Seismic Assessment of the Bell Tower of Santa Maria Del Carmine: Problems and Solutions

A complete structural analysis of the bell tower of Santa Maria del Carmine in Naples (Italy) has been developed by using a 3D FE model based on the results of detailed experimental investigations in situ. Linear analysis for gravity loads, linear modal analysis, and nonlinear static analysis (Push Over) were carried out in order to assess the seismic capacity of the structure. A check of local out-of-plane failure mechanisms was also performed to verify if the structure is able to attain a global behavior. Problems and solutions related to the different methods are presented and discussed.     

Lessons Learned from Seismic Analysis of a Seven-Story Concrete Test Building

A uniaxial shake table test of a full-scale slice of a seven-story reinforced concrete wall building was performed at the University of California, San Diego. A 2D analytical model that primarily employed fiber-based beam-column elements was used for a blind prediction of the global response of the building to the imposed input accelerations. An improved analytical model, which adequately simulates the building's dynamic response and comparison of measured and analytical results, is presented. The lessons learned from participation in the blind prediction with particular attention to the effects of issues commonly ignored in analytical modeling of concrete buildings are included.     

Definition of Seismic Input for Out-of-Plane Response of Masonry Walls: I. Parametric Study

Response of masonry walls to out-of-plane excitation is a complex, yet inadequately addressed theme in seismic analysis. The seismic input expected on an out-of-plane wall (or a generic “secondary system”) in a masonry building is the ground excitation filtered by the in-plane response of the walls and the floor diaphragm response. More generally, the dynamic response of the primary structure, which can be nonlinear, contributes to the filtering phenomenon. The current article delves into the details and results of several nonlinear dynamic time-history analyses executed within a parametric framework. The study addresses masonry structures with rigid diaphragm response to lateral loads. The scope of the parametric study is to demonstrate the influence of inelastic structural response on the seismic response of secondary systems and eventually develop an expression to estimate the seismic input on secondary systems that explicitly accounts for the level of inelasticity in the primary structure in terms of the displacement ductility demand. The proposed formulation is discussed in the companion article.     

Statistical Characterization of Structural Demand under Earthquake Loading. Part 2: Robust Estimation of the Dispersion of the Data

Performance-based earthquake engineering methodologies often require a probabilistic model of structural demand. Since observations masking the probability distribution of the majority of the data are frequently found, robust estimation methods are proposed to estimate the probabilistic model parameters (i.e., central value and dispersion). The performance of thirty-three robust dispersion estimators is evaluated, for different sample sizes, using the chord rotation, curvature, shear force, and inter-story drift demands obtained after analyzing five reinforced concrete structures under real earthquake records scaled to several intensities. Based on the results, combinations involving dispersion and central value (defined in a companion article) estimators are proposed.     

Seismic Vulnerability of Building Contents for a Given Occupancy Due to Multiple Failure Modes

A methodology is presented for assessing the seismic vulnerability of inventories of contents to multiple failure modes. An ordering method to find out probabilities of failure of a conditional mode upon the survival of the other modes is applied. The procedure considers the statistical correlation of failure modes due to the dynamic response, such as sliding and/or overturning, of contents and also to non structural components. This methodology was applied to inventories of four types of occupancy (house, school, office, and hospital) located in Mexico City, considering that all contents are situated at ground level. Expected damage functions for these inventories show large differences between them, the house and school inventories being the least vulnerable, and the hospital inventory, the most vulnerable, even for low intensities.     

Passive Control of Steel Storage Racks for Parmigiano Reggiano Cheese under Seismic Accelerations

Recent earthquakes in Italy resulted in the collapse of steel storage racks for aging Parmigiano Reggiano cheese, damaging a huge number of cheese wheels. In order to improve the seismic performance of surviving racks with low-budget solutions, when replacement cannot be considered, we investigate the possibility of using viscous dampers that connect the racks to a surrounding structure. Time-history analyses with natural and spectrum-compatible artificial accelerograms allow one to determine the optimal damping factor that reduces both the stress in the rack and the actions transmitted to the constraining structure. Results confirm the noteworthy benefits of the proposed retrofitting system.     

Effect of Nonlinearity of Frame Buildings on Peak Horizontal Floor Acceleration

Using representative numerical models of eight code-designed steel moment-resisting frame buildings and several ground motions, time-history analyses are performed and a critical evaluation of Peak Horizontal Floor Acceleration (PHFA) demands is conducted. The frames are modeled alternatively as linear and nonlinear systems to isolate the effect of building nonlinearity on PHFA. In most cases, PHFA is reduced when nonlinear behavior of a building is considered; however, in some cases, significant amplification of PHFA is observed. Results from the numerical study provide insight into the trend of modal response modification factors presented taking ground motion spectral shape into account.     

Design and Assessment Spectra for Retrofitting of RC Buildings

This article presents a novel approach for deriving Retrofit Design Spectra (RDS) that are intended for use in preliminary development and assessment of seismic upgrading scenarios of existing structures. The new spectral representation relates the characteristics of the intervention method chosen as the core of the upgrading strategy, with the ductility and strength demand of the retrofitted structure. The methodology utilized for the derivation of the RDS is based on the Capacity Spectrum Method where the capacity curve is described by relationships for global and local intervention methods that are parameterized in terms of fundamental response quantities. The proposed spectra provide direct insight into the complex interrelation between the characteristics of the intervention method and the implications of the upgrading scenario on demand. Alternative retrofit solutions are thus assessed in an efficient way. A case study is used to illustrate practical application of the new approach.     

Seismic Response of Base-Isolated Benchmark Building with Variable Sliding Isolators

The seismic response of base-isolated benchmark building with variable sliding isolators like variable friction pendulum system (VFPS), variable frequency pendulum isolator (VFPI), and variable curvature friction pendulum system (VCFPS), along with conventional friction pendulum system (FPS), was studied under the seven earthquakes. The earthquakes are applied bi-directionally in the horizontal plane ignoring vertical ground motion component. The shear type base-isolated benchmark building is modeled as three-dimensional linear elastic structure having three degrees of freedom at each floor level. Time domain dynamic analysis of the benchmark building was carried out with the help of constant average acceleration Newmark-Beta method and nonlinear isolation forces was taken care by fourth-order Runge-Kutta method. The base-isolated benchmark building is investigated for uniform isolation and hybrid isolation in combination with laminated rubber bearings through the performance criteria and time history response of important structural response parameters like floor accelerations, base displacement, etc. It is observed that variable sliding isolators performed better than conventional FPS due to their varying characteristic properties which enable them to alter the isolator forces depending upon their isolator displacements thus improves the performance of the structure. The VFPS efficiently controls large isolator displacements and VFPI and VCFPS improve super structural response on the cost of isolator displacement. It is also observed that the hybrid isolation is relatively better in comparison to the uniform isolation for the benchmark building.     

Seismic Response of Rolling Isolation Systems with Concave Friction Distribution

This article attempted to improve the isolation performance of a rolling isolation system by assuming that the rolling friction force gradually and linearly increased with the relative displacement between the isolator and the ground. After the rolling isolation system under different ground motions was calculated by a numerical analysis method, it obtained more regular results than that of other uneven friction distributions. Results shows that the considered concavely distributed friction force can not only dissipate the earthquake energy, but also change the structural natural period. These functions improve the seismic isolation efficiency of the structural relative displacement in comparison with the general uniform distribution of rolling friction coefficient.