Glued-in Rods Research Articles

Experiment and enhancement of compressive strength perpendicular to the grain of inorganic-bonded bamboo composite

ABSTRACT The inorganic-bonded bamboo composite (InorgBam) is a novel type of bamboo-based composite: a combination of magnesium oxysulfide inorganic adhesive and bamboo fiber strips, which exhibits significant material anisotropic characteristics with compressive strength perpendicular-to-grain typically lower than that of parallel-to-grain. The impact of loading form including full-area compression, middle and end local compression on strength perpendicular-to-grain was examined. The enhancement of compressive strength perpendicular to the grain using the glued-in rods (GiRs) method was tested. A prediction formula for ultimate load-carrying capacity perpendicular to the grain of enhanced InorgBam material was proposed considering the influence of load form and depths of GiRs. Results indicate that the full-area compression perpendicular to the grain exhibits a higher load-carrying capacity compared to the middle and end local compression. The GiRs method significantly enhances the compression strength and deformation behavior perpendicular to the grain of InorgBam material. The compressive load-carrying capacity and elastic modulus of the enhanced specimens can be increased by 83% and 157%, respectively. The prediction formula based on the replacement ratio of GiRs can well predict the strength of enhanced specimens.

Evaluation of shear performance of timber-timber composite joints

The mechanical performance of timber composite floors is influenced by the degree of composite action between the components. In this study, the shear strength performance of cross-laminated timber and glued laminated timber composite floors based on the joining method was evaluated by push-out test. Eight types of timber-timber composite joints were evaluated using three different methods: lag screw joints, glued-in rod joints using fully threaded bolts and glass fiber reinforced plastic, and hybrid joints. Strength characteristics were derived to make theoretical predictions on the load-carrying capacity of the joints. The results showed that the glued-in rod joints were superior to the lag screw joints, with slip coefficients and ductility measured as 10 times and 2.5 times higher, respectively. The reliability of the strength characteristics of the glued-in rod joints was remarkably different depending on the presence or absence of anti-adhesive tape applied to the timber-to-timber joint surface. The load capacity of the hybrid joint, which combines mechanical and glued-in rod joining methods, was 47% higher than that of the lag screw joint and 38% higher than that of the glued-in bolt joint. In the European Yield Model modified to estimate the load capacity of joints, the rope effect and the yield moment of the fasteners had a remarkable impact on the predicted load capacity.

Experimental Investigation of Cross-Laminated Timber Connections with Glued-In Rods under Monotonic and Cyclic Loading

Experimental Investigation of Cross-Laminated Timber Connections with Glued-In Rods under Monotonic and Cyclic Loading

Experimental and analytical evaluation of the tension capacity of edgewise connected glued-in rods in mass ply panels

The length of mass timber wall panels is a limiting factor in designing taller buildings. Splice designs are needed to maintain panel transportability while transferring shear and moment forces from higher floors to the foundation under lateral loading. One such splice design utilizes structural adhesive to glue threaded steel rods into the ends of wall panels being connected. This paper reports tests of the tension capacity of glued-in rods embedded in Mass Ply Panels (MPP). Twenty glued-in rods were tested under monotonic and cyclic protocols. Embedment depths ranged between 304.8 mm (12 in.) and 812.8 mm (32 in.). Load and displacement were measured during tests to report values per ISO 6891 and an international code council acceptance criteria document. Elastic stiffness, peak capacity, design capacity, and a predictive capacity equation were determined. Results showed a similar stiffness for all embedment depths and a negligible difference between peak capacities from monotonic and cyclic testing. While the data reported is only directly applicable for analysis of the specific MPP and epoxy combination used in the test program, the methodology herein can be utilized for future testing of timber-adhesive glued-in rods.

Regression Models for the Description of the Behaviour of Modern Timber Joints

Joints in timber structures are today typically designed in a simplistic manner, i.e., by assuming linear elastic behaviour or neglecting their real stiffness by assuming ideal pinned or fixed conditions. While such assumptions may be acceptable for simple structures, they do not reflect the real behaviour of joints in complex structures, and could, in some cases, lead either to an over-conservative or even unsafe design. Therefore, a more accurate and realistic representation of the nonlinear behaviour of joints with mechanical fasteners is needed. The most common modern timber joints with mechanical fasteners are realized with dowels, bolts, glued-in rods, or self-tapping screws. In this paper, an overview of the impact of the most influential parameters on the shape of the load-displacement curves of these joints under common static loading is given. The joints were differentiated according to the characteristics of their nonlinear load-displacement behaviour. Different analytical models from the literature for the description of the load-displacement curves of timber joints were reviewed. The performance and suitability of these models for describing the variety of nonlinear load-displacement behaviours of joints were evaluated and the advantages and limitations of each model were identified. It was found that the Richard–Abbott model is the most suitable to parametrize a variety of timber joints and to capture the variability of the test data by its parameters. Such an analytical model can be used to incorporate a parametrized, more realistic, nonlinear load-displacement representation of the behaviour of joints in reliability analyses, structural design software, and design guidance for modern timber structures.

Combined effects of axial and lateral loading for Glued-In steel rods in laminated veneer lumber

Glued-in rod timber connections are used to achieve structural continuity in timber structural members and as moment connections due to their high efficiency, stiffness and axial load transition. Existing studies have focused on axial withdrawal load capacity but there is limited research on laterally loaded glued-in rods and combined effects of lateral and axial loading which is common loading condition for all connections. This study investigates the relationship between axial and lateral loading in the ductile failure modes of glued-in steel rods in hardwood LVL. In all specimens an unbonded length was provided based on the latest design recommendations to mitigate splitting failure. The experimental findings suggest that the introduction of lateral load had no effect on the axial load capacities of the rods when the governing failure mode was rod yielding. This is not currently addressed in Eurocode 5. The lateral force capacity exceeded the design code prediction by 82%, and design recommendations are discussed for more accurate estimation of the lateral capacity. The use of the component method can be adopted to estimate accurately the rotational stiffness of moment connections with glued-in rods in LVL.

Mechanical behavior of glued-in GFRP rod in glubam: Experimental and analytical study

Fiber reinforced polymer (FRP) rod is a reasonable alternative to steel rod used in glued-in rod engineered bamboo structures, mainly attributed to its significantly higher strength-weight ratio and excellent corrosion resistance, while this field of study is almost empty. To fill this research gap, a total of 95 glued laminated bamboo (glubam) joints with single glued-in glass FRP (GFRP) rod were tested in a pull-pull tension loading program, aiming to shed light on the influence of anchorage length, rod diameter, bonding length-diameter ratio, glue-line thickness and rod-to-grain angle on the mechanical behavior. Particular emphasis was placed on the initial stiffness analysis and the explanation of the bond-slip mechanism based on the strain distribution of GFRP rod. Approximately 30% and 65% of the glued-in glubam joints can be categorized as the pure bonding failure at the glubam-adhesive interface and the shear failure in the glubam, respectively. It is found that the shear strength and initial stiffness of glubam joint decrease with increasing of the bonding length, the bonding length-diameter ratio, and the glue-line thickness, but the two indexes increase with increasing of GFRP rod diameter. The shear strength and initial stiffness exhibit an initial upward and then downward trend when the rod-to-main fiber direction angle varied from 0° to 90°. The analysis results reveal that the distribution of the local slip stiffness is non-uniform along the bonding length, also meaning that the local bond-slip relationships are varied at different locations. Based on the single-parameter correlation analysis, a strength model and an initial stiffness model are proposed for predicting the mechanical performance of glubam joints with glued-in GFRP rod for a potential application in evaluating actual glubam joints.

Characterizing the Performance of Adhesive Used in Glued-In Rod Timber Connections at Elevated Temperatures

A glued-in rod, which combines timber, a metal rod, and structural adhesive, is a type of connection whose fire performance is complicated to define since the rod depends on the adhesive’s thermomechanical properties. The objective of this study was to characterize the fire performance of adhesives used in glued-in rods. A total of five structural adhesives were tested: three epoxies and two polyurethanes. The tests performed consisted of applying an axial load to the glued-in rods after heating the connection to a target temperature. Load-slip curves were generated for each sample to determine their behavior at different temperatures. The results show that a reduction of up to 70% can occur in the initial stiffness of the glued-in rod when the temperature at the bond line exceeds the glass transition temperature of the adhesive determined by a dynamic mechanical analysis. This research helps to determine the guidelines for the fire design of glued-in rods and related testing and ultimately leading to a design method for providing fire-resistance to connections made of glued-in rods.

Pull-Out Performance of Timber Joints with Glued-In Densified Wood Dowels

Densified wood (DW) dowel is worth considering as an alternative to steel rod for timber joints with glued-in rods, because it is more naturally harmonized with timber members, and has better resistance against corrosion and lower thermal conductivity. This paper compares the pull-out performance of timber joints with glued-in DW dowels to that of threaded steel rods, loaded parallel to the grain 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%. After being conditioned at a temperature of 20°C and relative humidity of 65%, the pull-out capacity of the glued-in DW dowels having an anchorage length of 10 times the dowel diameter was close to 75% of that of the glued-in threaded steel rods. The impact of service environment was found to be greater for the timber joints with glued-in threaded steel rods than the timber joints with glued-in DW dowels.

Distributed fiber optic strain sensing in axially loaded glued-in steel rods in glued-laminated timber

The rise in popularity of mass timber structures globally has increased the demand for high-performance timber connections. Glued-in rod connections which are advantageous compared to other dowel-type connections because of their high strength and stiffness, have been the subject of extensive research in the literature; However, the lack of an in-depth understanding of their behavior and a uniform set of guidelines for their design continues to limit the use of glued-in rods in practice. To develop an improved understanding of the behavior of glued-in rod connections this paper examines, for the first time, the use of distributed fiber optic sensors to measure the complete strain distribution along the length of a glued-in rod connection. Axial pullout tests were conducted on twenty-five glued-in rod connections in glued-laminated timber with varying embedment lengths and glue-line thicknesses. Results of the study demonstrate the ability of fiber optic sensors to capture the full strain distribution along the length of the steel rod and along the epoxy-adhesive interface, enabling the study of localized behavior that would be difficult to measure using conventional strain gauges. In addition, results demonstrate the ability of distributed fiber optic strain sensors to infer axial stress and force distributions along the length of a glued-in rod connection, which are compared with theoretical distributions from the Volkersen model, as well as measure bond-slip behavior.

Numerical modeling investigation of cross-laminated timber connections consisting of multiple glued-in rods

Glued-in rods are stiff and high-capacity connections that are used in timber structures. Regardless of the many advantages of glued-in rods, research on the glued-in rods in CLT is limited, especially on numerical modeling. This paper provides the numerical modeling principles, validation details, and parametric studies of glued-in rods embedded on the edge of CLT. The numerical modeling was performed on a 3D finite element basis, and the cohesive surface method was used to define the bond lines along the rods. To validate the numerical models, 24 replica experiments were performed and investigated the effect of the rod diameter and of the embedment length on the pull-out strength of rods embedded perpendicular, parallel, and on the boundary of two cross-wised layers. The numerical models were validated according to the maximum load, stiffness, as well as the failure mode of the glued-in rods. The numerical models showed high reliability in simulating the experiments and predicted the strength of the glued-in rods with a maximum of 4% difference. After validation of the numerical models, the parametric study covered the pull-out strength investigation of rods with 20, 24, and 30 mm diameter and anchorage lengths of 250, 350, and 450 mm embedded in the perpendicular, parallel, and on the boundary of cross-wised layers on the edge of 5 and 7 layer CLT panels. The findings showed that increasing the embedment length and rod diameter enhanced the pull-out strength of the glued-in rods, regardless of where the rod was positioned on the CLT's edge. Rods embedded perpendicular to the grain showed the highest pull-out strength, and two rods with 30 mm diameter and 450 mm embedment lengths reached 961 kN pull-out strength. Numerical models showed that for the same diameter and embedment length of two rods embedded on the parallel and on the boundary of two cross-wised layers reached 836 and 738 kN pull-out strength, respectively. Finally, A design equation is provided to determine the pull-out strength of the glued-in rods embedded in CLT based on the shear strength of the bondline.

Modification Model of Glued-In Rods Splice Connection Using Statistical Analysis for Mengkulang Glulam Timber

The statistical study of the glued-in rod splice connection for Mengkulang glulam timber is presented in this research. This type of connection is used in many applications, such as bridge construction and wide hall, besides becoming increasingly popular due to its cost-effectiveness and ease of installation. Using statistical analysis to evaluate the performance of glued-in rod splice connections is relatively new. Statistical analysis can assess the connection’s performance by examining the glued-in rod splice connection’s strength, stiffness, and durability. Glued-in rods have several advantages over traditional mechanical connections generally used in beam design, such as higher stiffness, more uniform stress distribution, fewer rod corrosion problems and better appearance. Due to this limitation, the standard design for glued-in rods using glulam is the estimated extrapolation for solid timber guidelines. The main objectives of this research were to develop the pull-out model and validate the effectiveness of the model equation for glued-in rods parallel (GRPS0°) and perpendicular (GRPS90°) to the grain directions using a statistical package for the social sciences (SPSS). The variables examined were the number of rods, diameter, length, spacing, the kind of glue utilised, and the number of adhesive layers. In conclusion, the model development clearly shows that most of the parameters achieved the R2 more than 80% accurate for both parallel (GRPS0°) and perpendicular (GRPS90°) to the grain directions.

Experimental study and analysis of the bond-anchorage properties of laminated flattened-bamboo lumber connections with glued-in steel rod

To improve the utilization rate of raw bamboo and reduce the amount of adhesive, this paper studied a new type of laminated bamboo lumber, that is, laminated flattened bamboo lumber. The monotonic pull-out tests were carried out on 56 specimens with glued-in steel rods of three different diameters (12 mm, 16 mm, and 20 mm, respectively; the thickness of the adhesive layer was 3 mm) of laminated flattened bamboo lumber, and the effect of anchorage length and diameter of the steel bar on the mechanical properties of bond anchorage were studied. In addition, the specimens with a diameter of 12 mm and an anchorage length of 100 mm were selected to study the effect of different thicknesses of the adhesive layer (between 2 mm and 4 mm) on the mechanical properties of bonded anchorage. The results showed that the failure modes could be divided into three types. For the specimens with the same anchorage length, the larger the diameter of the glued-in steel bar was, the larger the ultimate pullout load would be; when the diameter of the steel bar was the same, the ultimate pullout load of the specimens increased with the increase of the anchorage length. When the diameter of the glued-in steel bar was 12 mm, the average bond strength decreased with the increase in slenderness ratio. When the diameter of the glued-in steel bar was 16 mm and 20 mm, the average bond strength first increased and then decreased with the increase of the slenderness ratio, and the turning slenderness ratio points were 8.75 and 5, respectively. The ANOVA analysis with parameters revealed that the rebar’s diameter and length significantly impacted the bond-anchorage characteristics of the glued-in rod connection in laminated flattened bamboo lumber.

Influence of glue-free zones on the withdrawal capacity of glued-in steel threaded rods

The hidden nature of a glued-in rod joint presents considerable challenges with regards to quality control, and there has been minimal research on the subject to fully understand the influence of defects on the joint performance. In this study, voids in adhesive line or glue-free zones were simulated in various depths of the embedded rod, and the results were compared to a reference sample population without defects. Withdrawal capacity of glued-in steel threaded rods were lower compared to reference group samples without gluing defects, when glue simulated voids or glue-free zones were positioned in the middle part and upper (closer to sample crosscut surface) part of the glued-in rods. And no difference was observed of simulated glue-free zones in the lower (the deepest) part, closer to the end of the glued-in rod, compared to reference group samples without gluing defects.

Experimental Bond Behaviour of Glued-In Rod Connection for Mengkulang Glulam under Pull-Out Loading

Mechanical joint and adhesive joint are the two most common types of timber connections. In the case of timber construction, bonded-in rods offer a long-term, aesthetically acceptable alternative to some of the more conventional steel moment connections. Bonded-in rod connections in timber need many desirable attributes inefficiency, manufacture, performance, aesthetics and cost. This paper presents pull-out experimental testing for glued-in rod made of Mengkulang (tarrietia javanica) glulam joints. Hundred and seven (107) specimens were prepared, each with a single glued-in rod parallel and perpendicular to the grain. The steel treaded rod with a diameter of 12 mm, 16 mm and 20 mm with three numbers of adhesive (Sikadur-30) thicknesses of 2 mm, 3 mm and 4 mm were used in this experiment. The pull-out tests observations were on the effects of adhesive thickness, parallel and perpendicular grain directions and modes of failure of the specimens. The result obtained that 4 mm adhesive thickness was the strongest and parallel specimens showed better results than the perpendicular specimens. The pull-out failure modes are affected by the selected factors, i.e. the adhesive thickness, rod diameter and grain directions. Most of the specimens show failures in the timber besides the adhesive to timber interface.

Low-temperature curing of adhesives – Large-scale experiments

ABSTRACT In contrast to mechanical joining techniques, which can be manufactured under any ambient conditions, adhesively bonded joints always require some minimum temperatures – typically above 10 °C – in order to cure safely. Due to this limitation, either many technical applications exclude adhesives right from the start or practitioners at high costs are forced to adapt their production processes to the specific environmental requirements of the polymers to be cured. As a response to these manufacturing challenges, a new process for accelerated curing – induction heating with Curie particles (CP) – was studied to cure three different structural adhesives (two epoxy resins and one polyurethane) at low temperatures. The CP are added to the adhesives as a typical filler material and can only be heated by an externally applied electromagnetic field up to their material-specific Curie temperature T c. Thus, a self-regulating process is created, which effectively prevents the adhesives from overheating while simultaneously eliminating the need to control curing temperatures by external measures like IR cameras. Recently, the authors published a series of papers in which CP were used to cure at ambient temperatures (+23 °C); the results of which are now to be extended towards low-temperature curing. For that, an experimental campaign was carried out using the exemplary connection type of Glued-in Rods (GiR), which are frequently used in various timber engineering applications. In detail, the heating behaviour of inductively cured GiR conditioned at –10 °C and –30 °C was compared to GiR inductively cured starting from +23 °C. In addition, reference sets with and without added CP were produced, whereby all GiR were subjected to tensile tests in the following. Afterwards, the series were compared on the level of load–displacement curves, failure loads, as well as observed fracture patterns. The results proved that CP-curing is capable of curing adhesives in temperature ranges currently not intended for structural adhesives by technical regulations. When cured under low-temperature conditions, the GiR involving epoxy adhesives showed a fracture behaviour that proved to be equal to that of the references. The failure loads of the 2 K-PUR dropped to 50–75% of the reference values, which, however, is strongly assumed to be related to moisture on the cold adherends and not to a general unsuitability of polyurethane adhesives for the process – an assumption that will be validated by low-temperature experiments using single lap shear joints presented in a subsequent study.

Shear performance of assembled shear connectors for timber–concrete composite beams

This paper presents three types of assembled shear connectors consisting of a steel component anchored to timber by screws and glued-in rods (GiRs) for timber-concrete composite (TCC) beams. Single-shear tests were carried out to evaluate the shear performance of the proposed shear connectors. The test results showed that the anchors bent obviously and finally failed in “single-hinge” and “double-hinge” yield modes under lateral load. The timber surrounding the anchors was obviously crushed, and cracks in concrete were also observed during testing. The shear connectors with I-shaped steel anchored by GiRs exhibited the highest shear capacity of 158.92 kN. The folded steel plate shear connectors with GiRs and screws showed the highest slip modulus (38.41 kN/mm), and the highest ductility with an average coefficient of 29.6, respectively. In general, the shear connectors anchored with GiRs showed better shear performance compared to the screwed shear connectors. Finally, numerical simulation results indicated that the simulated load–slip curves were generally in good agreement with the test curves. The anchor diameter and strength and the frictional coefficient between anchors and the wall of the holes in timber have significantly influenced the shear performance of the proposed shear connectors.

Ductile Moment-Resisting Timber Connections: A Review

In the last two decades, high-rise timber buildings have been built using the glulam truss system, even with limited openings. Moment-resisting timber frames (MRTF) with semi-rigid beam-to-column connections can be an architecture-friendly way to provide a load-carrying system to vertical and horizontal loads for timber buildings. In these structures, connections of adequate ductility are crucial to ensure robustness and energy dissipation. This paper presents a review of the main types of timber beam–column moment connections with improved ductility and proposes to carry out a ductility assessment of these connections based on the most relevant ductility factors. Joints have a significant influence on the global performance of MRTF, and the application of ductile connections have improved the mechanical parameters of the timber frame. The reinforced bolted slotted-in steel plate and glued-in rods connections have similar mechanical performance, with high rotation capacity and good ultimate moment, but exhibited different failure modes under cyclic loading. The connections were classified within ductility classes. In general, the glued-in steel rods presented better results because of the high influence of steel profiles in the connection yielding. Despite the excellent mechanical behavior, the reinforced bolted slotted-in steel plate connections presented medium ductility values.

Experimental investigations of glued-in rod connections in CLT

The widespread availability of cross-laminated timber (CLT) provides opportunities to extend the use of wood structures beyond low-rise residential construction. Glued-in rods (GiR) are an interesting technical solution for numerous timber structural applications, amongst them, the not yet exploited potential in conjunction with CLT. This paper summarises experimental investigation on the performance of GiR in CLT. Two 5-ply CLT panel thicknesses (139 and 175 mm), two steel rod diameters (dR = 12.7 and 19.1 mm), and five anchorage lengths (la = 6dR, 10dR, 12dR, 14dR and 18dR) were considered in applications parallel and perpendicular to the CLT major strength axis. A total of 220 uni-axial quasi-static monotonic tension tests were conducted. The results, assessed in terms of load-carrying capacity (ranging from 14 kN to 154 kN) and failure modes (plug-shear failure and lamination tear-out), demonstrated the impact of the connection’s geometric design parameters and that steel rods glued into CLT offer an alternative high capacity connection. The results will serve as the benchmark for subsequent numerical modelling, including the determination of joint capacity.

Mechanical performance of glued-in rod glulam beam to column moment connection: An experimental study

Engineered timber elements are gaining wide acceptance in construction with the increased practice of mass timber structures. The design of moment resistance connection is a contentious issue amongst practitioners and researchers. However, studies available on the performance of timber frame moment resisting connections made of various engineered timber sections are quite limited. This paper presents the outcome of a research study on the experimental assessment of the mechanical performance of a glued in rod (GIR) to glue laminated timber (GLT) beam to column moment connection. The research was carried in two stages: (1) investigating the pull-out behaviour of a GIR embedded in GLT and (2) verification of a full scale GLT moment connection using GIRs. The results of GIR pull-out testing revealed that the failure is mostly characterised by interface (GIR to GLT) shear bond delamination and slippage. Rod slip failure mode in the GLT was also observed in the full-scale connection tests. Subsequently, using the experimental data gathered in the two stages of testing, a simple approach to estimate the moment capacity of full-scale connection using three parameters and an analytical approach to estimate the rotational stiffness of GIR to GLT connection are presented. Furthermore, existing design formulations to predict the moment capacities of GIR to GLT are compared with the experimental data. The study enables a better understanding of the mechanical performance of a GIR to GLT moment resistance connection. Further, studies are needed with different parameters that influence the behaviour of GIR to GLT connections.