Stresses in Curved Glued-Laminated Timber Beams: Experimental Study

The distribution of stresses within the curved portion of double tapered and pitched glued-laminated timber beams was studied experimentally. Four small beams were built and tested after being instrumented with strain-gauge rossettes. The four test specimens had the same roof angle, B = 20?. Their ratio depth at midspan to radius of curvature was, respectively, 0.00, 0.110, 0.250, and 0.500. The beams were symmetrically point-loaded to produce pure bending on the curved central portion. The strains were recorded and the stresses were computed according to Hooke’s law for an orthotropic material. The elastic constants were determined from compression and bending tests on specimens cut from the beams. Taking the nominal bending stress at midspan as a reference, the experimental stresses were expressed in terms of stress factors Kr (for the radial direction) and Ke (for the tangential direction). These factors were compared with those obtained by means of an available theoretical solution and the agreement was shown to be good. Both experimental and theoretical results suggest that current design practice underestimates the maximum radial stress. (perpendicular to the grain) in the cases considered.

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