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- Shape memory alloys behaviour: a reviewPublication . Lobo, Paulo Silva; Almeida, João; Guerreiro, LuísShape memory alloys are used in a variety of fields, such as medical or aeronautical. Other fields of knowledge have been researching these materials, attracted by their capacity to dissipate energy through high-strain hysteretic cycles without significant residual strains. Because of these interesting properties for seismic protection, an example of the possible beneficiaries of these materials are civil engineering structures. This paper reports a bibliographic review on the characteristics and uniaxial macroscale constitutive models for shape memory alloys, of interest for a significant number of applications, most often based on wires and bars. The constitutive model assessment focuses on mechanical and kinetic laws, as well as on the energy balance law, of relevance for dynamic loadings. Some characteristics of these materials are still not sufficiently well known, especially those related to ageing. With regard to behaviour prediction, the most frequently used uniaxial constitutive models result in similar responses.
- Conceptual design of transfer structuresPublication . Ribeiro, Gonçalo; Almeida, João; Lobo, Paulo SilvaA transfer structure (TS) is a structure that alters the load path of the gravity loads, shifting the line of thrust laterally to a different vertical alignment. Transfer structures are introduced in buildings that feature discontinuities in some columns or walls and where a direct load path to the foundations is not possible. They usually represent major elements of the structure and their impact on building cost and construction time can be substantial. This paper presents an overview of existing transfer systems and provides guidance on their design and construction. Extensive research on buildings with transfer structures all over the world was carried out (more than 100 examples were analyzed) with the aim of developing a rational typology of these structures. The results can be broken down into five main types: BEAM, TRUSS, INCLINED STRUT, PLATE, and ARCH & TIE.
- Analysis and construction of transfer structures: a case studyPublication . Ribeiro, Gonçalo; Almeida, João; Lobo, PauloA transfer structure of a building is a structure that alters the load path of the gravity loads, shifting the line of thrust laterally to a different vertical alignment. They usually represent major elements of a structure and their impact on building cost and construction time can be substantial. The design for deflection control is frequently the primary consideration when defining the geometry of a transfer element, given their usual long spans and the high magnitude of the forces involved. Considerations of robustness and disproportionate collapse may also be key for the design of transfer structures as these are often regarded as critical elements for the overall stability of the building. Furthermore, the sequence of construction should be modelled through a construction-staged analysis, as it greatly affects deflections as well as final forces distribution. This paper provides guidance and highlights the key aspects that are likely to determine the structural design of transfer structures, as well as typical construction methods and challenges. It also presents a comparative study between two different types of transfer structures for the same building: an alternative composite scheme for the post-tensioned concrete transfer grid of the St. Gabriel Tower (Lisbon) was designed and the most relevant factors are highlighted.
- Bond-slip effect in the assessment of RC structures subjected to seismic actionsPublication . Lobo, Paulo Silva; Almeida, João; Guerreiro, LuísThe effect of bond-slip in the assessment of reinforced concrete structures under static or dynamic cyclic loads with numerical models may be significant. Its relevance is discussed in this paper, by analysis of the correlation of experimental and analytical results. The latter were obtained with a perfect bond-based model and with a fiber-section beam-column model which makes it possible to consider the effect of bond-slip in the vicinity of exterior as well of interior joints of reinforced concrete frame structures. The experimental results consist of a shaking table test of a reinforced concrete frame, with predominant flexural condition, in agreement with the premisses of this research. The model with bond-slip was capable of predicting the structural behaviour in a very satisfactory manner. Furthermore, the results of the assessment including bond-slip are significantly more accurate than those assuming perfect bond.
- Structural design of transfer structuresPublication . Ribeiro, Gonçalo; Almeida, João; Lobo, Paulo SilvaA transfer structure is a structure that alters the load path of the gravity loads, shifting the line of thrust laterally to a different vertical alignment. Transfer structures are introduced in buildings that feature discontinuities in vertical elements and where a direct load path to the foundations is not possible. This paper presents an overview of existing transfer systems and provides guidance on their design and construction. Extensive research on buildings with transfer structures was carried out with the aim of developing a rational typology of these structures. The results can be broken down into five main types: BEAM, TRUSS, INCLINED STRUT, PLATE, and ARC H & CABLE. In addition, transfer structures’ design is often outside the scope of normal code guidance and may require a degree of engineering judgment. This paper also highlights the key aspects that determine the structural design of transfer structures, as well as typical construction methods.
- Efeito do escorregamento dos varões no recentramento de estruturas de betão armadoPublication . Lobo, Paulo Silva; Almeida, João; Guerreiro, LuísÀ medida que o conhecimento da resposta das estruturas de betão armado solicitadas por sismos foi sendo adquirido, a perceção da importância do controlo dos deslocamentos máximos e residuais, para reduzir danos e tornar a reparação economicamente viável, foi aumentando. A resposta no tempo de um pórtico de betão armado, acoplado a vários tipos de dissipadores (elasto-plásticos, viscosos e baseados em ligas com memória de forma – passivos e semiativos) foi avaliada. O comportamento não linear da estrutura, incluindo o escorregamento dos varões nos nós das vigas-colunas, foi modelado com elementos finitos de fibras. Para comparação, realizaram-se também análises com aderência perfeita. As soluções histeréticas passivas não reduziram satisfatoriamente os deslocamentos, enquanto os dissipadores semiativos resultaram em deslocamentos máximos semelhantes aos dos dissipadores viscosos lineares. A comparação das respostas com escorregamento e com aderência perfeita permite observar diferenças significativas, tanto nos deslocamentos máximos como nos deslocamentos residuais.