"静载挠度" can be translated into English as "static deflection under dead load" or more concisely as "static deflection" (when the context clearly implies it's under static loading conditions, such as dead load).
Static deflection under dead load: This full phrase explicitly describes the deflection occurring under a constant, unchanging load (dead load), which is useful for clarity in technical documents.
Static deflection: In many engineering contexts, especially when discussing structural behavior under static loads, this term is sufficient and widely understood.
Choose the version that best fits your specific technical or communication needs.