Structural assessment and strengthening measures for a cantilevered road deck (original) (raw)
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Structural Engineering International, 2013
The main strategic goal in the assessment of the existing Swiss national road network is to provide a high level of availability of the roads for traffic and reduce interferences caused by construction or repair works. Therefore, renovation works tend to be executed in large maintenance sections for which the complete infrastructure is repaired in order to ensure a period of 15 years without the need for additional construction works. Before 2008, the existing bridges were maintained mostly individually under the responsibility of local cantonal administrations. Entering into the new maintenance strategy requires a careful assessment of the structural conditions. Visual inspections and laboratory testing programs are required in order to bring the structural condition of different structures to a similar level and to fulfil all standards as long as costs are not disproportional to the benefits. Structural safety is evaluated according to the new Swiss code for existing structures, SIA 269, which was published in 2011. For typical short span bridges and overpasses from the early 1970s, which represent the largest number of existing objects, focus has to be set on the shear verifications of slabs without stirrups as well as on the bending capacity of cantilever slabs. Within the structural assessment, actions, material properties, geometrical properties and structural models shall be updated. Partial safety factors can also be updated by means of semi or full probabilistic approaches, in order to verify structural safety.
Safety assessment of existing concrete slab bridges for shear capacity
Applications of Statistics and Probability in Civil Engineering
The assessment of the structural safety of existing bridges and viaducts becomes increasingly important in many countries due to the age of the structures and an increase in traffic loads. Many structures need to be reassessed in order to find out whether the safety requirements are met. Most existing standards, however, are developed for the design of new structures. This paper summarises the recent developments with respect to the specification of the target reliability levels for existing structures. It appears from total life cost optimisation that application of the same target reliability levels for existing structures as for new structures is uneconomical. Further, in some cases the cost optimisation seems to yield rather low reliability levels and human safety criteria become decisive for specification of the target reliabilities of existing structures. In this paper old concrete slab bridges without shear reinforcement are studied. Probabilistic calculations are performed in order to calibrate partial factors satisfying the target reliabilities under traffic load. These partial factors can be used by engineers in level I probabilistic calculations. In this way the often over-costly application of safety standards intended for new structures can be avoided in the reassessment of existing structures.
10th International Conference on Short and Medium Span Bridges, 2018
The Canadian Highway Bridge Design Code of 2014 specifies values applied loads on bridge railing to determine the applied moment and tension force for the design of the deck slab cantilever. However, these moment and tensile force values are as yet unavailable. This research investigates the geometrical variables and load locations effect on the structural performance of the edge stiffened cantilever slab, which are subjected to horizontal line load. Finite Element Modeling software was utilized to conduct linear elastic analysis of concrete barrier rigidly connected to deck slab cantilevers. The geometrical properties include the linearly varying slab thickness, the transverse cantilever length, the longitudinal barrier length, and the varying wall thickness. Edge and mid-span loading at variable heights were determined based on the type of the barriers. Three-dimensional finite element models were constructed to extract design data for the shear and moment values for the wall, and tensile force and moment for the cantilever slab. Design data were analyzed using nonlinear regression analysis to provide simplified expressions, which can be used to determine the factored forces and moments needed for the structural design of the bridge barrier-deck joint as well as the deck slab cantilever due to vehicle impact forces.
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Recommendations for the Shear Assessment of Reinforced Concrete Solid Slab Bridges
As a result of the heavier live load models and more conservative shear approaches prescribed by the recently implemented Eurocodes, a large number of existing reinforced concrete solid slab bridges in the Netherlands were found to be shear-critical. The beneficial effect of the transverse load redistribution in slabs under concentrated loads is not taken into account. To quantify this effect, a comprehensive number of experiments was carried out. These results are used to formulate recommendations for the assessment practice for the case of solid slab bridges. The recommendations focus on the effective width over which the axle load can be distributed and its lower bound, the beneficial effect of transverse load redistribution and the influence of the yield strength of the reinforcement on the lower bound of the shear capacity. These recommendations are implemented in the “Quick Scan” method, leading to a significant reduction of the shear stresses.
First International Conference on Bridge Maintenance, Safety and Management IABMAS, Barcelona 2002, 2002
Due to the design concept of inclined principal stresses for shear forces applied in the 1960's and 1970's, prefabricated prestressed concrete girders often exhibit insufficient shear resistance according to current standards, since the applied high prestressing ratios allowed reinforcement of the webs with secondary reinforcement only. From the replacement of a 30-year-old road deck, several prefabricated girders became available for full-scale tests. The major results of four-point loading tests and asymmetric three-point loading tests are briefly reported. A step-by-step concept is proposed for the checking of the structural safety of existing concrete structures. This concept also contains refined checks according to the theory of plasticity. Discontinuous stress fields as lower-bound solutions are shown and explained for one of the full-scale tests. Conclusions on checking the structural safety of existing concrete structures are drawn.
Recommendations for the Shear Assessment of Reinforced Concrete Slab Bridges from Experiments
Structural Engineering International, 2013
Upon assessment of existing reinforced concrete short-span solid slab bridges according to the recently implemented Eurocodes that include more conservative shear capacity provisions and heavier axle loads, a number of these structures were found to be shear-critical. The results from recent experimental research on the shear capacity of slabs indicate that slabs benefit from transverse load distribution. Recommendations for the assessment of solid slab bridges in shear are developed on the basis of these experiments. A load spreading method for the concentrated loads is proposed and the applicability of superposition of loading is studied. The resulting most unfavourable position for the design trucks is provided and implemented in the so-called Dutch "Quick Scan" method (QS-EC2). Cases of existing bridges are studied with the previously used QS-VBC as well as with the QS-EC2 that includes the recommendations. As a result of the assumed transverse load distribution, the shear stress to be considered at the support based on the recommendations becomes smaller.
Applying Experimental Results to the Shear Assessment Method for Solid Slab Bridges
Concrete 2013, Gold Coast, Australia, 2013
The combination of increased live loads and a more conservative shear capacity in the recently implemented Eurocodes, resulted in a large number of existing solid slab bridges in the Netherlands being shear-critical upon assessment. However, an enhancement of the shear capacity can occur in slabs under concentrated wheel loads due to transverse load redistribution. To quantify this effect, a comprehensive series of experiments on slabs and slabs strips under a concentrated load near to the support and under a combination of a concentrated and a line load was carried out. The experiments show the difference in behaviour for slabs, carrying the load in a two-dimensional way, as compared to beams in shear. The results from the laboratory research are used to develop recommendations, that are easily used in combination with the codes. These recommendations are implemented in a spreadsheet-based first-level assessment tool, the Quick Scan method. The assessment with this tool of selected cases of existing solid slab bridges shows that applying the experimental results into the assessment practice leads to an improved selection ability of the Quick Scan method.
2016
This study builds on the methods of analyses with respect to cantilever slabs in the Canadian Highway Bridge Design Code (CHBDC), and recommends new simplified equations for the intensity of the transverse moment and shear force at the base of the cantilever overhang due to applied vertical truck loading. A parametric study was conducted using finite-element modelling on bridge deck cantilevers with variable lengths and slab thicknesses. Different end stiffening arrangements were considered, including the presence of PL-3 barriers walls (recently renamed to TL-5) as well as the concrete curb supporting intermittent steel posts carrying the bridge railing. The barrier length changed from 3 to 12 m, while the cantilever length ranged from 1.0 to 3.75 m. The results of this study complement the empirical expressions developed by others to determine the minimum required factored moment and tensile force resistance at the deck-barrier junction, induced by horizontal railing loads. Furthe...
Performance of Existing Reinforced Concrete Arch Bridges Under Current Non Seismic Loads
8th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering Methods in Structural Dynamics and Earthquake Engineering, 2021
The present analytical work deals with the assessment of the performances of Reinforced Concrete (RC) Deck Arch Bridges under the non-seismic loading conditions required by the current mandatory Italian codes. In particular, the attention is focused on a specific RC deck arch bridge typology, better known as the "Maillart Type Arch Bridge", which is characterized by a very stiff deck beam and a slender and wide vault. As well as other existing RC structures which were designed under only gravity loads and without specific structural details, such as lower limits for longitudinal and transverse reinforcement bars, these bridges could be damaged by loading conditions not considered at the time of design. For the evaluation of the main critical issues related to the current performance of such bridges under the current non-seismic loading conditions, it has been defined a large inventory of simulated arch bridges in accordance to the design procedures usually adopted in 1950s which considered only gravitational loads, i.e. self-weight and moving loads. Each bridge of the inventory is modelled and studied by means of a Linear Gravitational analysis implemented in the structural software SAP2000, with support of an Application Programming Interface (API), such as Matlab. Due to the differences between the current loads and those considered at the design time and to the approximations of the design strategies of the time, a performancebased analysis of the existing bridges under non-seismic loads is important for the stakeholders as much as for the decisionmakers in order to plan risk mitigation programs and prioritize eventual retrofit interventions for risk reduction.