After Debris Impact

After the dust and smoke cleared following the collapse of WTC 1, damage to WTC 7 was observed primarily on the south face near the southwest corner, between Floors 5 to 17 (Section 5.5). Seven exterior columns were severed (six columns on the south face and one column on the west face). The interior damage was not visible but, based on engineering judgment and interview accounts by individuals that were in or around WTC 7, estimates of interior structural damage between the exterior walls and the core were made. Chapter 5 describes the damage observed from photos and videos, and the structural damage in the southwest region is summarized in Section 5.5.3.

The WTC 7 structural damage resulted from debris falling from WTC 1. In a similar fashion, the building located at 130 Liberty Street (referred to as Deutsche Bank or the Bankers Trust building), was damaged by falling exterior panels from WTC 2 as it collapsed. NIST was granted access to inspect floors where damage occurred in the building on 130 Liberty Street on August 21 and 22, 2006. The debris from WTC 2 had penetrated the north face of the 130 Liberty Street building and caused damage to Floors 9 through 22, as shown in Figure 2-30 and Figure 2-31. The north face had severed spandrel beams between exterior columns, with the damage extending into the interior that grew in magnitude as the debris fell. Figure 2-31 shows that the floor beams framing into intact exterior columns remained in place, but the SFRM in the immediate vicinity of the damage was knocked off.

Figure 2-32 shows the extent of the damage that was documented by the FEMA WTC Building Performance Study (McAllister 2002). Immediately after the damage was incurred, the ceilings and column enclosures were still in place, so possible SFRM damage in other parts of the building could not be observed.

6 Bankers Trust Building

6.1 Introduction

The Bankers Trust building at 130 Liberty Street, also referred to as the Deutsche Bank building, withstood die impact of one or more pieces of column-tree debris raining down from the collapsing south tower (WTC 2). Although the debris sliced through the exterior façade, fracturing spandrel beam connections and exterior columns for a height of approximately 15 stories, the building sustained only localized damage in the immediate path ofthe debris from WTC 2 (hereafter referred to as the impact debris) (Figures 6-1 and 6-2). There were no fires in this building. [emphasis added] The ability of this building to sustain significant structural damage yet arrest the progression of collapse is worthy of thorough study. Unlike WTC 1, 2, and 7, which collapsed completely, the Bankers Trust building provided an opportunity to analyze a structure that suffered a moderate level of damage, to explain the structural behavior, and to verify the analytical methods used. The following sections describe the building structure, the extent of damage, and the computational methods that were used to analyze the structure.

6.2 Building Description

The Bankers Trust building is a steel-frame commercial office structure, designed and constructed circa 1971. Bankers Trust was designed by Shreve, Lamb & Harmon Associates P. C. Architects; Peterson and Brickbauer Associated Architects; the Office of James Rudderman Structural Engineers, and Jaros Baum and Bolles Mechanical and Electrical Engineers. The building measures 560 feet in height with 40 stories above grade and 2 below. It is located directly across Liberty Street from the former site of WTC 2, about 600 feet due south of the southeast corner of WTC 2.

Figure 6-1

North face of Bankers Trust building with Impact damage

between floors 8 and 23.

Photo credit: FEDERAL EMERGENCY MANAGEMENT AGENCY