The Collaborative International Dictionary of English v.0.48:

Straining \Strain"ing\,
   a. & n. from Strain.
   [1913 Webster]

   Straining piece (Arch.), a short piece of timber in a
      truss, used to maintain the ends of struts or rafters, and
      keep them from slipping. See Illust. of Queen-post.
      [1913 Webster]