https://orcid.org/0000-0001-6585-8620
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ABSTRACT
Gaps are very common in the mortise-tenon (M-T) joints of traditional timber structures. To investigate the rotational behavior of straight M-T joints with gaps, the mechanical mechanism and contact states between the mortise and tenon for the straight M-T joints with gaps were analyzed. A moment-rotation theoretical model of straight M-T joint with gap, based on the embedded compressive and friction mechanisms of the contact surfaces, was proposed and verified by the cyclic loading tests of four 1/3.2-scaled straight M-T joint specimens with different gaps. To further predict the deformation modes and hysteretic behavior of the joint involving gap, nonlinear numerical analyses were performed using ABAQUS. Results indicated that the predictions of theoretical and numerical model were in good accordance with the experimental results. Then, the parametric analyses were carried out based on the validated finite element model, the effects on the rotational behavior of straight M-T joint of major parameters, such as the friction coefficient of wood, vertical gaps, and horizontal gaps, were analyzed. It is found that the initial rotational stiffness, yielding moment, peak moment, and ductility of the joint with gap increased with an increase in the friction coefficient. The initial rotational stiffness, yielding moment, and peak moment of the joint remarkably decreased with the increase of the vertical and horizontal gap. The ductility of joint significantly reduced with the increasing vertical gap, however, the joint slightly improved with an increase in the horizontal gap.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Nomenclature
| M-T | = | Mortise-tenon |
| M - θ | = | Moment-rotation |
| μ | = | The friction coefficient |
| ε | = | The strain of wood |
| fc,90 | = | The yield strength perpendicular to the grain of wood |
| εcu | = | The ultimate strain perpendicular to the fiber direction of wood |
| xb | = | The EC zone heights of the contact area II of the joint with gap |
| lb | = | The lengths of the EC area II |
| bT | = | The width of the tenon |
| = | The height of the tenon | |
| bM | = | The width of the mortise |
| L | = | The diagonal line length of the tenon |
| θ | = | The rotation of the joint |
| F1 | = | The compression force of the EC area I of the tenon |
| f1 | = | The friction force of the EC area I |
| ε1,max | = | The maximum strain in the EC area I of the tenon |
| he | = | Half the tenon height |
| θ0 | = | The slipping rotation |
| F2,e | = | The compression force in the area II under the elastic state |
| d | = | The distance from the loading point of the beam to the column surface |
| F2,p | = | The compression force at EC zone II under elasto-plastic state |
| lp,II | = | the plastic segment length of the EC area II |
| F1,p | = | The compression force of EC area I |
| le,I | = | The length of the elastic segment for the EC area I |
| le,II | = | The length of the elastic segment in the EC zone II |
| Mp | = | The bending moment of the straight M-T joint with gap under the plastic state |
| θy,I | = | The rotation at which the EC zone I begins to get into the plastic state |
| DG | = | The damage degree |
| δH | = | The size of horizontal gap |
| MTG | = | The M-T joint specimen with gaps |
| C3D8R | = | The 3-D linear reduced integration solid element |
| EC | = | Embedded compression |
| FE | = | Finite element |
| σ | = | The stress strength of wood |
| Ec,90 | = | The compressive elastic modulus perpendicular to the grain of wood |
| εcy | = | The compressive yield strain perpendicular to the fiber direction of wood |
| xa | = | The EC zone heights of the contact area I of the joint with gap |
| la | = | The length of the EC area I |
| δ | = | The height of the tenon being weakened |
| lT | = | The length of the tenon |
| hM | = | The height of the mortise |
| dC | = | The diameter of the column |
| φ | = | The angle between the diagonal line and the upper surface of the tenon |
| F | = | The external load |
| F2 | = | The compression force of the EC area II of the tenon |
| f2 | = | The friction force of the EC area II |
| ε2,max | = | The maximum strain in the EC area II of the tenon |
| Ms | = | The bending moment of the joint in the slipping state |
| F1,e | = | The compression force in the area I under the elastic state |
| Me | = | The bending moment for the straight M-T joint with gap in the elastic contact state |
| F1,e | = | The compression force at EC zone I under elasto-plastic state |
| le,II | = | The elastic segment length of the EC area II |
| Mep | = | The bending moment for the straight M-T joint with gap in the elasto-plastic state |
| F2,p | = | The compression force of EC area II |
| lp,I | = | The length of the plastic segment for the EC area I |
| lp,II | = | The length of the plastic segment in the EC zone II |
| θy,II | = | The rotation at which the EC area II starts to enter the plastic state |
| θu | = | The ultimate rotation |
| Δu | = | The referenced ultimate displacement |
| MT0 | = | The intact M-T joint specimen |
| 3-D | = | Three-dimensional |