31 research outputs found
Device-independent entanglement quantification and related applications
We present a general method to quantify both bipartite and multipartite
entanglement in a device-independent manner, meaning that we put a lower bound
on the amount of entanglement present in a system based on observed data only
but independently of any quantum description of the employed devices. Some of
the bounds we obtain, such as for the Clauser-Horne-Shimony-Holt Bell
inequality or the Svetlichny inequality, are shown to be tight. Besides,
device-independent entanglement quantification can serve as a basis for
numerous tasks. We show in particular that our method provides a rigorous way
to construct dimension witnesses, gives new insights into the question whether
bound entangled states can violate a Bell inequality, and can be used to
construct device independent entanglement witnesses involving an arbitrary
number of parties.Comment: 4 pages + appendix, resubmitted versio
SEISMIC DESIGN OF CROSS-LAMINATED TIMBER BUILDINGS
The increasing interest in cross-laminated timber (CLT) construction has resulted in multiple international research projects and publications covering the manufacturing and performance of CLT. Multiple regions and countries have adopted provisions for CLT into their engineering design standards and building regulations. Designing and building CLT structures, also in earthquake-prone regions is no longer a domain for early adopters, but is becoming a part of regular timber engineering practice. The increasing interest in CLT construction has resulted in multiple regions and countries adopting provisions for CLT into their engineering design standards. However, given the economic and legal differences between each region, some fundamental issues are treated differently, particularly with respect to seismic design. This article reflects the state-of-the-art on seismic design of CLT buildings including both, the global perspective and regional differences comparing the seismic design practice in Europe, Canada, the United States, New Zealand, Japan, China, and Chile
Longitudinal bar buckling behavior
Reinforced concrete columns might fail because of buckling of the longitudinal reinforcing bar when exposed to earthquake motions. Depending on the hoop stiffness and the length-over-diameter ratio, the instability can be local (in between two subsequent hoops) or global (the buckling length comprises several hoop spacings).
To get insight into the topic, an extensive literary research of 19 existing models has been carried out including different approaches and assumptions which yield different results. Finite element fiberanalysis was carried out to study the local buckling behavior with varying length-over-diameter and initial imperfection-over-diameter ratios. The comparison of the analytical results with some experimental results shows good agreement before the post buckling behavior undergoes large deformation. Furthermore, different global buckling analysis cases were run considering the influence of different parameters; for certain hoop stiffnesses and length-over-diameter ratios local buckling was encountered. A parametric study yields an adimensional critical stress in function of a stiffness ratio characterized by the reinforcement configuration.
Colonne in cemento armato possono collassare per via dellâinstabilitĂ dellâarmatura longitudinale se sottoposte allâazione di un sisma. In funzione della rigidezza dei ferri trasversali e del rapporto lunghezza dâinflessione-diametro, lâinstabilitĂ puĂČ essere locale (fra due staffe adiacenti) o globale (la lunghezza dâinstabilitĂ comprende alcune staffe).
Per introdurre alla materia, Ăš proposta unâesauriente ricerca bibliografica di 19 modelli esistenti che include approcci e ipotesi differenti che portano a risultati distinti. Tramite unâanalisi a fibre e elementi finiti si Ăš studiata lâinstabilitĂ locale con vari rapporti lunghezza dâinflessione-diametro e imperfezione iniziale-diametro. Il confronto dei risultati analitici con quelli sperimentali mostra una buona coincidenza fino al raggiungimento di grandi spostamenti. Inoltre, il caso dâinstabilitĂ globale Ăš stato simulato valutando lâinfluenza di vari parametri; per certe configurazioni di rigidezza delle staffe e lunghezza dâinflessione-diametro si hanno ottenuto casi di instabilitĂ locale. Uno studio parametrico ha permesso di ottenere un carico critico adimensionale in funzione del rapporto di rigidezza dato dalle caratteristiche dellâarmatura
Floor diaphragms in multi-storey timber buildings
This thesis studies the behaviour of diaphragms in multi-storey timber buildings by providing
methods for the estimation of the diaphragm force demand, developing an Equivalent Truss
Method for the analysis of timber diaphragms, and experimentally investigating the effects of
displacement incompatibilities between the diaphragm and the lateral load resisting system
and developing methods for their mitigation.
The need to better understand the behaviour of diaphragms in timber buildings was
highlighted by the recent 2010-2011 Canterbury Earthquake series, where a number of
diaphragms in traditional concrete buildings performed poorly, compromising the lateral load
resistance of the structure. Although shortcomings in the estimation of force demand, and in
the analysis and design of concrete floor diaphragms have already been partially addressed by
other researchers, the behaviour of diaphragms in modern multi-storey timber buildings in
general, and in low damage Pres-Lam buildings (consisting of post-tensioned timber members)
in particular is still unknown. The recent demand of mid-rise commercial timber buildings of
ten storeys and beyond has further highlighted the lack of appropriate methods to analyse
timber diaphragms with irregular floor geometries and large spans made of both light timber
framing and massive timber panels.
Due to the lower stiffness of timber lateral load resisting systems, compared with traditional
construction materials, and the addition of in-plane flexible diaphragms, the effect of higher
modes on the global dynamic behaviour of a structure becomes more critical. The results from
a parametric non-linear time-history analysis on a series of timber frame and wall structures
showed increased storey shear and moment demands even for four storey structures when
compared to simplistic equivalent static analysis. This effect could successfully be predicted
with methods available in literature. The presence of diaphragm flexibility increased
diaphragm inter-storey drifts and the peak diaphragm demand in stiff wall structures, but had
less influence on the storey shears and moments. Diaphragm force demands proved to be
significantly higher than the forces derived from equivalent static analysis, leading to
potentially unsafe designs. It is suggested to design all diaphragms for the same peak demand;
a simplified approach to estimate these diaphragm forces is proposed for both frame and wall
structures.
Modern architecture often requires complex floor geometries with long spans leading to stress
concentrations, high force demands and potentially large deformations in the diaphragms.
There is a lack of guidance and regulation regarding the analysis and design of timber
diaphragms and a practical alternative to the simplistic equivalent deep beam analysis or costly
finite element modelling is required. An Equivalent Truss Method for the analysis of both light
timber framed and massive timber diaphragms is proposed, based on analytical formulations
and verified against finite element models. With this method the panel unit shear forces (shear
flow) and therefore the fastener demand, chord forces and reaction forces can be evaluated.
Because the panel stiffness and fastener stiffness are accounted for, diaphragm deflection,
torsional effects and transfer forces can also be assessed. The proposed analysis method is
intuitive and can be used with basic analysis software. If required, it can easily be adapted for
the use with diaphragms working in the non-linear range.
Damage to floor diaphragms resulting from displacement incompatibilities due to frame
elongation or out-of plane deformation of walls can compromise the transfer of inertial forces to the lateral load resisting system as well as the stability of other structural elements. Two
post-tensioned timber frame structures under quasi-static cyclic and dynamic load,
respectively, were tested with different diaphragm panel layouts and connections investigating
their ability to accommodate frame elongations. Additionally, a post-tensioned timber wall
was loaded under horizontal cyclic loads through two pairs of collector beams. Several
different connection details between the wall and the beams were tested, and no damage to
the collector beams or connections was observed in any of the tests. To evaluate the increased
strength and stiffness due to the wall-beam interaction an analytical procedure is presented.
Finally, a timber staircase core was tested under bi-directional loading. Different connection
details were used to study the effect of displacement incompatibilities between the
orthogonal collector beams. These experiments showed that floor damage due to
displacement incompatibilities can be prevented, even with high levels of lateral drift, by the
flexibility of well-designed connections and the flexibility of the timber elements.
It can be concluded that the flexibility of timber members and the flexibility of their
connections play a major role in the behaviour of timber buildings in general and of
diaphragms specifically under seismic loads. The increased flexibility enhances higher mode
effects and alters the diaphragm force demand. Simple methods are provided to account for
this effect on the storey shear, moment and drift demands as well as the diaphragm force
demands. The analysis of light timber framing and massive timber diaphragms can be
successfully analysed with an Equivalent Truss Method, which is calibrated by accounting for
the panel shear and fastener stiffnesses. Finally, displacement incompatibilities in frame and
wall structures can be accommodated by the flexibilities of the diaphragm panels and relative
connections. A design recommendations chapter summarizes all findings and allows a designer
to estimate diaphragm forces, to analyse the force path in timber diaphragms and to detail the
connections to allow for displacement incompatibilities in multi-storey timber buildings
Lateral performance of a Pres-Lam frame designed for gravity loads
This paper analyses the lateral load performance of a post-tensioned timber (Pres-Lam) frame which was designed with the primary function of supporting gravity loading. A full scale, two bay frame was used and subjected to quasi-static horizontal displacement. A total of four tests were performed, one with only the post-tensioning cables to resist horizontal loading and three with the addition of sacrificial steel elements externally attached and acting as dissipative reinforcing. This external reinforcing increased the moment capacity of the frame connections and the ability of the frame to release energy through hysteretic damping. Following a description of the test setup the results show that although the primary functions of the post-tensioning is to reduce section height and increase bay length under gravity loading it will also provide a significant contribution to the lateral resistance of the structure. Finally, a simplified design procedure is presented which allows assessing the magnitude of this contribution
Seismic testing of post-tensioned Pres-Lam core walls using cross laminated timber
With the increasing demand for multi-storey timber buildings in areas with high wind loads and high seismic activity, stiff lateral load resisting systems are becoming a crucial design component. Post-tensioned Pres-Lam mass timber lift shafts and stairwell core walls not only provide a strong and very stiff lateral load resisting system, but also damage limiting response in the case of a large seismic event. This paper describes the results of experimental tests on Cross-Laminated Timber (CLT) Pres-Lam core walls tested under bi-directional quasi-static seismic loading. In the first configuration the CLT wall panels were connected in the corners with screws, while in the second configuration, steel pivotal columns were introduced at the corners and the CLT wall panels were connected to the steel columns with dissipative U-shaped Flexural Plates (UFPs). Overall the testing showed that the Pres-Lam system, when used for structural timber core walls subjected to bidirectional loading regimes, sustains nominal damage after large drift demands. By adding ductile screw-connections or steel columns with UFPs at the corners additional strength and dissipation capacity is obtained. Friction between the CLT panels improved the seismic performance of the structure, which in Serviceability Limit State (SLS) conditions led to rigid behaviour of the splices between the panels. Displacement incompatibilities between the floor diaphragm and the core walls were accommodated by locating the connections at the centre of the walls, or by pinned connections in the corner pivotal columns. Relative displacements between orthogonally running connector beams were accommodated by using flexible connections out-of-plane. Under low axial forces there was horizontal sliding of the walls at the foundation level, but this was not observed when larger post-tensioning forces were applied