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RE: Manhole cap

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First, I would like to thank Tim Rudolph for faxing me some information from
Roarks.

Daryl,
Yes, you are correct in the the manhole caps can be purchased, and that a 2
ft. thick slab could be used.

In my situation there are some restraints due to the site that will not
allow 24" of concrete thickness at the cap at minimum cost, however, as I
said in my original post, I had 9" to work with for slab thickness.
Actually, I guess I said the slab had been designated as 9", but that is
what I was given to work with.  I was able to squeak 12" for a portion of
the top slab due to how culverts are entering the manhole. 

Thanks to all those that replied.  And again thanks to Tim Rudolph.

Joe 

Joseph R. Grill, P.E. (Structural)
Shephard - Wesnitzer, Inc.
Civil Engineering and Surveying
P.O. Box 3924
Sedona, AZ  86340
PHONE (928) 282-1061
FAX (928) 282-2058
jgrill(--nospam--at)swiaz.com
 


-----Original Message-----
From: Daryl Richardson [mailto:h.d.richardson(--nospam--at)shaw.ca] 
Sent: Saturday, July 22, 2006 9:37 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Manhole cap

Fellows,

        I may be wrong here; but it seems to me that you can buy cast iron 
or cast steel manhole covers complete with supporting rim as a stock item. 
It follows that you can cast a concrete "plate" top slab that is two feet 
(610 mm) thick for only a couple of hundred dollars worth of concrete.

        It seems to me that it is a waste of valuable engineering time to do

anything more than the most simple analysis and over design the thing.  I 
would be inclined to assume a 12" wide beam on each side of the hole and 
design top and bottom steel for a five foot span with a point load at 
midspan.  I would then wrap the bars with ties designed to resist 
shear/torsion as calculated by some equally simplified procedure.  I would 
also use a similar pattern of steel rotated 45 degrees to fill in the 
"corners" around the round hole.

        My above comments are intended for a "one of" design.  if this is 
for a factory standard where many thousands will be mass produced then a 
much more sophisticated approach is required.

        Respectfully submitted.

Regards,

H. Daryl Richardson

----- Original Message ----- 
From: "Gary L. Hodgson and Assoc." <ghodgson(--nospam--at)bellnet.ca>
To: <seaint(--nospam--at)seaint.org>
Sent: Saturday, July 22, 2006 6:33 AM
Subject: Re: Manhole cap


> Joe,
> I have Roark's book but there are no examples of square or rectangular 
> plates with holes in them. The closest is circular plates which are used a

> lot for washers, springs,trunnions, etc. You might consider a circle which

> would cover or slightly overlap your square. If you want to try one, I can

> fax or e-mail you the appropriate case--let me know. Also, there is a 
> company called Arcon (Arkon?) Engineering which sells various software 
> solutions at reasonable prices. One of them is the round plate with a 
> round hole in the centre, with various loads. I didn't buy that one but 
> looked at the demo. The three I bought were $40 each, several years ago.
> Gary
>
> Joseph R. Grill wrote:
>> is there anyone out there with a Roarks (spelling?) that might cover a 
>> square plate with a hole in the center?
>> Joe
>>
>>     ----- Original Message -----
>>     *From:* Joe Grill <mailto:jgrill(--nospam--at)swiaz.com>
>>     *To:* seaint(--nospam--at)seaint.org <mailto:seaint(--nospam--at)seaint.org>
>>     *Sent:* Thursday, July 20, 2006 3:34 PM
>>     *Subject:* Manhole cap
>>
>>     O.K. Guys and Gals,
>>
>>     Please be patient while I try to explain. And please understand
>>     that I am not a bridge engineer and no bridge engineers in the
>>     office. I have been stuck with this little problem.
>>
>>     I have to do a design for a cast-in-place manhole. The manhole
>>     plan dimensions are 5 ft square (clear dimension at the interior).
>>     I have a cast-in-place top slab which has a 24" manhole frame and
>>     lid centered in the slab. I am assuming that I have to use the
>>     AASHTO loading and, where I am confused, the AASHTO load factors.
>>     I have a copy of the 16^th edition of AASHTO. The slab, so far,
>>     has been designated as 9" thick, with a "d" depth of 7".
>>
>>     I think I have only to look at AASHTO "Load Factor Design Group
>>     IA" which has a gamma=1.3, beta d=1.0 (for flexural members) and
>>     an (L+I)n=2.2. Go ahead and tell me if I am wrong with this so far.
>>
>>     Since the slab span (assuming one-way because of the 24" hole in
>>     the middle) is about 5 ft. I have calculated an impact factor of 1.3.
>>
>>     Here is where I really start getting confused.
>>
>>     Is the factored live load 1.3x2.2(16x1.3)=59.5kips (using a 16kip
>>     wheel load, HS20-44)? Wow, that's 3.7 times the service load. I
>>     get a wheel imprint of 8"x20".
>>
>>     With this information, I have placed the wheel imprint at a corner
>>     of the slab ("d" dist. From the two faces). For beam shear I get a
>>     "b" length of 20+8+(3x7")=49" giving me an allowable shear
>>     phi*Vn=32.5 kips using 4000 psi concrete. I think shear is a
>>     problem, but my boss ( a civil guy) will say that he has seen many
>>     manhole caps like this out there.
>>
>>     This is just the shear question of the problem. The flexural
>>     questions I have yet to get to. Basically compounded due to the
>>     hole in the center.
>>
>>     Hope this all makes sense.
>>
>>     Thanks,
>>
>>     Joe
>>
>>     Joseph R. Grill, P.E. (Structural)
>>
>>     Shephard - Wesnitzer, Inc.
>>
>>     Civil Engineering and Surveying
>>
>>     P.O. Box 3924
>>
>>     Sedona, AZ 86340
>>
>>     PHONE (928) 282-1061
>>
>>     FAX (928) 282-2058
>>
>>     *jgrill(--nospam--at)swiaz.com*
>>
>
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