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- Influence of the SMA constitutive model on the longitudinal seismic response of RC bridgesPublication . Nunes, Pedro; Lobo, Paulo SilvaSeveral studies indicate that the re-centring capacity presented by superelastic Shape Memory Alloys (SMA) can reduce the displacements of structures subjected to earthquakes. To quantify the errors of numerical predictions with different constitutive models, peak, relative and residual displacements of four two-framed reinforced concrete (RC) bridges, linked by SMA bars, subjected to seismic actions, were numerically assessed. Different ratios of the elastic natural period of vibration of the frames of the bridges were adopted. Lumped plasticity models were used to simulate the behaviour of the reinforced concrete columns. Five SMA uniaxial models were considered, combining linear, nonlinear, isothermal and nonisothermal conditions. The seismic action was modelled by real accelerograms. The results show that the relative displacements are more sensitive to the adopted SMA model than the peak and residual displacements. Significant relative differences, up to 70%, were obtained.
- 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.
- 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.
- The Effect of Bond-Slip in the Numerical Assessment of RC Frames Under Cyclic LoadingPublication . Lobo, Paulo S.; Almeida, J.; Guerreiro, L.Bond-slip may have significant influence on the assessment, with numerical models, of reinforced concrete structures subjected to cyclic loadings, whether static or dynamic. Its influence is discussed with the correlation of experimental and analytical results, where two numerical models are considered, including a perfect bond fiber-section finite element formulation and a force-based fiber-section model including bond-slip in the vicinity of the frame joints, both exterior and interior. In this case, the model implemented makes it possible to consider the coupling effect of the response of the beams adjacent to the joint, and the models are constructed from the geometrical and material characteristics of the structure, without any calibration procedures. The experimental results are from a reinforced concrete column and a beam-column subassemblage, both subjected to static cyclic loadings, with predefined displacements sequences for the element-ends, and from a shaking table test of a one bay two-story reinforced concrete frame structure. The comparisons show that the considered bond-slip based model makes it possible to satisfactorily predict the response of reinforced concrete frames under both static and dynamic cyclic loadings. The influence of reinforcement slippage was evaluated by comparison of the previous results with those obtained with the perfect bond-based model. This made it possible to conclude that the accuracy of the model considering bond-slip is significantly superior to that of the perfect bond model. Furthermore, responses obtained with the previous model show the pinching effect, which is characteristic of reinforced concrete structures and significantly changes the hysteretic dissipated energy, not delivered by the latter model. This can also be seen in the effect of bond-slip in the response of the fibers which model the reinforcing rebars.