scott

Adrian, MI

-----Original Message-----
From: David Topete [mailto:d.topete73@gmail.com]

Sent: Friday, June 06, 2008 3:00 PM
To: SEAINT
Subject: Tornado Alley construction

http://www.journalrecord.com/article.cfm?recid=89512

It's amazing what uplift straps and sill bolts can do to prevent a house from flying away... Granted, I'm out here in eqk country so tornadoes (or hurricanes) are not readily designed for. But, with all the damage from tornadoes each year, especially through "Tornado Alley," wouldn't most building departments want to scrap the IRC and its prescriptive methods (if that is the code in effect) in favor of anchor bolts and roof straps???

--
David Topete, SE

--
David Topete, SE

RE: Story Drift - Cracked or Uncracked Section Properties

Cd is purely the "switch" from an elastic deformation to an assumed inelastic (I say assumed as it is an approprimation...not an exact analysis). When you do you elastic analysis, you should be using cracked section properties.

Regards,

Scott

Adrian, MI

-----Original Message-----
From: Paul Blomberg [mailto:paul.blomberg@gmail.com]
Sent: Friday, June 06, 2008 4:25 PM
To: seaint
Subject: Story Drift - Cracked or Uncracked Section Properties

We are checking some concrete moment frame calcs and debating internally about using the cracked or uncracked concrete section properties for the structural analysis. There is some discussion that Cd (deflection amplification factor) incorporates the loss of stiffness as the concrete cracks while most believe that Cd increases the elastic deflections (using cracked section properties) to to account for inelastic behavior and that the elastic deflection is based on a cracked section. The code is a mix of a north African national code with incorporation of ACI 318-05 and ASCE 7-05 just for fun.

So on this fine Friday, anyone want to chime in on this debate. When do you use the uncracked section properties of concrete versus the cracked section properties?

Paul.

RE: Tornado Alley construction

That article kind of glances over the fact that it was an F1 tornado (a baby tornado on the Fujita Scale)...talking wind speeds that are 73 to 112 mph. Now, I am not saying that I would want to be sitting there gawking at it as it headed for me, but in the grand scheme of things it ain't bad at all. Add to that the fact that according to the article it never got closer than 3/4 of mile to "well built houses". Thus, while the straps and anchor bolts (assuming installed properly and such) are a very good thing and I am certainly not suggesting that they are a bad I did, I would argue in the case outlined in the article it is a rather decent stretch to believe that they were the reason why there was no damage...the more likely reason was at the location of those homes, the winds speeds likely did not even get past the standard wind design speed for most of the country (90 mph) as dictated by code.

What the article neglects to mention is that _IF_ you are in the path of a serious tornado (say F3 or higher), there is likely not much one can do to prevent your home from being majorly trashed without doing MAJOR overdesign (i.e. forget wood...we are talking CMU or R/C with a significant amount of reinforcing...and even then there are situations where projectiles in very substantial tornados can still penetrate unreinforced CMU or concrete sections...take a look at the description of an F5 on this page: http://www.tornadoproject.com/fscale/fscale.htm ...note the part that says: "steel reinforced concrete structures badly damaged.") relative to current codes. The current codes in the US don't come any where near designing homes to with stand direct hits of a tornado...and it is not just because tornado alley jurisdictions may not require straps or such. The reality is that if an F3 or greater directly hits your home, all the straps in the world will likely not save it...they might mitigate the damage...it is debateable if they will mitigate the damage enough that the home would be savagable...but then strictly speaking, traditionally codes are not about the financial health or repairability of the structure but rather does the structure survive long enough and well enough so that your tushie is largely unharmed in any significant way.

I will say it again...I am not saying that straps and such are NOT a good idea...they are. But, they should not give someone the false sense of security that if an F3 or greater tornado (maybe even a F2) that directly hits their house that their house will be unscathed or even minimally damaged...if you have a direct hit of an F3 or greater, your house is most likely toast, with or without straps.

Regards,

Scott

Adrian, MI

-----Original Message-----
From: David Topete [mailto:d.topete73@gmail.com]
Sent: Friday, June 06, 2008 3:00 PM
To: SEAINT
Subject: Tornado Alley construction

http://www.journalrecord.com/article.cfm?recid=89512

It's amazing what uplift straps and sill bolts can do to prevent a house from flying away... Granted, I'm out here in eqk country so tornadoes (or hurricanes) are not readily designed for. But, with all the damage from tornadoes each year, especially through "Tornado Alley," wouldn't most building departments want to scrap the IRC and its prescriptive methods (if that is the code in effect) in favor of anchor bolts and roof straps???

--
David Topete, SE

Re: Tornado Alley construction

Point taken. I wonder if companies like Simpson "or equal" :-) have presentations in such areas... It's baffling...

On Fri, Jun 6, 2008 at 1:19 PM, Dave Adams <davea@laneengineers.com> wrote:

David,

The use of the IRC is limited to regions not exceeding 110 mph … anything beyond that you have to use the IBC. However, a general lack of enforcement & inspection in many regions of the U.S. happens irrespective of the code being used. The IRC is a good starting point because there are many regions where it works quite well. Besides that, the IRC specifically states that if roof elements experience an uplift pressure of 20psf or greater (using the "components and cladding" table provided in Chapter 3), the designer MUST provide straps, etc. to complete an uplift load path to the foundation (an "engineered condition", which may be mixed with an otherwise "prescriptive" residence). The State of Florida also adopted it as a model document for residential design and added their own modifications as they needed. Been that way for a long time.

Regards,

Dave K. Adams, S.E., P.Eng.

Lane Engineers, Inc.

Tulare, CA

www.training4engineers.com

From: David Topete [mailto:d.topete73@gmail.com]
Sent: Friday, June 06, 2008 12:00 PM
To: SEAINT
Subject: Tornado Alley construction

http://www.journalrecord.com/article.cfm?recid=89512

It's amazing what uplift straps and sill bolts can do to prevent a house from flying away... Granted, I'm out here in eqk country so tornadoes (or hurricanes) are not readily designed for. But, with all the damage from tornadoes each year, especially through "Tornado Alley," wouldn't most building departments want to scrap the IRC and its prescriptive methods (if that is the code in effect) in favor of anchor bolts and roof straps???

--
David Topete, SE

--
David Topete, SE

Re: Story Drift - Cracked or Uncracked Section Properties

Yep, cracked section properties, then amplify the drifts.

-gm

On Fri, Jun 6, 2008 at 1:32 PM, <Tom.Hunt@fluor.com> wrote:

Paul,

I believe you have to use cracked section properties in accordance with ACI 318-05 Sections 10.10 and 10.11.

Thomas Hunt, S.E.
Fluor

"Paul Blomberg" <paul.blomberg@gmail.com>
06/06/2008 01:24 PM
Please respond to seaint

To
seaint <seaint@seaint.org>

cc

Subject
Story Drift - Cracked or Uncracked Section Properties

We are checking some concrete moment frame calcs and debating internally about using the cracked or uncracked concrete section properties for the structural analysis. There is some discussion that Cd (deflection amplification factor) incorporates the loss of stiffness as the concrete cracks while most believe that Cd increases the elastic deflections (using cracked section properties) to to account for inelastic behavior and that the elastic deflection is based on a cracked section. The code is a mix of a north African national code with incorporation of ACI 318-05 and ASCE 7-05 just for fun.

So on this fine Friday, anyone want to chime in on this debate. When do you use the uncracked section properties of concrete versus the cracked section properties?

Paul.
------------------------------------------------------------ The information transmitted is intended only for the person  or entity to which it is addressed and may contain  proprietary, business-confidential and/or privileged material.   If you are not the intended recipient of this message you are  hereby notified that any use, review, retransmission, dissemination,  distribution, reproduction or any action taken in reliance upon  this message is prohibited. If you received this in error, please  contact the sender and delete the material from any computer.    Any views expressed in this message are those of the individual  sender and may not necessarily reflect the views of the company.   ------------------------------------------------------------ 

Re: Story Drift - Cracked or Uncracked Section Properties

Paul,

I believe you have to use cracked section properties in accordance with ACI 318-05 Sections 10.10 and 10.11.

Thomas Hunt, S.E.
Fluor

"Paul Blomberg" <paul.blomberg@gmail.com>
06/06/2008 01:24 PM
Please respond to seaint

To	seaint <seaint@seaint.org>
cc
Subject	Story Drift - Cracked or Uncracked Section Properties

We are checking some concrete moment frame calcs and debating internally about using the cracked or uncracked concrete section properties for the structural analysis. There is some discussion that Cd (deflection amplification factor) incorporates the loss of stiffness as the concrete cracks while most believe that Cd increases the elastic deflections (using cracked section properties) to to account for inelastic behavior and that the elastic deflection is based on a cracked section. The code is a mix of a north African national code with incorporation of ACI 318-05 and ASCE 7-05 just for fun.

So on this fine Friday, anyone want to chime in on this debate. When do you use the uncracked section properties of concrete versus the cracked section properties?

Paul.

------------------------------------------------------------ The information transmitted is intended only for the person  or entity to which it is addressed and may contain  proprietary, business-confidential and/or privileged material.   If you are not the intended recipient of this message you are  hereby notified that any use, review, retransmission, dissemination,  distribution, reproduction or any action taken in reliance upon  this message is prohibited. If you received this in error, please  contact the sender and delete the material from any computer.    Any views expressed in this message are those of the individual  sender and may not necessarily reflect the views of the company.   ------------------------------------------------------------

Story Drift - Cracked or Uncracked Section Properties

So on this fine Friday, anyone want to chime in on this debate. When do you use the uncracked section properties of concrete versus the cracked section properties?

Paul.

RE: Tornado Alley construction

David,

The use of the IRC is limited to regions not exceeding 110 mph … anything beyond that you have to use the IBC. However, a general lack of enforcement & inspection in many regions of the U.S. happens irrespective of the code being used. The IRC is a good starting point because there are many regions where it works quite well. Besides that, the IRC specifically states that if roof elements experience an uplift pressure of 20psf or greater (using the “components and cladding” table provided in Chapter 3), the designer MUST provide straps, etc. to complete an uplift load path to the foundation (an “engineered condition”, which may be mixed with an otherwise “prescriptive” residence). The State of Florida also adopted it as a model document for residential design and added their own modifications as they needed. Been that way for a long time.

Regards,

Dave K. Adams, S.E., P.Eng.

Lane Engineers, Inc.

Tulare, CA

www.training4engineers.com

From: David Topete [mailto:d.topete73@gmail.com]
Sent: Friday, June 06, 2008 12:00 PM
To: SEAINT
Subject: Tornado Alley construction

http://www.journalrecord.com/article.cfm?recid=89512

It's amazing what uplift straps and sill bolts can do to prevent a house from flying away... Granted, I'm out here in eqk country so tornadoes (or hurricanes) are not readily designed for. But, with all the damage from tornadoes each year, especially through "Tornado Alley," wouldn't most building departments want to scrap the IRC and its prescriptive methods (if that is the code in effect) in favor of anchor bolts and roof straps???

--
David Topete, SE

Re: Tornado Alley construction

I'll sum it up in one word: NAHB

>>> On 6/6/2008 at 2:00 PM, "David Topete" <d.topete73@gmail.com> wrote:

http://www.journalrecord.com/article.cfm?recid=89512

Re: Tornado Alley construction

Dave

There you go trying to apply logic and common sense to building departments.........ask the code writers if Tornadoes happen much more frequency than hurricanes why aren't there special wind zones and requirements for those zones..........and if they do have these requirements in place maybe plan check should be required for structures in those areas. The big assumption is that the plan checker knows what they are looking at.......big mistake sometimes.

Joe Venuti
Johnson & Nielsen Associates
Palm Springs, CA

Get trade secrets for amazing burgers. Watch "Cooking with Tyler Florence" on AOL Food.

Tornado Alley construction

http://www.journalrecord.com/article.cfm?recid=89512

Re: structural observation

My understanding of structural observations is that you are going to
confirm substantial conformance with the design intent. I try to be
clear in my communication that I'm not a building inspector, nor am I
taking the place of them. I'm there to go through the site and see if
I see anything that is different than what we designed. To me,
lateral detailing is the most important thing to check since that is
the least understood by builders and the most often overlooked by
inspectors.

Ultimately though, confirming that the job conforms to code and to the
plans is the job of the contractor and the inspector.

Hope that helps.

Chris

On Fri, Jun 6, 2008 at 10:22 AM, DA ENGINEERING <dnae@cox.net> wrote:
> Hi everyone,
> I will try again to get input
> thanks in advance
>
> structural observation to residential jobs
>
> engineer go to the site see all element beams, posts, connections, shear
> walls , nailing , plywood
> anchor bolts etc...........
> but when it come to verify the location of beams under post above
> how you make sure it line up , is not offset, is that the responsibility
> of the engineer
> who observe the job, framer , contractor, or city's inspector and for CBC
> 2007 special inspection
> I think it will be difficult for observation's engineer to verify
> specially for large scale homes with 100 beams three story to do that
>
> thanks in advance for your input and experience
>
> my second question if there offset between beam and post above
> and is hard to get anything added
> what is acceptable for example 1 1/8 inch plywood
> 3/4 inch plywood
> to span 16 inch over joists with point load = 3.0 kip to 5.0 kips?!
>
> thanks for input
>
> Dave A.

******* ****** ****** ****** ******* ****** ****** ********

RE: structural observation

You should also get the CASE National Practice Guidelines for The Structural Engineer of Record. This is 16 pages and will let you know what can be expected of you as SER and what you can expect to bill as Additional Services.

Christopher Banbury, PE

President

Ark Engineering, Inc.

PO Box 10129, Brooksville, FL 34603

22 North Broad ST, Brooksville, FL 34601

Phone: (352) 754-2424

Fax: (352) 754-2412

www.arkengineering.net

From: DA ENGINEERING [mailto:dnae@cox.net]
Sent: Friday, June 06, 2008 1:31 PM
To: seaint@seaint.org
Subject: structural observation

Hi everyone,

I will try again to get input

thanks in advance

structural observation to residential jobs

engineer go to the site see all element beams, posts, connections, shear walls , nailing , plywood

anchor bolts etc...........

but when it come to verify the location of beams under post above

how you make sure it line up , is not offset, is that the responsibility of the engineer

who observe the job, framer , contractor, or city's inspector and for CBC 2007 special inspection

I think it will be difficult for observation's engineer to verify

specially for large scale homes with 100 beams three story to do that

thanks in advance for your input and experience

my second question if there offset between beam and post above

and is hard to get anything added

what is acceptable for example 1 1/8 inch plywood

3/4 inch plywood

to span 16 inch over joists with point load = 3.0 kip to 5.0 kips?!

thanks for input

Dave A.

structural observation

Hi everyone,

I will try again to get input

thanks in advance

structural observation to residential jobs

engineer go to the site see all element beams, posts, connections, shear walls , nailing , plywood

anchor bolts etc...........

but when it come to verify the location of beams under post above

how you make sure it line up , is not offset, is that the responsibility of the engineer

who observe the job, framer , contractor, or city's inspector and for CBC 2007 special inspection

I think it will be difficult for observation's engineer to verify

specially for large scale homes with 100 beams three story to do that

thanks in advance for your input and experience

my second question if there offset between beam and post above

and is hard to get anything added

what is acceptable for example 1 1/8 inch plywood

3/4 inch plywood

to span 16 inch over joists with point load = 3.0 kip to 5.0 kips?!

thanks for input

Dave A.

Re: Seismic loads using ASCE 7

We work in similar areas (we're based in Modesto) and have found the
same thing. My understanding is that the UBC was far too conservative
in assigning that part of California to zone 3, and the new code
reflects more a more accurate assessment of seismic hazards in the
area. We're following the new code and always assuming a RHO of 1.3,
even though on many of the light framed residential jobs we do, RHO is
more likely 1. That bumps up the value a bit, and makes us feel more
comfortable.

We typically saw Wind loading govern for central valley jobs even
under the old code since many of the houses are in open areas where
Exposure C is required. With the new code, we're finding that Wind
still governs (just by a bit more). The wind loads are sometimes a
bit less than what they were under the UBC, though not by much. So
our designs wind up being about the same as they were before.

Hope that helps.

Chris

On Fri, Jun 6, 2008 at 9:43 AM, Dave Adams <davea@laneengineers.com> wrote:
> Happy Friday, everyone!
>
>
>
> One of the things that we are sort of struggling with here (old "zone 3"
> country) is that we are finding seismic loads via ASCE 7 wind up being less
> (sometimes uncomfortably) than what we used to calculate using the 1997
> UBC. As a result, we've sort of adopted our own internal "company minimum
> seismic coefficient" that we are comfortable with. Are most people
> discovering the same thing and what are your thoughts?
>
>
>
> Thanks!
>
>
>
> Dave K. Adams, S.E., P.Eng.
> LANE ENGINEERS, INC.
> 979 N. Blackstone Street
>
> P.O. Box 1059
> Tulare, CA 93275
>
> Direct Line: (559) 688-5263
>
> Direct FAX: (559) 688-8388
>
> E-Mail: davea@laneengineers.com
>
> Web: www.training4engineers.com
>
>

******* ****** ****** ****** ******* ****** ****** ********

Re: Seismic loads using ASCE 7

Dave

We have decided to use the values obtained with simplified lateral and wind since it gives values closer to former UBC load values. Using Equivalent Lateral method we are getting values in the range of .115 - .148 which we are not comfortable with either.

In a message dated 6/6/2008 9:40:46 A.M. Pacific Daylight Time, davea@laneengineers.com writes:

Happy Friday, everyone!

One of the things that we are sort of struggling with here (old "zone 3" country) is that we are finding seismic loads via ASCE 7 wind up being less (sometimes uncomfortably) than what we used to calculate using the 1997 UBC. As a result, we've sort of adopted our own internal "company minimum seismic coefficient" that we are comfortable with. Are most people discovering the same thing and what are your thoughts?

Thanks!

Dave K. Adams, S.E., P.Eng.

Joe Venuti
Johnson & Nielsen Associates
Palm Springs, CA

Get trade secrets for amazing burgers. Watch "Cooking with Tyler Florence" on AOL Food.