Extract sum shear force logic

StructureHelperCommon/Models/Forces/IFactoredForceTuple.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace StructureHelperCommon.Models.Forces
+{
+    public interface IFactoredForceTuple
+    {
+        IForceTuple ForceTuple { get; set; }
+        IFactoredCombinationProperty CombinationProperty { get; set; }
+    }
+}