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Connections in mass timber structural systems are critical for transferring lateral forces from mass timber elements such as shear walls and diaphragms. Cross-laminated timber (CLT) is a prominent mass timber material used to manufacture these wall and floor assemblies. Although research exists that investigated the fire performance of CLT walls and floors, very little investigation has been devoted to the thermal performance of the connection systems themselves. This void in the data and knowledge surrounding CLT connections is an impediment for modeling the elevated temperature performance of CLT structures. Therefore, a series of shear tests were conducted on a CLT L-bracket connection assembly to characterize the thermal degradation of peak loads and initial stiffness as a function of exposure duration at a given temperature. A total of 116 specimens, including four control specimens, were tested according to a matrix of 28 exposure duration-temperature combinations. Two analytical models are developed to explain the thermal degradation—one assuming a mechanism based on first-order kinetics and the second using a statistical regression. The results of this work indicate that the degradation of peak load and initial stiffness with respect to exposure duration occurred at a linear rate and depended on temperature, according to the Arrhenius activation energy theory. This research is a step toward a holistic evaluation of elevated temperature modeling of CLT structures. [ABSTRACT FROM AUTHOR]

This research investigated the mechanical characteristics of cross-laminated timber (CLT) connections fastened with structural wood screws, also known as self-tapping screws (STS). The CLT connection assemblies were toe-screwed (TS) at 45° and cyclically tested in tension and in-plane shear to evaluate the failure modes and applicability as seismic connections in CLT shear walls. The connection assemblies were representative of full-scale CLT shear walls connected to CLT floors as often seen in platform construction. Toe-screwed CLT connections exhibited screw fracture, head pull-through, and pinched hysteresis loops. Mechanical connection properties and backbone curves were extracted for comparison with design estimates. A head pull-through design method was developed, which predicted peak strength within 5% of test results. Connection parameters for ASCE/SEI 41 idealized-component curves were presented for use in performance-based design nonlinear-static pushover analysis. Combining the presented ASCE/SEI 41 parameters with the proposed design method and test results provides a simple and reasonably accurate nonlinear toe-screwed connection response curve. Partially threaded washer-headed screws were found to be superior to fully threaded screws in seismic applications due to their 15 times greater ultimate deformation capacity, substantially greater energy dissipation, similar peak strength, and similar elastic stiffness. However, the yield strength of partially threaded STS was found to be 48% of the yield strength of fully threaded STS. [ABSTRACT FROM AUTHOR]

The development of cross-laminated timber (CLT) technology has opened up new opportunities for low-density hardwood species, which have traditionally not been rated as construction-grade materials for structural engineering applications. Several characteristics of CLT, namely thermal performance, seismic behavior, and speed of construction, have raised interest among designers. The CLT technology has recently been used for residential and nonresidential multistory buildings and it has been identified as one of the ways of achieving tall timber building construction. As CLT gains acceptance in the industry, low-density wood species, not specified in current ANSI standards, need to be investigated for potentially successful use in CLT panels. This paper presents a study that demonstrates the viability of a Forest Stewardship Council (FSC) certified sustainable plantation grown low-density species, hybrid poplar (marketed as Pacific Albus), for use in performance-rated CLT panels by following the ANSI/APA PRG-320-2012: Standard for performance-rated cross-laminated timber shear and bending test guidelines to determine the structural viability of the CLT panels. [ABSTRACT FROM AUTHOR]

• Cross-laminated timber rocking walls dissipate energy through connection damage. • Slip-friction connections were originally developed for steel structures. • The SFC system was designed as a hold-down in a self-centering CLT rocking wall. • Quasi-static, cyclic tests with SFC connections showed elastic-plastic behavior. • Passive damping was close to typical idealized friction hysteresis models. Cross-laminated timber (CLT) rocking walls limit internal building forces and dissipate seismic energy mostly through severe connection damage and related wood crushing. While collapse-prevention and life-safety performance can be achieved, the connections and CLT walls are permanently damaged and may be unreliable for resisting aftershocks. Slip-friction connections (SFCs), also known as slotted-bolted connections, are highly resilient passive dampers originally developed for steel structures. As part of a thorough research program to apply SFCs to CLT rocking walls, connection tests were conducted to better understand a novel application of multiple modern timber technologies. The research objectives were to design and test a slip-friction connection connected to cross-laminated timber with inclined self-tapping screws (STS) to determine the stiffness and passive damping properties of the assembly. The SFC system was designed for use as a slip-friction hold-down in a self-centering CLT rocking wall system. A series of quasi-static, cyclic axial tests with slip-friction connections was shown to impart ductile and elastic–plastic characteristics to an otherwise non-ductile CLT connection. Because the timber connection forces were limited below the STS yield strength by the slip-friction connectors, no wood damage was observed during SFC sliding. Compared to other sources, passive damping was found to be excellent and close to typical idealized friction hysteresis models. The slip-friction connections are a unique design using an efficient CLT to SFC connection, with no slack, that performs consistently after consecutive tests. Additionally, cursory equivalent-viscous-damping ratios were extracted for the elastic range of the STS to steel connection for small amplitude excitations below the slip force threshold. [ABSTRACT FROM AUTHOR]