In some markets, the elastic deflections of vehicles are regulated with regard to ground clearance, but in most cases, the limitations on deflections are a matter of functionality. That is, the deflections of the trailer chassis should not introduce problems in opening and closing doors. For certain special trailers, such as low-bed trailers, the requirements on the elastic deflections may limit the choice of material.

Since all steel grades have the same Young’s modulus, the bending stiffness is determined by geometry. That is, simply reducing the sheet thickness of the consisting profiles will reduce the bending stiffness if the outer geometry remains the same. For a trailer chassis, the longitudinal beams determine the bending stiffness in the vertical direction. If the stiffness reduction is problematic, increasing the height of the cross-sections can improve the bending stiffness.

Increasing the height of the beam is the most efficient way to increase the bending stiffness. However, in areas where the height of the beam is restricted, the bending stiffness can be improved by increasing the flange width, as in the illustration below. This measure can also be taken in critical areas to reduce the working stress level and improve the stiffness in the lateral direction  of the beams.  Using modern manufacturing techniques, the flange width can be tailored over the length of the beam according to the load distribution. However, the width can only be increased to a certain degree because the thickness of the flange is reduced. The flange on the compressed side can become too slender and local buckling may occur. This will limit the material utilization of the flange. If the existing trailer beam is already very high, shear buckling of the slender web may limit the possibility to increase the height and reduce the thickness of the web. More information on instability and calculation methods are found in the SSAB Design Handbook. 

 

Variable flange width can be introduced to improve the bending resistance and the bending stiffness in critical areas.