Pressure Distribution in Block Glue Lines Analyzed by Theory of Beams on Elastic Foundation

Block gluing of glulam beams is an effective production method to obtain massive wooden elements of cross-sections with very large dimensions. Due to the extensive gluing areas, it is difficult to impose clamping pressures similar to those as in standard glulam productions. The paper analyzes the pressure distribution perpendicular and parallel to the clamping bars by means of plain stress continuum analysis and more notably by theory of beams on elastic foundation. Hereby the stiffness perpendicular to the grain of the beams is realized implicitly by the bedding stiffness. Closed form solutions are given to determine pressures and desirable cambers of the clamping bars. The effect of nonlinear pressure distribution was investigated experimentally with a full scale block glued specimen tested in block shear, delamination and bending whereby the test results are compared against glue line thicknesses. The test results showed a good agreement with the analysis for higher glue line thicknesses at the calculated low pressure areas. In the mechanical tests, no correlation between the rather thin glue line thicknesses and strength values was detected.