Design and development of dissipative anchoring system for seismic strengthening of heritage structures

The scope of this research is to develop the next generation of dissipating grouted anchoring systems for the seismic strengthening of historical masonry structures. Historic masonry buildings often experience out-of-plane failure due to the lack of effective connection between perpendicular walls. The insertion of steel elements at corner connections is commonly applied in rehabilitation practice to control this collapse mode and locally increase the strength and stiffness of the structure. Nonetheless, they are unable to dissipate the seismic forces rather than through cracking and yielding of the steel elements, as they present limited dissipative and ductility capacity. To this purpose, the proposed system integrates a friction-based dissipative device with stainless-steel anchors grouted within the thickness of walls. The system provides 1) effective connections between panels and reduced intrusiveness, 2) energy dissipation capacity, and additional ductility. The proposed framework addresses the assessment and refinement of the dissipative system by means of experimental and numerical activities and provides a displacement-based design tool for its implementation to heritage buildings. The first goal of this research is the refinement of a patented prototype of a friction-based device to improve its short-term performance as well as deliver a reliable and robust long-term behaviour. This task is performed according to a test-analyse-redesign procedure that can be used to improve the durability and stability of a typical friction-based device. The performance of the innovative system is then investigated by experimental tests performed on specimens reproducing a strengthened masonry connection. To address the technical gap in design codes, the second aim of this research is to propose a design method for the implementation of the dissipative system within the framework of the displacement-based design. The design procedure is applied to a case-study structure and the performance of the building strengthened by the innovative anchoring system is determined by non-linear dynamic analysis. Performance’s comparisons between different strengthening solutions are drawn, emphasizing that the additional ductility capacity reduces the seismic demand, thus resulting in a less invasive intervention in compliance with the requirements of current codes

Traditional and Innovative Approaches in Seismic Design

This special issue collects selected papers about a wide range of innovative applications in earthquake engineering. These studies were presented during the 2nd Edition of the International Workshop “Traditional and Innovative Approaches in Seismic Engineering”, held in Pisa in March 2017. The topics refer to the investigation of traditional and innovative materials for earthquake engineering applications: masonry, reinforced concrete, steel, structural glass and timber. In particular, advanced analytical and numerical analyses are described for considering effects of strength and material irregularities and rocking behavior under seismic excitations on historic buildings and industrial facilities. Experimental tests are also illustrated with the purpose of investigating the strengthening on masonry arches due to lime-based mortar composites and of obtaining reliable values of stiffness for moment resisting steel-timber connections. Among the innovative approaches, studies on original pavilions made of long-spanned TVT-portals braced with hybrid glass-steel panels are illustrate

Seismic Assessment and Retrofit of Reinforced Concrete Structures

Many constructions are built with reinforced or prestressed concrete, and most of them are designed or expected to resist earthquake actions in addition to gravity loads. To limit the effects of seismic events on reinforced or prestressed concrete structures, many attempts have been made by researchers in order to (i) improve the knowledge of the response of materials (steel bars and concrete) and members by means of laboratory tests, (ii) develop numerical and capacity models, (iii) enhance procedures for the dynamic analysis and assessment of the seismic performance of structures and (iv) suggest innovative interventions for the seismic retrofit of old and damaged reinforced or prestressed concrete structures. This Special Issue is a collection of 11 important research works that cover a wide range of problems related to the previously mentioned research fields. Both researchers and practical engineers are expected to greatly benefit from this Special Issue in view of their own work and for a better comprehension of the response of r.c. members and structures

Performance of shape memory alloy rehabilitated bridge columns under sequential earthquakes

While civil infrastructure systems have played a pivotal role in the provision of essential services and facilities for human life and public society, weaknesses of the systems to natural and man-made hazards has emerged as a major public concern. As a way to improve the resilience and sustainability of the current and future infrastructure systems, utilization of new, smart materials such as shape memory alloy (SMA) in civil engineering application has been drawing keen attention of industry and academia. Among many, active confinement technique using SMA’s shape memory effect (SME) demonstrated a great potential in retrofitting and/or repairing seismically deficient RC bridge columns. In order to gain recognition as an effective seismic retrofit/repair strategy and systemize its application, however, it is necessary to thoroughly study the unique behavior of this new material and its impact on the performance of the structural system under diverse circumstances. In this research, three main objectives are established. First, a series of shake table test is carried out to investigate dynamic responses of SMA retrofitted/repaired RC columns. Two reduced scale (1/6th) RC cantilever columns retrofitted or repaired with SMA spirals at the plastic hinge zones are tested under bidirectional seismic excitations at varying levels of intensity. The dynamic testing is expected to show the realistic seismic behavior of the SMA confined RC columns which were not able to be captured in the previous quasi-static cyclic loading tests. Second, this research also numerically studies the seismic performance of a SMA retrofitted multiple frame bridge when subjected to sequences of main shock-aftershock ground motions. Beyond exploring the responses of the columns at the component level, the impact of retrofitting a single or multiple columns with different levels of confinement pressure on the overall performance of the bridge is studied including interactions with other bridge components such as abutments or expansion joints. Furthermore, the seismic damage status and post-earthquake functionality of the SMA retrofitted bridge after multiple earthquake events are assessed. Lastly, an advanced evaluation method which effectively combines numerical and experimental approaches, named material testing incorporated (MTI) simulation is newly developed. In addition to seismic loading, this new method experimentally derives the realistic material behavior of SMAs at varying situations affected by chemical and/or thermal changes, and incorporates the measured data into the numerical analysis to predict the structure’s overall response

Composite confinement systems for RC column repair and construction under seismic loads: Concept, characterization and performance

This study aims at developing, characterizing and validating an integrated composite confinement system of conventional jackets for: (1) repair and retrofit of existing bridge columns; and (2) construction of new bridge columns, subjected to earthquake excitations. A new composite steel confinement jacket was proposed by combining a thin steel sheet and prestressing strands as a hybrid jacket, incorporating active and passive confining pressure on damaged RC columns. Both experimental and analytical studies were conducted to understand the performance and effectiveness of the proposed repair method. The experimental study involved two 1/2-scale lap-spliced deficient RC bridge columns originally tested to failure under reversed cyclic loading. The proposed jacket was designed and implemented to repair the damaged columns to achieve the required performance level after repair intervention for service and ultimate limit states. Experimental results indicated that both repaired columns exceeded the strength and ductility of their as-built columns. The stiffness of the second column designed for ultimate limit state was completely restored. Analytical studies and collapse analyses on the seismic performance of post-mainshock repaired bridges subjected to mainshock-aftershock sequences demonstrated the efficacy of the proposed technique under severe mainshock-severe aftershock attacks. Another new composite confinement system of a fiber reinforced polymer (FRP) sheet wrapped around a polyvinyl chloride (PVC) tube with energy dissipation medium in between was developed for new bridge columns construction. This composite system is essentially a FRP-confined concrete-filled PVC tube, featuring exceptional durability properties of PVC materials in addition to high strength of the FRP fabrics. Experimental tests under uniaxial compression and flexural loading were undertaken to establish the representative stress-strain behavior of confined concrete filled PVC tubes (CCFPT). Experimental studies clearly demonstrated that the CCFPT system outperforms conventional FRP jacket. The intermediate energy dissipation medium is critical to make the post-peak behavior more ductile. Analytical studies were conducted and equations were derived for the prediction of the ultimate strength and strain of a CCFPT system --Abstract, page iv

Post-earthquake damage classification and assessment: case study of the residential buildings after the Mw = 5 earthquake in Mila city, Northeast Algeria on August 7, 2020

On August 7th, 2020, a magnitude Mw = 5.0 earthquake shook 5 km north of Mila city center, northeast of Algeria, causing substantial damage directly to structures, and indirectly from induced impacts of landslides and rock falls, ultimately disrupt to everyday civilian life. Given the recent significant seismic occurrences in the region, a detailed and comprehensive examination and assessment of post-earthquake damage is critical to Algeria. This is primarily because masonry, concrete, and colonial-era structures are sensitive to horizontal motions caused by seismic waves, and because masonry and concrete structures constitute a substantial portion of today’s Algeria's build environment. We present a post-earthquake investigation of the Mila earthquake, starting from the earthquake source, and a catalogue of buildings type, damage categorization, and failure patterns of residential structures in Mila's historic old town, where colonial-era brick buildings prevail. We find that structures that represent notable architectural achievements were severely damaged as a result of the earthquake. Data acquired during the immediate post-earthquake analysis was also evaluated and discussed. The graphical representations of the damages are detailed and complemented by photos. This seismic event has shown the fragility of Algeria's building stock, which must be addressed properly in future years. This study reports on an overall estimate of residential buildings in Mila's lower city, as well as an evaluation of the seismic vulnerability of three neighborhood towns (El-Kherba, Grareme-Gouga, and Azzeba). A generic database for graphical surveys and geometric research was developed and implemented making it possible to evaluate the shear strength on-site. The broad observations, collated data, and consequences were then loaded into the 3Muri structural verification program. Nonlinear static analysis was conducted to analyze probable failure paths and compare the real damage to the software results.publishe

Proceedings of IWAMISSE 2018 the International Workshop on Advanced Materials and Innovative Systems in Structural Engineering: Seismic Practices

The International Workshop on Advanced Materials and Innovative Systems in Structural Engineering: Seismic Practices, IWAMISSE 2018, is co-organised by The International Federation for Structural Concrete Turkey Branch, fib-Turkey, and Istanbul Technical University, ITU, on November 16, 2018 at ITU. The International Federation for Structural Concrete, fib, is a not-for-profit association formed by 45 national member groups and approximately 1000 corporate and individual members. The fib’s mission is to develop at an international level the study of scientific and practical matters capable of advancing the technical, economic, aesthetic and environmental performance of concrete construction. Istanbul Technical University (ITU) was established in 1773 and is a state university which defined and continues to update methods of engineering and architecture in Turkey. It provides its students with innovative educational facilities while retaining traditional values, as well as using its strong international contacts to mould young, talented individuals who can compete not only within their country borders but also in the global arena. With its educational facilities, social life and strong institutional contacts, ITU has always been preferred by Turkey’s most distinguished students since its foundation and has achieved justified respect. The workshop covers the topics of advanced materials and innovative systems in structural engineering with a focus on seismic practices as well as other issues related with steel fiber reinforced concrete, anchors/fasteners, precast structures, and recent advances on different types of structural systems such as reinforced concrete, steel, and reinforced masonry structures. This proceeding book contain sixteen papers from ten countries worldwide. We have no doubt that the up-to-date subjects covered during the workshop will be extremely beneficial for the workshop participants both from academia and industry. We would like to thank all authors for their contributions to the workshop as well as the members of the International Scientific Committee for their rigorous work for reviewing the papers. We also gratefully acknowledge the support of the sponsoring companies and we express our sincere thanks to organization committee for their tireless efforts in the overall organization of the workshop. Many thanks go as well to undergraduate and graduate students from ITU for their assistance during all stages of the workshop

Integrated nonlinear modelling strategies for the seismic analysis of masonry structures

In the last decades, significant interest has raised in modelling and analysing the structural response of unreinforced masonry (URM) buildings. This aims at conceiving and designing effective interventions to reduce the vulnerability towards seismic actions. Studies based on costly structural testing are often limited to few benchmark cases, making numerical modelling an excellent option to extend experimental results and a valid solution for understanding URM structural behaviour. Advanced discrete models are widely employed among the available numerical strategies to predict the URM dynamic response, thanks to their ability to account for the heterogeneous nature of masonry and to simulate its behaviour up to the complete collapse. If, on the one hand, the low degree of idealisation of discrete models allows their employment for the extension of experimental tests, on the other hand, they require expert users, the definition of a large number of mechanical parameters and a high computational effort. This last drawback often limits the use of advanced discontinuum models in the engineering practice or for seismic risk studies, which require the execution of multiple analyses. In this work, a modelling approach, based on the Applied Element Method (AEM), was combined with more simplified models to exploit the discrete model potential and overcome its limits. To this aim, the AEM was employed as a benchmark to calibrate/validate simplified modelling strategies, improving their reliability when compared to advanced model outcomes. In this context, AEM models were used as a reference to enhance the Equivalent Frame Model (e.g. the presence of irregular distribution of openings) and to validate a new strength criterion associated with the failure mechanism encountered in a new masonry typology. In the absence of a large suite of experimental tests exploring all the possible setup or configurations, the AEM can provide precious information. On the other hand, the AEM can help to investigate situations requiring a higher level of detail, such as the design of the timber retrofitting system analysed in this work. The ability of the AEM to simulate the structural behaviour up to the complete collapse was also used to investigate the effect of different percentages of ground floor opening on the dynamic response of Dutch terraced houses, performing benchmark analyses to calibrate SDOF models employed for the development of fragility functions associated with the different layouts. Finally, AEM models were employed for substructuring façade models of masonry buildings whose global response was effectively studied by equivalent frame models. The aim of the study was to predict the debris extent involved in the collapse of URM façades in case of earthquake loadings. Such an integrated numerical procedure allowed considering a large suite of seismic inputs, overcoming the time-consuming issue

Assessment of seismic performance of reinforced concrete frame buildings with or without infill wall in Bhutan

This study is the first comprehensive research work undertaken on the seismic performance of the masonry infilled reinforced concrete frame buildings in Bhutan. An extensive numerical investigation is carried out and probabilistically predicted the damages of the existing buildings in Bhutan under the expected earthquake ground motions. The findings from this study would go a long way in saving the lives of the people and their properties from the earthquakes in the future