Evaluation of Approaches to Characterize Seismic Isolation Systems for Design

Current design codes generally use an equivalent linear approach for preliminary design of a seismic isolation system. The equivalent linear approach is based on effective parameters, rather than physical parameters of the system, and may not accurately account for the nonlinearity of the isolation system. This article evaluates an alternative normalized strength characterization against the equivalent linear characterization. Considerations for evaluation include: (1) ability to effectively account for variations in ground motion intensity; (2) ability to effectively describe the energy dissipation capacity of the isolation system; and (3) conducive to developing design equations that can be implemented within a code framework.     

Response Sensitivity of Highway Bridges to Randomly Oriented Multi-Component Earthquake Excitation

In two-dimensional and single axis three-dimensional finite element analyses, the ground motion incidence angle can play a significant role in structural response. The effect of incidence angle for three-dimensional excitation and response is investigated in this paper for response of highway bridges. Single-degree-of-freedom elastic and inelastic mean spectra were computed from various orientation techniques and found indistinguishable for combinations of orthogonal horizontal components. Probabilistic seismic demand models were generated for the nonlinear response of five different bridge models. The negligible effect of incidence angle on mean ensemble response was confirmed with a stochastic representation of the ground motions.     

Parametric Sensitivity of Ground Motion Pulse Filter for Response Control of Base-Isolated Buildings

Recently, the authors have proposed ground motion pulse filters for designing effective active and semi-active controllers for base-isolated structures subject to near-field earthquakes. The controller design is realized by augmenting the structural system equation with state-space model of the pulse filter. It has been observed that the resulting controllers are capable of simultaneously reducing peak values of base displacement, superstructure drift, and accelerations of the base and the superstructure simultaneously within practical range of control forces. Since the pulse model depends on ground pulse period, ground pulse decay factor, and the pulse shape factor, a parametric sensitivity analysis is carried out to find pulse parameters for a broad range of earthquakes. It is found that the performance of the controller doesn't vary significantly if the pulse period is underestimated by 50% or overestimated by 20% with respect to the actual ground pulse period, the ground decay factor is between 0.15 and 0.35 and the pulse shape factor is between 1 and 3.     

Evaluation of Strength Hierarchy of Beam-Column Joints of Existing RC Structures under Seismic Type Loading

To evaluate the strength hierarchy, three different types of exterior beam-column joint, i.e., gravity load designed, non ductile and ductile, following two different codes are considered. Strength of different components of beam-column joint, i.e., column, beam, and joint core, is individually calculated from different failure criteria. Shear strength of the joint is evaluated from softened strut and tie model. Strength hierarchy, ultimate strength, and critical failure modes of the specimens are analytically estimated and found to be well corroborated with the experimental results. The study will help in designing the earthquake resistant RC structures in a more rational way.     

Statistical Characterization of Structural Demand under Earthquake Loading. Part 1: Robust Estimation of the Central Value of the Data

This article is the first of two companion articles addressing the statistical characterization of seismic demand. Performance-based earthquake engineering methodologies often require the characterization of central value estimates of structural demand. Since outliers can occur in the data, central value estimates should be determined by robust estimation methods. The performance of 50 robust central value 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, seven estimators are proposed for different sample sizes.     

Computational Modeling of the Seismic Performance of Beam-Column Subassemblies

Analytical studies are carried out to investigate the effectiveness of finite element modeling procedures in accurately capturing the nonlinear cyclic response of beam-column subassemblies. The analyses are performed using program VecTor2, employing only default or typical material constitutive models and behavior mechanisms in order to assess analysis capabilities without the need for special modeling techniques or program modifications. The specimens considered cover a wide range of conditions, and include interior and exterior seismically and non seismically designed beam-column subassemblies. It is shown that finite element analyses can achieve good accuracy in determining the strength, deformation response, energy dissipation, and failure mode of reinforced concrete beam-column subassemblies under seismic loading conditions.     

Beam-Column Joint Model for Nonlinear Analysis of Non-Seismically Detailed Reinforced Concrete Frame

An efficient and simplified plane beam-column joint model that can describe the strength deterioration, stiffness degradation, and pinching effect was developed for the nonlinear analysis of non-seismically detailed reinforced concrete frames. The proposed beam-column joint model is a super-element consisting of eight spring components and one panel zone component, representing the bond-slip mechanism of the longitudinal reinforcement and the shear deformation mechanism of the joint concrete core region, respectively. In order to represent the dynamic response at the system level, the elastic constitutive law is applied to the eight connector springs, while the Bouc-Wen-Baber-Noori (BWBN) model is adopted to describe the hysteretic behavior of the panel zone component. For the implementation of the finite element analysis, the algorithmically consistent tangent of the BWBN model is derived as a uni-axial constitutive model, while the initial stiffness of the panel zone component is determined by the concrete compression strut assumption. The accuracy and efficiency of the proposed beam-column joint model were calibrated at both the component and structural levels by comparing the simulated results with the experimental data for non-seismically detailed joint sub-assemblages and a reinforced concrete plane frame.     

Seismic Fragility Assessment of Lightly Reinforced Concrete Structural Walls

Development of fragility functions is a pertinent stage in seismic performance assessment of structures. A database of lightly Reinforced Concrete (RC) walls under simulated seismic loading is compiled from the literature to establish the drift-based seismic fragility functions. To classify the damage states experienced by RC walls, the Park-Ang Damage model is amended in this research. Then, the modified Bouc-Wen-Baber-Noori hysteresis model is implemented in ABAQUS to predict the hysteresis behavior of RC walls. Thereafter, the proposed hysteresis model is employed to develop the seismic fragility curves of low to mid-rise RC walls in Singapore using incremental dynamic analysis approach.     

Theoretical and Numerical Seismic Analysis of Masonry Building Aggregates: Case Studies in San Pio Delle Camere (L’Aquila,Italy)

Masonry building aggregates are large parts of the Italian building heritage often designed without respecting seismic criteria. The current seismic Italian code does not foresee a clear calculation method to predict their static nonlinear behavior. For this reason, in this article a simple methodology to forecast the masonry aggregate seismic response has been set up. The implemented procedure has been calibrated on the results of two FEM structural analysis programs used to investigate three masonry building compounds. As a result, a design chart used to correctly predict the base shear of aggregate masonry units starting from code provisions has been set up.     

Foreign ceramic tradition,local clays: the Handmade Burnished Ware of Tell Kazel (Syria)

Late Bronze Age Handmade Burnished Ware (HMBW) from Tell Kazel was studied by thin-section petrography and neutron activation analysis in order to investigate its manufacturing technology and origin of production. Results show that the majority of the HMBW fabric groups point to a local area of production while a few petrographic loners might have been produced elsewhere in the Akkar Plain or imported. The manufacturing technique, in terms of clay paste recipe, forming and finishing techniques, is however new in the Tell Kazel pottery assemblage, hinting at the work of foreigners present at the site. The historical and archaeological contexts further suggest that these foreigners were some of the Sea Peoples and the stylistic and analytical data further reinforce the link between the northern Levant and the western Mediterranean.