Limitations of wind decomposition to diaphragms
Certain building shapes need extra consideration if simple wind loads have been applied, or if wind loads have been applied to wall panels set to decompose to diaphragms.
As illustrated by the following examples, buildings containing discrete towers (and thus containing disconnected rigid diaphragms) are a particular concern.
Wind load perpendicular to disconnected diaphragms
The load is then decomposed to the diaphragms at each level in proportion to the width of each diaphragm.
Wind load parallel to disconnected diaphragms
- if using wind wall panels - you would need to decompose to members or nodes instead of to diaphragms
- if using Simple Wind loads - there is no workaround, you would have to manually input the loads as diaphragm loads instead.
Diaphragms less than 5% of simple wind load width ignored
In Tekla Structural Designer, if the projected width of a rigid diaphragm in the direction that the load is acting is less than 5% of the simple wind load width it is assumed to be ineffective.
Consider the following example which consists of 4 levels and has a simple wind load applied over the full height of the building.
This changes at the roof (level 4). The only structure at this level is the lift core as shown below.
At this level the width of the diaphragm is now significantly smaller than the width of the load. In this case, because it is less than 5% of the load width, the diaphragm is ignored. As it is the only diaphragm at the top level a "Wind load profile applied above top diaphragm" warning message is displayed against that level in the Simple Wind Loading dialog when the load is created.
As it is only a warning it does not prevent the analysis from proceeding, however the diaphragm load applied to level 3 is significantly larger than it would otherwise have been.
This is because the full width is used for the loaded area above and below level 3 when calculating the diaphragm load to be applied to it.