טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMouradjalian Hagop
SubjectDevelopment of a non-destructive testing method of roadside
safety guardrails
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Emeritus Itzhak Shmulevich
Dr. Zvi Anosh Asaf
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Safety guardrails role is to reduce the severity of vehicle crashes. During a crash the safety guardrail should absorb energy and return a veering vehicle back to the road with minimum passenger injuries and vehicle damage.

In recent years, many findings indicate that safety guardrails across many roads in Israel contain faults. Faulty safety guardrails may impair their purpose for which they were installed for and in some cases increase the severity of the injury. The aim of this research is to develop a non-destructive testing method based on the frequency response of a roadside safety guardrail for its integrity evaluation by experiments and finite element analysis.

During the research an explicit dynamic finite element simulation of a vehicle collision into an ESP 2.0 safety guardrail was developed and validated for evaluation of the crash severity during a vehicle collision into a safety guardrail that contains faults. The second simulation model used in the research is a modal frequency response analysis of the safety guardrail; this simulation model was validated against experimental results conducted during the research. The main benefits of this model are its ability to present the modal shape vectors, eliminating the need for positioning many sensors in the experiment setup for mode shapes extraction, and its simplicity in examination of complex experimental scenarios.

Three different ESP 2.0 safety guardrails were excited in the conducted experiments by a pendulum designed in the research. The Pendulum excitation caused a transient decaying response in the safety guardrail; as a result the data analysis was performed by 3D presentation of a spectrogram using STFT transform. The advantage of a spectrogram presentation is in its ability to illustrate changes in the frequency response of a structure throughout the sample time. Using slices along the frequency axis of the spectrogram, the excitation amplitudes and the damping ratios were calculated. The guardrail faults were identified by finding deviations in the average calculated parameters of a fault free guardrail section.

The identification ability of the developed method is demonstrated in finding diverse faults. It was found that by this method it is possible to identify the following faults: a loose central bolt, a missing central bolt, different soil types where the guardrails are embedded, a tree touching the rail, irregular post assembly with a drilled hole and an added external plate and identification feasibility for partially embedded (short) posts in soil. The described faults identification was conducted by excitation and measurement at the fault location. Further In the study a preliminary attempt was made to identify faults of a loose central bolt and a missing central bolt from a distance. It was found that identifying these faults from a 4 meter distance is feasible and possibly also from a distance of 10 meters, however these preliminary results need to be validated with the developed method. The unique and main contribution of this research is the development of a practical method for non-destructive faults identification in assembled safety guardrails.