Add beam shear classes

StructureHelperLogics/Models/BeamShears/IStirrupByDensity.cs

@@ -0,0 +1,19 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace StructureHelperLogics.Models.BeamShears
+{
+    /// <summary>
+    /// Implement logic for calculation of bearing capacity of stirrups by value of their density
+    /// </summary>
+    public interface IStirrupByDensity : IStirrup
+    {
+        /// <summary>
+        /// Direct density of stirrups, N/m
+        /// </summary>
+        double StirrupDensity { get; set; }
+    }
+}