Seismic Damage Assessment of Reinforced Concrete Grain Silos

This paper deals with seismic performance and damage assessment of concrete grain silos. An existing large silo is taken as a case study to conduct the numerical analyses. A global damage index based on target displacement is proposed to quantify numerically different damage states of the structure. To this aim, the classical N2 method is extended to adaptive multimodal to evaluate seismic performance of the structure for increasing pic ground acceleration levels with taking into account degradation of stiffness and modification of modal characteristics. The seismic capacity of the silo is evaluated, as an averaged curve, by conducting pushover and several incremental dynamic analyses using artificial and recorded accelerograms. The seismic demand is derived from the design spectrum of the Algerian seismic code (RPA 2003). The target displacement is determined by taking into account both the participation of the dominant modes, and the degradation of the structure’s modal characteristics. The nonlinear behavior of the structure’s walls is modeled by using nonlinear multilayered shell elements. The effect of the stored granular material is included through distributed equivalent masses. It is found that when the structure modal characteristics are updated as its stiffness is degraded, the target displacement is correctly computed. Whereas, it wrongly grows indefinitely, with increasing PGA, when constant modal characteristics of the intact structure are assumed, as usually done. The proposed global damage index is compared to three existing reliable indices. It better reflects the different damage states of studied silo.

Evaluation of Seismic Site Amplification Using 1D Site Response Analyses at Ba Dinh Square Area, Vietnam

This study presents a case study on ground response analysis of one of the important cultural heritages in Hanoi, Vietnam. One-dimensional nonlinear and equivalent linear site response analyses which are commonly applied to solve the problem of seismic stress wave propagation are performed at the Ba Dinh square area. A measured in-situ shear wave velocity profile and corresponding geotechnical site investigation and laboratory test data are utilized to develop the site model for site-specific ground response analysis. A suite of earthquake records compatible with Vietnamese Design Code TCVN 9386: 2012 rock design spectrum is used as input ground motions at the bedrock. A few concerns associated with site-specific ground response evaluation are analyzed for both nonlinear and equivalent linear procedures, including shear strains, mobilized shear strength, and peak ground acceleration along with the depth. The results show that the mean maximum shear strains at any soil layer are less than 0.2% in the study area. A deamplification portion within the soil profile is observed at the layer interface with shear wave velocity reversal. The maximum peak ground acceleration (PGA) at the surface is about 0.2 g for equivalent linear analysis and 0.16 g for nonlinear analysis. The ground motions are amplified near the site natural period 0.72 s. The soil factors calculated in this study are 1.95 and 2.07 for nonlinear and equivalent linear analyses, respectively. These values are much different from the current value of 1.15 for site class C in TCVN 9386: 2012. A comparison of calculated response spectra and amplification factors with the local standard code of practice revealed significant discrepancies. It is demonstrated that the TCVN 9386: 2012 soil design spectrum is unable to capture the calculated site amplification in the study area.

Seismic Performance of a High-Rise Building by Using Linear and Non-Linear Methods

In this paper, the seismic behavior of existing reinforced concrete tall building is investigated by the linear and nonlinear dynamic analysis. The selected reinforced concrete structure was designed according to “Turkey Seismic Code-2007” (TEC-2007). A typical 41 story reinforced concrete building is designed. Turkey Building Earthquake Code-2018 (TBEC-2018) is utilized for evaluating the seismic performance of the selected building. Natural earthquake acceleration record selected and adjusted for compatibility with the adopted design spectrum, is used. A performance analysis according to the TBEC-2018 in a 41-story reinforced concrete shear wall-framed structure in Istanbul where active fault lines are located. The selected reinforced concrete shear wall unsymmetrical plan tall building is located in Istanbul, Turkey. The performance goals of the reinforced concrete shear wall structure are evaluated by applying procedures of the TBEC-2018 and nonlinear dynamic analysis. According to the Code, the reinforced concrete shear wall building is not expected to satisfy life safety performance levels under design earthquake.

Estudio comparativo de análisis y diseño de estructuras aporticadas de hormigón armado, aplicando los espectros de la microzonificación sísmica del cantón Portoviejo y los espectros de la NEC-15

La ciudad de Portoviejo cuenta desde el 2017 con espectros de diseño específicos resultados del estudio de microzonificación sísmica del cantón. Esta investigación se origina por el escaso uso que se da a los espectros de diseño indicados en el estudio de microzonificación por parte de calculistas estructurales, quienes continúan usando los espectros que se indican en la Norma Ecuatoriana de la Construcción del 2015 para analizar y diseñar las estructuras, tanto de hormigón armado como de acero estructural. El objetivo de esta investigación es medir las variaciones de desplazamientos laterales y esfuerzos globales en estructuras aporticadas de hormigón armado mediante un análisis sísmico, empleando tanto los espectros de la norma ecuatoriana como los espectros de la microzonificación sísmica de Portoviejo. Se analizaron seis estructuras, tres de ellas regulares en planta y en elevación, las cuales eran de tres, cinco y ocho niveles de altura y otras tres estructuras irregulares de tres y dos niveles. Las estructuras fueron modeladas en Etabs, y se usó el análisis sísmico modal espectral en que se variaba el espectro de diseño. En cuanto a los espectros de la microzonificación se usaron los indicados para las microzonas M4 y M5 mientras que los espectros de la norma considerados corresponden a la zona sísmica VI en suelos tipo D y E consistentes con los tipos de suelo de las microzonas M4 y M5. Adicionalmente se evaluó la variación del área de aceros de refuerzo en elementos principales. De este esta investigación se puede concluir que: i) en las estructuras de dos, tres y cinco niveles, los desplazamientos se amplificaron al emplear los espectros de la microzonificación sísmica, la microzona 4 entrega el mayor valor. En la estructura de ocho niveles los espectros de la norma dan los mayores desplazamientos. ii) en la estructura de ocho niveles los mayores esfuerzos de corte y momento se presentaron al emplear los espectros de la norma ecuatoriana de la construcción. iii) al diseñar las estructuras los resultados no presentaron una variación significativa, se obtuvo una mínima diferencia en cuanto a los aceros de refuerzos longitudinales. iv) en la ciudad de Portoviejo, las estructuras construidas con frecuencia no superan los tres niveles y al ser diseñadas con los espectros de la norma se estaría subestimando la aceleración sísmica de diseño. Se recomienda el uso de los espectros de la microzonificación, que son resultado de un trabajo específico para las condiciones de la ciudad. Palabras claves: Microzonificación Sísmica, Espectros de Diseño, Análisis Sísmico, Diseño Sísmico. Abstract— The Portoviejo city has since 2017 with specific design spectrum results of the study of seismic microzoning in the canton. This research originates from the limited use given to the design spectrum indicated in the microzonation study by structural engineers, who continue to use the spectrum indicated in the 2015 Ecuadorian Construction Standard to analyze and design the structures, both reinforced concrete and structural steel. The objective of this investigation is to measure the variations of lateral displacements and global efforts in structures provided with reinforced concrete to be analyzed seismically using both the spectrum of the ecuadorian norms and the spectrum of the seismic microzoning of Portoviejo. Six structures were analyzed, three of them regular in plan and elevation, which were three, five and eight levels high and three other irregular structures of three and two levels. The structures were modeled in Etabs, and the spectral modal seismic analysis was used, varying the design spectrum. Regarding the microzonation spectrum, those indicated for microzones M4 and M5 were used, while the spectrum of the standard considered correspond to seismic zone VI in soils type D and E consistent with the soil types of microzones M4 and M5. Additionally, the variation of the area of reinforcement steels in main elements was evaluated. From this research it can be concluded that: i) in the structures of two, three and five levels, the displacements were amplified by using the spectrum of the seismic microzonation, the microzone 4 generated the highest value. In the eight-level structure the spectrum of the norm give the greatest displacements. ii) in the eight-level structure the greatest cutting and momentum efforts were presented when using the spectrum of the Ecuadorian construction standard. iii) when designing the structures, the results did not show a significant variation, a minimum difference was obtained regarding the longitudinal reinforcement steels. iv) in the city of Portoviejo, the structures built frequently do not exceed three levels and being designed with the spectrum of the standard would be underestimating the seismic acceleration of design. The use of microzonation spectra is recommended, which are the result of specific work for city conditions. Keywords: Seismic microzonation, Design spectrum, Seismic Analysis, Seismic Design.

Cyclic engagement of hysteretic steel dampers in braced buildings: a parametric investigation

Hysteretic steel dampers have been effectively used to improve the seismic performance of framed buildings by confining the dissipation of seismic energy into sacrifical, replaceable devices which are not part of the gravity framing system. The number of cycles sustained by the dampers during the earthquake is a primary design parameter, since it can be associated to low-cycle fatigue, with ensuing degradation of the mechanical properties and potential failure of the system. Current standards, like e.g. the European code EN 15129, indeed prescribe, for the initial qualification and the production control of hysteretic steel dampers, cyclic tests in which the devices are assessed over ten cycles with amplitude equal to the seismic design displacement dbd. This paper presents a parametric study focused on the number of effective cycles of the damper during a design earthquake in order to assess the reliability of the testing procedure proposed by the standards. The study considers typical applications of hysteretic steel dampers in low and medium-rise steel and reinforced concrete framed buildings and different ductility requirements. The results point out that the cyclic engagement of the damper is primarily affected by the fundamental period of the braced building and the design spectrum, and that, depending on these parameters, the actual number of cycles can be substantially smaller or larger that recommended by the standards. A more refined criterion for establishing the number of cycles to be implemented in testing protocols is eventually formulated.

Policy Assemblages and Policy Resilience: Lessons for Non-Design from Evolutionary Governance Theory

Evolutionary governance theory (EGT) provides a basis for holistically analyzing the shifting contexts and dynamics of policymaking in settings with functional differentiation and complex subsystems. Policy assemblages, as mixes of policy tools and goals, are an appropriate unit of analysis for EGT because they embody the theory’s emphasis on co-evolving elements within policy systems. In rational practice, policymakers design policies within assemblages by establishing objectives, collecting information, comparing options, strategizing implementation, and selecting instruments. However, as EGT implies, this logical progression does not always materialize so tidily—some policies emerge from carefully considered blueprints while others evolve from muddled processes, laissez faire happenstance, or happy accident. Products of the latter often include loosely steered, unmoored, and ‘non-designed’ path dependencies that confound linear logic and are understudied in the policy literature. There exists the need for a more intricate analytical vocabulary to describe this underexplored ‘chaotic’ end of the policy design spectrum, as conjuring images of ‘muddles’ or ‘messes’ has exhausted its usefulness. This article introduces a novel metaphor for non-design—the bird nest—to bring studies of policy design and non-design into lexical harmony.

Site-Response Analysis Using the Shear-Wave Velocity Profile Correction Approach

ABSTRACT The traditional approach used to incorporate site response into the ground-motion hazard analysis is to compute a design spectrum for a rock-site condition and then propagate the rock motion from the base of the soil model to the surface. The main limitation with this approach is that it can be inconsistent with the ground-motion models (GMMs) used to develop the input rock motion. The VS profile implicit in the GMMs is unlikely to match the site-specific VS profile (value and gradient), because the GMMs were developed for ground motions from different VS profiles over large regions and are unlikely to match the profile of any one site well. This article presents the VS profile correction method for developing surface ground motions as an alternative to the soil-over-rock approach routinely used in earthquake engineering practice. This approach is similar to the standard soil-over-rock analysis, but uses different input motions and involves performing two site response analyses—one for the generic profile associated with the GMM(s) and one for the site-specific profile—then applying the ratio of the two site response analysis results to correct the design spectrum for the reference site condition developed using the GMMs. Two example applications are included to illustrate the VS profile correction methodology as well as some of the challenges that may arise when doing so.

Influence of Transient and Partial Footing Separation on the Seismic Response of Skewed Bridges with Soil Support

Previous research has shown that the transient and partial footing separation is one of the effective methods to reduce the impact of earthquakes on bridge structures. The separation will not only temporarily stop the transfer of seismic load to structures, but also activate rigid-like body motions of the bridge piers. Most of current investigations involving footing uplift only focused on straight bridges. The influence of skew angle is rarely considered. Even though skewed bridges are common and more vulnerable to seismic load. This work reveals the simultaneous influence of skew angle and footing uplift on soil on seismic response of bridges. A bridge with a 30∘ or 45∘ skew angle, in addition to a straight bridge, was excited using a large-scale shake table. The ground excitations were stochastically simulated based on design spectrum of New Zealand standard. The result revealed that with increasing skew angle bridges will have frequent footing uplifts. In the case of a straight bridge, although allowing footing uplift is beneficial in reducing the bending moment at the pier support, it increases the longitudinal girder displacement. In contrast, in the case of 30∘ and 45∘ skewed bridges, uplifts increase the bending moments of piers and the displacements of the girder, especially in the transverse direction.