Reinforced Masonry Walls – Partial Grout Out of Plane ASD

Most text decide to conveniently use a fully grouted wall. Well this is great but fully grouting walls can lead to unnecessary expenses and also add to seismic weight.  Therefore we will look at how to design and analyse a partially grouted wall. We’ll first cover ASD solutions for out-of-plane forces. See here for Strength Design.

References

The notes and spreadsheet below are based on MSJC 2008 (2005 is similar)

Ref 1 ACI 530/ASCE 5/TMS 402 direct number references are for the 2005 version however the method does not change up through the 2013 version. Found here

Notes and Tedds Calc:

Reinforced Masonry Out of Plane ASD – Equilibrium Method Notes

Reinforced Masonry Wall Out-of-Plane Axial Bending and Shear – ASD Tedds

Design/Analysis:

1.) Determine a required eccentricity, ed=M/P based on loading.
2.) Assume actual masonry stress is equal to allowable, fm=Fm=1/3f’m
3.) Find stress in steel based on compatiblity which must be less than allowable. fs<Fs
4.) Based on equilibrium sum forces P+Cf+Cw-T=0 solve for Pns.
5.) Based on equilibrium sum moments and solve for Mns.
6.) find actual eccentricty ea=Mns/Pns.
7.)ea=ed
8.) Check Pns>P, Mns>M
9.) check fa<Fa

Questions/Comments:

1.) The shear area is subject to engineering judgment. Becasuse the section may have net tension it may be more conservative to only use the area in compression. However the are is subject to compression may have a higher shear capacity.

2.) Notice that the axial stress (fa) is based on the axial load and the grouted area + mortared area of the full section (not just the area in compression). This value (fa) is then checked against the allowable axial stress (Fa) that has been reduced for slenderness. We have made sure that the masonry compression stress Fm is not exceeded by setting the maximum compressive stress (fm) equal to the allowable (Fm) and then starting our analysis by iterating the calculation and finding the neutral axis.
Examples:

Will Update Soon!

Some further discussion:
http://eng-tips.com/viewthread.cfm?qid=313424

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