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## Re: [TowerTalk] Dimensions of a tower concrete base

 To: Bert Almemo Re: [TowerTalk] Dimensions of a tower concrete base n8de@thepoint.net Tue, 02 Sep 2008 18:53:09 -0400 mailto:towertalk@contesting.com>
 ```Seems no one quoted the K7LXC Directive: DO WHAT THE TOWER MANUFACTURER SAYS. Don N8DE Quoting Bert Almemo : > > > Hi guys, > > Thanks for all responses, comments and suggestions regarding the dimensions > of a concrete base for a tower or other support structure. > > It seems almost everyone wants to elaborate on the issue and also wants to > put my question into different scenarios. Again, not being a structural > engineer, isn't there a general rule as to what design provides the best > support for a free standing tower or similar structure regardless of other > circumstances? > > I was hoping to get some indication from the experts on TT which way to go > as I'm not spending thousands of dollars to use the services of a structural > engineer. I just want an opinion from you experienced guys. It's only a 55ft > free standing tower with a medium sized tri-bander on top. So far I'm more > confused than when I started this thread. Thanks. > > 73 Bert, VE3OBU > > > > > > -----Original Message----- > From: towertalk-bounces@contesting.com > [mailto:towertalk-bounces@contesting.com] On Behalf Of kr7x1@verizon.net > Sent: Tuesday, September 02, 2008 12:24 PM > To: Al Williams > Cc: towertalk@contesting.com > Subject: Re: [TowerTalk] Dimensions of a tower concrete base > > Hi Al: > > In the case of a cantilever (free standing) structure say like a ham tower, > the wind or seismic force developed is horizontal (lateral). This force > creates a cantilever moment at the base equal to w*L^2 / 2 where w is the > lateral force per unit length and L is the height of the structure. This is > the cantilever moment at the base. The lateral load also has to be resisted > by the base along with the moment. The base horizontal (lateral) reaction is > w*L. Then the weight of the structure also creates a force to be resisted by > the base which is the weight of the appurtances (antennas, rotators, > feedlines, the foundation weight, north facing fake owl, etc). > > Thus the base (foundation) needs to be designed to resist the vertical load > of the structure, the lateral load and the cantilever moment due to the > horizontal wind or seismic enviromental loading. > > In a nut shell, the foundation has to resist being pushed into the ground, > moved through the ground and rotated in the ground all at the same time. > > Foundation strength or resistance to the applied loading is totally a > function of the soil characteristics at the location being considered. > This is the big variable. The IBC has a table that gives conservative > generalized values to use for these soil characteristics if a geotechnical > analysis and report is not available for the specific location. > > Regards > Lonberg Design Group, Ltd. > H.S. Lonberg, P.E.,S.E. > President > > > > On Tue, Sep 2, 2008 at 8:18 AM, Al Williams wrote: > >> Please explain the difference between "lateral force" and "the moment >> inherent in this type of structure" >> and how they effect on tahe strength of the foundation. >> >> k7puc >> >> >> ----- Original Message ----- From: "Hank Lonberg" >> To: "'Bert Almemo'" ; >> Sent: Monday, September 01, 2008 9:14 PM >> Subject: Re: [TowerTalk] Dimensions of a tower concrete base >> >> >>> Bert: >>> >>> The best answer to your generalized questions is; it depends. >>> >>> Depends if the foundation is supporting only vertical load as in a >>> guyed structure. >>> Depends if the foundation is to support a cantilevered or free >>> standing structure with both lateral force, vertical force and the >>> moment inherent in this type of structure. >>> Depends if the designer is trying to utilize a spread footing type of >>> foundation. >>> Depends if the designer is trying to utilize a post type of >>> foundation. >>> Depends heavily on the soil's characteristics and strength that you >>> are trying to utilize. >>> >>> So you see, your question does not have a closed form of solution, >>> but depends on what you are trying to accomplish and what type of >>> loading the structure you are trying to support will impart to the >>> foundation. >>> >>> A case can be made for either the shallow spread footing type of >>> foundation or the smaller footprint deeper foundation. The trick is >>> to size them adequately for the loading condition versus the soil >>> conditions expected. >>> >>> Gut level, the amount of concrete for either design is most likely >>> similar. >>> >>> Regards >>> Lonberg Design Group, Ltd. >>> H.S. Lonberg, P.E.,S.E. >>> President >>> >>> -----Original Message----- >>> From: towertalk-bounces@contesting.com >>> [mailto:towertalk-bounces@contesting.com] On Behalf Of Bert Almemo >>> Sent: Monday, September 01, 2008 8:51 PM >>> To: 'Bob Maser'; towertalk@contesting.com >>> Subject: Re: [TowerTalk] Dimensions of a tower concrete base >>> >>> Hi Bob, >>> >>> Thanks for your reply. Yes, I think you missed the point. >>> Sorry! I'm talking >>> about the concept in principle not if the total weight is exactly the >>> same. >>> According to the experts, the weight of the base has very little to >>> do with the support of the structure. The weight only makes up for >>> about 10% of the forces needed to support a given structure. 90% or >>> so comes from the soil/dirt/sand enclosing the base. I'm not an >>> expert in structural engineering and can't probably explain this >>> properly. >>> >>> Anyway, back to my question - in principle is there a difference in >>> force/strength to support a structure if the base is deeeper or >>> shallower having basically the same weight and volume? >>> >>> 73 Bert, VE3OBU >>> >>> >>> >>> >>> >>> -----Original Message----- >>> From: Bob Maser [mailto:bmaser@tampabay.rr.com] >>> Sent: Monday, September 01, 2008 8:49 PM >>> To: Bert Almemo >>> Subject: Re: [TowerTalk] Dimensions of a tower concrete base >>> >>> The last time I looked, 3x3x6=54 and 4x4x4=64 so 64 will weigh more >>> than 54 will. Am I missing something? >>> >>> Bob W6TR >>> ----- Original Message ----- >>> From: "Bert Almemo" >>> To: >>> Sent: Monday, September 01, 2008 2:35 PM >>> Subject: [TowerTalk] Dimensions of a tower concrete base >>> >>> >>>> In general, is it better to go deep than wide when digging >>> for a tower >>>> base, >>>> i.e. does a deeper base give better support than a shallower >>> one with >>>> basically the same volume? Is 3x3x6 better than 4x4x4 with >>> everything else >>>> being equal. Thanks. >>>> >>>> 73 Bert, VE3OBU >>>> >>>> >>>> _______________________________________________ >>>> >>>> >>>> >>>> _______________________________________________ >>>> TowerTalk mailing list >>>> TowerTalk@contesting.com >>>> http://lists.contesting.com/mailman/listinfo/towertalk >>> >>> No virus found in this incoming message. >>> Checked by AVG - http://www.avg.com >>> Version: 8.0.169 / Virus Database: 270.6.14/1645 - Release >>> Date: 9/1/2008 >>> 7:19 AM >>> >>> _______________________________________________ >>> >>> >>> >>> _______________________________________________ >>> TowerTalk mailing list >>> TowerTalk@contesting.com >>> http://lists.contesting.com/mailman/listinfo/towertalk >>> No virus found in this incoming message. >>> Checked by AVG - http://www.avg.com >>> Version: 8.0.169 / Virus Database: 270.6.14/1645 - Release >>> Date: 9/1/2008 7:19 AM >>> >>> _______________________________________________ >>> >>> >>> >>> _______________________________________________ >>> TowerTalk mailing list >>> TowerTalk@contesting.com >>> http://lists.contesting.com/mailman/listinfo/towertalk >>> >>> >>> -- >>> No virus found in this incoming message. >>> Checked by AVG. >>> Version: 7.5.524 / Virus Database: 270.6.14/1645 - Release Date: >>> 9/1/2008 7:19 AM >>> >>> >> >> _______________________________________________ >> >> >> >> _______________________________________________ >> TowerTalk mailing list >> TowerTalk@contesting.com >> http://lists.contesting.com/mailman/listinfo/towertalk > _______________________________________________ > > > > _______________________________________________ > TowerTalk mailing list > TowerTalk@contesting.com > http://lists.contesting.com/mailman/listinfo/towertalk > No virus found in this incoming message. > Checked by AVG - http://www.avg.com > Version: 8.0.169 / Virus Database: 270.6.14/1647 - Release Date: 9/2/2008 > 6:02 AM > > _______________________________________________ > > > > _______________________________________________ > TowerTalk mailing list > TowerTalk@contesting.com > http://lists.contesting.com/mailman/listinfo/towertalk > _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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