Added guidance for using the IDesignResult class

docs/BHoM_oM/Structure_oM/Design-Results.md

@@ -0,0 +1,112 @@
+## Design Results
+Design results represents the outputs from design checks carried out by bespoke engine methods. They are explicit in their properties and relate to specific design codes and actions. 
+
+This is intentional and preferred to more generic implementations such as having a generic `Parameters` property of type `Dictionary<string,double>` where the properties can fluccuate between implementations.
+
+To provide consistency across different design result objects a base `IDesignResult` is provided that inherits from existing classes in the `Structure` and `Analytical` namespaces.
+
+### Base Class
+The base class for all structural design results is stored in `BH.oM.Structure.Design` as an `IDesignResult` which inherits from the [`IStructuralResultClass`](https://github.com/BHoM/BHoM/blob/develop/Structure_oM/Results/IStructuralResult.cs) and [`IResultItem`](https://github.com/BHoM/BHoM/blob/cded0de0047171577144479fe8165684648f1ac3/Analytical_oM/Results/IResultItem.cs). 
+
+### Creating your own design result class
+The first decision to make is what namespace our class will sit in.
+
+#### Namespaces
+The namespace is used to designate the design code, for example `BH.oM.Structure.Design.Eurocode`, `BH.oM.Structure.Design.AISC` or `BH.oM.Structure.Design.SHC`.
+
+This keeps the object and engine method names clean. 
+
+These can be extended to materials too (e.g. `BH.oM.Structure.Design.Eurocode.Timber` and `BH.oM.Structure.Design.Eurocode.Steel`).
+
+!!! tip
+
+	We do not need to include the subsection and part of the code in the namespace - that is covered in the designation `ENum`.
+
+Next, we need to decide on an object name.
+
+#### Class name
+Name the class after the structural action being checked such as `Tension, `Bending` or `Torsion` using the language in the design code. 
+
+#### Designations
+This is an `Enum` that is included on the specific object to designate the specific version or annex of that code.
+
+!!! example "What a steel design designation might look like"
+    ```c#
+	    public enum SteelDesignation
+		{
+			[Description("Part 1-1: General rules and rules for buildings")]
+			[DisplayText("UK National Annex to EN 1993-1-1:2005")]
+			UK_NA_EN_1993-1-1_2005_A1-2014 = 0,
+			[Description("Specification for structural steel buildings")]
+			[DisplayText("AISC 360-22 : 2022")]
+			AISC_360-22_2022 = 1
+		}
+    ```
+
+#### Example Class
+Bringing together those decisions, we can create a class for tension design in accordance with EN 1993-1-1:2005 + A1:2014
+
+!!! example "What a tension design class in Eurocode may look like"
+    ```c#
+	namespace BH.oM.Structure.Design.Eurocode
+	{
+
+		[Description("An object that contains the outputs from a tension check.")]
+		public class Tension : IDesignResult, IImmutable
+		{
+			/***************************************************/
+			/**** Properties                                ****/
+			/***************************************************/
+			[Description("Id of the structure. Unused for many results.")]
+			public virtual IComparable ObjectId { get; }
+
+			[Description("Identifier for the Loadcase or LoadCombination that the result belongs to. Is generally name or number of the loadcase, depending on the analysis package.")]
+			public virtual IComparable ResultCase { get; }
+
+			[Description("Positive index, starting at one. Only set for cases with modal outputs such as dynamic cases.")]
+			public virtual int ModeNumber { get; }
+
+			[Description("Time step for time history results.")]
+			public virtual double TimeStep { get; }
+
+			[Description("The utilisation of the design check.")]
+			public virtual double Utilisation { get; }
+
+			[Description("The specific national annex the design check relates to.")]
+			public virtual SteelDesignation NationalAnnex { get; }
+
+			[Description("The partial safety factor for the resistance of cross-sections.")]
+			public virtual double GammaM0 { get; }
+
+			[Force]
+			[Description("The design axial force derived from the characteristic load multiplied by the relevant partial safety factors.")]
+			public virtual double DesignAxial { get; }
+
+			[Force]
+			[Description("The design ultimate resistance of the net cross section subject to tension.")]
+			public virtual double ResistanceAxial { get; }
+		}
+	}
+    ```
+
+1. Note that properties such as `Area` are not stored on the `TensionDesign` object as that is queryable from the `Bar.SectionProperty.Area` to avoid bloating objects and duplicating data. 
+2. Only properties that are dervied from the design code should be stored on the `DesignCheck` object.  
+3. [Quantity Attributes](https://github.com/BHoM/BHoM/tree/develop/Quantities_oM/Attributes) are used to specify the units (adhering to the BHoM SI). 
+
+Similar classes can be derived for `CompressionDesign`, `BucklingDesign` and `ShearAndTorsionDesign`.
+
+!!! tip
+
+	The `IImmutable` is not strictly required on the class definition as it's implicit from `IDesignResult` but it's clearer to state explicitly. You can read from about [`IImmutable` here.](https://bhom.xyz/documentation/BHoM_oM/Base_oM/Interfaces/IImmutable/)
+
+#### Hashing
+Specific results can be identified using a combination of `ObjectId`, `ResultCase`, `TimeStep`, `ModeNumber`. 
+
+For example, when a user wants to retrieve a specific result from a database. 
+
+!!! tip
+
+	If you are writing multiple iterations of design results to a database you will need to include an iteration property on your design result object.
+
+
+