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7-�4-04; i7:40 ;Lester Bulldin� �S ��-v��s �/�j �;3203955376 # 2/ 28 <br /> I <br /> LESTER BUILDIN6S Lester Building Systems, i��. <br /> 1111 Second Aveoue Sonth <br /> • La9lrs Pnuie�Mimewta 55354 <br /> 7'el:320.395.2531 <br /> Fu:3?A.395.2969 <br /> June 4,2004 www.la�uuiwings.wm <br /> Paul Boor PE <br /> Dear Building Official, <br /> Agricultural post frame buildings have long relied on in-situ hydration of dry concrete mix far foundations. <br /> These foundations are used to resiet vertical gravity loads and occasionally wind induced pullout farcea via <br /> cancrete collma. While this practice l�as a long and successful history,only recently has technical <br /> inforrnation become available to provide a scientific basis for design of these footings. <br /> The attached ASA.E document`In-Situ Hydration of a Dry Concrete Mix'outiinae tests that were recently <br /> conducted at the University of Wisconsin-Madison. These tests show that dry concrete mix is hydrated by <br /> soil moisdue. After four weeks the minimum compressive strength far any of the tested samples was 1227 <br /> psi. Fwther,as noted in the discussion,this value is low because the samples were tested when fully waber <br /> logged. Samples that were not submerged in water tested eignificantly higher. After 24 weeks the <br /> minimum strength tested was 1748 psi with average strength far the 18 test specimena of 3466 psi <br /> spproaching that of the best normally hydrabeci concrete. (Page 12-16) <br /> Recently Lester has developed a footing system using dry concrote mix placed below a 4"x 1T'pre-cast <br /> cancrete footing. This system called Pro-Cast Plus has several key advantages. <br /> — Immediate capacity provided by the pre-cast footing. <br /> — Ability to produce larga diameter footings on demand by adding dry concrete mix. <br /> — C�t effective for small numbers of footings. <br /> — Allows immediate colunm placement and back filling. <br /> — Simplifies scheduling by eliminatin�the need for ready-mix concrete. <br /> While Pro-Cast Plus footings have several key advantages,they do rely on in-situ hydration to reach deaign <br /> capacity. Both anecdotal aad test data indicate thie process d�oes readily occur and produces concrote with <br /> good strength. Aawever,im-situ}rydration does rely on the vagaries of sail and weather to provide the <br /> conditions required to hydrate the cement Recognizing this fact,Lester engineers have been very <br /> canservative in the design of Pre-Cast Plus footing by using the following design aseurnptions. <br /> — Maximum column reaction is limited to 8000#. <br /> — The bottom 2"of concrete mix is ignored per ACI recommendations despite the fact that the hole is <br /> cleaned and ta�nped prior to placing the dry concrete mix. <br /> — Design concrete strer►gth is limited to 500 psi while the ingredients used to form the dry concrete <br /> mixture are proportioned to provide a minimum 4000 psi concrete mix. <br /> These aseumptions cause Pre-Cast Plus footings to have a significantly higher factor of safety than standard <br /> caet in place footings. The high safety factar means these footinge will perfarm as designed. <br /> Sincerely, <br /> I���� <br /> Paul Boor PE <br /> Engincering Manager <br /> Lester Building Systems <br />