Resistance and Failure Modes of Axially Loaded Groups of Screws

Abstract

Screwed connections provide high resistance in strength and stiffness. Arranged to a group the screws interact and influence each other in dependency of their in-between spacings. A test setup was found to investigate (i) the influence of the spacings in-between the screws, and (ii) the anchoring depths on the failure modes and resistances of groups of screws. We conducted tests on axially loaded and under a stress-fiber angle of 90° placed groups of screws in solid timber (ST) and glued laminated timber (GLT) of Norway spruce. Steel fracture, withdrawal failure and also block shear failure mode, till now for self-tapping screws not considered by design codes, were observed. Additionally and based on a simple mechanic load shearing consideration model for the block shear failure mode was developed for the investigated axially loaded groups of screws. Verification with test results confirms congruent but conservative results. © RILEM 2014.