Wtc 7

Read NIST NCSTAR 1A, Final Report on the Collapse of World Trade Center Building 7 (WTC 7), and answer the following questions (total 100 points):

Please describe: (a) the structural frame of WTC 7, and (b) how major loads were transferred in WTC 7. (10 point)

The structural frame is the floor systems and bracing members that are responsible for maintaining the vertical stability of the building under the various loads. The structural frame of WTC 7 was designed to distribute the weight of the building and resist wind loads by including columns, floor assemblies, spandrel beams, girders, and transfer elements. The WTC 7 consisted of four tiers, the lowest floors contained the Con Edison substation. From the 7th to the 47th floor WTC 7
The passive fire protection included sprayed fire-resistive material (SFRM) applied to the structural steel and under of the metal floor decking. The active fire protection included fire sensors and alarms, notification systems, automatic fire sprinklers, water supplies, and smoke management. (NIST,
Columns had a 3 hour rating referenced to the Standard Fire Test (ASTM E 119), beams were also required to have a 2 hour rating which didn’t require sprinklers but WTC 7 was equipped with sprinklers. The SFRM that was applied was known as Monokote MK-5, it was applied to a 22mm (7/8in) thickness to the columns, and 48mm (1 7/8 in) to the lighter columns. They applied 13mm (1/2 in) to the beams, and 10mm (3/8 in) to the bottom of the metal deck. Inspections were done which found that the correct SFRM was applied in WTC to the respected columns, beams, and metal decks. There was an array of smoke detectors which would sound alarms on the floor of detection and the one above. There were also fire rated walls between tenant spaces, and tenant spaces and the building core (Page 59). There was a Fire Command Station on the 3rd floor, which would transmit the fire signal to the fire department. There were also smoke barriers in forms of walls and smoke dampers with air movement that would exhaust the smoke out of WTC 7. WTC 7 contained a three-zone system of sprinkler and standpipes. The low zone consisted of 1st floor through 20th floor which came from the water main with a backup water coming from the water main with a supplemental pump. The mid-level zone 21st-39th was supplied by two larger storage tanks on the 46th floor. If backup water was needed it was pumped from the water main. The primary and