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The primary two functions of a Grade/Tie Beam in spread footing and/or pile caps foundation system is to support the Slab-On-Grade (S.O.G) and/or to take the moment from eccentric footing (or moment from lateral loads example wind and seismic). While the pile cap level and depth may differ from one site and another the level of the slab-on-grade is fixed by architectural constraint.

My questions are:

  1. What is the most suitable level for a grade/tie beam is it at the slab-on-grade level or the footing level and what will happen if the beam is at the S.O.G level and the footing is subjected to moment?
  2. How to design such a beam, meaning what are the loads and how to calculate the lateral loads (especially shear and moment) from loads such as seismic and wind?
  3. In what Section of the ACI and Eurocode is the Tie/Grade Beam is mentioned and is it always required (meaning for all soil types and seismic zones ...)?

Tie/Grade Beam at different levels sections

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The grade beam typically must be supported by competent soil. In some cases they are designed as per recommendation of soils report for specific tasks such as integrating soldier piles or supporting suspended structures such as utility rooms not getting support from their own foundation, or hillside structures overhanging over the slope. Then they are designed as beams with the caveat that they may be under the soils and need rebar cover as per concrete under the grade.

The reason is the grade beams can and do transfer column or pylon moments and thus impart at times significant bearing force to the soil.

The slab on grade is usually over the grade with humidity and moisture membrane of 4 inches of gravel and is not a critical component of the structure.

So grade beam is typically at a lower level unless it's Height is enough to join the slab.

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  • $\begingroup$ Hi Kamran Thank you for your Reply. one more question if the grade beam is supported by the soil how it is designed? do you have any article or pdf file that shows how the calculation of such a beam ? and how to calculate the loads from lateral forces such as seismic and wind? and is it always necessary to use this beam to tie the foundation (footings or pile caps)? $\endgroup$
    – J.Daou
    Aug 20 '19 at 12:22
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    $\begingroup$ @J.Daou, for example, let's say we have a column that has 200kips load and an overturning moment of 100kips.ft. attached on each side to 10ft long grade beam. the grade beam must resist the moment by q/ft reaction such that q^2/2*10=100kips. because of triangular reaction distribution. $\endgroup$
    – kamran
    Aug 20 '19 at 15:00
  • $\begingroup$ Thank you Kamran for this example. $\endgroup$
    – J.Daou
    Aug 20 '19 at 18:01

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