ConcreteBucklingCalculator was added

StructureHelperLogics/NdmCalculations/Buckling/IEilerCriticalForceLogic.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace StructureHelperLogics.NdmCalculations.Buckling
+{
+    internal interface IEilerCriticalForceLogic : ICriticalBucklingForceLogic
+    {
+        double LongForce { get; set; }
+        double StiffnessEI { get; set; }
+        double DesignLength { get; set; }
+
+    }
+}