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<br />This generally results in elevation of the
<br />manufactured home two to three feet above grade,
<br />The use of techniques to achieve additional eleva-
<br />tion should not override the minimum re-
<br />quirements for steel frame support and set-up as
<br />specified in the manufactured home's installation
<br />manual and ANSI Standard A225,1-1982, In
<br />general, spacing of supporting members should
<br />not exceed 10 feet and additional intermediate
<br />supports may be required for concentrated loads
<br />or areas adjacent to large wall openings, In some
<br />cases, perimeter blocking may be required by the
<br />manufacturer and must also be provided in any
<br />elevated installation,
<br />Piers-As shown in Figure 3,9, a pier foundation
<br />system uses brick, concrete masonry units (CMU),
<br />or ,cast-in-place c~ncrete, L~teral forces are Figure 3.10 Large Pier Design
<br />resisted through vertical steel reinforcement, brac-
<br />ing, ana ancIfOtirtg-an-a augmented by ttle deaa--BUllt-up piers shoulooelaiawilh-lype-M or S-- ~ - -
<br />weight of the pier and footing, mortar. Hollow concrete masonry units should be
<br />filled with concrete or high strength mortar after
<br />reinforcement as shown in Figure 3,11,
<br />
<br />
<br />. ..'
<br />'.' ..
<br />:.,. :;~
<br />
<br />>!::
<br />
<br />~; :;I::~
<br />.' ,:. ~
<br />
<br />
<br />Figure 3.9 Pier Designs
<br />
<br />Generally piers have a low resistance to lateral
<br />forces, This, in addition to the potential for scour
<br />and erosion of the footing, makes the use of piers
<br />inappropriate in areas subjected to floodwater
<br />velocity,
<br />Built-up piers are generally effective for eleva,
<br />tions up to 10 feet, depending on their size, rein-
<br />forcement, soil conditions, and anticipated lateral
<br />forces, In general, height should be limited to a
<br />maximum of 10 times their least dimension, with
<br />square piers preferable to rectangular piers to
<br />minimize affected loads,
<br />In all but a few cases built-up piers should be
<br />a minimum of 12 inches by 12 inches and rein-
<br />forced with a minimum of four No, 5 steel bars,
<br />These minimum requirements apply whether the
<br />pier is freestanding or laterally braced, In cases
<br />where large loads are anticipated, the pier cross
<br />section should be increased or additional rein-
<br />forcement such as cross bracing added, A larger
<br />cross section can be obtained by using piers two
<br />feet or more in width with the long dimension
<br />placed parallel to any anticipated flow, as shown
<br />
<br />in Figure 3,10, buried at least 30 inches below
<br />grade,
<br />
<br />.
<br />
<br />rlood new DirectIon
<br />
<br />..:'" X<0";;"=>::. .~;<<:;: '%.. -,'
<br />
<br />:.' :>,:,:":':;;;:~;:"'
<br />
<br />
<br />
<br />m--------r--------r----..-.j-.:-
<br />
<br />.........-. .-...........-...-...-'....-...-......-.........
<br />}mrr?InEfC~~;~;;TYrr:T?
<br />... .......... ...............................
<br />
<br />........ ......................
<br />: ,
<br />
<br />::.~;:2sj:::::~::;::.::::-;:;:;:,:;~~-;:~~:;:E~~5~t~:;::':::'
<br />
<br />~-----_._-----~--------------------------~-
<br />
<br />~(~
<br />(~)
<br />
<br />;:
<br />
<br />Contrete Iiroullng
<br />
<br />
<br />Steel
<br />Reinforcing
<br />
<br />Figure 3.11 Filling of Piers
<br />
<br />Cast-in-place concrete piers can also be used
<br />and are essentially reinforced concrete columns,
<br />They are cast in forms set in machine or hand-
<br />dug holes, The holes can be widened or belled
<br />at the base to form a footing integral with the pier,
<br />or a separate footing can be constructed as shown
<br />in Figure 3,12, In the few cases where soil bear-
<br />ing capacity may be adequate to support the
<br />maximum vertical load and no flood velocity is
<br />anticipated, the footing can be eliminated and
<br />loads left to end bearing and friction between soil
<br />and pier.
<br />
<br />22
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