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Maria Mavragani - One of the best experts on this subject based on the ideXlab platform.

  • Root resorption after leveling with super-elastic and conventional Steel Arch wires: a prospective study
    Progress in Orthodontics, 2014
    Co-Authors: Kawa Alzahawi, Espen Færøvig, Pongsri Brudvik, Maria Mavragani
    Abstract:

    Background The aim of this prospective study was to compare root resorption after the leveling phase of treatment, performed by either super-elastic or conventional multi-stranded stainless Steel Arch wires. Methods From a total of 156 future orthodontic patients in a private clinic, 82 were included in the study after excluding those who earlier had orthodontic or endodontic treatment or signs of resorption. Patients were equally arbitrary allocated into two groups, where leveling was performed either with super-elastic heat-activated or conventional multi-stranded stainless Steel Arch wires. Root length loss was calculated using pre-treatment and post-leveling periapical radiographs. Results The use of super-elastic Arch wires did not significantly increase the severity of root resorption, except for tooth 31, while it reduced leveling time compared to conventional stainless Steel wires. Crossbite of maxillary lateral incisors seemed to be a risk factor for resorption. Conclusion Incisor root resorption after leveling did not differ significantly between patients treated with super-elastic and conventional stainless Steel Arch wires, except for a mandibular incisor.

  • Root resorption after leveling with super-elastic and conventional Steel Arch wires: a prospective study.
    Progress in orthodontics, 2014
    Co-Authors: Kawa Alzahawi, Espen Færøvig, Pongsri Brudvik, Olav E. Bøe, Maria Mavragani
    Abstract:

    The aim of this prospective study was to compare root resorption after the leveling phase of treatment, performed by either super-elastic or conventional multi-stranded stainless Steel Arch wires. From a total of 156 future orthodontic patients in a private clinic, 82 were included in the study after excluding those who earlier had orthodontic or endodontic treatment or signs of resorption. Patients were equally arbitrary allocated into two groups, where leveling was performed either with super-elastic heat-activated or conventional multi-stranded stainless Steel Arch wires. Root length loss was calculated using pre-treatment and post-leveling periapical radiographs. The use of super-elastic Arch wires did not significantly increase the severity of root resorption, except for tooth 31, while it reduced leveling time compared to conventional stainless Steel wires. Crossbite of maxillary lateral incisors seemed to be a risk factor for resorption. Incisor root resorption after leveling did not differ significantly between patients treated with super-elastic and conventional stainless Steel Arch wires, except for a mandibular incisor.

Kawa Alzahawi - One of the best experts on this subject based on the ideXlab platform.

  • Root resorption after leveling with super-elastic and conventional Steel Arch wires: a prospective study
    Progress in Orthodontics, 2014
    Co-Authors: Kawa Alzahawi, Espen Færøvig, Pongsri Brudvik, Maria Mavragani
    Abstract:

    Background The aim of this prospective study was to compare root resorption after the leveling phase of treatment, performed by either super-elastic or conventional multi-stranded stainless Steel Arch wires. Methods From a total of 156 future orthodontic patients in a private clinic, 82 were included in the study after excluding those who earlier had orthodontic or endodontic treatment or signs of resorption. Patients were equally arbitrary allocated into two groups, where leveling was performed either with super-elastic heat-activated or conventional multi-stranded stainless Steel Arch wires. Root length loss was calculated using pre-treatment and post-leveling periapical radiographs. Results The use of super-elastic Arch wires did not significantly increase the severity of root resorption, except for tooth 31, while it reduced leveling time compared to conventional stainless Steel wires. Crossbite of maxillary lateral incisors seemed to be a risk factor for resorption. Conclusion Incisor root resorption after leveling did not differ significantly between patients treated with super-elastic and conventional stainless Steel Arch wires, except for a mandibular incisor.

  • Root resorption after leveling with super-elastic and conventional Steel Arch wires: a prospective study.
    Progress in orthodontics, 2014
    Co-Authors: Kawa Alzahawi, Espen Færøvig, Pongsri Brudvik, Olav E. Bøe, Maria Mavragani
    Abstract:

    The aim of this prospective study was to compare root resorption after the leveling phase of treatment, performed by either super-elastic or conventional multi-stranded stainless Steel Arch wires. From a total of 156 future orthodontic patients in a private clinic, 82 were included in the study after excluding those who earlier had orthodontic or endodontic treatment or signs of resorption. Patients were equally arbitrary allocated into two groups, where leveling was performed either with super-elastic heat-activated or conventional multi-stranded stainless Steel Arch wires. Root length loss was calculated using pre-treatment and post-leveling periapical radiographs. The use of super-elastic Arch wires did not significantly increase the severity of root resorption, except for tooth 31, while it reduced leveling time compared to conventional stainless Steel wires. Crossbite of maxillary lateral incisors seemed to be a risk factor for resorption. Incisor root resorption after leveling did not differ significantly between patients treated with super-elastic and conventional stainless Steel Arch wires, except for a mandibular incisor.

Jin Cheng - One of the best experts on this subject based on the ideXlab platform.

  • Reliability analysis of a long span Steel Arch bridge against wind-induced stability failure during construction
    Journal of Constructional Steel Research, 2009
    Co-Authors: Jin Cheng
    Abstract:

    Abstract An efficient and accurate algorithm is proposed to evaluate the reliability of long span Steel Arch bridges against wind-induced stability failure during construction. The algorithm is developed based on stochastic finite-element method. Uncertainties in static wind load-related parameters are incorporated in the algorithm. The proposed algorithm integrates the finite-element method and the first-order reliability method. A long span Steel Arch bridge with a main span length of 550 m built in China is considered as an illustrative example. Two different construction stages are chosen for reliability analysis. Construction stage I involves the construction process before closure of main Arch ribs. At Construction stage II, all remaining parts of the bridge have been completed except the stiffening girder of the main span. Three components of wind loads (drag force, lift force and pitch moment) acting on both Steel girder and Arch ribs are considered in the study. Results of the study show that the Steel Arch bridge at construction stage II is more vulnerable to wind-induced stability failure than that at construction stage I. Further, a detailed parametric study show that the variations of wind speed with height, drag force of wind loads, design wind speed at the bridge site and static aerodynamic coefficients have significant effects on the probability of wind-induced stability failure during the construction stages for the Steel Arch bridge.

  • ultimate load carrying capacity of the lu pu Steel Arch bridge under static wind loads
    Computers & Structures, 2003
    Co-Authors: Jin Cheng, Jian-jing Jiang, R.-c. Xiao, H F Xiang
    Abstract:

    This paper investigates the ultimate load carrying capacity of the Lu Pu Bridge under static wind loads through the spatial finite element model. Both geometric and material nonlinearities are involved in the analysis. The Lu Pu Bridge is a long-span half-through-type Steel Arch bridge with a 550 m-long central span under construction in Shanghai, China. This will be the longest central span of any Arch bridge in the world. Three load combinations are used in the ultimate load capacity analysis of the bridge. Combination I: combined dead and live loads over the entire bridge. Combination II: combined dead and wind loads. Combination III: combined dead load, wind load and live load over the entire bridge. Ultimate load capacity of the bridge is first investigated under load combinations I and II. Attention is paid mainly to investigate the load capacity of the bridge under load combination III. In the case of load combination III, the influences of several parameters (i.e., loading sequence, three components of wind loads and wind loads of individual bridge element) on the ultimate load capacity of the bridge are discussed. It is concluded that wind loads result in significant reduction in the ultimate load capacity when applied wind loads become large.

  • Ultimate behavior of long-span Steel Arch bridges
    Structural Engineering and Mechanics, 2002
    Co-Authors: Jin Cheng, Jian-jing Jiang, R.-c. Xiao, H F Xiang
    Abstract:

    Because of the increasing span of Arch bridges, ultimate capacity analysis recently becomes more focused both on design and construction. This paper investigates the static and ultimate behavior of a long-span Steel Arch bridge up to failure and evaluates the overall safety of the bridge. The example bridge is a long-span Steel Arch bridge with a 550 m-long central span under construction in Shanghai, China. This will be the longest central span of any Arch bridge in the world. Ultimate behavior of the example bridge is investigated using three methods. Comparisons of the accuracy and reliability of the three methods are given. The effects of material nonlinearity of individual bridge element and distribution pattern of live load and initial lateral deflection of main Arch ribs as well as yield stresses of material and changes of temperature on the ultimate load-carrying capacity of the bridge have been studied. The results show that the distribution pattern of live load and yield stresses of material have important effects on bridge behavior. The critical load analyses based on the linear buckling method and geometrically nonlinear buckling method considerably overestimate the load-carrying capacity of the bridge. The ultimate load-carrying capacity analysis and overall safety evaluation of a long-span Steel Arch bridge should be based on the geometrically and materially nonlinear buckling method. Finally, the in-plane failure mechanism of long-span Steel Arch bridges is explained by tracing the spread of plastic zones.

  • Ultimate load carrying capacity of long-span Steel Arch bridges
    2002
    Co-Authors: Jin Cheng, Jian-jing Jiang, R.-c. Xiao, H F Xiang
    Abstract:

    This paper investigates the ultimate load carrying capacity of a long-span Steel Arch bridge up to failure and evaluates the overall safety of the bridge. The example bridge is a long-span Steel Arch bridge with a 550 m-long central span under construction in Shanghai, China. Ultimate load carrying capacity of the bridge is investigated using three methods. Comparisons of the accuracy and reliability of the three methods are given. A parametric study is conducted to investigate the effects of various parameters on the ultimate load-carrying capacity of the bridge. The results show that the distribution pattern of live load and yield stresses of material have important effects on bridge behaviour.

Tsutomu Usami - One of the best experts on this subject based on the ideXlab platform.

  • seismic demand of buckling restrained braces installed in Steel Arch bridges under repeated earthquakes
    Journal of Earthquake and Tsunami, 2011
    Co-Authors: Xi Chen, Hanbin Ge, Tsutomu Usami
    Abstract:

    A Steel Arch bridge originally designed against moderate earthquakes is retrofitted by installation of buckling-restrained braces (BRBs) to sustain severe earthquakes. Two retrofitting methods are considered to obtain good seismic performance of this Arch bridge. The original model and retrofitted models subjected to the major earthquakes are investigated by dynamic analyses using 12 patterns of severe (level 2) earthquakes as input ground motions. It is found that the retrofitted models using BRBs can greatly improve seismic performance (displacement, section force, strain, reaction force, etc.) of the Steel Arch bridge. In addition, to investigate the influence of repeated earthquakes on the seismic responses of the main structure and the demands of BRBs, 12 patterns of earthquake ground motions are repeated by three times. Based on the analytical results, the seismic demands of BRBs against repeated earthquakes are obtained, and the required capacity of BRBs is recommended using a safety factor concluded by comparing the demands under the earthquake applied one and three times. Finally, the influence of the different yield stress on the demand of BRBs is examined by changing the Steel grade of BRBs.

  • a seismic upgrading method for Steel Arch bridges using buckling restrained braces
    Earthquake Engineering & Structural Dynamics, 2005
    Co-Authors: Tsutomu Usami, Zhihao Lu, Hanbin Ge
    Abstract:

    In this study the employment of buckling-restrained braces (BRBs) as energy dissipation dampers is attempted for seismic performance upgrading of Steel Arch bridges and the effectiveness of BRBs to protect structures against strong earthquakes is numerically studied. With buckling restrained, BRB members can provide stable energy dissipation capacity and thus damage of the whole structure under major earthquakes can be mitigated. Cyclic behaviour of such members is addressed with a numerical simulation model, and a strength design method for BRBs is proposed. BRBs are then placed at certain locations on the example Steel Arch bridge to replace some normal members with two schemes, and the effect of the two installation schemes of BRBs for seismic upgrading is investigated by non-linear time-history analyses under various ground motions representing major earthquake events. Compared with the seismic behaviour of the original structure without BRBs, satisfactory seismic performance is seen in the upgraded models, which clarifies the effectiveness of the proposed upgrading method and it can serve as an efficient solution for earthquake-resistant new designs and retrofit of existing Steel Arch bridges. Copyright © 2005 John Wiley & Sons, Ltd.

  • Seismic performance upgrading of Steel Arch bridges using brace dampers against longitudinal directional earthquake motions
    Fourth International Conference on Advances in Steel Structures, 2005
    Co-Authors: Kenji Hioki, Tsutomu Usami, Tetsuhiko Aoki
    Abstract:

    Publisher Summary The chapter discusses the seismic performance upgrading of Steel–Arch bridges using brace dampers against longitudinal-directional earthquake motions. Seismic performance upgrading and retrofit approaches are of great significance for aseismic consideration for Steel–Arch bridges against major earthquakes. The chapter presents a seismic performance upgrading approach for Steel–Arch bridges using buckling-restrained braces as dampers against longitudinal-directional earthquake motions. Inelastic behavior of a representative Steel–Arch bridge with buckling-restrained braces is investigated by three-dimensional modeling time-history analyses and compared with the result from the original structure. It is found that the replacement of diagonals of some parts by buckling-restrained braces can greatly improve seismic performances of the Steel–Arch bridge.

  • seismic performance evaluation of Steel Arch bridges against major earthquakes part 2 simplified verification procedure
    Earthquake Engineering & Structural Dynamics, 2004
    Co-Authors: Zhihao Lu, Tsutomu Usami, Hanbin Ge
    Abstract:

    The performance-based philosophy has been accepted as a more reasonable design concept for engineering structures. For this purpose, capacity evaluation and demand prediction procedures for civil engineering structures under earthquake excitations are of great significance. This work presents a displacement-based seismic performance verification procedure including capacity and seismic demand predictions for Steel Arch bridges and investigates its applicability. Pushover analyses is employed as a basis in this method to investigate the structure's behaviors. A failure criterion for Steel members accounting for the effect of local buckling is involved and an equivalent single-degree-of-freedom (ESDOF) system with a simplified bilinear hysteretic model formulated using pushover analyses results is introduced to estimate the displacement capacity and maximum demand of Steel Arch bridges under major earthquakes. To check the accuracy of the proposed method, seismic capacities and demands from multi-degree-of-freedom (MDOF) time-history analyses with Level-II design earthquake record inputs modeling major earthquakes are used as benchmarks for comparison. By a case study, it is clarified that the proposed prediction procedure can give accurate estimations of displacement capacities and demands of the Steel Arch bridge in the transverse direction, while insufficient for the longitudinal direction, which confirms the conclusion drawn in other structure types about the applicability of pushover analyses.

  • seismic performance evaluation of Steel Arch bridges against major earthquakes part 1 dynamic analysis approach
    Earthquake Engineering & Structural Dynamics, 2004
    Co-Authors: Tsutomu Usami, Zhihao Lu, Hanbin Ge, Takeshi Kono
    Abstract:

    In this study the inelastic behavior of Steel Arch bridges subjected to strong ground motions from major earthquakes is investigated by dynamic analyses of a typical Steel Arch bridge using a three-dimensional (3D) analytical model, since checking seismic performance against severe earthquakes is not usually performed when designing such kinds of bridge. The bridge considered is an upper-deck Steel Arch bridge having a reinforced concrete (RC) deck, Steel I-section girders and Steel Arch ribs. The input ground motions are accelerograms which are modified ground motions based on the records from the 1995 Hyogoken-Nanbu earthquake. Both the longitudinal and transverse dynamic characteristics of the bridge are studied by investigation of time-history responses of the main parameters. It is found that seismic responses are small when subjected to the longitudinal excitation, but significantly large under the transverse ground motion due to plasticization formed in some segments such as Arch rib ends and side pier bases where axial force levels are very high. Finally, a seismic performance evaluation method based on the response strain index is proposed for such Steel bridge structures. Copyright © 2004 John Wiley & Sons, Ltd.

Hanbin Ge - One of the best experts on this subject based on the ideXlab platform.

  • seismic demand of buckling restrained braces installed in Steel Arch bridges under repeated earthquakes
    Journal of Earthquake and Tsunami, 2011
    Co-Authors: Xi Chen, Hanbin Ge, Tsutomu Usami
    Abstract:

    A Steel Arch bridge originally designed against moderate earthquakes is retrofitted by installation of buckling-restrained braces (BRBs) to sustain severe earthquakes. Two retrofitting methods are considered to obtain good seismic performance of this Arch bridge. The original model and retrofitted models subjected to the major earthquakes are investigated by dynamic analyses using 12 patterns of severe (level 2) earthquakes as input ground motions. It is found that the retrofitted models using BRBs can greatly improve seismic performance (displacement, section force, strain, reaction force, etc.) of the Steel Arch bridge. In addition, to investigate the influence of repeated earthquakes on the seismic responses of the main structure and the demands of BRBs, 12 patterns of earthquake ground motions are repeated by three times. Based on the analytical results, the seismic demands of BRBs against repeated earthquakes are obtained, and the required capacity of BRBs is recommended using a safety factor concluded by comparing the demands under the earthquake applied one and three times. Finally, the influence of the different yield stress on the demand of BRBs is examined by changing the Steel grade of BRBs.

  • a seismic upgrading method for Steel Arch bridges using buckling restrained braces
    Earthquake Engineering & Structural Dynamics, 2005
    Co-Authors: Tsutomu Usami, Zhihao Lu, Hanbin Ge
    Abstract:

    In this study the employment of buckling-restrained braces (BRBs) as energy dissipation dampers is attempted for seismic performance upgrading of Steel Arch bridges and the effectiveness of BRBs to protect structures against strong earthquakes is numerically studied. With buckling restrained, BRB members can provide stable energy dissipation capacity and thus damage of the whole structure under major earthquakes can be mitigated. Cyclic behaviour of such members is addressed with a numerical simulation model, and a strength design method for BRBs is proposed. BRBs are then placed at certain locations on the example Steel Arch bridge to replace some normal members with two schemes, and the effect of the two installation schemes of BRBs for seismic upgrading is investigated by non-linear time-history analyses under various ground motions representing major earthquake events. Compared with the seismic behaviour of the original structure without BRBs, satisfactory seismic performance is seen in the upgraded models, which clarifies the effectiveness of the proposed upgrading method and it can serve as an efficient solution for earthquake-resistant new designs and retrofit of existing Steel Arch bridges. Copyright © 2005 John Wiley & Sons, Ltd.

  • seismic performance evaluation of Steel Arch bridges against major earthquakes part 2 simplified verification procedure
    Earthquake Engineering & Structural Dynamics, 2004
    Co-Authors: Zhihao Lu, Tsutomu Usami, Hanbin Ge
    Abstract:

    The performance-based philosophy has been accepted as a more reasonable design concept for engineering structures. For this purpose, capacity evaluation and demand prediction procedures for civil engineering structures under earthquake excitations are of great significance. This work presents a displacement-based seismic performance verification procedure including capacity and seismic demand predictions for Steel Arch bridges and investigates its applicability. Pushover analyses is employed as a basis in this method to investigate the structure's behaviors. A failure criterion for Steel members accounting for the effect of local buckling is involved and an equivalent single-degree-of-freedom (ESDOF) system with a simplified bilinear hysteretic model formulated using pushover analyses results is introduced to estimate the displacement capacity and maximum demand of Steel Arch bridges under major earthquakes. To check the accuracy of the proposed method, seismic capacities and demands from multi-degree-of-freedom (MDOF) time-history analyses with Level-II design earthquake record inputs modeling major earthquakes are used as benchmarks for comparison. By a case study, it is clarified that the proposed prediction procedure can give accurate estimations of displacement capacities and demands of the Steel Arch bridge in the transverse direction, while insufficient for the longitudinal direction, which confirms the conclusion drawn in other structure types about the applicability of pushover analyses.

  • seismic performance evaluation of Steel Arch bridges against major earthquakes part 1 dynamic analysis approach
    Earthquake Engineering & Structural Dynamics, 2004
    Co-Authors: Tsutomu Usami, Zhihao Lu, Hanbin Ge, Takeshi Kono
    Abstract:

    In this study the inelastic behavior of Steel Arch bridges subjected to strong ground motions from major earthquakes is investigated by dynamic analyses of a typical Steel Arch bridge using a three-dimensional (3D) analytical model, since checking seismic performance against severe earthquakes is not usually performed when designing such kinds of bridge. The bridge considered is an upper-deck Steel Arch bridge having a reinforced concrete (RC) deck, Steel I-section girders and Steel Arch ribs. The input ground motions are accelerograms which are modified ground motions based on the records from the 1995 Hyogoken-Nanbu earthquake. Both the longitudinal and transverse dynamic characteristics of the bridge are studied by investigation of time-history responses of the main parameters. It is found that seismic responses are small when subjected to the longitudinal excitation, but significantly large under the transverse ground motion due to plasticization formed in some segments such as Arch rib ends and side pier bases where axial force levels are very high. Finally, a seismic performance evaluation method based on the response strain index is proposed for such Steel bridge structures. Copyright © 2004 John Wiley & Sons, Ltd.

  • applicability of pushover analysis based seismic performance evaluation procedure for Steel Arch bridges
    Engineering Structures, 2004
    Co-Authors: Zhihao Lu, Hanbin Ge, Tsutomu Usami
    Abstract:

    An investigation on the application of a capacity and demand prediction procedure based on a nonlinear pushover analysis and an equivalent single-degree-of-freedom (ESDOF) system approximation for seismic performance evaluation of Steel Arch bridges, as well as limitations of the pushover analysis is presented here. The procedure is applied to the transverse direction of two representative Arch bridges with different spans for capacity and demand estimation. Displacement capacities are obtained by conducting pushover analysis until the ultimate state of the structure is reached, determined by a failure criterion proposed for thin-walled Steel members governed by the local buckling-induced failure. Displacement demands under major earthquakes are estimated by ESDOF systems formulated using pushover analysis results. Capacities and demands are then compared with those from rigorous nonlinear time–history analyses on multi-degree-of-freedom (MDOF) models for verification and acceptable accuracy of the pushover analysis-based procedure is evidenced. Furthermore, applicability of the pushover analysis involving the fundamental mode only for seismic performance evaluation is extensively investigated considering the higher mode effect. A factor to account for higher mode contribution to seismic response is proposed and an applicable range of using the pushover analysis is quantitatively specified.