Add shape factors for composite analyses

docs/user_guide/results.rst

@@ -136,6 +136,8 @@ Plastic Analysis
     ~sectionproperties.analysis.section.Section.get_pc_p
     ~sectionproperties.analysis.section.Section.get_mp
     ~sectionproperties.analysis.section.Section.get_mp_p
+    ~sectionproperties.analysis.section.Section.get_sf
+    ~sectionproperties.analysis.section.Section.get_sf_p
 
 .. _label-material-affects-results:
 

src/sectionproperties/analysis/plastic_section.py

@@ -204,46 +204,51 @@ def calculate_plastic_properties(
         if progress and task is not None:
             progress.update(task_id=task, advance=1)
 
-        # if there are no materials specified, calculate shape factors
+        # calculate shape factors
+        props = section.section_props
+
+        if (
+            props.sxx is None
+            or props.syy is None
+            or props.s11 is None
+            or props.s22 is None
+        ):
+            msg = "Property save failed."
+            raise RuntimeError(msg)
+
+        # for a geometric only analysis sf = s / z
         if list(set(section.materials)) == [pre.DEFAULT_MATERIAL]:
             if (
-                section.section_props.zxx_plus
-                and section.section_props.zxx_minus
-                and section.section_props.zyy_plus
-                and section.section_props.zyy_minus
+                props.zxx_plus
+                and props.zxx_minus
+                and props.zyy_plus
+                and props.zyy_minus
             ):
-                section.section_props.sf_xx_plus = (
-                    section.section_props.sxx / section.section_props.zxx_plus
-                )
-                section.section_props.sf_xx_minus = (
-                    section.section_props.sxx / section.section_props.zxx_minus
-                )
-                section.section_props.sf_yy_plus = (
-                    section.section_props.syy / section.section_props.zyy_plus
-                )
-                section.section_props.sf_yy_minus = (
-                    section.section_props.syy / section.section_props.zyy_minus
-                )
+                props.sf_xx_plus = props.sxx / props.zxx_plus
+                props.sf_xx_minus = props.sxx / props.zxx_minus
+                props.sf_yy_plus = props.syy / props.zyy_plus
+                props.sf_yy_minus = props.syy / props.zyy_minus
             if (
-                section.section_props.s11
-                and section.section_props.s22
-                and section.section_props.z11_plus
-                and section.section_props.z11_minus
-                and section.section_props.z22_plus
-                and section.section_props.z22_minus
+                props.z11_plus
+                and props.z11_minus
+                and props.z22_plus
+                and props.z22_minus
             ):
-                section.section_props.sf_11_plus = (
-                    section.section_props.s11 / section.section_props.z11_plus
-                )
-                section.section_props.sf_11_minus = (
-                    section.section_props.s11 / section.section_props.z11_minus
-                )
-                section.section_props.sf_22_plus = (
-                    section.section_props.s22 / section.section_props.z22_plus
-                )
-                section.section_props.sf_22_minus = (
-                    section.section_props.s22 / section.section_props.z22_minus
-                )
+                props.sf_11_plus = props.s11 / props.z11_plus
+                props.sf_11_minus = props.s11 / props.z11_minus
+                props.sf_22_plus = props.s22 / props.z22_plus
+                props.sf_22_minus = props.s22 / props.z22_minus
+        else:
+            if props.my_xx and props.my_yy:
+                props.sf_xx_plus = props.sxx / props.my_xx
+                props.sf_xx_minus = props.sf_xx_plus
+                props.sf_yy_plus = props.syy / props.my_yy
+                props.sf_yy_minus = props.sf_yy_plus
+            if props.my_11 and props.my_22:
+                props.sf_11_plus = props.s11 / props.my_11
+                props.sf_11_minus = props.sf_11_plus
+                props.sf_22_plus = props.s22 / props.my_22
+                props.sf_22_minus = props.sf_22_plus
 
         if progress and task is not None:
             progress.update(

src/sectionproperties/analysis/section.py

@@ -1184,7 +1184,8 @@ def calculate_plastic_properties(
         Note:
             If materials are specified, the values calculated for the plastic section
             moduli are displayed as plastic moments (i.e :math:`M_p = f_y S`) and the
-            shape factors are not calculated.
+            shape factors are calculated as the ratio between the plastic moment and the
+            yield moment.
 
         Warning:
             The geometric properties must be calculated prior to the calculation of the
@@ -1197,7 +1198,7 @@ def calculate_plastic_properties(
 
           - Plastic centroids (centroidal and principal axes)
           - Plastic section moduli (centroidal and principal axes)
-          - Shape factors, non-composite only (centroidal and principal axes)
+          - Shape factors (centroidal and principal axes)
         """
         # check that a geometric analysis has been performed
         if self.section_props.cx is None:
@@ -3167,22 +3168,25 @@ def get_mp_p(self) -> tuple[float, float]:
     def get_sf(self) -> tuple[float, float, float, float]:
         """Returns the cross-section centroidal axis shape factors.
 
-        This is a geometric only property, as such this can only be returned if material
-        properties have *not* been applied to the cross-section.
+        For a geometric-only analysis, the shape factor is defined as the ratio between
+        the plastic section modulus and the elastic section modulus. For a composite
+        analysis the shape factors is defined as the ratio between the plastic moment
+        and the yield moment.
+
+        .. note::
+            For composite analyses, the ``plus`` values will always equal the ``minus``
+            values as the yield moment occurs when the first fibre reaches its yield
+            strength. For geometric-only analyses, the elastic section moduli is
+            calculated with respect to the top and bottom fibres (i.e. ``plus`` and
+            ``minus``).
 
         Returns:
             Centroidal axis shape factors with respect to the top and bottom fibres
             (``sf_xx_plus``, ``sf_xx_minus``, ``sf_yy_plus``, ``sf_yy_minus``)
 
         Raises:
-            RuntimeError: If material properties have been applied
             RuntimeError: If a plastic analysis has not been performed
         """
-        if self.is_composite():
-            msg = "Attempting to get a geometric only property for a composite analysis"
-            msg += " (material properties have been applied)."
-            raise RuntimeError(msg)
-
         if (
             self.section_props.sf_xx_plus is None
             or self.section_props.sf_xx_minus is None
@@ -3202,22 +3206,25 @@ def get_sf(self) -> tuple[float, float, float, float]:
     def get_sf_p(self) -> tuple[float, float, float, float]:
         """Returns the cross-section principal axis shape factors.
 
-        This is a geometric only property, as such this can only be returned if material
-        properties have *not* been applied to the cross-section.
+        For a geometric-only analysis, the shape factor is defined as the ratio between
+        the plastic section modulus and the elastic section modulus. For a composite
+        analysis the shape factors is defined as the ratio between the plastic moment
+        and the yield moment.
+
+        .. note::
+            For composite analyses, the ``plus`` values will always equal the ``minus``
+            values as the yield moment occurs when the first fibre reaches its yield
+            strength. For geometric-only analyses, the elastic section moduli is
+            calculated with respect to the top and bottom fibres (i.e. ``plus`` and
+            ``minus``).
 
         Returns:
             Principal bending axis shape factors with respect to the top and bottom
             fibres (``sf_11_plus``, ``sf_11_minus``, ``sf_22_plus``, ``sf_22_minus``)
 
         Raises:
-            RuntimeError: If material properties have been applied
             RuntimeError: If a plastic analysis has not been performed
         """
-        if self.is_composite():
-            msg = "Attempting to get a geometric only property for a composite analysis"
-            msg += " (material properties have been applied)."
-            raise RuntimeError(msg)
-
         if (
             self.section_props.sf_11_plus is None
             or self.section_props.sf_11_minus is None

src/sectionproperties/post/post.py

@@ -675,7 +675,7 @@ def print_results(
         try:
             my_xx, my_yy = section.get_my()
             table.add_row("my_xx", f"{my_xx:>{fmt}}")
-            table.add_row("my_yy-", f"{my_yy:>{fmt}}")
+            table.add_row("my_yy", f"{my_yy:>{fmt}}")
         except RuntimeError:
             pass
 
@@ -735,7 +735,7 @@ def print_results(
         try:
             my_11, my_22 = section.get_my_p()
             table.add_row("my_11", f"{my_11:>{fmt}}")
-            table.add_row("my_22-", f"{my_22:>{fmt}}")
+            table.add_row("my_22", f"{my_22:>{fmt}}")
         except RuntimeError:
             pass
 
@@ -913,26 +913,24 @@ def print_results(
             pass
 
     # print cross-section sf
-    if not is_composite:
-        try:
-            sf_xx_plus, sf_xx_minus, sf_yy_plus, sf_yy_minus = section.get_sf()
-            table.add_row("sf_xx+", f"{sf_xx_plus:>{fmt}}")
-            table.add_row("sf_xx-", f"{sf_xx_minus:>{fmt}}")
-            table.add_row("sf_yy+", f"{sf_yy_plus:>{fmt}}")
-            table.add_row("sf_yy-", f"{sf_yy_minus:>{fmt}}")
-        except RuntimeError:
-            pass
+    try:
+        sf_xx_plus, sf_xx_minus, sf_yy_plus, sf_yy_minus = section.get_sf()
+        table.add_row("sf_xx+", f"{sf_xx_plus:>{fmt}}")
+        table.add_row("sf_xx-", f"{sf_xx_minus:>{fmt}}")
+        table.add_row("sf_yy+", f"{sf_yy_plus:>{fmt}}")
+        table.add_row("sf_yy-", f"{sf_yy_minus:>{fmt}}")
+    except RuntimeError:
+        pass
 
     # print cross-section sf_p
-    if not is_composite:
-        try:
-            sf_11_plus, sf_11_minus, sf_22_plus, sf_22_minus = section.get_sf_p()
-            table.add_row("sf_11+", f"{sf_11_plus:>{fmt}}")
-            table.add_row("sf_11-", f"{sf_11_minus:>{fmt}}")
-            table.add_row("sf_22+", f"{sf_22_plus:>{fmt}}")
-            table.add_row("sf_22-", f"{sf_22_minus:>{fmt}}")
-        except RuntimeError:
-            pass
+    try:
+        sf_11_plus, sf_11_minus, sf_22_plus, sf_22_minus = section.get_sf_p()
+        table.add_row("sf_11+", f"{sf_11_plus:>{fmt}}")
+        table.add_row("sf_11-", f"{sf_11_minus:>{fmt}}")
+        table.add_row("sf_22+", f"{sf_22_plus:>{fmt}}")
+        table.add_row("sf_22-", f"{sf_22_minus:>{fmt}}")
+    except RuntimeError:
+        pass
 
     console = Console()
     console.print(table)

tests/analysis/test_yield_moment.py

@@ -70,6 +70,15 @@ def test_rectangle():
     assert check_yield_index(stress, "sig_zz_m11") == pytest.approx(1.0)
     assert check_yield_index(stress, "sig_zz_m22") == pytest.approx(1.0)
 
+    # check shape factors
+    sec.calculate_plastic_properties()
+    sf_xx, _, sf_yy, _ = sec.get_sf()
+    sf_11, _, sf_22, _ = sec.get_sf_p()
+    assert sf_xx == pytest.approx(1.5)
+    assert sf_yy == pytest.approx(1.5)
+    assert sf_11 == pytest.approx(1.5)
+    assert sf_22 == pytest.approx(1.5)
+
 
 def test_rectangle_rotated():
     """Test the yield moment of a simple rotated rectangle."""
@@ -92,6 +101,12 @@ def test_rectangle_rotated():
     assert check_yield_index(stress, "sig_zz_m11") == pytest.approx(1.0)
     assert check_yield_index(stress, "sig_zz_m22") == pytest.approx(1.0)
 
+    # check shape factors
+    sec.calculate_plastic_properties()
+    sf_11, _, sf_22, _ = sec.get_sf_p()
+    assert sf_11 == pytest.approx(1.5)
+    assert sf_22 == pytest.approx(1.5)
+
 
 def test_isection():
     """Test the yield moment of an isection."""
@@ -119,6 +134,22 @@ def test_isection():
     assert check_yield_index(stress, "sig_zz_m11") == pytest.approx(1.0)
     assert check_yield_index(stress, "sig_zz_m22") == pytest.approx(1.0)
 
+    # check that shape factors with a geometric-only analysis match the composite
+    sec.calculate_plastic_properties()
+    sf_xx_c, _, sf_yy_c, _ = sec.get_sf()
+
+    geom = i_section(d=200, b=100, t_f=10, t_w=5, r=12, n_r=8)
+    geom.create_mesh(mesh_sizes=0, coarse=True)
+    sec = Section(geometry=geom)
+    sec.calculate_geometric_properties()
+    sec.calculate_plastic_properties()
+
+    sf_xx_plus, sf_xx_minus, sf_yy_plus, sf_yy_minus = sec.get_sf()
+    assert sf_xx_c == pytest.approx(sf_xx_plus)
+    assert sf_xx_c == pytest.approx(sf_xx_minus)
+    assert sf_yy_c == pytest.approx(sf_yy_plus)
+    assert sf_yy_c == pytest.approx(sf_yy_minus)
+
 
 def test_rectangle_composite():
     """Test the yield moment of a composite rectangular section."""

tests/post/test_get_results.py

@@ -798,19 +798,13 @@ def test_get_plastic(sec_no_mat_and_mat):
     assert sf_yy_plus == pytest.approx(1.5)
     assert sf_yy_minus == pytest.approx(1.5)
 
-    with pytest.raises(RuntimeError):
-        rect_mat.get_sf()
-
     # check sf_p
     sf_11_plus, sf_11_minus, sf_22_plus, sf_22_minus = rect_no_mat.get_sf_p()
     assert sf_11_plus == pytest.approx(1.5)
     assert sf_11_minus == pytest.approx(1.5)
     assert sf_22_plus == pytest.approx(1.5)
     assert sf_22_minus == pytest.approx(1.5)
 
-    with pytest.raises(RuntimeError):
-        rect_mat.get_sf_p()
-
 
 def test_get_effective_material():
     """Tests effective material properties."""