1,721,162 research outputs found
Seismic response of viaducts and bridges isolated with FPS
Full text linkThis study deals with the evaluation of the seismic isolation of bridges equipped with single concave friction
pendulum devices, by comparing the case in which the rigid abutment is present (i.e., multi-span continuous deck bridge)
or not (i.e., single column bent viaduct). Two multi degree-of-freedom models are considered for the two cases, while the
FPS behaviour is modelled including the velocity dependency. Furthermore, the comparison is carried out by varying the
modelling parameters (i.e., pier and deck fundamental period, mass ratio and friction coefficient). The uncertainty in the
seismic input is also included by subjecting the two systems to a set of different natural ground motions. The equation of
motions are solved in non-dimensional form for both the models in order to obtain the maximum non-dimensional
displacement of the substructure. This has led to the evaluation of the optimal sliding friction coefficient able to minimize
the maximum non-dimensional pier displacement with the aim of studying the differences between the two numerical
models
Optimal Response of Isolated Multi-span Continous Deck Bridges Subjected to Near Fault and Far Field Events
Full text linkThe present study analyses the optimal friction coefficient for the seismic isolation of composite bridges, equipped with single concave friction pendulum (FPS) devices. The bridge is modelled through a six-degree-of-freedom system while the FPS friction property is described through a model that accounts for the dependency on the velocity. By introducing a time scale and a length scale, a nondimensional analysis has been used to solve the equations of motion. In detail, the response is analysed independently on the peak ground acceleration-to-velocity ratio. Furthermore, two different sets of seismic events are considered: far field and near fault. Then, many bridge models are analysed by changing different parameters (i.e., pier period, deck period, mass of the deck and of the pier and friction coefficient). By minimizing the substructure response, an optimum value of the friction coefficient is computed as function of the ratio between the period of the deck and the period of the seismic input
Robustness analysis of reinforced concrete structures: design issues
No full textThe goal of this work is to evaluate the structural robustness of a reinforced concrete building, designed in a highly seismic area, in order to define some improvements of the design criteria. In particular, a five-storey and four-span 2D frame designed according to Italian and European code rules, also accounting for the seismic design, is presented. Some modifications are considered in terms of continuity of longitudinal bars in order to investigate effects on the structural robustness. Those applied modifications are then checked to respect the ultimate limit state and seismic capacity-design verifications. Then, using the finite element software Atena 2D, displacement-controlled pushdown analyses are performed. By studying the resulting force-displacement capacity curves, the capability of the structure to show a from a robustness view point is analysed
Robustness improvements for 2D reinforced concrete moment resisting frames: Parametric study by means of NLFE analyses
Full text linkThis study develops a 2D computational parametric analysis of ordinary reinforced concrete (RC) frames, located in seismic zone, with the aim to evaluate some design suggestions with respect to their effectiveness in increasing the structural robustness. Specifically, a five-storey and four-span 2D RC moment resisting frame is considered, designed in a highly seismic area according to both Italian and European codes. Subsequently, respecting the seismic design code provisions through a cyclic design procedure, some modifications are suggested regarding the layout of the longitudinal reinforcement bars of the beams to exploit the continuity, Vierendeel behavior and influence of the side face reinforcement bars in the beams. For the different modifications, nonlinear finite element pushdown analyses of the whole frames are performed by imposing a monotonically increasing vertical displacement at the point of the column removal in Atena-2D and considering the presence of the orthogonal framed systems. Furthermore, two different failure scenarios are examined. The numerical force-displacement capacity curves corresponding to the different proposed design suggestions are investigated and compared. The results have demonstrated the effectiveness in improving the structural robustness of the proposed solutions, especially, of the side face reinforcement bars with respect to both flexural and catenary behavior. The outcomes have also highlighted the compatibility between design criteria of both robustness and earthquake engineering
Evaluation of the Failure Probability of a 2D RC Frame Subjected to Column Loss
Full text linkThis study regards the evaluation of the failure probability of a symmetrical 2D reinforced concrete frame
composed of 4 spans and 5 floors, in case of an accidental event which causes the central base column loss. The frame is an internal one of a typical building designed in a highly seismic area, characterised by a high ductility class. The frame is modelled in the non-linear finite elements software Atena 2D, accounting for both geometrical and material nonlinearities.
The uncertainties relevant to the problem are included by sampling both material and action variables,
adopting the Latin Hypercube Sampling technique. To compute the failure probability associated to the accidental scenario, two sets of analyses are considered: the first set to compute the capacity of the structure against the column removal by means of displacement-controlled pushdown analysis; the second set to evaluate the demand in terms of external loads, properly combined within the accidental combination according to the codes. The external load is then amplified in order to include the dynamic effects characterising a scenario of a structural member loss. Finally, the probability of the demand exceeding the capacity is evaluated
Influence of the Pier-abutment-deck interaction on the Seismic Response of Bridges Equipped with FPS
Full text linkThis work regards the analysis of the seismic response of bridges isolated with single concave friction pendulum devices, including or neglecting the presence of the rigid abutment. Two six degree-of-freedom models are considered for the two cases, in order to represent the response of the elastic reinforced concrete pier and of the infinitely rigid reinforced concrete deck. The behavior of the friction pendulum isolators accounts for the non-linear dependency of the friction coefficient on the sliding velocity. The comparison is carried out by including the aleatory uncertainty in the seismic input (i.e., accounting for different natural records with different characteristics) and by varying the modelling properties within a parametric analysis. Finally, by solving the equations of motion in nondimensional form, the difference between the two models are deepened in terms of influence of the seismic isolation
Optimal single concave sliding device properties for isolated multi-span continuous deck bridges depending on the ground motion characteristics
Full text linkThe present study investigates the analysis of the optimal friction coefficient with respect to the seismic performance of isolated multi-span continuous deck bridges, equipped with single concave friction pendulum (FPS) isolators. A six-degree-of-freedom system is used to model the structural system and the FPS friction property is described by means of a law that considers the dependency on the velocity. The equations of motions have been implemented in nondimensional form by considering the peak ground acceleration-to-velocity ratio (PGA/PGV) and the peak ground acceleration (PGA) as ground motion parameters for two different sets of seismic records: near-fault and far-field inputs. In addition, different bridge models are considered for various parameters (i.e., pier period, deck period, friction coefficient and mass of the structural system). The results show the effectiveness of the PGA/PGV ratio within the proposed nondimensionalization together with the existence of an optimum value of the friction coefficient that minimizes the nondimensional response of the pier. At the end, a linear regression expression is presented with the aim to compute the optimal value of the normalized friction coefficient as a function of the deck period and PGA/PGV ratio, which can be used in the preliminary phase to design the FPS bearings. Additionally, a multivariate non-linear regression expression is also provided to evaluate the pier response
Determination of epistemic uncertainties in non-linear finite-element analyses of slender reinforced concrete elements
No full textThis work deals with the evaluation of model uncertainties in non-linear finite-element analyses of
reinforced concrete columns having high slenderness. The use of numerical models to investigate the
response of reinforced concrete members imply the need of simplifications of epistemic nature. In the
study, the epistemic uncertainty is evaluated by comparing the results of 40 experimental tests on slender reinforced concrete columns to the outcomes of non-linear finite-element simulations. The tests
have been reproduced considering different model assumptions: two software and three concrete tensile
behaviour. The model uncertainty has been then probabilistically treated in order to account for the
influence of the experimental uncertaint
Machine learning modelling of structural response for different seismic signal characteristics: A parametric analysis
Full text linkThe present study investigates the best seismic parameters for modeling the dynamic response of various non-linear structural systems by comparing different Machine Learning (ML) algorithms. A total of 400 synthetic excitations were generated and analyzed against 23 seismic parameters. These signals were used in a step-by-step numerical analysis to calculate the dynamic responses of 1000 single-degree-of-freedom (SDOF) systems with varying mechanical properties. The data obtained from these responses were processed using 20 ML algorithms, including linear regression, tree, support vector machine (SVM), boosted and bagged trees, and artificial neural network (ANN). Each ML algorithm used a single seismic parameter as input to determine the most predictive parameters for modeling structural responses, defining the high predictive seismic parameters (HPSP) set. To validate the obtained results, the most effective model predictions have been compared with the results of the parametric step-by-step analyses performed for a new group of natural ground motions. The findings demonstrate that with a properly calibrated training phase, considering the specific site hazard and selecting seismic parameters from the HPSP set, the ML model can accurately estimate seismic responses whit a significantly reduced computational effort. This study underscores the potential of integrating ML techniques into the performance-based seismic design approach
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