Experimental and analytical evaluation of the in-plane behaviour of as-built and strengthened traditional wooden floors. (15th May 2020)

• Record Type: Journal Article
• Authors: Mirra, Michele; Ravenshorst, Geert; van de Kuilen, Jan-Willem
• Is Part Of: Engineering structures. Volume 211(2020)
• Publication Date: 2020-05-15
• Subjects: Timber floors -- Seismic rehabilitation -- Strengthening techniques -- Floor stiffness -- Retrofitting; a Heart-to-heart distance between the main joists (mm) -- a' Heart-to-heart distance between the secondary purlins (mm) -- Av. Average value of a quantity measured in the experimental tests -- b Width of the cross-section of the main joists (mm) -- b' Width of the cross-section of the secondary purlins (mm) -- B Width of the diaphragm, intended as the dimension parallel to the horizontal load (mm) -- bp Width of the plywood panel (mm) -- CLT Cross-Laminated Timber -- CoV Coefficient of variation -- E Young's Elastic Modulus of wood (MPa) -- Edyn Dynamic Modulus of Elasticity of wood (MPa) -- Edyn, 0 Dynamic Modulus of Elasticity of plywood panels in the direction parallel to the fibres of the outer layers (MPa) -- Edyn, 90 Dynamic Modulus of Elasticity of plywood panels in the direction perpendicular to the fibres of the outer layer (MPa) -- Ejoists Dynamic Modulus of Elasticity measured for the joists (MPa) -- Eplanks Dynamic Modulus of Elasticity measured for the planks (MPa) -- F Horizontal load (kN) -- FRP Fibre Reinforced Polymers -- Gfloor Equivalent shear modulus of the timber diaphragm, calculated according to test results and static scheme (MPa) -- Geq Equivalent shear stiffness of the timber diaphragm (N/mm) -- h Height of the cross-section of the main joists (mm) -- h' Height of the cross-section of the secondary purlins (mm) -- I Moment of inertia according to the loading direction (mm4) -- K Stiffness of the diaphragm at a certain level of displacement (kN/mm) -- K0 Initial stiffness of the connection according to Foschi's exponential model (kN/mm) -- K1 Post-yielding stiffness of the connection according to Foschi's exponential model (kN/mm) -- K2 Initial secant stiffness of the diaphragm, calculated at 2 mm displacement (kN/mm) -- K20 Equivalent secant stiffness of the diaphragm, calculated at 20 mm displacement (kN/mm) -- L Length of the diaphragm, intended as the dimension orthogonal to the horizontal load (mm) -- lp Length of the plywood panel (mm) -- lu Ultimate displacement reached in a monotonic test of timber shear walls (mm) -- LVDT Linear Variable Differential Transformer -- LVL Laminated Veneer Lumber -- M0 Initial moment given by the connection according to Foschi's exponential model (kNmm) -- Mi Moment generated by a nail couple, opposing to the deflection of the diaphragm (kNmm) -- Mp Plastic bending moment of a nail (kNmm) -- m. c. Moisture content of wood (%) -- n Number of tested specimens -- njoists Total number of joists of the diaphragm -- nplanks Total number of planks of the diaphragm -- OSB Oriented Strand Board -- PGA Peak Ground Acceleration (m/s2) -- t Thickness of the floor planking (mm) -- T Tensile strength of a nail (MPa) -- tp Thickness of the plywood panels (mm) -- w Width of the planks (mm) -- Xi Coordinate of the i-th nail couple along the joist (mm) -- δ (Maximum) in-plane deflection measured on top of the diaphragm (mm) -- φ Rotation of the nail couple at the plank-joist intersection (rad) -- ρ Density of wood (kg/m3); Structural engineering -- Periodicals; Structural analysis (Engineering) -- Periodicals; Construction, Technique de la -- Périodiques; Génie parasismique -- Périodiques; Pression du vent -- Périodiques; Earthquake engineering; Structural engineering; Wind-pressure; Periodicals; 624.105
• DOI: 10.1016/j.engstruct.2020.110432
• Languages: English
• ISSNs: 0141-0296

Abstract

Highlights: As-built flexible timber diaphragms may be not suitably regarded as shear walls. A plywood panels overlay increases the dissipative properties of timber diaphragms. A single value of stiffness cannot properly describe the nonlinear floors' response. Orthotropic behaviour of timber diaphragms is strongly mitigated after strengthening. Abstract: Traditional timber floors cannot normally withstand horizontal seismic loads without large deformations. This may lead to a corresponding out-of-plane collapse of masonry walls in existing buildings. This situation is even more critical in the Netherlands, around the city of Groningen, where human-induced earthquakes started to take place. Since no seismic events have been experienced until recently, none of the existing buildings was designed with seismic events in mind, with no exception for the timber floors: therefore, it was necessary to characterize their in-plane response. To obtain representative results, firstly floor and roof samples were extracted from existing buildings. The relevant material properties were determined, together with the plank-joist connections behaviour. Replicas were then built with new material and tested to confirm the similarity in response compared to extracted samples. Based on these results, full-scale replicated diaphragms were constructed, and tested quasi-static reversed-cyclic in their plane, either parallel or perpendicular to the joists. Besides characterizing as-built diaphragms, a simple strengthening technique with plywood panels was applied as well, improving their in-plane response in terms of strength, stiffness and energy dissipation, as test results confirm. This study is concluded with an analytical characterization of the diaphragms' in-plane response, for as-built and strengthened configurations.