Alex Sixie Cao

Last Name

Cao

First Name

Alex Sixie

ORCID

0000-0002-8455-5892

Organisational unit

08809 - Frangi, Andrea (Tit.-Prof.)

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Publications 1 - 10 of 30

Lateral stiffening systems for tall timber buildings – tube-in-tube systems
Binck, Charles; Cao, Alex Sixie; Frangi, Andrea (2022)
Wood Material Science & Engineering
In this paper, an adaptable and architecturally flexible lateral stiffening system for tall timber buildings between 50 and 147 m is developed and investigated. The system is based on a tube-in-tube concept. The internal tube consists of a braced timber core, and the external tube consists of a frame structure with semi-rigid beam-column joints in the facade. Based on a finite element framework, more than 500 000 simulations with different configurations are carried out to assess the performance of the lateral stiffening system subjected to wind loading. The resulting data is used to assess the feasibility of the tube-in-tube system and stiffness requirements for the beam-column joints.
Pendulum impact hammer tests on glued laminated timber beams
Cao, Alex Sixie; Houen, Magnus Trabolt; Lolli, Marco; et al. (2022)
Report / Institute of Structural Engineering ETH Zurich
Self-camber of timber beams by swelling hardwood inlays for timber–concrete composite elements
Müller, Katharina; Grönquist, Philippe; Cao, Alex Sixie; et al. (2021)
Construction and Building Materials
Timber–concrete composites (TCC) are smart solutions for slabs in residential and office buildings regarding the sustainable and performance-optimized use of materials. However, a non-negligible disadvantage is the deflection of the timber elements caused by in-situ concrete casting during construction. This paper presents an approach to camber timber elements without external forces by using the innate swelling capacity of wood. Oven-dried hardwood inlays can be inserted transversally into cuts on the top side of a timber element. After an increase of the moisture content in the inlays, the swelling pressure will result in a self-camber of the timber element. In this study, a procedure for prediction of the self-camber is derived and the model is validated using an experimental test series. The results demonstrate that the self-camber of spruce elements using beech inlays is both feasible and predictable. On this basis, practical application scenarios for TCC elements in timber engineering are shown and discussed.
The influence of damping on progressive collapse analysis
Cao, Alex Sixie; Frangi, Andrea (2023)
COMPDYN Proceedings ~ COMPDYN 2023: 9th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering. Proceedings Volume II
The most common method of modeling damping in structures is with equivalent viscous damping with the Rayleigh damping model. However, it is well-known that the Rayleigh damping model may cause spurious damping forces and nonphysical behavior for inelastic structures. Remedies have been proposed to overcome these problems, such as various incremental versions using the tangent stiffness or the use of modal damping instead. These may be appropriate for inelastic structures with negligible changes of the vibration modes, and without softening behavior for the Rayleigh damping models. In progressive collapse analyses, these damping models may be inappropriate because of the radical change in vibration modes, as well as the changes to the mass and stiffness matrix. In this paper, initial and incremental versions of the Rayleigh and modal damping models are presented and compared for a structure undergoing progressive collapse. The damping model is not critical if the objective is to assess the response until the first failure. However, the choice of the damping model may lead to large dissimilarities after the first failure in a progressive collapse analysis.
Modelling progressive collapse of timber buildings
Cao, Alex Sixie; Esser, Lukas; Frangi, Andrea (2024)
Structures
An efficient and accurate numerical model is indispensable for assessing structural robustness and progressive collapses. This paper presents a parametric numerical framework for the modelling of progressive collapses of inelastic timber buildings subjected to the loss of arbitrary members using dynamic analysis with large deformations and an incremental damping scheme. The model can simulate true separation and removal of elements, as well as debris tracking and impact loading derived from classical mechanics. The framework is demonstrated on a moment-resisting timber frame building with linear-elastic members and inelastic beam–column connections with hysteresis subjected to ground-floor column-loss scenarios. It can be used for large-scale analyses to assess the structural robustness of a wide range of building types, materials, and damage scenarios.
Theoretical studies of tall timber buildings subjected to service-level wind loads
Cao, Alex Sixie; Stamatopoulos, Haris (2021)
World Conference on Timber Engineering (WCTE 2021)
Wind-induced vibrations is one of the main design considerations for tall timber buildings due to their flexibility and lightweight nature. Some approaches to solve this problem are the addition of extensive bracing elements, the introduction of semi-rigid connections or the addition of extra mass. In this paper, the response of planar moment-resisting skeleton frames and braced frames with diagonal elements is calculated, and a comparison of peak accelerations between the gust factor approach and a dynamic time-history approach is performed.
Influence of attacker's prior knowledge on the performance of redundant systems
Iannacone, Leandro; Cao, Alex Sixie (2025)
14th International Conference on Structural Safety and Reliability - ICOSSAR'25
The main objectives of civil engineering structures are to provide functional spaces for societal activities and shelter from the environment. To ensure the safety of such structures, design standards employ methods derived from structural reliability to achieve a target safety level throughout the operational life of structures for expected loading. However, disruptions may occur to a system that involve the initial damage to one or more components. To manage the consequences of system disruptions, robustness strategies can be used to enhance the robustness of a system. Previous research has shown that targeted risk-reducing measures are the most efficient. Therefore, knowledge on the system disruptions is crucial for informing decision-making on appropriate counter-measures. In this paper, initial damage scenarios to redundant systems with a mix of brittle and ductile components are investigated and the effect of prior knowledge of an attacker are quantified using probabilistic and combinatorial analysis. The results are presented in β–π diagrams, which compare the reliability and robustness of systems in a visual medium. The results show that for the same component reliabilities, brittle systems are less robust than ductile systems. In mixed systems, the initial damage that leads to the lowest robustness is not always the loss of only ductile components, but often a combination of damage to ductile and brittle components. In a deliberate attack on a system, there is a large reduction in the robustness and reliability, depending on the prior knowledge of the attacker and the severity of the attack. This analysis shows the importance of considering the prior knowledge of an attacker on the system performance, and facilitates the development of targeted counter-measures and design strategies.
Mixed Element Method for Progressive Collapse Analysis: Method Description and Verification
Cao, Alex Sixie; Frangi, Andrea (2023)
Lecture Notes in Civil Engineering ~ Proceedings of the 2022 Eurasian OpenSees Days
The finite element method is the most widely used numerical method for progressive collapse analysis and analysis of structures subjected to extreme loading. However, it is computationally expensive for problems where discontinuities occur. In progressive collapse analysis, an example of a discontinuity is when two or more elements separate because of failure. Variations of the finite element method, such as the extended finite element method and other numerical methods, can model such discontinuities but become computationally expensive. For large-scale analyses of progressive collapse, the method must be computationally efficient and be able to model relevant discontinuities. In this paper, a discrete method called the mixed element method is presented and compared with the finite element method in a case study. Results from the case study demonstrate small deviations between the two methods in modal analyses and different static and transient loading situations. The mixed element method uses elements that are available in common finite element software and can therefore be implemented in any finite element software.
A unified constitutive model for pressure sensitive shear flow transitions in moderate dense granular materials
Cheng, Xiaohui; Xiao, Shize; Cao, Alex Sixie; et al. (2021)
Scientific Reports
Granular shear flows exhibit complex transitional regimes that are dramatically affected by the pressure level and shear stress state. New advances in granular shear tests at low pressure have enlightened the understanding of the two granular shear flow transitions: between quasi-static and moderate shear flows, and between steady-state and transient shear flows. However, a unified constitutive model to describe these two transitions is yet to develop. In this work, a simplified and unified model is proposed based on innovative triaxial shear flow tests, using two dimensionless physical variables. Model results validated against experimental data suggest that the shear flow transition between a quasi-static to a moderate Isotach type flow state is highly pressure-dependent. At extremely low pressure, the granular viscosity becomes the primary mechanism, suppressing the quasi-static mechanism even under “quasi-static” shear rates. In transient to steady state granular flow transitions, a mobilized shear stress ratio or mobilized friction coefficient between zero and the critical state ratio for consolidated granular packings is taken into consideration. This is coupled with the mechanism of granular viscosity. These findings have not been discussed before and are of great relevance to granular mechanics as well as space and earthquake engineering.
Pendulum Impact Hammer Tests on Spruce Glued Laminated Timber – Preliminary Results
Cao, Alex Sixie; Lolli, Marco; Frangi, Andrea (2022)
Civil-Comp Conferences ~ Proceedings of the Fourteenth International Conference on Computational Structures Technology
In this paper, preliminary results are presented on pendulum impact hammer tests on full-scale glued laminated timber specimens with dimensions 200x200x3600 mm for the first time. For the tests, a pendulum with an effective mass of 3500 kg and length 4700 mm was built. The pendulum was instrumented with a high-speed camera, angular encoder, optical position-tracking system, and accelerometers. By considering potential energies and the damping in the system, the material toughness was determined to be between 327 and 534 kJ/m2. The maximum impact forces were determined from the deceleration of the pendulum during impact and were between 3565 and 4106 kN. The failure time was determined qualitatively from high-speed imagery to be between 10.18 and 11.58 ms. The dissipated energy is roughly equivalent to the kinetic energy of a 500 kg projectile traveling at 30 km/h.

Publications 1 - 10 of 30

Alex Sixie Cao

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