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Dr. Maja Ahac
University of Zagreb - Faculty of Civil Engineering

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Research Keywords & Expertise

0 Maintenance Management
0 Superstructure Optimisation
0 Railway Engineering
0 Noise and Vibration
0 planning and analysis of transportation systems

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Noise and Vibration

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Short Biography

I was born in Zagreb, Croatia. I studied civil engineering at the University of Zagreb and obtained my MCE degree in 2007, and a Ph.D. degree in 2013 at the Department of Transportation Engineering (Chair for Railways) at the Faculty of Civil Engineering. Currently, I am an associate professor at Faculties Master courses in the field of traffic flow theory, railways design and construction, transport systems, and urban railways. My research interests are the behavior of railway and tram tracks superstructure during exploitation, rail traffic noise and vibrations analysis, and track geometry degradation modeling for design and maintenance optimization. I am also involved in professional projects for tram track design and maintenance and traffic noise mitigation measures.

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Journal article
Published: 12 May 2021 in Sustainability
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Challenges that emerge in roundabout design are mostly related to space constrictions and provision of appropriate deflection around the central island. This can result in speed profiles on roundabouts that might reduce their potential as a noise abatement measure. Because of this, the impact of a roundabout on noise levels and its applicability as a traffic calming device and a noise abatement measure should be investigated in the early design stage, by modeling noise levels. In this paper, the following hypothesis is tested: vehicle movement trajectories, defined during the fastest path performance check in roundabout early design phase, can be used as the road traffic noise sources when modeling noise at roundabouts using static noise model. This procedure (1) simplifies the preparation of the noise model, (2) results in a model that is closer to the real-world in terms of traffic flow conditions, (3) allows the noise calculations in the early stages of roundabout design, and (4) includes the influence of roundabout deflection on calculated noise levels. The abovementioned simplifications of the road traffic noise modeling process should encourage the optimization of roundabout geometry in terms of its noise reduction capabilities in the preliminary design phase of these intersections.

ACS Style

Saša Ahac; Maja Ahac; Josipa Domitrović; Vesna Dragčević. Modeling the Influence of Roundabout Deflection on Its Efficiency as a Noise Abatement Measure. Sustainability 2021, 13, 5407 .

AMA Style

Saša Ahac, Maja Ahac, Josipa Domitrović, Vesna Dragčević. Modeling the Influence of Roundabout Deflection on Its Efficiency as a Noise Abatement Measure. Sustainability. 2021; 13 (10):5407.

Chicago/Turabian Style

Saša Ahac; Maja Ahac; Josipa Domitrović; Vesna Dragčević. 2021. "Modeling the Influence of Roundabout Deflection on Its Efficiency as a Noise Abatement Measure." Sustainability 13, no. 10: 5407.

Review
Published: 08 January 2021 in Sustainability
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Despite the long-term experience in the application of noise walls, the uncertainty in wall panel service life efficiency is almost equal between panels built from established and new materials, which are—because of the desire to increase the sustainability of noise walls—developing at an ever-faster pace. The presented meta-analysis of data collected during a systematic review of concrete, metal, and wood panels’ acoustic and non-acoustic characteristics, long term performance, and cradle-to-gate sustainability aims to reduce this uncertainty and support the process of noise wall design and management by shifting the emphasis in decision making from construction costs to the long-term sustainability of the road traffic noise mitigation project. The multi-criterial analysis showed that when choosing a panel, preference should be given to those using lightweight concrete materials. A further comprehensive cradle-to-grave assessment of lightweight concrete panels with expanded clay and recycled tire rubber aggregates, which was performed to fill a knowledge gap observed in the literature and identify opportunities for the improvement of lightweight concrete sustainability, showed that the main environmental impacts of these panels are due to their production processes and that the way to reduce such impacts is to use panels made with aggregates from secondary raw materials.

ACS Style

Maja Ahac; Saša Ahac; Stjepan Lakušić. Long-Term Sustainability Approach in Road Traffic Noise Wall Design. Sustainability 2021, 13, 536 .

AMA Style

Maja Ahac, Saša Ahac, Stjepan Lakušić. Long-Term Sustainability Approach in Road Traffic Noise Wall Design. Sustainability. 2021; 13 (2):536.

Chicago/Turabian Style

Maja Ahac; Saša Ahac; Stjepan Lakušić. 2021. "Long-Term Sustainability Approach in Road Traffic Noise Wall Design." Sustainability 13, no. 2: 536.

Journal article
Published: 20 March 2020 in Transportation Research Procedia
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The main factors that affect the choice of the intersection type when constructing a new or reconstructing an existing intersection are desired traffic flow rate and achievable traffic safety. At the same time, a significant challenge is to find optimal solutions for (re)construction and traffic organization at intersections in settlements, especially in agglomeration centers, due to their specific and, in most cases substantial, spatial and traffic constraints. This paper presents the examination of the functional efficiency of the introduction of roundabouts in the road network of Našice Town. As the location for the analysis, a section of county road 4168 is selected, which includes two consecutive 4-legged signalized intersections. For the purpose of the investigation presented in this paper, these signalized intersections are to be substituted with two single lane roundabouts. Conceptual design of these roundabouts includes prescribed performance checks: swept path analysis, speed and visibility checks. Finally, the rating of the analyzed road corridor functional efficiency and dynamics of intersections reconstruction is given based on the defined levels of service for the current state and the intersection reconstruction proposals.

ACS Style

Maja Ahac; Saša Ahac; Mihael Devald; Šime Bezina. Analysis of the functional efficiency of small town arterial thoroughfare (Case Study of Našice Town). Transportation Research Procedia 2020, 45, 242 -249.

AMA Style

Maja Ahac, Saša Ahac, Mihael Devald, Šime Bezina. Analysis of the functional efficiency of small town arterial thoroughfare (Case Study of Našice Town). Transportation Research Procedia. 2020; 45 ():242-249.

Chicago/Turabian Style

Maja Ahac; Saša Ahac; Mihael Devald; Šime Bezina. 2020. "Analysis of the functional efficiency of small town arterial thoroughfare (Case Study of Našice Town)." Transportation Research Procedia 45, no. : 242-249.

Conference paper
Published: 10 September 2019 in 5th Symposium on Doctoral Studies in Civil Engineering
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This paper shows, on the example of the tram system operated in the city of Osijek, the effect of the quality of tram track geometry on the tram travel speed, i.e. on the change in transport supply and, consequently, in transport demand. Degraded quality of the tram track geometry has a direct impact on tram speed and, hence, on the increase in travel time. Consequently, degraded quality of track geometry affects the level of service and, finally, the number of passengers in the tram transport system. Negative impacts of the tram track geometry degradation on proper operation of the tram transport system can be reduced by proper planning and timely maintenance of tram tracks.

ACS Style

Igor Majstorović; Maja Ahac. Effect of track geometry quality on tram transport system indicators. 5th Symposium on Doctoral Studies in Civil Engineering 2019, 1 .

AMA Style

Igor Majstorović, Maja Ahac. Effect of track geometry quality on tram transport system indicators. 5th Symposium on Doctoral Studies in Civil Engineering. 2019; ():1.

Chicago/Turabian Style

Igor Majstorović; Maja Ahac. 2019. "Effect of track geometry quality on tram transport system indicators." 5th Symposium on Doctoral Studies in Civil Engineering , no. : 1.

Proceedings article
Published: 17 May 2018 in Road and Rail Infrastructure V
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ACS Style

Maja Ahac; Stjepan Lakušić; Janusz Madejski; Ivo Haladin. Application of Osijek’s tram tracks geometry analysis results in their reconstruction strategy development. Road and Rail Infrastructure V 2018, 1 .

AMA Style

Maja Ahac, Stjepan Lakušić, Janusz Madejski, Ivo Haladin. Application of Osijek’s tram tracks geometry analysis results in their reconstruction strategy development. Road and Rail Infrastructure V. 2018; ():1.

Chicago/Turabian Style

Maja Ahac; Stjepan Lakušić; Janusz Madejski; Ivo Haladin. 2018. "Application of Osijek’s tram tracks geometry analysis results in their reconstruction strategy development." Road and Rail Infrastructure V , no. : 1.

Proceedings article
Published: 17 May 2018 in Road and Rail Infrastructure V
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ACS Style

Saša Ahac; Maja Ahac; Tea Cvitanović; Barbara Trupković. Zagreb metro plans – current issues and future development. Road and Rail Infrastructure V 2018, 1 .

AMA Style

Saša Ahac, Maja Ahac, Tea Cvitanović, Barbara Trupković. Zagreb metro plans – current issues and future development. Road and Rail Infrastructure V. 2018; ():1.

Chicago/Turabian Style

Saša Ahac; Maja Ahac; Tea Cvitanović; Barbara Trupković. 2018. "Zagreb metro plans – current issues and future development." Road and Rail Infrastructure V , no. : 1.

Conference paper
Published: 15 September 2017 in IOP Conference Series: Materials Science and Engineering
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Rail vehicles in interaction with a railway structure induce vibrations that are propagating to surrounding structures and cause noise disturbance in the surrounding areas. Since tram tracks in urban areas often share the running surface with road vehicles one of top priorities is to achieve low maintenance and long lasting structure. Research conducted in scope of this paper gives an overview of newly designed tram track structures designated for use on Zagreb tram network and their performance in terms of noise and vibration mitigation. Research has been conducted on a 150 m long test section consisted of three tram track types: standard tram track structure commonly used on tram lines in Zagreb, optimized tram structure for better noise and vibration mitigation and a slab track with double sleepers embedded in a concrete slab, which presents an entirely new approach of tram track construction in Zagreb. Track has been instrumented with acceleration sensors, strain gauges and revision shafts for inspection. Relative deformations give an insight into track structure dynamic load distribution through the exploitation period. Further the paper describes vibro-acoustic measurements conducted at the test site. To evaluate the track performance from the vibro-acoustical standpoint, detailed analysis of track decay rate has been analysed. Opposed to measurement technique using impact hammer for track decay rate measurements, newly developed measuring technique using vehicle pass by vibrations as a source of excitation has been proposed and analysed. Paper gives overview of the method, it's benefits compared to standard method of track decay rate measurements and method evaluation based on noise measurements of the vehicle pass by.

ACS Style

Ivo Haladin; Stjepan Lakušić; Maja Ahac. Vibro-acoustic performance of newly designed tram track structures. IOP Conference Series: Materials Science and Engineering 2017, 236, 12046 .

AMA Style

Ivo Haladin, Stjepan Lakušić, Maja Ahac. Vibro-acoustic performance of newly designed tram track structures. IOP Conference Series: Materials Science and Engineering. 2017; 236 ():12046.

Chicago/Turabian Style

Ivo Haladin; Stjepan Lakušić; Maja Ahac. 2017. "Vibro-acoustic performance of newly designed tram track structures." IOP Conference Series: Materials Science and Engineering 236, no. : 12046.

Book chapter
Published: 18 January 2017 in Urban Transport Systems
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ACS Style

Maja Ahac; Stjepan Lakusic. Track Gauge Degradation Modelling on Small Urban Rail Networks: Zagreb Tram System Case Study. Urban Transport Systems 2017, 1 .

AMA Style

Maja Ahac, Stjepan Lakusic. Track Gauge Degradation Modelling on Small Urban Rail Networks: Zagreb Tram System Case Study. Urban Transport Systems. 2017; ():1.

Chicago/Turabian Style

Maja Ahac; Stjepan Lakusic. 2017. "Track Gauge Degradation Modelling on Small Urban Rail Networks: Zagreb Tram System Case Study." Urban Transport Systems , no. : 1.

Research article
Published: 10 April 2016 in Shock and Vibration
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Tram system is a backbone of public transportation in the City of Zagreb. In the last decade, its fleet has been renewed by 142 new low-floor trams. Shortly after their introduction, it was observed that they have a negative impact on the exploitation behavior of tram infrastructure, primarily on the durability of rail fastening systems. Because of that, it was decided to modify existing rail fastening systems to the new track exploitation conditions. When the (re)construction of tram infrastructure is carried out by applying new systems and technologies, it is necessary to take into account their impact on the future propagation of noise and vibration in the environment. This paper gives a short overview of the characteristics of the two newly developed rail fastening systems for Zagreb tram tracks, their application in construction of experimental track section, and performance and comparison of noise and vibration measurements results. Measured data on track vibrations and noise occurring during passage of the tram vehicles is analyzed in terms of track decay rates and equivalent noise levels of passing referent vehicle. Vibroacoustic performance of new fastening systems is evaluated and compared to referent fastening system, in order to investigate their ability to absorb vibration energy induced by tram operation and to reduce noise emission.1. IntroductionTram system is a backbone of public transportation in the City of Zagreb. It consists of more than 116 km of tram tracks, used daily by 180 tram vehicles. In the last decade, systems manager Zagreb Electric Tram (ZET) Ltd. has renewed its fleet by purchasing 142 new low-floor trams TMK 2200, produced by CROTRAM consortium. Another 28 low-floor trams have since then been commissioned from the same consortium. Shortly after the introduction of new low-floor trams, it was observed that this fleet modernization has increased exploitation demands on other components of tram infrastructure, that is, the power supply system and track superstructure.Regarding the effects on the track superstructure, the main consequences of the new vehicles introduction have been increase in loading forces, altered load distribution, and altered geometry of wheel and rail contact surface. This is because new low-floor trams are heavier (on average, up to 60%), with differently located center of gravity and different wheel profiles compared to the old ones [1]. These changes in tram track exploitation parameters have caused more frequent rail fastening system failures, which reflected in the increased rail wear and accelerated track geometry degradation. In event of such mayor rolling stock renewal, track structure parameters have to be evaluated [2, 3] and modified. Because of that, ZET Ltd. has decided to adjust existing rail fastening systems to the new track exploitation conditions. This was done through technical collaboration with the University of Zagreb Faculty of Civil Engineering, considering the vast experience and expertise in design and supervision of railway and tram track structures. Through similar cooperation, there have been several successful design changes to basic tram track superstructures in order to achieve better vibroacoustic performance and durability, that is, in tight curves [4], at busy level crossings [5] and tracks constructed over underground garage structures [6]. Apart from acoustic properties, major concerns in designing a suitable fastening system are vibrations and impact loads due to running surface discontinuities, which occur at switches and crossings [7, 8].When developing any new rail track system, calculations, modeling, and testing of new systems individual components material, and system as a whole, are not sufficient for its direct application in everyday engineering practice. It was therefore decided to conduct monitoring of new fastening systems exploitation behavior. This was done by construction of the test track section with built-in new fastening systems [9]. On it, the following continuous and periodic measurements were made:(i)Visual inspections of track superstructure.(ii)Measurements of track and weld geometry.(iii)Measurements of stresses and strains of tracks reinforced concrete foundation slab.(iv)Measurements of the tracks dynamic properties (i.e., vibration damping). In urban areas, due to the proximity between the tram tracks and the residential buildings, from the perspective of the surrounding residents but also the tram users, the problem of rail traffic noise and vibrations is particularly pronounced. Therefore, if the (re)construction of tram infrastructure is carried out by applying new systems and technologies, it is necessary to take into account their impact on the future propagation of noise and vibration in the environment. This paper gives a short overview of the characteristics of the two newly developed rail fastening systems for Zagreb tram tracks, their application in construction of the test track section, and performance and comparison of noise and vibration measurements results. Data on rail vibrations occurring during passage of the tram vehicles will demonstrate the ability of the track experimental constructions to absorb vibrations and thus prevent their propagation in the environment. The greater is the ability of the rail fastening systems to effectively attenuate rail vibrations induced by passing tram vehicle, the lesser will be the propagation of noise and vibration in the environment.2. Development and Characteristics of New Rail Fastening SystemsThe primary role of the rail fastening system is positioning and fixing of the rails and transferring the vehicle load from the rails to the track substructure. Generally, the type and characteristics of fastening system are chosen depending on the required elasticity of the track, planned load, and type of rail. On major part of Zagreb tram tracks, grooved rails are discreetly laid on the levelling layer, made out of micro synthetic concrete, and built on reinforced concrete slab. The distance between levelling layer supports is one meter in the tram rolling direction. Rails are fixed to these blocks by several different types of fastening systems [7], mostly by(i)direct elastic fastening system ZG 3/2 (Figure 1(a)) with 140 MN/m stiffness, developed during the 1980s and still used on about 20% of network;(ii)indirect elastic fastening system with decreased stiffness PPE (Figure 1(b)) with 50 MN/m stiffness, developed during the 1990s in order to increase tram track life span and used on about 10% of network;(iii)indirect elastic fastening system DEPP (Figure 1(c)) with 40 MN/m stiffness, developed in order to solve all the essential flaws of its predecessors and used on about 50% of network.Figure 1: Schematic cross sections of rail discrete bearings with ZG-3/2, PPE, and DEPP fastening systems. By reducing the fastening systems stiffness, vehicle load is transferred to greater number of bearings (supports). This reduces the strain of individual bearing and the speed of load increment and prolongs the life of both the bearings and rails. Reducing the stiffness also lowers the rails frequency, which reflects positively on the overall construction of the track and reduces tram traffic noise and vibration. However, the above-mentioned indirect elastic fastening systems reflect state of the art and the demands on the exploitation behavior of the tracks from the beginning of the 1990s, which do not meet today’s highly complex exploitation requirements on Zagreb’s tram tracks:(i)large tram traffic volume (individual sections of Zagreb’s tram tracks that have a traffic volume of up to 15 million gross tons per year),(ii)high vehicle passing frequency (vehicle frequency which is less than 90 seconds between vehicles on individual sections),(iii)high wheel loads on low-floor trams (more than 3.5 tons per wheel),(iv)strict tolerances regarding the narrow, 1000 mm gauge, track geometry. Based on the above requirements, during the last few years the faculty has developed five different concepts for new fastening systems. Two of them, with working titles 21-CTT (Classic Tram Track) (the name was chosen because the structure of the system is an upgrade of the existing indirect elastic systems) and 21-STT (Slab Tram Track), were chosen for further development. Their characteristics, production requirements, and installation methods best match previous experiences in the construction and maintenance of tram tracks in Zagreb.21-CTT system (Figure 2(a)) places the rails discreetly on the levelling layer, made out of micro synthetic concrete, built on reinforced concrete slab (Figure 3). The distance between supports is one meter in the tram rolling direction. The rail foot is supported by neoprene pads placed on ribbed steel plate, laid on the levelling layer. To ensure the durability of individual components and ease the installation during construction and dismantling during the track reconstruction, the underside of the ribbed steel plate is fitted, by vulcanization process, with elastic pad. Vulcanization process enabled production of a compact element electrically isolated from other components (anchors) but also provided additional elasticity of the whole fastening system.Figure 2: Schematic cross sections of rail discrete bearings with 21-CTT and 21-STT fastening systems.Figure 3: Design model of tram track structure with 21-CTT fastening system.21-STT system (Figure 2(b)) represents a completely new solution for tram tracks superstructure construction in Croatia. Its main advantage over the previous systems is that the levelling layer (which is quite difficult to construct) is replaced by two block precast concrete sleepers laid on reinforced concrete base slab, one meter apart (Figure 4). Upper reinforced concrete slab is constructed after track horizontal and vertical alignment adjustment. This is a direct elastic fastening system, with one elastic pa

ACS Style

Stjepan Lakušić; Ivo Haladin; Maja Ahac. The Effect of Rail Fastening System Modifications on Tram Traffic Noise and Vibration. Shock and Vibration 2016, 2016, 1 -15.

AMA Style

Stjepan Lakušić, Ivo Haladin, Maja Ahac. The Effect of Rail Fastening System Modifications on Tram Traffic Noise and Vibration. Shock and Vibration. 2016; 2016 ():1-15.

Chicago/Turabian Style

Stjepan Lakušić; Ivo Haladin; Maja Ahac. 2016. "The Effect of Rail Fastening System Modifications on Tram Traffic Noise and Vibration." Shock and Vibration 2016, no. : 1-15.

Journal article
Published: 18 December 2015 in Transport
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Tram track system management is a complex, costly and interdisciplinary process. It involves construction, monitoring and maintenance of track infrastructure and rolling stock, and public transport organization. Track management cost reduction requires development of a modern management system that is based on integration and mutual complementarity of engineering and maintenance activities. The first step of its establishment is increasing the proportion of planned predictive-preventive track maintenance at the expense of corrective maintenance. This requires creation of a maintenance-planning model. Its basic prerequisite is the development of a mathematical model of tram track degradation during exploitation. The research presented in this paper describes the creation of mechanisticempirical models for tram tracks (narrow) gauge degradation by adopting the modelling methodology used on the classic railway constructions. Two types of tram tracks are observed: tracks with indirect elastic rail fastening system and stiffer direct elastic rail fastening system. These models represent the first step towards establishing a predictive maintenance system on Zagreb tram tracks.

ACS Style

Maja Ahac; Stjepan Lakušić. TRAM TRACK MAINTENANCE-PLANNING BY GAUGE DEGRADATION MODELLING. Transport 2015, 30, 430 -436.

AMA Style

Maja Ahac, Stjepan Lakušić. TRAM TRACK MAINTENANCE-PLANNING BY GAUGE DEGRADATION MODELLING. Transport. 2015; 30 (4):430-436.

Chicago/Turabian Style

Maja Ahac; Stjepan Lakušić. 2015. "TRAM TRACK MAINTENANCE-PLANNING BY GAUGE DEGRADATION MODELLING." Transport 30, no. 4: 430-436.

Journal article
Published: 01 July 2013 in Romanian Journal of Transport Infrastructure
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The paper describes the analysis of tram traffic noise situation in residential areas in the vicinity of Drzic Avenue, one of the major routes between the northern and southern part of the Croatian capital city Zagreb, and the effect of low barriers placed by the tracks on tram noise mitigation. In order to evaluate the effect of planned protection measure, noise models were produced and verified with short-term field measurements. Calculations were conducted by means of noise prediction software, using European interim noise prediction method and 3D model of analyzed area. Finally, the results of noise calculations for existing tram traffic situation and planned measure of protection are presented on noise maps.

ACS Style

Maja Ahac; Stjepan Lakusic; Saša Ahac; Vesna Dragčević. The Analysis of Low Noise Protection Barriers Influence on Tram Traffic Noise Levels. Romanian Journal of Transport Infrastructure 2013, 2, 1 -9.

AMA Style

Maja Ahac, Stjepan Lakusic, Saša Ahac, Vesna Dragčević. The Analysis of Low Noise Protection Barriers Influence on Tram Traffic Noise Levels. Romanian Journal of Transport Infrastructure. 2013; 2 (1):1-9.

Chicago/Turabian Style

Maja Ahac; Stjepan Lakusic; Saša Ahac; Vesna Dragčević. 2013. "The Analysis of Low Noise Protection Barriers Influence on Tram Traffic Noise Levels." Romanian Journal of Transport Infrastructure 2, no. 1: 1-9.