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(1) Bridges in Croatia, (2) Seismic Assessment during regular operation Case study 1: Precast prestressed simply supported girder bridge Case study 2: Reinforced concrete frame bridge with V shaped piers Case study 3: Set of six continuous grill type continuous superstructures (3) Seismic assessment developed for arch bridges Revealing ductility levels (4) Post Earthquake Rapid Damage Assessment Case study: Eight bridges in Glina County (5) Shortcomings vs. Hidden reserves (6) Conclusions

According to Eurocode HRN EN 1991-2 and Croatian National Annex HRN EN 1991-2/NA highway and expressway bridges need to be designed for Load Model 1 (heavy vehicles) and Load Model 3 (special vehicles) traffic loads. Classes of special vehicles are defined in Annex A of HRN EN 1991-2, while the Croatian National Annex requires the use of 15 axle special vehicle with total weight of 3000 kN and axle loads of 200 kN. The simultaneity of LM1 and LM2 is also covered by the standard, depending on the travel speed of the special vehicles. Design practice has shown that these design requirements have notable impact on bridges in the 30 to 100 m span range. In this paper, the results of a parametric study on a group of continuous girder bridges with different spans and carriageway widths are presented, to determine the exact difference in resulting hogging and sagging moments and shear forces between LM1 and LM3 Load Models. Thus, the governing Load Model and its effect on the design for the relevant range of bridges is determined. A recommendation is made as to when each Load Model should be used in design.

A large part of the Croatian territory is in an extremely seismically active area. This was proven by two strong earthquakes that have occurred in the last two years. In such events, it is very important to provide corridors for safe evacuation of people and transport of aid to the earthquakeaffected areas. In these earthquakes, bridges, as a crucial element of the transportation infrastructure, mostly suffered only minor damage, but sufficient enough to raise questions about their actual earthquake resistance. Most bridges in the last century were built with minimal or no seismic regulations, using smooth reinforcement. Columns, as main structural elements for seismic resistance of bridges, often deviate from the classic rectangular and circular cross-sections for which guidelines exist in the literature and in the codes. In these elements, hidden reserves in bearing capacity can be found when allowing the development of plastic joints and deformations within the plastic region. The rotation of the end section with the rotation of one or two sections at the level of the plastic joint gives the total rotational capacity, which directly affects the stiffness of the formed elements and, consequently, the seismic response of the whole structure. Evaluation of this behavior presents a real challenge in the assessment of the actual seismic resistance of such structures. This paper presents an experimental and numerical analysis of the scaled bridge pier models under horizontal and vertical load. The level of deformations, stresses, displacements and crack distribution of column elements are analyzed, and conclusions are given regarding the basic indicators of seismic resistance.

In the last two years two major earthquakes shook northwest Croatia. The first one was in March 2020 with the epicenter 10 km north of Zagreb with a magnitude of ML=5.5, and the second stronger one was in December 2020 with the epicenter 50 km southeast of Zagreb near the town of Petrinja with the magnitude of ML=6.2. Both earthquakes caused severe structural damage to Zagreb city and nearby settlements, and throughout the whole Sisak-Moslavina County. Recorded structural damage ranged from severe damage including total collapse (about 11% of buildings) to light or moderate damage (65% of buildings). Total damage was estimated by World Bank to be around 17 billion euros for 73.000 affected buildings. The first earthquake caused the most damage to the old part of Zagreb city with historical masonry and timber multistory residential buildings, most of which are now around 100 years old. The second earthquake caused damage to a more spread-out area encompassing mostly smaller family houses of mixed reinforced concrete and/or masonry structures, but also linear infrastructure (roads, bridges, pipelines) and soil damage (landslides, liquefaction, sinkholes). After both earthquakes, teams of Civil Engineers were organized by a Civil Protection Authority and led by experts from the Faculty of Civil Engineering Zagreb to perform a rapid post- earthquake assessment of structural safety. The assessment was done according to the prepared methodology which includes a five-level damage classification system and three-level usability labels. This paper will give an overview of the damage classification work with case study examples of the damage and usability grades.

Numerous bridges in Croatia, as well as around the world, are currently approaching their designed service life of 50 or 100 years. They are designed according to previous codes with much lower actions, so an evaluation of their load-bearing capacity is necessary. At the European level, there is still no specific standard that would help engineers in assessment of existing structures, while the application of standards for new structures is too conservative. In this article, the assessment of two reinforced concrete bridges on the Croatian national road is presented using two methods for calibrating partial safety factors proposed in fib Bulletin 80. These are the design value method (DVM) and the adjusted partial safety factor method (APFM), which use a specified reliability index and reference period to determine a reduced value of the partial safety factor, which is then used to determine the design value of action and resistance. These methods are used to evaluate the load-bearing capacity of bridge superstructures exposed to dead load and traffic. The used methods are compared with the Eurocode for new structures and conclusions are drawn.

Klimatske promjene se već događaju i utječu na sve aspekte života pa tako i graditeljstvo, imajući višestruki utjecaj na stabilnost, nosivost i uporabljivost konstrukcija. Fokus ovog rada je analiza utjecaja na betonske mostove u morskom i planinskom okolišu te su detaljno razmotrena dva najveća rizika: utjecaj klimatskih promjena na koroziju armature i seizmički kapacitet kroz pregled znanstvenih rezultata i analizu studija slučaja. U svrhu bolje prilagodbe infrastrukture klimatskim promjenama istaknute su greške koje je potrebno izbjeći te primijenjene mjere prilagodbe za povećanje trajnosti i nosivosti konstrukcija.

U radu je dan pregled forenzičkog inženjerstva u građevinarstvu, strategije koja slijedi nakon otkazivanja mostova. Provedena je statistička analiza i sistematizacija raspoloživih podataka o otkazivanjima mostova u cijelom svijetu u vremenskom razdoblju od 1966.- 2020. godine. Detaljno je analizirano više od 600 slučajeva djelomičnog ili potpunog rušenja mostova te su analizirani uzroci koji su doveli do njihovog otkazivanja. Do otkazivanja svakog od ovih mostova najčešće nije došlo uslijed samo jednog faktora, već je glavni uzrok je najčešće okidač u uzročnoposljedičnom slijedu niza događaja koji su tome pridonijeli. Sukladno tome, osim glavnih uzroka, za svaki od analiziranih slučajeva naveden je i utjecaj ljudskog faktora kao preduvjeta koji je doveo do otkazivanja. U drugom dijelu rada opisani su tipovi progresivnog kolapsa kao kritičnog načina otkazivanja konstrukcija, s naglaskom na mostove, kao i pregled teorije robusnosti konstrukcija. Dane su smjernice i pristupi projektiranju u cilju sprječavanja katastrofalnih otkazivanja i stvaranja robusnijih konstrukcija. Opisani su načini postizanja robusnosti kod projektiranja novih te ojačavanja postojećih mostova, uz praktične primjere iz prakse., A review of forensic structural engineering, which is a strategy that follows after bridge failure, is presented in the paper. A detailed statistical analysis, and worldwide systematisation of available bridge failure data for the 1966-2020 period, are given. More than six hundred cases of partial or full collapse of bridges are analysed in detail, and causes that have led to their failure are examined. Failure of each of these bridges was in most cases not caused by a single factor, i.e. the main cause was most often just a trigger in the cause-and-effect sequence of events that contributed to such failure. Consequently, in addition to main causes, the influence of human factor, as a precondition leading to failure, is considered in each of the analysed cases. Types of progressive collapse, being a critical structural failure mechanism, are described in the second part of the paper, with an emphasis on bridges. An overview of the theory of structural robustness is also given. Design guidelines and approaches, aimed at preventing catastrophic failure and creating more robust structures, are presented. Methods for achieving robustness in the design of new bridges and in the strengthening of the existing ones are also described, and practical real-life examples are provided.

Existing bridge maintenance policy, where bridge assessment is based on results of visual inspection is not sufficient since reinforcement corrosion, as the main degradation process of concrete bridges, cannot be timely detected. Hence, new approach, where visual inspection is combined with simple, rapid and cost-effective non-destructive testing (NDT) is presented and demonstrated on the case study: Adriatic Bridge across Sava River in Zagreb. NDT on the bridges includes crack detection, determination of geometry and crack cause identification, estimation of strength and dynamic elastic modulus of concrete, rebar detection, measurements of rebar diameter, concrete cover, electrical resistivity of concrete and half-cell potential. Application of NDT increases the objectivity of the visual inspection results and allows detection of invisible defects, what was confirmed by additional destructive testing on the case study. Utilization of results obtained by visual inspection and NDTs in numerical models for service life prediction of structure is discussed, highlighting the importance of inclusion of performance indicators variation due to non-uniformity of concrete quality (local cracks, damage).

When assessing an existing bridge, the application of conservative design load and resistance models can cause unnecessarily high maintenance costs. On the other hand, sophisticated methods based on probabilistic approach require greater effort and are also demanding for practical application. Consequently, multi-level assessment procedures are considered appropriate, whereby complexity and accuracy increase consecutively through the levels. Namely, if the bridge meets the requirements at the first assessment level - on the safe side, no further complicated steps are needed. Otherwise, a more complex assessment step should be carried out in which we are closer to the real values of the structure's performance and resistance. In this paper, (i) the multi-level assessment of road bridges for traffic load and (ii) the multi-level seismic assessment of arch bridges, will be overviewed. In addition, recommendations for further development of assessment procedures will be provided, based on undergoing research. The first research branch explores the value of implementing the Bridge-Weigh-in-Motion measurements together with the probabilistic approach in assessment of existing road bridges. The second research branch aims to reveal seismic resistance of bridge elements with nonstandard sections and smooth reinforcement designed without contemporary rules for ductile behaviour.

Bridge databases in Croatia, collection and management of data Developments on the (seismic) assessment of existing bridges Monitoring or data acquisition systems for existing bridges, with a particular focus on old, deteriorating bridges

Mostovi su važan dio prometne infrastrukture, a podaci dobiveni ocjenom seizmičke oštetljivosti mostova važan čimbenik u donošenju odluka o postupcima sanacije i o postupcima koji slijede nakon potresa. U Hrvatskoj postoji značajan broj mostova koji su izgrađeni prije stupanja na snagu niza normi HRN EN 1998 za seizmički proračun konstrukcija, te je stoga važno provesti ocjenu njihove potresne oštetljivosti. Ocjenjivanje mostova provodi se pomoću krivulja vjerojatnosti oštećenja. U radu je prikazana metodologija izrade krivulja vjerojatnosti oštećenja uz prikaz osnovnih tipova mostova u Hrvatskoj.

Faculty of Civil Engineering, Education, Research, Practice, Projects, Chair for Bridges

Das Qualitätsmanagement von Strukturen aus Stahl- und Spannbeton, insbesondere jener von Straßenbrücken unterscheidet sich innerhalb Europas stark von Staat zu Staat. Diese Publikation gibt nicht nur einen Überblick über den aktuellen Stand der Technik, sondern es wird ein Vorschlag für eine holistische Performance-Bewertung von Brücken aus Konstruktionsbeton vorgestellt. Um die Vorgehensweise bei der Qualitätskontrolle von Straßenbrücken und infolgedessen die Entscheidungsfindung zur Umsetzung von Instandhaltungsmaßnahmen auf einen einheitlichen Standard zu bringen, hat sich das europäsche Forschungsprojekt COST (European Cooperation in Science & Technology) Action TU1406 zum Ziel gesetzt, eine in Europa allgemein gültige Richtlinie zur Erstellung von Qualitätskontrollplänen zu entwickeln. Die COST TU 1406 befasst sich mit der Erhebung der für die Zustandsbeurteilung von Straßenbrücken relevanten Leistungsindikatoren (performance indicators). Um Daten in Bezug auf diese Performance-Indikatoren zu sammeln, wurden die Mitgliedsstaaten der COST Action ersucht, sämtliche Informationen aus bereits in Anwendung befindlichen Dokumenten, wie Richtlinien und Normen, sowie aus Forschungsdokumenten zu erheben. In diesem Beitrag werden die Prozesse hinsichtlich der Erhebung und Dokumentation der Daten sowie deren Evaluierung eingehend beleuchtet. Ein wesentlicher Teil war auch die Homogenisierung und Kategorisierung der Ergebnisse aus den Erhebungen, um in weiterer Folge Performance- Indikatoren zu identifizieren und diese dann sogenannten Key-Performance-Indikatoren zuzuordnen. Die Erhebung der Performance- Indikatoren und die Definition von Key- Performance-Indikatoren waren wesentliche Schritte zur Entwicklung einer standardisierten Richtlinie zur Erstellung von Qualitätskontrollplänen für Straßenbrücken auf europäischer Ebene.

Current policies of bridge management system at different road authorities in Croatia are presented in this paper. Although reinforcement corrosion is the major cause of concrete bridge deterioration, quality control plan that would provide efficient and effective bridge management system has not been implemented on satisfactory level to assure pro-active maintenance. Quality control plan for concrete bridges vulnerable to reinforcement corrosion, proposed in this research, includes visual inspection supplemented with the non- destructive testing and structural health monitoring as well as numerical models for service life predictions using recently developed 3D chemo-hygro-thermo mechanical model. The proposed quality control plans will be demonstrated on six concrete bridges of different load-bearing type, age, material and traffic demands exposed to continental and maritime environment.

Adriatic coast is characterized by multi-hazard environment: high salinity of the Adriatic Sea, strong winds, high seismicity and extreme traffic load during summer tourist season. Case studies of Adriatic large span reinforced concrete arch bridges confirm chloride induced corrosion as the main degradation mechanism. In order to provide better bridge assessment and optimal maintenance planning, the coupled 3D chemo-hygro-thermo mechanical (CHTM) model was developed in order to enable a realistic simulation of reinforcement corrosion processes, taking into account influence and interaction of numerous material, structural, environmental and climate performance indicators. Climate performance indicators are of great importance to precisely determine environmental loads on structures. Structural health monitoring, non-destructive testing and visual inspections are essential for model verification through comparison of numerical results and data obtained on existing bridges providing a base for more accurate prediction of the remaining service life of structures.

In this paper and following further research, key indicators to be monitored, for achieving efficient and effective performance of existing concrete arch bridge, through their design lifetime, will be revealed. Namely, on one hand, under the auspices of undergoing COST Actions TU 1406 (Quality specifications for roadway bridges, standardization at a European level) with a support of the COST Action TU 1402 (Quantifying the Value of Structural Health Monitoring), bridge performance aspects for achieving goals crucial for optimal bridge management are analysed. Categorisation process of operational based performance indicators is under progress, aiming further extension of operational database with the research- based one, particularly in the area of monitoring based performance indicators. On the other hand, research on development of assessment procedures for existing arch bridges is developing through several years in Croatia as a part of an extensive project to develop their appropriate maintenance strategy. To define a correct structural model of the existing structure and to perform adequate structural analysis, in order to properly assess the existing bridge, it is necessary to identify desired knowledge level of the existing structure based on the bridge importance. In order to get a valuable link between a certain indicator measurement (performance indicator) and corresponding property of structure (structural performance type or performance goal) of interest at the desired knowledge level, it is of a great importance to establish adequate data collection using appropriate monitoring methods for arch bridges. Therefore, this paper will show how the experience with Adriatic arch bridges serves as a base to extend the national project to the European level in order to prepare comprehensive guidelines for data collection to reach required knowledge level and to properly assess performance abilities of arch bridges in general.

In bridge management systems, multi-objective decision-making has emerged as a decision support technique to integrate various technical information and stakeholder values. Different multicriteria decision making techniques and tools have been developed in the last three decades. This paper presents an overview of different approaches to multi-objective decision making at the object and network level, with the purpose of incorporating different aspects of bridge performance goals, which may vary according to technical, environmental, economic and social factors. The example of application of analytic hierarchy process (AHP), as one of the multi criteria decision making method, to a illustrative case study is presented in the paper.

This paper presents experimental results of static and dynamic response of damaged RC beams strengthened with CFRP strips and sheets. Three prestressed RC beams with T cross section were tested. Beams were subjected to monotonic loading with increasing load steps with four-point bending setup in order to generate different damage levels in specimens. CFRP strengthening was applied on the specimens after they were damaged by loading to 50% of their flexural capacity. Modal tests were carried out after each loading-unloading cycle. Beams were excited by the impact hammer. Frequency response functions were processed using Dewesoft software to obtain natural frequencies, and corresponding damping ratios and mode shapes.

The paper provides a brief overview of recently developed fully coupled 3D chemo-hygro-thermo- mechanical model for simulation of chloride induced corrosion, before and after depassivation of steel as well as its consequences on degradation of reinforced concrete structures. Emphasis of this paper is given on the initiation phase of corrosion in order to analyse the influence of crack width and depth on the transport processes in concrete before depassivation of the steel rebar. The application of the model is illustrated on analysis of the reinforced concrete beam exposed to the cracking due to 4 point bending and influence of seawater. The numerical results of chloride content in concrete are compared with the results obtained on the Maslenica Motorway Bridge after 13 years of exposure to maritime conditions. Good agreement of numerical results and data obtained on the bridge is basis to predict remaining service life of the bridge. According to the assumption of the numerical analysis, depassivation of the reinforcement bar in un- cracked concrete is achieved after 100 years of exposure, while threshold chloride concentration on the level of the rebar in cracked concrete is reached within 1 year after crack opening. The service life will be shorter if the cracks in concrete are wider and deeper.

The tradition in construction of reinforced concrete arch bridges in Croatia and experiences gained through their assessment enabled the improvement of seismic assessment of this type of bridge. In this paper, original assessment procedure is overviewed in order to reveal interactions off different types of performance indicators. The attempt of their systematization into three main categories: structural, environmental and economic indicators is done as a step towards their quantification.

An overview of the performance indicators’ categorization based on results of the screening process of the inspection and evaluation documents for roadway bridges performed under the auspices of COST action TU 1406 is proposed. Additionally research based indicators are contemplated in order to raise existing European maintenance practice to a higher level.

Assessment and rehabilitation of existing bridges, and concrete structures in general, has become an important issue for civil engineers nowadays. There are several factors causing structural deterioration of bridges. Along with aggressive environment and ageing of material, bridges are exposed to increasing traffic loads, due to rapid growth in volume and weight of heavy vehicles. Furthermore, more than fifty percent of bridges in the region are more than forty years old and designed with previous design standards, which increases the need for strengthening. Among the various methods for increasing capacity of existing bridges available today, external post- tensioning provides very efficient solutions for small and medium span bridges, because of the speed of construction and minimal disruption to traffic flow. Scope of this paper is to give an insight on external PT technique and its application in retrofitting and strengthening of existing bridges. Case studies of assessment and repairing of two bridges in the region using external PT will be presented. There are several design, detailing, durability and construction issues that need to be considered with special care when designing an external PT system. Anchorage zones and deviators should be carefully designed and detailed to ensure transfer of forces to concrete. Furthermore, effects of the new forces introduced to the system must be carefully evaluated, as they depend on condition of existing bridge.

Experiences from COST Action Vice-chair on benefits and possibilities about participation in European Cooperation in Science and Technology (COST).

With this lecture an overview of COST Action TU1406 Working Group 1 achievements in revealing performance indicators for road bridges is presented. Possible harmonisation between COST Action TU1406 and TU1402 is contemplated and related tasks are identified. Upon identifying performance indicators that may be detected/evaluated and possibly quantified with available SHM technologies (e.g. corrosion progress, cracks evolution, deflection evolution, fatigue damage evolution, score criticality, weight in motion monitoring, ...) their importance in achieving crucial performance goals should be weighted.

In the past few years, significant worldwide research has been done regarding condition assessment of roadway bridges, namely through the use of non- destructive tests, monitoring systems and visual inspection techniques. Obtained values, which provide information regarding the assessed bridge state condition, are then compared with previously established goals. As a result, there are currently several methodologies to evaluate bridge condition. A similar problem was addressed with roadway pavements in the past. Although this was a worldwide problematic, in Europe it was solved through COST Action 354 (performance indicators for pavements). More recently, the concept of performance indicator was introduced, simplifying communication between consultants, operators and owners. However, large deviations continue to exist on how these indicators are obtained and, therefore, specific actions should be undertaken in order to standardize this procedure. It is verified that Quality Control (QC) plans should always address the assessed performance indicators and pre- specified goals. However, these latter values are even more difficult to obtain as they are highly subjective.

Povećanja u prometnom opterećenju, starost i agresivno djelovanje okoliša glavni su razlozi propadanja postojećih cestovnih mostova. Analiza i ocjenjivanje njihove pouzdanosti neophodni su za daljnju upotrebu. Korištenje normi za nove konstrukcije kod ocjenjivanja postojećih u praksi se nije pokazalo isplativo. U radu su navedene glavne razlike u postupku proračuna novih i postojećih mostova, objašnjene su probabilističke metode za procjenu pouzdanosti, pojam indeksa pouzdanosti i primjena Bayesove analize, te je dan kratki pregled stranih normi za ocjenjivanje postojećih mostova.