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    Computer simulation of recycled content guardrail post impacts
    (Asce-Amer Soc Civil Engineers, 2004) Atahan, AO; Ross, HE
    Guardrail posts made of recycled plastics are becoming candidates for use in roadside safety features due to the nature of exhibiting properties that are useful in absorbing energy. Relatively few studies have specifically addressed the performance of recycled guardrail posts in strong-post guardrail systems. Few have reported success in this area. In this study, a detailed computer simulation Study is performed to evaluate the crashworthiness of the recycled content guardrail posts. Results of a full-scale crash test are also used to verify the accuracy of the finite element models used in the simulation study. Based on the investigation, it is demonstrated that computer simulations call effectively model the dynamic response behavior of a crash event and provide valuable information about the impact performance of recycled content guardrail posts. Crash Simulation results indicate that when proper quality recycled posts are used the guardrail system has the potential for meeting the National Cooperative Highway Research Program Report 350 recommendations.
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    Design and simulation of an energy absorbing underride guard for heavy vehicle rear-end impacts
    (Inderscience Enterprises Ltd, 2003) Atahan, AO
    Recent passenger car-heavy vehicle rear-end crashes demonstrate the importance of rear underride guard designs for heavy vehicle applications. Currently specified rear underride guards have many shortcomings, such as structural strength and energy dissipation capacity, clearance from ground, and other design aspects. As a result of these inadequacies in underride-guard design, many lives are lost every year when passenger cars slide underneath heavier vehicles. In this study, design modifications to an underride guard that minimally complies with the requirements contained in FMVSS 223/224 are evaluated. A previously performed crash test on the guard using a compact passenger car demonstrated the potential for excessive vehicle underride and passenger compartment intrusion problems. After the full-scale crash test, a detailed finite-element study is performed to investigate the shortcomings of the design. The accuracy of the underride guard model is partially validated using both a quasi-static and a full-scale crash test. After the validation, the guard is modified to improve its structural behaviour and energy-dissipation capacity. Four crash-test simulations are performed on the modified guard model to verify its effectiveness in energy dissipation and preventing intrusion into the passenger compartment. In these simulations, two vehicle speeds of 48 km/h and 56 km/h and two impact positions of 0% and 50% offsets are used to fully verify the acceptability of the modified guard model. Simulation results show that the modified rear underride guard performs much better than the original design. The guard dissipated a significant amount of the impacting vehicle's energy and showed no potential for passenger-compartment intrusion in any simulation. The deceleration of the vehicle was also within acceptable limits. Based on these results, it can be concluded that the improved guard performed well and the implementation of this particular underride guard on heavy vehicles looks promising.
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    Design and simulation of two wooden-post W-beam guardrails to eliminate wheel snagging
    (Inderscience Enterprises Ltd, 2004) Atahan, AO; Cansiz, OF
    Recent crash tests on strong-post round- and rectangular-wood W-beam guardrail systems demonstrate that wheel snagging can be a serious concern for vehicle stability and impact severity. There are several methods that exist to minimise wheel snagging in strong-post guardrail systems. This paper aims to investigate the effect of one of those methods: the increased offset distance between post and W-beam rail. Extensive simulation studies are performed to determine optimum offset distances between the post and W-beam in both systems. Different designs with varying offset block depths are evaluated and their impact performances are compared. LS-DYNA, a versatile, nonlinear, large deformation, finite-element program is utilised to analyse different alternatives. Guardrail models previously validated against full-scale crash tests were used in the analysis. Simulation findings suggest that tendency to wheel snagging reduces with increased offset depths. 260-mm depth was determined to be the optimum offset distance between the wooden posts and W-beam. Simulation results show that when a nominal 260-mm offset distance is provided, wheel snagging and associated vehicle instability and impact severity can be alleviated in wooden-post guardrail systems.
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    Evaluation of recycled content guardrail posts
    (Asce-Amer Soc Civil Engineers, 2002) Atahan, AO; Bligh, RP; Ross, HE
    In recent years, there has been an increased interest in the use of recycled materials in highway-related areas by state agencies and research organizations. In the present paper, guardrail posts manufactured from recycled materials are evaluated for possible use in conventional strong-post guardrail systems. Basic physical and mechanical properties of posts are determined through static laboratory tests such as flexure, creep, and density. Their response to environmental variables such as temperature, moisture. and freeze/thaw are investigated through exposure tests. The dynamic response performance of the posts is determined using pendulum impact tests. Static cantilever bending tests have shown that recycled posts are more flexible than conventional wood and steel posts, however, the ultimate load capacities for several recycled posts are comparable to that of conventional posts. The pendulum test results show that the energy absorption of some of the recycled posts is as high as that of conventional wood posts. As a result, the overall performance of recycled posts compares favorably with conventional posts.
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    Finite element simulation of a strong-post W-Beam guardrail system
    (Sage Publications Ltd, 2002) Atahan, AO
    Computer simulation of vehicle collisions has improved significantly over the past decade. With advances in computer technology, nonlinear finite element codes, and material models, full-scale simulation of such complex dynamic interactions is becoming ever more possible. In this study, an explicit three-dimensional nonlinear finite element code, LS-DYNA, is used to demonstrate the capabilities of computer simulations to supplement full-scale crash testing. After a failed crash test on a strong-post guardrail system, LS-DYNA is used to simulate the system, determine the potential problems with the design, and develop an improved system that has the potential to satisfy current crash test requirements. After accurately simulating the response behavior of the full-scale crash test, a second simulation study is performed on the system with improved details. Simulation results indicate that the system performs much better compared to the original design.
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    Finite-element crash test simulation of New York Portable Concrete Barrier with I-shaped connector
    (Asce-Amer Soc Civil Engineers, 2006) Atahan, AO
    Uses of finite-element simulations in designing and analyzing roadside hardware has increased significantly over the past decade. Due to considerable progress in computer technology in conjunction with nonlinear finite-element software, outcome of complex vehicle-roadside hardware collisions can be accurately predicted using simulation programs. In this paper, the finite-element simulation program LS-DYNA was used to analyze and improve the crash test behavior of New York Department of Transportation Portable Concrete Barrier (NYPCB). A full-scale crash test demonstrated that the current NYPCB design was unable to meet national standards. Inspections after the test revealed that the welding at metal connectors forming the joint between the barrier segments was not properly fabricated. A finite-element representation of the crash-tested barrier was developed with a special fillet weld with failure model and subjected to crash testing using the nonlinear finite-element code LS-DYNA. This baseline model simulation was intended to replicate the failed crash test and validate the fidelity of the finite-element models. Qualitative and quantitative comparisons show that the baseline model simulation was successful in replicating the failed crash test. Upon validation, an improved NYPCB model was developed by using proper welding details and subjected to full-scale impact simulation to determine whether this design would satisfy the crash testing requirements. Results of the simulation were encouraging. It was predicted that the barrier would successfully contain and redirect the impacting vehicle in a stable manner. Subsequent full-scale crash testing on the NYPCB with proper welding details passed the NCHRP Report 350 requirements and substantiated LS-DYNA predictions.
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    Impact analysis of a vertical flared back bridge rail-to-guardrail transition structure using simulation
    (Elsevier Science Bv, 2005) Atahan, AO; Cansiz, OF
    Bridge rail-to-guardrail transitions are designed to shield unprotected ends of bridge rails, which are fixed-obstacle hazards. These structures should provide an effective transition between longitudinal barriers with different lateral stiffness and contain and redirect impacting vehicles without any contact with the rigid sections of the system. Recently. a full-scale crash test was performed on a vertical flared back concrete bridge rail-to-guardrail transition design to evaluate its compliance with the NCHRP Report 350 test level 3 requirements. Due to vehicle rollover the design failed to meet the requirements. To gain an insight about the crash test details, a finite element simulation study was performed. Accuracy of the simulation was verified using qualitative and quantitative comparisons. Based on in-depth examination of crash test and simulation recordings, W-beam height of 685 mm was determined to be the main cause for vehicle rollover. In the light of this finding, the current transition model was modified to have 8 10 mm top rail height. Subsequent simulation results predict that the improved model performs much better in containing and redirecting the impacting vehicle in a stable manner. No wheel snagging was observed due to increased rail height. The overall performance of the transition design was so good that consideration is given to testing it to next level of testing, test level 4. Therefore, a follow up finite element simulation study is recommended. (C) 2004 Elsevier B.V. All rights reserved.
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    Impact behaviour of G2 steel weak-post W-beam guardrail on nonlevel terrain
    (Inderscience Enterprises Ltd, 2003) Atahan, AO
    The G2 steel weak-post W-beam guardrail system has been used along Turkish highways extensively. This system is characterised by larger dynamic deflections in a collision and is considered more forgiving compared to other stiffer barriers. The impact performance of the system is found to be satisfactory on a level terrain. However, in Turkey there are several locations where G2 systems are installed on the slope break point adjacent to steep roadside slopes, and the impact performance of G2 systems under these circumstances has never been investigated. In this study, the impact behaviour of G2 guardrail systems on nonlevel terrain is investigated. LS-DYNA, a dynamic, nonlinear, large deformation finite element analysis program is used to predict the crash performance of G2 systems installed adjacent to roadside slopes. A baseline simulation of the G2 system modelled on level ground is conducted, and the performance is compared with the results of a full-scale crash test. Results show good agreement. A series of G2 system models placed adjacent to 1:1, 2:1, 4:1, 6:1, 8:1, and 10:1 roadside slopes are then developed and the findings obtained from these simulations are compared. The results of the analysis substantiate the risk of vehicle instability when the roadside slope adjacent to the guardrail becomes steeper than 6:1 horizontal to vertical.
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    Improvements to G4(RW) strong-post round-wood, W-beam guardrail system
    (Asce-Amer Soc Civil Engineers, 2005) Atahan, AO; Cansiz, ÖF
    Strong-post round-wood W-beam guardrail, G4(RW), is a common longitudinal barrier used in Texas. Recent crash tests on the system demonstrate its effectiveness in containing and redirecting a 2,000-kg pickup truck. Even though the guardrail performed satisfactorily according to National Cooperative Highway Research Program Report 350 requirements, there were concerns about the stability of the vehicle due to excessive wheel snagging on the posts. In this study, a modification to the existing design is evaluated to improve the stability of an impacting vehicle. LS-DYNA, a dynamic, nonlinear, large deformation finite element modeling code is used to analyze and compare the performance of alternate designs. A baseline finite element model of the existing system is developed to replicate the observed crash test behavior of the G4(RW). The fidelity of the baseline model is verified against full-scale crash test results. To improve the vehicle stability, the current design was modified to include guardrail posts with shorter embedment depth. An optimum post embedment depth was determined and used in the second simulation study. Finite element analysis results show that an improved G4(RW) system eliminates wheel snagging on posts, reduces sudden vehicle deceleration and therefore improves the stability of an impacting vehicle significantly.
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    A recommended specification for recycled content guardrail posts
    (Canadian Science Publishing, Nrc Research Press, 2004) Atahan, AO
    In this paper, results of an experimental study aimed to assess the suitability of a recycled content guardrail post as a substitute for conventional wooden guardrail post are, presented: A series of static and dynamic tests performed on the recycled content guardrail posts show that the strength and energy dissipation of recycled posts are comparable to those of conventional wooden guardrail post. A full-scale crash test, using a 2000-kg pickup truck traveling at 100 km/h and making contact at a 25degrees angle, is also performed on the recycled content plastic-post W-beam guardrail system to evaluate its strength and structural adequacy. The barrier performed acceptably for National Cooperative Highway Research Program (NCHRP) report 350 test designation 3-11. Results of the crash test show that the recycled content guardrail post and W-beam guardrail can successfully contain and redirect an errant vehicle, and they can be a potential substitute for nationally used guardrail posts. Finally, a recommended specification is developed for the recycled content guardrail posts based on a series of test procedures and performance levels.