Every bunk bed has a weight limit, though the weight limit for bunk beds is not the same for every material. Check your manufacturers specification and adhere to the recommendations to keep yourself, or your children safe.
There are standards set out by safety regulating bodies that require bunk beds to undergo vigorous testing. The tested weight for all bunk beds is 180kg but manufacturers may reduce this weight limit for safety precautions. The bunks should be able to hold restless children, teenagers and some adults. If the weight limit set by manufacturers is over the tested weight, they may be unsafe to use, otherwise they have undergone their own extensive testing.
As you can imagine, metal bunk beds can hold a lot more weight than bunk beds made of other materials due to its strength. Most manufacturers of metal bunk beds will recommend a weight limit between 70kg to 115kg. The top bunk will often have a lower weight limit than the top bunk for safety precautions. Some manufacturers will keep the tested weight of 180kg for the lower bunk, but will heavily reduce the weight limit, by half in some cases, of the top bunk. This decreases the risk of the top bunk falling and harming the person below, or the person on the top bunk.