In this paper a precise model is established for deflection prediction of mechanically jointed beams with partial composite action. High accuracy of the proposed method is demonstrated through comparison with a comprehensive finite element (FE) modelling for a timber-concrete partial composite beam. Next, the obtained numerical results are compared with gamma-method, a well-known simplified solution for timber engineers according to the Eurocode 5. Validity and accuracy level of the gamma-method are investigated for various boundary conditions as well as different values of beam length-to-depth ratio, and discussed in details.
Cross-laminated timber (CLT) is an engineered wood product made up of layers of structurally graded timber, where subsequent layers are oriented orthogonally to each other. In CLT, the layers oriented in transverse direction, generally termed as cross-layer, are subjected to shear in radial–tangential plane, which is commonly known as rolling shear. As the shear modulus of cross-layers is significantly lower than that in other planes, CLT exhibits higher shear deformation under out-of-plane loading in contrast to other engineered wood products such as laminated veneer lumber (LVL) and glue laminated timber (GLT). Several analytical methods such as Timoshenko, modified gamma and shear analogy methods were proposed to account for this excessive shear deformation in CLT. This paper focuses on the effectiveness of Timoshenko method in hybrid CLT, in which hardwood cross-layers are used due to their higher rolling shear modulus. A comprehensive numerical study was conducted and obtained results were carefully analyzed for a range of hybrid combinations. It was observed that Timoshenko method could not accurately predict the shear response of CLTs with hardwood cross layers. Comprehensive parametric analysis was conducted to generate reliable numerical results, which were subsequently used to propose modified design equations for hybrid CLTs.
Glulam members which are manufactured with Japanese cedar plantation timber are constructed into a box type of portal frames to investigate the moment-resisting performance when subjected to a lateral load. The joints of the frame are connected using aluminium connectors and self-tapping screw fasteners, and the placement of fasteners on the connection are arranged into three patterns. The loading protocol is applied laterally in seven cyclic stages for the racking test. The maximum lateral load of 51.4 kN is attained for the portal frame fastened using self-tapping screws arranged in square pattern, followed by single circular pattern and double circular pattern. Resulted dissipated energy obtained from the portal frame with square pattern placement is 1224.2 kNmm during the cyclic loading stages, higher than the other fastener arrangement by 20%. The allowable shear strength of the box-type portal frame is decided by the load corresponding to the shear deformation of 1/120 radian.
Cross laminated timber (CLT), as a structural plate-like timber product, has been established as a load bearing product for walls, floor and roof elements. In a bending situation due to the transverse shear flexibility of the crossing layers, the warping of the cross section follows a zigzag pattern which should be considered in the calculation model. The Refined Zigzag Theory (RZT) can fulfill this requirement in a very simple and efficient way. The RZT, founded in 2007 by A. Tessler (NASA Langley Research Center), M. Di Sciuva and M. Gherlone (Politecnico Torino) is a very robust and accurate analysis tool, which can handle the typical zigag warping of the cross section by introducing only one additional kinematic degree of freedom in case of plane beams and two more in case of biaxial bending of plates. Thus, the RZT-kinematics is able to reflect the specific and local stress behaviour near concentrated loads in combination with a warping constraint, while most other theories do not. A comparison is made with different methods of calculation, as the modified Gamma-method, the Shear Analogy method (SA) and the First Order Shear Deformation Theory (FSDT). For a test example of a two-span continuous beam, an error estimation concerning the maximum bending stress is presented depending on the slenderness L/h and the width of contact area at the intermediate support. A stability investigation shows that FSDT provides sufficiently accurate results if the ratio of bending and shear stiffness is in a range as stated in the test example. It is shown that by a simple modification in the determination of the zigzag function, the scope can be extended to beams with arbitrary non-rectangular cross section. This generalization step considerably improves the possibilities for the application of RZT. Furthermore, beam structures with interlayer slip can easily be treated. So the RZT is very well suited to analyze all kinds, of shear-elastic structural element like CLT-plate, timber-concrete composite structure or doweled beam in an accurate and unified way.