ridgepole vs tie beam

ridgepole

noun
  • A beam along the ridge of a roof to which the rafters are attached. 

  • A horizontal pole that supports the roof of a ridge tent 

tie beam

noun
  • a horizontal beam that serves to prevent two other structural members from separating while forming the base of a triangular truss for a pitched roof. 

How often have the words ridgepole and tie beam occurred in a corpus of books? (source: Google Ngram Viewer )