Andi Asiz

Connection System of Massive Timber Elements Used in Horizontal Slabs of Hybrid Tall Buildings

This paper discusses connections between Cross-Laminated-Timber (CLT) floor slabs and steel framework of hybrid tall buildings. Using the example of a 24-story building analysis, it is shown that such connections can be made using simple fasteners like large screws to enforce efficient diaphragm action in the critical case of CLT slabs subjected to lateral seismic or wind events. Results of laboratory tests on connections between CLT slabs and structural steel members are presented to prove this.

Failure mechanisms in wood-based materials: A review of discrete, continuum, and hybrid finite-element representations

Abstract Challenges arise in finite element (FE) analyses that predict mechanical failure in wood-based materials because their structural complexity is difficult to mimic. When considered at the macro scale, wood and engineered wood composites can reasonably be assumed to behave as homogenous continua. However, accurate meso- and micro-scale representations require a different approach. Models employing discrete FEs are robust tools for detailed failure analysis, because the elements can be made to mimic the functions of morphological structures in the material. Hybrid models that meld continuum and discrete FEs also show good promise as generalised analysis tools, but as yet their development is in its infancy. In the future, beyond mechanical damage, other energy sinks also need to be included in models, and computational efficiency should be improved. In this overview, the advantages and limitations of alternative FE representations are demonstrated in terms of failure processes in wood-based materials via case analyses.

Demands placed on steel frameworks of tall buildings having reinforced concrete or massive wood horizontal slabs.

This paper presents the relative demands that alternative floor and roof slab constructions place on the steel frameworks of relatively tall composite construction buildings. Slab types examined were standard steel and reinforced concrete (SRC) composite plates and prefabricated massive wood plates constructed from cross-laminated timber (X-Lam). Case studies for six-storey and 24-storey buildings addressed how the stresses and deflections of the steel framing members are influenced by the choice of slab type for load combinations associated with gravity forces, and lateral forces generated as a result of wind or seismic actions. It is shown that using X-Lam slabs places much lower stress demands on steel frameworks because the self-weight of the slabs is only about one-third of the weight of mechanically equivalent SRC slabs. Maximum lateral drifts for buildings with X-Lam slabs under earthquake and wind loads are predicted to be in the order of half to two-thirds of those for similar buildings with SRC slabs, with the greatest reductions being for the 24-storey building. Therefore, use of X-Lam slabs opens up the possibility of either reducing the amount of steel in tall buildings or improving the performances of systems without increasing the steel content. As constructability and fire performance are key issues for large buildings, how to make construction joints that permit rapid assembly of systems is discussed and fire protection strategies are outlined.

Analysis of aging of piezoelectric crystal resonators

Aging of piezoelectric (quartz crystal) resonator has been identified as one of the most important quality control problems of quartz crystal products. Aging is defined as frequency change with time. Aging in quartz resonators can be due to several sources: mass transfer due to contamination inside the resonator enclosure, stress-strain in the resonator blank, quartz defect, etc. In this study, the stress-strain effect, which has been believed as a dominant factor contributing to aging, is studied. The stress-strain effect is caused mainly by the long-term viscoelastic properties of bonding adhesive that attach quartz crystal plate to the ceramic base package. With the available accelerating testing method under elevated temperatures, the stress-strain induced aging in the quartz crystal resonators can be investigated. Because of the miniaturized size of the resonator, a digital image analysis method called image intensity matching technique (IIMT) is applied to obtain deformation patterns in the quartz blank due to thermal load. Our preliminary results showed that the unsymmetric thermal deformations may be a dominant contributing factor to aging. For simulation purposes, finite-element analysis is used to investigate the deformation patterns (i.e., stress-strain distributions) and corresponding natural frequency shift in the piezoelectric resonators. The viscoelastic behavior of mounting adhesives is incorporated into the analysis to show the dominant effect of long-term behavior of stress-strain developed in the crystal resonators. Also, some geometrical aspects-such as uneven mounting supports due to distances, volumes and heights of the adhesives-are simulated in the model.

Experimental study and theoretical prediction of aging induced frequency shift of crystal resonators and oscillators

Abstract Frequency shift, due to quartz crystal resonator aging, has been identified as one of the most important quality control problems of quartz crystal products. The problem becomes more significant due to the device miniaturization and high precision standards for telecommunication applications. Since aging induced frequency shift occurs during a long time frame, it is necessary to predict the long-term behavior of the devices based on the short-term data obtained under an accelerated environment. One the other hand, frequency shift is associated with quite large random variation, and thus, a proper probabilistic theory should be used for analyzing test data and for developing a reliable prediction model. Accelerated testing was performed for various types of crystal resonators under elevated temperatures. The frequency shifts of the devices were measured at different testing periods. Markov chain model was used to characterize the frequency shift of the devices. The obtained short-term test results were used for calibrating the probabilistic transition matrix of Markov chain model. The model can then be used for predicting the long-term frequency shift. The time–temperature superposition principle in viscoelasticity was adopted to address the shift in time under different temperatures.

Effectiveness of Distributed Mass Damper Systems for Lightweight Superstructures

AbstractDistributed mass damper (DMD) systems are discussed as a method of suppressing lateral motions of superstructures during wind storms and earthquakes. Potentially, DMD systems are a technology that is economical enough for widespread application to buildings or other structures. Focus is placed on lightweight superstructures as a reflection of the trend toward the use of ultra-lightweight floor slabs in high-rise buildings. Results of model-scale experiments are presented that show that tuned mass damper (TMD) systems that add between 1.3 and 2% to the total superstructure gravitational mass are effective methods of increasing damping in superstructures and reducing peak lateral accelerations during forced vibration events. In those experiments, tuned sloshing dampers (TSDs) were employed in conjunction with floor and roof plates that simulated ultra-lightweight slabs constructed from cross-laminated timber (CLT), which is a new material option in North America. The use of TSDs was a surrogate for ...

Control of Building Sway and Force Flows Using Ultralightweight Slabs

AbstractDesign analyses are presented to demonstrate the technical advantages of substituting ultralightweight slab materials like cross-laminated-timber (CLT) for reinforced concrete (RC) floors and roofs of low-rise and high-rise hybrid building superstructures. Such substitution reduces the gravitational masses of slab by at least two-thirds without reducing functionality as bending or diaphragm slabs. Specific illustrations of design impacts of using CLT are given for hybrid building superstructures where steel or RC frameworks are the primary means of resisting effects of gravity forces associated with occupied built spaces. Results shown apply to two-story buildings in which effects of lateral forces associated with wind or seismic loads are resisted entirely by a steel moment framework, and six- and twenty four–story buildings in which RC shear walls within building cores primarily resist effects of such lateral loads. Consideration is also given to how fire engineering design decisions can impact ...

Experimental study and prediction of frequency shift of piezoelectric ceramic packages

Frequency shift, due to quartz crystal resonator aging, has been identified as one of the most important quality control problems of quartz crystal products. The problem becomes more significant due to the device miniaturization and high precision standards for telecommunication applications. Since aging induced frequency shift occurs during a long time frame, it is necessary to predict the long-term behavior of the devices based on the short-term data obtained under an accelerated environment. On the other hand, frequency shift is associated with quite large random variation, and thus, a proper probabilistic theory should be used for analyzing test data and for developing a reliable prediction model. Accelerated testing was performed for various types of crystal resonators under elevated temperatures. The frequency shifts of the devices were measured at different testing periods. Markov chain model was used to characterize the frequency shift of the devices. The obtained short-term test results were used for calibrating the probabilistic transition matrix of Markov chain model. The model can then be used for predicting the long-term frequency shift. The time-temperature superposition principle in viscoelasticity was adopted to address the shift in time under different temperatures.

Failure Analysis of Engineering Wood Products

This paper synthesizes information in the literature and results of studies at the University of New Brunswick (UNB) to provide guidance on failure analysis of engineering wood products (EWP). EWP are either solid materials like lumber and glued-laminated-timber, or composites manufactured by hot-pressing veneers, wafers or strands of wood that were pre-coated with synthetic adhesives. Important issues include size of specimen effects on apparent strength and how to handle situations where stress concentrations arise. Consideration is given to both bodies that are nominally undamaged and those that are pre-damaged (cracked) at the time of loading. This elucidates the extent to which one might validly apply common continuum failure theories. Limitations of continuum theories, whether or not they assume existence of a crack(s), are that they can not always reliably predict the load level at which damage initiates, nor the location of failures. Also, most theories cannot predict how failures propagate once initiated. This reflects limitations in theoretical postulates when applied to EWP (Smith et al 2003). Even when they have a physically correct basis fracture mechanics models still depend on an analyst’s ability to correctly locate cracks. An advanced ‘bridging fiber’ model has been developed to include closing forces to crack surfaces in a zone behind the crack tip (Smith and Vasic 2003). The closing forces replicate the effect of partially peeled wood cells that toughen any naturally formed crack. This means that the bridging crack model is capable of capturing a transition from an artificial crack to a ‘natural’ crack condition, meaning that it can be used to model crack propagation processes. Other fracture models cannot represent the artificial to natural crack transition so are unsuitable for predicting crack growth. Ability to predict crack growth equals ability to predict collapse loads for initially stable systems.