Reinforced Masonry Deflection

[FisherStruct]

I am aware of the limit of l/600 on unreinforced masonry deflection, but I am not aware of a limit on deflection of reinforced masonry. Does anyone know of a code or an orginization that would give this reinforced masonry deflection limitations? Thank you...

 

[dik]

Canadian Code Requirements Span/480 (thank goodness for cut and paste):

12.4 Beams-Deflection

12.4.1
Deflections of beams shall be checked when the clear span exceeds 15d.

12.4.2
immediate deflections shall be computed using the modulus of elasticity, E,, for masonry as specified in Clause 8.3.1 and the effective moment of inertia of Clause 8.3.2.

12.4.3
The total immediate plus long-term deflection may be determined in accordance with Clause 8.3.

12.4.4
Total immediate plus long-term deflection of beams shall not exceed span/480.

8.3.1 Modulus of Elasticity

8.3.1 .l
The modulus of elasticity of steel reinforcement, Es may be taken as 200 000 MPa.

8.3.1.2
The modulus of elasticity, Es of masonry made of concrete or clay units shall be determined in accordance with Clause 8.3.1.4 or may be taken as Es = 850f'm MPa but not greater than 20 000 MPa.

8.3.1.3
The modulus of elasticity, Em of masonry made of stone or other types of units shall be determined in accordance with Clause 8.3.1.4.

8.3.1.4
The modulus of elasticity of masonry determined experimentally shall be based on the secant modulus of at least five prisms tested in accordance with CSA Standard CAN/CSA-A369.1. The modulus shall be measured over a stress range extending from 0.05 to 0.33 of the measured mean prism compressive strength. The modulus shall be based on the average value.

8.3.2 Effective Moment of Inertia for Deflection calculations at Specified Loads

8.3.2.1
The effective moment of inertia, Ieff to be used in deflection calculations for reinforced and unreinforced walls and columns and for reinforced beams shall be calculated in accordance with Clauses 8.3.2.2 to 8.3.2.4.
Note: For the determination of the effective moment of inertia for very slender walls, see Clause 11.2.4.3.3.

8.3.2.2
Unless stiffness values are obtained by a more comprehensive analysis, immediate deflection shall be calculated using the modulus of elasticity for masonry, Em specified in Clause 8.3.1 and the effective moment of inertia, Ieff determined as follows, except that Ieff shall not be greater than Io:

Ieff = (Mcr^3/Ma)*Io + (1 - (Mcr^3/Ma)*Icr)

where
Mcr = (phi*ft + fcs)*Io / yt

ft = the appropriate flexural tensile strength value from Table 6
fcs = unfactored axial load, P, divided by A,
Ma = maximum moment due to specified loads.

Icr may be calculated with the effects of axial loads included.

8.3.2.3
For continuous spans, Ieff may be taken as the average of the values from Clause 8.3.2.2 for the critical positive and negative moment sections. For prismatic members, Ieff may be taken as the value obtained from Clause 8.3.2.2 at midspan for simple spans and at the support for cantilevers.

8.3.2.4
Unless values are obtained by a more comprehensive analysis, the total immediate-plus-longterm deflection for flexural members shall be obtained by multiplying the immediate
deflection (caused by the sustained load) by the factor calculated from
(1 + (s /(1 + 5Op’))

where
P ’ = the value at midspan for simple and continuous spans and at the support for cantilevers.

The time dependent factor, S, may be taken as equal to
(a) 1 .O for a sustained load of 5 years or more;
(b) 0.7 for a sustained load of 12 months;
(c) 0.6 for a sustained load of 6 months; and
(d) 0.5 for a sustained load of 3 months.

 

[dik]

There was an erratum to the code, and

Ieff = (Mcr^3/Ma)*Io + (1 - (Mcr^3/Ma)*Icr)

should read:

Ieff = [(Mcr/Ma)^3]*Io + [1 - (Mcr/Ma)^3]*Icr

 

[FisherStruct]

Thank you...that is very helpful.

 

[dik]

I guess the cut and paste is not foolproof, either... I think that's got 'em all...

12.4.2
immediate deflections shall be computed using the modulus of elasticity, Em for masonry as specified in Clause 8.3.1 and the effective moment of inertia of Clause 8.3.2.

8.3.1.2
The modulus of elasticity, Em of masonry made of concrete or clay units shall be determined in accordance with Clause 8.3.1.4 or may be taken as Em = 850f'm MPa but not greater than 20 000 MPa.