Taken from an exchange I had with somebody on a message board:
Originally Posted by poetrychic
...considering the design of the buildings, hollow with (in reality) very little structural support
This is one of the major flaws in the 911 Commission report (which is where I assume you got it from.)
From the 911 Commission Report: "...the outside of each tower was covered by a frame of 14 inch wide steel columns...These exterior walls bore most of the weight of the building. The interior core of the buildings was a hollow steel shaft, in which elevators and stairwells were grouped."
This statement is patently false. The core of the towers was not a "hollow steel shaft" but an array of 47 massive steel support columns (also commonly referred to as "core columns") which bore "most of the weight of the building." In the picture below, the core columns are on the left, and the outer perimeter columns can be seen if you look "straight ahead."
I did a quick search and found this text. I'm sure you can verify with a little effort.
"At the time of construction, most new skyscrapers were built around grid-style steel skeletons. In this design, the support structure is spread throughout the entire building. Metal beams are riveted end to end to form vertical columns, and at each floor level, these vertical columns are connected to horizontal girder beams. The support columns are all internal, so the outside of the building doesn't have to hold up anything but its own weight. These outer curtain walls can be made of just about anything, including ordinary glass.
The WTC team took a slightly different approach. They decided to build long "tubes," where all the support columns would be around the outside of the building and at the central core of the building.Essentially, each tower was a box within a box, joined by horizontal trusses at each floor.
The outer box, measuring 208 feet by 208 feet (63x63 m), was made up of 14-inch (36-cm) wide steel columns, 59 per building face, spaced just over 3 feet (1 m) apart. On every floor above the plaza level, the spaces between the columns housed 22-inch (56-cm) windows. Yamasaki, who had a pronounced fear of heights, felt that the small windows made the building feel more secure. The columns were covered with aluminum, giving the towers a distinctive silver color. The inner box at the core of each tower measured about 135 feet by 85 feet (41x26 m). Its 47 heavy steel columns surrounded a large open area housing elevators, stairwells and restrooms.
This design had two major advantages. First of all, it gave the building remarkable stability. In addition to shouldering some of the vertical load (the weight of the building), the outer steel columns supported all of the horizontal forces acting on the tower (the force of the wind). This meant the inner support structure was completely dedicated to the huge vertical loads."
So, if the 911 Commission (which was to provide us the "fullest possible account") goofed on something as basic and important as this; how can we possibly trust they've been "thorough" in the rest of their investigative work?