A multi-level strategy for successively improved structural analysis of existing concrete bridges: examination using a prestressed concrete bridge tested to failure (original) (raw)
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Non-linear finite-element analysis of the shear response in prestressed concrete bridges
Magazine of Concrete Research, 2009
For the structural assessment of concrete bridges, the non-linear finite-element method has become an important and increasingly used tool. The method has shown a great potential to reveal higher load-carrying capacity compared with conventional assessment methods. However, the modelling method used for reinforced and prestressed concrete members subjected to shear and torsion has been questioned. The aim of this study is to present an analysis method for evaluation of the load-carrying capacity of prestressed concrete bridges, when failure resulting from shear and torsion is the main problem. The modelling method used was previously worked out and verified for shear-type cracking and shear failure. Here, shell elements with embedded reinforcement were used together with non-linear material models, taking into account the fracture energy of cracking plain concrete and the reduction of the concrete compression strength owing to lateral tensile strain. Analyses with the method proposed have shown to predict the shear response and the shear capacity on the safe side. In the work presented here, the load-carrying capacity of a box-girder bridge was evaluated as a case study. The whole bridge was modelled, but only the part that was most critical to shear and torsion was modelled according to the method previously worked out and was combined with beam elements for the rest of the bridge. The case study showed a substantially higher load-carrying capacity for the bridge compared with the assessment with conventional methods. In the evaluation, several possible safety formats were used in combination with the non-linear finite-element method. It was shown that the format using partial safety factors gave unrealistic conservative results; it is more correct to use the semi-probabilistic formats for non-linear finite-element analysis.
Computational Assessment of Prestressed Concrete Bridges
IABSE Congress Report, 2012
A current challenge for engineers is the conservation of existing structures which includes maintenance, assessment and, if necessary, strengthening. For the evaluation of the load carrying capacity and the remaining service life, detailed knowledge of material properties is required and a structural model should be used, with which the stress state can reliably be analysed. In this paper, concrete hollow box girder bridges (single and multi-cell cross sections) are examined. First, on the basis of a case study it is shown how eccentrically arranged traffic loads are introduced into the system. For this, a 3d finite element model with the assumption of linear elastic material behaviour is used. The results are compared to those of a beam based calculation where, regarding the shear forces, considerable differences are found.
A multi-level structural assessment strategy for reinforced concrete bridge deck slabs
Structure and Infrastructure Engineering, 2016
This paper proposes a multi-level assessment strategy for reinforced concrete bridge deck slabs. The strategy is based on the principle of successively improved evaluation in structural assessment. It provides a structured approach to the use of simplified as well as advanced non-linear analysis methods. Such advanced methods have proven to possess great possibilities of achieving better understanding of the structural response and of revealing higher load-carrying capacity of existing structures. The proposed methods were used for the analysis of previously tested two-way slabs subjected to bending failure and a cantilever slab subjected to a shear type of failure, in both cases loaded with concentrated loads. As expected, the results show that more advanced methods yield an improved understanding of the structural response and are capable of demonstrating higher, yet conservative, predictions of the load-carrying capacity. Nevertheless, the proposed strategy clearly provides the engineering community a framework for using successively improved structural analysis methods for enhanced assessment in a straight forward manner.
Structural Assessment of Bridge Girders in Shear
Structural assessment has become a major challenge in bridge engineering. Very often it is not possible to evaluate structural behaviour and strength on the basis of design equations, but more refined procedures have to be applied. Unlike in the design, where not all the requirements and boundary conditions are known and therefore a certain precaution ought to be determinant, for the examination modelling has to be more detailed and should enable the consideration of the actual conditions. For a large number of existing bridge structures the behaviour in shear is most likely to be relevant in the assessment. There are two main reasons for that: On the one hand, some of the former design concepts are not sufficiently reliable, on the other hand, corrosion of steel and deterioration of concrete may cause deficiencies with respect to strength. In this contribution a structured procedure for the analysis and assessment of reinforced concrete members subjected to shear is presented. In a first or preliminary evaluation the Generalized Stress Field Approach may be utilized and in cases where a higher level of precision is required a more general method, derived from the Cracked Membrane Model, can be applied. The two methods are outlined and their application is explained with help of an example analysis.
Structural Concrete, 2013
The design shear resistance of an existing structure can be evaluated with analytical design procedures and numerical procedures provided by non-linear finite element analyses. The new fib Model Code 2010 proposes different calculation methods that fall into four different levels of approximation. As the level of approximation rises, so the complexity and the accuracy of the calculated shear resistance increases. Non-linear finite element analyses belong to the highest level of approximation, but although they are more and more becoming a customary tool in the daily design process, building codes do not provide guidance on how to perform these analyses. This paper describes non-linear finite element analyses performed on prestressed beams, which underwent shear failure during experimental loading, in order to assess and criticize the finite element approaches. The aim of this work is to propose guidelines for numerical simulations in order to reduce model and user factors. The results obtained from the non-linear finite element analyses have been compared with the analytical results using different levels of approximation. The design shear resistance obtained with the highest level of approximation, level IV, derived from non-linear finite element analyses, turned out to be higher than the design shear resistance obtained with analytical procedures (levels I/II/III).
A guide to non-linear finite element modelling of shear and torsion in concrete bridges
2000
A guide to non-linear finite element modelling of shear and torsion in concrete bridges HELÉN BROO, KARIN LUNDGREN, MARIO PLOS ABSTRACT Non-linear finite element (FE) analysis has become an important tool for structural design and assessment of reinforced concrete structures. When shear and torsion are limiting the capacity of a structure, three dimensional non-linear finite element methods often show higher load-carrying capacity compared to conventional analyses; therefore there is much to gain by using these methods, especially at assessment of existing structures. The reason for the higher capacities evaluated are mainly a more favourable load distribution when the structure is analysed in three dimensions and that the fracture energy associated with concrete cracking is included. In order to be able to use these higher capacities in reality, it is important that the modelling method is verified and to be aware of possible limitations. Recommendations are given concerning analysis methods and how a verification can be done, both concerning the capability of the program and concerning the actual FE model.
Full-Range Analysis of Multi-Span Prestressed Concrete Segmental Bridges
Procedia Engineering, 2011
The in-situ concrete stitches of prestressed concrete segmental bridge are locations of potential weakness for the entire bridge deck but relatively little work has been carried out in this area. The effects of the performance of in-situ stitches on the global behaviour of bridge deck are not well understood. As most existing techniques cannot cope with such full-range analyses, a numerical technique has been developed for conducting full-range analyses of continuous prestressed concrete bridges under incremental loads or displacements. The bridge is modelled as a series of beam elements each of which is governed by the corresponding moment-curvature relationship of a representative section within it. While most of the existing techniques are only capable of analysing the behaviour of continuous prestressed concrete beams up to the peak load-carrying capacity, the present technique can extend well into the post-peak range, which is crucial to the investigation of ductility or deformability. The development and verification of the technique are presented in this paper.
Advanced Bridge Capacity and Structural Integrity Assessment Methodology
2013
The bridge is a basic element of all surface transportation networks. In military theaters of operation, transportation routes that cross bridges are essential for deploying personnel, supplies, and heavy equipment, as well as for facilitating communications. It is essential that the structural capacity of each bridge along a military route be assessed in order to avoid overloading the bridge or unnecessarily hindering military operations by overestimating or underestimating its capacity. For reinforced concrete structures, information about the number, size, and orientation of steel reinforcement is necessary to make a strength assessment. Since reinforcement is not visible externally, making an accurate assessment without design drawings is extremely difficult. The objective of this project was to develop more reliable means of in-field capacity assessment of reinforced concrete bridges by making improved estimates of the level of longitudinal and shear reinforcement. The proposed assessment procedure is based on comparing measured structural response under controlled loading conditions to predicted structural response from analysis. This report presents results from a preliminary sensitivity study of the analytically predicted response of simply supported reinforced concrete T-beam girders that have varying levels of longitudinal and shear reinforcement. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.
Structure and Infrastructure Engineering, 2013
The safety of existing bridges can be studied through nonlinear numerical models, assisting decisions of dismantle, repair or change of use and avoiding unnecessary or inappropriate interventions. Filament beam models due to their simplicity and low computational demand are adequate for the engineering practice as an alternative to 2D and 3D FEM. In this communication, the structural assessment of a prestressed concrete bridge with low shear reinforcement-the Wassnerwald Viaduct in Switzerland-is presented. The bridge was dismantled due to, among other reasons, not complying with the shear safety standards. The girders of the bridge, which were submitted to full-scale in situ load tests, were numerically simulated by means of a nonlinear filament beam model considering axial force-shear-bending interaction recently developed by the authors. Hypothetical strengthening solutions with external prestressing were also studied.