Structural Engineering: 2007-04-29

Saturday, May 5, 2007

Invitation to ETABS2000 discusssion forum

Hi,

This is an invitation to ETABS2000 forum, a proffessional group for CIVIL engineers who are familiar with computer design of structures, using ETABS2000 software. If you feel your friends or colleagues are interested in this issue, please forward this email for them.

In this group, besides discussions about ETABS2000, any discussion about building CODES and other CSI softwares like SAP, SAFE and SECTION DESIGNER are welcomed.

Here you will find many experienced engineers, you can ask your questions and also answer to others' problems. I hope I will meet you in this group soon.

To become a member of this group, click the following link:

http://groups.yahoo.com/group/etabs2000/join?referer=1

Best Regards,
Etabs2000 group moderator,
Hossein Mardanlo

Searching for free downloadble books

Hi,

I am searching for free downloadble books and specially solved problems in following subjects:

1-Theory of Elasticty

2-Dynamic of Structures

3-Structres Stability

4-Basics of Finite element methods

any suggestion?

Hossein Mardanlu

Re: why the moment frame must be capable to resist at least 25% of lateral loads?

Thanks for answers. My second question is why 25%? Is there any logic behind it or it is base on experimental observations?

----- Original Message -----

From: Gerard Madden, SE

To: seaint@seaint.org

Sent: Thursday, May 03, 2007 10:39 AM

Subject: Re: why the moment frame must be capable to resist at least 25% of lateral loads؟

It's a back up frame in case the walls begin to yield/fail. The 25% comes in because, in general, the shearwalls will be very stiff in comparison to the moment frames, so when you consider rigidity, the frames will get very little load and the shearwalls will get all the load.

Rshearwall >>>> Rmoment Frame

So, to ensure that the moment frames can do some work and are stout enough, the magical 25% of the seismic load is in there. So what you do is take your building base shear, divide it by 4, and make your shearwalls inactive in your model and design the frames assuming those shearwalls aren't doing anything.

Usually the shearwalls are at the core/center of the building and the moment frames are at the perimeter. By having stouter Moment frames, it will also reduce torsional irregularity concerns somewhat, although still the shearwalls will be much stiffer and still receive the brunt of the load.

-g

On 5/3/07, hossein mardanlo <hosein.mardanloo@gmail.com> wrote:
Hi,

In lateral load bearing system, where two kinds of bracing and moment frames
are cmbined, seismic codes require that the moment frame must be capable to
resist at least 25% of lateral loads. My question is what is the theoritical
point behind this requirement?

Thanks,

******* ****** ******* ******** ******* ******* ******* ***
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-gm

Thursday, May 3, 2007

Re: Rationale for Sprinklers on Trucks...

Ben-

But isn't the test fire used for the 2 hr rating significantly less intense than a gasoline fueled fire? The fire at the maze burned for nearly two hours.

Regards,

Bill Cain, SE

Berkeley CA

-----Original Message-----
From: Ben.Yousefi@SMGOV.NET
To: seaint@seaint.org
Sent: Thu, 3 May 2007 11:01 AM
Subject: RE: Rationale for Sprinklers on Trucks...

Another idea worth considering is fire retardant paint on the steel. Intumescent paint has been used effectively in structures for along time. You can get rating of up to 2 hours with it. And, it won't cover the steel like monokote would, so it can still be visually inspected.

Ben Yousefi, SE

Santa Monica, CA

From: Benjamin Maxwell [mailto:enginerd666@yahoo.com]
Sent: Thursday, May 03, 2007 10:36 AM
To: seaint@seaint.org
Subject: RE: Rationale for Sprinklers on Trucks...

Stupid idea, but how about requiring fire suppression systems on the tanker trucks themselves? Put the solution, if deemed necessary, on the cause of the problem, not the receiving end. Government agencies may be cash strapped, but we all know the oil companies aren't.

Donald Bruckman <bruckmandesign@verizon.net> wrote:

I'm not even sure any fireproofing or fire suppression system could have overcome 8600 gallons of burning gasoline anyway. A system capable of that would have to cost a ton of money for a very rare occurrence. Vehicle fires occur on overpasses all the time and do not bring down the span. This was an anomaly.

From: Fred Turner [mailto:turner@stateseismic.com]
Sent: Thursday, May 03, 2007 8:48 AM
To: seaint@seaint.org
Subject: Rationale for Sprinklers on Steel Bridges

Since no one died in the MacArthur Maze Fire it doesn't seem appropriate to rationalize the need for sprinklers on bridges on the basis that building codes require sprinklers in buildings to meet a life safety performance objective at this juncture. The more salient issue is that choke points exist in our transportation systems that, if disrupted, will cause widespread economic losses. Attention to enhancing redundancy and reliability of these systems is needed. Fire protection systems may not provide the best approach to manage this type of risk. The San Francisco Bay Area is fortunate that redundancy in the form of alternative routes already exist in the freeway system around the MacArthur Maze damage. We may not be so fortunate after future incidents.

Fred

Fred Turner, Staff Structural Engineer, California Seismic Safety Commission, a public policy advisory agency, Turner@stateseismic.com, 1755 Creekside Oaks Dr. #100 Sacramento, CA 95833 Phone: 916-263-5506 Ext. 227 or 916-263-0582 Fax: 916-263-0594

Benjamin H. Maxwell, S.E.

Ahhh...imagining that irresistible "new car" smell?
Check out new cars at Yahoo! Autos.

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RE: Rationale for Sprinklers on Trucks...

Return Receipt

Your RE: Rationale for Sprinklers on Trucks...
document:

was Tom Hunt/AV/FD/FluorCorp
received
by:

at: 05/03/2007 11:10:13 PDT

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RE: Rationale for Sprinklers on Trucks...

Another idea worth considering is fire retardant paint on the steel. Intumescent paint has been used effectively in structures for along time. You can get rating of up to 2 hours with it. And, it won’t cover the steel like monokote would, so it can still be visually inspected.

Ben Yousefi, SE

Santa Monica, CA

From: Benjamin Maxwell [mailto:enginerd666@yahoo.com]
Sent: Thursday, May 03, 2007 10:36 AM
To: seaint@seaint.org
Subject: RE: Rationale for Sprinklers on Trucks...

Donald Bruckman <bruckmandesign@verizon.net> wrote:

I’m not even sure any fireproofing or fire suppression system could have overcome 8600 gallons of burning gasoline anyway. A system capable of that would have to cost a ton of money for a very rare occurrence. Vehicle fires occur on overpasses all the time and do not bring down the span. This was an anomaly.

From: Fred Turner [mailto:turner@stateseismic.com]
Sent: Thursday, May 03, 2007 8:48 AM
To: seaint@seaint.org
Subject: Rationale for Sprinklers on Steel Bridges

Since no one died in the MacArthur Maze Fire it doesn't seem appropriate to rationalize the need for sprinklers on bridges on the basis that building codes require sprinklers in buildings to meet a life safety performance objective at this juncture. The more salient issue is that choke points exist in our transportation systems that, if disrupted, will cause widespread economic losses. Attention to enhancing redundancy and reliability of these systems is needed. Fire protection systems may not provide the best approach to manage this type of risk. The San Francisco Bay Area is fortunate that redundancy in the form of alternative routes already exist in the freeway system around the MacArthur Maze damage. We may not be so fortunate after future incidents.

Fred

Fred Turner, Staff Structural Engineer, California Seismic Safety Commission, a public policy advisory agency, Turner@stateseismic.com, 1755 Creekside Oaks Dr. #100 Sacramento, CA 95833 Phone: 916-263-5506 Ext. 227 or 916-263-0582 Fax: 916-263-0594

Benjamin H. Maxwell, S.E.

Ahhh...imagining that irresistible "new car" smell?
Check out new cars at Yahoo! Autos.

Re: why the moment frame must be capable to resist at least 25% of lateral loads؟

It's a back up frame in case the walls begin to yield/fail. The 25% comes in because, in general, the shearwalls will be very stiff in comparison to the moment frames, so when you consider rigidity, the frames will get very little load and the shearwalls will get all the load.

Rshearwall >>>> Rmoment Frame

So, to ensure that the moment frames can do some work and are stout enough, the magical 25% of the seismic load is in there. So what you do is take your building base shear, divide it by 4, and make your shearwalls inactive in your model and design the frames assuming those shearwalls aren't doing anything.

Usually the shearwalls are at the core/center of the building and the moment frames are at the perimeter. By having stouter Moment frames, it will also reduce torsional irregularity concerns somewhat, although still the shearwalls will be much stiffer and still receive the brunt of the load.

-g

On 5/3/07, hossein mardanlo <hosein.mardanloo@gmail.com> wrote:

Hi,

In lateral load bearing system, where two kinds of bracing and moment frames
are cmbined, seismic codes require that the moment frame must be capable to
resist at least 25% of lateral loads. My question is what is the theoritical
point behind this requirement?

Thanks,

******* ****** ******* ******** ******* ******* ******* ***
*   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:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad@seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted
*   without your permission. Make sure you visit our web
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--
-gm

RE: Rationale for Sprinklers on Trucks...

Donald Bruckman <bruckmandesign@verizon.net> wrote:

I'm not even sure any fireproofing or fire suppression system could have overcome 8600 gallons of burning gasoline anyway. A system capable of that would have to cost a ton of money for a very rare occurrence. Vehicle fires occur on overpasses all the time and do not bring down the span. This was an anomaly.

From: Fred Turner [mailto:turner@stateseismic.com]
Sent: Thursday, May 03, 2007 8:48 AM
To: seaint@seaint.org
Subject: Rationale for Sprinklers on Steel Bridges

Since no one died in the MacArthur Maze Fire it doesn't seem appropriate to rationalize the need for sprinklers on bridges on the basis that building codes require sprinklers in buildings to meet a life safety performance objective at this juncture. The more salient issue is that choke points exist in our transportation systems that, if disrupted, will cause widespread economic losses. Attention to enhancing redundancy and reliability of these systems is needed. Fire protection systems may not provide the best approach to manage this type of risk. The San Francisco Bay Area is fortunate that redundancy in the form of alternative routes already exist in the freeway system around the MacArthur Maze damage. We may not be so fortunate after future incidents.

Fred

Fred Turner, Staff Structural Engineer, California Seismic Safety Commission, a public policy advisory agency, Turner@stateseismic.com, 1755 Creekside Oaks Dr. #100 Sacramento, CA 95833 Phone: 916-263-5506 Ext. 227 or 916-263-0582 Fax: 916-263-0594

Benjamin H. Maxwell, S.E.

Ahhh...imagining that irresistible "new car" smell?
Check out new cars at Yahoo! Autos.

RE: why the moment frame must be capable to resist at least 25% of lateral loadsØŸ

The moment frame is intended as a back up system. In case the shear walls or braced frames get substantially compromised, you want to ensure that a moment frame system capable of resisting at least fraction of a load is still working for you.

Ben Yousefi, SE

Santa Monica, CA

From: Derek Westphal [mailto:westphaldp@yahoo.com]
Sent: Thursday, May 03, 2007 8:17 AM
To: seaint@seaint.org
Subject: Re: why the moment frame must be capable to resist at least 25% of lateral loadsØŸ

It has to do with the relative stiffness of the two systems. In order to take advantage

of the higher R factors you could just add a mini moment frame and call it a dual

system. The 25% factor is the penalty for taking a shear wall from R=5.5 to R=8.5.

hossein mardanlo <hosein.mardanloo@gmail.com> wrote:

Hi,

In lateral load bearing system, where two kinds of bracing and moment frames
are cmbined, seismic codes require that the moment frame must be capable to
resist at least 25% of lateral loads. My question is what is the theoritical
point behind this requirement?

Thanks,

******* ****** ******* ******** ******* ******* ******* ***
* 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:
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* http://www.seaint.org/sealist1.asp
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* Questions to seaint-ad@seaint.org. Remember, any email you
* send to the list is public domain and may be re-posted
* without your permission. Make sure you visit our web
* site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********

Ahhh...imagining that irresistible "new car" smell?
Check out new cars at Yahoo! Autos.

Re: Steel Member Check for Seismic Loading

On May 3, 2007, at 9:17 AM, Paul Blomberg wrote:

> It looks like the engineer was evaluating the loads at a 45 degree
> angle and did SRSS (square root of the sum of the squares) to sum
> the forces and stresses. This seems like a reasonable approach
> when both orthogonal forces don't occur at the same time.
That's what I thought at first, but you wouldn't base the stress
calculation on Fbx alone in that case--you'd use {fa/Fa + root[(fbx/
Fbx)^2+(fby/Fby^2)]} < 1.0

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw@skypoint.com | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania
1864)
http://www.skypoint.com/~chrisw/

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RE: Rationale for Sprinklers on Steel Bridges

I’m not even sure any fireproofing or fire suppression system could have overcome 8600 gallons of burning gasoline anyway. A system capable of that would have to cost a ton of money for a very rare occurrence. Vehicle fires occur on overpasses all the time and do not bring down the span. This was an anomaly.

From: Fred Turner [mailto:turner@stateseismic.com]
Sent: Thursday, May 03, 2007 8:48 AM
To: seaint@seaint.org
Subject: Rationale for Sprinklers on Steel Bridges

Since no one died in the MacArthur Maze Fire it doesn't seem appropriate to rationalize the need for sprinklers on bridges on the basis that building codes require sprinklers in buildings to meet a life safety performance objective at this juncture. The more salient issue is that choke points exist in our transportation systems that, if disrupted, will cause widespread economic losses. Attention to enhancing redundancy and reliability of these systems is needed. Fire protection systems may not provide the best approach to manage this type of risk. The San Francisco Bay Area is fortunate that redundancy in the form of alternative routes already exist in the freeway system around the MacArthur Maze damage. We may not be so fortunate after future incidents.

Fred

Fred Turner, Staff Structural Engineer, California Seismic Safety Commission, a public policy advisory agency, Turner@stateseismic.com, 1755 Creekside Oaks Dr. #100 Sacramento, CA 95833 Phone: 916-263-5506 Ext. 227 or 916-263-0582 Fax: 916-263-0594

Re: Steel Member Check for Seismic Loading

On May 3, 2007, at 8:15 AM, 남윤호 wrote:

> I have the old calculation(1984 made) of steel code check for
> seismic excitation loading.
>
> In generally steel check for combined bending and axial stress
> interaction is as follows:
> fa/Fa + fbx/Fbx + fby/Fby < 1.0 -----------(1)
> However, the old calculation used the steel check formula under 2
> directions horizontal seismic loading(1g each) as follows:
> fa/Fa + root(fbx^2+fby^2)/Fbx < 1.0 -----------(2)
>
> Is it reasonable using equation (2) that steel code checked under 2
> directions horizontal seismic loading? If it is reasonable, why do
> you think using Eq. (2)?
I've never seen your eq 2 specified before, but it's the correct
relationship for round sections like pipe. (1) is correct for a
section with a rectangular envelope but if you were to use it with
pipe you'd get the stress at a 'corner' that doesn't exist. You
should work out the algebra for yourself, so you understand what's
going on.

RE: welding spec for appearance

Modern Steel Construction put out a brochure on Architecturally Exposed
Structural Steel available free at:

http://www.aisc.org/Template.cfm?Section=Bookstore&Template=/Ecommerce/Produ
ctDisplay.cfm&ProductID=2138

hth,

Michel Blangy

Michel Blangy, P.E.

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

Re: welding spec for appearance

On May 3, 2007, at 7:15 AM, Andy Richardson wrote:

> What specification or requirements should I use to ensure a nice
> looking weld. Any ideas?
Welds are basically practical things. What you really want is no
spatter, no arc strikes, no pits or undercut and especially no
cracking. These are all quality issues that you're going to need so
the welds function. The nearest I've ever come to a specification for
appearance is the term 'workmanlike appearance,' in the ASME Code,
which has doubtless been replaced by a some gender neutral term by
now. The AWS (see AWS web site) probably has some nice fuzzy
specifications for architectural weld details.

You can also specify that the contour be ground smooth or even
polished. If you're using 300 or 400 series stainless base metal
there's a problem with discoloration that's sometimes difficult to
deal with. I think there are procedures for minimizing discoloration--
see the Lincoln Electric web site for some suggestions about welding
procedures or consumables for your situation.

If I were really concerned with this, I'd ask the welding contractor
what's possible and get some sample welds to check with your
architect. It may cost you a few bucks--welders don't work free, but
it'll help with the architect/engineer cultural divide. Over here on
the dark side we don't have architects, but we do have marketeers who
offer all the same helpful commentary. ('Eeeew! That's so not, like,
pretty, you know? Can't you just, like, glue it or something?')

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

Rationale for Sprinklers on Steel Bridges

Fred

Re: why the moment frame must be capable to resist at least 25% of lateral loadsØŸ

It has to do with the relative stiffness of the two systems. In order to take advantage

of the higher R factors you could just add a mini moment frame and call it a dual

system. The 25% factor is the penalty for taking a shear wall from R=5.5 to R=8.5.

hossein mardanlo <hosein.mardanloo@gmail.com> wrote:

Hi,

In lateral load bearing system, where two kinds of bracing and moment frames
are cmbined, seismic codes require that the moment frame must be capable to
resist at least 25% of lateral loads. My question is what is the theoritical
point behind this requirement?

Thanks,

******* ****** ******* ******** ******* ******* ******* ***
* 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:
*
* http://www.seaint.org/sealist1.asp
*
* Questions to seaint-ad@seaint.org. Remember, any email you
* send to the list is public domain and may be re-posted
* without your permission. Make sure you visit our web
* site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********

Ahhh...imagining that irresistible "new car" smell?
Check out new cars at Yahoo! Autos.

Re: Steel Member Check for Seismic Loading

Paul,

There is another implication; only Fbx is used. Since laterally unsupported W sections could have somewhat lower stresses about one axis this would make the check even more conservative.

I am not familiar with equation 2. Perhaps there are explanations in the applicable code that would help to clarify its use.

Regards,

H. Daryl Richardson

----- Original Message -----

From: Paul Blomberg

To: seaint@seaint.org

Sent: Thursday, May 03, 2007 8:17 AM

Subject: Re: Steel Member Check for Seismic Loading

It looks like the engineer was evaluating the loads at a 45 degree angle and did SRSS (square root of the sum of the squares) to sum the forces and stresses. This seems like a reasonable approach when both orthogonal forces don't occur at the same time.

Paul.

On 5/3/07, 남윤호 <yhnam@kopec.co.kr> wrote:

Dear All,

I have the old calculation(1984 made) of steel code check for seismic excitation loading.

In generally steel check for combined bending and axial stress interaction is as follows:

fa/Fa + fbx/Fbx + fby/Fby < 1.0 -----------(1)

However, the old calculation used the steel check formula under 2 directions horizontal seismic loading(1g each) as follows:

fa/Fa + root(fbx^2+fby^2)/Fbx < 1.0 -----------(2)

Is it reasonable using equation (2) that steel code checked under 2 directions horizontal seismic loading? If it is reasonable, why do you think using Eq. (2)?

Yoonho Nam, PE

Shaw Stone & Webster Nuclear

Re: welding spec for appearance

I assume you want the welds ground smooth. Place in the specs that the welds are to be ground smooth and match the final finish. Then have the contractor mock up a trial piece and have the architect and engineer evaluate their technique and results as part of the submittal program. Once agreed on, the mock up sample is the goal for all the welds and the contractor knows exactly what is expected and what he needs to do.

Paul.

On 5/3/07, Andy Richardson <chuzman@gmail.com> wrote:

I am helping the architect with some custom handrail connections. Considering the amount of effort that is being put into these handrails, I want to be sure that the appearance of the exposed welds matches the rest of the construction. What specification or requirements should I use to ensure a nice looking weld. Any ideas?

Thanks,
Andy Richardson
Bluffton, SC

Re: Steel Member Check for Seismic Loading

It looks like the engineer was evaluating the loads at a 45 degree angle and did SRSS (square root of the sum of the squares) to sum the forces and stresses. This seems like a reasonable approach when both orthogonal forces don't occur at the same time.

Paul.

On 5/3/07, 남윤호 <yhnam@kopec.co.kr> wrote:

Dear All,

I have the old calculation(1984 made) of steel code check for seismic excitation loading.

In generally steel check for combined bending and axial stress interaction is as follows:

fa/Fa + fbx/Fbx + fby/Fby < 1.0 -----------(1)

However, the old calculation used the steel check formula under 2 directions horizontal seismic loading(1g each) as follows:

fa/Fa + root(fbx^2+fby^2)/Fbx < 1.0 -----------(2)

Is it reasonable using equation (2) that steel code checked under 2 directions horizontal seismic loading? If it is reasonable, why do you think using Eq. (2)?

Yoonho Nam, PE

Shaw Stone & Webster Nuclear

Steel Member Check for Seismic Loading

Return Receipt

Your Steel Member Check for Seismic Loading
document:

was Tom Hunt/AV/FD/FluorCorp
received
by:

at: 05/03/2007 07:02:15 PDT

Any views expressed in this message are those of the individual
sender and may not necessarily reflect the views of the company.
------------------------------------------------------------

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

RE: welding spec for appearance

That can be so subjective. I did a job like that and we found a railing on a nearby building that had very good looking welds. The contractor and I agreed that these welds would be the criteria that had to be matched on our job. It worked.

Bob Garner, S.E.

From: Andy Richardson [mailto:chuzman@gmail.com]
Sent: Thursday, May 03, 2007 5:16 AM
To: seaint@seaint.org
Subject: welding spec for appearance

I am helping the architect with some custom handrail connections. Considering the amount of effort that is being put into these handrails, I want to be sure that the appearance of the exposed welds matches the rest of the construction. What specification or requirements should I use to ensure a nice looking weld. Any ideas?

Thanks,
Andy Richardson
Bluffton, SC

Steel Member Check for Seismic Loading

Return Receipt

Your Steel Member Check for Seismic Loading
document:

was Tarik Berair/TECHNIP
received
by:

at: 03/05/2007 15:16:51

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

Steel Member Check for Seismic Loading

Dear All,

I have the old calculation(1984 made) of steel code check for seismic excitation loading.

In generally steel check for combined bending and axial stress interaction is as follows:

fa/Fa + fbx/Fbx + fby/Fby < 1.0 -----------(1)

However, the old calculation used the steel check formula under 2 directions horizontal seismic loading(1g each) as follows:

fa/Fa + root(fbx^2+fby^2)/Fbx < 1.0 -----------(2)

Is it reasonable using equation (2) that steel code checked under 2 directions horizontal seismic loading? If it is reasonable, why do you think using Eq. (2)?

Yoonho Nam, PE

Shaw Stone & Webster Nuclear

welding spec for appearance

Re: Alternate design method

Jim and Scott,
I graduated in 1962 when Ultimate Strength Design or Strength Design was
one chapter or was in an Appendix of out text-books.
The so-called alternate method was the "method"
Gary

Jim Bessley wrote:
> yes, an older version. None of my texts have an example. I have the
> "Notes" corresponding to that ACI code. It does not have an example
> using the alternate provisions. I'm guessing that if you go back far
> enough you go beyond the change to using the strength principles and
> changing load and phi factors then reducing the allowables.
> Jim
>
> Up a bit late last night?
>
> On 5/1/07, *Scott Maxwell* <smaxwell@engin.umich.edu
> <mailto:smaxwell@engin.umich.edu>> wrote:
>
> Jim,
>
> There is a chance an older version of PCA's Notes might have some
> examples
> of the use of the "Alternative Design Method", maybe including a wall
> example. I used to have an older version, but I don't know where
> I have
> it at this point.
>
> My concrete text book does not.
>
> Regardless, since the "Alternative Design Method" bascially points you
> back to the Strength Design provisions in the code (i.e. Chapter
> 10 and
> Chapter 14), you still more than likely need an example of
> Strength Design
> anyways...and there is a pretty good chance that PCA's Notes might
> have
> that.
>
> Regards,
>
> Scott
> Adrian, MI
>
>
> On Tue, 1 May 2007, Jim Bessley wrote:
>
> > Scott,
> > I understand all of that regarding your comments. I would still
> like to
> > find an example.
> >
> > I do, however, appreciate your comments and thoughts on the matter.
> > Jim
> >
> > On 5/1/07, Scott Maxwell <smaxwell@engin.umich.edu
> <mailto:smaxwell@engin.umich.edu>> wrote:
> > >
> > > Jim,
> > >
> > > What code are you under? Technically, under the current ACI
> 318 (ACI
> > > 318-05...as well as 318-02), the "alternative method" (aka
> allowable
> > > stress design) is no longer permitted. ACI 318 did leave a
> comment in the
> > > commentary that says that you may still use it, but the commentary
> > > technically has no force. The exception is if you are doing
> some sort of
> > > environmental structure (i.e. tank), then you would use ACI
> 350, which I
> > > believe still has the "alternative method" included.
> > >
> > > I would encourage you to use the main provisions in the code (
> i.e.
> > > strength design). If you need examples to better understand those
> > > provisions, then you can get PCA's Notes on the use of ACI
> 318. I would
> > > assume that they would have an example of strength design of a
> wall with
> > > axial load and flexure.
> > >
> > > Regards,
> > >
> > > Scott
> > > Adrian, MI
> > >
> > >
> > > On Tue, 1 May 2007, Jim Bessley wrote:
> > >
> > > > Gary,
> > > > Sorry for the confusion. Appendix A in the ACI 318-95
> Code. Section
> > > > A.6(and the associated commentary
> > > > RA.6) states that compression members with or without
> flexure must be
> > > > proportioned using the strength design methods from chapter
> 10 and that
> > > > capacities are to be taken as 40% of those from chapter
> 10. Section
> > > > A.2.1says load factors and reduction factors are to be taken
> as unity.
> > > > I haven't
> > > > had to do a lot of wall design in concrete, and I don't have any
> > > references
> > > > or texts that provide an example for this situation with
> compression and
> > > > bending using the appendix.
> > > > Jim
> > > >
> > > > On 5/1/07, Gary Loomis <gloomis@masterengineersinc.com
> <mailto:gloomis@masterengineersinc.com>> wrote:
> > > > >
> > > > > Old "alternate design method". Do you mean working
> stress design?
> > > > >
> > > > >
> > > > >
> > > > > Gary W. Loomis, P.E., Senior Structural Engineering
> > > > >
> > > > > Master Engineers and Designers, Inc.
> > > > >
> > > > > -----Original Message-----
> > > > > *From:* Jim Bessley [mailto: jbessley@gmail.com
> <mailto:jbessley@gmail.com>]
> > > > > *Sent**:* Tuesday, May 01, 2007 4:45 PM
> > > > > *To:* seaint@seaint.org <mailto:seaint@seaint.org>
> > > > > *Subject:* Alternate design method
> > > > >
> > > > >
> > > > >
> > > > > I have to look at a wall section using the old "alternate
> design
> > > method"
> > > > > in concrete. The wall section will have both lateral and
> axial
> > > loads. It
> > > > > has been a very long time since I used this method, if
> ever. does
> > > anybody
> > > > > out there have an example that I can get from you that
> will explain
> > > the
> > > > > process. The "99 ACI code uses strength design with
> different phi and
> > > load
> > > > > factors, which have me confused.
> > > > >
> > > > > Any help would be appreciated.
> > > > > thanks,
> > > > > Jim B.
> > > > >
> > > >
> > >
> > > ******* ****** ******* ******** ******* ******* ******* ***
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why the moment frame must be capable to resist at least 25% of lateral loads؟

Hi,

In lateral load bearing system, where two kinds of bracing and moment frames
are cmbined, seismic codes require that the moment frame must be capable to
resist at least 25% of lateral loads. My question is what is the theoritical
point behind this requirement?

Thanks,

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

Wednesday, May 2, 2007

Re: Alternate Design Method

Jim,

The basics are there. If you understand the basics of WSB flexure (i.e.
can draw the strain diagram, corresponding stress diagram, and then draw a
FBD with resultants C and T and know what C and T are equal to), then you
can add in the axial load into the FBD should be able to go from there.
More than likely you should be able to find such a situation in a masonry
textbook.

That covers the basic principles. But, you need to ensure that the code
provision actually match and use basic principles as well as what the code
uses as allowable stress values assuming it does use basic principles.

Regards,

Scott
Adrian, MI

On Wed, 2 May 2007, Jim Bessley wrote:

> Robert and Michael,
> Thank you for the replies. I do, however, have this information and have
> used it before. I am looking for is an example for combined bending and
> axial load. I have used the masonry text before, but I don't think it the
> axial load capacity calculations will be the same.
> Thanks for your time. I do appreciate it.
> Jim
>
> On 5/2/07, Garner, Robert <rgarner@moffattnichol.com> wrote:
> >
> > I recall you have to check the allowable bending moment based on
> > allowable concrete stress, also:
> >
> >
> >
> > M = 0.5 * f'c * j * k * b * d^2
> >
> >
> >
> > Correct me if I'm wrong. It's been a long, long time.
> >
> >
> >
> > You could also get a masonry design book. Masonry WSD is just like
> > Concrete WSD.
> >
> >
> >
> > Bob Garner, S.E.
> >
> >
> >
> >
> >
> > R. Garner
> >
> > Moffatt & Nichol
> >
> > Tel.: (619) 220-6050
> >
> > Fax.: (619) 220-6055
> >
> > e-mail: rgarner@moffattnichol.com
> >
> >
> > The information contained in the e-Mail, including any accompanying
> > documents or attachments, is from Moffatt & Nichol and is intended only for
> > the use of the individual or entity named above, and is privileged and
> > confidential. If you are not the intended recipient, be aware that any
> > disclosure, dissemination, distribution, copying or use of the contents of
> > this message is strictly prohibited. If you received this message in error,
> > please notify us.
> >
>

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

Re: Alternate Design Method

Michael,

Correct...for pure bending.

If you including an axial load, then you need to include the P load in the
free-body diagram along with the T (tension steel) resultant and C
(concrete compression) resultant. It is not just C=T. But P=C-T. And
the moment equation of the FBD also needs to include the moment due to the
axial load (depends on what point you take it about).

Regards,

Scott
Adrian, MI

On Wed, 2 May 2007, Michael Hemstad wrote:

> On Tue, 1 May 2007, Jim Bessley wrote:
> > Scott,
> > I understand all of that regarding your comments. I would still like to
> > find an example.
> >
> > I do, however, appreciate your comments and thoughts on the matter.
> > Jim
>
>
> Working Stress Design is not dead yet.
>
> If you're analyzing an existing section:
> 1. Figure out the depth to reinforcing, d.
> 2. Calculate rho.
> 3. Find N, the ratio of Young's Moduli. For your purposes, use N = 12 - fc' (about 9).
> 4. Calculate k, the depth of the compression wedge (to the neutral axis)
>
> k = sqrt(2 rho * N + (rho * N)^2) - rho * N (usually about 0.3)
>
> 5. Calculate j: j = 1 - k/3 (usually about 0.9)
> 6. Calculate allowable moment:
>
> M = As fs j d/12
>
> If you know the reinforcing grade (yield), use fs = 0.5Fy with a maximum of 24 ksi. If unknown:
>
> If the structure was built prior to 1954, Fy = 33 ksi; use fs = 18 ksi.
> If the structure was built after about 1985, you can safely assume Fy = 60 ksi and fs = 24 ksi.
> Between these dates, assume Fy = 40 ksi and fs = 20 ksi.
>
> The 1954 date I lifted from an old (1983) copy of the AASHTO Manual for Maintenance Inspection of Bridges.
>
> To cut down on the blitz of emails screaming about how Grade 60 steel was common before 1985, yes, it was; but there was still design being done with Grade 40. For instance, by me, as directed by my first boss.
>
>
> If for some odd reason you're designing a new section by WSD, it's a little harder to explain by email. When we were doing WSD, we used tables; you'd calculate M/bd^2 and enter the table, pull out a value for rho, and off you'd go. When I programmed WSD into my calculator, it involved solving a cubic equation based on first principles. Good fun, that. However, if you really, really want to do it, there's a shortcut equation, hitherto unpublished, that will get you remarkably close:
>
> for M = the design moment PER FOOT OF WIDTH, in foot-kips; fs in ksi; and d in inches,
>
> As = (M^1.04) * 11.84/(fs * d) giving you square inches of reinforcing.
>
> I'm pretty sure it's unpublished because I curve-fit the thing, and I don't think I've told anyone. It works great for spreadsheets. If you have trouble, Scott can help you.
>
> HTH,
> Mike
>
>
> Michael Hemstad, P.E.
>
>
> Meyer, Borgman and Johnson, Inc.
>
> 12 South Sixth Street
> Suite 810
> Minneapolis, MN 55402
> (612) 338-0713 (main)
> (612) 604-3621 (direct)
> (612) 337-5325 (fax)
> www.mbjeng.com
>
>

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Re: Alternate Design Method

Robert and Michael,
Thank you for the replies. I do, however, have this information and have used it before. I am looking for is an example for combined bending and axial load. I have used the masonry text before, but I don't think it the axial load capacity calculations will be the same.
Thanks for your time. I do appreciate it.
Jim

On 5/2/07, Garner, Robert <rgarner@moffattnichol.com > wrote:

I recall you have to check the allowable bending moment based on allowable concrete stress, also:

M = 0.5 * f'c * j * k * b * d^2

Correct me if I'm wrong. It's been a long, long time.

You could also get a masonry design book. Masonry WSD is just like Concrete WSD.

Bob Garner, S.E.

R. Garner

Moffatt & Nichol

Tel.: (619) 220-6050

Fax.: (619) 220-6055

e-mail: rgarner@moffattnichol.com

The information contained in the e-Mail, including any accompanying documents or attachments, is from Moffatt & Nichol and is intended only for the use of the individual or entity named above, and is privileged and confidential. If you are not the intended recipient, be aware that any disclosure, dissemination, distribution, copying or use of the contents of this message is strictly prohibited. If you received this message in error, please notify us.

Alternate Design Method

I recall you have to check the allowable bending moment based on allowable concrete stress, also:

M = 0.5 * f'c * j * k * b * d^2

Correct me if I'm wrong. It's been a long, long time.

You could also get a masonry design book. Masonry WSD is just like Concrete WSD.

Bob Garner, S.E.

R. Garner

Moffatt & Nichol

Tel.: (619) 220-6050

Fax.: (619) 220-6055

e-mail: rgarner@moffattnichol.com