The first and most important design advice is to keep the structure simple. Reduce the number of parts and utilize modern manufacturing techniques to integrate attachments and minimize the number of welded joints. For the chassis main beams, we recommend that you use a single piece for the flanges and the web throughout the full length of the trailer. This solution reduces the number of welds, especially in the transverse direction, which is important from a fatigue point of view.

Reinforcement plates are frequently used on both webs and flanges to increase the load-carrying capacity and stiffness of the chassis. While this measure can be beneficial from a static perspective, it can do more harm than good from a fatigue perspective.

In a main beam, manufactured from single pieces along the length without any reinforcement plates, the longitudinal weld of the I-beam will determine the fatigue life. When the trailer is loaded, the lower flange will be subjected to tensile stresses in the lengthwise direction in line with the weld. If a reinforcement plate is welded to the lower flange, there will be a transverse loading of the welded joint that reduces fatigue life by at least 8 times (see illustration below).

Introducing a reinforcement plate to the web or the flange also creates a stress concentration at the welded joint, since there will be a stiffness gradient in this area. Therefore, this weld joint will limit the fatigue life of the chassis and may cause cracking problems in an upgraded design where the working stress level is higher.

Reinforcement plates welded to the lower flange will rapidly reduce the fatigue life.