The cores of the twin towers were massively built and thoroughly reinforced skeletons of immense steel columns and massive bracing. They were designed to carry the full load of the buildings several times over. Just the fact that they're misleading and lying about, and suppressing information about the actual construction of the cores of the towers is evidence enough of a cover-up, and reason enough for a proper investigation.

Here's the blueprint of the 110the floor core of the north tower. It shows the placement of the columns and bracing. You can change the resolution so you can see them in much greater detail...

http://911research.wtc7.net/wtc/evidence/plans/frames.html


Here's some pictures of the core as it's being built. You can see the columns and the bracing...

http://whatreallyhappened.com/IMAGES/wtc1_core.jpg

http://911research.wtc7.net/wtc/evidence/docs/low_core.jpg


Here's more information about the construction of the cores...

http://911research.wtc7.net/wtc/evidence/blueprints.html

http://911research.wtc7.net/wtc/arch/core.html


This video graphically shows how the cores were constructed...

http://www.youtube.com/watch?v=qJ11i6fi7KQ