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It sounds like you're referring to the UK "Green Book" for structural steelwork connections. The full title is usually (often called the Green Book), published by the Steel Construction Institute (SCI) and the British Constructional Steelwork Association (BCSA) .
There are two main volumes commonly referred to as the Green Book, depending on the connection type: SCI P358: Simple Joints to Eurocode 3 : This is the most common "Green Book." It covers nominally pinned connections structural steel connections the green book pdf
: Connections between steel columns and concrete foundations. It sounds like you're referring to the UK