21-Story Modular Hotel Raised
The Roof for Texas World Fair in 1968

Members of the Modular Building Institute (MBI) recently attended The American Institute of Architects (AIA) show in San Antonio. Representing the modular building industry to architects that traveled from all over the United States to that locale presented a particularly interesting opportunity to champion the merits of the accelerated building process. Just one short block from the convention center stands a 21-story example of modular construction that has become a part of the historical landscape of San Antonio, as well as an early and ever-present example of the engineering feats modular construction can undertake.

The Hilton Palacio del Rio Hotel is proudly pointed out to visitors as a 'modular' hotel with a history worthy of landing it on the famed Riverwalk boat tour for review and discussion. The hotel was highlighted in AIA's guidebook to local architecture, prompting MBI to speak to the construction company that undertook this engineering feat in 1968. Zachry Construction Corporation (Zachry), also located in the heart of San Antonio and actual owner of the hotel, provided this original story written in 1968 about the project upon its construction. Interestingly, the piece is timeless in that the application could happen just as easily today.


The Hilton Palacio del Rio Hotel is a milestone, not only for the City of San Antonio, but for the modular construction industry as well. Built by H.B. Zachry Company (now Zachry Construction Corporation) across the street from the site of HemisFair, the Texas World's Exposition of 1968, the 500-room deluxe hotel was designed, completed and occupied in an unprecedented period of 202 working days. This is an achievement of which H.B. Zachry Sr. and each of his workers can well be proud.

Of the Palacio del Rio's 21 stories, the first four were built of conventional, reinforced concrete for support facilities. At the same time, an elevator and utility core, also of reinforced concrete, were slip formed to a full height of 230 feet. From the fifth floor to the 20th, modules were stacked and connected by welding of steel embedments.

The 496 rooms were placed by crane in 46 days. The 21st floor, an area which contains a grand ballroom and other required public space, was constructed of light steel and enclosed by an aluminum window hall. The building is served by six elevators (four public and two freight), has a swimming pool on its fifth floor and occupies a half an acre site in downtown San Antonio.



By giving the room a pre-determined magnetic heading and by "feathering" the vertical propeller, the operator atop the "flying" room controlled the direction of each unit as it was being hoisted to a precise location.



The hotel's room modules were pre-cast from light-weight structural concrete. Before arriving on the construction site, each room was fully decorated, including color TV, AM/FM radios, beds, carpeting, bottle openers, automatic coffee makers, ash trays, etc. The units are 32 feet 8 inches and 29 feet 8 inches long, 13 feet wide and 9 feet 6 inches high. They weigh 35 tons each and were manufactured at a plant located eight miles from the project site.

Zachry set up a production line consisting of two rows of eight room-size forms that produced eight complete units daily. The working crews were composed, as an average, of more than 100 men who completed a designated task 496 times.

The casting process was started by coating the permanent, hinged, outer forms with a forming release agent. Reinforcing steel for floors was added, and in 30 minutes, six and a half cubic yards of lightweight ready-mix concrete was poured to form a five-inch thick floor. When the concrete had set, it was hard finished and was allowed to cure for several hours. After that, crews placed steel reinforcing for the walls and ceilings, installed plumbing, electrical conduits and positioned block-outs for doors and other openings. In 30 minutes, fifteen and a half cubic yards of light weight ready-mix concrete for walls and ceilings were poured and vibrated into place.

Each module received a code number that keyed its position during the whole process, including date of erection and its exact placement in the building. Once on the site, a 350hp crane equipped with a special 36-foot diameter ring base and a 270-foot boom maneuvered them into place. So that they could literally be "flown" into place without turning or dangling in mid-air, a Sikorsky helicopter stabilizing tail section was attached to each room at job site. The tail, rotor, engine, magnetic compass and a set of automatic controls were fastened to a platform attached to the top of each unit. By giving the room a pre-determined magnetic heading and by "feathering" the vertical propeller, the operator atop the "flying" room controlled the direction of each unit as it was being hoisted to a precise location.

An average of 17 modules was placed each day. Because the module placement had to match the elevator shaft, each unit had to be set exactly on the unit underneath, at a precise elevation, with a maximum working tolerance of 3/4 inch to prevent creeping. Plumbing and wiring conduits were run up a 20-inch chase between modules for quick connections to individual rooms. In their final location, the reinforcing rods, extending from the lip at the corridor end of each room, were welded together. Forms were then placed under the interlacing rods and concrete poured to join the extensions in order to form the corridor's floor. Removable panels in the corridors were then added to close the 20-inch chase which provides access to the continuous vertical mechanical and electrical chaseways.

With its unique shape enhanced by the glow of the yellow balcony lighting at night, the Hilton Palacio del Rio Hotel reminds one of a golden apiary and also of Zachry's first major venture in the field of modular construction; yet, only as a first step in its permanent search for new horizons to conquer . . .

About Zachry Construction Company

Zachry Construction Corporation (ZCC) is a privately owned construction and industrial maintenance service company based in San Antonio, Texas. ZCC and its affiliates operate from coast to coast, with a concentration of projects in the southern United States. Over the past 83 years, ZCC and its affiliates have completed thousands of projects, including power generation plants, chemical refineries, retrofit air quality control systems, highways, bridges, dams, commercial buildings and more. ZCC works on both public- and private-sector projects across all major construction business sectors. To learn more, visit www.zachry.com.


To learn more about commercial modular construction and its applications, visit Modular Building Institute: The Voice Of Commercial Modular ConstructionTM.

Story (c) Zachry Construction Company and reprinted upon Zachry permission. All rights reserved.

(c) 2007. Modular Building Institute. All rights reserved