Von grundlegender Bedeutung für die Berechnung nachgiebig verbundener Biegeträger ist das sog. γ‐Verfahren. In diesem Beitrag werden die Grundlagen und die exakten Lösungen für das γ‐Verfahren ...ausgearbeitet. Das in der deutschen und europäischen Holzbau‐Normung zur Berechnung nachgiebig verbundener Biegeträger mit maximal drei Einzelquerschnitten verankerte Verfahren wird auf Biegeträger mit beliebig vielen Einzelquerschnitten erweitert.
Translation
The γ‐procedure for calculation of partially composite beams consisting of flexibly jointed cross‐section with any number of sub‐elements: general method
The so‐called γ‐procedure is essentially important for the calculation of partially composite beams consisting of flexibly jointed cross‐section. In this paper, the basic principle and the exact solution of the γ‐procedure are described. In the German and European standards of timber structures, partially composite beams with a maximum number of three sub‐elements can be calculated. This paper proposed a method that can extend the calculation of partially composite beams with any number of sub‐elements.
The maintenance of historic wooden structures requires the assessment of the timber elements that compose them. The accurate knowledge of their mechanical performance is a fundamental aspect to ...guarantee conservation, safety, and usability. In this work, the assessment of the mechanical properties of timber was done by visual and machine strength grading. The visual grading rule developed for new wooden products was applied, as well as that established by the Italian standard for historic load-bearing structures. Machine grading was also performed by simulating the procedures applicable to the dismantled or in situ elements. The strength and stiffness values expected according to the different strength grading procedures were compared with the values obtained from destructive tests. As a result of visual grading, the modulus of elasticity was in line with the provisions of the standardization, while the characteristic strength was lower. With machine grading the yields were lower, but the characteristic strength values of the classes were respected, especially if combined with a visual inspection rejecting decayed or damaged pieces. The modulus of elasticity, however, was higher than that of the class, thus being underestimated.
•Prediction of the mechanical properties of historic load-bearing wooden structures is crucial for their conservation.•Visual and machine strength grading were applied on dismantled timber and verified through destructive tests.•Bending strength was lower than expected by applying the visual grading rules, the modulus of elasticity was in line.•The machine grading led to lower yields, but the characteristic strength of the classes were respected.
•An investigation of the behaviour of CLT shearwalls with openings is undertaken.•Failure modes related to either mechanical anchor or CLT panel are studied.•Full-scale shearwall tests were used to ...validate a proposed numerical model.•Input parameters for numerical model were obtained from component level tests.
An investigation of the mechanical behaviour of CLT shearwalls, where either door or window openings are cut out of the panel, is undertaken. The main aim of the study is to investigate failure modes related to either mechanical anchor or CLT panel, based on the geometrical dimensions and mechanical properties of shearwall. The results of six full-scale monolithic CLT shearwalls with window or door openings are presented and discussed. The results obtained from the full-scale shearwall tests are used to validate a proposed numerical model, where input parameters, such as the mechanical properties of the CLT panels and mechanical anchors, are obtained from component level tests on beams and connections in isolation. The study shows that differently from single-panel shearwalls with no openings, brittle failure in the CLT panels is a possible mode of failure, which needs to be considered in design. The failure mode in the CLT panels is observed to occur either in bending or net shear in the lintel beams. The proposed numerical procedure is found capable of estimating the maximum load with reasonable accuracy, and the model predictions of the failure mode, number of centre of rotations, and the overall deformation of the CLT panel are accurate for all the studied specimens.
Sustainably sourced engineered wood products (EWP) such as cross-laminated timber (CLT) floor panels are viable alternatives to conventional concrete and steel, however their inherent natural ...variability increases perceived risks and limits wide-spread adoption. The reliability index (β) is the metric used by design standards to communicate allowable structural risk. Although not included directly in any structural capacity equations, it governs all the partial resistance factors and load amplification factors that inform those design code calculations. CLT floors have significant partial resistance factors due to the natural variability of the material that effectively penalise the calculated design strength of those products. By exploring their reliability there is the potential to allow these products to be designed more efficiently, leading to increased competitiveness among traditional materials and less waste. A novel statistical capacity prediction model that goes beyond a simple averaged-value strength assumption to include consideration of the variability between individual boards within a panel was validated against experimental data. A CLT database of 237 out-of-plane bending test results was collected for the first time to inform an appropriate model error factor. Monte Carlo simulation (MCS) approaches were adopted to predict the reliability levels of CLT panels by defining the material, geometrical and loading parameters as random variables and assigning each a mean, coefficient of variation and appropriate distribution. The target and calculated reliability levels were compared across both Eurocode 5 and the North American codes ANSI/APA PRG 320 and CSA O86 as the preeminent CLT design codes internationally. This study found that the calculated reliability levels met or exceeded both codes in most scenarios. The impacts of width, load ratio, material strength distribution, and CLT layups on the expected failure probabilities were explored with sensitivity analyses. The MCS framework was also applied to the calibration of an appropriate resistance factor for CLT design to inform the potential creation of an Australian CLT design code. A resistance factor of 0.85 was calibrated which falls between the equivalent European and North American code resistance factors.
Carbon fiber reinforced polymer (CFRP) is increasingly used to strengthen the flexural, shear, axial, and seismic performance of existing timber structures, but CFRP-timber interfacial debonding can ...substantially weaken the composite action and trigger catastrophic structural failure. Therefore, efficient nondestructive evaluation method is needed to inspect the interfacial debonding, flaws, and imperfections after the installation and periodically during the service of CFRP strengthened timber structures. This study is the first work to investigate nondestructive evaluation of CFRP-timber interfacial condition using active microwave thermography (AMT). AMT utilized microwave as an excitation to generate heat in CFRP and to indirectly detect the interfacial defect from the temperature anomaly on the surface of CFRP. Ten CFRP-timber specimens with different shapes and sizes of interfacial defects were tested under AMT. The experimental results showed that AMT can intuitively detect the CFRP-timber interfacial debonding at the earliest within 8 s to 11 s, which has advantages in speed and visualization. It should be noted that the blur effect can decrease the precision of detection of the shape, especially sharp corners, of the defect. The comparison between specimens with different parameters showed that larger areas of debonding can be detected easily while small ones cannot. In this study, defects with a diameter ≥ 7 mm can be detected.
•It is the first work to investigate nondestructive evaluation of CFRP-timber interface condition using active microwave thermography (AMT).•The experiment investigated CFRP-timber specimens with interfacial defects of different shapes, positions, and sizes under AMT conditions.•The experimental results showed that AMT can accurately detect the CFRP-timber interfacial debonding within 8 s, and defects with a diameter ≥ 7 mm can be detected.
•The joints are fractured locally at variable cross-section and tenon neck.•The critical energy release rate increases and then decreases as the looseness grows.•The moment of the joint increases ...initially and then reduces with cracks increase.•The amount of tenon pull-out of loose joints decreases as compression increases.
A looseness is typical damage of mortise-tenon joints in ancient timber structures. Brittle fractures of loose joints are likely to occur, leading to joint failure during earthquakes. This study conducts pseudo-static tests on three groups of full-scaled through-tenon joints to examine the fracture damage and seismic behavior of the loose mortise-tenon joints and determines fracture damage modes of through-tenon joints with different looseness. It uses the acoustic emission method to measure the ring count on the tenon surface, along with each joint's critical load and critical energy release rate and then analyzes the fracture damage performance of different tenon joints. In addition, this research investigates the hysteretic and skeleton curve, stiffness degradation curve, and tenon pulling quantity of the joint under various fracture damage states. The results showed that the fracture failure mode of the through-tenon joint is a fracture in the variable cross-section and along the local tenon neck. During the loading process, the critical energy release rate initially increases and then decreases as the looseness grows. In addition, with the increase of crack mouth opening displacement (CMOD) and crack length, the bending moment of the joint firstly increases and then decreases. When the variable cross-section breaks and the tenon neck partially cracks, the joints' bending moment and stiffness reduce with increasing looseness. With the increase in local embedment compression in the lower side of the beam end and the mortise, the amount of tenon pull-out of loose joints decreases under positive and negative loading.
This paper presents the experimental results on the fire resistance of traditional timber mortise-tenon joints with looseness, decay and cracking in the jointing area. Static loading test and fire ...resistance tests were conducted on six full scale joint specimens. The development of the temperature, the charring depth and rate, and the degradation of the rotational stiffness of the joints with fire exposure time was quantified. It was found that the service damage can have significant influence on the fire resistance of the traditional timber mortise-tenon joints. The charring rate calculated from the beam and column cross-sections is close to the recommended value in design code for softwood. The displacement of the damaged joints with wood decay and cracking increased by 69% and 90%, respectively, with respect to that of the undamaged joint after 30 min of dire exposure. The rotational stiffness of a damaged joint after 30 min of fire exposure can drop down to 11.4% of the initial rotational stiffness of a sound joint at ambient temperature. The influence of the stiffness degradation of joints on the moment redistribution and fire endurance of neighbouring beams and columns is worth of further investigation.
•Two mechanics-based analytical models were developed for predicting the deflection and resistance of balloon-type CLT shear wall system.•The developed analytical models were capable of reasonably ...predicting the deflection and resistance of single- and coupled-panel balloon-type CLT shear walls tested under in-plane lateral loads.•The influence of the vertical load, wall aspect ratio, and vertical joint on the structural performance of the balloon-type CLT shear walls was successfully investigated using the verified elastic-base model.
Besides platform-type construction method, a rarely investigated balloon-type method, in which the walls are continuous for the entire height of the building and the floor panels are attached to the walls at each floor, can also be used to construct Cross Laminated Timber (CLT) buildings. The balloon-type method endures several key advantages to the CLT buildings, such as reducing connections and avoiding accumulating compression perpendicular to grain in the floors, thus being a viable solution for high-rise buildings. In this paper, two mechanics-based analytical models (rigid- and elastic-base models) were developed for predicting the deflection and resistance of balloon-type CLT shear wall system. The developed analytical models incorporate the contribution of the wall bending and shear deformation, as well as contribution from the wall rocking and sliding, and the slip in the vertical joints between panels, on the overall wall deflection. The resistance of this system was assumed to be governed by the hold-downs, shear connectors, and vertical joints, if present. The analytical models were validated against the test results of four balloon-type CLT shear walls in two configurations tested under monotonic or cyclic load. The verified analytical models were used to investigate the influence of vertical load, wall aspect ratio, and vertical joint on the structural performance of the balloon-type CLT shear wall. The developed analytical models provide a mechanics-based approach for researchers and engineers to predict the structural performance of balloon-type CLT shear walls. The wall test results and the parameter analysis results gave a valuable insight into the structural behavior of the balloon-type CLT shear walls.
When dealing with timber structures, the characteristic strength and stiffness of the material are made highly variable and uncertain by the unavoidable, yet hardly predictable, presence of knots and ...other defects. In this work, we apply the sparse grids stochastic collocation method to perform uncertainty quantification for structural engineering in the scenario described above. Sparse grids have been developed by the mathematical community in the last decades, and their theoretical background has been rigorously and extensively studied. The document proposes a brief practice-oriented introduction with minimal theoretical background, provides detailed instructions for the use of the off-the-shelf Sparse Grid Matlab kit (freely available online and straightforward to use) and discusses two preliminary examples inspired from timber engineering problems that highlight how sparse grids exhibit superior performances compared to the plain Monte Carlo method.
•An Uncertainty Quantification methodology is applied to timber-like structures.•IGA collocation is used for solving the equilibrium equations.•Smolyak and adaptive sparse grids are used for managing random parameters.•This methodology requires no coding effort and outperforms Monte Carlo.
•In historical structures, wooden elements are often degraded by superficial insect attacks.•Neglecting the contribution of degraded areas to the load bearing capacity of the beam can be an ...over-conservative approach.•A reduction coefficient of degraded wood is defined based on theoretical calculation and experimental investigation.•The reduction coefficient can be applied to the mechanical properties of degraded areas so to include them in structural calculation.•A value of n = 5 is proposed for the reduction coefficient.
Existing timber structures are often affected by peripheral degradation due to insect attack. The contribution of the degraded areas of the beam cross-section to the load bearing capacity is usually neglected, leading to an over-conservative approach to the structural verification of historic wooden constructions. This work analyses timber elements dismantled from a nineteenth century building by means of a comprehensive geometrical survey, the evaluation of the degraded portion of the cross-section and by destructive bending tests. An iterative procedure based on the linear elastic theory of composite beams was set up to define a reduction coefficient of the mechanical properties of degraded wood, in order to include the contribution of the degraded parts during the structural calculation. The analytical procedure proved to be effective only for timber elements without localised major defects or anomalies, such as woodworking or internal decay, which may alter the linear elastic flexural behaviour of the beam. The values obtained of the reduction coefficient ranged from 1.7 to 5.0 and were successfully verified by numerical models.
