Connection node for modular building structures

A connection node assembly for use in connecting an upper prefabricated building module to a lower module. Hollow vertical edge supports of the building modules have top and bottom connection parts. A connecting bolt can be passed through the top part of an upper vertical support in the upper building module and seated within the bottom part of that vertical support with the shank extending downward. The shank engages a threaded aperture in a connecting nut secured within the top part of a corresponding lower vertical support in the lower building module. Diaphragm plates sandwiched between the upper and lower vertical supports are used to tie horizontally placed modules together.