Structural timber and glulam in compression perpendicular to grain

The characteristic strength values for compression perpendicular to grain as they appear in EN 338 (structural timber) and prEN 1194 (glulam) are currently up for discussion. The present paper provides experimental results based on EN 1193 that may assist in the correct assignment of such strength values. The dominant failure mode of glulam specimens is shown to be fundamentally different from that of structural timber specimens. Glulam specimens often show tension perpendicular to grain failure before the compression strength value is reached. For structural timber of normal sawing pattern no failure is visible until after compression strength is reached; ultimately, a shear failure mode becomes predominant. Despite the different failure modes, test results show that the levels of characteristic compression strength perpendicular to grain are of the same order for structural timber and glulam. The values are slightly lower than those appearing in prEN 1194 and less than half of those appearing in EN 338 that is currently being revised. The paper presents a numerical analysis to prove both the significant role of tension perpendicular to grain stresses in the failure mode of the glulam specimens and the combined roles of shear and tension perpendicular to grain stresses in the ultimate failure mode of structural timber.