Set default values for delta parameters in form 4.2 from nen_en_1992_…

blueprints/codes/eurocode/nen_en_1992_1_1_c2_2011/chapter_4_durability_and_cover/formula_4_2.py

@@ -17,9 +17,9 @@ def __init__(
         self,
         c_min_b: MM,
         c_min_dur: MM,
-        delta_c_dur_gamma: MM,
-        delta_c_dur_st: MM,
-        delta_c_dur_add: MM,
+        delta_c_dur_gamma: MM = 0,
+        delta_c_dur_st: MM = 0,
+        delta_c_dur_add: MM = 0,
     ) -> None:
         """[:math:`c_{min}`] Calculates the minimum concrete cover [:math:`mm`].
 
@@ -35,10 +35,16 @@ def __init__(
             [:math:`c_{min,dur}`] The minimum concrete cover based on environmental conditions based on art. 4.4.1.2 (5) [:math:`mm`].
         delta_c_dur_gamma: MM
             [:math:`Δc_{dur,γ}`] An additional safety requirement based on art. 4.4.1.2 (6) [:math:`mm`].
+            The value of [:math:`Δc_{dur,γ}`] for use in a Country may be found in its National Annex.
+            The recommended value is O mm. 0 mm is the default value in the formula if not specified otherwise.
         delta_c_dur_st: MM
             [:math:`Δc_{dur,st}`] A reduction of minimum concrete cover when using stainless steel based on art. 4.4.1.2 (7) [:math:`mm`].
+            The value of [:math:`Δc_{dur,st}`] for use in a Country may be found in its National Annex.
+            The recommended value, without further specification, is 0 mm. 0 mm is the default value in the formula if not specified otherwise.
         delta_c_dur_add: MM
             [:math:`Δc_{dur,add}`] A reduction of minimum concrete cover when using additional protection based on art. 4.4.1.2 (8) [:math:`mm`].
+            The value of [:math:`Δc_{dur,add}`] for use in a Country may be found in its National Annex.
+            The recommended value, without further specification, is 0 mm. 0 mm is the default value in the formula if not specified otherwise.
         """
         super().__init__()
         self.c_min_b = c_min_b
@@ -51,9 +57,9 @@ def __init__(
     def _evaluate(
         c_min_b: MM,
         c_min_dur: MM,
-        delta_c_dur_gamma: MM,
-        delta_c_dur_st: MM,
-        delta_c_dur_add: MM,
+        delta_c_dur_gamma: MM = 0,
+        delta_c_dur_st: MM = 0,
+        delta_c_dur_add: MM = 0,
     ) -> MM:
         """For more detailed documentation see the class docstring."""
         raise_if_negative(

tests/codes/eurocode/nen_en_1992_1_1_c2_2011/chapter_4_durability_and_cover/test_formula_4_2.py

@@ -30,6 +30,21 @@ def test_evaluation(self) -> None:
 
         assert form_4_2 == pytest.approx(expected=manually_calculated_result, rel=1e-4)
 
+    def test_evaluation_default_values(self) -> None:
+        """Test the evaluation of the result using the default values for delta parameters."""
+        # Example values
+        c_min_b = 15  # mm
+        c_min_dur = 20  # mm
+        form_4_2 = Form4Dot2MinimumConcreteCover(
+            c_min_b=c_min_b,
+            c_min_dur=c_min_dur,
+        )
+
+        # Expected result, manually calculated
+        manually_calculated_result = 20
+
+        assert form_4_2 == pytest.approx(expected=manually_calculated_result, rel=1e-4)
+
     def test_raise_error_when_negative_c_min_b_is_given(self) -> None:
         """Test the evaluation of the result."""
         # Example values