The tower was designed to rest on a continuous reinforced concrete mat, 4 feet thick, with the base of the slab 24 feet below street level.
What makes the Texas Commerce Bank Building revolutionary in the civil engineering world is not so much the building itself, but its foundation. Initial studies for the type of foundation to be used began in the fall of 1927. William E. Simpson, the building's chief structural engineer, suggested using a mat foundation, something new for Houston's multistory buildings.
Simpson enlisted the advice of Dr. Charles (Karl) Terzaghi, known as the "Father of Soil Mechanics," who just two years earlier had published his Erdbaumechanik, which first outlined the theory of consolidation of clay soil.
The foundation design for the Texas Commerce Bank Building was the first application of the then new field of soil mechanics to foundation construction in the Houston region. Since 1927, plain reinforced concrete mats have been the norm for tall buildings in Houston.
- At the outset of the project, the plans were to construct a 32-story tower, 112 by 109 feet, 425 feet high of fireproofed structural steel. The remainder of the site was to be occupied by a five-story building of reinforced concrete.
- Months after the mat foundation was complete and the steel erected to the 14th floor, Jesse H. Jones, the building owner, stated his desire for the building to be not only the tallest building in Texas but the tallest west of the Mississippi, requiring the addition of four stories. The foundation accepted the additional load with no adjustments, although the steel columns required strengthening.
- The tower was designed to rest on a continuous reinforced concrete mat, 4 feet thick, with the base of the slab 24 feet below street level. The columns transfer their load to the slab by means of reinforced footings, 6.5 by 5.5 feet, 4 feet thick, which in turn rest on square slabs 10 by 10 feet, 2 feet thick. The columns of the adjacent concrete building rest on 9-foot-square spread footings independent of the mat.
- Underground conditions were visible to Dr. Terzaghi from the level of the partially excavated basement by means of a lined test shaft in one corner. A 6-inch-wide vertical strip was left unlined on one face of the shaft to allow examination of the soil in an undisturbed condition. A test boring was augered in the bottom of the test shaft to a depth of 47 feet.
- Two nearby buildings, the Niels Esperson Building and the Petroleum Building (both built in1927), were constructed using (roughly) 20-foot-long concrete piles. Dr. Terzaghi refuted the need for concrete piles and instead, recommended supporting the building on a mat.
- Settlement readings were made on nine of the columns resting on the mat. By 1947, the total settlement had reached about 3 < inches, which was in good agreement with Dr. Terzaghi's prediction.
- The Texas Commerce Bank Building was the first in which field welding was used extensively in the erection of the structural steel frame.