Analytischer Ansatz zur Erfassung von Tragfähigkeitssteigerungen infolge von Schubverstärkungen in Bauteilen aus Brettschichtholz und Brettsperrholz

Abstract

Analytical approach to determine the increase in loadcarrying capacity due to shear reinforcement in structural elements from glued-laminated and cross-laminated timber This article presents an analytical approach to determine the load-carrying capacity of timber elements from glued-laminated or cross-laminated timber, featuring shear reinforcements like self-tapping screws. Using matrix format, the approach is based on common theoretical concepts and constitutive equations for material properties. It uses the structural anisotropy of the cross-sections with shear reinforcement, also enabling to incorporate the semi-rigid composite action between the reinforcement and the wood material. The description of the general approach is followed by a comparison with experimental data from tests on both timber products. It is shown that shear reinforcements have a distinct positive influence on cross-laminated timber elements. Shear reinforcement by self-tapping screws in glued-laminated timber elements does in contrast only result in a small increase in shear stiffness and shear strength.Bild 1 Selbstbohrende Vollgewindeschrauben nach abZ-9.1-519 [1]Self-tapping screws according to abZ-9.1-519 [1] AUFSATZ ARTICLEBild 2 Schubverstärkungen aus Vollgewindeschrauben in BSH-Träger (links) und in BSP-Element (rechts) Self-tapping screws as shear reinforcement in glulam beam (left) and in CLT-element (right) Bild 3 Querschnittsaufbau von Brettsperrholz Principle structure of cross-laminated timber Bild 4 Schubverformung und Rollschubversagen eines Brettsperrholzelementes Shear deformation and rolling-shear failure of a CLT-element

Assessing the integrity of glued-laminated timber elements

“…But unfortunately, not every structure meets these design, construction, and maintenance requirements, as documented in several publications, e.g. [10][11][12][13][14]. The most frequent damage affecting the integrity of the cross-section is cracking, see Fig.…”

“…); or doubts whether the assumptions applied during the design are fulfilled, e.g. no inspection for longer period or negative results of an investigation, an unexpected degradation, accidental loads, new knowledge, or, unfortunately extreme incidents like the collapse of the ice rink in Bad Reichenhall in 2006 [10] and a series of other failures of timber structures in Europe over the course of few years [11][12][13][14]. These incidents prompted an international research focus on the assessment of timber structures, specifically the RILEM technical committee ''AST'' [16] and a task force within COST Action ''E55'' [17].…”

“…1. Evaluation of 245 cases of damaged large-span timber structures [14]; type of damage (left) and causes of damage (right). non-destructive (NDT) and semi-destructive (SDT) assessment techniques [20][21][22][23].…”

“…14. Schematic of effective member width in dependence of location and depth of cracks in comparison to required width to transfer existing stresses, here shear stresses [14].…”

“…[55,[59][60][61] but the measured crack dimensions and location are to be evaluated individually for each structure. When considering structural boundary conditions it should be differentiated between cracks in areas of high shear and areas of high tension perpendicular to the grain stresses, see Fig 14 [14,55].…”