Thank you for your answer.
But I've already enabled the collapse function, without results.
Please see the official T3 Demo page at http://demo.t3-framework.org/joomla30/index.php/en/
Typography menu has a submenu.
Try to resize the page as a small device and see how the submenu doesn't expand after the collapse.
according your suggestion, I also checked the "Joomla Pages Menu item" in the official T3 Demo page, and I see that it is shown in the same way, without any expansion.
But collapse menu in the previous T3 blank template with Bootstrap 2 were structured to show all submenus: see our home page http://www.con-vivium.com/ and resize it as a small device.
How to show the full navigation in smal devices with T3 BS3 Blank Template?
A template without full navigation is unusable.
Thank you in advance.