Pushover Analyses of Hand-Loaded Steel Storage Shelving Racks

Among the various types of industrial solutions used to store goods and products, the light duty hand loaded shelving rack (SR) typology represents a very popular solution for domestic applications, libraries and for superstores/markets open to the public. Despite the limited cost, an eventual collapse could result in significant damage of stored goods, injuries, and potentially the loss of human life, with the possible consequence of a long suspension of commercial activities. This reflects directly on the great importance of a correct design that, despite the large use of SRs, is nowadays developed with approaches characterized by inadequate levels of reliability.

A research program on SRs is currently in progress in Italy, with the aim of improving the rules for both static and seismic design and this article presents a combined experimental-numerical study. Both component and pushover tests have been carried out, that are shortly summarized. Overall frame response has been simulated by means of advanced finite element software able to capture key features of the nonlinear response of slender frames with mono-symmetric cross-section members.     

A Fast and Efficient Simulation of the Far-Fault and Near-Fault Earthquake Ground Motions Associated with the June 17 and 21, 2000, Earthquakes in South Iceland

The two M_w 6.5 earthquakes on June 17 and 21, 2000, respectively, in the populated South Iceland Seismic Zone (SISZ) significantly augmented the Icelandic database of strong ground motions, and several strong velocity pulses were recorded at near-fault sites. The strong motions are interpreted via the Specific Barrier Model (SBM) and a mathematical model of near-fault velocity pulses. The data indicates self-similar source scaling and significantly greater attenuation of seismic waves than in other interplate regions. Through inversion of the data a new attenuation function for the SISZ has been adopted, which results in unbiased simulations. For the first time, the characteristics of the recorded near-fault pulses have been identified and compared to the worldwide database of such records. The SBM and the near-fault pulse model combine naturally in a fast and efficient synthesis of realistic, broad-band strong ground motions in the far-fault and near-fault region. Such simulations are showcased for the June 2000 earthquakes and indicate that the modeling approach adopted in this study is an effective tool for the estimation of realistic earthquake ground motions in the SISZ.     

Application of In-Test Model Updating to Earthquake Structural Assessment

Analytical methods are frequently utilized for structural assessment due to their simplicity and cost-effectiveness. However, modeling of material inelasticity and geometric nonlinearity under reversed inelastic deformations is still very challenging and its accuracy is difficult to quantify. On the other hand, realistic experimental assessment is costly, time-consuming, and impractical for large or spatially extended structures. Hybrid simulation has been developed as an approach that combines the realism of experimental techniques with the economy of analytical tools. In hybrid simulation, the structural is divided into several modules such that the critical components are tested in the laboratory, while the rest of the structure is simulated numerically. The equations of motion solved in the computer enable the integration of the analytical and experimental components at each time increment. The objective of this article is to apply a newly developed identification and model updating scheme to acquire the material constitutive relationship from the physically tested specimen during the analysis to two complex hybrid simulation case studies. The identification scheme is developed and verified in a companion article, while the two experiments presented in this article are selected such that they address different structural engineering applications. First, a beam-column steel connection with heat treated beam section is analyzed. Afterwards, the response of a multi-bay concrete bridge is investigated. The results of these two examples demonstrate the effectiveness of model updating to improve the numerical model response as compared to the conventional hybrid simulation approaches.     

Subsoil Interventions Effect on Structural Seismic Response. Part I: Validation of Numerical Simulations

Subsoil interventions to enhance the static soil resistance and reduce deformations may alter significantly the seismic response of the complex soil-foundation-structure system. The aim of this article is to have an insight in the physics of the problems encountered and to validate an adequate numerical modeling procedure to study these effects of the intervention in the global response of the system. Validation concerns wave propagation, site effects, and dynamic soil-structure-interaction issues including the intervention beneath the foundation. Theoretical models-expressions and experimental results from centrifuge tests have been used. The proposed numerical model is proven very efficient to describe the complex dynamic phenomenon and anticipate the seismic response after the employment of subsoil interventions.     

Rocking Behavior of Irregular Free-Standing Objects Subjected to Earthquake Motion

Free-standing rigid objects and structures are dominantly found to exhibit rocking behavior and can be vulnerable to overturning during an earthquake as demonstrated by numerous past earthquake events. Such objects are typically considered to be displacement sensitive with their rocking response being well presented by the Peak Displacement Demand (PDD) parameter of the supporting floor’s motion. This in turn can be directly related to an object’s width (along the direction of motion) for assessing its vulnerability to overturn. Such findings have been sufficiently justified by refined dynamic analysis supported by experimental evaluations which were based on rigid blocks with uniform geometric format (i.e., regular in their mass distribution). However, vulnerable rocking objects can be asymmetric and accordingly their sensitivity to floor displacement cannot be directly related to their width. The key parameter which defines irregular objects’ response to rocking motion is represented by the degree of eccentricity of their center of mass. In this study, the well-known rocking equation of motion is reconfigured and devised to model the rocking responses for 280 irregular objects undergoing eight earthquake motions which included artificial and recorded earthquakes. Analytical results obtained from solving the adjusted equation of motion were evaluated with sophisticated finite element (FE) models simulating the 280 irregular cases. This experimentally validated FE modeling approach was found to be time- and cost-effective for understating the rocking behavior of asymmetric objects as well as clarifying an interesting relationship between the object’s damping level and the condition of the supporting base (i.e., whether being provided with supports at the points of rotation or not). The rocking response of irregular objects was found to be highly influenced by the level of eccentricity of the object when excited by motions with high displacement amplitudes, while such influence was not found noticeable by wider objects. Based on the developed trends between the maximum top displacement of irregular objects and the PDD, an expression for estimating the rocking amplitudes is proposed which is a function of the object’s eccentricity.     

Seismic Reliability Assessment of a High-Voltage Disconnect Switch Using an Effective Fragility Analysis

This article deals with evaluation of the seismic vulnerability of a high-voltage vertical disconnect switch, one of the most vulnerable elements of electric substations. The main objective of the research is to evaluate the seismic fragility of the apparatus using a new effective method. By combining standard reliability methods for time-invariant problems with the response surface technique, this original procedure called “EFA” (Effective Fragility Analysis) permits the evaluation of fragility curves using a very limited number of numerical simulations. On the basis of experimental tests, to determine the mechanical characteristics of the disconnect switch components (ceramic, joints, etc.) the fragility curves of the equipment analyzed are carried out. The results are discussed and compared with the results of Monte Carlo simulations, which confirm the reliability of the procedure.     

Probabilistic Seismic Performance Assessment of Classes of Buildings Using Physics-Based Simulations and Ground-Motion Prediction Equations

We discuss the applicability of two different near field representations of seismic input within the capacity-demand diagram method for seismic performance assessment of classes of buildings in urban areas. The two representations of seismic input used are: (1) synthetic accelerograms obtained from 3D wave simulations of random rupture scenarios are used to estimate seismic risk, through the Monte-Carlo approximation; and (2) random realizations of elastic spectral displacement obtained through ground-motion prediction equations. The implementation of the proposed formulation in evaluating the seismic performance of two classes of buildings in the town of Sulmona, Italy, indicates that empirical ground-motion prediction equations, combined with non-iterative methods for estimating the inelastic seismic demand, can produce results comparable to the physics-based simulations.