Shear Behavior of Different Connections for Cross-Laminated Timber-Concrete Composite Floor
Abstract
This study aimed to investigate the effects of wood species, screw inclination angle, screw arrangement, notch depth, and load-to-grain direction on slip modulus and shear strength of screw connection and notch connection for cross-laminated timber (CLT) concrete floor under push-out tests. A total of 65 push-out tests were conducted to investigate slip modulus and the shear strength of screw connection and notch connection for the CLT concrete composite floor.<br>The push-out test results investigated the influence of wood species, screw inclination angle, screw arrangement, notch depth, and load-to-grain direction. The test results showed that double plastic hinges in the screw under compressive loaded and single plastic hinges in the screw from the timber side were the main failure mechanisms in the timber-concrete composite (TCC) screw connection.<br>The results showed that higher CLT density enhances shear properties, including the slip modulus (from 30.51% to 110%) and shear strength (from 11.19 % to 57.45%) of the screw-in TCC screw connection. The TCC connections with a screw-grain angle at 90 and 45 had a greater slip modulus ranging from 3.12 kN/mm to 4.35 kN/mm and shear strength ranging from 34.96 kN to 22.32 kN than did with a screw-to-grain angle at 60, but it had a lower ductility ratio, ranging between from 2.27 to 2.71 than did with a screw-to-grain angle at 60. The slip modulus and shear strength of TCC connection made from larch CLT and pine CLT with a screw arrangement of X45 were higher from 4.40 kN/mm to 5.23 kN/mm than did with a screw arrangement of 45.<br>The prediction slip modulus for screw connections in TCC ranged from -18.85% to 13.01% in all the test configurations, and the prediction was considered to reflect the slip modulus well. A new format for the prediction equation of slip modulus of screws on TCC floor is proposed in the current study considering the effects of wood density, the diameter of screws, penetration depth of screws, and screw-to-grain angle screw-on slip modulus on TCC floor. The prediction shear strength of screw connection is within a range from -30% to 7% in all the test configurations.<br>The TCC notch connector with a greater density had greater slip modulus and shear strength ranging from 16.08 kN/mm to 18.85 kN/mm (14.70%) and from 24.45 kN to 31.25 kN (21.78%) than the pine species. The slip modulus of TCC connections with a notch depth of 30, 40 mm of 13.18%, and 16.02% lower than that with a notch depth of 20 mm, whereas the slip modulus with a notch depth of 50 mm of 4.73% is greater than those with a notch depth of 20 mm. The shear strength of TCC connections with a notch depth of 30, 40, and 50 mm was 9.39%, 37.97%, and 67.20% greater than those with a notch depth of 20 mm. In TCC, CLT with a load-to-grain direction of 00 with a notch depth of 20 mm and 40 mm had greater slip modulus and shear strength ranging from 39.37% to 203.27% than did with a load-to-grain direction of 900. In TCC, CLT with a load-to-grain direction of 00, the ductility ratio at a depth notch of 20 mm had a greater of 33.16%, but a depth notch of 40 mm had a lower of 9.85%.<br>The prediction of slip modulus of the notch connection in TCC ranges from -20% to -3% in all the test configurations. A new format for the prediction equation of slip modulus of a notch on a TCC floor is proposed in the current study considering the effects of wood density, notch depth, and thickness of CLT panel on slip modulus on a TCC floor. The prediction of shear strength of the notch connections in TCC within a range from -27% to 3%.<br>This study evaluated the effects of wood species, screw-to-grain angle, screw arrangements, notch depth, load-to-grain direction for screw connections, and notch connection on TCC floors under shear loads. TCC connections using different wood species of CLT panels, screw-to-grain angle, and screw arrangements showed different shear properties for slip modulus, strength, displacement, ductility ratio, and failure behaviors. The main failure behaviors for screw connections were crushing failure on CLT, cracking failure on concrete, single plastic hinge failure in the shear tension-loaded, double plastic hinges failure in the shear compression-loaded, and fracture failure of screw connectors. TCC connections using different wood species of CLT panels, notch depth, and load-to-grain direction showed different shear properties for slip modulus, strength, displacement, ductility ratio, and failure behaviors. The main failure behaviors for notch connections were crushing failure on CLT, rolling shear failure on CLT, cracking failure on CLT, crushing failure on concrete, and cracking failure on concrete.<br>New developed predicting equations predict slip modulus and the shear strength for TCC using screw connectors with accuracy from -30% to 13.1% for slip modulus and shear strength and for TCC using notch connectors with accuracy from -27% to 3% for slip modulus and shear strength, respectively. This study suggests the predicted equation is reliable and can be used for the design of TCC floors with screw and notch connections.
Reference
Van Sy PHAM. (2022). Shear Behavior of Different Connections for Cross-Laminated Timber-Concrete Composite Floor. Elsevier BV. https://doi.org/10.2139/ssrn.4229164
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