•Dynamic test data were used to validate a detailed FE-model of a glulam truss.•Beam model with Guyan reduced connections is very accurate, fast, and useful.•Connection stiffnesses reduced to springs ...yield fair accuracy and are simpler.•Eurocode 5 underestimates the in-plane stiffness values of the connections by 2/3.
The rise of wood buildings in the skylines of cities forces structural dynamic and timber experts to team up to solve one of the new civil-engineering challenges, namely comfort at the higher levels, in light weight buildings, with respect to wind-induced vibrations. Large laminated timber structures with mechanical joints are exposed to turbulent horizontal excitation with most of the wind energy blowing around the lowest resonance frequencies of 50 to 150 m tall buildings. Good knowledge of the spatial distribution of mass, stiffness and damping is needed to predict and mitigate the sway in lighter, flexible buildings. This paper presents vibration tests and reductions of a detailed FE-model of a truss with dowel-type connections leading to models that will be useful for structural engineers. The models also enable further investigations about the parameters of the slotted-in steel plates and dowels connections governing the dynamical response of timber trusses.
In view of the development of heavy timber seismic-resistant structures, in the context of modern seismic design approach, a possible solution is to allow the timber structure to dissipate a part of ...the seismic energy. Since timber is a material with an elastic-fragile behaviour, the dissipative function should be delegated to connections, through plastic deformation of steel connectors. However, joints are primary structural elements, with a crucial role in bearing the design loads. Therefore, the role of seismic energy dissipation should be conveniently assumed by ad hoc devices.
In this context, the paper deals with the application of fluid viscous dampers (FVD) to timber frames: FVDs dissipate seismic energy, while timber elements and steel connections remain elastic. Specifically, 2D single-storey structures with dissipative bracing systems, equipped with FVDs, in different configurations, are studied, assuming several rates of possible dampings. Non-linear dynamic time history analyses are performed (SAP2000, v18). Results are discussed showing significant reduction of the structural mass compared to the non-dissipative ones, recentering capability of the structures, high dissipative capacity, simpler elastic connections. The reduction of production and maintenance costs follows. All these involve the efficiency of the structural performance and sustainability under earthquakes.
•In historical wooden structures degradation due to insect attacks is common.•A software routine is presented to quantify degradation depth by drilling resistance.•The routine was optimized and ...verified on wooden beams with satisfactory results.•Drilling profiles were informative with degradation by cerambycids, but not with anobiid attacks.
The assessment of insect degradation on the surface of timber elements is a key point in evaluating the safety of wooden buildings. The depth and the degree of the insect attack are necessary data to determine the resistant section of the load-bearing elements.
To the aim, the resistance drilling is applied as non-destructive technique in the on-site inspection. Here, a routine is proposed and verified to automatically process the resistance data and to identify the presence of insect decay.
Twelve wooden beams disassembled from an old timber structure were used as experimental material: five to optimize the routine and seven to verify the output after the optimization. In total, 78 % of the measurements showed an error of less than 5 mm and 86 % less than 10 mm when compared to the determination made by an expert operator on the same drilling profiles. Comparing the non-destructive measurements with the cross-sections cut from the beams, the profiles seemed very informative when the degradation was caused by cerambycids, but less so with anobiid attacks.
SCARF JOINTS IN GLUED LAMINATED TIMBER OF PARICÁ Terezo, Rodrigo Figueiredo; Rosa, Talitha Oliveira; Furtado, Francisco Raphael Cabral ...
Floresta,
06/2021, Letnik:
51, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Glued Laminated Timber (GLULAM) is manufactured by joining wood lamellae glued in parallel to each other. GLULAM with larger longitudinal dimensions can be obtained by gluing the tops of two wood ...lamellae. The gluing of the tops can be done using wedge-shaped scarf joints. However, the joints produce a discontinuity in the wood, being areas considered as susceptible to rupture. In this way, the objectives were to evaluate four slopes (1:6; 1:8; 1:10 and 1:12) in scarf joints of Schizolobium parahyba var. amazonicum timber for use with structural purposes; and glued laminated timber beams – GLULAM manufactured with the scarf joint with the best performance by the modulus of elasticity – MOE (theoretical and analytical MOE values). Each laminated timber used to produce the test specimens was classified by visual inspection that aimed at the absence of defects, such as knots. The test specimens were adapted to the four-point static bending test and to the tensile strength test in parallel to the grain direction, in accordance to the NBR 7190 (1997). The slope of 1:12 showed the best results, while the slope of 1:6 presented the lowest results when compared with the control. The beams of 5 x 9.5 x 220 cm, composed of joints with slopes of 1:12, showed MOE values statistically equal to those of beams without joints. The scarf joint proved to be an alternative for use in glulam beams of paricá, as it presents stiffness and strength comparable with those of beams without a joint.
Asymptotic geodesic gridshells are a novel structural system that is fabricated from straight and flat planks. The planks are elastically bent and twisted around their slender dimension to achieve ...the desired geometry, while the tall dimension creates structural stiffness. This system combines the geometric features of asymptotic and geodesic curves to create a hybrid tri-hex network on doubly curved surfaces, and provides a stable grid to resist its self-weight and external loads. To comprehensively explore the structural capabilities of asymptotic geodesic gridshells, a full-scale timber gridshell prototype was designed and built. Loading tests, including local and one shell asymmetrical loading, were carried out to examine the structural behaviour of the gridshell. A nonlinear finite-element model was developed and subsequently validated using experimental data. The evaluation of the timber gridshell revealed its high performance under uniformly distributed loads, and the simulation indicated a viable live load capacity of 7.0 kN/m². In a parametric study, the influence of the polar array layout, the joint rotation stiffness, and the support condition on the structural performance of the hybrid gridshell are analysed. Parameters influencing the achievable span are discussed regarding strength, stiffness and buckling behaviour for future design considerations.
•Development of a full-scale timber gridshell prototype utilizing asymptotic geodesic design principles.•Comprehensive loading experiments, including local area and one-shell asymmetrical loading, to investigate the structural behaviour.•Development and validation of a nonlinear FE model to assess the gridshell's performance under various loading conditions.•Parametric study examining the impact of polar array layout, joint rotation stiffness, and support condition on structural performance.•Dimensional analysis of the achievable scale, considering strength, stiffness and buckling behaviour.
•Energy-absorbing connections (EAC) are investigated to improve energy-dissipation in timber assemblies under blast loading.•Typical load-displacement relationships are described and obtained from ...dynamic testing in a shock tube and static testing.•Configurations with well-defined plateau were capable of dissipating a significant amount of energy.•Single-degree-of-freedom (SDOF) and finite element analysis (FEA) were validated for predicting the performance of EACs.•An example of the application of EACs in a mass timber assembly is demonstrated.
This study presents the results of an experimental program investigating the use of steel energy-absorbing connections (EAC) for the purpose of improving the energy dissipation capabilities of timber assemblies. The performance of the EACs is investigated both experimentally and numerically. A total of thirty-six specimens, representing nine configurations, including angle and circular hollow-steel sections, were tested under quasi-static and dynamic loading. The results of the study showed that connection configurations with well-defined plateaus were capable of dissipating a significant amount of energy and as such can be used in design for blast mitigation. Scalability of resistance based on the connection's depth was shown to be achievable experimentally. The welding configurations were shown to impact the behaviour significantly, and thus the details used in manufacturing must be identical to those assumed in design. The resistance curves of the EAC configurations investigated were reasonably predicted using Finite Element models. Analysis with single degree of freedom utilizing resistance curves obtained experimentally or from the finite element model mimicked the observed behaviour of the EACs. An example of the application of EACs in a mass timber assembly is demonstrated. This example showed that a 247 % increase in the energy absorption of the system might be obtained when compared to glulam members with idealized simply-supported boundary conditions.
•Four-point bending of reinforced and prestressed glulam beams with CFRP bars.•Bonded bar and end anchors result into a highly improved strength and stiffness.•Stiffness further increased for ...prestressed compared to passively reinforced.•End anchors with nuts allow for re-tightening and thus reduce the prestress loss.
This paper describes an experimental test program and theoretical analysis which examines the reinforcing in flexure of glued laminated timber (glulam) beams using bonded-in carbon fiber reinforced polymer (CFRP) bars. A series of four-point bending tests were conducted till failure on unreinforced, passively reinforced and prestressed Douglas fir glulam beams in a simply-supported scheme. The focus of this research was to evaluate the reinforcing efficiency of both passively reinforced and prestressed beams. Test results showed that the flexural capacity of the reinforced, prestressed, prestressed & reinforced (bottom prestressed and top reinforced) beams greatly increased by 64.8%, 93.3% and 131%, respectively. While the maximum improvement of the bending stiffness reached 42.0%. Another important finding was that the extreme fiber tensile strain of timber beams at failure could be remarkably increased due to the presence of the tension reinforcement, which indicated it overcomes the effects of local defects and therefore the failure mode was changed from brittle tension failure to ductile compression failure. Based on the experimental results, a theoretical model was proposed to predict the flexural capacity of unreinforced, reinforced and prestressed timber beams, which was validated by the test data.
In the scope of European Cooperation in Science and Technology-Wood Science for Conservation of Cultural Heritage (COST IE0601-WoodCultHer) (available at
http://www.woodculther.org
) it was agreed to ...produce Guidelines for the Assessment of Historic Timber Structures, covering the principles and possible approaches for the safety assessment of old timber structures of historical relevance that could be used as the basis for possible European Standards, as discussed with CEN/TC346 (Conservation of Cultural Heritage).
This approach was targeted at all those concerned with the conservation of heritage buildings. These guidelines should also help decision-making regarding the need for immediate safety measures. The aim is to guarantee that inspection and assessment measures provide the necessary data for historical analysis, structural safety assessment, and planning of intervention works, while having minimal impact on the building fabric (the original materials, structural systems, and techniques).This article provides information on the criteria to be used in the assessment of load-bearing timber structures in heritage buildings. It covers the preliminary assessment (desk survey, preliminary visual survey, measured survey, structural analysis, and preliminary report), as well as the detailed survey of timbers (with a special emphasis on visual strength grading on site) and carpentry joints. The subsequent diagnostic report and the detailed design of repairs are outside its scope.
•Non-linear bending models for wood considering composite reinforcement.•Selected issues in estimating and numerical modelling stiffness and strength of FRP-reinforced timber beams.•Application of ...the generalised Hill yield criterion with a distinction between compressive and tensile yield stresses.
The paper presents selected methods for modelling bent timber beams strengthened with fibre-reinforced polymers (FRP). The assumptions are described, and the main analytical models representing the non-linear bending behaviour of wood are shown. Based on the models presented, analytical approaches considering reinforcement in the tension zone are proposed. The problem of determining the appropriate material parameters of the wood used in analytical calculations and numerical models is discussed. The main numerical methods used in timber analyses are presented. The Hill yield criterion and the generalised Hill yield criterion are discussed in more detail. A method for retrospective estimation of material properties of wood taking into account non-linear material models and fitting the generalised Hill yield criterion is described. Experimental bending tests of technical-scale beams reinforced with composites are presented. The numerical analysis was carried out and discussed. The generalised Hill yield criterion was applied to represent the behaviour of the wood, distinguishing the different yield stresses in compression and tension. The suitability of using non-linear models and advanced strength criteria in the numerical analysis of timber elements is discussed.
This study is aimed at investigating those parameters related to timber flooring that can affect the acceptability of vibration behaviour of a timber floor in a residential building in view of the ...criteria stated in Eurocode EC5. The timber floor investigated is made of OSB/3 floorboards and timber joists. The parameters that are investigated in this study are thickness of flooring, floor joist span, joist spacing and connection of floorboards to the joists. In this context, two cases are considered. First: the flooring is nailed or screwed to the joists and no composite action or interaction is obtained between joists and floorboards. Second: the flooring is glued sufficiently to the joists and full interaction is obtained. The result suggests that glued floorboards perform much better with respect to natural frequency, static deflection and peak floor velocity than nailed or screwed floorboards. In almost all cases of glued floorboards, the result complies fully with the Eurocode 5 design vibration requirements. However, as floor lengths increase, the static deflection will increase beyond the allowable limit, especially for relatively thin floor panels and relatively widely spread joists. For both cases, increasing floorboards thickness and decreasing the joist span by adding more beams can yield even better results to satisfy the requirement of vibration comfort.
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