No there's no real format for file structure. But there are best practices.
That's about as basic as it gets. The real question is what is this site for? Is it your personal site, is it for a client, are other developers going to work on it?
If it's your own personal site. Structure it however you want. It only has to make sense to you and as long as you can find what you need it's all good.
If the site is for a client or if other developers are going to work on it. Just make sure it makes sense, and I wouldn't go too deep in the directories. Like two or three deep max.
also you have to keep the site's URLs in mind. Like in your example the index.html file in the articles dir will look like this.
That's kind of an ugly URL.