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Investigating Stone Masonry Arch Bridges in Greece Employing In-situ Measurements and Numerical Predictions
Abstract
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.
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There are many historic stone arched bridges in Japan. To prevent their damage due to earthquakes and to leave them for posterity, it is important to understand their structural integrity and failure mechanism against earthquakes. In this study, dynamic behaviors of several stone arched bridges are simulated using the 3-dimentional DEM. Firstly, by inputting a impulse wave to the models as an input ground motion, their first natural frequencies in three directions are computed, and their vibration characteristics are investigated. Secondly, seismic behaviors are computed and the failure occurrence mechanism is investigated. Effects of the material properties of the backfill and the span length on seismic behaviors and failure patterns are also investigated. Finally, effectiveness of reinforcement by inserting mortar between stones is verified.
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.
Rakanji stone arch bridge built in 1920 over Yamakuni River, Honyabakei, Oita, has three spans of about 26m and total length of the bridge is about 89.3m. For the purpose of obtaining the data concerning dynamic structural properties of Rakanji stone arch bridge, both microtremor measurement by ambient vibrations and acceleration by traffic vibrations are measured. From the material tests, Young's modulus and compressive strength of the stone and the mortar are estimated to be 17000MPa, 5500MPa - 7800MPa, 28.5MPa and 4MPa - 9MPa, respectively. From the results of dynamic tests, the fundamental frequencies of Rakanji stone arch bridge are estimated to be about 5.3Hz and 7.6Hz in out-of-plane and vertical directions, respectively. Its natural modes are identified by ARMAV (Auto Regressive Moving Average) and ERA (Eigensystem Realization Algorithm) models comparing with the results obtained by FEA (Finite Element analysis).
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.
This paper reports on the sensitivity of earthquake response and damage of long span masonry stone bridges to near field (impulsive type) and far field earthquakes. Towards that objective, the Konitsa Bridge is used as a case study. The particular bridge was selected for offering certain unique features such as long span, built right on an active fault, survived a recent pair of near-filed type earthquakes with minimal damage and finally, construction material mechanical properties and strength could be deduced from a recently collapsed similar bridge in the area. The multifaceted study integrated in-situ measurements of dynamic characteristics, laboratory tests on representative stone and mortar materials and a series of finite-element analyses based on non-linear modelling using a combination of discontinuous and continuous representations to capture the behavior of bridge structural component interface and interaction as well as mortar-stone interaction and failure. In addition to the ground motion records of the recent seismic activity at the Konitsa Bridge location, four additional earthquake records representing near-field and far-field families were utilized to assess the stone bridge sensitivity. The study revealed that far-field earthquakes are far more destructive than near-field counterparts, a finding in full agreement with studies on near field earthquake effects on nuclear structures. The applicability of earthquake damage indicators such as CAV, Arias intensity and energy rate, typically used for conventional and nuclear structures, was evaluated based on the numerical analysis results.
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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