Structural Analysis of in-Plane Loaded CLT Beams

Abstract

Cross laminated timber (CLT) is a versatile engineered timber product that is increasingly well-known and of global interest in several applications such as full size plane or linear timber elements. The aim of this study involves investigating the performance of CLT beams loaded in-plane by considering bending and shear stress analysis with a special emphasis on the in-plane shear behavior including the complex internal structure of CLT. Numerical analysis based on 3D-FE models was used and compared with two existing analytical approaches, namely representative volume sub element (method I) and composite beam theory (method II). The separate verification of bending and shear stresses including tree different shear failure modes was performed, and a good agreement was obtained. The main difference between the results relates to shear failure mode in the crossing areas between the orthogonally bonded lamellas in which the distribution of shear stresses τzx over the crossing areas per height of the CLT beam is not in accordance with the analytical assumptions. The presented analyses constitute the first attempt to contribute to the on-going review process of Eurocode 5 with respect to CLT beams loaded-in plane. Currently, regulations on designing these types of beams do not exist, and thus experimental and numerical investigations are planned in the future.Keywords: cross laminated timber; in-plane loading; FE-analysis; shear stress; normal stress; shear failure modes ANALIZA NOSIVOSTI CLT GREDA OPTEREĆENIH U RAVNINI ELEMENTA Sažetak: Križno lamelirano drvo (CLT) svestrani je inženjerski proizvod na bazi drveta koji je sve poznatiji i globalne važnosti u različitim primjenama poput pločastih i linijskih elemenata velikih dimenzija. Prikazani rad usmjeren je na istraživanje ponašanja CLT greda opterećenih u ravnini elementa, uzimajući u obzir analizu naprezanja od savijanja i posmika, s naglaskom na posmična naprezanja u ravnini elementa i složenu unutrašnju strukturu CLTa. Numerička analiza bazirana na 3D-FE modelima uspoređena je s dvama postojećim analitičkim pristupima pod nazivom reprezentativni volumni pod element (metoda I) i kompozitna štapna teorija (metoda II). Provedena je odvojena verifikacija naprezanja od savijanja i posmika uzimajući u obzir tri različita posmična mehanizma sloma, pri čemu je dobiveno dobro slaganje rezultata. Glavna razlika među rezultatima vezana je za posmični mehanizam sloma na kontaktu ortogonalno lijepljenih lamela, gdje se raspodjela posmičnih naprezanja τxz po lijepljenom kontaktu po visini CLT grede ne poklapa s teoretskim pretpostavkama. Prikazana analiza početni je doprinos trenutačno revidiranog Eurokoda 5, vezano za CLT grede opterećene u ravnini elementa. Trenutačno ne postoje propisi za njihovo dimenzioniranje pa su stoga daljnja eksperimentalna i numerička istraživanja ove tematike u planu. Ključne

Experimental Investigation of Cross Laminated Timber Elements with Holes or Notches at In-Plane Beam Loading Conditions

“…for 100 mm ≤ b ≤ 200 mm (13) where τ xy,net is the maximum net shear stress for a prismatic beam without a hole or notch, k b is the lamination width factor, and where k h2 and k n are the stress concentration factors according to Equations ( 14) and (15), as follows:…”

“…where τ tor,z is the maximum torsional shear stress for a prismatic beam without a hole or notch, k b is the lamination width factor according to Equation (13), n CA is the number of crossing areas in the beam width direction, m is the number of longitudinal laminations in the beam height direction and k h1 and k n are the stress concentration factors according to Equations ( 15) and ( 18), as follows:…”

“…The proposed model is generally based on the original model for prismatic CLT beams previously presented by Flaig [6] and Flaig and Blass [4,11] and on the use of stress concentration factors that account for holes or notches in CLT beams. However, the original model of Flaig and Blass [4,11], which was also used in the ongoing revision of EC5 [8] suffers from some drawbacks in terms of assumptions regarding the distributions of internal forces and shear stresses acting in the crossing areas, as pointed out in [12][13][14][15][16]. Recent 3D numerical-FE analyses, as presented by Jeleč et al [16,17] and Danielsson et al [18], indicate significant differences in the force and stress predictions in the crossing areas compared with the original model.…”

Cross-laminated timber (CLT) – a state of the art report

“…Capacity proofs FM I and FM II include verification of the expression (23): (23) In case of FM III, the theory of composite girders is used to calculate three components of shear stress according to expressions (24), (25) and 26 Proposed analytical method assumes a uniform distribution of torsional shear stress τ tor in beam height and width direction, wherein recent studies based on 3D numerical analysis indicate non uniform distribution in beam height [72,73] and beam width direction [74], respectively.…”