torsion constant and polar area moment misunderstanding fix (issue 38)

BriefFiniteElementNet/Elements/_1DCrossSectionGeometricProperties.cs

@@ -97,6 +97,8 @@ public static _1DCrossSectionGeometricProperties Calculate(PointYZ[] points,bool
                     buf.Qy = 0;
                     buf.Qz = 0;
                 }
+
+                buf.J = buf.Iy + buf.Iz;//we assume torsion constant equal to polar area moment, but this is only right for 
             }
 
             return buf;
@@ -107,6 +109,7 @@ public static _1DCrossSectionGeometricProperties Calculate(PointYZ[] points,bool
         private double _az;
         private double _iy;
         private double _iz;
+        private double _j;
         private double _qy;
         private double _qz;
         private double _iyz;
@@ -189,7 +192,7 @@ public double Iz
         /// </value>
         /// <remarks>
         ///     /
-        /// Iy= | Z . dA
+        /// Qy= | Z . dA
         ///    /A
         /// </remarks>
         public double Qy
@@ -206,7 +209,7 @@ public double Qy
         /// </value>
         /// <remarks>
         ///     /
-        /// Iz= | Y . dA
+        /// Qz= | Y . dA
         ///    /A
         /// </remarks>
         public double Qz
@@ -223,10 +226,10 @@ public double Qz
         /// </value>
         /// <remarks>
         ///     /          /
-        /// J= | ρ². dA = | (y²+z²).dA = <see cref="Iy"/> + <see cref="Iz"/> 
+        /// Jx = | ρ². dA = | (y²+z²).dA = <see cref="Iy"/> + <see cref="Iz"/> 
         ///    /A         /A
         /// </remarks>
-        public double J
+        public double Jx
         {
             get { return _iy + _iz; }
         }
@@ -247,5 +250,21 @@ public double Iyz
             get { return _iyz; }
             set { _iyz = value; }
         }
+
+
+        /// <summary>
+        /// Gets the torsional constant.
+        /// </summary>
+        /// <value>
+        /// Torsion Constant which is involved in the relationship between angle of twist and applied torque
+        /// </value>
+        /// <remarks>
+        /// Note that polar moment of area is not same as torsional constant J. have a look at issue #38 in github or https://en.wikipedia.org/wiki/Torsion_constant#cite_note-1
+        /// </remarks>
+        public double J
+        {
+            get { return _j; }
+            set { _j = value; }
+        }
     }
 }

BriefFiniteElementNet/Sections/UniformGeometric1DSection.cs

@@ -20,13 +20,17 @@ public class UniformGeometric1DSection : Base1DSection
         public override void GetObjectData(SerializationInfo info, StreamingContext context)
         {
             info.AddValue("_geometry", _geometry);
+            info.AddValue("_jOverride", _jOverride);
+            info.AddValue("_resetCentroid", _resetCentroid);
 
             base.GetObjectData(info, context);
         }
 
         protected UniformGeometric1DSection(SerializationInfo info, StreamingContext context) : base(info, context)
         {
             _geometry = (PointYZ[])info.GetValue("_geometry", typeof(PointYZ[]));
+            _jOverride = (double)info.GetValue("_jOverride", typeof(double));
+            _resetCentroid = (bool)info.GetValue("_resetCentroid", typeof(bool));
         }
 
         public UniformGeometric1DSection()
@@ -38,6 +42,12 @@ public UniformGeometric1DSection(PointYZ[] geometry)
             _geometry = geometry;
         }
 
+        public UniformGeometric1DSection(PointYZ[] geometry,double jOverride)
+        {
+            _geometry = geometry;
+            _jOverride = jOverride;
+        }
+
         PointYZ[] _geometry;
 
         /// <summary>
@@ -70,11 +80,40 @@ public bool ResetCentroid
             }
         }
 
+        /// <summary>
+        /// Gets or sets the overrided value for torsion constant J.
+        /// </summary>
+        /// <remarks>
+        /// As there is no (simple) analytic solution to find torsion constant for non circular sections, this should be manually set.
+        /// If <see cref="JOverride"/> is set to positive value, then value is used in torsion stiffness matrix.
+        /// if <see cref="JOverride"/> is set to zero (by default) or negative value, then polar moment of area is used in torsion stiffness matrix.
+        /// </remarks>
+        public double JOverride
+        {
+            get
+            {
+                return _jOverride;
+            }
+
+            set
+            {
+                _jOverride = value;
+            }
+        }
+
         private bool _resetCentroid = true;
+        private double _jOverride;
 
         public override _1DCrossSectionGeometricProperties GetCrossSectionPropertiesAt(double xi)
         {
-            return _1DCrossSectionGeometricProperties.Calculate(this.Geometry,this._resetCentroid);
+            var buf = _1DCrossSectionGeometricProperties.Calculate(this.Geometry, this._resetCentroid);
+
+            if (_jOverride > 0)
+                buf.J = _jOverride;
+            else
+                buf.J = buf.Jx;
+
+            return buf;
         }
 
 

BriefFiniteElementNet/Sections/UniformParametric1DSection.cs

@@ -24,6 +24,7 @@ public override void GetObjectData(SerializationInfo info, StreamingContext cont
             info.AddValue("_iz", _iz);
             info.AddValue("_ay", _ay);
             info.AddValue("_az", _az);
+            info.AddValue("_j", _j);
 
             base.GetObjectData(info, context);
 
@@ -36,6 +37,7 @@ protected UniformParametric1DSection(SerializationInfo info, StreamingContext co
             _iz = info.GetDouble("_iz");
             _ay = info.GetDouble("_ay");
             _az = info.GetDouble("_az");
+            _j = info.GetDouble("_j");
         }
 
         public UniformParametric1DSection()
@@ -49,12 +51,12 @@ public UniformParametric1DSection()
         /// <param name="iy">The Second Moment of Area of section regard to Z axis.</param>
         /// <param name="iz">The Second Moment of Area of section regard to Y axis.</param>
         /// <param name="j">The polar moment of inertial.</param>\
-        [Obsolete("param J not being used. use UniformParametric1DSection(double a, double iy, double iz) instead")]
         public UniformParametric1DSection(double a, double iy, double iz, double j)
         {
             _a = a;
             _iy = iy;
             _iz = iz;
+            _j = j;
         }
 
         /// <summary>
@@ -84,6 +86,7 @@ public UniformParametric1DSection(double a)
         private double _az;
         private double _iy;
         private double _iz;
+        private double _j;
 
         /// <summary>
         /// Gets or sets a.
@@ -156,23 +159,20 @@ public double Iz
         }
 
         /// <summary>
-        /// Gets the polar moment of inertia (J).
+        /// Gets the torsional constant.
         /// </summary>
         /// <value>
-        /// The polar moment of inertial.
+        /// Torsion Constant which is involved in the relationship between angle of twist and applied torque
         /// </value>
         /// <remarks>
-        /// this is read only property, to change it set either <see cref="Iy"/> or <see cref="Iz"/> as J=Iy+Iz
-        ///     /          /
-        /// J= | ρ². dA = | (y²+z²).dA = <see cref="Iy"/> + <see cref="Iz"/> 
-        ///    /A         /A
+        /// Note that polar moment of area is not same as torsional constant J. have a look at issue #38 in github or https://en.wikipedia.org/wiki/Torsion_constant#cite_note-1
         /// </remarks>
         public double J
         {
-            get { return _iy + _iz; }
+            get { return _j; }
+            set { _j = value; }
         }
 
-
         public override _1DCrossSectionGeometricProperties GetCrossSectionPropertiesAt(double xi)
         {
             var buf = new _1DCrossSectionGeometricProperties();
@@ -182,6 +182,8 @@ public override _1DCrossSectionGeometricProperties GetCrossSectionPropertiesAt(d
             buf.Az = this._az;
             buf.Iy = this._iy;
             buf.Iz = this._iz;
+            buf.J = this.J;
+
 
             return buf;
         }