Non-linear finite-element analysis of the shear response in prestressed concrete bridges

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. \ua9 2009 Thomas Telford Ltd

Pre-study of Dynamic Amplification Factor for Existing Road Bridges

The Swedish Road network has, since 2018, been divided into four bearing capacity classes (BKs)—BK1–BK4. The heaviest allowed gross vehicle weight increased when BK4 was introduced, from 64 tonnes (BK1) to 74 tonnes (BK4). The Swedish Transport Administration aims, by 2025, to classify 60 % of the strategic road network for the heavy transport industry as BK4, increasing to 70–80 % by 2029. However, to reach these goals, it is estimated that over 700 bridges will need to be strengthened or replaced.This study, using a site-specific investigation to calculate the assessment dynamic ratio (ADR), showed that some of these bridges could be upgraded to BK4. A review of the literature indicated that light vehicles tend to have high dynamic amplification factors (DAFs), but light vehicles do not have critical load effects and are therefore not relevant from a design perspective. Instead, heavy vehicles are critical for the design. Both experimental and analytical investigations have shown that heavy gross vehicle weights result in low DAF values.This report proposes effective ways to collect site-specific dynamic traffic load information and a methodology to produce site-specific dynamic allowances using both experimental measurements and numeric models. It also explains how this methodology can be adopted by transportation agencies to study bridges along transport corridors.Findings from the pre-study have resulted in the following research proposals: sitespecific field measurements to quantify DAFs, guidelines for numerical modelling of vehicle–bridge interactions (VBIs), DAF for each limit state, three–dimensional analysis of VBIs, the introduction of gross vehicle weight into DAF equations, and pilot tests of proposed frameworks for transport corridors. The authors believe that several topics can be covered within the framework of a PhD project

Recommendations for Assessment of Reinforced Concrete Slabs: Enhanced structural analysis with the finite element method

Reinforced concrete structures show a pronounced non-linear response, with cracking of concrete for service loads and reinforcement yielding and concrete crushing at ultimate load. With non-linear finite element (FE) analysis, the structural response can be captured, and such analyses have shown great potential to reveal higher load carrying capacity compared to simplified and linear analysis methods. A multi-level structural assessment strategy, developed in previous research, provides a framework for more advanced, successively improved analysis of reinforced concrete slabs.This report provides recommendations for practicing structural engineers on structural assessment using FE analysis. The focus is on enhanced assessment with non-linear FE analysis, and the scope is reinforced concrete slabs with limited membrane effects. The intention is to facilitate the use of non-linear analysis in engineering practice by providing detailed recommendations on how such analyses can be made to provide increased understanding of the structural behaviour and reliable estimations of the load-carrying capacity of concrete slabs. However, the framework presented is general, and the approach can in many aspects also be used for other types of reinforced concrete structures. The recommendations given here are based on previous research performed by the authors, information from literature and engineering judgement based on practical experience. They are intended to give conservative estimates of the load-carrying capacity, fulfilling the required safety level. The report includes a thorough description of the assessment strategy. The global safety format recommended for non-linear analysis is presented and its application for different assessment levels is described. Furthermore, recommendations on how to take deterioration into account are given. Non-linear FE analysis of concrete structures is presented together with general advices for its application. Furthermore, general recommendations are presented for simplified and linear analysis, corresponding to today’s practice. For assessment with non-linear FE analysis, detailed recommendations for use in engineering practice are presented. Advices are given on idealization of the structure, choice of material models, determination of material parameters, modelling and analysis. Furthermore, the evaluation of structural response, determination of load carrying capacity and response under service conditions are described. For non-linear analysis with shell elements, resistance models on higher Level-of-Approximation according to Model Code 2010 are used. Finally, examples are showing the application of the strategy on two slabs tested in laboratory and one bridge deck slab

Development of modelling strategies for two-way RC slabs

Analyses of tested two-way reinforced concrete (RC) slabs were carried out with varying modelling choices to develop better modelling strategies. The aim was to study how accurately the response of a slab subjected to bending could be predicted with nonlinear finite element (FE) analysis using three-dimensional (3D) continuum elements, and how the modelling choices might influence the analysis results. The load-carrying capacity, load-deflection response, crack pattern and reaction-force distribution of the two-way slab studied were compared to experimental data available. The influence of several modelling parameters was investigated, including geometric nonlinearity, element properties, concrete model, reinforcement model and boundary condition. The results show the possibility of accurately reflecting the experimental results concerning load-carrying capacity, load-deflection response and crack pattern giving proper modelling choices. Moreover, the reaction force distribution was found to be highly influenced by the stiffness of the supports

Samarbetsprojekt för effektivare brobyggande

Den svenska anläggningsbranschen har i ett flertal utredningar fått skarp kritik på grund av dålig produktivitet. Forskning visar på samma tendenser i övriga Europa och USA. Vissa mätningar tyder på att byggandet i den svenska anläggningsbranschen har en kostnadsökning som är dubbelt så hög jämfört med övriga branscher under de senaste 20 åren. Låg produktivitet och låg innovationsförmåga i byggbranschen leder till högre kostnader som inte garanterat ger en högre kvalitet. Trenden behöver vändas så att avkastningen på investeringar i vår infrastruktur ökar! Det första steget är att integrera konstruktions- och produktionsprocesserna, vilket ger kortare ledtider för både planering och uppförande av byggnadsverk. Onödigt långa byggtider orsakar störningar för andra aktörer i samhället. I ett pågående doktorandprojekt, som är ett samarbete mellan Trafikverket, WSP och Chalmers, söks möjligheten till att öka produktiviteten inom den svenska anläggningsbranschen. Huvudspåret är att utveckla och industrialisera brobyggandet. En effektivare byggindustri skapar möjligheter till att generera ett mervärde för samhället där mervärdet exempelvis kan motsvaras av att konstruktioner byggs med högre kvalitet till samma kostnad som idag alternativt samma eller högre kvalitet till en lägre kostnad än idag. Bortsett från rena kostnader bör naturligtvis en effektivare byggindustri också se till att lösningar väljs utifrån ett hållbart samhälle men med bibehållen fokus på produktivitet och innovation. En sådan lösning kan variera från själva processen till konstruktionsdetaljer

Anchorage in naturally corroded specimens taken from existing structures

In an on-going project, the anchorage capacity of naturally corroded steel reinforcement wasinvestigated experimentally. The beam specimens were taken from edge beams of Stallbacka Bridge in Sweden.The specimens showed different extent of corrosion induced damage; from no sign of corrosion to extensivecracking and spalling of the concrete cover. After consideration of different possible test setups, a fourpoint bending test indirectly supported with suspension hangers was chosen. The beams were strengthenedwith transverse reinforcement around the suspension hangers to avoid a premature failure. Eight successfultests have been carried out so far; in all these, a diagonal shear crack preceded an anchorage failure. The anchoragebehaviour was examined through monitoring the applied load, free-end slip and mid-span deflection.The test results can be used to extend our knowledge concerning the structural behaviour of corroded reinforcedconcrete structures to field conditions

Anchorage of corroded bars: eccentric pull-out tests and numerical analysis

Eccentric pull-out tests were carried out to study (a) the influence of cover cracking and (b) the effect of stirrups, on the bond of corroded bars. Next, an earlier developed corrosion model was extended to include the effect of rust flowing through corrosion cracks. The extended model was used in detailed three-dimensional analyses of the tests. The tests and analyses showed an important effect of the cover cracking in terms of loss of confinement and the flow of rust through the cracks. They also indicated that the bond behavior and the failure were strongly governed by the position of the anchored bar, i.e. corner or middle positions, and the level of the corrosion attack. Stirrups played an important role after cover cracking, as they then became the primary source of confinement. Furthermore, corrosion of stirrups led to a more extensive cover cracking for a relatively low level of corrosion attack

Anchorage of corroded bars: eccentric pull-out tests and numerical analysis

Eccentric pull-out tests were carried out to study (a) the influence of cover cracking and (b) the effect of stirrups, on the bond of corroded bars. Next, an earlier developed corrosion model was extended to include the effect of rust flowing through corrosion cracks. The extended model was used in detailed three-dimensional analyses of the tests. The tests and analyses showed an important effect of the cover cracking in terms of loss of confinement and the flow of rust through the cracks. They also indicated that the bond behavior and the failure were strongly governed by the position of the anchored bar, i.e. corner or middle positions, and the level of the corrosion attack. Stirrups played an important role after cover cracking, as they then became the primary source of confinement. Furthermore, corrosion of stirrups led to a more extensive cover cracking for a relatively low level of corrosion attack

Influence of frost on the bond between steel and concrete

One of the severe types of deterioration in concrete structures is associated with the volume expansion of concrete caused by freezing and thawing of concrete. Frost damage in concrete is caused by the volume expansion of freezing water in the concrete pore system. Thereby, tensile stresses are initiated and micro and macro-cracks are introduced into the concrete body, which leads to a type of severe damage known as internal frost damage. This mechanism not only affects the material properties of concrete such as tensile and compressive strength and elastic modulus of concrete, but also, influences the bond strength between the reinforcement and surrounding concrete in damaged regions

Influence of frost on the bond between steel and concrete

One of the severe types of deterioration in concrete structures is associated with the volume expansion of concrete caused by freezing and thawing of concrete. Frost damage in concrete is caused by the volume expansion of freezing water in the concrete pore system. Thereby, tensile stresses are initiated and micro and macro-cracks are introduced into the concrete body, which leads to a type of severe damage known as internal frost damage. This mechanism not only affects the material properties of concrete such as tensile and compressive strength and elastic modulus of concrete, but also, influences the bond strength between the reinforcement and surrounding concrete in damaged regions