Two official architectural drawings of the Twin Towers plan - including authentic certificates !!! World Trade ...

Two official architectural drawings of the Twin Towers plan - including authentic certificates !!! World Trade Center. New York, 1967
Plan No. 171 of 109th FLOOR PLAN dated 31/7/1967. Black ink. 63x46 cm. Printed drawing.

Plan No. 135 of the 77th FLOOR PLAN dated 7/31/1967. Blue ink. 63x46 cm. Printed drawing.

In both drawings is a reading on the top right, and the names of the companies that participated in the project from the bottom left: MINORU YAMASAKI & ASSOCIATES, EMERY ROTH & SONS, JAROS BAUM & BOLLES, HELLE & JACKSON. The two drawings are accompanied by certificates of authenticity.

A total of 273 drawings of the towers that were used by the architects in the various stages of construction in the late 60s and early 70s are known, many of the drawings were shelved by the firm after their construction was completed. A number of additional copies of these drawings are known to have been kept in the basements of the building but they were completely destroyed during the 9/11 attacks. The offices of the Yamasaki company that planned the construction of the buildings indicate that the last plans they had were thrown away in 2003. The known drawings that remained were transferred to the Michigan archives after the Yamaski company closed its offices in 2010, and in fact these are the only known original plans. In recent years it has been reported that one of the drawings is in Venezuela, but it is not clear exactly where.

The drawings before us originate from a man who received the plans directly from the Yamasaki offices who saw their preservation as an unnecessary burden and threw a huge archive of historical documents dealing with the original plan of the buildings into the rubbish bin. After a while the company became aware of the magnitude of the mistake of not attaching sufficient importance to those documents and waged a legal battle for several years against the current owner, which was eventually approved by the court as the sole winner and the undisputed owner of the collection. From it, with certificates of authenticity for each drawing.

Design

Yamasaki's design for the World Trade Center, unveiled to the public on January 18, 1964, called for a square plan approximately 208 feet (63 m) in dimension on each side.[32][34] The buildings were designed with narrow office windows 18 inches (46 cm) wide, which reflected Yamasaki's fear of heights as well as his desire to make building occupants feel secure.[35] His design included building facades clad in aluminum-alloy.[36] The World Trade Center was one of the most-striking American implementations of the architectural ethic of Le Corbusier and was the seminal expression of Yamasaki's gothic modernist tendencies.[37] He was also inspired by Arabic architecture, elements of which he incorporated in the building's design, having previously designed Saudi Arabia's Dhahran International Airport with the Saudi Binladin Group.[38][39] 

A typical floor layout and elevator arrangement of the WTC towers

A major limiting factor in building height is the issue of elevators; the taller the building, the more elevators are needed to service it, requiring more space-consuming elevator banks.[40] Yamasaki and the engineers decided to use a new system with two "sky lobbies"—floors where people could switch from a large-capacity express elevator to a local elevator that goes to each floor in a section. This system, inspired by the local-express train operation used in New York City's subway system, [41] allowed the design to stack local elevators within the same elevator shaft. Located on the 44th and 78th floors of each tower, the sky lobbies enabled the elevators to be used efficiently. This increased the amount of usable space on each floor from 62 to 75 percent by reducing the number of elevator shafts.[42] Altogether, the World Trade Center had 95 express and local elevators.[43]

The structural engineering firm Worthington, Skilling, Helle & Jackson worked to implement Yamasaki's design, developing the framed-tube structural system used in the twin towers.[44] The Port Authority's Engineering Department served as foundation engineers, Joseph R. Loring & Associates as electrical engineers, and Jaros, Baum & Bolles (JB&B) as mechanical engineers. Tishman Realty & Construction Company was the general contractor on the World Trade Center project. Guy F. Tozzoli, director of the World Trade Department at the Port Authority, and Rino M. Monti, the Port Authority's Chief Engineer, oversaw the project.[45] As an interstate agency, the Port Authority was not subject to the local laws and regulations of the City of New York, including building codes. Nonetheless, the World Trade Center's structural engineers ended up following draft versions of New York City's new 1968 building codes.[46]

The exterior structure of the Twin Towers

The framed-tube design, introduced in the 1960s by Bangladeshi-American structural engineer Fazlur Rahman Khan, [47] was a new approach that allowed more open floor plans than the traditional design that distributed columns throughout the interior to support building loads. Each of the World Trade Center towers had 236 high-strength, load-bearing perimeter steel columns which acted as Vierendeel trusses.[48][44] The perimeter columns were spaced closely together to form a strong, rigid wall structure, supporting virtually all lateral loads such as wind loads, and sharing the gravity load with the core columns.[44] The perimeter structure containing 59 columns per side was constructed with extensive use of prefabricated modular pieces, each consisting of three columns, three stories tall, connected by spandrel plates.[49] The spandrel plates were welded to the columns to create the modular pieces off-site at the fabrication shop.[50] Adjacent modules were bolted together with the splices occurring at mid-span of the columns and spandrels. The spandrel plates were located at each floor, transmitting shear stress between columns, allowing them to work together in resisting lateral loads. The joints between modules were staggered vertically, so that the column splices between adjacent modules were not at the same floor.[46] Below 7th floor to the foundation, there were fewer, wider-spaced perimeter columns to accommodate doorways.[49][44]

The core of the towers housed the elevator and utility shafts, restrooms, three stairwells, and other support spaces. The core of each tower was a rectangular area 87 by 135 feet (27 by 41 m) and contained 47 steel columns running from the bedrock to the top of the tower. The large, column-free space between the perimeter and core was bridged by prefabricated floor trusses. The floors supported their own weight as well as live loads, providing lateral stability to the exterior walls and distributing wind loads among the exterior walls.[51] The floors consisted of 4-inch (10 cm) thick lightweight concrete slabs laid on a fluted steel deck. A grid of lightweight bridging trusses and main trusses supported the floors.[49] The trusses connected to the perimeter at alternate columns and were on 6 foot 8 inch (2.03 m) centers. The top chords of the trusses were bolted to seats welded to the spandrels on the exterior side and a channel welded to the core columns on the interior side. The floors were connected to the perimeter spandrel plates with viscoelastic dampers that helped reduce the amount of sway felt by building occupants.

Hat trusses (or "outrigger trusses") located from the 107th floor to the top of the buildings were designed to support a tall communication antenna on top of each building.[49] Only 1 WTC (north tower) actually had an antenna fitted; it was added in 1978.[52] The truss system consisted of six trusses along the long axis of the core and four along the short axis. This truss system allowed some load redistribution between the perimeter and core columns and supported the transmission tower.[49]

The framed-tube design, using steel core and perimeter columns protected with sprayed-on fire resistant material, created a relatively lightweight structure that would sway more in response to the wind compared to traditional structures, such as the Empire State Building that have thick, heavy masonry for fireproofing of steel structural elements.[53] During the design process, wind tunnel tests were done to establish design wind pressures that the World Trade Center towers could be subjected to and structural response to those forces.[54] Experiments also were done to evaluate how much sway occupants could comfortably tolerate; however, many subjects experienced dizziness and other ill effects.[55] One of the chief engineers Leslie Robertson worked with Canadian engineer Alan G. Davenport to develop viscoelastic dampers to absorb some of the sway. These viscoelastic dampers, used throughout the structures at the joints between floor trusses and perimeter columns along with some other structural modifications, reduced the building sway to an acceptable level.[