الفهرس 
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Abstract
The aim of this thesis is to study the generated loads in the heavy vehicles.
The application has been made on a tractor semi-trailer vehicle, with rigid frame and passive suspension systems taking two dimensional response variables into consideration to analyze the dynamic loads. For this purpose, the effects of the following factors have been studied:
• Vehicle speed
• Road surface roughness taking the longitudinal correlation between the
vehicle axles into consideration
• Fifth wheel position
• Loading conditions (laden and unladen)
The equations of motion of the vehicle with nine degrees of freedom have been derived applying the Lagrange’s energy approach.
The equations of motion have been formulated in a matrix form and represented by second order differential equations. Using these equations, a direct transfer function of the vehicle degrees of freedom has been formulated. Also, another transformed transfer function has been formulated to calculate the following response variables:
• The dynamic tyre loads
• The dynamic suspension loads
• The dynamic fifth wheel load (vertical and horizontal)
A computer program has been made using the PC MA TLAB software to simulate the vehicle motion when it moves with different speeds on different random road surfaces. This program is used to calculate random response variables of the tractor semi-trailer (power spectral density functions and root mean square values). An eignvalues technique incorporated with frequency responses to harmonic excitation are used to estimate the natural frequencies ofthe vehicle system which used to validate the random responses.
The results showed that.