A1 - Building Torsional Irregularity Control
For either of two perpendicular earthquake directions, Torsional Irregularity Coefficient ηbi, which expresses the ratio of the maximum relative story drift at any floor to the average relative drift in the same direction at that story, is greater than 1.2.
According to TBDY 2018 Table 3.6, the determination of the relative storey drifts is made according to Equivalent Earthquake Load method , taking into account the ± 5% additional eccentricity effects.
Loads generated according to equivalent earthquake load method are separate and are used only in the irregularity checks. These downloads can be checked from structural tree in the program interface.
A1 irregularity is important in the selection of the linear analysis method to be applied for the building as per TBDY 2018 220.127.116.11. However in the section Linear Earthquake Analysis Procedure Selection, the mode combination method that we used in this building can be used in all buildings in accordance with the earthquake regulation.
Irregularity checks are detailed in the earthquake code report. As seen in the table below, there is no A1 type irregularity in the building.
If this report is desired to be checked, the determination is made over the displacements of the elements given in the report by using the equivalent earthquake load method results in the perspective screen - analysis display - deformations subtab.
For X direction +5 %, the values of FX+ need to be checked from the load cases. If we want to examine the 4th floor ∆i,max value, the values read at the upper joint of the PLZ016 column and the node connected to the 2nd floor are in the above images.
∆i,max and ∆i,min values can be read from the program interface and all of them can be controlled with excel.