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cumulative-overturning

A resource regarding cumulative overturning in the Strong-Wall® shearwall specification process.

Steel Strong-Wall Cumulative Overturning Consideration

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<h1>
  Steel Strong-Wall<sup>&reg;</sup> Cumulative Overturning: Key Consideration in
  Strong-Wall Shearwall Specification Process
</h1>

<div class="row">
  <div class="col-sm-10">
    <p>
      When specifying a premanufactured shearwall for a project, several factors
      need to be considered, such as load values, seismic/wind requirements,
      wall width and height, wall placement, etc. Cumulative Overturning is
      another critical factor often overlooked in multi-story applications.
    </p>

    <h2>Calculating Cumulative Overturning for Pre-Manufactured Shearwalls</h2>

    <p>
      Designers are accustomed to accounting for cumulative overturning when
      specifying multi-story, site-built plywood shearwalls. However, when
      specifying premanufactured shearwalls, designers typically calculate shear
      loads based on the building geometry and code loading requirements. A wall
      is then selected based on its ability to meet or exceed the required shear
      load using manufacturer-provided allowable shear load tables.
    </p>

    <p>
      What can get lost when considering shear capacity only is that the
      shearwall is not only governed by shear, but also by a combination of
      other limit states, including
      <em
        >drift, tension and compression, flexure, anchor rod tension, and
        concrete or wood bearing stress</em
      >. For single-story walls, the allowable shear given in the load tables is
      the lowest value of the various limit states. However, additional care
      must be taken in the analysis of multi-story shearwalls to account for the
      way the loads are distributed over the height of the building.
    </p>

    <h2>Cumulative Overturning and Stacked-Wall Applications</h2>

    <p>
      In multi-story structures, shear and the associated overturning forces due
      to seismic/wind requirements must be carried down to the foundation by the
      building&rsquo;s lateral force resisting system. These forces are
      cumulative over the height of the building, and shear forces applied at
      the second or third levels of a structure will generate much larger base
      overturning moments than the same shears applied at the first story. If
      cumulative overturning is not considered, the design may result in forces
      several times higher than the capacity of the lower wall, anchor bolts and
      foundation anchorage.
    </p>

    <p>
      When specifying stacked shearwall applications, it&rsquo;s imperative to
      consider cumulative overturning. The load values for Simpson
      Strong-Tie&reg; stacked Steel Strong-Wall shearwall applications reflect
      the impact of cumulative overturning and thus appear significantly
      different than other shearwall manufacturers.
    </p>

    <p>
      The effects of cumulative overturning are automatically taken into account
      when designing shearwalls with the
      <a
        href="https://www2.strongtie.com/webapps/strongwallshearwallselector"
        target="_blank"
        >Strong-Wall Shearwall Selector web application</a
      >.
    </p>
  </div>

  <div class="col-sm-2">
    <img
      alt="fea_ssw"
      src="https://embed.widencdn.net/img/ssttoolbox/x6b65qoo3o/exact/fea_ssw.png"
    />
    <caption>
      Simpson Strong-Tie Steel Strong-Wall shearwall rendered in Finite Element
      Analysis (FEA). When evaluating the performance of complex structural
      components, our engineers use this computer simulation to complement our
      full-scale testing program.
    </caption>
    <br />
    <a class="target" href="#" data-toggle="modal" data-target="#VideoModal">
      
      <img
        alt="co_anim"
        src="https://embed.widencdn.net/img/ssttoolbox/efxifafw08/exact/co_anim.png?quality=100"
      />
    </a>

    <div
      class="modal fade"
      id="VideoModal"
      tabindex="-1"
      role="dialog"
      aria-hidden="true"
    >
      <div class="modal-dialog">
        <div class="modal-content">
          <div class="modal-header">
            <span
              type="button"
              class="modal-close"
              data-dismiss="modal"
              aria-hidden="true"
            ></span>
            <h4>Cumulative Overturning Animation</h4>
          </div>
          
          <div class="modal-body group">
            <div class="box embed-container">
              <iframe
                class="ss-video-iframe"
                src="https://www2.strongtie.com/wcms/htmlanimation/overturn_v5.html"
                frameborder="0"
              ></iframe>
            </div>
          </div>
          
        </div>
        
      </div>
      
    </div>
    
  </div>
</div>

<div class="row">
  <div class="col-sm-12">
    <h3 class="h4">Additional Resources</h3>
    <ul>
      <li>
        <a href="https://www2.strongtie.com/wcms/htmlanimation/overturn_v5.html"
          >Cumulative Overturning Analysis Animation</a
        >
      </li>
      <li>
        <a href="/strongrodsystems_lateralsystems/landing"
          >Solutions for Structures Taller Than Two Stories</a
        >
      </li>
      <li>
        <a href="/steelstrongwallshearwalls_strongwallshearwalls/category"
          >Steel Strong-Wall Product Pages</a
        >
      </li>
      <li>
        <a href="/about/research-testing-innovation"
          >Simpson&rsquo;s Research &amp; Testing</a
        >
      </li>
      <li>
        <a href="/resources/literature/strong-wall-shearwalls-catalog"
          >Strong-Wall Shearwall Catalog</a
        >
      </li>
    </ul>
  </div>
</div>


  <h2>Shear Only vs. Shear and Cumulative Overturning Analysis</h2>
<div class="row">
  <div class="col-sm-10">
  <p>
    The graphic illustration below compares how the total allowable shear load
    is impacted when the effects of cumulative overturning are included in the
    analysis. As a point of reference (Figure A), a one-story, nine-foot tall
    shear wall with a 5,000-lb. lateral load capacity is used. The reference
    wall has a resulting base overturning moment capacity of 45,000 ft.-lb. and
    an overturning force of 22,500 lb. assuming a 2 ft. moment arm. As
    illustrated, if the same base shear is applied over two stories, the
    overturning at the base of the wall exceeds the one-story application by 60%
    (Figure B). When proper consideration of cumulative overturning is included
    in the design, the total allowable shear load on a stacked wall is reduced
    (Figure C).
  </p>
</div></div>

<div class="col-md-12">
  <img
    alt="Shear Only vs. Shear and Cumulative Overturning Analysis"
    src="http://embed.widencdn.net/img/ssttoolbox/ei3lk1fcep/exact/C-L-SW21-55a-2021.png?quality=100"
  />
</div>

<p><strong>*Example calculations:</strong></p>
<p>
  (2nd-Story Shear Load x Total Story Height) + (1st-Floor Shear Load x
  1st-Story Height) = Overturning Moment &gt; Baseline Limit of the Lowest Panel
  (3,000 lb. x 18') + (2,000 lb. x 9') = 72,000 ft.-lb. > 45,000 ft.-lb.
  (Overturning Moment) &div; (Moment Arm) = Overturning Force &gt; Baseline
  Limit of the Lowest Panel (72,000 ft.-lb.) &div; (2 ft.) = 36,000 lb. &gt;
  22,500 lb.<br />
  (Overturning Moment) &div; (Moment Arm) = Overturning Force &gt; Baseline
  Limit of the Lowest Panel (72,000 ft.&ndash;lb.) &div; (2 ft.) = 36,000 lb.
  &gt; 22,500 lb.
</p>
<p>
  Note: Loads shown are for illustrative purposes only. Redistribution of
  earthquake loads per building code requirements will compound the effects of
  cumulative overturning.
</p>

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Resources including links to literature and information for structural residential and commercial building in Canada.

Literature and Links for Canada