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Isolated Piers R404.1.9.2

Discussion in 'Residential Structural Codes' started by Francis Vineyard, Aug 8, 2018.

  1. Francis Vineyard

    Francis Vineyard Sawhorse

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    Considering frost depth and measuring the height from the top of the footing how would you interpret the location high lighted in R404.1.9.2 to support the girder for exterior bearing walls?

    R404.1.9.2 Masonry piers supporting floor girders. Masonry piers supporting wood girders sized in accordance with Tables R502.5(1) and R502.5(2) shall be permitted in accordance with this section. Piers supporting girders for interior bearing walls shall have a minimum nominal dimension of 12 inches and a maximum height of 10 feet from top of footing to bottom of sill plate or girder. Piers supporting girders for exterior bearing walls shall have a minimum nominal dimension of 12 inches and a maximum height of 4 feet from top of footing to bottom of sill plate or girder. Girders and sill plates shall be anchored to the pier or footing in accordance with Section R403.1.6 or Figure R404.1.5(1).
    Floor girder bearing shall be in accordance with Section R502.6.

    R606.7 (2012 R606.6) Piers. The unsupported height of masonry piers shall not exceed ten times their least dimension. When structural clay tile or hollow concrete masonry units are used for isolated piers to support beams and girders, the cellular spaces shall be filled solidly with concrete or Type M or S mortar, except that unfilled hollow piers may be used if their unsupported height is not more than four times their least dimension. Where hollow masonry units are solidly filled with concrete or Type M, S or N mortar, the allowable compressive stress shall be permitted to be increased as provided in Table R606.5.
     
  2. linnrg

    linnrg Sawhorse

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    not sure what the total question here is. I think the references are for piers inside the building envelope therefore not a frost concern.
    for exterior piers where there is back fill at all sides so the only portion unsupported is from the soil up to the top of the pier. For exterior piers there is the frost depth and load values to determine a proper footing and pier height which I would be concerned with. I have not had anyone do masonry for residential in a long time - most use sono tubes with big foot. Bigger footings and bigger sono tube diameter can also be considered depending upon the load. Are you seeing masonry columns/piers at exterior locations that support structure above?
     
  3. Francis Vineyard

    Francis Vineyard Sawhorse

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    Perhaps my confusion is how does an interior (crawl space or basement) pier support an exterior bearing wall?

    Otherwise I don't understand how these two sections are not in conflict.
     
  4. linnrg

    linnrg Sawhorse

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    I should have read every word more carefully. The above quoted section is a subcategory of "Isolated masonry piers". Since I find no reference in section R404.1.9 for reinforcing except in certain seismic zones (where it says to use engineering) I am assuming that the reason behind the 4' dimension is because of it being unreinforced. Maybe the masonry reference in R404.1.1 would describe this limitation. I have the ACI for concrete but do not for masonry.
     
  5. steveray

    steveray Sawhorse

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    Also look out for:

    R602.10.9 Braced wall panel support. Braced wall panel
    support shall be provided as follows:
    1. Cantilevered floor joists complying with Section
    R502.3.3 shall be permitted to support braced wall
    panels.
    2. Raised floor system post or pier foundations supporting
    braced wall panels shall be designed in
    accordance with accepted engineering practice.
     
  6. Francis Vineyard

    Francis Vineyard Sawhorse

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    The code proposal reason provided below implies that R404.1.9.2 is applicable to basements and crawl spaces. How would you know for sure?

    So have you seen or know of an isolated pier in a basement or crawl space that supports a girder for an exterior wall? Seems it would be a beam.

    Note separation walls of 2-family dwelling and townhouses are not defined as exterior walls. Also notice the definition of exterior wall in the 2018 IRC now references IECC!

    Reason: The purpose of this proposal is to introduce provisions for isolated masonry piers used as foundations for raised wood floor systems. Masonry pier foundations are a common construction method. However, besides a brief mention in R606.6, no other guidance is given for the construction of these piers, other than a reference in R602.10.6 calling for engineered design of piers supporting braced wall panels. Language is proposed for Chapter 4 to provide prescriptive guidance for isolated masonry piers constructed inside a basement or crawlspace. The language proposed for R404.1.9 for masonry piers is based on the empirical design limits contained in the MSJC. The language is adopted from the paragraph on Foundation Piers in NCMA’s TEK Note 5-3A: “Concrete Masonry Foundation Wall Details”. Further limits are provided for piers supporting floor girders, braced wall panels, and for piers in high-seismic or flood hazard areas. The language in R602.10.6 is modified and coordinated with the proposed R404.1.9 language to allow prescriptive design of short exterior masonry piers and of isolated interior masonry piers complying with R404.1.9. Taller masonry piers supporting an elevated deck, sunroom, or other substantially raised portion of a dwelling are relegated to engineered design. It was the original intent of R602.10.6 to address these full-height piers, not to require engineered design for every raised wood floor/crawlspace regardless of pier height.

    RB80–09/10
     

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