Structural Engineering: 2008-09-21

Saturday, September 27, 2008

Simpson Titen Screws in Existing Concrete Stemwall

I'm doing a residential addition and I 'm trying to connect a new girder to an existing stemwall footing.

Looking at the Simpson 2008 catalog, page 140, I see that there is a tabulated capacity of 3,950 lbs for a HU46 using (12)-1/4" diameter x 2-3/4" Titen Screws. This comes to a little over 300 lbs per screw. According to the tabulated values, the full capacity of the screw is 400 pounds each. However, in the literature on the website (http://www.simpsonanchors.com/catalog/mechanical/titen/loads_sheartension.html), there is a reduction in shear capacity if the anchors are spaced closer than 3" down to half the capacity at 1-1/2". I downloaded the HU46 hanger from the Simpson website and the spacing of the holes is 1", which is less than the minimum spacing for the screw.

Am I missing something?

Alternatively, I have considered using a LGUM46 with (4)-3/8" diameter x 4" long Titen HD screws. Using Simpson's ASD tables, I get a full capacity of 1,585 lbs per anchor. The reduction factor for spacing is 0.804. I looked at the reduction factor for edge distance using the minimum value of 1-3/4" and that factor is 0.24. The load is due to gravity, therefore the shear load is not towards the edge. I'm not sure if I should consider this reduction factor or not. I know that ACI 318 Appendix D would use 2x the capacity if the load is not towards the edge, but I don't know the basis of the ASD tables. I guess I should/could use the Simpson calculator, but I haven't yet.

Should I consider the 0.24 factor for edge distance? If so, this reduces the capacity to below my design load in a few cases.

Regards,

T. William (Bill) Allen, S.E.

ALLEN DESIGNS

Consulting Structural Engineers
V (949) 248-8588 • F(949) 209-2509

RE: Doug. Fir Lumber Grades

Thanks again to Dave, and to Thor for their responses, and maybe I should be contacting one of the wood industry organizations because my questions still is: Is there actually a stamp put on lumber saying "No. 1 and Better", or does this mean that the lumber delivered to the job site will be a mixture of No. 1, Dense No. 1, and Select Structural? Thor's response sounds like this is the case. But, if all of the pieces were marked "No. 1", wouldn't this qualify for "No. 1 and Better"?

Still unsure of this,

Larry Hauer S.E.

> From: thor@yosemite.net
> To: seaint@seaint.org
> Subject: Re: Doug. Fir Lumber Grades
> Date: Sat, 27 Sep 2008 07:52:21 -0500
>
> Larry,
>
> My understanding of the "No. 1" and "No. 1 and Better" grades is simply that
> it's easier/more efficient to sort lumber by grade when there are fewer
> grades; e.g., sorting lumber into piles of No. 1 *and* Select Structural
> takes more skill (and then more yard space for separate stacks of lumber
> grades) than just putting all the lumber into one pile if it's at least No.
> 1 grade.
>
> The reward for engineers is getting slightly higher allowable stresses,
> since there are supposedly some pieces that will be better than No. 1.
> However, for specifying new lumber I wouldn't trust No. 1 and Better to
> actually be provided. I once called a lumber yard to ask what grade lumber
> they had available--the answer was "We carry 'number one construction
> grade'." Okay.... is it 'number 1', or is it 'construction'?? I've also
> specified select structural and had people complain that it cost more than
> No. 1 and the 'guy at the lumber yard' said the two grades are exactly the
> same.
>
> Have fun!
>
> Thor Matteson, SE
> www.shearwalls.com
>
>
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Re: Doug. Fir Lumber Grades

Larry,

My understanding of the "No. 1" and "No. 1 and Better" grades is simply that
it's easier/more efficient to sort lumber by grade when there are fewer
grades; e.g., sorting lumber into piles of No. 1 *and* Select Structural
takes more skill (and then more yard space for separate stacks of lumber
grades) than just putting all the lumber into one pile if it's at least No.
1 grade.

The reward for engineers is getting slightly higher allowable stresses,
since there are supposedly some pieces that will be better than No. 1.
However, for specifying new lumber I wouldn't trust No. 1 and Better to
actually be provided. I once called a lumber yard to ask what grade lumber
they had available--the answer was "We carry 'number one construction
grade'." Okay.... is it 'number 1', or is it 'construction'?? I've also
specified select structural and had people complain that it cost more than
No. 1 and the 'guy at the lumber yard' said the two grades are exactly the
same.

Have fun!

Thor Matteson, SE
www.shearwalls.com

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Friday, September 26, 2008

RE: Doug. Fir Lumber Grades

Larry,

Last year I built a project using No.1 and Better and Select Structural DF beams and rafters to fit an historic structure. At the lumber yard I seem to recall the "No.1 and Better" had a stamp on it that said just that. My 1991 code lists a Dense No.1 that had a better stress value than No.1. But you can't use that value today for checking (E) lumber. The old grading rules might explain what the differences were. But you're still limited to using today's lumber stress values, from the current code.

Deflection may govern in a long purlin and the better lumber is only going to have a slightly better E value. Ponding of old panelized roofs is pretty common due to long-term deflection. An over-deflected purlin will also suffer from vibrations. The old lumber just won't work for new added equipment loads.

For a typical panelized roof with new equipment they're probably going to need to replace the purlins or reinforce them with sistered joists. Shear may also be a factor at the ends. The metal hangers need to be verified. Can you tell what type they are? If not can you analyze a custom hanger?

One solution may be to add new larger purlins in between the existing purlins at the equipment perimeter and leave the roof intact.

Dave Gaines, P.E.

Structural Project Engineer
HDR ONE COMPANY | Many Solutions
251 S. Lake Ave, Suite 1000
Pasadena, CA 91101
T: 626.584.4960
F: 626.584.1750
email: david.gaines@hdrinc.com

From: Larry Hauer [mailto:lhauer@live.com]
Sent: Friday, September 26, 2008 2:06 PM
To: seaint@seaint.org
Subject: RE: Doug. Fir Lumber Grades

Thanks to Gerald and Dave for their input. Yes, I've gone through this before with panelized roofs and know the problems. I gues my new question is: To use the values for "No.1 and Better", would the piece of lumber have to be stamped as such? As far as I know, back in the '70's there was no such grade, so I imagine lumber of that era couldn't be designed as such. Do lumber pieces used today have a stamp that actually says "No. 1 and Better", if that is what is called for in the wood specs, or is it something like a mixture of No. 1 and Sel. Str.?

Thanks again,

Larry

Subject: RE: Doug. Fir Lumber Grades
Date: Fri, 26 Sep 2008 12:53:26 -0500
From: David.Gaines@hdrinc.com
To: seaint@seaint.org

Larry,

For a panelized roof system the owners and contractors probably did not use "No.1 and Better" grade of purlins and subpurlins. You may need to get up on a lift and find a few grade stamps to confirm the contractor used what was shown on the plans. Another way to confirm (E) lumber grading is to compare the actual size and position of knots to the WWPA or WCLIB lumber grading rules, but that requires a bit more skill and research.

Gerard has made a good point. You won't be able to make the (E) 1970's joists or purlins calc out for new loads using today's allowable stress values. You'll have to reinforce them or replace them for new loads. Check the beams and girders too. You may find elevated stress levels. Good luck.

Dave Gaines, P.E.

(626) 410-3631 cell
(626) 794-4117 home
(626) 584-4960 office direct line

gainesengr@earthlink.net

From: Larry Hauer [mailto:lhauer@live.com]
Sent: Friday, September 26, 2008 6:57 AM
To: Struct. Eng. Assoc.
Subject: Doug. Fir Lumber Grades

I am checking an existing "panelized" roof system, (cira 1970's), for the addition of equipment and screening on the roof. Ever since, I believe, the '94 UBC there have been stress values for doug. fir 2x and 4x for "No. 1" and "No. 1 and Better", and I have never understood when it is appropriate to use the "No. 1 and Better" values. Can anyone shed some light on this?

Thanks in advance,

Larry Hauer, S.E.

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RE: Doug. Fir Lumber Grades

Subject: RE: Doug. Fir Lumber Grades
Date: Fri, 26 Sep 2008 12:53:26 -0500
From: David.Gaines@hdrinc.com
To: seaint@seaint.org

Larry,

Dave Gaines, P.E.

(626) 410-3631 cell
(626) 794-4117 home
(626) 584-4960 office direct line

gainesengr@earthlink.net

From: Larry Hauer [mailto:lhauer@live.com]
Sent: Friday, September 26, 2008 6:57 AM
To: Struct. Eng. Assoc.
Subject: Doug. Fir Lumber Grades

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Re: Tank settlement

Yes, flexible ej's are available in these sizes. Depends on type of pipe. Here is a link for DI pipe. There are others for other pipes.

http://www.ebaa.com/Products/Flex-Tend/

>>> Padmanabhan Rajendran <prajendran@ymail.com> 9/26/2008 2:45 PM >>>

I doubt if you will find flexible pipe in 30" pipe size for your application. As I wrote in my earlier email, you may have to plan on getting rid of the bulk of settlement during hydrotest.

I have used the flexible pipe solution with 8" pipe on a 200' dia tank. Due to various considerations and constraints the tank was supported on a 5' thick concrete mat. The schedule would not allow for extended hydrotest. Thus, a plan was required to make the tank work without hurting the pipes and the tank. The estimated settlement for the mat supported tank was 20". The flexible hose was custom designed. The first pipe support was adjustable in the sense that the height could be lowered as the tank was settling. The owner is supposed to have a program to monitor settlement and adjust the pipe support height as necessary. After the settlement is stabilized, the adjustable pipe support will be replaced with a hard one. Pipe stress analysis was performed, taking in to account tank settlement to assure that the pipe will not be adversely stressed and the resulting nozzle loads were checked against API 650 allowables (Appendix P).

If the pipe carries a chemical or a petroleum product, you need to be concerned with the compatibility of the material used in the flexible "pipes" with the liquid carried by the pipe. Please call the tech support in the following companies and discuss your requirements.

http://www.ptfe-hose.com/cpbf.htm
www.thermoflotulsa.com

Rajendran

--- On Fri, 9/26/08, Bhavin Shah <bhavin.design@gmail.com> wrote:

From: Bhavin Shah <bhavin.design@gmail.com>
Subject: Re: Tank settlement
To: seaint@seaint.org
Date: Friday, September 26, 2008, 4:28 PM

Thanks for the reply.

Can you give any reference for the flexible pipe coupling for 200mm of
the differential settlement ?

Thanks
Bhavin

On 9/24/08, Paul Blomberg <paul.blomberg@gmail.com> wrote:
>
> 150 mm (6") is a lot of settlement.  Talk to the Geotechnical
Engineer on
> methods to lower the settlement.  Alternatives include piles and different
> soil stabilization techniques.  You might also be able to place overburden
> on the site to allow the soil column to consolidate, then remove the
> overburden and place the tank.  This technique might take a long time to
be
> effective in clayey soils.
>
> Again, the  Geotechnical Engineer is the person to talk with.
>
> I have used a flex connection on the tank pipes when settlement was
expected
> over the long haul.  That pipe coupling accommodated the differential
> movement (200mm) without overstressing the pipe.  I don't know if they
are
> available for a 30" diameter pipe.
>
> Paul.
> Phoenix, AZ. USA
>
>
> On Wed, Sep 24, 2008 at 10:18 AM, Bhavin Shah
<bhavin.design@gmail.com>
> wrote:
> > This is regarding tank (15.0m diameter & 15.0m height) supported
on
> > ring wall (inside of the ring wall has been filled up with the
> > compacted sand.) resting on clayey soil.
> >
> > For design of the foundation total settlement at the tank has been
> > considered as 150mm (immediate settlement =15mm + consolidation
> > settlement = 135mm) as per the soil report.  However, as informed by
> > Piping engineer, for pipes (30" dia.)connected to the tank,
> > permissible differential settlement is only 50mm because of the
> > congested plant and as per the flexibility analysis.
> >
> > Kindly advice what measures may be taken so that tank foundation can
> > be designed for 150mm of the settlement.
> >
> > Thanks
> > Bhavin
> >
>

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RE: Hardy Frame Moment Frame

I would respectfully caution Mr Gallart that his post could be construed as borderline SPAM. My opinion is that the information is helpful, but perhaps should have been written differently … maybe with a comment that is specific to whatever was being discussed on moment frames, then direct the readers to Hardy’s product.

From: Garner, Robert [mailto:rgarner@moffattnichol.com]
Sent: Friday, September 26, 2008 11:09 AM
To: seaint@seaint.org
Subject: RE: Hardy Frame Moment Frame

Thank you, I will certainly check this out. I have tried to use the "patented" Side-Plate" system before, but Dave Houghton's licensing fees to use this system always "blew it out of the water". I will have to see what this costs through the Hardy boys.

Bob Garner, S.E.

From: Henry Gallart [mailto:HGallart@sideplate.com]
Sent: Friday, September 26, 2008 10:28 AM
To: seaint@seaint.org
Subject: Hardy Frame Moment Frame

Since the list is discussing the subject of Moment Frames I feel obligated to make you aware that Hardy Frames, Inc. offers a Pre-engineered, Prequalified, and Pre-fabricated Special Moment Frame (SMF) solution that is available now for light frame construction. The Hardy Frame® Moment Frame has been in full production for over two years and it uses the patented SidePlate Connection Technology which is evaluated as an SMF by ICC-ES and LA-City evaluation reports.

For more information on the Hardy Frame® Moment Frame, visit their website at www.hardyframe.com and/or call them at 800-754-3030 and request the latest catalog with over 300 standard frames.

Henry Gallart, S.E.

RE: Hardy Frame Moment Frame

Bob Garner, S.E.

From: Henry Gallart [mailto:HGallart@sideplate.com]
Sent: Friday, September 26, 2008 10:28 AM
To: seaint@seaint.org
Subject: Hardy Frame Moment Frame

Henry Gallart, S.E.

RE: Doug. Fir Lumber Grades

Larry,

Dave Gaines, P.E.

(626) 410-3631 cell
(626) 794-4117 home
(626) 584-4960 office direct line

gainesengr@earthlink.net

From: Larry Hauer [mailto:lhauer@live.com]
Sent: Friday, September 26, 2008 6:57 AM
To: Struct. Eng. Assoc.
Subject: Doug. Fir Lumber Grades

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Hardy Frame Moment Frame

Henry Gallart, S.E.

Re: Tank settlement

Thanks for the reply.

Can you give any reference for the flexible pipe coupling for 200mm of
the differential settlement ?

Thanks
Bhavin

On 9/24/08, Paul Blomberg <paul.blomberg@gmail.com> wrote:
>
> 150 mm (6") is a lot of settlement. Talk to the Geotechnical Engineer on
> methods to lower the settlement. Alternatives include piles and different
> soil stabilization techniques. You might also be able to place overburden
> on the site to allow the soil column to consolidate, then remove the
> overburden and place the tank. This technique might take a long time to be
> effective in clayey soils.
>
> Again, the Geotechnical Engineer is the person to talk with.
>
> I have used a flex connection on the tank pipes when settlement was expected
> over the long haul. That pipe coupling accommodated the differential
> movement (200mm) without overstressing the pipe. I don't know if they are
> available for a 30" diameter pipe.
>
> Paul.
> Phoenix, AZ. USA
>
>
> On Wed, Sep 24, 2008 at 10:18 AM, Bhavin Shah <bhavin.design@gmail.com>
> wrote:
> > This is regarding tank (15.0m diameter & 15.0m height) supported on
> > ring wall (inside of the ring wall has been filled up with the
> > compacted sand.) resting on clayey soil.
> >
> > For design of the foundation total settlement at the tank has been
> > considered as 150mm (immediate settlement =15mm + consolidation
> > settlement = 135mm) as per the soil report. However, as informed by
> > Piping engineer, for pipes (30" dia.)connected to the tank,
> > permissible differential settlement is only 50mm because of the
> > congested plant and as per the flexibility analysis.
> >
> > Kindly advice what measures may be taken so that tank foundation can
> > be designed for 150mm of the settlement.
> >
> > Thanks
> > Bhavin
> >
>

Doug. Fir Lumber Grades

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Gabe Bohm/TECHNIP-USA is out of the office.

I will be out of the office starting 09/25/2008 and will not return until
10/09/2008.

Bharat Patel is in charge of the department during my absence. For all
project matters, please contact the respective Lead Engineers.

Thursday, September 25, 2008

Re: Shear center of L-shape 'concrete' beam

The section in question is in no way thin. And the coords are pretty close to the centreline intersection.

On Fri, Sep 26, 2008 at 8:31 AM, sam2000 . (sam2000) <sam2000@cyber.net.pk> wrote:

Whatever ANSYS or any other software says, This is simple mechanics logic. The shear flow is along the length of any thin section. Thus the center has to be at the intersection of the two centerlines in an angle.

Syed A Masroor
Consulting Structural Engineer
Karachi, Pakistan

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--
Alexander Bausk
CAD manager, Structural engineer at
Nuclear Engineering&Research Lab
Dnipropetrovsk, Ukraine

RE: Shear center of L-shape 'concrete' beam

On Sep 25, 2008, at 3:04 PM, Alexander Bausk wrote:

> Well, here's a brute force solution. I've fed my Ansys/ED with your
> section and it says the shear center is at x=147.5mm, y=182.3mm.
> It's halfway from centroid to centerline intersection.

Whatever ANSYS or any other software says, This is simple mechanics logic. The shear flow is along the length of any thin section. Thus the center has to be at the intersection of the two centerlines in an angle.

Syed A Masroor
Consulting Structural Engineer
Karachi, Pakistan

Re: Tank settlement

No foundation may design to take 150mm settlement.

- it is better to make flexible joints
1- cut the pipes before the tank as cantilever support to the tank
2- connect the two pieces of pipes by flexible winding rubber.
3- fastening the rubber with the pipes by metal rings .

Dr- hamida
Syria

----- Original Message -----
From: "Bhavin Shah" <bhavin.design@gmail.com>
To: <seaint@seaint.org>
Sent: Wednesday, September 24, 2008 10:18 AM
Subject: Tank settlement

> This is regarding tank (15.0m diameter & 15.0m height) supported on
> ring wall (inside of the ring wall has been filled up with the
> compacted sand.) resting on clayey soil.
>
> For design of the foundation total settlement at the tank has been
> considered as 150mm (immediate settlement =15mm + consolidation
> settlement = 135mm) as per the soil report. However, as informed by
> Piping engineer, for pipes (30" dia.)connected to the tank,
> permissible differential settlement is only 50mm because of the
> congested plant and as per the flexibility analysis.
>
> Kindly advice what measures may be taken so that tank foundation can
> be designed for 150mm of the settlement.
>
> Thanks
> Bhavin
>
> ******* ****** ******* ******** ******* ******* ******* ***
> * Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> * This email was sent to you via Structural Engineers
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>

Re: Tank settlement

One of the things you may recommend is:

Install sand wick drains (vertical) in the soil and fill the tank water in stages. At each stage of loading, wait for the settlement to occur until the rate of settlement has dropped to an "acceptable" limit. This method would accelerate the settlement of the stratum. After completing this procedure connect the piping to the tank. You will have to consult with the geotechnical engineer to determine the size, depth and spacing of the wick drains and, the rate of hydrostatic loading of the tank.

Rajendran

--- On Wed, 9/24/08, Bhavin Shah <bhavin.design@gmail.com> wrote:

From: Bhavin Shah <bhavin.design@gmail.com>
Subject: Tank settlement
To: "seaint@seaint.org" <seaint@seaint.org>
Date: Wednesday, September 24, 2008, 5:18 PM

This is regarding tank (15.0m diameter & 15.0m height) supported on
ring wall (inside of the ring wall has been filled up with the
compacted sand.) resting on clayey soil.

For design of the foundation total settlement at the tank has been
considered as 150mm (immediate settlement =15mm + consolidation
settlement = 135mm) as per the soil report. However, as informed by
Piping engineer, for pipes (30" dia.)connected to the tank,
permissible differential settlement is only 50mm because of the
congested plant and as per the flexibility analysis.

Kindly advice what measures may be taken so that tank foundation can
be  designed for 150mm of the settlement.

Thanks
Bhavin

******* ****** ******* ******** ******* ******* ******* ***
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*   This email was sent to you via Structural Engineers 
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Re: Question on independent structurally

1- the regular definition for independent structural mean no any connection to other structural or existing building .

and shall deflect free and no connection from the foundations and up to the roof.

2- since the differential settlement will be no problem the best solution complete separate foundations design

the existing building as a property line.

Dr-hamida

Syria

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

From: J.M. Cohen

To: seaint@seaint.org

Sent: Thursday, September 25, 2008 11:42 AM

Subject: Question on "independent structurally" w.r.t. foundations

I am seeking a publishd definition in a code, specification, or possibly in design guidelines that defines "structural independent" with respect to foundations.

We need to design a new addition to an existing building that must be "structurally independent" from the existing building.

We know what to do above the foundation.

What about the foundation? Must the foundations be physically separate with non-overlapping pressure bulbs? Or, can the new foundation (say, footings) have rebar doweled into then grouted, and cast against the existing foundation (again, say, footings) *if* the geotechnical engineer doesn't think that differential settlement will be a problem?

Thank you!

S.T.

Re: Shear center of L-shape 'concrete' beam

On Sep 25, 2008, at 3:04 PM, Alexander Bausk wrote:

> Well, here's a brute force solution. I've fed my Ansys/ED with your
> section and it says the shear center is at x=147.5mm, y=182.3mm.
> It's halfway from centroid to centerline intersection.
I think I'll stick to my guns. First, it isn't my section. In fact I
don't know what the section in the first post actually is. Hence the
little himily on symmetry.

Second, I've been using ANSYS for 30 years. I've found a few bugs and
it sure hasn't kept me from making mistakes but violate first
principles? Never.

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/members/chrisw/

Re: Shear center of L-shape 'concrete' beam

Wontae, Christopher,

Well, here's a brute force solution. I've fed my Ansys/ED with your section and it says the shear center is at x=147.5mm, y=182.3mm. It's halfway from centroid to centerline intersection.

On Thu, Sep 25, 2008 at 7:08 PM, Christopher Wright <chrisw@skypoint.com> wrote:

On Sep 25, 2008, at 7:49 AM, Alexander Bausk wrote:

In most general case, the flexural centre coordinates are described by a rather complex integral equation, given in Martin Sadd's book on elasticity of 2005.
I'll write more if I find a more usable equation.

You're overcomplicating the problem. _Mechanics of Materials_ by Popov (2nd ed 1952) on page 145 has a 3 page explanation with examples, including an angle. Mostly words, many pictures a few formulas, no integral equations. First principles--you gotta love 'em.

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/members/chrisw/

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--
Alexander Bausk
CAD manager, Structural engineer at
Nuclear Engineering&Research Lab
Dnipropetrovsk, Ukraine

RE: Question on "independent structurally" w.r.t. foundations

You say "We need to design a new addition to an existing building that must be 'structural independent' from the existing building". Were does this requirement come from? Project/owner requirements? A code provision? A suggestion from someone?

I ask because if it is a project/owner requirement, then I would ask them how they define "structurally independent". If it is a code requirement, then you would need to look to see if the code defines it and if not, then use your best interpretation.

Personally, I would define it as a seperate foundation system that does not adversely effect the performance of the existing foundation system (i.e. does not impose new load on the existing foundation and does not impose additional loading issues to the soil that supports existing foundation such that additional settlement or overbearing pressures occur).

Regards,

Scott

Adrian, MI

-----Original Message-----
From: J.M. Cohen [mailto:sammie2810@yahoo.com]
Sent: Thursday, September 25, 2008 2:42 PM
To: seaint@seaint.org
Subject: Question on "independent structurally" w.r.t. foundations

I am seeking a publishd definition in a code, specification, or possibly in design guidelines that defines "structural independent" with respect to foundations.

We need to design a new addition to an existing building that must be "structurally independent" from the existing building.

We know what to do above the foundation.

What about the foundation? Must the foundations be physically separate with non-overlapping pressure bulbs? Or, can the new foundation (say, footings) have rebar doweled into then grouted, and cast against the existing foundation (again, say, footings) *if* the geotechnical engineer doesn't think that differential settlement will be a problem?

Thank you!

S.T.

Question on "independent structurally" w.r.t. foundations

I am seeking a publishd definition in a code, specification, or possibly in design guidelines that defines "structural independent" with respect to foundations.

We need to design a new addition to an existing building that must be "structurally independent" from the existing building.

We know what to do above the foundation.

What about the foundation? Must the foundations be physically separate with non-overlapping pressure bulbs? Or, can the new foundation (say, footings) have rebar doweled into then grouted, and cast against the existing foundation (again, say, footings) *if* the geotechnical engineer doesn't think that differential settlement will be a problem?

Thank you!

S.T.

Re: Shear center of L-shape 'concrete' beam

On Sep 25, 2008, at 7:49 AM, Alexander Bausk wrote:

> In most general case, the flexural centre coordinates are described
> by a rather complex integral equation, given in Martin Sadd's book
> on elasticity of 2005.
> I'll write more if I find a more usable equation.
You're overcomplicating the problem. _Mechanics of Materials_ by
Popov (2nd ed 1952) on page 145 has a 3 page explanation with
examples, including an angle. Mostly words, many pictures a few
formulas, no integral equations. First principles--you gotta love 'em.

Re: Shear center of L-shape 'concrete' beam

On Sep 25, 2008, at 7:23 AM, Wontae Kim wrote:

> I have more questions to your answers posted.
> Do you think that shear center is on 'the centerline of a vertical
> leg'?
If you're talking about an angle, the shear center is at the
intersection of both legs--the heel of the angle. If you're talking
about a section with a single axis of symmetry, the shear center is
on that axis, but it's actual location depends on the details of the
section. A standard channel for example has the shear center at half-
depth and on the opposite side of the web from the flanges. If you
have a doubly symmetric section the shear center coincides with the
section centroid. The shear center of any wide flange or standard I-
section is at the half-depth and half-width. (I think I'm repeating
myself)

The short answer to your question is 'not necessarily.' The real
answer is, 'If what you call the 'vertical leg' is an axis of
symmetry, the shear center is on the vertical leg. If the vertical
leg isn't an axis of symmetry, the shear center is elsewhere.

> So, is shear center the intersection of vertical and horizontal
> centerline rather than center of mass?
Only for a doubly symmetric section. Try to use the right
terminology. 'Center of mass' is used when you're talking about
weights and balances; The term 'centroid' is used when you're
referring to cross-section geometry. You don't want to get these
terms confused. You might also want to go back and read up on the
definition of shear center in your structural design book.

Steel stilts - Wood house

I am considering a seismic upgrade for an existing two story wood house
that stands on 14 foot steel tube columns concentrically brace. The
connections are butt welded to the columns.

These brace connections are not allowed in this seismic zone for new
construction.

The two story wood framing can be analyzed as though its base is at the
top of the steel braced frame.

Is there any concept or code that would prevent me using the flexibility
of the wood to isolate the braced frame from the otherwise high shear
loads due to its rigidity?

I am considering the Nonlinear Static Procedure (NSP) in the ASCE 41-06
"Seismic Rehabilitation of Existing Buildings". My thought is that there
is virtually no weight laterally and rigidly attached to the rigid steel
frame. The horizontal and vertical wood diaphragms will absorb energy
and possibly reduce seismic forces that would otherwise buckle the
braces and fail the connections. The connections then might not require
to be cut back for new steel gusset plates that would allow some yielding.

Otherwise I might consider this a voluntary upgrade and reduce the
criteria to a level that the owner can afford.

David Merrick, SE

Re: Shear center of L-shape 'concrete' beam

Wontae,

While those suggesting the legs intersection seem to be correct, I have looked through the available literature and found formulas only for sections with one axis of symmetry like channel beam. Now the issue seems interesting to me, too.

In most general case, the flexural centre coordinates are described by a rather complex integral equation, given in Martin Sadd's book on elasticity of 2005.
I'll write more if I find a more usable equation.

Regards,
Alex.

On 9/25/08, Wontae Kim <kimwontae@email.com> wrote:

Christopher W., Jordan T. & David T.

Thanks for your responses!

I have more questions to your answers posted.
Do you think that shear center is on 'the centerline of a vertical leg'?

So, is shear center the intersection of vertical and horizontal centerline rather than center of mass?

I am looking forward to your more inputs.

Thanks!

--
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--
Alexander Bausk
CAD manager, Structural engineer at
Nuclear Engineering&Research Lab
Dnipropetrovsk, Ukraine

Re: Shear center of L-shape 'concrete' beam

Christopher W., Jordan T. & David T.

Thanks for your responses!

I have more questions to your answers posted.

Do you think that shear center is on 'the centerline of a vertical leg'?

So, is shear center the intersection of vertical and horizontal centerline rather than center of mass?

I am looking forward to your more inputs.

Thanks!

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Get a Free Account at www.mail.com!

Wednesday, September 24, 2008

RE: DL weight vs Ordinary/Special Moment Frames

Ben,

Thank you very much for the reply. Much appreciated.

Joe Grill

From: Yousefi, Ben [mailto:Ben.Yousefi@mountainview.gov]
Sent: Wednesday, September 24, 2008 4:34 PM
To: seaint@seaint.org
Subject: RE: DL weight vs Ordinary/Special Moment Frames

You are correct on all your assessments. Reducing the roof dead load will resolve the issue.

Ben Yousefi, SE, CBO
Chief Building Official
City of Mountain View, CA
(650) 526-7007
ben.yousefi@mountainview.gov

From: Joseph R. Grill [mailto:jrgrill@cableone.net]
Sent: Wednesday, September 24, 2008 10:30 AM
To: seaint@seaint.org
Subject: DL weight vs Ordinary/Special Moment Frames

I am looking at a project located in a SDC D. It is a custom home, with (at this point) exposed steel frames so appearance is critical to the client. At this point the roofing is a tile roof which is running the dead load up to about 27 psf. The architect also has some very heavy rock veneered walls with a DL >20 psf (closer to 100psf with veneer on two sides). The structure is less than 35 ft in height and only one story.

ASCE 7-05 Section 12.2.5.6 would suggest (in my understanding) that an Ordinary Moment Frame would not be acceptable due to the weight of the roof DL. The weight of the roof tributary to the frames is greater than 20 psf. It appears that even though the veneered walls are greater than 20 psf it is not a problem since the heavy walls are less than 35’ in height (or at least the heavy walls are not over 35 ft above the base).

ASCE 7-05 Section 12.2.5.7 seems to push the frame design into the Intermediate or Special Frames. Although it allows the heavier roof for the Ordinary Frame, it seems to limit the weight of the walls to 20 psf not matter the height.

My first question is, is my understanding of these two sections correct?

My second question is, if the architect changes the roofing to a lighter shingle which will reduce the roof DL to something below 20 psf can I design the frames for an Ordinary Moment Frame even with the heavy veneered walls?

Thank you all for the help.

Joe Grill

Torsional moment transferred to the slab from the torsional beam

Hi,

I read an interesting paper, which says:

"a portion of the unbalanced moment is transferred to the column by a vertical balancing couple

in the form of vertical shear acting at the face of the column, while another portion is transferred

by a horizontal force couple (flexure) occurring within the slab depth.

ACI318, Chapter 11, indicates that approximately 60% of the unbalanced moment is transferred

by flexure, with balance transferred by shear..."

[page 10.21, Chapter 10, Concrete Construction Engineering Handbook, 2nd Ed. Edited by Dr. Nawy.]

I am more interested in shear-moment transfer mechanism between slab and torsional beam.

If slab is cast monolithically to edge beam, bending moment applied on slab will cause torsion on edge beam.

In this case, doesn't slab contribute torsional resistance of edge beam at all?

What about interior beam with unbalanced moment?

If anybody knows a paper or book regarding this topic, please let me know.

Thanks!

Wontae

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RE: wood ledger to concrete

Tim,

To the Australian code (AS1720) for perpendicular to the grain and parallel to the grain, Hankinson’s formula is not required: if used it simply reproduces the tabulated values. Its use is to adjust the tabulated values for angles other than 90 and 0 degrees.

For the ledger I believe the bolt forces are perpendicular to the grain. But our loading code (AS1170.0) has minimum lateral resistance requirements for connections, if not otherwise controlled by wind load or earthquake loading. There is thus also a force parallel to the grain, to be considered.

Regards

Conrad Harrison

B.Tech (mfg & mech), MIIE, gradTIEAust

mailto:sch.tectonic@bigpond.com

Adelaide

South Australia

From: Pinyon Engineering [mailto:timrudolph@att.net]
Sent: Thursday, 25 September 2008 07:01
To: seaint@seaint.org
Subject: wood ledger to concrete

I am designing an wood deck ledger with siginficant snow loading. In the old days I would have used Enercalc 5.8 and accept the black box answer it gave me. but now in this enlightend age - I question everything. the ledger design is a beam spanning between the bolts - calc the beam, look at the NDS for th bolt values - got it so far- Looking at Enercal 5.8 ledger design it uses the Hankison formula and checks diagonal force and resulting diagonal wood stress.

I haven't found a similar problem using the hankison formula in this way.

what is the correct way to calculate a wood ledger attached to concrete?

I am in digest mode but will check the site index often

Tim Rudolph

Pinyon ENgineering

RE: DL weight vs Ordinary/Special Moment Frames

You are correct on all your assessments. Reducing the roof dead load will resolve the issue.

Ben Yousefi, SE, CBO
Chief Building Official
City of Mountain View, CA
(650) 526-7007
ben.yousefi@mountainview.gov

From: Joseph R. Grill [mailto:jrgrill@cableone.net]
Sent: Wednesday, September 24, 2008 10:30 AM
To: seaint@seaint.org
Subject: DL weight vs Ordinary/Special Moment Frames

My first question is, is my understanding of these two sections correct?

Thank you all for the help.

Joe Grill

wood ledger to concrete

I haven't found a similar problem using the hankison formula in this way.

what is the correct way to calculate a wood ledger attached to concrete?

I am in digest mode but will check the site index often

Tim Rudolph

Pinyon ENgineering

RE: Tank settlement

I agree with Paul. I too have used a flex connection.

Another option is to do a different type of foundation. You could do a deep foundation system (helical piers, caissons, or driven piles) to significantly reduce settlement, or you could do a soil stabilization effort after the fact. You could do a urethane foam injection to densify the soil and negate the initial settlements. I have heard of this procedure working in the past though have never experienced it. I have heard the success stories (of course).

Dave Maynard

Gillette, WY

From: Paul Blomberg [mailto:paul.blomberg@gmail.com]
Sent: Wednesday, September 24, 2008 11:46 AM
To: seaint@seaint.org
Subject: Re: Tank settlement

150 mm (6") is a lot of settlement. Talk to the Geotechnical Engineer on methods to lower the settlement. Alternatives include piles and different soil stabilization techniques. You might also be able to place overburden on the site to allow the soil column to consolidate, then remove the overburden and place the tank. This technique might take a long time to be effective in clayey soils.

Again, the Geotechnical Engineer is the person to talk with.

I have used a flex connection on the tank pipes when settlement was expected over the long haul. That pipe coupling accommodated the differential movement (200mm) without overstressing the pipe. I don't know if they are available for a 30" diameter pipe.

Paul.

Phoenix, AZ. USA

On Wed, Sep 24, 2008 at 10:18 AM, Bhavin Shah <bhavin.design@gmail.com> wrote:

This is regarding tank (15.0m diameter & 15.0m height) supported on
ring wall (inside of the ring wall has been filled up with the
compacted sand.) resting on clayey soil.

For design of the foundation total settlement at the tank has been
considered as 150mm (immediate settlement =15mm + consolidation
settlement = 135mm) as per the soil report. However, as informed by
Piping engineer, for pipes (30" dia.)connected to the tank,
permissible differential settlement is only 50mm because of the
congested plant and as per the flexibility analysis.

Kindly advice what measures may be taken so that tank foundation can
be designed for 150mm of the settlement.

Thanks
Bhavin

Re: Tank settlement

As Mr. Paul said 150 mm is quite a lot. It could affect the pipe connections. Similar situations we never experienced more than 15 mm settlement in India. If the soil inside the ring wall is compacted in layers and on the top of the soil filling if you provide a compacted gravel layer settlement can be controlled to the minimum.

Ravinath.M

Kuwait

On Wed, Sep 24, 2008 at 8:45 PM, Paul Blomberg <paul.blomberg@gmail.com> wrote:

150 mm (6") is a lot of settlement. Talk to the Geotechnical Engineer on methods to lower the settlement. Alternatives include piles and different soil stabilization techniques. You might also be able to place overburden on the site to allow the soil column to consolidate, then remove the overburden and place the tank. This technique might take a long time to be effective in clayey soils.

Again, the Geotechnical Engineer is the person to talk with.

I have used a flex connection on the tank pipes when settlement was expected over the long haul. That pipe coupling accommodated the differential movement (200mm) without overstressing the pipe. I don't know if they are available for a 30" diameter pipe.

Paul.

Phoenix, AZ. USA

On Wed, Sep 24, 2008 at 10:18 AM, Bhavin Shah <bhavin.design@gmail.com> wrote:

This is regarding tank (15.0m diameter & 15.0m height) supported on
ring wall (inside of the ring wall has been filled up with the
compacted sand.) resting on clayey soil.

For design of the foundation total settlement at the tank has been
considered as 150mm (immediate settlement =15mm + consolidation
settlement = 135mm) as per the soil report. However, as informed by
Piping engineer, for pipes (30" dia.)connected to the tank,
permissible differential settlement is only 50mm because of the
congested plant and as per the flexibility analysis.

Kindly advice what measures may be taken so that tank foundation can
be designed for 150mm of the settlement.

Thanks
Bhavin

--
Thanks & Regards.
Ravinath Manhacheri

രവിനാ‍ഥ് മഞ്ഞാചേരി