Search

This paper presents the experimental results of a study investigating the behavior of bolted glued-laminated (glulam) timber brace connections with slotted-in steel plates under monotonic and cyclic loading. A total of 12 brace specimens with one or two slotted-in steel plates and two different bolt sizes were studied with the aim to determine the ductility of the connections and brace assemblies. The use of self-tapping screws as perpendicular-to-grain reinforcement to prevent splitting and enhance brace ductility was also investigated. The results of the study showed that both connections in a brace can experience significant plastic deformations if the connections exhibit a postyield hardening response. In braces with connections that exhibited postyield softening, plastic deformations were limited to one of the brace connections, resulting in lower brace ductility ratios. The use of self-tapping screws was found to be effective at preventing splitting and increasing the connection yield and ultimate strengths, while also increasing the brace ductility when compared with an identical connection without reinforcement tested under cyclic loading. [ABSTRACT FROM AUTHOR]

Mass timber is gaining popularity in the North American architectural, engineering, and construction (AEC) industry as a viable and sustainable building material. Owing to the water storage potential of mass timber, durability is of concern as a result of long-term exposure to moisture during building construction and service. The importance of monitoring mass timber subjected to moisture degradation during construction and occupancy of a building is critical in determining the longevity and viability of mass timber products. In situ moisture monitoring deployment techniques are currently inconsistent across building case studies. The objective of this review is to investigate: (1) relevant types of moisture content (MC) sensors and their applications in mass timber construction; and (2) practices for deploying MC sensors in mass timber construction. Cross-laminated timber (CLT), nail-laminated timber (NLT), and glue-laminated timber (Glulam) are typical mass timber products, each of which varies in thickness, manufacturing processes, and species composition. In addition, MC sensors have a range of applications, installations, and accuracies. The variability of mass timber products and MC sensors lead to multiple combinations of moisture monitoring techniques. Mass timber moisture monitoring installation and deployment practices have been recommended based on the literature review and case study analysis performed. [ABSTRACT FROM AUTHOR]

This study proposed a novel type of self-centering (SC) timber beam–column connection utilizing shape memory alloy (SMA) bars and investigated its cyclic behavior through experimental and numerical studies. In this SC connection, anchor bars consisting of SMA bars, steel bars, and couplers were utilized to connect the beam and column and achieve SC and energy dissipation capabilities. The configuration of the SC timber beam–column connection and material properties of the SMA bars were first introduced. The cyclic behavior of the SC timber beam–column connection was systematically investigated through experimental and numerical studies. A series of cyclic loading tests were conducted on the SC timber beam–column connection to evaluate its stiffness, SC, and energy dissipation capabilities, and the effect of multiearthquake loading. A detailed finite element model of the timber connection was also built and validated using the experimental results. Results indicated that the timber connection could exhibit a desirable flag-shaped hysteretic behavior, indicating favorable SC and moderate energy dissipation capabilities. The connection remained functional without any repair work after experiencing two consecutive cyclic loads up to 4% drift ratios, demonstrating its potential to withstand multiple seismic events. [ABSTRACT FROM AUTHOR]

Due to the corrosion of fasteners by water-based preservatives, the preserved timber in outdoor environments can decrease the service life of the metal fasteners. In addition, the segregation of timber members and metal fasteners is also difficult during the demolition of timber structures. Wooden fasteners can be a promising alternative to metal fasteners because they have favorable resistance against corrosion and are more naturally harmonized with timber members. This paper studied the pull-out performance of dried densified wood (DW) dowels embedded into glued laminated timber (glulam) parallel to the grain with three different embedded lengths in two ambient environments with a temperature of 20°C and relative humidity (RH) of 65% and with a temperature of 20°C and relative humidity of 85%. The hygroscopic swelling of the dried DW dowels with a long embedded length can provide the favorable friction locking to transfer the axial load. [ABSTRACT FROM AUTHOR]

Glued laminated bamboo (glubam) is an engineered bamboo for the potential usage in structures as an alternative to timber-based glulam. This paper focuses on the impact toughness and static bending strength of glubam, with the goal to provide basic understanding and experimental data for impact design of engineered bamboo structures. Two types of glubam, i.e., thin-strip and thick-strip glubams were investigated through impact pendulum and quasi-static bending tests. For the thick-strip glubam, testing parameters also included three types of manufacturing conditions with different degrees of carbonization of composing bamboo strips. Both comparisons among different types of glubam, and between dynamic and static bending results can effectively identify the impact resistance and mechanical properties of glubam. The dynamic impact loading resulted in higher instability and had failure modes different from quasi-static tests for glubam specimens. Experimental values of toughness, modulus of elasticity (MOE) and modulus of rupture (MOR) at different loading speed conditions are obtained. [ABSTRACT FROM AUTHOR]

Limited research exists on the deformation compatibility behavior of mass timber beam-to-column connections. Therefore, to investigate this behavior, large-scale experimental monotonic testing was performed on five different glue-laminated (glulam) beam-to-column connections. The purpose of this research was to create a better fundamental understanding of the deformation compatibility behavior of mass timber beam-to-column connections. Three connections were custom-designed connections, and two were pre-engineered connections. Specimens included the presence of cross-laminated timber (CLT) decking on the beam, as well as combined lateral and gravity loading. Monotonic tests pushed specimens to a target story drift of 7.2% at a rate of 0.51 mm/s. The data were analyzed, and the yield force, yield displacement, initial stiffness, secant stiffness, and connection classification (categorized as either rigid, semirigid, or flexible) were calculated for each connection. Per the connection classification methodology used, all connections were classified as flexible (simple) connections. However, the pre-engineered connections use substantially more screws and plates thereby increasing the cost and effort of installation. The results demonstrate that in some cases simple custom connections can have a larger yield force and initial stiffness than pre-engineered connections, and due to the reduction in number of screws, there was less damage within the connection at the completion of the test. The forces required to push connections to 2% drift all exceeded the lateral force capacity of the connections; however, all connections maintained load-carrying capacity throughout testing. [ABSTRACT FROM AUTHOR]

The deformation compatibility behavior of glue-laminated (glulam) beam-to-column connections is not yet well understood. To investigate this behavior, 10 specimens representing five different glulam beam-to-column connections were tested under lateral cyclic loading. Three of the connections were custom-designed connections and two were pre-engineered connections. Specimens were large-scale glulam beam-to-column connections, and testing included combined gravity and lateral loading as well as the presence of a cross-laminated timber (CLT) deck. Connection characteristics such as yield force, initial stiffness, secant stiffness, and energy dissipation were calculated and compared across connections as well as observations made during testing. Results from the experimental testing indicated that pre-engineered connections demonstrated overall better performance than the custom connections. Pre-engineered connections had the largest remaining secant stiffness by the end of the loading protocol, greater energy dissipation, and larger average yield forces than the custom connections. Although all connections tested exceeded their lateral design capacities at drift levels less than 2% drift, all connections maintained load-carrying capacity throughout testing. [ABSTRACT FROM AUTHOR]

Self-centering heavy timber frames rely on the self-centering beam-column timber connections to limit damage and provide the recentering capability. However, low compressive strength and stiffness perpendicular to the grain of the timber columns have long been a design challenge, which yields low initial post-tensioning forces and possibly a significant loss of post-tensioning forces over the building service life. To address this issue, this paper proposes a new design solution for the self-centering steel-timber hybrid beam-column connections, in which the timber column is replaced by a steel-timber composite column. Cyclic tests were conducted on four beam-column connection specimens with post-tensioning. During the gap-opening, the composite column provided a stiff foundation to the timber beam. The hysteretic curves of all four connections were in a flag shape. Compared with self-centering beam-column timber connections that had the same geometry and material properties, the proposed connection had a larger connection stiffness and an improved efficiency of dissipating energy. After the cyclic loading, the loss of post-tensioning force of the proposed connection was also lower than that of the counterpart timber connections. [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]

This paper presents experimental testing on glulam beam–column moment-resisting connections using glued-in rods (GiRod) and compares the results with model predictions. Three connection geometries and varying numbers of rods and member size were tested and compared. This experiment will be helpful in grounding research by bringing in new experimental results and proposing an innovative experimentation method. Experimental results showed the high efficiency of glued-in rod connections to transfer loads and bending moment between spruce pine glulam timber members. The observed limit states of the connections were failed steel rods in ductile tensile yielding or wood splitting around the anchorage installed perpendicularly to the grain in the column. It was found that the tested connections behaved as a semirigid moment-resisting connection and exhibited a ductile failure mode when wood splitting was avoided by design. Comparison of experimental results with model predictions showed good agreement, with a deviation under 15% for the moment capacity of the connection. [ABSTRACT FROM AUTHOR]

In order to reduce the use of adhesives, the development of adhesive-free engineered wood products is one of the research focuses in timber structures. This paper studies the mechanical properties of cross-laminated timber beams connected by densified wood (DW) dowels. Four-point bending tests were performed to study the influence of the arrangement and number of DW dowels on the bending strength and effective bending stiffness of the dowelled cross-laminated timber (DCLT) beams with three layers. The modified planar shear test was adopted to determine the effective shear properties of the DCLT. Cross-laminated timber (CLT) beams were also tested as references. Although the bending and shear properties of the DCLT were lower than those of the CLT, the DCLT showed a significantly larger ductility. The gamma method is promising for determining the effective bending stiffness of the DCLT using the effective shear modulus obtained from the shear test. [ABSTRACT FROM AUTHOR]

Cross-laminated timber (CLT) panels have been adopted as main structural elements in the mass timber constructions that have recently caught the attention from different stakeholders. The enhanced mechanical performances allow the design of impressive structures like tall buildings. However, not so much is known about the performance of CLT panels under service life condition. In this context, the strain distribution taken from an experimental campaign carried out using Digital Image Correlation (DIC) is considered as a basis to investigate the stress distribution presented by CLT panels under cyclic moisture variations. Four CLT configurations promoting different moisture flow were conditioned in climatic chambers for 324 days at a constant temperature of 20°C, and with a humidity cycle varying every 21 days between 30% and 90%, getting constant at 65% after the first 142 days. Strains calculated through DIC, along with moduli of elasticity defined by ultrasound tests, were used to estimate strained and released stresses, respectively, before and after cutting specimens. Results show that sealing CLT panels play an insignificant role on distribution of stress induced by cyclic moisture, but peak stresses, both tension and compression resulted from wetting and drying cycles, respectively, were reduced in many specimens, especially when longitudinal faces were sealed. Moreover, as general recommendations to take in the design of CLT panels regarding moisture changes, it is possible to identify the need to limit the longitudinal length of panels, to use more thin layers rather than less thick ones, and to protect panels in the longitudinal direction, owing to high stress concentrated along this direction, particularly in the borders. [ABSTRACT FROM AUTHOR]

The objective of this study was to monotonically test two 7.32×7.32-m (24×24-ft) cross-laminated timber (CLT) diaphragms designed using the provisions of ANSI/AWC 2021 (AWC. 2021. Special design provisions for wind and seismic. ANSI/AWC SDPWS-2021, Leesburg, VA: AWC). Each diaphragm used twelve 1.22×3.66-m (4×12-ft) CLT panels and plywood splines or glulam beams at panel shear connection locations. Diaphragms were tested in simple-span bending in general accordance with ASTM E455 (ASTM. 2017. Standard test method for static load testing of framed floor and roof diaphragm constructions for buildings. ASTM E455-2017. West Conshohocken, PA: ASTM), used 8d common [ 3.3×63.5-mm (0.131×2.5-in.)] nails for panel-to-panel spline connections used proprietary 7.9×200-mm (5/16×7-7/8-in.) screws for panel-to-beam connections. The calculated allowable seismic shear design capacity for both configurations, based on the panel shear connections, was 60.5 kN (13.6 kips) per reaction. The diaphragm tested with load applied parallel to the long dimension of the CLT panels failed due to spline nail withdrawal at 4.0 times the allowable seismic design capacity. The diaphragm tested in the orthogonal orientation did not fail at the safe working capacity of the steel test frame, which was 6.0 times the allowable seismic design capacity. Although this testing provided empirical verification that the SDPWS design provisions met the minimum strength target underlying the design requirements, it also identified opportunities for potential future research to reduce design conservatism. Experimental results from a series of diaphragm connection tests correlated to the connections used in the full-scale diaphragm testing are described in the Part 2 companion study (Line et al., forthcoming). [ABSTRACT FROM AUTHOR]

The objective of this study was to conduct tests on diaphragm connection configurations that either matched or were similar to those used in the full-scale diaphragm tests described in the Part 1 companion study (Line et al. 2022). The goal was to quantify their lateral load-deformation performance as an isolated assembly to assist in further understanding the measured full-scale diaphragm behavior. Diaphragm connection configurations tested include the custom steel tension strap, panel-to-beam screw connections, and panel-to-panel nailed spline connections. Withdrawal strength, dowel bending yield strength, dowel bearing strength, and fastener dimensions, as well as the oven-dry specific gravities of the cross-laminated timber (CLT) and glulam materials used to fabricate the full-scale diaphragms were also quantified. The diaphragm connection lateral load test data for the proprietary screws and spline nails met or exceeded their target nominal capacities calculated in accordance with ANSI/AWC 2018 (AWC. 2018. National design specification for wood construction. ANSI/AWC NDS-2018, Leesburg, VA: AWC) for each connection configuration. Additionally, the overstrength was well aligned with the overstrength performance observed in the full-scale diaphragm tests. The dependence of full-scale diaphragm strength on the strength of its connections and the large overstrength in panel-to-beam screw connections quantified in this study highlight an opportunity to achieve more efficient designs with fewer screws. To do so would likely require the allowable lateral design strengths for screwed connections to be established empirically or by explicit consideration of various connection failure limit states. [ABSTRACT FROM AUTHOR]

Design models for timber structures with fire-resistance requirements usually take into account the loss in cross section due to charring and the temperature-dependent reduction in strength and stiffness of the residual cross section. Standards for glued timber elements like glued-laminated timber beams have assumed that structural adhesives do not influence the fire resistance, but further specifications of adequate adhesive requirements are missing. Investigations were therefore conducted to determine the influence of different adhesives on the load-carrying behavior of glued-laminated timber beams in fire. Large-scale fire-resistance tests in combination with extensive finite-element analyses showed that a modification of the zero-strength layer thickness of d0 = 7 mm currently used in a standard design code should be discussed for glued-laminated timber loaded in bending in a future release of this design code. An increase of the zero-strength layer d0 considering the finger-joint strength depending on the approved structural adhesive is not needed. [ABSTRACT FROM AUTHOR]

In glued-laminated timber (glulam), fracture may occur at the interface of two adjacent laminae that mostly have different growth ring orientations. The double cantilever beam (DCB) tests for Mode I fractures and three-point bending end-notched flexure (3ENF) tests for Mode II fractures were performed to obtain the interlaminar fracture toughness of glulam with focus on the influence of growth ring orientations. Experimental and numerical results show that the effect of growth ring orientations of two adjacent laminae on Mode I and Mode II interlaminar fracture toughness is slight. [ABSTRACT FROM AUTHOR]

To study the lateral resistance of bolted glued-laminated (glulam) timber post and beam structures, two monotonic tests and eight cyclic tests were performed on full-scale, one-story, one-bay timber post and beam construction specimens. Four laterally strengthened structural systems were considered: a frame with an X-brace, a frame with a K-brace, a frame with a knee-brace, and a frame filled with light wood shear walls. Seismic performances were evaluated according to the experimental phenomena, hysteretic characteristics, stiffness degradation, strength degradation, and energy dissipation capacity. The results showed that the frame with an X-brace system and the frame with a K-brace system provided markedly better elastic stiffness but lower ductility. The frame with a knee-brace system showed increased elastic stiffness compared with the simple frame system and provided higher ductility compared with both the frame with the X-brace system and the frame with the K-brace system. Additionally, the frame filled with the light wood shear walls system performed well in terms of elastic stiffness and ductility. Finally, some suggestions were presented to improve the lateral resistance and ductility of each structural system. [ABSTRACT FROM AUTHOR]

This study aims to develop an improved understanding of the interfacial bond behavior of softwood glulam joints with bonded-in threaded steel rod. A total of 39 glulam joints with bonded-in single-threaded steel rods were tested to failure in the pull-pull configuration. The test results were presented in term of failure modes, load-relative movement response, pullout strength, and the corresponding slip. The distributions of bonded-in rod axial strain, interfacial bond stress, and relative movement were also analyzed to evaluate the local bond stress- relative movement response in the bond line. The results confirmed that the bond-relative movement response is dependent on the locations along the anchorage length, and the bond-relative movement responses located near both the loaded end and the anchorage end were observed to be stiffer than those at other locations. Finally, the predictions for the load capacity of the glulam joints with bonded-in threaded steel rod were carried out based on several existing empirical formulas. [ABSTRACT FROM AUTHOR]

Tests regarding the long-term behavior of posttensioned timber connections have been performed at the ETH in Zurich. The aim of these tests is to estimate the loss in tendon force that can be expected during the lifetime of a structure. Several posttensioned beam and beam-column timber specimens exposed to controlled and uncontrolled environmental conditions and loaded only with the axial prestressing force have been monitored for more than one year. The force in the tendon was measured together with the strains in the specimens and temperature and relative humidity in the testing environment. Creep tests performed on small glulam timber blocks loaded in compression have been started as well. The estimated creep coefficients parallel and perpendicular to the grain are used to calculate the losses with an analytical model for the larger posttensioned specimens. A prestressing loss in the range of 5-10%, depending on the geometrical properties and environmental conditions, has been found at the end of the one-year testing. Such a percentage is likely to increase up to 30% at the end of a 50-year service. Careful consideration has been given to identify the different variables affecting the losses of prestressing force in the long-term, including the environmental conditions. The tendon force losses were compared to the results obtained by a simple analytical model. A parametric study based on the model was performed in order to check whether the suggested ash reinforcement in the column is beneficial regarding tendon force losses in the long-term. [ABSTRACT FROM AUTHOR]

This paper summarizes the results of an experimental study on the rotational behavior of bolted beam-to-column glulam connections reinforced using locally cross-laminated glulam members. Twenty-two full-scale connection specimens were tested through monotonic and reversed cyclic loading, from which the moment / rotational angle relationships were established. The results indicated that the cross-laminated technique leads to a more ductile failure mode with cross-aligned inner layers of laminas fractured, in contrast to the perpendicular-to-wood-grain tensile failure of unreinforced connections. The connection maximum moment was found to increase by 52% and 46% under monotonic and cyclic loading, respectively; moreover, the deformability ratio evaluated on the basis of the rotation angles corresponding to the yielding and maximum moments of the connections was increased by 94%. Locally cross-laminated connections were also found to dissipate more energy (25%) than unreinforced connections. A comparison of the cross-laminated technique with self-tapping screws indicated that the respective reinforcing effects were comparable with that of the screws being slightly higher. Because the locally cross-laminated technique is readily incorporated into the production of cross-laminated timber products, it may have broad applications in heavy timber-bolted connections. [ABSTRACT FROM AUTHOR]

This article studies the possibility of using market available glued-laminated timber (GLT) based on melamine-urea-formaldehyde (MUF) adhesives as an alternative to traditional solid timber sleepers. The study comprised an examination of the effect of creosote treatment on the short-term and durability after accelerated aging of the glue lines (delamination and shear strength) and the potential for full sapwood penetration by the creosote. Creosote treatment showed a negative effect on shear strength and delamination, more severe in the nonstructural than the structural GLT specimens tested. Full penetration of creosote into the sapwood was not achieved. GLT elements based on MUF adhesives can be considered an alternative to solid wood sleepers if specific grading of lamellas, proper treatment schedule, and highly controlled factory production are implemented. [ABSTRACT FROM AUTHOR]