One way distribution floor load on composite deck

Hi,

Hopefully this should be a quick one as I'm new to Staad.

I've created a composite deck and defined the span direction. I'm now trying to define a floor load but it won't let me define a direction for one way distribution for the load on the composite floor in the way I have been able to do for loads on user defined groups (I can tick the 'one way distribution' box but it won't allow me to change from the default distribution direction). I'm trying to line this up with the span direction I've chosen for the floor but the default happens to be in the other direction.

Is there a way to do this? and/or is there a better load type to use for this situation?

Thanks :)