Add stirrup update strategy

StructureHelperCommon/Models/Forces/IDistributedLoad.cs

@@ -0,0 +1,21 @@
+namespace StructureHelperCommon.Models.Forces
+{
+    /// <summary>
+    /// Implement properties of 
+    /// </summary>
+    public interface IDistributedLoad : IBeamSpanLoad
+    {
+        /// <summary>
+        /// Value of uniformly distributed load, N/m
+        /// </summary>
+        double LoadValue { get; set; }
+        /// <summary>
+        /// Coordinate of start of load, m
+        /// </summary>
+        double StartCoordinate { get; set; }
+        /// <summary>
+        /// Coordinate of end of load, m
+        /// </summary>
+        double EndCoordinate { get; set; }
+    }
+}