Saeed Shojaei - PHD student, Shahid Rajaee Training Teacher University
Seyedmohammadjavad Zeidi - undergraduate student, Shahid Rajaee Training Teacher University
Ali Rahmani - Assitant professor, Shahid Rajaee Training Teacher University
Ali Mirmohammadi - Assitant professor, Shahid Rajaee Training Teacher University

Initially, the first aim of the present study is to model 3-axle rigid truck by developing a code in Matlab. At the next step, each equation should be drive by acquisition of lagrange approach. After driving equations successfully, validation will be performed by some result from Bohao Li master thesis. Although the present approach is totally different from the approach that Boahao Li used in his analysis but deviation of the present results from that thesis on average is 7 percent. This approach until now utilizes 19 degree of freedom for determining natural frequency and dominant motion. With having dominant motion, it is possible to clarify which region is in endanger of resonance. This paper presents a very small part of the results that have gathered and for watching new result in this field, it is recommended to read our future paper.

natural frequencies, mode shapes, Lagrange method, multi-axles truck