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Queen post truss and its elements

Short answer

A queen post truss for 8–12 m spans consists of a tie beam (tension), principal rafters, two queen posts, a straining beam (compression) between them, a straining sill below, and struts to mid-span of rafters. It provides clear space between posts.

Sketch a queen post truss with its corresponding elements and explain the function of each element.

A queen post truss is used for spans of about 8-12 m. It has two vertical queen posts instead of one king post, joined at the top by a horizontal straining beam and at the bottom by a straining sill.

                          ridge
                           /\
                          /  \
                         /    \   principal rafter
     straining beam --> +------+
                       /|      |\
                      / |      | \
                     /  |      |  \
             strut  /\  |      |  /\  strut
                   /  \ |      | /  \
                  /    \|      |/    \
                 +======+======+======+  <- straining sill
                 +--------------------+  <- tie beam
                wall                 wall
       the two vertical members | | are the queen posts
ElementFunction
Tie beamTakes the horizontal thrust of the rafters (tension); carries the queen posts
Principal raftersCarry the roof load through purlins; compression and bending
Queen posts (2)Vertical tension members which hold up the tie beam at two points and receive the thrust of the struts at their feet
Straining beamHorizontal strut between the heads of the queen posts; resists the inward thrust of the principal rafters
Straining sillMember on the tie beam between the feet of the queen posts; keeps them apart and resists the thrust of the struts
Struts/bracesInclined members from the feet of the queen posts to the principal rafters; support the rafters midway and reduce their span
Purlins and cleatsPurlins carry the common rafters and are held by cleats
Common rafters, battensDirectly support the roof covering
Wall plateSpreads the load on the wall

Span and use: spans of 8-12 m for halls, godowns and workshops. Compared with a king post truss it covers a larger span, and the clear space between the queen posts can be used (for example, as an attic or store).

✓ Answer checked by Claude Opus 5.5 (high effort)

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