•The influence of axial force is evaluated on M-V interaction.•Corrosion is considered for prestressed tendons.•Bending shear interaction domains are provided for prestressed structures.•The proposed ...procedure can be applied to new and existing prestressed bridges.•The case-study of the Polcevera viaduct in Italy is presented.
Existing prestressed concrete structures suffer from degradation of prestressing for two main reasons: a defect of the sheath infills (cement grout) of bonded tendons, and corrosion of steel strands. These two causes, often concomitant, lead to a reduction over time of the effectiveness of initial prestressing, in addition to the ordinary tension losses due to concrete shrinkage and creep, and to steel relaxation. In many cases a consequence of bad grouting in bonded tendons is that the structure shows an intermediate behavior between that of external prestressing and that of internal bonded prestressing. This, added to damage to wires due to corrosion, makes it essential for the designer to be able to check sections of existing structures considering the interaction between the characteristics of the stress together with the changing state of tendons.
In this paper a methodology for performing safety checks through M-V interaction domains with axial force N due to prestressing and external loads in the structural scheme is presented. The modification of the behavior between the intact and the degraded section due to corrosion and the consequences of bond loss are shown and discussed together with the influence of compressive axial force due to the structural scheme. Finally, an application is proposed on an emblematic case study: the deck sections of the Polcevera viaduct in Genoa.
It is considered that the best way to calculate the earthquake response of sheds on viaducts, is to use an integral model of the shed and the viaduct. Calculations based on integral models require a ...vast amount of work because of the need to understand the structural design of both the shed and the viaduct. This report describes the factors affecting the earthquake response of sheds. A method is proposed for estimating the maximum response displacement of sheds considering the coupled vibration behavior between the shed and the viaduct based on structural design information obtained for the shed and the viaduct. The applicability of this method was verified under the earthquake conditions that appear in the seismic design standards for railway structures.
Computational fluid dynamics simulations were performed to investigate flow and pollutant dispersion in a 2D street canyon of aspect ratio
H
/
W
= 1. Different from other works, the combination of ...the presence of viaduct and indoor-outdoor temperature differences Δ
T
is investigated for different approaching wind velocities. For larger wind velocity (2 m/s, Froude number
Fr
~3.06–12.24) the typical clockwise vortex leads to higher concentrations of both gas and small particles at the leeward side of the street and in the leeward-side rooms; the vortex is enhanced under large Δ
T
(20 K) improving the dispersion of pollutants. For smaller velocity (0.5 m/s,
Fr
~0.19–0.77) the appearance of an anti-clockwise vortex leads to a strong accumulation of gas and particles at the windward side and in the windward-side rooms under low Δ
T
(5 K); increasing the Δ
T
raises the dispersion of pollutants with consequent lower concentrations in the rooms (up to an average of 67% with respect to the isothermal case for gaseous pollutants), but accumulation close to the ground level at both windward-side and leeward-side rooms. In the presence of viaduct, together with the main vortex above the viaduct which causes concentrations increasing from low-level to high-level leeward-side rooms, two vortices are generated below it. Still Δ
T
= 20 K improves the dispersion of pollutants, leading up to a maximum of about 30% lower gaseous concentrations in the rooms. In general, lower concentrations of gas and particles are found for larger velocity, indicating that the mechanical turbulence dominates over the buoyancy effects, which become crucial for smaller velocity. This study confirms previous findings that viaducts may improve pollutant dispersion under large velocity if only one viaduct-level pollutant source exists and indoor-outdoor Δ
T
conditions can mitigate street air pollution.
The development and utilization of underground space is an effective way to make intensive use of resources, solve "big city disease" and achieve high-quality development. The expansion and ...renovation of underground space in a central urban area is likely to cause serious damage to surrounding structures. In this study, a deep foundation excavation for the reconstruction of an urban subway station in the Greater Bay Area was chosen for analysis using the finite element method. Different from common excavation engineering, the interaction between the three coupling factors of train dynamic load, foundation excavation, and viaduct pile foundation were analyzed. Six different cases were calculated considering different working conditions of excavation depth and train dynamic load. Soil was evaluated using modified Cam-Clay model. The physical parameters of the soil were determined through on-site and laboratory tests. The results were compared with monitoring data, and the accuracy of the finite element model was verified. The settlement and influence range of the soil, and displacement and internal forces of viaduct piles were analyzed. The maximum settlement of the soil occurred in the direction of the short side of the foundation pit. The maximum value was approximately 0.53 times the excavation depth. The settlement increased by approximately 49% when applying the train load. The dynamic load had an aggravating influence on the horizontal displacement of the top of the pile, with a maximum increase of 51%. Moreover, the dynamic load increased the negative bending moment of the viaduct piles. This study provides a reference for the design and construction of geotechnical engineering projects.
Most finite element model updating (FEMU) studies on bridges are acceleration-based due to their lower cost and ease of use compared to strain- or displacement-based methods, which entail costly ...experiments and traffic disruptions. This leads to a scarcity of comprehensive studies incorporating strain measurements. This study employed the strain- and acceleration-based FEMU analyses performed on a more than 50-year-old multi-span concrete highway viaduct. Mid-span strains under heavy vehicles were considered for the strain-based FEMU, and frequencies and mode shapes for the acceleration-based FEMU. The analyses were performed separately for up to three variables, representing Young's modulus adjustment factors for different groups of structural elements. FEMU studies considered residual minimisation and the error-domain model falsification (EDMF) methodology. The residual minimisation utilised four different single-objective optimisations focusing on strains, frequencies, and mode shapes. Strain- and frequency-based FEMU analyses resulted in an approximately 20% increase in the overall superstructure's design stiffness. This study shows the benefits of the intuitive EDMF over residual minimisation for FEMU, where information gained from the strain data, in addition to the acceleration data, manifests more sensible updated variables. EDMF finally resulted in a 25-50% overestimated design stiffness of internal main girders.
The seismic performance of a steel tubular bridge pier in a five-span continuous girder bridge system was evaluated through dynamic non-linear time-history analysis under strong ground motions. The ...seismic performance of the hollow steel tubular (HST) and partially concrete-filled steel tubular (PCFST) bridge piers was assessed with different eccentricities of superstructure. Considering the variation of ground classification under rare earthquakes, six seismic waves were input. The analytical results indicate that the eccentricity of superstructure has little effect on the maximum displacement response of the HST bridge piers and the PCFST bridge piers under ground motion excitations in the longitudinal (LG) direction; however, under the ground motion excitations in the transverse (TR) direction, the maximum displacement response of the bridge piers increases when the eccentricity (e/H) increases from 0 to 0.2, which implies that eccentricity affects the seismic response of the two types of piers. Both in the LG direction and TR direction, the HST piers have reached their yield strengths; stress concentration and local buckling were observed around the plastic hinge zone and the load bearing capacity decreases. Although the PCFST piers entered the elasto-plastic range, the expansion of local buckling deformation of the steel tubular column has been restrained by the concrete in-fill. According to the simulated results, the PCFST pier exhibits high ductility and bearing capacity, which can improve the seismic performance of the bridge system.
The construction of many railway structures predates those for roads. Yet, up until today they have continued to enable safe and stable railway operations, thanks to good maintenance management. This ...means that even on major lines, some structures have an age exceeding 70 years. While there is high demand for railway structure repair and reinforcement technology, restoration technologies including for functional improvements are also needed. This paper therefore gives an overview of the current state of railway bridges and viaducts and introduces recent research and development trends in restoration technology for bridges and viaducts developed by the Railway Technical Research Institute.
Damage to lower parts of viaducts caused by impact from under-passing high vehicles is relatively frequent. One such incident, in which a viaduct was damaged by the impact from a truck with an ...improperly assembled hydraulic crane, is considered in this work. The analysis is based on a detailed object damage evaluation, 3D laser scanning, and numerical simulations. The aim of the study is to accurately model the vehicle impact into the viaduct's span. The objective is to diagnose internal damage and to assess the proposed repair concept. No other method will allow discovery of the internal damage, including whether the pre-stressing tendons have been damaged or not. The computational model considers non-linear system dynamics including advanced material definition and the technology of tendon pre-stressing. All complex stages of structural assembly are included in the simulations and the extent of bridge damage is diagnosed. This approach makes it possible to reliably restore the collision event and to assess the safety of internal structural parts. The results from the numerical simulation correspond to the damage measured on the full-scale object. The conducted research indicates that tendons were not damaged as a result of vehicle impact. The structure may be strengthened by means of assembling prestressed concrete girders at both ends. This restoring concept is confirmed analytically. The strengthened structure is intended to show an even greater safety reserve. The proposed strengthening substantially improved structural stiffness, significantly reducing concrete damage and tendon stress in the case of a similar impact in the future. The proposed methodology can also help with research and in practice to assess the safety of other similarly struck and damaged bridges.
•Reliable and effective concrete viaduct modelling method•Analysis of viaduct damage caused by the impact of the crane•Safety assessment of the damaged viaduct•Evaluation of the proposed strengthening method
•The long-term settlement behaviour of metro viaduct piers in soft soil was investigated using an 8-year field monitoring.•Cumulative pier settlements and differential settlement between adjacent ...piers approached/exceeded limits after 8 years.•The influences of geological conditions, pile types and nearby excavation on the pier settlements were analyzed.
This study aims to investigate the long-term settlement behavior of metro viaduct piers in soft soil in Shanghai. Field monitoring was conducted for eight years, from the official opening until 2021. The results indicate that the settlement rate of the majority of piers was higher in the initial years and gradually reduced since 2017. Up to 2021, the maximum cumulative settlement St was 15.9 mm, which accounted for 0.8 times the limit of St (Ut). Seven settlement troughs were observed during the monitoring period. Muddy soil and nearby rivers significantly influenced the long-term pier settlements. St decreased proportionally with the thickness of the muddy soil. Piers located near the river experienced higher settlements than those located farther away, with a maximum settlement difference of 0.28–0.42 Ut. The influence of the river on St extended up to a range of 3–4 times the width of the river (Wr). Additionally, there were noticeable differences in settlement between piers constructed with tubular piles and those constructed with bored piles, particularly during the first two years after completion. Under similar conditions, the St of piers with tubular piles were 0.28 Ut (5.5 mm) larger than those of piers with bored piles on average. In addition, the slope k between the excavation-induced pier settlement and the ratio of the excavation depth to the distance was closely related to the type of retaining structure. The ratio of k values for the pit wall soil reinforcement, row piles and diaphragm wall was approximately 4:2:1. To prevent excessive pier settlement under similar geological conditions, it is recommended to employ a more rigid retaining structure and avoid using a soil-reinforced enclosure for pit walls.
Das im Zeitraum von 1901 bis 1909 für den viergleisigen Betrieb errichtete Chemnitzer Viadukt wird unter Auflagen des Denkmalschutzes für eine zeitgemäße Nutzung technisch instand gesetzt und ...verstärkt. Dabei werden die inneren beiden Überbauten mit Gleisen für den künftigen Schienenverkehr ausgestattet, die äußeren Überbauten zur Unterbringung von Inspektions‐, Wartungs‐ und Rettungswegen sowie der technischen Ausstattung genutzt. Der ca. 275 m lange und 17,50 m breite Brückenzug besteht aus zwei Bogen‐ und zehn Balkenfeldern. Bei der technischen Instandsetzung wurden die inneren Überbauten der Balkenfelder erneuert und als Stahl‐Beton‐Verbundkonstruktion ausgeführt. Die übrigen Konstruktionen wurden instand gesetzt, ertüchtigt und mit einer Stahlbetonkonstruktion oberhalb der Tonnenbleche ergänzt. Im vorliegenden Beitrag wird zunächst eine Übersicht zum bestehenden Bauwerk und der künftigen Nutzung gegeben. Es folgen Erläuterungen zur Planung, Ausschreibung und Ausführung der Baumaßnahmen. Im Anschluss werden verschiedene Maßnahmen zur technischen Instandsetzung und Verstärkung beschrieben. Der Beitrag schließt mit einer kurzen Zusammenfassung der beim Chemnitzer Viadukt gesammelten Erfahrungen zum Bauen im Bestand und dem Denkmalschutz.
Translation
Technical rehabilitation and strengthening of the Chemnitz viaduct
The Chemnitz viaduct, which was built between 1901 and 1909 for a four‐track operation, is being technically refurbished and reinforced for modern use in accordance with the requirements of the historical monument preservation. The two inner tracks will be used for future railway traffic, while the outer bridge structures will accommodate inspection, maintenance and emergency routes as well as technical equipment. The approx. 275 m long and 17.50 m wide bridge structure consists of two arch and ten beam segments. During the technical repair, the inner beam segments were renewed and constructed as a steel‐concrete composite structure. The other structures were repaired, strengthened and supplemented with a reinforced concrete structure above the hump plates. This article begins with an overview of the existing structure and its prospective use. This is followed by explanations of the planning, tendering and execution of the construction work. Subsequently, various measures for technical repair and reinforcement are described. The article concludes with a brief summary of the experience gained with the Chemnitz viaduct in terms of refurbishment and monument protection.
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