1,721,023 research outputs found
Simulation of seismic collapse of simple structures with energy-based procedures
No full textCharacterization of structural collapse is one of the key components of performance based earthquake engineering (PBEE) design. Usually, in seismic codes, the point of dynamic structural collapse due to earthquakes is based on parameters approaching subjective threshold values. Instead, energy-based formulations have raised as a more physical and robust approach in understanding the balance between the seismic energy input into the systems and the structural energy dissipated. In this paper a comparison between different energy-based methodologies is shown. Particularly, the formulation of a kinetic energy-based methodology is proposed and compared with the gravitational and intrinsic energy-based procedures, and with the results of the pushover analysis. The results show that the collapse state evaluated with the kinetic energy-based criterion is compatible with gravitational energy-based collapse technique in which its results were verified through some experimental tests. While in gravitational energy based method the amount of gravitational force should necessarily be significant, the proposed kinetic energy procedure predicts collapse point regardless of gravitational force. It also predicts local damage and hinge formation reasonably. The methods were investigated using single-degree systems (SDOFs) and a three story steel frame. According to outcomes, the proposed procedure can be used as an acceptable method for determination of collapse time, drift, and local damage
Characterization of Dissipated Energy Demand
No full textPerformance-Based Earthquake Engineering (PBEE) aims at designing structures that are able to satisfy multiple target performance levels at different ground motion intensities. The performance levels can be introduced into the overall design process through energy concepts. It is acknowledged that the design of structures protected by control systems such as base isolation or energy dissipation devices can be efficiently optimized by using an energy-based approach. The energy-based design approach incorporated within the probabilistic framework of the performance-based design is a promising design method. In its development, three important energy-based dissipation parameters are critically needed to evaluate, which are the ratio of hysteretic energy to input energy EH/EI, normalized cumulative damage η, as well as the equivalent number of cycles neq. Therefore, this study has taken a comprehensive investigation of these parameters for four hysteretic systems of structures with the vibration period of 0.05s–4s for 7 damping ratios, that is 0.02, 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5, and 6 ductility factors, that is 2, 3, 4, 5, 6 and 8. Empirical formulas of predicting the mean values and standard deviations of the energy-based dissipation parameters are proposed as a function of vibration period, damping ratio, and ductility factors. The proposed predictive models can be easily and conveniently used to evaluate the energy-based dissipation parameters in a deterministic and probabilistic manner in the energy-based design in the framework of PBEE
Evaluation of optimal lateral resisting systems for tall buildings subject to horizontal loads
Full text linkThe tendency of modern designs towards optimal structures often leads to the lightest and best performing choice among a large set of design alternatives. In a similar scenario, the introduction of automated tools to further guide designers in achieving efficient solutions has been a recurrent topic for mechanical and structural engineers, over the past decades. Nowadays, topology optimization is considered a powerful preliminary design tool to determine the optimal material distribution in a design domain, i.e. the most effective configuration that satisfies a given set of prescribed constraints while reducing the consumption of structural material. Among different applications in the field of Civil Engineering, this work focuses on the definition of optimal layouts of lateral resisting systems for multi-storey steel building frameworks subject to lateral loads using topology optimization techniques. The objective of the research is to illustrate the benefits deriving from the introduction of automated routines within the preliminary design stage and establish reliable guidelines for performing accurate and objective optimization procedures. Since the optimal material distribution follows the load flow within the structure, optimal topologies are especially sensitive to the alteration of support and loading conditions: different loading scenarios naturally lead to distinct optimal layouts. In order to avoid the loss of objectivity and preserve the optimality of the results, the effects that preliminary modelling and loading assumptions produce on final layouts are investigated. Numerical applications to high-rise building models are presented and discussed
Energy-Based Topology Optimization Under Stochastic Seismic Ground Motion: Preliminary Framework
No full textThe growing availability of suitable computational resources to support the design of complex and large buildings makes the topology optimization more and more attractive to achieve high structural performances while reducing the use of building materials and thus cutting the total costs. In case of buildings under dynamic loads, displacement- and acceleration-based criteria are most commonly employed in topology optimization for preventing damage in structural components and protecting high-frequency sensitive non-structural components, respectively. The present work introduces the energy-based topology optimization of large structures as a more effective design approach to mitigate damage due to earthquake. The inherent randomness of the seismic excitation is taken into account by means of the random vibration theory, in such a way to avoid the direct integration of the motion equations for a large number of records. Topology optimization is performed via Solid Isotropic Material with Penalization (SIMP) method and resorting to an analytical evaluation of the gradient. A stationary-type stochastic seismic ground motion is considered in the preliminary framework presented in this study, whereas the final case study here discussed is concerned the search of the optimal layout for a lateral resisting system in a multi-story building subjected to earthquake
A new modular structural system for tall buildings based on tetrahedral configuration
Full text linkInspired by the high mechanical performance of diagrid structures, the minimization of material consumption on braced tubes and the expressive potency of tensegrity modular structures, this work proposes an innovative three-dimensional system for tall buildings. A new modular structural system generated from the assembly of tetrahedral units is investigated. The paper integrates insights on the architectural implications and mechanical performance of the reticular system arranged in repetitive triangular-based modules. The impact of different geometric configurations of the structural members on the economic design is also discussed and recommendations for the optimal topology are made. Guidelines for the design and analytical formula for accessing preliminary member sizes are proposed on the basis of stiffness requirements
Near-fault earthquakes with pulse-like horizontal and vertical seismic ground motion components: Analysis and effects on elastomeric bearings
No full textNear-fault earthquakes have been largely studied in the last years by paying special attention to the occurrence of a pulse-like horizontal seismic ground motion, and to the related effects on structural systems. Conversely, less attention has been paid on the vertical component of the ground motion in such seismic events. Within this framework, the present study is meant at investigating a fairly overlooked special case, that is the occurrence of near-fault earthquakes exhibiting a pulse-like seismic ground motion along the horizontal direction and the vertical one. Specifically, the variational mode decomposition technique is employed to prepare and characterize two subsets of near-fault earthquake records that consist of fault-normal and vertical seismic ground motion components. One subset collects earthquake records with pulse-like waveform in both velocity components, whereas a pulse-like waveform in the fault-normal velocity component only takes place in the earthquake records of the second subset. If both fault-normal and vertical components embed a dominant pulse-like waveform, then it is found that the ratio of the corresponding pulse periods well correlates with the pulse period along the fault-normal direction, while it is uncorrelated with respect to the pulse period along the vertical direction. Next, it is investigated the displacement demand of high-damping rubber bearings for base-isolated buildings under earthquake records characterized by a horizontal impulsive ground motion together with either a pulse-like or a nonpulse-like vertical shaking, provided that the pulse period in the horizontal direction is similar and the peak ground accelerations are individually the same after scaling. Final results shows that the maximum displacement of elastomeric bearings subjected to a pulse-like horizontal ground motion is moderately amplified, on average, when the vertical excitation is also pulse-like
Preliminary insights on the inelastic seismic response of structural systems under pulse-like ground motion
No full textNear-fault pulse-like seismic events exhibit a pulse in the velocity time history that mainly occurs in the strike-normal direction at locations towards which the earthquake rupture has propagated. The large damage potential associated with such seismic events is due to high displacement and velocity demands, together with the transmission of a large amount of energy in a relatively short time. In presence of specific geological conditions, they can also reveal unusual peaks of the spectral values in the long-period range. Additionally, it is well known that the intensity level of the vertical shaking close to the causative fault can be exceptionally high. Within this framework, the present study presents a preliminary sensitivity analysis of the inelastic response of structural systems under near-fault pulse-like ground motion accounting for the vertical component through the P-Delta effect for better understanding the damage potential of such seismic events and for supporting the development of proper design guidelines. First, some seismic records have been selected and processed. The dominant pulse embedded in the selected records and the corresponding pulse period value are derived
through a recent methodology based on the Variational Mode Decomposition technique. Several nonlinear dynamic analyses are then performed. Specifically, elastic and inelastic response spectra are first calculated taking into account the whole seismic signal and the dominant pulse only, without and with vertical seismic component and P-Delta effect. In doing so, acceleration, velocity, displacement and energy spectra are carried out and analyzed. The preliminary results here reported indicate that for large fundamental periods of the oscillator (e.g., larger than 3 s) the response can be significantly higher when the vertical component of the accelerogram and P-Delta effect are also taken into account.
Moreover, it is found that the nonlinear behavior of the oscillator can have a beneficial or detrimental effect. The outcomes of this preliminary analysis aim at providing useful insights toward a better characterization of the seismic demand in inelastic structural systems subjected to pulse-like seismic events
Energy based design of a timber-steel multi-story building
No full textEnergy-based methodology is utilized to design novel timber-steel hybrid core wall system. The timber-steel core wall system consists of cross laminated timber (CLT), steel columns, angled brackets and t-stub connections. The CLT wall panels are stiff and strong, and ductility is provided through the steel t-stub connections. The structural system was modelled in SAP2000 finite element program. The hybrid system is explained in detail and validated using first principles. To evaluate performance of the hybrid core system, a 7-story building was designed using both forced-based design and energy based design (EBD) approaches. Performance of the structure was evaluated using 10 earthquakes records selected for 2500 return period and seismicity of Vancouver. The results clearly served as a good example of the benefits of EBD compared to conventional forced based design approaches
Rintc project: Influence of structure-related uncertainties on the risk of collapse of Italian code-conforming reinforced concrete buildings
No full textThis paper reports on the results of an ongoing Research Project aimed at computing the risk of collapse in new buildings conforming to the Italian Seismic Design Code. Companion papers describe the overall Research Project, funded by the Italian Civil Protection Department (DPC), its different application areas (reinforced concrete, masonry, steel buildings, etc), the overall seismic risk calculation procedure and the ground motion selection process followed to identify the recorded ground motions used for the multi-stripe analyses for ten different ground motion intensities. This papers describes the multivariate statistical model of the structure-related uncertainty developed with reference to reinforced concrete buildings, describing the variability of material properties as well as model error terms of the adopted response models for both RC members and masonry infills. The paper describes also the efficient sampling procedure adopted and discusses the results of the nonlinear analyses, both static and dynamic, carried out under different assumptions on the correlation structure for the selected reinforced concrete buildings (namely 6- and 9-storey moment resisting frame)
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