Merge pull request #243 from robbievanleeuwen/stress_warping_reqs

Loosen warping reqs for stress analysis

Author: robbievanleeuwen

docs/source/rst/analysis.rst

@@ -71,8 +71,9 @@ A stress analysis calculates the section stresses arising from a set of forces
 and moments. Executing this method returns a :class:`~sectionproperties.analysis.section.StressResult`
 object which stores the section stresses and provides stress plotting functions.
 
-..  note:: A geometric and warping analysis must be performed on the Section
-  object before a stress analysis is carried out.
+..  note:: A geometric analysis must be performed on the Section object before a stress
+  analysis is carried out. Further, if the shear force or twisting moment is non-zero
+  a warping analysis must also be performed.
 
 ..  warning:: The stress analysis in *sectionproperties* is linear-elastic and does not
   account for the yielding of materials or any non-linearities.

sectionproperties/analysis/section.py

@@ -1043,8 +1043,8 @@ def calc_plastic(progress=None):
             calc_plastic()
 
     def calculate_stress(self, N=0, Vx=0, Vy=0, Mxx=0, Myy=0, M11=0, M22=0, Mzz=0):
-        """Calculates the cross-section stress resulting from design actions and returns a
-        :class:`~sectionproperties.analysis.section.StressPost` object allowing
+        """Calculates the cross-section stress resulting from design actions and returns
+        a :class:`~sectionproperties.analysis.section.StressPost` object allowing
         post-processing of the stress results.
 
         :param float N: Axial force
@@ -1055,33 +1055,35 @@ def calculate_stress(self, N=0, Vx=0, Vy=0, Mxx=0, Myy=0, M11=0, M22=0, Mzz=0):
         :param float M11: Bending moment about the centroidal 11-axis
         :param float M22: Bending moment about the centroidal 22-axis
         :param float Mzz: Torsion moment about the centroidal zz-axis
+
         :return: Object for post-processing cross-section stresses
         :rtype: :class:`~sectionproperties.analysis.section.StressPost`
 
-        Note that a geometric and warping analysis must be performed before a stress analysis is
-        carried out::
+        Note that a geometric analysis must be performed prior to performing a stress
+        analysis. Further, if the shear force or torsion is non-zero a warping analysis
+        must also be performed::
 
             section = Section(geometry)
             section.calculate_geometric_properties()
             section.calculate_warping_properties()
             stress_post = section.calculate_stress(N=1e3, Vy=3e3, Mxx=1e6)
 
-        :raises RuntimeError: If a geometric and warping analysis have not been performed prior to
-            calling this method
+        :raises RuntimeError: If a geometric and warping analysis (if required) have not
+            been performed prior to calling this method
         """
 
         # check that a geometric and warping analysis has been performed
-        if (
-            None
-            in [
-                self.section_props.area,
-                self.section_props.ixx_c,
-                self.section_props.cx,
-                self.section_props.j,
-            ]
-            and self.section_props.omega is None
-        ):
-            err = "Perform a geometric and warping analysis before carrying out a stress analysis."
+        if None in [
+            self.section_props.area,
+            self.section_props.ixx_c,
+            self.section_props.cx,
+        ]:
+            err = "Perform a geometric analysis before carrying out a stress analysis."
+            raise RuntimeError(err)
+
+        if self.section_props.omega is None and (Vx != 0 or Vy != 0 or Mzz != 0):
+            err = "Perform a warping analysis before carrying out a stress analysis "
+            err += "with non-zero shear forces or torsion moment."
             raise RuntimeError(err)
 
         def calc_stress(progress=None):
@@ -1115,6 +1117,16 @@ def calc_stress(progress=None):
 
                 # loop through all elements in the material group
                 for el in group.elements:
+                    # get element omega and psi
+                    if self.section_props.omega is None:
+                        omega_el = None
+                        psi_shear_el = None
+                        phi_shear_el = None
+                    else:
+                        omega_el = self.section_props.omega[el.node_ids]
+                        psi_shear_el = self.section_props.psi_shear[el.node_ids]
+                        phi_shear_el = self.section_props.phi_shear[el.node_ids]
+
                     (
                         sig_zz_n_el,
                         sig_zz_mxx_el,
@@ -1148,9 +1160,9 @@ def calc_stress(progress=None):
                         phi,
                         j,
                         nu,
-                        self.section_props.omega[el.node_ids],
-                        self.section_props.psi_shear[el.node_ids],
-                        self.section_props.phi_shear[el.node_ids],
+                        omega_el,
+                        psi_shear_el,
+                        phi_shear_el,
                         Delta_s,
                     )
 
@@ -2214,6 +2226,12 @@ def get_stress_at_points(
         :rtype: List[Union[Tuple[float, float, float], None]]
         """
 
+        # ensure warping analysis completed for shear and torsion
+        if self.section_props.omega is None and (Vx != 0 or Vy != 0 or Mzz != 0):
+            err = "Perform a warping analysis before carrying out a stress analysis "
+            err += "with non-zero shear forces or torsion moment."
+            raise RuntimeError(err)
+
         action = {
             "N": N,
             "Mxx": Mxx,
@@ -2251,26 +2269,46 @@ def get_stress_at_points(
                 sig = None
             elif len(tri_ids) == 1:
                 tri = self.elements[tri_ids[0]]
+
+                if self.section_props.omega is None:
+                    omega_el = None
+                    psi_shear_el = None
+                    phi_shear_el = None
+                else:
+                    omega_el = self.section_props.omega[tri.node_ids]
+                    psi_shear_el = self.section_props.psi_shear[tri.node_ids]
+                    phi_shear_el = self.section_props.phi_shear[tri.node_ids]
+
                 sig = tri.local_element_stress(
                     p=pt,
                     **action,
                     **sect_prop,
-                    omega=self.section_props.omega[tri.node_ids],
-                    psi_shear=self.section_props.psi_shear[tri.node_ids],
-                    phi_shear=self.section_props.phi_shear[tri.node_ids],
+                    omega=omega_el,
+                    psi_shear=psi_shear_el,
+                    phi_shear=phi_shear_el,
                 )
             else:
                 sigs = []
                 for idx in tri_ids:
                     tri = self.elements[idx]
+
+                    if self.section_props.omega is None:
+                        omega_el = None
+                        psi_shear_el = None
+                        phi_shear_el = None
+                    else:
+                        omega_el = self.section_props.omega[tri.node_ids]
+                        psi_shear_el = self.section_props.psi_shear[tri.node_ids]
+                        phi_shear_el = self.section_props.phi_shear[tri.node_ids]
+
                     sigs.append(
                         tri.local_element_stress(
                             p=pt,
                             **action,
                             **sect_prop,
-                            omega=self.section_props.omega[tri.node_ids],
-                            psi_shear=self.section_props.psi_shear[tri.node_ids],
-                            phi_shear=self.section_props.phi_shear[tri.node_ids],
+                            omega=omega_el,
+                            psi_shear=psi_shear_el,
+                            phi_shear=phi_shear_el,
                         )
                     )
                 sig = (

sectionproperties/tests/test_stress.py

@@ -0,0 +1,50 @@
+import pytest
+import sectionproperties.pre.library.primitive_sections as primitive_sections
+from sectionproperties.analysis.section import Section
+
+# define geometry
+rect = primitive_sections.rectangular_section(b=50, d=100)
+rect.create_mesh(mesh_sizes=0)  # coarse mesh
+sec = Section(rect)
+
+
+# test stress runtime errors
+def test_stress_runtime_errors():
+    # check runtime error with no analysis performed
+    with pytest.raises(RuntimeError):
+        sec.calculate_stress()
+
+    sec.calculate_geometric_properties()
+
+    # check runtime errors with shear/torsion applied, no warping analysis
+    with pytest.raises(RuntimeError):
+        sec.calculate_stress(Vx=1)
+        sec.get_stress_at_points(pts=[[10, 10]], Vx=1)
+
+    with pytest.raises(RuntimeError):
+        sec.calculate_stress(Vy=1)
+        sec.get_stress_at_points(pts=[[10, 10]], Vy=1)
+
+    with pytest.raises(RuntimeError):
+        sec.calculate_stress(Mzz=1)
+        sec.get_stress_at_points(pts=[[10, 10]], Mzz=1)
+
+    # check no runtime errors with no shear/torsion applied
+    sec.calculate_stress(N=1)
+    sec.calculate_stress(Mxx=1)
+    sec.calculate_stress(Myy=1)
+    sec.calculate_stress(M11=1)
+    sec.calculate_stress(M22=1)
+
+    sec.calculate_warping_properties()
+
+    # check no runtime errors after warping analysis
+    sec.calculate_stress(N=1)
+    sec.calculate_stress(Mxx=1)
+    sec.calculate_stress(Myy=1)
+    sec.calculate_stress(M11=1)
+    sec.calculate_stress(M22=1)
+    sec.calculate_stress(Vx=1)
+    sec.calculate_stress(Vy=1)
+    sec.calculate_stress(Mzz=1)
+    sec.get_stress_at_points(pts=[[10, 10]], Mzz=1)