United Steelworkers Building

United Steelworkers Building

Formerly	IBM Building, I.W. Abel Building, Five Gateway Center
Company type	Office building
Industry	Office real estate
Founded	1964
Founder	Equitable Life Assurance Society (developer)
Headquarters	Pittsburgh , United States
Area served	Downtown Pittsburgh
Owner	United Steelworkers labor union

The United Steelworkers Building, initially known as the IBM Building and also referred to as the I.W. Abel Building or Five Gateway Center, is a prominent office tower situated in Downtown Pittsburgh, Pennsylvania. Built by the Equitable Life Assurance Society between 1961 and 1964, it formed part of the Gateway Center initiative that revitalized much of the Point district. This structure is recognized on the National Register of Historic Places as a contributing element of the Pittsburgh Renaissance Historic District and holds landmark status granted by the Pittsburgh History and Landmarks Foundation.

The architectural design was crafted by Curtis and Davis Architects and Engineers from New Orleans, with structural engineering provided by Worthington, Skilling, Helle & Jackson. The building is notable for its unique load-bearing steel diagrid exoskeleton, an innovative approach that was among the first to utilize diagrid and framed tube construction methods, representing a milestone in office building design.

History

Developed by the Equitable Life Assurance Society as a component of the Gateway Center redevelopment, the project transformed a former warehouse district into a contemporary office complex. Erected on the site previously occupied by the Wabash Terminal train shed—demolished in 1953—the construction involved removing 104 substantial concrete piers. The groundbreaking took place on December 5, 1961, with dedication following on March 19, 1964.

Initial occupants included IBM, which leased floors one through four, and U.S. Steel, occupying floors five through thirteen. In 1973, ownership transferred to the United Steelworkers labor union, who remain both owners and tenants. The building was renamed in 1989 in honor of former USW president I.W. Abel.

Architecture

At the time of its completion, the IBM Building's architecture was groundbreaking, featuring a load-bearing steel exoskeleton supported by eight piers alongside a central core containing elevators and mechanical systems. This structural approach enabled expansive open floor layouts free from interior columns. It stands as an early example of "framed tube" engineering, a technique later adopted in skyscrapers such as the John Hancock Center and the World Trade Center. The frame was designed by structural engineers John Skilling and Leslie E. Robertson, who also contributed to the World Trade Center's design.

This building incorporated one of the earliest diagrid frameworks—a diagonal grid system that significantly reduced steel consumption compared to traditional framing methods. The structural frame relies on just six vertical columns supporting the utility core. Constructed from 252 prefabricated units welded together onsite, its façade alternates between stainless steel bands and glass panels. This intricate structural system set a precedent for subsequent larger-scale diagrid constructions like 30 St Mary Axe.

A further notable aspect is the tailored use of varying steel grades according to each member’s strength requirements—a departure from conventional uniform steel application. Engineers initially established the frame’s geometry before iteratively determining yield strength specifications for each component. Steel supplied by U.S. Steel varied from standard carbon steel at 36 ksi (250 MPa) to high-strength alloy steel rated at 100 ksi (690 MPa). During assembly, beams were color-coded to ensure accurate placement throughout construction.