Three-dimensional finite solid element model for Japanese post and beam connection Jung-Pvo HONG Department of of British Columbia Vancouver.Canada David BARRETT Department of Wood Science,University of British Columbia Vancouver,Canada Summary A three-dimensional finite element(3D FE)model for Japanese post and beam connection was developed using a newly-developed 3D FE wood foundation model.This is the pioneering FE model for multiple nail connections.Details of model development were presented.Simulated results were compared with available experimental data.Limitations of the model and needs for model improvement were discussed. 1.Introduction e CP-T ndard c ttachi a beam in traditiona connector with ten Japanese hen,a mo I with the In thi CP-T plate foundation method which was newly developed by Ho el,the 2.Model description and子o the undary Stefanescu's tests [2].Any influence from loose DOSt. mm x 105 mm cross 400 developed w ouglas-fir, the CP fir employed in the
Three-dimensional finite solid element model for Japanese post and beam connection Jung-Pyo HONG Post Doctoral Fellowship Department of Wood Science, University of British Columbia Vancouver, Canada David BARRETT Professor Emeritus Department of Wood Science, University of British Columbia Vancouver, Canada Summary A three-dimensional finite element (3D FE) model for Japanese post and beam connection was developed using a newly-developed 3D FE wood foundation model. This is the pioneering FE model for multiple nail connections. Details of model development were presented. Simulated results were compared with available experimental data. Limitations of the model and needs for model improvement were discussed. 1. Introduction The Japanese CP-T connection is a standard connection for attaching a post to a beam in traditional Japanese post and beam construction. This connection consists of a CP-T steel plate connector with ten Japanese standard ZN65 nails. Often, a mortise and tenon joint is combined with the CP-T plate to strengthen the joint. In this study, based on the 3D FE single nailed connection model using wood foundation method which was newly developed by Hong [1], a 3D FE analysis for the CP-T connection with mortise and tenon joint was conducted. To validate the connection model, the experimental data of the CP-T connection tests available from Stefanescu [2] were cited. 2. Model description Fig. 1 The reference test setup by Stefanescu [2] (units: mm) Fig. 1 and Fig. 2 show the configuration of Stefanescu’s CP-T connection test and the corresponding 3D FE connection model. Dimensions of the connection and the boundary conditions of the model conformed to the Stefanescu’s tests [2]. Any influence from loose or tight wood-to-wood contact in the mortise and tenon joint was not considered. The CP-T plate was installed on one side, which is a typical connection detail. The connection was loaded by pulling a steel pin through the post. Stefanescu used Canadian coastal Western Hemlock for the post and beam, which had a 105 mm × 105 mm cross section and a range of specific gravity (SG) from 0.39 to 0.47; however, since the single nailed connection model was developed with Douglas-fir, the CP-T connection model used also the material models of Douglas fir employed in the single connection model
coredeangmen AN Fig.2 Three-dimensional FE CP-T connection model and the boundary conditions Table 1 shows the material parameters used for the CP-T connection model.Details of the ection with width of 4.5xnail diameter,d Wood foundation with square cross section facilitated meshing work on this overlapped regions. Table i mate rs of three dim For For wood Material parameters* material model foundation material mode Elastic modulus:L(MPa) 16900 740 Elastic modulus:R=T (MPa) 830 140 Elastic shear modulus:RL=LT (MPa) 1740 Elastic shear r nodulus:RT(MPa) 201 50 Poisson's ratios:RL,LT,RT() 0.018.0.37,0.38 0.07,0.37,0.38 Compressive,tensile yield stress:L,R(=T)(MPa) 44.3.4.5 18.l,5.7 Compressive,tensile tangent modulus:L.R(=T)(MPa) 169,8.3 7.4,1.4 432,1.3 3.2,3.2 17.4,3.0 1.40.5 the yield e of MPmu For C r 200 GPad Por lastic model was assumed with the yield stress of 250 MPa *L=longitudinal,R=radial and T=tangential direction
Fig. 2 Three-dimensional FE CP-T connection model and the boundary conditions To embody the connection brick elements (SOLID45 from ANSYS) that are eight-noded, quadrilateral isoparametric element are used. The surface-to-surface contact elements were defined on every contact interface with frictional coefficient of 0.7 for wood involved contact and 0.3 for steel-to-steel contact (CONTA174 and TARGE170 from ANSYS). Table 1 shows the material parameters used for the CP-T connection model. Details of the procedures to determine the material parameters and the rationale of wood foundation method can be found in companion paper [3]. The wood foundation was chosen to have a square cross section with width of 4.5×nail diameter, d (= 3.3mm) as shown in Fig. 3. Since the nail spacing of the connection was too narrow to accommodate the two adjacent the 4.5×d foundations, overlap of the foundations was inevitable. Wood foundation with square cross section facilitated meshing work on this overlapped regions. Table 1 Material parameters of three-dimensional finite element models for wood, wood foundation and steel used for the CP-T connection model. Material parameters * For wood material model For wood foundation material model Elastic modulus: L (MPa) 16900 740 Elastic modulus: R=T (MPa) 830 140 Elastic shear modulus: RL= LT (MPa) 1740 140 Elastic shear modulus: RT (MPa) 301 50 Poisson’s ratios: RL, LT, RT ( ) 0.018, 0.37, 0.38 0.07, 0.37, 0.38 Compressive, tensile yield stress: L, R (=T) (MPa) 44.3, 4.5 18.1, 5.7 Compressive, tensile tangent modulus : L, R (=T) (MPa) 169, 8.3 7.4, 1.4 Shear yield stress : RL (=LT), RT (MPa) 43.2, 1.3 3.2, 3.2 Shear tangent modulus : RL (=LT), RT (MPa) 17.4, 3.0 1.4, 0.5 For nail, elasto-perfectly plastic model was assumed with the yield stress of 360 MPa, modulus of 200 GPa and Poisson’s ratio of 0.3. For CP-T plate, an elasto-perfectly plastic model was assumed with the yield stress of 250 MPa, modulus of 200 GPa and Poisson’s ratio of 0.3. * L = longitudinal, R = radial and T = tangential direction
3.Results 3.1 Excerpts from Stefanescu's experimental reports the connection eccentr during o ing:an Ihis titing Fig.3 The square wood foundations incorporated with an average tilting angle ()of 2.8 degrees between post and beam in wood member models the 0mmongeancomomiapo.tetoiohelidacnetdnweucdst first.then.the force (pressure)-controlled loading method was tried. were the m ajor failure modes.However,during the process of model development,it was ved by stefanescu r21 (a)a tilted cp.tco under loadin nail pull-out and the CP-I plate in shear 3.2 Simulated deformation of the CP-T connection the post.Although the force ing behaviour because it was due to the rotation of the post only and ed
Fig. 3 The square wood foundations incorporated in wood member models 3. Results 3.1 Excerpts from Stefanescu’s experimental reports Stefanescu [2] reported that one-side attachment of the CP-T plate to the post made the connection eccentric during loading; and eventually, the connection was tilted toward the plate side, due to the twisted beam and post, as shown in Fig. 4-A. This tilting behaviour was observed for all eight tests with an average tilting angle (θ) of 2.8 degrees between post and beam. This phenomenon necessitated deliberation on the loading scheme and boundary condition for the FE model. For an original model, the boundary condition was set with all fixed nodes on the side surfaces of the 400 mm-long beam conforming to the fixtures of bolted connections in the real test; and, for the loading scheme, an incremental displacement-controlled loading method was used at first, then, the force (pressure)-controlled loading method was tried. Failure modes of the connection, which were photographed by Stefanescu [2], are shown in Fig.4-B and C. Perpendicular to grain tension splitting of the beam member, nail pull-out and plate shear were the major failure modes. However, during the process of model development, it was discovered that the most influential failure on model prediction was end-tearout of nail in the tenon. More details of end-tearout effect on the simulated results will be presented in section 3.4. Fig.4 Actual deformations observed by Stefanescu [2]; (A) a tilted CP-T connection under loading, θ was the tilting angle, (B) failure mode; perpendicular to grain tension splitting, (C) failure mode; nail pull-out and the CP-T plate in shear 3.2 Simulated deformation of the CP-T connection Fig. 5 and Fig. 6 show the progress of the simulated deformation when displacement-controlled, and force (pressure)-controlled loading were applied to the connection model. It was found that the model using an incremental displacement-controlled loading scheme could not simulate the tilting behaviour of the connection. It provided only a uniformly vertical translation of the post. Although the force (pressure)-controlled loading scheme represented the tilting behaviour, it did not agree with actual tilting behaviour because it was due to the rotation of the post only and the bottom sill was not twisted
thesmaed dfomion by the displacemen-ed scheme 2.2mr 3.1n 4.4m 6.6mm 12.3mm Fig.6 Progress of the simulated deformation by the force(pressure)-controlled loading scheme (sectioned views) ent of th of the real rmation due to the pir
1.6mm 2.0mm 2.5mm 3.6mm 5.3mm 7.0mm Fig. 5 Progress of the simulated deformation by the displacement-controlled loading scheme (Sectioned views) 1.3mm 2.2mm 3.1mm 4.4mm 6.6mm 12.3mm Fig. 6 Progress of the simulated deformation by the force (pressure)-controlled loading scheme (sectioned views) In fact, the boundary condition of the model provided rigid constraints. No displacement of the nodes that were fixed in all degree of freedom was allowed. However, the beam fixtures of the real test consisted of two bolted connections that had allowed the beam to twist. Also, the loading steel pin linking the post to the crosshead permitted swivelling of the post and deformation due to the pin
the met eme appear ddca"ngidco 3.3 Simulated deformation of nails and CP-T plate ement-contr loading met out from the bottom sill and intensively plastic bending. Simulated Y-directional plastic stra tours in the CP-Tplat e )n e CpTe ande 3.4 Load-deformation curve of the CP-T connection 3.4.1 Initial model Simulated load-deformation curves under Simulated curve of the initial model 10 of this poo inabilityof the model to predict fractures was suspected as one of the major causes. odned FE mod In the cP-T connection.the three middle nails ou 40 e bottom sill penetrated into
embedment on the wood post. These discrepancies between the model and the real test resulted in highly stiff predictions of the load-deformation response compared to experimental observations. Therefore, assuming that the real connection tests were conducted under ideally rigid constraints, the deformation simulated by the displacement-controlled method was deemed reasonable. Fig. 4-C appears the case of deformation under ideally rigid constrains. 3.3 Simulated deformation of nails and CP-T plate Fig. 7 shows the simulated deformation of nails and CP-T plate under displacement-controlled loading. Judging from Stefanescu’s results, deformation simulated by the displacement-controlled loading method agreed more closely with the experimental observations than the force-controlled loading method. The flexural deformation of the three nails penetrating the tenon showed nail pullout from the bottom sill and intensively plastic bending. Simulated Y-directional plastic strain contours in the CP-T plate appears good agreement with the experimental observation. Compared to Fig. 4-C, the contour showed a good indication of the plate shear failure that was observed in the real tests. Fig. 7 The Y-directional plastic strain contour in the nails (left) and the CP-T plate under displacement-controlled loading (right) 3.4 Load-deformation curve of the CP-T connection 3.4.1 Initial model Fig. 8 Simulated load-deformation curves of the initial and the modified CP-T model Simulated load-deformation curves under displacement-controlled loading are superimposed on Stefanescu’s experimental curves in Fig. 8. Simulated curve of the initial model showed high load-carrying capacity compared to the experimental curves. Although causes of this poor load-deformation prediction may be due to many sources such as different wood species, the rigid boundary conditions and the tilting member. The inability of the model to predict fractures was suspected as one of the major causes. In the CP-T connection, the three middle nails out of the five nails in the bottom sill penetrated into the tenon. The typical failure type of nails penetrating into the tenon is shown in Fig. 9