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The main objective of this work is to characterize the stress–strain relationship of cross-laminated timber (CLT) wall panels when loaded in compression and how different confinement mechanisms provide compression reinforcement for the CLT panels. CLT crushing tests were performed to define the behavior of CLT under compression up to the failure point, defined here as the strain at which the gross stress falls by 20% from the peak value. Testing included monotonic uniform compression experiments of five-ply CLT with specimens that were 0.457 m wide by 1.52 m long. The motion of the specimens perpendicular to loading direction was restrained at midlength to prevent buckling. Twelve specimens were tested, including six bare CLT specimens and six reinforced specimens of CLT—three with self-tapping screws while the other three with self-tapping screws and an additional U-shape steel plate at the bottom of the specimens. Various damage points were observed during the tests, including (1) point at the onset of damage (through visual observation and instrumental observation) (2) point of initiation of strength degradation, (3) point at which buckling occurs, (4) point at which 25.4 mm delamination was observed, and (5) failure point. Three axial compression stress–strain models were adopted, calibrated, and compared. Results indicate that a stress–strain model combining linear and cubic functions for the elastic and softening responses, respectively, captures well the CLT inelastic behavior under compression. [ABSTRACT FROM AUTHOR]

While the use of cross-laminated timber (CLT) panels for building construction has increased over the last several decades, current standards and existing literature provide limited information regarding the design of CLT diaphragms or the prediction of their deflections when subjected to wind and strong earthquake motions. This paper presents the design and assessment of a CLT diaphragm that was part of a full-scale two-story structure subjected to shake-table testing. An analytical model is proposed for diaphragm deflection accounting for in-plane shear and bending stiffness, as well as the stiffness of various connections. Moreover, a refined numerical modeling strategy is proposed in order to consider phenomena such as panel-to-panel gap closure. Results indicate that the analytical model yields conservative results both in terms of deflections and forces when compared to the numerical model that simulates similar sources of strength and stiffness. The analytical model is suitable for the design of symmetric diaphragms with regular shapes, whereas the numerical model can also be used to model asymmetric diaphragms with irregular shapes. [ABSTRACT FROM AUTHOR]

New building code changes enable mass timber panels (MTP), including cross-laminated timber (CLT), to be used in moderate and tall buildings as a floor system, usually with a concrete topping. A floor system of CLT composite with a reinforced concrete topping slab can provide increased stiffness and strength, making the system more advantageous. Present connection methods used to produce composite action within timber-concrete composites (TCC) have limitations when considering constructability or performance. This study presents experimental results from four (4) shear connectors for CLT-concrete composite floor systems, including three developed for this study. The connectors included self-tapping screws (STS) at 45-degrees, a modified lag screw with an integral plate washer that bears on the CLT surface at installation, a steel angle anchored only at the end of the span, and an inverted-T steel section with stem perforations. Different tests were performed on the different connectors including individual fastener tests, push-off group tests, and full-scale one-way bending tests. The push-off group tests showed that the proposed washer-screw exhibited higher stiffness and strength than a conventional STS. The full-scale one-way bending testing showed that the STS specimen exhibited the lowest strength of the alternatives. The inverted-T section exhibited the highest stiffness, while the other three connections had similar stiffness to the STS. [ABSTRACT FROM AUTHOR]

Connections play a vital role in the transfer of lateral forces and energy dissipation in cross-laminated timber (CLT) structural systems. However, moisture exposure (e.g., rain during or after construction) can affect the durability of CLT structural members and their connections due to the hygroscopic nature of wood. Limited knowledge exists on the moisture performance of CLT connections. Therefore, in this study, a CLT shear wall-to-diaphragm angle bracket connection was exposed to simulated rain and relative humidity cycling (wetting) and subsequent redrying followed by mechanical loading cyclic testing. Four wood species (Douglas-fir, southern pine, Norway spruce, and spruce-pine-fir) and three wetting durations were applied to understand the effect of moisture intrusion on the connection performance, which was evaluated in terms of strength, stiffness, and energy dissipation. Two force–displacement backbone models were fitted to the experimental data. The results suggest a statistically significant increase (9%–15% for different species) in the peak strength and no change in the stiffness and energy dissipation capacity after the wetting and redrying cycles. However, additional studies should be conducted to gain further insight into the observed increase in load-carrying capacity. Additionally, the authors caution against considering any strength increase until further studies are conducted. [ABSTRACT FROM AUTHOR]

Over the past decade, cross-laminated timber (CLT) panels have gained popularity worldwide. To achieve larger spans and to increase the resistance to diaphragm seismic and wind forces to be transferred through CLT floor or roof systems, CLT-concrete composite (CCC) floors have been developed as an alternative. While significant testing has been performed under gravity loading, limited experimental data exist on the in-plane performance of CCC systems. This study presents results from an experimental program designed to characterize the in-plane shear behavior of CCC diaphragm connections using different CLT to concrete screw connector orientations in a test setup that simulates the expected seismic load path in diaphragms for platform-type construction. Tested variables include concrete slab thickness, composite screw angle, and single spline connection systems consisting of nails or screws. Experimental results and observed damage progression from cyclic testing are presented and discussed. Results indicate that CCC systems achieved increased stiffness and strength values when compared to bare-CLT systems, but slab thickness did not influence the strength and stiffness of the system for the load paths simulated. Additionally, CCC floor systems with 45° composite screw connectors displayed increased strength but overall similar stiffness values when compared to the CCC systems with 90° composite screws. The results provide useful engineering parameters, such as elastic stiffness, peak load, displacement capacity, and ductility ratios that can be used in the development of codified design parameters or in performance-based designs. [ABSTRACT FROM AUTHOR]

Abstract Cross-laminated timber (CLT) is becoming increasingly adopted into North American construction, yet little is known about the impacts of environmental exposure (e.g., to rain during construction) on its long-term performance. The lack of protocols for on-site moisture protection in North America makes it a pressing matter to determine general moisture responses of this material in order to establish a behavioral baseline for practitioners and future researchers. A CLT floor panel sample was exposed to cycles of wetting and drying in an environmental chamber. During these cycles, physical and geometrical properties of the panel were monitored. Testing results indicate that discontinuities in the layup CLT affects the hygroscopic behavior of the product. While the panel showed high dimensional stability, it also exhibited checking, cupping, and interfacial shearing after cycling. Bending test results before and after cycling indicated a reduction of the structural capacity due to the weathering. Highlights • Gaps in the surface, in conjunction with wane, created a matrix of openings for ingress. • Moisture can remain or continue to accumulate at the core, even during drying conditions. • Checking, cupping and inter-facial shearing were pronounced, especially at edges. • A reduction of the structural capacity was observed in the weathered samples. • MC sampling should account for high spatial variability and acute sensor sensitivity. [ABSTRACT FROM AUTHOR]