Hello, Ide does not have its own horizontal load calculation. I will say that you can get information on how to calculate the horizontal load in most regulations, articles and books on the subject, but you already described how to calculate the horizontal load in an article you wrote. The thrust you calculated in your article is the total resultant thrust acting on the wall. You need to find the lower and upper pressure values of this thrust and enter it into the program. That is, if the pressure acting on the wall you describe in the article is triangular, so your top pressure value is Value1= 0, your lowest pressure value is Value2=Gamma*h*Ka (Note Fi=30 for Ka=0.333) Enter the pressure thrusts you have obtained as a horizontal load on the panel. . Also don't forget to add new loading combinations according to this horizontal thrust. Then idecad will do the analysis and design for you and you will probably get a more suitable wall section. Best regards