Cantilever Rack Validation Changes (V2)

Model

Base Section

The rack base is now modeled using a stronger section. This represents the fact that each base is made up of two side-by-side C sections.

We have doubled the values of the Moment of Inertia (Ixx), Area (A), Linear Mass (M) and the Torsional Constant (J).

The impact of this change is to reduce the amount of deflection experienced by the column.

Base Anchors

The rack anchors (pins) are now inset from the ends of the base as specified in the part database (50mm if no offset is specified).

We have removed the anchor from the short side of single sided bases. According to FEM 10.2.09 (9.8) “A base support in tension is only allowed to take into account when there is an anchoring capable of resisting the design tension force.” Single sided racks exert a tension force far greater than the anchor can handle, which causes the anchor to pull out, or stretch, effectively removing it from the structure.

The diagrams below show the change to the model and its impact on the shear force.

The impact of this change is to increase the amount of deflection experienced by the column. This increase in deflection is not fully compensated by the stronger base section. So, this can cause previously passing racks to fail.

Double sided racks are generally unaffected by this change.

Before (with pin)
Before (with pin)
After (without pin)
After (without pin)

Checks

Base Checks

We now check the base bending moments against the limits specified by AS 4600:2018. This is performed for both static and seismic loads. V1 omitted these checks completely.

The limits specified by AS 4600:2018 are doubled for bases composed of two side-by-side C sections.

The impact of this change is that previously passing racks can now fail if the base is under-specified. This usually impacts only single sided racks.

Combination Factor

We have reduced the combination factor from 1.0 to 0.9 for all fully-loaded deflection checks. This factor was already 0.9 for the bending, shear and compression checks.

This change was made in accordance with FEM 10.2.09 (7.2, eq 10) which explicitly specifies a combination factor of 0.9.

The impact of this change is to reduce the deflection of arms and columns. This could cause previously failing racks to pass now.