Known Bugs

For shear walls required to behave elastically under NBCC 2020 Clause 4.1.8.23, some versions of MASS could report an overly high ULS factored moment. This was caused by the elastic earthquake load being incorrectly included in the ULS moment calculation, which could make the wall appear to require more flexural capacity than necessary. The Clause 4.1.8.23 check itself, along with shear and deflection checks, was otherwise functioning correctly. This issue was resolved in MASS v4.3.1.

Previously, if the modulus of elasticity calculated from the user’s f’_m input exceeded 20,000 MPa (using E = 850 × f’_m), MASS flagged the design as failing. In v4.3, MASS caps the modulus of elasticity at 20,000 MPa for analysis so the design can still be evaluated. The user’s entered f’_m is unchanged; only the derived E is limited. For example, if f’_m = 30 MPa gives E = 25,500 MPa, MASS now uses E = 20,000 MPa in accordance with CSA S304-14 clause 6.5.2.

MASS occasionally outputs the wrong CSA S304-14 clause reference when showing a failing design. These have been addressed in Version 4.3.

1. When a slender wall was designed and the axial load limit was exceeded, MASS v4.2 would tell you that the design failed due to clause 10.4.1 not being met. This has been updated to the correct clause 10.7.4.6.4.
2. When the factored shear exceeded the shear resistance, MASS v4.2 would tell you that the design failed due to clauses 7.10.3 or 10.10.3 not being met. This has been updated to the correct clauses 7.10.2 or 10.10.2.
3. When the horizontal bar spacing exceeded the allowable maximum bar spacing, MASS v4.2 would tell you that the design failed due to clauses 10.15.1.2 and 16.4.5.3 not being met. This has been updated to the correct clauses 10.15.1.4 and 16.4.5.4.
4. When the factored shear exceeded the sliding shear resistance, MASS v4.2 would tell you that the design failed due to clause 10.10.5.2 not being met. This has been updated to the correct clause 10.10.5.1.

For walls designated as Moderately Ductile or Ductile, the masonry contribution to shear resistance, V_r, was not reflected in the reported value of V_r​ due to the shear strength attributed to masonry, v_m​, not being calculated. All other ductility classes were unaffected by this behavior. This bug has been corrected in Version 4.3, and v_m is now calculated.

Under Clause 11.2.6.4, the maximum stirrup spacing that can tie a 10M compression bar at the top of a beam is 160 mm. In standard CMU construction, cells occur at 200 mm spacing, so this requirement cannot be met when unmodified standard stretcher units are used for construction, and the design should fail with a reference to the clause. Earlier versions did not flag this condition.

A practical workaround for this issue is to employ high-lintel units, which accommodate the required reinforcement detailing. Users can define a high-lintel unit within the Material Database Editor and specify it as the selected block type. Using high-lintel units enables compliance with Clause 11.2.6.4 while maintaining 10M compression bars at the beam’s top.

Previously, some projects produced incomplete moment design results and resulted in shear failures because the left support condition was intermittently lost. Users could temporarily restore correct results by toggling the left support setting. Version 4.3 resolves this issue by preserving the left support state reliably, thus restoring full moment design output and correct shear checks without user intervention.

In MASS Version 4.0, the inelastic rotational demand θid\theta_{id}θid​ was calculated using drift values instead of elastic deflections. That inflated the calculated demand because the equation already accounts for amplified movement, so the same effect was effectively counted twice. The result was an overly conservative ductility check, making compliance appear harder to achieve than it should have been. This has been fixed in Version 4.1. 

This bug occurred because the program checked horizontal reinforcement against seismic spacing limits whenever an earthquake load was present, even in cases where the seismic hazard index was below the threshold for those tighter limits to govern. That made some designs unnecessarily conservative by requiring more joint reinforcement than needed, such as preventing spacing every third course at 600 mm in cases where it should have been acceptable. The same issue also affected shearline and multi-storey shear wall designs that used the underlying shear wall design logic. This bug was corrected in Version 4.1.

This bug occurred because the program amplified seismic in-plane shear on a storey-by-storey basis, using each element independently, instead of carrying the amplification associated with the critical section through the rest of the wall above it. That could make the design unnecessarily conservative by producing higher factored shear forces in upper wall elements than were actually required. This bug was corrected in a later release.This has been addressed in Version 4.1. 

This bug occurred because the program amplified the entire lateral in-plane load for seismic load cases instead of amplifying only the seismic component of that load. As a result, companion non-seismic lateral loads were unintentionally scaled up as well, which could make the required factored shear resistance appear higher than it should be and lead to an overly conservative design. This was addressed in Version 4.1.