How much downward deformation is acceptable for the inside of the crossmember on the lower flange?

The standard for allowable downward deformation of the inside of the crossmember on the lower flange is specifically defined to ensure the structural integrity and safety of the dry van. Accepting a deformation of 15mm reflects a balance between flexibility and maintaining the necessary strength to prevent failure during transit.

This standard helps to accommodate the stresses that occur under load, while also setting a limit that ensures the trailer remains functional and secure. If the deformation exceeds this threshold, it may indicate an underlying problem that could compromise the van's structural integrity, leading to potential failures or safety issues during operation. Maintaining this standard is crucial for quality control in the manufacturing and inspection processes of dry vans, ensuring that they can effectively carry loads without risk of damage or loss.

The other options represent levels of deformation that surpass acceptable limits, which would increase the risk of structural failure and inefficiency in load carrying.