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Re: Load combination 7. .6D+W+H

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One thing I have also checked is that the modulus of rupture of the
slab area resisting the uplift is not exceeded. I discount the slab
past any control joints as being effective.

Will

On Wed, Nov 5, 2008 at 11:26 AM, Harold Sprague <spraguehope(--nospam--at)hotmail.com> wrote:
> Because PEMB's have little DL, uplift resistance can be a problem.  Uplift
> resistance in the PEMB world is resisted by the footings with:
> 1.  The dead load of the footing
> 2.  The dead load of the soil and slab above the footing
> 3.  The shear resistance offered by the slab and footing
>
> In this manner you can have additional uplift resistance by spreading the
> uplift load out over a greater area predicated on the shear strength of the
> soil and slab.  Additional reinforcing can provide more shear resistance in
> the slab.  If more resistance is required, the foundation can be lowered to
> engage more soil.
>
> Regards, Harold Sprague
>
>
>
>> Subject: RE: Load combination 7. .6D+W+H
>> Date: Tue, 4 Nov 2008 09:44:39 -0800
>> From: YI(--nospam--at)summit-sr.com
>> To: seaint(--nospam--at)seaint.org
>>
>> I had a project recently where we designed the foundation for a metal
>> building. I used 0.6D load combination while keeping a 1.5 uplift
>> ratio. It was a big footing, and I wasn't quite convinced if this was
>> necessary. But I couldn't find any language about this one way or
>> another, in IBC / ASCE7.
>>
>>
>> YI YANG, S.E.
>>
>>
>> Do you really need to print this email?
>> -----Original Message-----
>> From: William Haynes [mailto:gtg740p(--nospam--at)gmail.com]
>> Sent: Tuesday, November 04, 2008 9:02 AM
>> To: seaint(--nospam--at)seaint.org
>> Subject: Re: Load combination 7. .6D+W+H
>>
>> The combination is for stability too. You use the combination 0.6D+W+H
>> and that is it. You don't have to subsequently use a 1.5 safety factor
>> or any additional dead load factors for stability after you have applied
>> the 0.6D+W+H load combination (it's not cumulative).
>>
>> Footing weights and retaining wall dead loads must also be multiplied by
>> 0.6 when using this combination, it's not just for concrete columns.
>> This combination applies to uplift and overturning. Dividing
>> 1/0.6=1.67 so the traditional 1.5 safety factor is more than accounted
>> for already.
>>
>> Will
>>
>>
>> On Tue, Nov 4, 2008 at 11:35 AM, Joseph Eribarne
>> <jeribarnese(--nospam--at)bak.rr.com> wrote:
>> > Sirs:
>> >
>> >
>> >
>> > We have some confusion on the application of ASCE7 ASD load
>> > combination 7, .6D+W+H.
>> >
>> >
>> >
>> > ASCE 7 Section 2.1 indicates that the load combinations shall be used
>> > for "a particular construction material throughout the structure." I
>> > understand that the .6D allows for the sometimes overestimating of the
>>
>> > dead load and that concrete columns, for example, should be
>> > proportioned for this load case as the reduced dead load sometimes
>> leads to the governing condition.
>> > Are these load combinations for the design of the materials only or
>> > are they also to be used for the overall stability of the structure
>> itself.
>> >
>> >
>> >
>> > Two quick examples:
>> >
>> > 1) We do many light framed steel structures and also foundation
>> design
>> > for prefabricated metal buildings. If, for example, the resulting
>> > .6D+W load combination results in a 6000# uplift, how much concrete
>> > footing weight (along with slab and soil overburden) must be placed.
>> > Is it 6000# or must it be 10000#. The latter will result in
>> > inordinately large footing on a very small building using a factor of
>> > .6D on a material weight that is known quite accurately with very
>> little chance of over estimating its weight.
>> > Anchor bolts and any attachments of course, should be designed for the
>>
>> > full .6D+W load.
>> >
>> > 2) Retaining walls: Must the retaining wall stability also be
>> designed
>> > for this case. Should there be a case where the unit weight of the
>> > wall, footing and soil is reduced 40% by using a .60 factor to resist
>> > overturning. This would even be more magnified where the retaining
>> > wall extends above grade and receives wind load (or is all of this
>> > ignored and the traditional FS of 1.5 is used for sliding and
>> > overturning? Or is it
>> > cumulative?) Or even just a free standing 8' high block wall fence
>> > receiving wind load. Should overturning be checked by reducing the
>> > unit weights of the wall? When using a program such as Retain Pro,
>> > one should redefine the unit weight of the materials to .6 of their
>> actual values?
>> >
>> > Again, I am asking about the overall stability of the structure, not
>> > the design of a particular element.
>> >
>> > Thanks for reading this and for your thoughts in advance.
>> >
>> >
>> >
>> > Joe Eribarne
>>
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