fix: gross properties sign

structuralcodes/sections/_generic.py

@@ -179,6 +179,8 @@ def compute_area_moments(geometry, material=None):
                 [0, 1, 0],
                 mesh_size=self.mesh_size,
             )
+            # Change sign due to moment sign convention
+            iyz *= -1
             # Integrate a dummy strain profile for getting first
             # and second moment respect z axis and product moment
             (
@@ -192,13 +194,15 @@ def compute_area_moments(geometry, material=None):
                 tri=tri,
                 mesh_size=self.mesh_size,
             )
+            # Change sign due to moment sign convention
+            izz *= -1
             if abs(abs(izy) - abs(iyz)) > 10:
                 error_str = 'Something went wrong with computation of '
                 error_str += f'moments of area: iyz = {iyz}, izy = {izy}.\n'
                 error_str += 'They should be equal but are not!'
                 raise RuntimeError(error_str)
 
-            return abs(sy), abs(sz), abs(iyy), abs(izz), abs(iyz)
+            return sy, sz, iyy, izz, iyz
 
         # Create a dummy material for integration of area moments
         # This is used for J, S etc, not for E_J E_S etc

structuralcodes/sections/section_integrators/_marin_integrator.py

@@ -44,7 +44,7 @@ def prepare_input(
         # and stress coefficients for each part.
         prepared_input = []
         # 1. Rotate section in order to have neutral axis horizontal
-        angle = atan2(strain[2], strain[1])
+        angle = -atan2(strain[2], strain[1])
 
         rotated_geom = geo.rotate(angle)
         # 2. Get y coordinate of neutral axis in this new CRS