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    Finite element simulation and failure analysis of fixed bollard system according to the PAS 68:2013 standard
    (Pergamon-Elsevier Science Ltd, 2022) Apak, Mustafa Yurdabal; Ergun, Murat; Ozen, Halit; Buyuk, Murat; Ozcanan, Sedat; Atahan, Ali Osman; Yumrutas, Halil Ibrahim
    Fixed bollards are very significant elements in providing urban roadside safety. These structures, called passive systems, allow pedestrians and disabled people to use sidewalks effectively and safely, as well as they have a crucial role in protecting the above-ground assets of infrastructure facilities against run-off-road (ROR) crashes. In this study, structural and safety performance analyses of fixed bollards that protect natural gas above ground Reducing and Metering Station-B (RMS-B) type regulating stations used in many points in Istanbul were made. In this regard, finite element (FE) models of the steel pipe of the fixed bollard, the concrete of the foundation and the soil where the bollard was mounted were created. Existing fixed bollards have been verified with accident data. In the light of the calibration and validation, numerical models were created and combined with the vehicle models specified in PAS 68:2013 standard to simulate dynamic behaviours. The combined FE models were analysed applying LS-DYNA software. As a result of the numerical analysis, the fixed bollard system cannot safely stop the 30000 kg N3, 18000 kg N3 and 7500 kg N2 class vehicles, and cannot prevent them from damaging the RMS-B. Besides, the fixed bollard system cannot provide safety at the speed level of 48 km/h, considering the urban speed limit for 3500 kg N1 and 2500 kg N1G class vehicles. However, the fixed bollard system can safely stop 1500 kg and 900 kg M1 class vehicles up to 64 km/h speed limit. These analyses revealed that considering the regional traffic characteristics of Istanbul, the existing fixed bollard systems are not sufficient for the protection of hazardous roadside facilities and need to be improved. Fullscale crash tests should be carried out in future studies to validate the FE simulation models. Furthermore, various bollard designs should be developed, especially urban road requirements.
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    A novel modular shallow mounted bollard system design and finite element performance analysis in ensuring urban roadside safety
    (Sage Publications Ltd, 2023) Apak, Mustafa Yurdabal; Ergun, Murat; Ozen, Halit; Buyuk, Murat; Yumrutas, Halil Ibrahim; Ozcanan, Sedat; Atahan, Ali Osman
    The safety of risky roadside zones such as kids' playgrounds, schools, bus stops, petrol stations, critical roadside facilities, and pavements are becoming a significant worldwide problem. This study focused on the roadside safety of critical above-ground assets of natural gas grids due to its consequences such as fire, blast, traffic interruptions, service downtime, and consumer displeasure during the repair process. In this regard, a novel modular shallow mounted bollard system was designed considering the disadvantages of conventional bollard systems in the literature and the demands/needs of related institutions. Numerical simulations were carried out to analyze the structural and safety performance capabilities of the originally designed bollard system following PAS 68:2013 standard. In addition, FE models were created and incorporated with the verified vehicle models to simulate dynamic behaviors. LS-DYNA software analyzed the FE models. As a result of the simulations, the newly developed fixed bollard design can safely stop vehicles that weigh 18,000 kg max., except for the 30,000 kg N3 class vehicle, up to 50 km/h. The results revealed that proposed bollard designs successfully met the standard requirements for the vehicle types and speed that represent general urban traffic characteristics. Thus, the new fixed bollard design will contribute to roadside safety in metropolitan areas by protecting critical hazardous roadside facilities. In the next stage, the newly designed barrier system should be optimized to lighten the system and reduce the costs.