Search

Seismic assessment and subsequent retrofitting of existing road bridges is a growing challenge for structural engineers in earthquake-prone areas. Following the two catastrophic earthquakes which occurred in the last two years in Croatia, the awareness (both from the engineers and public) for older existing road bridges is heightened. As they were designed according to old codes, and due to their age, deterioration, and increased traffic volume over the last decades, these bridges are in need of assessment (and retrofitting when required). The first part of the paper provides a theoretical overview of bridge behavior during seismic events and the identification of critical structural elements, based on the bridge type and size. In the second part, the review on the most commonly used techniques for seismic retrofitting of these bridges is given, with practical examples were available. The techniques are divided based on the corresponding structural elements and bridge types, with a focus on reinforced and prestressed concrete bridges as the most common bridge types in Croatia and the surrounding region.

Non-linear finite element analyses have intrinsic model and user factors that influence the results of the analyses. However, non-linear finite element analysis can provide a tool to assess safety using realistic descriptions of material behaviour with actual material properties. A realistic estimation of the existing safety and capacity of slender column elements can be achieved by means of "true" material properties. Nevertheless, it seems that for some structural components, such as slender columns, non-linear finite element analyses can, due to its complexity and its various setting parameters, cause the risk of overestimating the real performance of analysed components or systems. Hence, an invited expert group has carried out an investigation into the experimental testing and the prediction of the bearing capacity of slender columns by performing independent non-linear finite element analyses in order to determine the practical applicability, and its inconsistencies, with respect to the stability failure of slender columns. This work aims the characterization of modelling uncertainties, concerning the prediction of slender columns stability when forecasted by non-linear finite element analysis., This paper was partly carried out during research exchanges at TU Brno (BUT), Lehigh University (LU). The authors acknowledge also the financial support provided by the SAFEBRIDGE ATCZ190 EU Interreg project, the Scientific Grant Agency of the Ministry of Education of Slovak Republic, the Slovak Academy of Sciences VEGA No. 1/0696/14, and Slovak Research and Development Agency under the contract No. APVV-150658. The computational results presented have been achieved [in part] using the Vienna Scientific Cluster (VSC).

Traffic load models used for the design of new bridges are based on conservative assumptions and have not been proven efficient for assessing safety of existing bridges. In the case of existing bridges, it is reasonable to use load models that are based on bridge weigh-in-motion data which, in addition to axle loads and spacing of bridge-crossing vehicles, provide information on bridge behaviour under traffic load. This paper provides an overview of traffic load models, as well as guidelines on the use of weigh-in- motion data when assessing condition of existing road bridges.

U radu se raspravlja o gospodarenju mostovima u Hrvatskoj i njihovoj osjetljivosti na koroziju armature. Predlaže se, te na šest reprezentativnih mostova i razrađuje, novi pristup održavanju u kojemu se vizualni pregledi kombiniraju s nerazornim metodama. Koristeći tu metodologiju, moguće je ranije i točnije otkriti koroziju armature u konstrukcijskim elementima. Dobiveni rezultati i korelacije između različitih mjerenih parametara važni su ulazni podaci za predviđanje budućeg propadanja konstrukcije i odlučivanje o budućim aktivnostima održavanja., Management of bridges in Croatia and their vulnerability to reinforcement corrosion is discussed in the paper. New maintenance approach, where visual inspections are combined with the non-destructive testing methods, is proposed and demonstrated on six representative bridges. Using this methodology, reinforcement corrosion on structural elements may be detected earlier and more precisely. Obtained results as well as correlations between different measured parameters are important input parameters for prediction of future degradation of structures and decision making for future maintenance activity.

Bridge condition assessment in most European countries is based on visual inspection in combination with damage assessment of bridge components. For adequate bridge management, the assessment needs to be further developed to move from the bridge component level to the system functionality level and finally to the priority ranking level for repairs in the network. Although visual inspection provides only qualitative insights into bridge condition and cannot predict load-carrying capacity, it is still very often the only way to collect data on existing bridges and can provide very important information for evaluating structural safety, traffic safety, durability, and overall bridge condition. Therefore, this paper presents a unique procedure that establishes a relationship between a country-specific bridge condition assessment procedure based on visual inspection and the systematization of key bridge performance indicators developed within the European integrated management approach at three complementary and interrelated levels—component, system, and network levels. The assessment procedure for existing bridges initiates with damage assessment based on visual inspection of bridge components and runs through weighting at component, system, and network levels to the six most important key performance indicators (KPIs) for road bridges, which are organized as graphical and numerical inputs for ranking priority maintenance. These are bridge condition assessment, structural safety, traffic safety, durability indicator, availability, and the importance of the bridge in the network. The procedure is validated on a case study set of five real bridges, using the decision-making process as an example for the small sample size. The case study bridges differ in cross-section, type, and span (which vary from 9.5 to 72 m). The bridges were built between 1958 and 2001 and are located either on state or municipal roads in Croatia. The results, in terms of condition classification and priorities of future interventions within the representative group of bridges, justify the application of the described assessment procedure. Additional digitization efforts could easily implement the described assessment approach at the infrastructure network level.

Croatian bridges have been built in different times, always in step with or even ahead of the world’s achievements. In seismically active areas it is of paramount importance to design bridges with ductile behaviour. Many bridges built before the modern Eurocodes came into force, were designed according to standards which did not offer provisions for structural detailing facilitating their ductile behaviour. Unfortunately, we learnt hard way that earthquake is a natural phenomenon which can be expected to happen in our country, and which needs to be appropriately considered in the management of the existing transport infrastructure. This is because bridges are often its key elements, and the ability to use them immediately after an earthquake is extremely important.

Over the last 20 years, beside their primary educational activities, members of the Bridge Chair of the Zagreb Faculty of Civil Engineering Structural Department also worked professionally on main and execution designs of many bridges. Most of them are mid-span to large span bridges, requiring detailed seismic design, especially since their locations are predominantly in highly seismic active regions. These bridges were designed during the transition period from old seismic standards, to ENV pre-standards, and finally to EC8 standards. The evolution of these codes had a great impact on the design. New demands in terms of seismic behaviour influenced all aspects of design, from conceptual design (structural system and material options), sizing of elements, foundation type, bearing and damper layouts, special equipment selection, erection details, to maintenance requirements. An overview of seismic design requirements, solutions, and peculiarities for each of these bridges, which were recently constructed or are currently under construction, is presented in the paper. Since the design of the cable stayed bridge Franjo Tuđman in Dubrovnik, where fluid viscous dampers were first employed in Croatia, to the recent bridge designs, various approaches were utilized to mitigate and take over the seismic actions. Adequate solutions were found either by structural detailing and/or by installation of seismic isolators, depending on bridge structural systems, utilized materials, but also on the characteristics of foundation soil.

Modeli prometnoga opterećenja koji se primjenjuju pri proračunu novih mostova temelje se na konzervativnim pretpostavkama te se njihova upotreba u analizi postojećih mostova nije pokazala učinkovitom. Kod postojećih mostova preporučena je primjena modela prometnoga opterećenja temeljenog na mjerenju prometa u pokretu, koji osim osovinskoga opterećenja i razmaka, daje i podatke o ponašanju mosta pod prometnim opterećenjem. U ovome su radu dani pregled modela prometnoga opterećenja te smjernice o upotrebi podataka dobivenih mjerenjem prometa u pokretu prilikom ocjene stanja postojećih cestovnih mostova., Traffic load models used for the design of new bridges are based on conservative assumptions and have not been proven efficient for assessing safety of existing bridges. In the case of existing bridges, it is reasonable to use load models that are based on bridge weigh-in-motion data which, in addition to axle loads and spacing of bridge-crossing vehicles, provide information on bridge behaviour under traffic load. This paper provides an overview of traffic load models, as well as guidelines on the use of weigh-in-motion data when assessing condition of existing road bridges.

U seizmički aktivnim područjima poželjno je projektirati mostove duktilnog ponašanja. Veliki se broj postojećih mostova, projektiranih prema danas zastarjelim normama, a koje nisu nudile smjernice za oblikovanje elemenata za duktilno ponašanje, nalaze se u seizmički aktivnim područjima. Nepoznata je razina duktilnosti koju ti mostovi posjeduju. U ovome se radu razmatra jedan od bitnih pokazatelja seizmičke otpornosti starijih mostova sa stupovima u kojima je ugrađena glatka armatura – krivulja ovisnosti momenta savijanja i zakrivljenosti, M- krivulja. Uspoređeni su rezultati analitičkog, eksperimentalnog i numeričkog pristupa u određivanju krivulje te su doneseni zaključci o utjecaju proklizavanja glatke armature., In seismic areas, it is recommended to design bridges characterized by ductile behaviour. A large number of existing bridges designed according to outdated standards, without guidelines for ductile behaviour detailing, can be found in seismically active areas. The level of ductility exhibited by these bridges is unknown. A crucial seismic performance indicator for older bridges with piers containing round reinforcing bars, i.e. the bending moment-curvature curve (M- curve), is considered in this paper. The results of analytical, experimental and numerical approaches for determining the M- curve are compared, and conclusions on the effect of round reinforcement slippage are presented.

Concrete damage (cracks, voids and delamination) significantly influence initiation and propagation phase of reinforcement corrosion. The three methods are combined in the framework of this research: (i) on-site testing on concrete bridges, (ii) application of an advanced numerical model for service life prediction on existing structures and (iii) laboratory experiments on permeability of cracked concrete. The aim of this research is to determine the mutual interaction of material, structural, environmental and climate performance indicators under following degradation mechanisms: chloride induced corrosion of reinforcement in concrete and concrete cracking due to mechanical and non-mechanical loading. The broader aim is to predict bridge service life more precisely as a base for establishment of an optimal bridge quality control plan. The focus of the paper is application of on-site testing on existing bridges. Influence of cracks in concrete on reinforcement corrosion on existing structures can be determined by application of non-destructive testing, not only by measured values but also to define area of structure on which a crack has impact.

Paper reports findings from parametric analysis of open section constant height composite bridges with considered spans ranging from 20 to 70 m (for larger spans closed box girder section is recommended). For these spans, girder structural system is analyzed for permanent and traffic loads, and thus steel quantity determined according to Eurocode limit states. For each span, possible sections comprise various “I” girder types and various number of girders determined from variable bridge width, distinguishing two groups of sections – sections with only two main girders (comprising hunched deck plate of variable thickness) and sections with more than two girders (comprising constant thickness deck plate). Other considered parameters are section height, steel flange width and occurrence of web stiffeners for buckling verification. Analysis is performed on finite element models, according to typical construction stages, where composite section is activated only for loads applied after in‐situ concreating of deck slab. For each variable set, needed steel quantity is recorded. Graphical representation of all results is plotted in diagrams, showing section types and steel quantity for a given range of span lengths. In conclusion, comments are given for use of composite cross sections according to the bridge span length and width.

Condition assessment of six bridges: Maslenica Bridge, Šibenik Bridge, Adriatic Bridge, Bridge of Youth, Homeland Bridge and Žeinci Bridge are presented in the paper. The bridges are of different load-bearing type, age, material and traffic demands, but their in-service performance confirms steel corrosion in concrete as main deterioration cause. Influences of age, environment, climate and construction quality on bridge durability are analysed. The presented bridges will be used as case studies for proposed new methodology of pro-active bridge maintenance based on visual inspection complemented with the non- destructive testing and application of numerical model for service life prediction.

Numerous issues need to be considered in order to achieve efficient and effective performance of existing concrete arch bridge. Although the interaction of structural, environmental and economic indicators that affect certain structural performance is inevitable, they need to be segregated in order to more easily identify methods for their quantification. In this paper, following research on existing arch bridges in Croatia, performance indicators for assessment of arch bridges will be systematized, their interaction will be elaborated and the critical locations at the typical arch bridge will be established.

Numerous issues, including structural, environmental and economic indicators, that are to be considered in order to achieve efficient and effective performance of existing concrete arch bridge will be systematized and elaborated in this paper through the examples of several Croatian Adriatic arch bridges.

U članku se prikazuju rezultati studije izrađene na Građevinskom fakultetu u Zagrebu koju su naručile Hrvatske autoceste. Cilj je studije bio razviti nove tipove nadvožnjaka na autocestama koji će biti funkcionalni, sigurni za korisnike autoceste i estetski dobro oblikovani. Rezultati studije su tri nova, originalna tipa nadvožnjaka uz razradu mnogo detalja i varijantnih rješenja za primjenu koji će oplemeniti nove autoceste i unaprijediti jedan segment našeg građevinarstva., Results of the study comissioned by Hrvatske autoceste and prepared at the Faculty of Civil Engineering, Zagreb, are presented. The objective of the study was to develop new types of motorway overpasses that will be functional, safe for motorway users, and aesthetically pleasing. The study resulted in the definition of three new and original overpass types, with many details and practical alternatives that are sure to give new dignity to future motorways, and hence improve this segment of our civil engineering practice.