Live Load Reduction

The loading codes recognise that in a multi-storey building, the imposed (live/variable) loading may not exist on all floors simultaneously. The codes provide a method to reduce the axial loading on columns with increasing number of floors. In certain columns the axial force may be reduced by a percentage dependent on the number of floors (with loads qualifying for reduction) carried by the column under consideration.

MasterFrame enables you to very quickly specify the percentage reductions using either of two approaches.

1.Apply percentage reductions to the total live load being applied to the column, or

2.Apply percentage reductions to individual live floors loads supported by the column.

The defining of the floor levels uses a simple approach.

The reduced column axial force and pad foundation loading is linked to MasterKey Steel, Connections and Concrete design modules.

To apply live load reduction;

1.Select Loads > Live Load Reduction from the top menu bar.

2.Tick the ‘Apply LLR to column and foundation design’ option

3.Tick the ‘Apply LLR to total load instead of incremental load…’ option to use approach 1 above or omit the tick to use approach 2.

4.Specify the percentage reductions per floor/level, separating the values with semi-colons.

5.Specify the Minimum Level Height. MasterFrame uses this value to define the floors levels for the reduction percentage. If the local column height is less than the minimum level height the percentage reduction is not increased and the level number is not incremented.

6.Analyse the frame. When live load reduction is activated the analysis procedure conducts two sets of analysis, i.e. both with and without live load reduction. This enables the percentages and minimum level height to be modified post analysis, omitting the need to reanalyse the frame.

To view the reduced axial load;

1.From the Results menu select the Graphical Analysis Results.

2.Select to display the Geometry / Axial loads.

3.Check the ‘Show Values’ option to display the axial force value on the members in the frame geometry area. The axial force in the columns that are subject to live load reduction are shown with the full axial force minus the reduction force, eg, 768 – 146 kN where 146 kN represents the reduction force.

To modify the reduction parameters post analysis;

1.Select the Frame Loads button from the top tool bar.

2.In the Load Diagram panel click on the ‘Change live load reduction values’ button.

3.You can alter the reduction parameters. The reduction method can also be changed using the ‘Base reduction on total load’ tick box (checked for method 1 above).

4.Click Apply changes to activate the new parameters.

5.While viewing the axial force as described above the ‘Show results without live load reduction’ Remove button can be used to hide the force reduction values and can be redisplayed using the Restore button.