There are many applications which are able to split files based on the file format or the category like audio, video, databases, images, etc. based on the fact that you don't want to modify the file structure it's best to use a software application which splits the file by keeping the header information in one place so you can join the files later. You could try something like GSplit to achieve your goal.
Just add the file, select the number of pieces that the files has to be splited, select the destination folder and split your files. You can then later join them into one piece like the original file.