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IN-SITU MEASUREMENTS RELATED TO THE PERFORMANCE OF STONE MASONRY BRIDGES IN GREECE
... This fact combined with the resistance offered to this wind component by the facade of each bridge produced sufficient excitation source resulting in small amplitude vibrations that could be recorded by the employed instrumentation. The second type of excitation that was employed, namely vertical in-plane excitation, was produced from a sudden drop of a weight on the deck of each stone masonry bridge (Aoki et al. 2007;Manos et al. 2015aManos et al. ,2015bManos et al. , 2016Manos et al. , 2017Ozden et al 2012;Ruocci et al. 2013). ...
This study presents a method for validation of numerical models of stone masonry arch bridges using in-situ and laboratory measurements. These numerical models are utilized in assessing the expected performance of specific case studies of stone masonry bridge structures in Greece towards meeting the demands of extreme events that include design seismic loads. At first, the work focuses on in-situ measurements conducted at selected old stone masonry bridges, using up-to-date system identification techniques, in an effort to quantify their dynamic characteristics in terms of eigen-frequencies, eigen-modes and damping properties. This information provides a basis for realistic numerical simulations towards studying the structural behaviour of such stone masonry bridges and assessing their expected structural behaviour in extreme future seismic events. Selected in-situ measurements are presented together with their use in numerical models of various levels of complexity. Afterwards, a series of experimental tests are presented on bridge materials (stone blocks and mortar) and triplet shear and bending tests. Through the laboratory measurements non-linear constitutive material or interface laws are determined. Thus, the failure criteria of such structures are employed to 3d solid finite element models used for the seismic assessment of masonry bridge structures.
... Recently (7th December 2019), it was announced that the primary arch of the reconstructed new Plaka stone masonry bridge was completed by placing the top key stones at the top-middle of this primary arch. Manos et al. (2017) investigated, through a simplified linear analysis approach, the effect of the flooding forces acting on the Plaka bridge structure adopting the assumption that the foundation of its mid-pier footing was on a relatively flexible soil. ...
The present study presents a series of in-situ measurements conducted at selected old stone masonry bridges, using up-to-date system identification techniques, in an effort to identify their dynamic characteristics in terms of eigen-frequencies, eigen-modes and damping properties. All these information is part of a data base that can be used in the future as a reference for identifying noticeable changes in these dynamic characteristics as part of a structural health monitoring effort for these bridges. Moreover, this information provides a basis for build-ing realistic numerical simulations towards studying the structural behaviour of such stone masonry bridges and assessing their expected structural behaviour in extreme future seismic events. Selected in-situ measurements are presented together with their use in building numerical models of various levels of complexity. These numerical models are finally utilized in assessing the expected performance of specific case studies of stone masonry bridge structures in Greecetowards meeting the demands of extreme events that include design earth-quake loads. The described system identification technique can also be linked to specific actions, such as earthquake activity, and thus serve as warning for specific maintenance counter-measure.
Mexico has an important number of cities recognized by the UNESCO as World Heritage Site. Many of them have highway and railway bridges with an important historical value product of the construction techniques and materials implemented in those days. In spite of their importance, very few efforts have been led to study the masonry historic bridges’ origin and pathologies that eventually would conduct to a failure condition. The main objectives of this work are to identify the dynamic properties of the masonry historic bridges, to characterize, in a second stage, bridges pathologies, to develop numerical models that allow the correct identification of the structural components of the bridges and subsequently to identify the damage mechanisms of this type of structures, and finally to evaluate the influence of the epicentral distance and seismic fault on the seismic vulnerability of the bridges. The study determines the dynamic properties of five existing historical bridges by conducting a campaign of ambient vibration tests. These results allowed to calibrate numerical models used to construct fragility curves and to determine the seismic vulnerability of the bridges.
The study presents the results of an investigation that identifies among the available records in Greece those that reveal near-source characteristics, using a procedure based on damage potential parameters. The findings reaffirm the opinion that earthquakes with magnitude less than M ¼ 6.0 present near-source phenomena that can cause severe damage to relatively stiff structures, common in urban areas. Spectra from selected accelerograms of near-source records are compared with the corresponding elastic spectra of the current Greek Seismic Code, (EAK 2000), the impulsive character of the Greek near-source records is ascertained and shortcomings of EAK 2000 to account for near-source effects are demonstrated. Based on records from seismic events in Greece and records from international earthquakes of small-to-moderate magnitude, the study demonstrates that there exists a near-source magnitude-distance region, where the velocity pulses have smaller amplitude and period in comparison with earthquakes of great magnitude. A simplified representation of three pulse types is, also, adopted for near-source events. It is found that the type-A pulse related to permanent displacement phenomena does not characterize Greek records. In addition a simple criterion is developed to identify the most appropriate simplified pulse type for near-source seismic events independently of magnitude. r
The Summary results from a series of field experiments at a test site in Greece are presented, involving an in situ instrumented bridgepier model built on realistic foundation conditions, to study the dynamic behavior of structure-foundation-soil system. It was attempted to link the variation of its dynamic characteristics to certain changes in its structural system, including the development of structural damage. This measured response was next utilized to validate numerical tools capable of predicting influences arising from such structural changes as well as from soil-foundation interaction. This bridge-pier model was supported on soft soil deposits allowing the study of structure-foundation-soil interaction effects during low-to-medium intensity artificial excitations. The in situ experiments provided measurements that were used to verify fundamental analytical solutions for soil-structure interaction. They were also used to validate numerical simulations that were developed to predict the response of the studied structure and thus, back-evaluate modeling assumptions. The obtained accuracy of the numerical predictions must be partly attributed to sound knowledge of the mechanical properties of the pier model and of the soil, not necessarily the case in all practical applications. It is evident that more complex finite-element models can improve the quality of the prediction only in cases where their parameters can be defined equally well. A special study further focused on the radiation of the waves generated by the vibration of the bridge-pier model through the soil medium. It is deemed that this comprehensive experimental investigation of soil-structure interaction provides measurements of the system response and enhances our understanding of the physical phenomenon as a whole. (C) 2014 American Society of Civil Engineers.
Assessment of a monumental concrete arch bridge with a total length of 210 meters having three major spans of 30 meters and a height of 65 meters, which is located in an earthquake-prone region in southern part of the country is presented in this study. Three-dimensional finite element model of the bridge was generated using a commercially available general finite element analysis software and based on the outcomes of a series of in-depth acceleration measurements that were conducted on-site, the model was refined. By using the structural parameters obtained from the dynamic and the static tests, calibrated model of the bridge structure was obtained and this model was used for necessary calculations regarding structural assessment and evaluation.
The subject of earthquake engineering has been the focus of my teaching and research for many years. Thus, when Mario Paz, the editor of this handbook, asked me to write a Foreword, I was interested and honored by his request. Worldwide, people are beginning to understand the severity of the danger to present and future generations caused by the destruction of the environment. Earthquakes pose a similar threat; thus, the proper use of methods for earthquake-resistant design and construction is vitally important for countries that are at high risk of being subjected to strong-motion earthquakes. Most seismic activity is the result of tectonic earthquakes. Tectonic earthquakes are very special events in that, although they occur frequently, their probability of becoming natural hazards for a specific urban area is very small. When a severe earthquake does occur near an urban area, however, its consequences are very large in terms of structural destruction and human suffering.
Past earthquake disasters in Greece, during the last thirty years, demonstrate that the severity of destruction is not only due to the intensity of the seismic event but also to the urbanization of the affected region and the vulnerability of certain types of buildings. Considerable damage was sustained by both old unreinforced masonry structures as well as by relatively new multistory reinforced concrete structures with "soft story" at their ground floor level. The most important observations made during six past earthquake disasters are presented in a summary form and discussed. The most remarkable case of extensive structural damage was caused from the resent Athens 1999 earthquake. The consequent discussion focuses on the following issues: (1) Classification of structural damage and their underlying causes. (2) Repair and strengthening of damaged structures. (3) Upgrade the seismic design. (4) Plans for earthquake preparedness. (5) Assessing the vulnerability of certain type of structures (schools, hospitals, public buildings etc). (6) Education specialized in earthquake engineering. (7) The enrichment of the strong motion data base.
The focus of this paper is to illustrate the importance of model calibration and in situ vibration testing by comparing the finite element model predictions of the earthquake response of the two historical arch bridges, Osmanlı and Şenyuva, before and after model calibration. The three-dimensional finite element models of these two arch bridges, built in the ANSYS finite element program, are used to predict bridge dynamic characteristics, such as natural frequencies and mode shapes. Following the analytical study, ambient vibration tests were conducted to experimentally obtain dynamic characteristics of these two bridges. During ambient vibration tests, accelerometers were placed at several points on the bridge to collect the vibration response due to natural and operational excitation sources. Enhanced frequency domain decomposition and stochastic subspace identification techniques were used to extract the experimental natural frequencies, mode shapes and damping ratios. Finite element models of the two arch bridges were adjusted such that the model predictions reproduce the ambient vibration test results with increased fidelity. The behavior of the masonry arch bridges under earthquake excitation recorded during the Erzincan Earthquake in 1992 is simulated by both the initial and adjusted finite element models. The findings of this study emphasize the importance of model calibration and ambient vibration testing.
In this paper is studied the ultimate failure (limit) load of stone arch bridges. The proposed model is based on finite element analysis with interfaces, simulating potential cracks, which allow for unilateral contact with friction. Opening or sliding of some interface indicates crack initiation. The ultimate load has been calculated by using a path-following (load incrementation) technique. Lack of a solution at a certain level of loading indicates onset of failure. For the validation of the proposed method, which is based on the contact model, the ultimate failure load is recalculated by using a modern implementation of the classical collapse mechanism method based on linear programming. Finally, the beneficial effect of the fill on the limit load of a real bridge is estimated and compared with experimental results.
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Experimental Testing of a Masonry Arch Bridge Model Subject to Increasing Level of Damage
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