Add beam shear window

StructureHelperCommon/Models/Materials/IDirectMaterialStrength.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace StructureHelperCommon.Models.Materials
+{
+    public interface IDirectMaterialStrength
+    {
+    }
+}