Timber Frame Tension Joinery - Timber Frame Engineering Council

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Plastic hinges occur in the peg due to bending and are located at points of maximum moment (see Figure 3-5). This derivation is as follows: From equilibrium: x A P = (3-23) DF em For failure to occur, two plastic hinges must occur in the peg. Areas under the shear diagram give DF ( a − b) x DF ( d − c) x + 2 2 em A es D = 2 M (3-24) p DFem( a − b) = P (3-25) DF ( d − es c ) = P (3-26) Simplifying Equation 3-24, we obtain Px A + PxD = 4 M p (3-27) x D 4M p = −x P A (3-28) Total distance between hinges is x = x + x (3-29) A D 4M p 4FybD x = = P 6P 3 (3-30) Substituting Eq. 3-22 into Eq. 3-30 we obtain x = D ⎛ F 2Fyb⎜1+ ⎝ F 3F em em es ⎞ ⎟ ⎠ (3-31) As a numerical example, typical values for 1” Red Oak Pegs in Douglas Fir give a total distance between plastic hinges of 3.0 inches (using F yb = 12,601 psi, F em = 2070 psi, 17
and F es = 1728 psi) (see Sections 5.2 and 5.4). As will be discussed later, typical test results show hinges that are much closer together than is predicted with this yield mode. 3.4 Application of the European Yield Model to <strong>Timber</strong>-<strong>Frame</strong> Connections The yield model failure modes may be applied to timber frame connections since they are based on equilibrium and compatibility of materials and the only difference in the equations is the material used for the dowel. The wood pegs are assumed to yield in bending similarly to the steel dowels in the original derivation. Steel dowels yield plastically in bending with the entire cross-section deforming plastically after yielding is reached. It is important to note that the cross-section continues to gain resistance to load after the extreme fibers yield in tension or compression, up to the point where all of the material in the cross-section has yielded. After the entire section is yielded, the dowel can resist little additional load. Similar behavior occurs in wood as can be seen in Figure 3-6. Wood pegs are therefore assumed to yield plastically in bending. In the typical mortise and tenon joint (Figure 1-1), a state of double shear exists. For this reason, the following discussion will focus on the double shear yield model failure modes (Figure 3-2). The four modes of double shear failure can be assumed to apply. However, additional modes of failure have been observed in timber-frame connections. After comparing the theoretical hinge spacing of Mode IV to actual failed connections, where the hinge spacing is much closer than predicted, one must conclude that other factors exist to cause failure. The Mode IV equations are based on a simple bending failure in the dowel. Wood pegs, quite possibly, fail due to the combined effect of bending and shear on the cross-section. Since wood is so highly orthotropic, its strength is dependent on the loading orientation. Also, wood is typically weak in shear. This combined effect would tend to 18
Page 1 and 2: TIMBER FRAME TENSION JOINERY Richar
Page 3 and 4: Acknowledgments Acknowledgments go
Page 5 and 6: 5.4 Dowel Bearing Test Results.....
Page 7 and 8: List of Figures Page Figure 1-1 Typ
Page 9 and 10: List of Appendices Page Appendix A
Page 11 and 12: elasto-plastic behavior an ideal yi
Page 13 and 14: normal distribution orthotropic mat
Page 15 and 16: xiii
Page 17 and 18: Tie Beam Figure 1-2 American Timber
Page 19 and 20: 2. Timber Framing Background 2.1 Hi
Page 21 and 22: territories. Using the new construc
Page 23 and 24: Although timber framing is still a
Page 25 and 26: 3. European Yield Model and Propose
Page 27 and 28: strength, then the dowel could bend
Page 29 and 30: P III s = k3 ⋅D⋅ts ⋅F ( 2 + R
Page 31: The areas under the shear diagram c
Page 35 and 36: Figure 3-7 Combined Shear - Bending
Page 37 and 38: 3.5 Additional Yield Model Equation
Page 39 and 40: need to know the required load and
Page 41 and 42: Using the equivalent bolt diameter,
Page 43 and 44: 4. Peg Testing Procedures and Analy
Page 45 and 46: dowel diameter and the intercept of
Page 47 and 48: were taken for two orientations (e.
Page 49 and 50: affected by the deformation in the
Page 51 and 52: Figure 4-6 Orientation of Prelimina
Page 53 and 54: The main purpose of the full-size t
Page 55 and 56: 5. Test Results 5.1 Introduction Th
Page 57 and 58: Table 5-1 Bending Test Correlation
Page 59 and 60: Table 5-4 Bending Yield Strength Re
Page 61 and 62: 5.3 Shear Test Results 181 shear te
Page 63 and 64: 0.90 0.90 Specific Gravity 0.80 0.7
Page 65 and 66: Yield Stress τ (psi.) 3/4" Red Oak
Page 67 and 68: 5.4 Dowel Bearing Test Results The
Page 69 and 70: obtained from shear tests at variou
Page 71 and 72: To obtain allowable stress design v
Page 73 and 74: l e l v Figure 6-1 Full-size Test D
Page 75 and 76: each mode in the general yield mode
Page 77 and 78: 7. Conclusions and Recommendations
Page 79 and 80: Appendix A Derivation of Dowel Rota
Page 81 and 82: Appendix C NDS Yield Mode II, Alter
Page 83 and 84:
Appendix D NDS Mode III s , Alterna
Page 86 and 87:
Appendix E Standard Test Setup for
Page 88 and 89:
Appendix G Bending Test Data Summar
Page 90 and 91:
Summary of Bending Tests: Last Revi
Page 92 and 93:
Appendix H Shear Test Data Summary
Page 94 and 95:
Summary of 1-1/4" Red Oak Shear Tes
Page 96 and 97:
Summary of 1" White Oak Shear Tests
Page 98 and 99:
Appendix I Dowel Bearing Data Summa
Page 100 and 101:
Bibliography Abe M., and Kawaguchi,
Page 102:
Soltis, L. A.; Karnasudirdja, S.; L
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Timber Frame Tension Joinery - Timber Frame Engineering Council

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