Design of Cross Laminated Timber (CLT) - Calculation and Design Methods for Concentrated Loads

Sep 15, 2026

Uploaded by Adam

Paper focuses on calculation and design methods for Cross Laminated Timber (CLT) elements, emphasizing how shear deformation of cross layers affects load-bearing behavior. It analyzes normal and shear stress distributions created by concentrated loads in uniaxial simply supported systems using shear analogy and FEM with shell elements, then compares both results. A simplified approach is provided to account for shear deformation effects on longitudinal strain, and theoretical plus experimental studies address twisting stiffness and its structural impact.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages8

Reading Time20 min

AccessFree to download

Summary

1. Introduction

2. Calculation Model and Design

Composite theory and shear analogy

Stress verifications and standards

3. Concentrated Load

3.1 Shell-model – Shear Analogy

Design of Cross Laminated Timber (CLT) Peter Mestek Dipl.-Ing., Research Associate Heinrich Kreuzinger Univ.-Prof. Dr.-Ing. Stefan Winter Univ.-Prof. Dr.-Ing. Chair of Timber Structures and Building Construction, Technical University Munich, Germany Summary This paper is focused on calculation and design methods for Cross Laminated Timber (CLT) elements. The influence of the shear deformation of the cross layers and the resulting consequences to the load bearing behaviour is explained. The main focus lies in the stresses caused by concentrated loads. Normal and shear stress distribution in the area of a concentrated load is calculated and evaluated for uniaxial spanned systems according to the shear analogy and by an FEM-calculation with shell elements. The differences of the results are explained. A simplified method shows how to consider the influence of the shear deformation on the longitudinal strain of a simply supported beam stressed by a concentrated load. Furthermore theoretical considerations and experimental investigations into the twisting stiffness ofCLT-elements and its influence on load bearing behaviour are presented. 1. Introduction Advanced manufacturing technologies of modern timber construction enable the fabrication and use of large-sized plane elements. Beside timber frame construction with its high level of prefabrication the market share ofCLT-constructions is constantly increasing. The cross section ofCLT-elements is generally characterised by at least three glued board layers with orthogonally alternating orientation of neighboured layers. The load bearing behaviour of these plane elements is affected by the material and, due to the orthogonal orientation of the single layers, by the constructive anisotropy. Moreover the shear deformation including the ductile composite must be considered. Fig. 1 Shear deformation of a CLT-element Fig. 1 shows an element under shear stress resulting from load perpendicular to the plane. The cross layers are strained by rolling shear. Due to the low rolling shear stiffness, the deformation of the total section is caused almost exclusively by the deformation of the cross layers. The deformation figure infringes the Bernoulli hypothesis, which says, that straight lines perpendicular to the midsurface before deformation remain straight after deformation. This means that under certain circumstances the ductile composite of the layers in each direction has to be considered. 2. Calculation Model and Design For load perpendicular to the plane, the modelling ofCLT-elements can be carried out on the basis of the composite theory. It covers the strength and the stiffness of each single layer and enables the modelling of any cross section. The stress distribution results from the stiffness of the single layers. The basic approach is described in [1] and is listed in annex D ofthe DIN 1052:2004-08 [2] . Each case must be considered carefully in order to decide if the shear deformation has to be taken into account. One approach to the solution of this problem is the method of shear analogy by Kreuzinger [3] which is also listed in annex D ofthe DIN 1052 [2]. By the use of current plane frame programmes it enables to calculate CLT-elements including the ductile composite of the layers each direction. composite theory shear analogy Fig. 2 Distribution of longitudinal stresses Fig. 2 shows the normal stress distribution according to the composite theory and the shear analogy. Due to the ductile composite the stresses in the centre lines (σc,0,d / σt,0,d) of the layers decreases while the fraction of bending stress (σm,d) increases. Consequently the values of the edge stress – relevant for design-increase. Comment: According to [2], the elastic modulus has to be set to zero if the single boards are not edge-glued. The verifications for load perpendicular to the plane are to be found in chapter 10.7 ofthe DIN 1052 [2]. Following verifications

FAQs

How does shear deformation of the cross layers influence CLT load-bearing behavior?

Shear deformation causes a stress distribution that differs from predictions based on the Bernoulli hypothesis, meaning deformation is governed largely by the cross layers and affects bending-related stress fractions and design-critical edge stresses.

How are stresses under concentrated loads calculated in the paper?

Normal and shear stresses under concentrated loads are calculated for simply supported uniaxial systems using shear analogy and compared with FEM results using shell elements across vertical sections.

When can shear deformation effects be neglected, according to the paper?

For simply supported beams under uniformly distributed load, studies show negligible shear-deformation influence when the span-to-thickness ratio exceeds 20; under these boundary conditions the shear deformation can be neglected.

Sep 15, 2026

Uploaded by Adam