Add stirrup update strategy

StructureHelperCommon/Models/Forces/IConcentratedForce.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace StructureHelperCommon.Models.Forces
+{
+    /// <summary>
+    /// Implement properties for concentrated load in beam
+    /// </summary>
+    public interface IConcentratedForce : IBeamSpanLoad
+    {
+        /// <summary>
+        /// Coordinate of location of force along beam, m
+        /// </summary>
+        double ForceCoordinate { get; set; }
+        /// <summary>
+        /// Value of force, N
+        /// </summary>
+        double ForceValue { get; set; }
+    }
+}