Wen-Shao Chang

Rotational performance of traditional Nuki joints with gap I: theory and verification

The Nuki joints in Taiwan and Japan are similar in appearance; however, due to lack of wedges used in Nuki joints in Taiwan, the gap between the column and beam increases the complexity of timber joints. In this article, the rotational performance of traditional timber joints is reported. A theoretical model considering Hook’s law and Hankinson’s formula was developed for predicting the rotational performance of Nuki joints with gaps. A total of 24 specimens was tested and used to verify the rotational performance of timber joints. The proposed model not only predicts the rotational stiffness of Nuki joints, but can also estimate the initial slip of these joints. Good agreement was found between predicted and experimental data.

Non-homogeneous Thermal Properties of Bamboo

A Phyllostachys edulis (Moso Bamboo)sample’s density, heat capacity and thermal effusivity were obtained by a series of experiments. The porosity, thermal conductivity and thermal diffusivity were calculated. Based on these experimental values, this study discusses the Phyllostachys edulis sample’s microstructure characteristics and the causes of the variation of thermal properties along the radial direction.

On mechanical behavior of traditional timber shear wall in Taiwan I : background and theory derivation

The objectives of this study were to explore the mechanical behavior of traditional timber shear walls in Taiwan and to propose a theoretical model to predict their lateral force resistance. An extensive field investigation was conducted, and the dimensions, tectonic detail, and materials used were recorded. The data collected were used as the reference for theoretical derivation and experimental design. In the theoretical model, the moment resistance of entire shear walls was derived from the contributions of the moment-resisting capacity supplied not only by embedment and friction action between board units and beams but also the dowel action of bamboo nails. Timber shear walls with various geometric conditions and material properties are considered. The theoretical model demonstrated in this study can be used to predict the mechanical behavior of timber shear walls and will be verified by experiments in our next article.

Development of All-Wood Connections with Plywood Flitch Plate and Oak Pegs

This paper proposes a new method for beam-beam connections, which include plywood as slot-in plates connected by oak pegs. A total of 96 specimens were fabricated for tests to explore the minimum required end distances and spacing between pegs parallel to the grain. A new failure mode, termed shear wedge that is different from those found in previous research, was found. A spring model was also proposed in this study to investigate the stiffness of the connections, and feasibility of EC5 to be applied on the new proposed connections was also examined. The effective number was discussed in this study and modified in accordance to the experimental results. The result of this study shows the new connections proposed do not lead to brittle failure unless failure in plywood occurred.

An analytical model for embedment stiffness of a dowel in timber under cyclic load

The fundamental part of a dowel-type connection is the embedment of a steel dowel into the timber that surrounds it, and the stiffness of the timber in embedment is represented by the foundation modulus. A standard experimental method for identifying the foundation modulus under static load is modified to assess the secant stiffness exhibited under one-sided cyclic load. It is shown that the steady-state secant stiffness is significantly higher than the static stiffness under initial loading, and that, if the amplitude of the cyclic component of the load is sufficiently small, a simple analytical elastic model predicts the foundation modulus well. The analytical model is based on a complex stress function for the timber in embedment and the frictional interaction between the dowel and the timber. The foundation modulus calculated in this way can be used to predict the stiffness of complete connections for analysis of vibration in frames modelled with semi-rigid joints. Although the application of the model is limited to vibration about a non-zero mean load, with no load-sign reversal, this form of vibration encompasses various important types of in-service vibration of structures, such as that induced by turbulent wind or footfall.ZusammenfassungBei stiftförmigen Verbindungsmitteln ist die Bettung eines Stahldübels im umliegenden Holz von grundlegender Bedeutung. Die Steifigkeit des Holzes im Bereich der Lochleibung wird anhand des Bettungsmoduls ausgedrückt. Zur Beurteilung der bei zyklischer Schwellbelastung auftretenden Sekantensteifigkeit wurde ein Standardprüfverfahren zur Bestimmung des Bettungsmoduls bei statischer Belastung modifiziert. Es wurde gezeigt, dass die stationäre Sekantensteifigkeit signifikant höher ist als die statische Steifigkeit bei Anfangsbelastung und dass bei einer ausreichend kleinen Amplitude der zyklischen Belastungskomponente ein einfaches analytisches elastisches Modell zur Bestimmung des Bettungsmoduls gut geeignet ist. Das analytische Modell basiert auf einer komplexen Spannungsfunktion des Holzes im Bereich der Lochleibung sowie der Reibung zwischen Dübel und Holz. Der so berechnete Bettungsmodul kann bei den Schwingungsberechnungen in Tragwerken mit modellierten nachgiebigen Verbindungen zur Bestimmung der Steifigkeit dieser Verbindungen verwendet werden. Obwohl das Modell nur für eine Schwellbelastung gilt, deckt diese doch verschiedene wichtige Schwingungsbeanspruchungen in Bauwerken ab, wie zum Beispiel Wind- oder Trittbeanspruchung.

Viscoelastic embedment behaviour of dowels and screws in timber under in-service vibration

Dowel and screw connections in timber structures behave nonlinearly, even at loads which would be experienced in a structure in normal service. They exhibit hysteresis and creep as a result of both the viscoelastic behaviour of the timber itself and the frictional interaction between the timber and connecting elements, and stress concentrations are created which behave plastically, even at loads well below the nominal yield force of the connection. A fundamental process in the load transfer through such a connection is the embedment of the connector into the timber that surrounds it, and the frictional, nonlinear and time-dependent properties in that process are investigated here. A simple rheological model, a combination of Kelvin–Voigt viscoelastic elements, was fitted to the measured response of a block of timber in embedment by a plain dowel or screw. Experiments were performed in which an oscillating force was applied to the screw or dowel, representative of in-service vibration in a timber structure. The effects of plasticity and viscoelasticity were quantified by comparing equivalent linear stiffnesses for an oscillating load, a short-term change in static load, and an initial static loading. The results showed a stiffness, on average, 3.8 times higher under oscillating load than under initial static loading with the same peak force. By quantifying and modelling viscoelastic behaviour in timber around a connector, this work contributes to the development of damping and stiffness models for joints under oscillating load. Such models could be used to determine the contribution of connections to the dynamic response of long spans and tall buildings in timber.ZusammenfassungDübel- und Schraubverbindungen in Holzkonstruktionen weisen auch bei Belastungen, welche unter normalen Praxisbedingungen auftreten, ein nichtlineares Verhalten auf. Aufgrund des viskoelastischen Verhaltens von Holz als auch der Reibung zwischen dem Holz und dem Verbindungsmittel kommt es zu Hysterese und Kriechen, und es treten Spannungskonzentrationen auf, welche sich sogar bei Belastungen weit unter der nominalen Fließgrenze der Verbindung plastisch verhalten. Ein wesentliches Element der Kraftübertragung in solch einer Verbindung ist die Bettung des Verbindungsmittels im umliegenden Holz, und die reibungsbedingten, nichtlinearen und zeitabhängigen Eigenschaften in diesem Prozess werden hier untersucht. Ein einfaches rheologisches Modell, eine Kombination viskoelastischer Kelvin–Voigt Elemente, wurde an Lochleibungsversuche mit einem Bolzen oder einer Schraube angepasst. Es wurden Versuche durchgeführt, bei denen eine für Holzkonstruktionen unter Praxisbedingungen typische Schwellbelastung auf die Schraube oder den Bolzen aufgebracht wurde. Bestimmt wurde der Einfluss der Plastizität und der Viskoelastizität mittels Vergleich entsprechender Steifigkeiten bei Schwellbelastung, bei kurzzeitig wirkender Last und bei länger wirkender statischer Belastung. Die Ergebnisse zeigten, dass bei gleicher Spitzenbeanspruchung die Steifigkeit unter Schwellbelastung durchschnittlich 3,8 Mal höher war als unter länger wirkender statischer Belastung. Durch Bestimmung und Modellierung des viskoelastischen Verhaltens von Holz im Bereich eines Verbindungsmittels trägt diese Arbeit zur Entwicklung eines Dämpfungs- und Steifigkeitsmodells für Verbindungen bei dynamischer Beanspruchung bei. Solche Modelle könnten dazu dienen, um die Wirkung von Verbindungen auf das dynamische Verhalten hoher Holzgebäude und von Gebäuden mit großen Spannweiten zu bestimmen.

Shaking Table Test of the Taiwanese Traditional Dieh-Dou Timber Frame

ABSTRACT This article attempts to explore the dynamic behavior of traditional Dieh-Dou timber structure under different combinations of structural forms and vertical loads. Using time-history record (TCU 084) from the Chi-Chi earthquake, two semi full-scale specimens (Symmetric and Asymmetric) were tested. Results showed that the Symmetric specimen tends to be damaged more easily and faster than the Asymmetric one. Damage pattern generally begins from the bottom Dou members and subsequently spreading upwards to the upper Dou, horizontal Gong members, and adjoining Shu members. Friction force between the contact surfaces is crucial towards the maintenance of overall structure. Increase vertical loadings have significant effect on the natural frequencies and global stiffness of the structure. Using the Single-Degree-Of-Freedom (SDOF) system, the derived stiffness is generally in good agreement with the dynamic results of both forms. This study suggests that the effects of increasing vertical loadings should be taken into consideration for future evaluation.

Dynamic characteristics of Taiwanese traditional Dieh-Dou timber structures

This study attempts to explore the structural behaviour of traditional Dieh-Dou timber structure under different combinations of bracket structural forms and roof dead loads. The parameters used include two different structural forms (symmetric and asymmetric) and three different levels of roof weight (1.7, 2.6 and 3.5 tons) which represent the span distance between two parallel frames at 3, 4.5 and 6 meters. Two different semi full-scale specimens, made of China Fir (Cunninghamia lanceolata), were mounted and tested on the shaking table of National Centre for Research on Earthquake Engineering (NCREE) in Taipei. Time-history record (TCU 084) from the 1999 Chi-Chi earthquake in Taiwan was used to test at a level of 20, 42, 60, 80 and 100%. System identifications were carried out between every test to monitor the integrity of the structures. Results showed that increase vertical loadings will have significant effect on the natural frequencies and global structural stiffness of the specimens. Next, the experimental results were mapped with the theoretical model for initial stiffness prediction, whereby the entire structural frame was assumed to be a lump mass system with Single-Degree-Of-Freedom (SDOF). The predicted stiffness model is generally in good agreement with the dynamic results of both structural forms. This study suggests that the effects of increasing vertical loadings should be taken into consideration during future evaluation process. Although using SDOF system to estimate the initial stiffness seems highly probable, more work still

On mechanical behavior of traditional timber shear wall in Taiwan II: Simplified calculation and experimental verification

In the previous report of this ongoing study, results of an extensive field survey were collated and a theoretical model was proposed to predict the mechanical behavior of timber shear walls of traditional design in Taiwan. The initial objective of the present report was to propose a simplified calculation method for estimating the initial stiffness and yield strength of traditional timber shear walls. Based on the results of the field survey, a total of 15 full-scale specimens were tested to verify the theoretical model and simplified calculation proposed previously. Good agreement was found from comparison of analytical and experimental results. The results of this study show that the friction behavior between board units and beams plays the major role in resisting the lateral force applied on the timber shear wall, followed by the resistance supplied by embedment. The resistance provided by bamboo nails is minor due to the small section. Another trend found was that for set dimensions of a timber shear wall, the board width can be increased to obtain higher stiffness and strength of the shear wall.

Lateral-load resistance of cross-laminated timber shear walls

Cross-laminated timber shear wall systems are used as a lateral load resisting system in multistory timber buildings. Walls at each level typically bear directly on the floor panels below and are connected by nailed steel brackets. Design guidance for the lateral-load resistance of such systems is not well established and design approaches vary among practitioners. Two cross-laminated two-story timber shear wall systems are tested under vertical and lateral load, along with pullout tests on individual steel connectors. Comprehensive kinematic behavior is obtained from a combination of discrete transducers and continuous field displacements along the base of the walls, obtained by digital image correlation, giving a measure of the length of wall in contact with the floor below. Existing design approaches are evaluated. A new offset-yield criterion based on acceptable permanent deformations is proposed. A lower bound plastic distribution of stresses, reflecting yielding of all connectors in tension and cross-grain crushing of the floor panel, is found to most accurately reflect the observed behavior.