Publications

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Conference Paper
Buru, Stefan Marius, Válter Lúcio, and Corneliu Cismasiu. "PROTEDES - Protection of Strategic Buildings Against Blast - Final Report." PROTEDES2022. Região Sul da Ordem dos Engenheiros, Lisboa 2022.
Campian, C., M. Pop, C. Cismasiu, T. Josza, and A. Popa. "Seismic retrofitting of an existing steel structure." 17th International Multidisciplinary Scientific GeoConference SGEM 2017. Albena; Bulgaria 2017.
Santos, F. P., and C. Cismasiu. "Shape memory alloys in structural vibration control." EVACES'07 - Experimental Vibration Analysis for Civil Engineering Structures. FEUP, Porto, Portugal 2007. Abstract

The unique superelastic behaviour exhibited by shape memory alloys (SMAs) allows the material to recover after withstanding large deformations. This recovery takes place without any residual strains, while dissipating a considerable amount of energy. This property makes the SMAs particularly suitable for applications in vibration control devices. Numerical models, calibrated with experimental laboratory tests, are used to investigate the dynamic response of vibration control devices. These devices are built up of austenitic superelastic wires. The energy dissipation and re-centring capabilities, important features of these devices, are clearly illustrated by the numerical tests. One of these devices is tested as a seismic passive vibration control system in a simplified numerical model of a railway viaduct.

Cismasiu, Corneliu, and Filipe Pimentel Amarante dos Santos. "Shape Memory Alloys in Structural Vibration Control. Research at UNIC/DEC/FCT/UNL." International Conference "Tradition and Innovation". 60 Years of Civil Engineering Higher Education in Transilvania. Cluj-Napoca, Romania: UTCN, 2013. c60.pdf
Rebelo, Hugo, Gabriel Gomes, and Corneliu Cismasiu. "Simulação Numérica do Efeito de Explosivos em Painéis de Betão Armado Reforçados com Argamassas Armadas." BE2016. FCTUC 2016.
Cismasiu, C., and Amarante F. P. dos Santos. "Towards a semi-active vibration control solution based on superelastic shape memory alloys." 15th WCEE. Lisbon, Portugal 2012. 2012_wcee_0379.pdf
Conference Proceedings
Santos, F., C. Cismasiu, R. Perdigão, V. Bernardo, J. Sampayo, P. Candeias, A. Costa, A. Carvalho, and L. Guerreiro COMPORTAMENTO SÍSMICO DE LIGAÇÕES EM PASSADIÇOS PRÉ-FABRICADOS. 10º Congresso Nacional de Sismologia e Engenharia Sísmica. Ponta Delgada, 2016.artigosismica2016_submetido.docx
Bernardo, Vasco, André Oliveira, Filipe Amarante dos Santos, and Corneliu Cismasiu Vulnerabilidade e reforço sísmico de uma passagem superior pedonal pré-fabricada. 5as Jornadas Portuguesas de Engenharia de Estruturas. Lisboa, 2014.artigo_jpee2014.pdf
Journal Article
Freitas, J. A. T., and C. Cismaşiu. "Adaptive p-refinement of hybrid-{T}refftz finite element solutions." Finite Elements in Analysis and Design. 39 (2003): 1095-1121. Abstract

An adaptive p-refinement procedure for the implementation of the displacement model of the hybrid-{T}refftz finite element formulation is presented. The procedure is designed to select and implement automatically the degrees of freedom in the domain (displacements) and on the boundary (surface forces) of the element to attain a prescribed level of accuracy. This accuracy is measured on the strain energy of the system for a prescribed finite element mesh. Local measures of error can be easily accounted for. The performance of the adaptive procedure suggested is illustrated using two-dimensional potential problems.

Amarante dos Santos, Filipe, and Corneliu Cismaşiu. "Adaptive underslung beam using shape-memory alloys for frequency-tuning." Journal of Intelligent Material Systems and Structures (2016). AbstractWebsite

The present article addresses the study of an adaptive-passive beam structure with a shape-memory alloy based actuator. In order to mitigate adverse dynamic effects resulting from externally induced vibrations, the structure is able to automatically tune its natural frequency to avoid resonance. The adaptive-passive beam configuration is based on an underslung cable-stayed girder concept. Its frequency tuning is achieved by temperature modulation of the shape-memory alloy elements through a closed-loop control process based on a proportional-integral-derivative algorithm. The effectiveness of the proposed control solution is substantiated by numerical simulations and experimental tests on a small-scale prototype. The validated numerical model enables the simulation of the proposed control approach in a real-scale footbridge, subjected to a prescribed pedestrian loading. The results are very encouraging and show that, by activating the shape-memory alloy elements, the system is able to successfully shift its natural frequency and to mitigate the effects of induced vibrations.

Cismasiu, C., A. P. Ramos, I. D. Moldovan, D. F. Ferreira, and J. B. Filho. "Applied element method simulation of experimental failure modes in RC shear walls." Computers and Concrete. 19.4 (2017): 365-374.
G, Gomes, Lúcio V, Cismasiu C, and Rebelo H. B. "Blast Assessment - uma metodologia de avaliação." Construção Magazine.86 (2018): 18-23.
Freitas, J. A. T., C. Cismasiu, and Z. M. Wang. "Comparative analysis of hybrid-Trefftz stress and displacement elements." Archives of Computational Methods in Engineering. State of the art reviews. 6.1 (1999): 35-39.
dos Santos, Amarante F. P., and C. Cismasiu. "Comparison Between Two SMA Constitutive Models for Seismic Applications." Journal of Vibration and Control. 16 (2010): 897-914. AbstractWebsite

This paper analyses and compares the dynamic behavior of superelastic shape memory alloy (SMA) systems based on two different constitutive models. The first model, although being able to describe the response of the material to complex uniaxial loading histories, is temperature and rate independent. Thesecond model couples the mechanical and kinetic laws of the material with a balance equation considering the thermal effects. After numerical validation and calibration, the behavior of these two models is tested in single degree of freedom dynamic systems, with SMAs acting as restoring elements. Different dynamic loads are considered, including artificially generated seismic actions, in a numerical model of a railway viaduct. Finally, it is shown that, in spite of its simplicity, the temperature- and rate-independent modelproduces a set of very satisfying results. This, together with its robustness and straightforward computational implementation, yields a very appealing numerical tool to simulate superelastic passive control applications.

Amarante dos Santos, Filipe, Corneliu Cismasiu, and Francisco Braz Fernandes. "Cyclic Instability of Shape-Memory Alloys in Seismic Isolation Systems." International Journal of Structural Glass and Advanced Materials Research (2018): 1-14.
de Gomes, Gabriel Jesus, Valter José Guia da Lúcio, and Corneliu Cismasiu. "Development of a high-performance blast energy-absorbing system for building structures." International Journal of Protective Structures. 15.3 (2024): 484-508. AbstractWebsite

Shock absorbers have been widely used in the automotive and aeronautical industries for many years. Inspired on these devices, the paper presents an analytical and numerical assessment of a high performance protective system for building structures against blast loads, which is composed of a shielding element connected to the main structure, at the floor levels, through ductile Energy Absorbing Connectors (EACs). The EACs exploit the external tube inversion mechanism to absorb a significant part of the imparted kinetic energy from the blast wave. While the system prototype has been developed in laboratory, it was characterized and tested in a full-scale blast testing campaign. A validated finite element model was used next to analyze its performance in a more demanding design scenario. The introduction of EACs notably reduces the peak horizontal loads and the kinetic energy transferred to the protected structure, being expected a significant reduction of the stresses in the supporting vertical elements, in addition to the protection of structural and non-structural members. These results encourage further studies of the presented protective system that can be potentially employed for a large variety of blast threat scenarios, especially when increasing the stand-off is not a possible/viable option and sensitive facilities have to be protected.

Freitas, J. A. T., and C. Cismaşiu. "Developments with hybrid-{T}refftz stress and displacement elements." Computer Assisted Mechanics and Engineering Sciences. 8 (2001): 289-311. Abstract

The paper reports on the work on hybrid-{T}refftz finite elements developed by the Structural Analysis Research Group, ICIST, Technical University of Lisbon. A dynamic elastoplastic problem is used to describe the technique used to establish the alternative stress and displacement models of the hybrid-{T}refftz finite element formulations. They are derived using independent time, space and finite element bases, so that the resulting solving systems are symmetric, sparse, naturally $p$-adaptive and particularly well suited to parallel processing. The performance of the hybrid-{T}refftz stress and displacement models is illustrated with a number of representative static and dynamic applications of elastic and elastoplastic structural problems.

Santos, Filipe, Corneliu Cismasiu, Ildi Cismasiu, and Chiara Bedon. "Dynamic Characterisation and Finite Element Updating of a RC Stadium Grandstand." Buildings. 8.10 (2018): 141, 1-19.
Rebelo, H. B., D. Lecompte, C. Cismasiu, A. Jonet, B. Belkassem, and A. Maazoun. "Experimental and numerical investigation on 3D printed PLA sacrificial honeycomb cladding." International Journal of Impact Engineering. 131 (2019): 162-173.Website
Cismaşiu, C., A. Narciso, and F. Amarante dos Santos. "Experimental Dynamic Characterization and Finite Element Updating of a Footbridge Structure." Journal of Performance of Constructed Facilities.10.1061/(ASCE)CF.1943-5509.0000615 (2014).Website
de Gomes, Gabriel Jesus, Valter José Guia da Lúcio, Corneliu Cismasiu, and José Luis Mingote. "Experimental Validation and Numerical Analysis of a High-Performance Blast Energy-Absorbing System for Building Structures." Buildings. 13.601 (2023): 1-20.
Rebelo, Hugo Bento, Filipe Amarante dos Santos, Corneliu Cismasiu, and Duarte Santos. "Exploratory study on geodesic domes under blast loads." International Journal of Protective Structures (2019).
de Freitas, J., I. Moldovan, and C. Cismaşiu. "Hybrid-Trefftz displacement element for poroelastic media." Computational Mechanics (2011): 1-15. AbstractWebsite

The elastodynamic response of saturated poroelastic media is modelled approximating independently the solid and seepage displacements in the domain and the force and pressure components on the boundary of the element. The domain and boundary approximation bases are used to enforce on average the dynamic equilibrium and the displacement continuity conditions, respectively. The resulting solving system is Hermitian, except for the damping term, and its coefficients are defined by boundary integral expressions as a Trefftz basis is used to set up the domain approximation. This basis is taken from the solution set of the governing differential equation and models the free-field elastodynamic response of the medium. This option justifies the relatively high levels of performance that are illustrated with the time domain analysis of unbounded domains.

Freitas, J. A. T., and C. Cismaşiu. "Hybrid-{T}refftz displacement element for spectral analysis of bounded and unbounded media." International Journal of Solids and Structures. 40 (2003): 671-699. Abstract

The hybrid-{T}refftz displacement element is applied to the elastodynamic analysis of bounded and unbounded media in the frequency domain. The displacements are approximated in the domain of the element using local solutions of the wave equation, the Neumann conditions are enforced directly and the surface forces are approximated on the Dirichlet and inter-element boundaries of the finite element mesh. Two alternative elements are developed to model unbounded media, namely a finite element with absorbing boundaries and an unbounded element that satisfies explicitly the Sommerfeld condition. The finite element equations are derived from the fundamental relations of elastodynamics written in the frequency domain. The numerical implementation of these equations is discussed and numerical tests are presented to assess the performance of the formulation.

Santos, F. A., H. Rebelo, M. Coutinho, L. S. Sutherland, C. Cismasiu, I. Farina, and F. Fraternali. "Low velocity impact response of 3D printed structures formed by cellular metamaterials and stiffening plates: PLA vs. PETg." Composite Structures (2020): 113128. AbstractWebsite

This work studies the low-velocity impact response of 3D-printed layered structures made of thermoplastic materials (PLA and PETg), which form sacrificial claddings for impact protection. The analyzed structures are composed of crushable cellular cores placed in between terminal stiffening plates. The cores tessellate either honeycomb hexagonal unit cells, or hexagonal cells with re-entrant corners, with the latter exhibiting auxetic response. The given results highlight that the examined PETg protectors exhibit higher energy dissipation ratios and lower restitution coefficients, as compared to PLA structures that have the same geometry. It is concluded that PETg qualifies as an useful material for the fabrication of effective impact protection gear through ordinary, low-cost 3D printers.