Masonry Wall Panel - Design

The masonry wall panel element allows you to easily model, analyze and design masonry walls for in plane and out of plane loads for these specific codes:

• The 2016 TMS 402 ASD and 2013, 2011, 2008, 2005, 2002 and 1999 Editions of ACI 530 ASD
• The 2016 TMS 402 Strength and 2013, 2011, 2008, 2005, 2002 and 1999 Editions of ACI 530 Strength
• The 1997 edition of the UBC for ASD and Strength

Here we will explain the calculation concepts and code references used in the program. For general wall panel information, see the Wall Panels topic. For information on masonry design rules, see the Masonry Wall - Design Rules (this is where you can define block thickness and self-weight). For masonry wall modeling procedures, see the Masonry Wall - Modeling topic. For masonry wall results interpretation, see the Masonry Wall Results topic.

Note:

• All code references in this topic refer to the TMS 402-16 specification unless noted otherwise.
• References will be made to RMEH and NCMA. For more information on these designations, see the Masonry Wall - Design Rules topic.
• Walls designed in RISA meet all of the requirements for Ordinary Masonry Shear Walls except for the Minimum Reinforcement requirements of TMS 402-16 Section 7.3.2.3.1. That provision should be checked by hand outside of RISA.

Axial Design - ASD

In Plane Axial Stress, fa

The axial stress in a wall due to axial forces, fa, is calculated as:

This is applicable for all out of plane masonry calculations.

Note:

• The program does not design masonry for net tension forces. fa will equal 0 ksi in these cases.

In Plane Axial Capacity, Fa

The calculation of Fa is per either Equation 8-13 or 8-14, depending on the h/r ratio. These equations match Equations 8-18 and 8-19 if you assume Ast = 0. RISA conservatively uses only the masonry in calculating the compression capacity. The equations are as follows:

where:

• r is taken from the UBC-97 Table 21-H-1 (concrete masonry units) and Table 21-H-2 (clay masonry units).
• h = effective height of wall region = K*h_actual

Note:

• The program does not design masonry for net tension forces. If there is net tension, Fa will still equal the compressive capacity of masonry.

In Plane Design - Strength

In Plane Axial Strength, Pn

This is calculated from Equations 9-15 and 9-16:

Note:

• Keep in mind that A_n is calculated differently for NCMA vs RMEH. See the Masonry Wall - Design Rules topic for more information.
• h = effective height of wall region = K*h_actual

Note:

• The maximum usable masonry strain at the extreme compression fiber, e_mu, is assumed to be 0.0025. For assumptions of the extreme compression fiber for Seismic Detailing checks of Masonry Walls, refer to the Maximum Area of Flexural Tensile Reinforcement (Max. Flexural Rho Check - Strength) section.

Out of plane deflections are calculated based on the Wall's Finite Element Analysis using a modified thickness, tmod, for the wall plates. The modified thickness is calculated using the wall panel's out of plate cracked moment of inertia, Icr, which can be input in the Advanced tab of the Wall Panels spreadsheet.

Note:

• The original thickness of the wall panel is the actual thickness of the wall panel, not to be confused with the nominal thickness.

RISA-3D then uses Finite Element Analysis using the modified thickness of the plates to calculate the out of plane deflection of the wall.

Unreinforced Masonry Design - ASD

Axial Design - ASD

For out of plane design for axial and bending the program performs 3 checks: a compression check, a tension check, and a slenderness check.

Compression Check (per Equation 8-11)

where:

• f_a and F_a are computed the same way as for reinforced masonry.
• Note that fb/Fb is not considered for RISAFloor

Masonry Lintel Design - ASD

Here we will talk about specific calculations regarding lintel design for allowable stress design.

Note:

• There is no lintel design for unreinforced lintels. Regardless of whether you design the wall as reinforced or unreinforced, all lintel design will use reinforcement. Because unreinforced lintels are very uncommon it is not currently available.

Shear Stress, fv

This stress is calculated from Equation 8-21:

where:

• d = distance from extreme compression fiber in top of lintel to the centroid of reinforcement.

Shear Capacity, Fv

The program calculates the capacity, Fv, from Equation 8-25, which is shown in the previous In Plane Shear Capacity Fv section.

The program also checks to verify we do not exceed the Fv max value from Equations 8-23 and 8-24 (or interpolation between them) that is reported in the detail report.

Fvs is only required if fv > Fvm. If fv < Fvm, then the program will not add any shear reinforcement and Fvs = 0. If Fvs is required, then the program will back calculate a spacing, s, that will satisfy the steel shear capacity required. This shear spacing is reported in the detail report.

When shear reinforcement is required the program will also meet the d/2 or 48" spacing required by 8.3.5.2.1. If Fv max must be exceeded to pass the code check, the program will use Fv max as the capacity and state "Over Allowable" for the Shear Steel Spacing.

Note:

• The program does not do explicit seismic design, thus Equation 8-25 is not used.
• The M in the F_vm equation above is taken as the maximum moment in the region instead of the moment at the location where the shear is maximum. This is generally a conservative assumption.
• The detail report shows a stirrup with two legs. However, the program only considers one leg in the A_v calculation.

Bond Stress, u, and Bond Capacity U

The bond stress check is one that has been grandfathered in from the UBC-1997 specification section 2107.2.16 and is defined previously in the In Plane Bond Stress u section. Σo is the summation of the circumference of all vertical bars.

The bond stress capacity was defined previously in the Bond Stress Capacity U section.

Stresses fb and fs

The masonry bending stresses were defined previously in the Out of Plane Stresses fb and fs section.

Bending Capacity, Fm (Fb) and Steel Capacity, Fs

Section 8.3.4.2.2 states:

Section 8.3.3.1 defines the allowable steel stress, Fs.

Masonry Lintel Design - Strength

Here we will talk about specific calculations regarding lintel design for strength design.

Note:

• There is no lintel design for unreinforced lintels. Regardless of whether you design the wall as reinforced or unreinforced, all lintel design will use reinforcement. Because unreinforced lintels are very uncommon it is not currently available.

Shear Strength, Vn

The program calculates the capacity, Vn, total from Equation 9-17, which was shown previously in the In Plane Shear Strength Vn section.

The program also checks to verify the Vn max value from Equations 9-18 and 9-19 (or interpolation between them) that is reported in the detail report is not exceeded.

Vn,steel is only required if Vu > Phi*Vn,masonry. If Vu < Phi*Vn,masonry, then the program will not add any shear reinforcement and Vn,steel = 0. If Vn,steel is required, then the program will back calculate a spacing, s, that will satisfy the steel shear capacity required. This shear spacing is reported in the detail report.

If Vn max must be exceeded to pass the code check, the program will use Vn max as the capacity (so the wall fails in shear) and state "Over Allowable" for the Shear Steel Spacing.

Note:

• The M in the V_nm equation above is taken as the maximum moment in the region instead of the moment at the location where the shear is maximum. This is generally a conservative assumption.

Moment Strength, Mn

Lintel design in RISA does not account for axial force, thus Mn is calculated simply from:

Here are the calculations of other values reported in the detail report: