“Esthetically considered, it is true, perhaps, that the finest element in the Pennsylvania Station is the train hall, where the architect has dealt sincerely with his steel elements and has not permitted himself to cast a fond, retrospective eye upon the Roman baths.”Lewis Mumford
At the concourse, he sky and ground are inverted. Steel and glass gracefully perform spatial gymnastics. In contrast to the General Waiting Room, the concourse defied the gravitas of load-bearing construction. Thin columns of lightweight steel rise above the platforms and support a forest of complexity in the sky. Conversely, glass vaults bring the sun down to the tracks. Its exposed and utilitarian character expressed honesty and dignity.
The Concourse was a glass-roofed court used by outgoing patrons. The courtyard was surrounded by granite walls and a series of Guastavino-tiled domes. It extended the entire width of the station and was about 340 feet long by 210 feet wide (103.6m x 64 m.).
A flight of stairs descended to every platform. A boarding gate was placed at the top of each flight of stairs in the Concourse level. A pair of cast-iron Hutchinson indicators made by the National Indicator Company of New York were placed at each boarding gate, totaling 44. Each device featured aluminium sign cards painted in red that measured 17 by 32 inches, indicating the train track number, the destination and departure time. The track number at the top was illuminated from within, while the alluminium cards were illuminated by reflectors on the outside frame.
Broad flights of granite steps ascended to Eight Avenue, Thirty-first and Thirty-third Streets. On the easterly side of the Concourse, the walls of the Men’s and Women’s Waiting Room were articulated in semi-circular windows. This arrangement was a clear self-reference to McKim, Mead & White’s earlier work at the Boston Public Library. A large, rusticated arch fronted the thoroughfare that led to the General Waiting Room. The Concourse level extended northward past the Thirty-third Street to provide access with the carriage drives.
A complex arrangement of latticework supported the vaulted glass roof. It was designed by Westinghouse, Church, Kerr and Company in close collaboration with the engineers Purdy and Henderson. The roof consisted of a main barrel vault running parallel to the main axis of the General Waiting Room and three barrel vaults running perpendicular, creating groined intersections at several points. Diagonal trusses were placed at these intersections. The tympana at the ends of the barrel vaults were the only vertical faces.
The exposed columns were 3 feet square made up of four 8 by 8 inch angles. These were double-laced and combined with cross battens on all four sides. Diaphragms, equally double-laced, were placed horizontally at intervals of 10 feet, or every 3 modules. They rose uninterruptedly from their concrete footings to the springing line of the arches. The lattice-work consisted of a criss-crossed pattern of metal ties riveted to the angles. Rivets were of ⅞” diameter and of full hemispherical heads.
To avoid monotony, McKim, Mead & White requested Westinghouse Church Kerr & Co. a variance in height of the spring line for the multiple arches, as well as in the thickness of the ribs spanning the larger arches. The largest arch is formed at the main barrel vault, where the columns are distanced 98 feet at centers. The intrados of this arch form a perfect semi-circle. The bottom flange of the bent steel beam running along the arch. The height of this arch governs the height of the other barrels, stretching their shape to become elliptical. The north and south ends of the main barrel, which lead to the exits to 31st and 33rd Street, had additional supporting columns acting as mullions on the semi-circular openings within the arch.
Above the Guastavino domes runs a horizontal x truss around the courtyard.
Immediately after riveting work in the shop, the steelwork was covered in three coats of paint manufactured by the Toch Brothers of New York City. The first coat, named “Tockolith”, was of Graphite and covered through all joints and crevices. The finishing coat, No. 49 of “R.I.W.” damp-resistant paint, was of dark olive green color and was applied in two coats. Its manufacturers claimed that the finishing coat protected the steel work from the corrosive action of sunlight, locomotive gases, acid, and other fumes. The paint had elastic properties that withstood the constant vibrations caused by the ordinary movement of trains; it also insulated the steelwork against the electrolytic corrosion caused by stray current that leaked from the third rail of the tracks. A total of 25,000 gallons of R.I.W. paint was required to paint the exposed steelwork. No. 110 “R.I.W.”, another painting type for granite surface and equally manufactured by the Toch Brothers, was applied elsewhere in the station, totalling 60,000 gallons of paint.
The roof was clad in watertight puttyless skylights encased within a membrane of steel beams of Monel metal. Monel was an alloy invented by metallurgist Robert Crooks Stanley (1876–1951) and patented in 1905 by the International Nickel Company. The metal consisted of approximately 60% nickel and 40% copper, and small percentages of iron, manganese, silicon, and carbon. Pennsylvania Station was the first architectural project where Monel metal was used.
Before stainless steel and aluminum were mass-produced in the post-war era, Monel was more resistant to corrosion than iron, a desired property for a ceiling exposed to the fume-laden atmosphere of New York. It also was stronger than steel, proving ideal for the large spans of the roof vaults. Monel also had a low coefficient of thermal expansion, protecting the glass panes from breaking. More than 300,000 square feet of rolled sheets of Monel were used to cover the Concourse.
The plate glass diffused the sunlight, smoothing the shadows of the steel roof projected onto the interior surfaces of the Concourse. Some of these glass walls had special ventilator frames with two continuous contact surfaces. Each frame would slope inwards, keeping out drafts and rain.
Originally, the engineers specified to use ¼” thick wire glass, but safety tests proved it necessary to increase its thickness to ⅜”. The National Ventilating Company was in charge of installing nearly 220 tons of the Mississippi Wire Glass throughout the building.
The abutment of the steel with the traditional masonry walls was not gracefully handed. As the Royal Institute of British Architects pointed out, the “ungraceful joining with masonry” was further lamented because the masonry walls were just veneers covering the steel structure.
The Concourse was floored with vaulted glass, allowing sunlight down the Exit concourse and train tracks below (See Figure historic photo). These were made of glass prism and concrete. The translucent effect of the floor, combined with the glass-and-steel roof evoked the Natatio in the imperial Roman baths.The daylight was maximized with a specific glass prism that was known as No.30. Each prism measured 4 ⅞ by 4 ⅞ inches and a full inch thick. These prisms were set in galvanized cast-iron shields with an elastic compound. Each glass unit was encased in a shock-absorbing plastic and metal ring within the concrete slab. These large modules were supported by steel tie rods. The entire mechanism was patented as “Ray-Placeable” glass.