Balanced Cantilever Method Research Articles

Insights into structural assessment and long-term effects of a post-tensioned multispan concrete box girder bridge with vertically prestressed internal joints

The study focuses on multi-span prestressed bridges, where time-dependent effects like creep, shrinkage and prestress losses can have a significant impact on long-term behaviour. Specifically, the paper analyses a bridge constructed with the balanced-cantilever method and presenting the peculiarity of vertically prestressed internal joints, which significantly influence the deformed shape and require proper modelling approaches. The testing campaign is fundamental to achieve a deepened awareness of the actual behaviour of the bridge and to correctly reproduce it through a Finite Element (FE) model. The constructed FE model accurately predicts actual and future deformations and stresses, and allows simulating the actual service conditions of the structure. The novelty of the work presented in this paper lies in the development of a detailed model specifically tailored for the analysed bridge typology, considering real construction stages and long-term phenomena of both steel and concrete. The model has reached a high level of validation through the comparison of the results with extensive in-situ tests and theoretical formulations, so as to be able to achieve insights and learn important lessons on the long-term structural behaviour of post-tensioned bridges with special internal connections.

Structural Assessment of a Post‐Tensioned Box Girder Bridge affected by Concrete Creep

AbstractThe behavior of post‐tensioned concrete bridges is often influenced by time‐dependent phenomena, such as relaxation of prestressing steel, creep and shrinkage of concrete. For bridges built using the balanced cantilever method, the evolution of time‐dependent phenomena during the construction phase must be carefully considered. In common practice, the assessment of the structural safety of this bridge typology is a complex task due to the numerous factors and uncertainties involved in the evaluation process. Numerical models can be adopted to perform structural analyses at successive phases over bridges' lifetime, while destructive and non‐destructive evaluation methods are used to gather information to ensure that the numerical model matches the actual behavior of the bridge. In this context, this paper presents the structural behavior assessment of a multi‐span post‐tensioned box girder bridge with vertically prestressed internal joints. A numerical model was constructed to investigate on the effect of creep and construction phases on the actual stress/strain conditions of the bridge. To reduce model‐based uncertainties, compression tests were carried out on concrete cores extracted from the structure and the results of static load tests were used for model validation purposes.

Numerical comparative study on seismic response of half-span and full-span scaled models of a floating type cable-stayed bridge

This study compares the results of numerical simulations of half-span and full-span cable-stayed bridge models based on the seismic response of the pylons and main girders subjected to earthquake loads. The half-span model represents the most critical condition of the bridge during the construction phase, while the full-span model represents the bridge in operational phase. The three-dimensional finite-element modeling of the two bridge models uses data from the longest existing cable-stayed bridge in Indonesia which was scaled down geometrically to 1/160, using Midas CIVIL software. The Kobe earthquake record from the PEER Strong Motion Database was used in this study by applying the spectral matching method to modify its acceleration according to the location of the existing bridge being analyzed. This study also examines the influence of the directional effects of earthquake load relative to the longitudinal axis of the bridge, namely 0, 45, and 90 degrees. The results of the analysis show that for the half-span bridge model, the maximum acceleration occurs at the top of the pylon due to earthquake excitation at 90 degrees direction, with an amplification factor of 4.658, while the amplification factor in full-span bridge conditions is only 2.44. In addition, in both the half-span and full-span bridge models, the largest acceleration amplification factor occurs in the main girder that is caused by earthquake excitation at 90 degrees direction. The largest transverse displacement occurs at the free ends of the main girder, but not in the full-span model. The results of the study indicate that during the detailed design process the designer has to consider the effect of earthquake on the strength and stability of the bridge during construction especially if the balanced cantilever method applies.

Simulating creep induced moment redistribution in prestressed concrete bridges constructed by the balanced cantilever method: ad hoc traditional formulae versus real time-dependent analysis

Assessing available numerical techniques adopted to determine the design time-dependent moment for prestressed concrete segmental bridges constructed by the balanced cantilever method is of utmost importance to the bridge design community. In essence, despite some apparent diversity, there are basically two key conventional approaches to compute the design time-dependent moment accounting for creep effects for this type of bridges. The first is a family of varied simplified methods typically known to practicing designers and with pre-consensus on their reliability and effectiveness. Time-dependent moments retrieved from these classical methods always reside in an intermediate state falling between the results from “two” time-independent analysis cases, namely, (a) sequentially adding all partial permanent loads and prestressing pertaining to various construction steps using the part-bridge structural system corresponding to each step, and (b) assuming all loads and prestressing forces to be applied at-once to the final completed bridge. The second approach is through performing real sophisticated step-by-step time-dependent analysis using a specialized software. The research primary objective is to assess the validity/reliability of commonly used ad-hoc approaches that evolved over the years relying on simplified analyses/formulae to cater for time-dependent creep effects for this type of bridges. Aiming at realistic conclusions, three case-study real-world segmental balanced cantilever bridges over the Nile River in Egypt are elected. Midas Civil commercial package is used to perform time-dependent finite element analyses for the three bridges. Main parameters considered are, inter alia, time-dependent effects of creep and shrinkage of concrete, relaxation of prestressed steel, losses due to friction and anchor setting of prestressing tendons, sequence of construction, and construction-driven temporary change of support conditions (where applicable). The study concludes that creep-induced moment redistribution from simplified traditional formulae typically adopted in the literature may lead to a considerable error in estimating the design time-dependent moment in balanced cantilever bridges.

3D FE modeling of cable-stayed bridge according to ICE code

Abstract This article presents the performance of cable-stayed bridge by representing a model using the ANSYS program under the influence of a concentrated load and then comparing them with the experimental results. One model was used in the analytical, and one was (harp type 1) used in the length of the girder (4,500 mm), height of the pylon (1,480 mm), and depth of the flange for the girder (40 mm). If cable-stayed bridges are constructed using the balanced cantilever method, the stability problem of the girder is more significant during the construction stage than at the initial state. In this study, to investigate the ultimate behavior of cable-stayed bridges, experimental and analytical studies were conducted for one model: Harp type 1. At the limit state, several plastic hinges occurred and the girders buckle along the entire span. Numerical analysis was conducted for the experimental model, and the results of which showed good agreement with the experimental results. The influence of such kind of effects on the analysis and the structural behavior of cable-stayed bridges has been examined in detail in the study. The dimensions of the model were also compared with institute civil engineering Code in terms of the height of the tower to the main space, and Back Span to the main span ratio. It was close to standard specifications. A finite element procedure for the nonlinear analysis of cable-stayed bridges is first set up, and then, a detailed static deflection analysis of such bridges is carried out.

First application of the balanced lowering method to build two bridges in Austria

AbstractThis new bridge construction method consists of building the bridge girders in a vertical position and of rotating the bridge girders into the final horizontal position. In order to rotate the bridge girders, additional structural elements, in this case compression struts, are required. In some topographical situations, it will be more efficient to produce the bridge girders with this innovative method than with the traditional incremental launching method or the balanced cantilever method. The span of the bridge girders is reduced by the compression struts, which enables considerable savings in construction materials. This article explains the design and the first application of the balanced lowering method to build two bridges across the Lafnitz and Lahnbach rivers as part of the Fürstenfeld Motorway in the southeast of Austria. The good cooperation of the project participants allowed for the successful first‐time application of the method for the two bridges described in this article. The unproblematic application of the balanced lowering method for the prestressed concrete bridge with 2.0 m high bridge girders proved that considerable savings in resources and costs were possible compared to the originally planned steel‐concrete‐composite bridges with 4.2 and 4.6 m high bridge girders.

Long span post-tensioned box girder bridge in Bratislava

The paper describes an analysis and detailed design of the 470 m long D4 motorway bridge in the Slovak capital Bratislava. This bridge is a part of 2 932.50 m long D4 motorway crossing of the Danube River and its surrounding areas. The 210 m long main span of the post-tensioned three span box girder bridge is the longest span which has ever been built in Slovakia. The Ministry of Transportation and Construction of the Slovak Republic requirement was to cross all future rowing tracks by a single span. The depth of the cross section varies from 4.39 m at span to 13.09 m at piers. 35 m wide cross section carries 4-lane carriageway, median, sidewalk and cycling path. The central part of carriageway is built by the balanced cantilever method. The overhangs carrying outer lanes are built by wing traveller machine and supported by the precast struts. The bridge is currently under construction as a part of PPP project of Bratislava ring road (the motorway D4 Bratislava, Jarovce - Bratislava, Ivanka north section).

Design challenges resulting from construction of the River Dee Bridge, Aberdeen, UK

This paper sets out the challenges from the perspective of the designer associated with the construction of the River Dee Bridge built by the balanced cantilever method. The importance of managing the construction sequence and its impact on both the design and programme are discussed. Monitoring and managing the loads in the temporary works were crucial to ensuring the stability of the structure. The issues associated with the temporary jacking system and the monitoring adopted are also considered.

Additional Shear Stresses in Webs of Segmental Concrete Bridges due to Anchorage of Cantilever Tendons

The balanced cantilever method is the most widely used technique for the construction of large-span segmental prestressed concrete box-girder bridges. In order to control shear cracks at the service limit state, the principal tensile stresses in the webs are analyzed for all segmental bridges. Web shear cracking may occur for a number of reasons, one of them is the ignoring of shear stresses induced by the anchorage of cantilever tendons during the cantilevering process. This study aims to provide a clear understanding of anchorage-induced shear stresses in the webs of segmental box-girder bridges, including the underlying mechanisms, mechanical models, adverse effects, and design considerations. Case studies show that the peak shear stresses in the webs might have a significant increase due to this localized effect, while it cannot be captured by the beam-element analysis and is usually not considered in the routine design. To solve this problem, a practical approach is developed for evaluating the anchorage-induced shear stresses in the webs of segmental concrete box-girder bridges.

Prediction analysis of deflection in the construction of composite box-girder bridge with corrugated steel webs based on MEC-BP neural networks

This paper presents an efficient computational framework addressing the deflection prediction problem for prestressed concrete (PC) rigid frame bridge with corrugated steel webs (CSWs) erected by the balanced cantilever method. The framework consists of three stages of analysis: (1) obtain the datasets for establishing the prediction model, in which the input samples and output response are generated by the Latin hypercube sampling (LHS) technique and high-fidelity three-dimensional (3D) finite element (FE) model, respectively; (2) based on the datasets, an optimized neural network model that integrates with mind evolutionary computation (MEC) algorithm and back-propagation (BP) algorithm is established, then the model performance is evaluated by the statistical criteria; and (3) the well-trained MEC-BP model is used to predict the deflection for CSWs-PC bridge construction. The applicability and efficiency of the framework are demonstrated with a real CSWs-PC bridge. Results show that the proposed method achieves much better prediction performance than the conventional BP model, and can deliver an efficient prediction tendency for the deflection control of a CSWs-PC bridge during the complex construction process.

Buffeting Response of Cable-Stayed Bridge during Construction under Skew Winds and Pylon Interference

Buffeting is a kind of wind-induced vibration phenomenon of long-span cable-stayed bridges which is easy to occur. Balanced cantilever method is widely employed for the construction of cable-stayed bridge. The maximum double-cantilever state is the most dangerous state of wind resistance. Through the aeroelastic model wind tunnel experiment, the buffeting response of a cable-stayed bridge in construction under skew winds is studied in this paper. The variation law of buffeting response with the wind yaw angle is compared between the two cases with and without pylon. The experimental results show that for the same wind yaw angle the lateral and vertical buffeting responses of the main girder increase with the wind speed approximately in a quadratic curve, while the torsional buffeting response tends to increase linearly. At the same wind speed, the buffeting response of the main girder presents non-monotonic changes with increased wind yaw angle. Under skew winds, due to the disturbing effect of the pylon and the influence of the three-dimensional flow field, the buffeting response of the main girder will be affected by the aerodynamic interference of pylon. When the wind yaw angle is small, the interference effect is not obvious, with the increase of wind yaw angle and wind speed, the interference effect begins to appear. Generally speaking, the aerodynamic interference of the bridge pylon on the buffeting responses can be ignored.

Metode Konstuksi Precast Segmental Balanced Cantilever (Studi Kasus Jalan Layang Pasupati - Bandung)

Metode konstruksi precast segmental balanced cantilever, sebuah metode konstruksi yang dapatdipertimbangkan dalam pembangunan jalan layang atau jembatan. Dengan memanfaatkan efekkantilever seimbangnya maka struktur dapat berdiri sendiri tanpa diperlukannya sokongan lain sepertiperancah yang diletakkan di bawah jembatan, pelaksanaan konstruksi dapat dilakukan dari bagian atasstruktur. Dengan penggunaan metode tersebut maka seluruh aktivitas pembangunan tidak akanmengganggu kegiatan di bawahnya, seperti pembangunan jalan layang maka lalu lintas di bawah tidakakan terganggu, atau pembangunan jembatan di laut maka tidak ada pilihan pembangunan harusdilakukan dari atas struktur. Teknologi metode balanced cantilever sudah banyak digunakan untukpembangunan jembatan-jembatan di luar negeri, untuk di Indonesia diterapkan di proyekpembangunan jalan layang PASUPATI Bandung. Metode balanced cantilever mempunyaikeuntungan seperti tidak diperlukannya perancah, pembangunan dapat dilakukan dari bagian atasstruktur, tetapi di samping itu perlu dipertimbangkan juga nilai investasi yang cukup mahal untuk alatalatberat yang digunakan seperti launching gantry, pembangunan lahan casting yard dan pengadaanlow bed trailer yang butuh desain khusus sehingga manuvernya sanggup untuk semua kondisi medanyang digunakan.

Construction of precast segmental box girder bridge

New road segmental bridge have been built near the city of Žilina, aligned on European highway corridor. The use of segmental concrete box girder was chosen as the flexible system and appropriate method in a municipal zone. The same parallel precast post-tensioned box girder structures were used with main spans of 60.5 m for total length of 1042m. The balanced cantilever method, with the self-launching gantry was used for erection. The shorter end spans, adjacent to the abutment, had to be built by employing falsework. Generally, the early segmental bridges have not been realized without problems following to the structure collapse. In order to assure the safety under construction stage of bridges and subsequently in service, the data was collected during casting and erection of the bridges since August 2016 to November 2017. The experimental research was divided into the laboratory testing and continuous in-situ strain and temperature monitoring of the bridge superstructure. The paper illustrates fabrication and erection process of the bridge and some results of superstructure testing.

Long‐term material and structural behavior of high‐strength concrete cantilever bridge: Results of 20 years monitoring

In 1997, the Second Stichtse Bridge was built in the Netherlands using the balanced cantilever method. The use of high‐strength concrete was proposed. At that time, the long‐term behaviour of this material was not known, and no code provisions were applicable. Therefore, it was proposed to monitor the material behaviour and the deflections of the bridge. To evaluate the development of the concrete compressive strength and the concrete splitting tensile strength over time, concrete cubes were cast at the same time as each of the cantilever segments, and stored inside the bridge. These samples have been tested at different points in time to study the development of the strength as a function of the elapsed time. Creep and shrinkage measurements were carried out on samples stored inside the bridge as well as in the laboratory. Temperature and moisture were monitored as well. The deflections of the bridge superstructure have been measured periodically. These measurements can be compared to predictions from finite element models. Based on the available data, it is found that the concrete compressive and splitting tensile strength remain constant. The deflections are small, and the advanced finite element models resulted in good predictions.

Load testing of Highway Bridge

New segmental concrete bridge has been built near the city Žilina, aligned on European highway corridor E 50. The bridge is composed of the two separate precast prestressed box girder structure constructed by balanced cantilever method. The total length of both structures is 1042 m. The similar superstructure consists of a total of eighteen continuous spans with main spans of 60.5 m. The construction process, load carrying capacity and monitoring of the bridge has been investigated before the opening of the bridge. The paper presents verification of the structural behaviour of the bridge under static load compared to predicted model for both precast prestressed structures.

Assessment of an existing fully prestressed box-girder bridge

The N.S. da Guia Bridge is a 250 m-long post-tensioned box-girder bridge built in the late 1970s using the balanced cantilever method. During a routine inspection, a systematic cracking pattern that exhibited both longitudinal and transversal symmetry was detected in the webs and bottom slab, which raised concerns about the condition of the embedded post-tensioned cables. The working programme that was devised to perform the condition examination of the bridge is described. Besides a detailed visual inspection campaign and a short-term monitoring programme, non-destructive testing was also employed, most notably gamma-ray imaging of the internal tendons. Special attention is devoted to the numerical studies developed to explain the origin of the observed crack patterns. This information was crucial in order to decide on the best rehabilitation strategies. The crack pattern could be satisfactorily reproduced by taking into account the local stress conditions around the tendon anchorages, and the concerns related to the condition of the prestressed steel could be ruled out. The applied methodology constitutes an example of how detailed analysis techniques can be used in practice to help bridge owners evaluate the condition of special bridges and plan the rehabilitation intervention in a cost-effective way.

Long-Term Effects Monitoring on Prestressed Concrete Bridge

Balanced cantilever method is one most used method for the large span concrete bridge construction. Generally non-homogenous concrete structures with changing the structural system within its erection are sensitive to the deformation and stress prediction in time. Long-term monitoring system has become very important tool which enables to obtain basic information about actual structural behavior in time about stress and deformation level. It can also cover the other structural effects for example the temperature influence which can significantly affect to the later structural behavior. Generally bridge designers in practice do not have enough information about these influences within the structure erection over the time. Underestimating such above mentioned effects often causes that predicted values of stresses or deformation does not corresponded with the reality as was published for example in [1]. In boundary cases unexpected excessive deformations or crack opening due to the stresses distribution may lead to the serviceability problems, deterioration of aesthetics, and even early reconstruction of the bridge eventually. In this paper we would like to present some experiences with the long-term monitoring of bridge structure and performed structural analysis considering the real load history and structural scheme changing. Recorded strains development was compared with the numerical model results based on the expected behavior of prestressed concrete structure according to the European standard models, [3, 4].

Performance of in situ stitches in precast segmental bridges

In situ concrete stitching with subsequent prestressing is often used in construction to join together precast concrete segments. An example of an application is the stitching of the approaching decks of precast segmental bridges constructed using the balanced cantilever method. The relatively narrow stitches used in segmental bridges are often provided with nominal reinforcement only. Therefore, the in situ stitch is a location of potential weakness, but relatively little work has been done in this area. In light of this, extensive experimental and numerical studies on the behaviour of precast concrete members with in situ concrete stitches have been conducted. The effects of stitch width, prestressing force, concrete strength, bonding of tendon and provision of shear keys on the performance of such members are presented in this paper. Unlike members that are continuously cast, cracking initiates along the construction joint between the precast segment and the stitch at low load levels for members with in situ stitches, while no cracking is observed elsewhere. The cracks widen extensively as the load level increases and can become detrimental to the serviceability of the members. Such members should be designed so that the joints are subject to no tension under service load.

Control geométrico del tramo atirantado del Puente de la Constitución de 1812 sobre la Bahía de Cádiz

Geometric control of bridges erected using the balanced cantilever method is always complex. In this case, this has been compounded by the great structural flexibility, weight, and dimensions of the erected segments and the cable-stayed cross-section scheme.These uncertainties, added to the process of obtaining the geometry of the tower and deck, can be fully adjusted if an exhaustive control of all bridge elements is performed throughout the entire construction sequence.The rationale was based on the detailed prior segment assembling in the dockyard, and its positioning using an angle relative to the previously erected deck, establishing some adjustments to eliminate the calculated deviations. A special procedure was established for the geometric control of the joints between different decks in order to adjust precisions to welding tolerances.

El proceso constructivo del tramo atirantado del Puente de la Constitución de 1812 sobre la Bahía de Cádiz

Balanced cantilever method has been use to erect the cable-stayed section of the “Constitución de 1812” bridge over Cadiz Bay. Standard segments are 20m long and 34m width and weigh 4.000kN.The construction sequence has been determined by the ultimate resistance of the tower that must resist the unbalanced bending moments at both sides of the tower.