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[en] Poor performance of lightly reinforced and unconfined concrete structural walls have been observed in recent earthquake events. This research investigates the displacement capacity of such walls by comparing the results of a series of state-of-the-art finite element analyses for a range of different structural walls to that estimated using plastic hinge analyses. The common expressions used in estimating the yield curvature, yield displacement and plastic displacement are scrutinised for these types of walls. Some recommendations are given to improve the prediction of the displacement capacity of lightly reinforced and unconfined rectangular and C-shaped walls for flexural actions using a plastic hinge analysis. Importantly, a parameter has been recommended to be used in a “modified” approach for estimating the nominal yield displacement of lightly reinforced concrete walls. Different expressions are also recommended depending on the amount of longitudinal reinforcement used in the wall in comparison to that required to initiate secondary cracking. This is important for providing better estimations of the displacement capacity of RC structural wall buildings in low-to-moderate seismic regions such that vulnerability studies can be conducted.
[en] The Earthquake Model of Middle East (EMME) project was carried out between 2010 and 2014 to provide a harmonized seismic hazard assessment without country border limitations. The result covers eleven countries: Afghanistan, Armenia, Azerbaijan, Cyprus, Georgia, Iran, Jordan, Lebanon, Pakistan, Syria and Turkey, which span one of the seismically most active regions on Earth in response to complex interactions between four major tectonic plates i.e. Africa, Arabia, India and Eurasia. Destructive earthquakes with great loss of life and property are frequent within this region, as exemplified by the recent events of Izmit (Turkey, 1999), Bam (Iran, 2003), Kashmir (Pakistan, 2005), Van (Turkey, 2011), and Hindu Kush (Afghanistan, 2015). We summarize multidisciplinary data (seismicity, geology, and tectonics) compiled and used to characterize the spatial and temporal distribution of earthquakes over the investigated region. We describe the development process of the model including the delineation of seismogenic sources and the description of methods and parameters of earthquake recurrence models, all representing the current state of knowledge and practice in seismic hazard assessment. The resulting seismogenic source model includes seismic sources defined by geological evidence and active tectonic findings correlated with measured seismicity patterns. A total of 234 area sources fully cross-border-harmonized are combined with 778 seismically active faults along with background-smoothed seismicity. Recorded seismicity (both historical and instrumental) provides the input to estimate rates of earthquakes for area sources and background seismicity while geologic slip-rates are used to characterize fault-specific earthquake recurrences. Ultimately, alternative models of intrinsic uncertainties of data, procedures and models are considered when used for calculation of the seismic hazard. At variance to previous models of the EMME region, we provide a homogeneous seismic source model representing a consistent basis for the next generation of seismic hazard models within the region.
[en] Over the years, several local and regional seismic hazard studies have been conducted for the estimation of the seismic hazard in Turkey using different statistical processing tools for instrumental and historical earthquake data and modeling the geologic and tectonic characteristics of the region. Recently developed techniques, increased knowledge and improved databases brought the necessity to review the national active fault database and the compiled earthquake catalogue for the development of a national earthquake hazard map. A national earthquake strategy and action plan were conceived and accordingly with the collaboration of the several institutions and expert researchers, the Revision of Turkish Seismic Hazard Map Project (UDAP-Ç-13-06) was initiated, and finalized at the end of 2014. The scope of the project was confined to the revision of current national seismic hazard map, using the state of the art technologies and knowledge of the active fault, earthquake database, and ground motion prediction equations. The following two seismic source zonation models are developed for the probabilistic earthquake hazard analysis: (1) Area source model, (2) Fault and spatial smoothing seismic source model (FSBCK). In this study, we focus on the development and the characterization of the Fault Source model, the background spatially smoothed seismicity model and intrinsic uncertainty on the earthquake occurrence-rates-estimation. Finally, PSHA results obtained from the fault and spatial smoothed seismic source model are presented for 43, 72, 475 and 2475 years return periods (corresponding to 69, 50, 10, and 2% probability of exceedance in 50 years) for PGA and 5% damped spectral accelerations at 0.2 and 1.0 s.
[en] As part of an ongoing research project into the seismic response of partially grouted reinforced masonry (PG-RM) walls, this article presents the analysis of the experimental results of eight full-scale walls that were tested in laboratory under cyclic lateral loading. All walls tested were constructed using multi-perforated clay bricks and horizontally reinforced with ladder-type bed-joint reinforcement. Three design parameters were investigated in this research: wall aspect ratio, axial load level, and horizontal reinforcement ratio. The combined effect of these variables on shear response of the walls tested is analyzed and discussed. In addition, the accuracy of four shear expressions available in the literature is assessed against the experimental results obtained. The study has confirmed that a rise in the horizontal reinforcement ratio may lead to an increase in lateral capacity of PG-RM walls, although this effect would be more remarkable for square and slender walls. The results obtained also suggest that the influence of axial load level becomes more relevant as the aspect ratio decreases. In addition, moderate values of displacement ductility, ranging from 2.5 to 5.5, were estimated from a bilinear idealization. At the level of maximum lateral force, the average drift level for all walls tested in this experimental program ranged between 0.2 and 0.62%. Finally, the research also confirms the need to review the shear expressions currently available for the design and assessment of this type of walls.
[en] In presence of soil–structure interaction (SSI), changes in dynamic properties of the system can be related to nonlinearities in both the structural and soil response. Identifying the nonlinearities related to non-stationary phenomena due to structural damage is an important issue for damage detection and localization. In this study, a novel approach is proposed to identify the non-linear structural response of an instrumented building in presence of SSI. Considering the advantages provided by the use of the time–frequency representation to explore the time-variant behavior of the system, and the direct evaluation of the shear wave velocity by the use of the deconvolution interferometry to decouple structural response from soil response, a combined Stockwell Transform and deconvolution interferometry approach is presented. The combined approach is applied to a selected data set of a well-documented building, the Jalapa building, whose nonlinear response was already investigated with other methods. This offers the possibility to validate the results obtained by the proposed approach. Jalapa building is a reinforced concrete structure, located on soft clay in Mexico City. Both SSI effects and structural and nonstructural damage affected the building response during earthquakes in the 1990s. The building was retrofitted twice during its lifetime. The data of three events are considered when investigating the changes in dynamic properties of the structure due to damage and retrofitting. The results allow us to detect the different phases of non-linear structural response in a reasonable agreement with the documented status of the building after each event.
[en] The seismic performance of an elevated water tower with reinforced concrete staging structure—the oldest one in Florence—is analyzed in this paper. The tower, erected in 1905, is a major achievement by engineer Attilio Muggia, an Italian pioneer of reinforced concrete, and is now classified as modern heritage architecture. The structure is characterized by an atypical bracing layout, with all braces rising from the bottom left corner to the upper right corner at each bay of the three upper staging levels, and no braces on the first level. The time-history assessment study, carried out by a detailed finite element simulation of the water–tank dynamic interaction, shows unsafe response conditions of the first level columns starting from seismic action scaled at the basic design earthquake level. Based on these data, two retrofit measures are proposed, consisting either in integrating the existing reinforced concrete braces of the staging skeleton with additional steel braces, or incorporating a seismic isolation system, and namely a set of double curved sliders on top of the underground columns. From an architectural viewpoint, the former strategy meets the requirement of leaving the original staging elements exposed, whereas the latter causes no intrusion in the superstructure. The design criteria and technical installation details of the two systems are illustrated, along with the results of the seismic performance assessment analyses in both rehabilitated conditions, including the cost estimation of the interventions.
[en] The vulnerability of historic masonry structures and monuments under seismic loading including churches has been confirmed during major recent earthquake events. The current research focuses on pounding effects on masonry structures, a vulnerability factor that even though it is considered to be significant for the response of adjacent reinforced concrete structures is rarely taken into account for masonry structures in current engineering practice. The central church, the so called “Katholikon”, of the Kaisariani Monastery located in Athens, Greece, is selected as a case study of a historic structure that may present pounding phenomena because of its contact with an adjacent ecclesiastic structure, added during the 16th–17th centuries. The Katholikon, one of the finest Byzantine monuments of Greece, is a Byzantine crossed-dome church constructed during two separate structural phases build in contact during the 10th/11th and 16th/17th centuries, respectively. Based on data collected with the aid of an extensive experimental investigation of the monument different modeling approaches and different analysis methods were applied including time history and response spectrum analysis using the finite element method. The results indicate that pounding significantly affects the seismic response, while an individual analysis considering pounding is needed to provide accurate results. Also significant differences are observed between the results obtained from the response spectrum and the time history analysis suggesting that the usually applied response spectrum analysis does not always provide conservative results of the actual behavior.
[en] How can we evaluate the cost-effectiveness of retrofit interventions aiming at reducing the seismic vulnerability of an existing building? What level of shaking intensity should the retrofitted building sustain? These are open questions affecting either the pre-earthquake prevention, the post-earthquake emergency and the reconstruction phases. The (mis)conception that the cost of retrofit interventions would increase linearly with the level of safety required in designing the intervention often discourages stakeholders to consider alternative retrofit options. As a result, a minimum (in some cases prescribed by-law) level of safety is often targeted, leading in some cases to no-action. Furthermore, the performance measure enforcing owners to take action is generally evaluated following a deterministic approach. When the assessment does not directly reflect, even in simplified terms, epistemic uncertainties and aleatory randomness, it can result in misleading confidence on the expected performance. The present study aims at contributing to the delicate decision-making process of retrofitting existing structures, by developing a framework to assist stakeholders with the evaluation of the actual improvement of the performance, expressed in terms of reduction of collapse probability, of alternative strategies of intervention as well as targeted retrofit levels. With reference to a pre-1970 case study building located in New Zealand, alternative retrofit solutions are considered, targeting different levels of performance, and the probability of reaching collapse when considering a set of ground-motions is evaluated, providing a correlation between the deterministic safety index adopted in the design phase (named "Percentage of New Building Standard" adopting New Zealand regulations) and the expected annual probability of collapse.