Current Tendency in Timber Building in the World

1. TEMTIS 06-08Horsens, 11.09.2008A Design Model of Shear Wall Elements with Plaster BoardsAssoc. Prof. Dr. Miroslav PremrovUniversity of Maribor, Faculty of Civil Engineering

2. Current Tendency in Timber Building in the World • Tendency to multi-story prefabricated timber-frame houses. • At least F + 3 • It is important to assure beside fire resistance also a construction resistance stability.

3. Different Systems in Multi-Story Building a.)Platform Buildingb.) Balloon System c.) Massive System Frame System Space Frame System Multi-layer Panels Macro-panel System

4. 2. Timber-Framed Wall System • Although timber-framed walls are meantime connected they can be in static design considered as separated cantilever elements(Eurocode 5-1-1). 2.1. Static Design

6. 2.2. Composition of Timber-Framed Walls - timber frame, - fibreboards (as sheathing boards) - fiber-plaster boards, - plaster-cardboards, - OSB (Oriented Standard Board, North America,....)

7. timber frame boards Composition of a Timber Panel Shear Wall

9. 3. Strengthening of FPB • Ussing additional fibre-plaster boards (FPB) – very popular by producers • By reinforcing with classical steel diagonals in the tensile area of FPB • By reinforcing with carbon or high-strength syntetic fibres in the tensile area of FPB

10. 3.1. Additional Boards • The simplest case of reinforcing. • Usually used by producers. • Boards can be added: - symmetric, - asymmetric. • Resistance of boards is increased, but ductility is practically not changed.

11. What was increased? • The force forming the first crack for35,82%. • The crack extended by only for9%bigger forceto the internal board. • Destruction force for25,65%. What was decreased? • “Ductility”for 7,41%

12. 3.2. Reinforcing with Steel Diagonal Elements Static System of the Test Samples

13. Destruction force unreinforced: 20,18 kN; reinforced: 35,73 kN ratio = 1.77 Ductility Ductility was increased for 39,64%!

14. Comparison of the Measured Vertical Displacements F [kN] v [mm] unreinforced reinforced

15. Hotel Terme Zreče (3+M)

16. 3.3. Reinforcing with CFRP Diagonal Strips

17. 3.3.1. Test Configuration 1. The first group (G1) of three test samples was additionally reinforced with two CFRP diagonal strips (one in each FPB) of width 300 mm which were glued on the FPB using Sikadur-330 LVP. The strips were additionally glued to the timber frame to ensure the transmission of the force from FPB to the timber frame.

19. 2. The second group (G2) of three test samples was additionally reinforced with two CFRP diagonal strips of width 600 mm. The strips were glued on FPB and to the timber frame as in G1. 3. The third group (G3) of three test samples was additionally reinforced with two CFRP diagonal strips of width 300 mm as in G1 but they werenot glued to the timber frame.

21. Properties of the used materials

22. 3.3.2. Test Results Average force forming the first crack in FPB unreinforced: 17.67 kN G1: 24,28 kN G2: 32,13 kN G3: 35,90 kN

23. Average destruction force unreinforced: 26,02 kN G1: 40,33 kN G2: 46,27 kN G3: 36,26 kN

24. Test samples behaviour Further information on the behaviour of tested elements can be obtained by calculation of the "safety " (ci) and "ductility coefficients of FPB" (di) in the following forms:

25. Measured bending deflections under the force F (mm) un-strengthened samples G1 samples G2 samples G3

26. It is evident from figure that, similarly to the classical reinforcement with BMF steel diagonals presented in Dobrila and Premrov (2003), there is practically no influence on stiffness of any reinforcement before appearance of cracks in the un-strengthened FPB. This is logical because in this case the reinforcement is practically not activated at all and its stiffness in comparison to the stiffness of un-cracked FPB is small. After appearance of the first crack in the un-strengthened test samples (Fcr,uns = 17.67 kN) the influence of the CFRP strips is obvious and it depends on the strip’s dimensions as well as on the boundary conditions between the strips and the timber frame.

27. Measured average slips in the connecting area (mm) samples G1 samples G2 samples G3

28. Conclusions for G1 and G2 test groups Beside the fact that samples G1 and especially G2 demonstrated higher load-carrying capacity than samples G3, it is important to mention that samples G1 and G2 produced substantially smaller slip than samples G3, which never exceeded 1mm at the first crack forming. Therefore it can be assumed that the yield point of the fasteners was not achieved before cracks appeared at all! Consequently, the walls tend to fail because of the crack forming in FPB. In this case of strengthening the ductility of the whole wall element (see Fig. 6 for samples G1 and G2) practically coincides with the “ductility” of FPB, as proposed with d1 and d2 coefficients.

29. Conclusions for G3 test group In contrast, in G3 model, where the CFRP strips were unconnected to the timber frame, the slip (Δ) between the FPB and the timber frame was evidently higher than in samples G1 and G2, and exceeded 3mm when the first crack in FPB appeared. The load-displacement relation (F-Δ) of the fasteners was in this case at the force which produced first cracks almost completely plastic. Since the tensile strength of FPB is essentially improved, the walls tend to fail because of fastener yielding. Although the fibreboards in samples G3 demonstrated practically no deformation capacity (d3 ≈ 1.0, Eq.14) the ductility is formed (F-w diagram) over the fasteners yielding.

30. 4. Design Models • Shear model (EC 5) • Composite Beam Model

31. 4.1.Modelling of walls with wood-based sheathing boards -Shear Model (EC 5)

32. «Lower bound plastic method«Källsner and Lam (1995) a.)   behaviour of the joints between the sheet and the frame members is assumed to be linear-elastic until failure, b.) the frame members and the sheets are assumed to be rigid and hinged to each other.

33. Shear resistance - Method A Shear resistance - Method B

34. 4.2.Modelling of walls with fibre - plaster sheathing boards -Composite Beam Model

35. 4.2.1. »γ-method«(EC 5)Basic assumptions: • Bernoulli`s hypothesis is valid for each sub-component, • slip stiffness is constant along the element, • material behaviour of all sub-components is linear elastic.

36. Effective bending stiffness (EIy)eff of mechanically jointed beams

37. 4.2.2. Influnce of steel (CFPR) diagonal reinforcing

38. Shear deformation in one fiberboard is: Horizontal displacement of the fiberboard is: Axial force in the tensile steel diagonal is:

39. Horizontal displacement of the tensile steel diagonal is thus: If we consider continuity of horizontal displacements ub = us,we get for the total cross section of the fictive fiberboard:

40. Proposed Models: • Model with the fictive thickness of the board: • Model with the fictive width of the board:

41. a.) Normal panel (without reinforcement) b.) Panel with the fictive width c.) Panel with the fictive thickness

42. 4.2.3. Modelling of fasteners flexibility

43. Definition of slip modulus K

44. 4.1.4. Modelling of cracks in FPB Force forming the first crack in FPB:

45. Major assumptions of the cracked cross-section: • The tensile area of the fibreboards is neglected after the first crack formation. • The stiffness coefficient of the fasteners in the tensile connecting area (γyt) is assumed to be constant and equal to the value by appearing the first crack. • The stiffness coefficient of the fasteners in the compressed connecting area (γyc) is not constant and depends on the lateral force acting on one fastener. • The normal stress distribution is assumed to be linear.This simplification can be used only by assumption that behaviour of timber frame in tension is almost elastic until failure and that the compressive normal stress in timber and in FPB is under the belonging yield point.

47. Characteristic horizontal destruction force(according to the tensile stress in the timber stud)

48. 5. Numerical Example 5.1 Geometrical and material properties

49. Height of the wall: h = 263.5 cm • Staples: Φ1.53 mm, length l = 35 mm, constant spacing s = 75 mm

50. * The values are given for 12mm typical thickness of the board.