Glulam Structures Research Articles

Experimental study on the effectiveness of finger joint with variations in wood species toward bending strength of glulam beams

Recently, the utilization of timber as building materials was very promising for now and future. As renewable resources they have high mechanical properties, lightweight, environmentally friendly and economic. One of the most durable engineered wood products is glued-laminated timber which commonly called Glulam. Glulam is a material made of several layers of wood glued together with waterproof adhesive at specific pressure and temperature. The benefit of Glulam is enable to produce the structural member with longer span compared with solid wood. In other to obtain the structural Glulam with longer span, it required the finger joint connection on lamina layer. This study aims at to find out the effectiveness finger joint with variation in wood species towards flexural properties of Glulam beam. Experimental study have been done by using local wood Sengon and Rajumas as laminae and Biomatex as adhesive, at 0.6 MPa of clamp pressure. The variation of finger joint slope was tested are 1:8; 1:12; and 1:16. The result show that the glulam Sengon and Rajumas beam with slope finger joint of 1 over 12 produce the highest average bending strength of 299 kg/cm2 and 318 kg/cm2 respectively. The flexural strength of glulam Rajumas was 20% higher compared with glulam Sengon.

Cost optimisation of glued laminated timber roof structures using genetic algorithms

Roof structures comprising of heavy timber trusses and purlins made of glued laminated timber, as well as dowels and metal plates used as mechanical joints, are widely employed, among others, in agro-industrial settings that require large open areas. This paper presents the economic optimisation of such roof structures through the use genetic algorithm models. Two phases of optimisation were carried out: firstly, in two dimensions for a single truss and, then, an entire roof structure in three dimensions. Both models followed a discrete approach, i.e. the optimisation of the cross-section was limited by the characteristics of the commercially-available glulam timber boards, an aspect not yet included in the literature. Therefore, the models allowed the influence of the laminate thickness in the optimisation to be estimated, but also allow comparisons with the continuous cross-section variation found in the literature. Furthermore, the optimisation took into account a range of configurations of trusses, number of joints and separation between trusses and purlins. The genetic algorithms were shown as an efficient optimisation tool for roof glulam structures as a function of the laminate thickness. Among the results obtained, the most cost-effective solutions were those comprised of the fewer number of joints in the trusses and the lowest laminate thickness of those studied. Moreover, the optimal separations between trusses and purlins were also determined. Finally, a simplified method of optimum pre-dimensioning was also proposed.

Moisture content monitoring in glulam structures by embedded sensors via electrical methods

Moisture content monitoring in glulam structures by embedded sensors via electrical methods

Hysteretic Performance of Self-Centering Glulam Beam-to-Column Connections

AbstractThis paper investigates the hysteretic performance of self-centering beam-to-column connections for glulam structures. Such connections incorporate a posttensioned high-strength steel stran...

Moisture content monitoring in glulam structures by embedded sensors via electrical methods

In recent years, an increasing number of glulam structures have emerged in civil engineering, but their development is limited by durability issues. Degradations related to excessive moisture content (MC) or wetting/drying cycles were observed and can lead to severe structural damages. As a result, the development of continuous monitoring techniques of wood MC becomes essential. Currently, the mostly used MC control methods are based on electrical measurements (resistive or capacitive). Nevertheless, existing solutions are not practical to conduct measurements inside every lamella of glulam. In the light of these observations, it is proposed to transform glulam into “smart material” by embedding the MC monitoring system either inside or between lamellas, considering the major constraints of fabrication of this material (the small glue line thickness, the important bonding pressure, etc.). To achieve this, 4 measurement configurations using “pin-type” or “surface” electrodes were investigated with the following steps. First, a feasibility study was conducted to make sure of the good functionality of the measurement configurations. Thereafter, the selected configurations were used to monitor the MC variation (10–70%) in glulam specimens. At the same time, the influence of electrode spacing and bonding pressure on the electrical measurements was also investigated. Results show that the selected configurations are operational for the local MC measurement in the lamellas of glulam, regardless of the types of sensors used or the measured physical quantities (electrical resistance or capacitance). This study aims to provide valuable information for the future development of embedded MC monitoring system in glulam structures.

Evaluation of glue line shear strength of laminated timber structures using block and core type specimens

Monitoring and evaluation of glued laminated timber structures in service is essential to warrant its integrity, where non-destructive techniques play an important role. This paper describes the results obtained on glued laminated timber beams of maritime pine, with and without preservative treatment, and of spruce, exposed to natural outdoor environment as well as to artificial weathering. The assessment of glue lines’ shear strength was investigated through the extraction and testing of cores parallel and perpendicular to the glued lines and block shear specimens with 50 mm × 50 mm and 20 mm × 20 mm shear area. The results highlight the different performances of the various types of specimens tested, showing that the measured shear strength depends on the specimen size and that the size effect depends on the material strength giving a decreasing modification factor with the increase of strength in opposition to the constant factor suggested by standard EN 14080. They also show that shear testing of cores drilled perpendicular to the glued joints may be a promising tool in the assessment of glulam structures on site.

Moisture-induced stresses in glulam frames

Wood is a hygroscopic and moisture-sensitive material that seeks to achieve equilibrium moisture content (EMC) with its surrounding environment. For softwood timber structures exposed to variations in climate throughout their service life, this behaviour results in variable moisture-content gradients that cause moisture-induced stresses in the direction of and perpendicular to the fibres. Although Eurocode 5 (EC5) states that moisture-induced stresses should be considered, they are often not adequately dealt with in building design due to the difficulties in predicting the stresses involved by hand. Accordingly, there is a need for advanced computer tools to study how the long-term stress behaviour of timber structures is affected by creep and cyclic variations in climate. A beam model to simulate the overall hygro-mechanical and visco-elastic behaviour of (inhomogeneous) glulam structures is presented. A two-dimensional transient, non-linear moisture transport model for wood is also developed and linked with this beam model. The combined models are used to study the long-term deformations and stresses in a curved frame structure exposed to both mechanical loading and cyclic climate conditions. It is shown that the moisture-induced deformations and stresses are of such magnitude that the design codes employed should take them into account. Thus it is argued that climate-related loads should be treated as separate load contributions that can be included in different load combinations.

GFRP 보강적층판 및 GFRP rod를 이용한 낙엽송 집성재 문형라멘 구조의 수평가력 성능평가

The evaluation of the lateral load performance for larch glulam portal frames was carried out using glass fiber reinforced plastic (GFRP) as connector in two different systems: the GFRP-reinforced laminated plates combined with veneer, and GFRP rod joints glued with epoxy resins to replace usual metal connectors for the structural glulam rahmen joints. As a result the yield strength, ultimate strength, initial stiffness of glulams of GFRP rod joints glued with epoxy resin decreased to 49%, 52% and 61% compared to those of the conventional metal connector. This connector will be a stress device where the bonding strength between the GFRP rod and glued laminated timber is important. Thus, there will be a high possibility that a problem may occur when it is applied to the field. On the other hand, the GFRP-reinforced laminated plates and wood (Eucalyptus marginata) pin were measured all within 3% for all measurements of the yield strength, ultimate strength, initial strength and ductility factor, regardless of high cross sectional loss on the glued laminated timber slit joint. In addition, the variation of stiffness on the cycle was 35%, which was the lowest, confirming that it was almost the same performance as the specimen prepared with the metal connector.

Structural and Thermal Behaviour of a Timber-concrete Prefabricated Composite Wall System

Wood is the oldest building materials and still now it plays an important role in the construction sector. There are many general advantages in using timber for building purposes. First of all, it is an environmentally friendly, easily recyclable material; it has a low weight in relation to strength, which is advantageous for transport, handling and production; moreover wood has aesthetic qualities, which give great possibilities in architectural design. Lastly wooden structures have an excellent performance in case of earthquake if compared to traditional structures. In Europe the development of the timber-concrete composite structures (TCC) began during a shortage of steel for reinforcement in concrete in the beginning of XX century. TCC application was primarily a refurbishment technique for old historical buildings, during the last 50 years interest in TCC systems has increased, resulting in the construction also of new buildings. This paper presents the analysis of the structural and thermal behaviour of an timber-concrete prefabricated composite wall system, the Concrete Glulam Framed Panel (CGFP) which is a panel made of a concrete slab and a structural glulam frame. The research analyses the structural performance with quasi-static in-plane tests, focused on the in-plane strength and stiffness of individual panels, and the thermal behaviour of the system with steady state tests using an hot box apparatus. The results validate the efficacy of proposed system ensuring the resistance and the dissipative structural behaviour through the hierarchy response characterized by the wood frame, the braced reinforced concrete panel of the singular module and by the rocking effects of global system. On the other side hot-box measures demonstrated a high level of thermal resistance of the system reaching U-values around 0,20W m-2 K-1. Moreover experimental data permitted to calibrate a FEM model with which will be possible to study and analyse the panels in different conditions and configuration in both mechanical and thermal field.

Bonding Performance of Adhesives with Lamina in Structural Glulam Manufactured by High Frequency Heating System

The bonding performance of two types of wood adhesives, namely phenol-resorcinol-formaldehyde (PRF) resin and melamine-urea-formaldehyde (MUF) resin for glued laminated timber manufactured by high frequency (HF) heating was evaluated. The HF heating system consists of HF oscillator with dielectric heating system for curing adhesives, and hydraulic press system for clamping glued laminated timber. The designed frequency and output power of the HF system was as 5 MHz and 60 kW, respectively. To verify dielectric heating mechanism under HF oscillation, the heat loss factors of laminae and adhesives were measured. The results show that it is possible to selectively heat adhesives for their curing due to the remarkably higher loss factor of the adhesives than those of wood laminae. The temperature of adhesive in the bonding line reached up to the set temperature within a few seconds by high frequency oscillating, which advanced the curing of adhesive afterwards. The bonding performance, such as shear strength of bonding line, water soaking delamination, and boiling water soaking delamination of PRF resin met the requirement of Korean Standard (KS), however the MUF resin did not meet the KS requirement of boiling water soaking delamination. These results indicate that the HF heating system is successful to manufacture glued laminated timbers with PRF resins to meet the bonding requirements.

Evaluation of the Moisture Content in Stiffness Properties of Structural Glulam Beams

This research aimed to evaluate the influence of storage time (0, 96 hours) of Pinus elliottii pieces and the tests to obtaining modulus of elasticity (static bending and transversal vibration) in glued laminated timber beams, produced with resorcinol based adhesive and 0.8 MPa compaction pressure. After pieces were properly prepared, part of them was used in immediate three manufacturing glulam beams, tested after adhesive cure, and part stored for 96 hours under a roof with a temperature of 25°C and relative humidity of 60% for subsequent manufacturing and testing three other glulam beams. Results of analysis of variance (ANOVA) revealed that the storage period was significant influence in modulus of elasticity obtained in static bending test (8% reduction from 0 to 96 hours). This not occurred with modulus of elasticity obtained by transversal vibration test (no significant influence). ANOVA results showed equivalence of means in both test procedures.

Investigation of the structural performance of glulam beam connections using self-tapping screws

The characteristic strength properties of structural glulam connections assembled with self-tapping screws were examined following the ASTM testing procedure in the study. Four screw types with various numbers were designated at each connection of the beam–girder structure with different nailing schedules. The results indicated that the maximum load capacity and dissipated energy of a connection fastened with 10-mm self-tapping screws were higher than those with 8-mm screws. And, the screws with both double-threaded sections and fully threaded shanks were higher than those of single-threaded screws. An improvement on the initial stiffness of a connection was found when the number of self-tapping screws increased. The connections assembled with the toe-nailing approach from the beam’s bottom surface provided higher maximum loading capacity, medium initial stiffness, and a larger ductility factor, resulting in higher dissipated energy with less fragile failure. The derived allowable loading values for a beam–girder connection fastened with self-tapping screws using the face-nailing approach were close to the code values for bolted and pinned connections. And, a toe-nailing approach provided higher allowable loads for connections than using a face-nail approach.

Untersuchungen zur Festigkeit der Klebefugen von historischem Brettschichtholz

AbstractDer Beitrag befasst sich mit Untersuchungen zur Festigkeit von Kaseinverleimungen von Brettschichtholz in Hetzer‐Bauweise. Kaseinverleimungen treten heutzutage nur noch im Bereich von Instandsetzungsarbeiten an historischen Brettschichtholzkonstruktionen in Erscheinung.Eine Bewertung der Ergebnisse nach der DIN EN 392:1996 erwies sich als ungeeignet, da sich diese Norm auf moderne, auf Kunstharzen basierende Klebstoffsysteme bezieht. Um dennoch eine Bewertung vornehmen zu können, wurde auf frühere Veröffentlichungen zur Festigkeit von Kaseinverleimungen bzw. Regelwerke des Holzflugzeugbaus der 1950er‐Jahre zurückgegriffen.Die Auswertung eigener Untersuchungen ergab, dass Kaseinverleimungen auch nach 100 Jahren Nutzungsdauer, insbesondere unter Wechselwirkung von Feuchtigkeit und chemisch‐aggressiven Medien, eine relativ hohe Tragfähigkeit und Dauerhaftigkeit aufweisen.Studies on the strength of the adhesive joints of historic glued laminated timberThis paper presents a study on the strength of casein glue layers of glulam timber in Hetzer's construction method. Nowadays casein adhesive joints are only appearing in maintenance of historic glulam structures.An evaluation of the results according to DIN EN 392:1996 proved unsuitable, as this standard relates to modern, synthetic resins based adhesive systems. Therefore earlier publications on the strength of casein glue respectively regulations for wooden aircrafts from the 1950s were utilized in order to be able to assess these kind of adhesive joints.The results of this study revealed, that the casein adhesive joint has an relatively high loading capacity and durability even after 100 years especially under interaction of moisture and chemically aggressive media.

Engineered Wood in Cold Climate - Application to Monitoring of a New Swedish Suspension Bridge

Engineered wood is increasingly used in large structures in Europe, though little is known of its behavior in cold climate. This paper presents the structural health monitoring (SHM) system of a newly built suspension bridge with a deck of glulam timber as well as a bond stability study regarding cold climate performance of engineered wood. The bridge is located in Skellefteå in northern Sweden, and it connects two parts of the city situated on opposite shores of the Skellefteå river. In this ongoing study of the timber-bridge, a structural health monitoring system is employed to verify structural design and long-term performance. This 130m-span bridge is monitored using GNSS receivers, MEMS accelerometers, laser positioning systems, wireless moisture content sensors, strain gauges and weather stations. Data from the monitoring systems is analyzed regarding accuracy, complexity, costs and reliability for long time use. Engineered wood application in bridges, sports centers and timber buildings are discussed. Bond stability of glulam structures in cold climate is also examined in a range of experiments ranging from small glued wood joints to full size glulam bridge performance over time. From an engineered wood material point of view, the study is relevant to cold regions such as Scandinavia, Canada, Alaska, Russia, and the northern parts of China and Japan etc. The engineered wood constructions in these areas will be exposed to low temperature in a quite long period each year. The goal is to determine how engineered wood behaves when exposed to temperatures between 20 °C to -60 °C.

Effect of self-tapping screws on moisture induced stresses in glulam

Glulam structures in service may exhibit considerable moisture induced stresses perpendicular to grain that may affect the load-bearing capacity. An option to enhance the low tensile strength of glulam perpendicular to grain is the use of self-tapping screws, which has shown promising results in constant climates. In varying climates, however, the performance of such screw reinforcements is currently not well understood. The present paper reports results of both experiments and numerical simulations investigating the effect of self-tapping screws on moisture induced stresses arising in glulam exposed to single wetting and drying climate changes. It is shown that during wetting, the screw reinforcement significantly reduces the maximum tensile stresses arising in the cross section centre. With screw distances from 70 to 210mm, stress reductions by 70–30% are achieved (compared to unreinforced glulam beams). The tensile stresses arising between the reinforcing screws depend not only on the screw distance, but also strongly on the cross section width and the annual ring pattern of the laminates. During drying, the additional restraint caused by the reinforcing screws resulted in a slight increase of the tensile stresses at the cross section border. These were, however, rather low compared to the tensile stresses arising during wetting.

Critical review on the assessment of glulam structures using shear core samples

The problem of making inference on the performance of glued-laminated timber beams based on the shear strength of core samples is discussed. For the assessment of glued-laminated beams in existing structures, engineers are left with little guidance; often the standard for shear test of glue-lines (EN 392) is applied to evaluate aged or damaged components. Since the quality of the glue-line can vary significantly within and between members, multiple samples must be taken to get global estimates. The inherent limitations of the procedure are illustrated by the case study presented herein. Samples were taken from the beams of a decommissioned skating rink in Switzerland on different structural levels. A total of 20 bending and 128 shear tests were carried out on a representative large scale; additionally, 728 shear tests on small-scale core samples were conducted. The results demonstrate that core samples can be used to derive the local shear strength of glue-lines; however, no correlation with the shear and bending strength of adjacent large-scale beam sections was found. The results demonstrate that the common practice of assessing glued laminated timber based on the glue-line strength of core samples has to be critically re-evaluated; practical recommendations on how to improve the assessment are given.

Strengthening Mechanical Properties of Glulam with Basalt Fiber

This paper describes the strategy of improving the Mechanical Properties of timber and other wood-based glulam structures. This is achieved by bonding Basalt Fiber Reinforced Polymer (BFRP) composites to structural substrate externally. FRP Composite materials have been proven to be an effective way to traditional steel plate strengthening techniques for concrete structures from results of a variety of researchers over the past two decades; this paper shows the use of this material for same strengthening purpose in timber structures.The experimental program consisted in testing glulam flexural elements as follows: laminates are glued with two different Adhesives and two different lengths, both in natural form and reinforced by BFRP. All specimens were tested under three point bending at a predetermined loading increment rate, the lateral deflection were recorded regularly. The data processing consisted of bonding processes, load, deflection and moment curvature plots construction which were used for analysis and observations.The results revealed that there was a marked increase in the load bearing capacity of the timber flexural element, due to BFRP strengthening and there was also an increased rigidity in the member characteristics. Key words: Basalt Fibre Reinforced Polymer Composites; Structural Strengthening and Reinforcement; Glulam; HMR; BFRP

CuAz-3처리 리기다소나무 제재목을 이용한 구조용 집성재 성능 평가

구조용 집성재의 시장 수요가 확대되고 다양화되면서 교량이나 파고라와 같이 외기에 노출되는 조건에서 사용하기 위한 고 내구성 구조용 집성재에 대한 시장 요구가 증가할 것으로 예견된다. 따라서 본 연구는 국산 침엽수재로 제조되는 구조용 집성재에 적합한 방부처리 기술 및 기준을 개발하기 위한 목적으로 진행되었다. 본 연구에서는 방부처리된 국산 리기다소나무 제재목을 이용하여 구조용 집성재를 제조하고 제조 단계별 생산수율과 KS 품질기준 충족여부를 평가하였다. 방부집성재의 제조수율은 일반 집성재와 큰 차이를 나타내지 않았으며, 목재자원의 효율적인 활용을 위해서는 집성재 제조수율 향상방안과 함께 부산물에 대한 효율적 활용방안도 함께 검토되어야 한다. 리기다소나무 방부처리재의 경우 불균일한 방부약제 흡수량으로 인하여 구조용 집성재 제조용으로 적합하지 않은 것으로 확인되었으며, 집성재 제조 후에 유용성 방부제를 처리하는 방안에 대한 추가적인 검토가 요구되었다. Nowadays, market demand of structural Glulam is growing and diversifying. The durability of Glulam should be significantly considered when they are intended to apply for out-door use such as timber bridge and pergola. This study was aimed to develop the manufacturing process of preservative treated structural Glulam using domestic softwood species. 10 m long structural Glulam were manufactured from domestic pitch pine logs with CuAz-3 preservative treatment. At each manufacturing process, the production yield was evaluated. Finally, bending tests were performed to verify the structural performance of manufactured Glulam. From the results, it was shown that the preservative treatment process hardly influenced on the production yield. But domestic pitch pine was proved to not be suitable for making the preservative treated Glulam due to the large difference of preservative permeability between sapwood and heartwood.

Engineering Application of Glued Laminated Timber Structures in China

An overall outline is given for the development of the glued laminated timber structures in China. Different types of glulam structures built in recent years, such as gymnasium, bridges, public buildings, traditional architecture, landscape structures have been discussed. During the development of glulam structure in the future, raising design and produce level will be the most important question we confront and should be settled.

Feasibility of Ultrasonic Log Sorting in Manufacturing Structural Lamination from Japanese Cedar Logs

Because Japanese cedar shows lower mechanical performance, glued-laminated timber (glulam) can be a better way to utilize Japanese cedar for structural purpose. However, low yield of higher grade lami- nation from log makes it difficult to design structural glulam. This study was aimed to increase the yield of higher grade lamination and provide higher efficiency of manufacturing structural lamination by ultra- sonic log sorting technology. Logs were sorted by an existing log grading rule regulated by Korea Forest Research Institute (KFRI). It was found that the KFRI log grading rule contributed to finding better logs in viewpoint of the volumetric yield and it can reduce the number of rejected lumber by visual grading. However, it could not identify better logs to produce higher-grade products. To find an appropriate log-sorting-method for structural products, log diameter and ultrasonic time of flight (TOF) for the log were considered as factors to affect mechanical performance of resulting products. However, it was found that influence of log diameter on mechanical performance of resulting products was very small. The TOF showed a possibility to sort logs by mechanical performance of resulting products even though a co- efficient of correlation was not strong (R = 0.6). In a case study, the log selection based on the ultrasonic TOF of the log increased the yield of the outermost tension lamination (E8 or better grade, KS F 3021) from 2.6% to 12.5% and reduced LTE5 (lower than E5 grade) lamination from 43.6% to 10.3%, compared with the existing KFRI log grading rule.