When the curtain goes up at the Philadelphia Academy of Music for the opening of Carmen on Nov. 8, opera patrons will see little evidence of its $37-million renovation program even though the work included complex structural first aid for ailing structural members above the auditorium's ornate plaster ceiling.

OPULENCE Renovation preserved hall's special ambiance. (photo courtesy of The Philadelphia Orchestra)

And that's just the way the owner, the Philadelphia Orchestra Association, wants it. The goal of the ambitious six-year renovation program, dubbed the "Academy for the 21st Century," was to bring the 145-year-old building up to the standards of modern performance halls "while retaining the ambiance and feeling of gild," says George Shaeffer, who oversaw the construction on behalf of the association.

Construction began in 1996 and was completed almost entirely in phases during the summer when the resident companies--the Philadelphia Orchestra, the Opera Co. of Philadelphia and the Pennsylvania Ballet--were on tour. Each summer's work was a separate guaranteed maximum price package completed in windows that were typically 100 to 120 days long. "Our goal was to have everything fabricated and stored prior to starting construction since the deadline of the first show was always looming," says Vincent D'Antonio, project manager for construction management firm L.F. Driscoll Co., Bala Cynwyd, Pa.

The academy renovation included extensive mechanical, electrical and acoustical work, underpinning of the stage house foundations, construction of a new stage and orchestra pit, restoration of the auditorium ceiling and replacement of the rope and sandbag rigging with a mechanized system using cables and counterweights.

But the most delicate work was a fix for failing timber trusses above the auditorium. Problems with the trusses were first discovered in 1989 while local structural engineer Keast & Hood Co. was checking field conditions in the attic space as part of an earlier project to add elevators to the academy. The structural problems were considered serious enough to evacuate the building during intermission. The engineer devised temporary steel splints but advised the academy that a long-term solution would be needed, says Constantine Doukakis, principal at Keast & Hood.

As the permanent solution, Keast & Hood devised a system of supplemental steel trusses. Four 10-ft, 6-in.-deep steel trusses would run parallel to the eight existing timber trusses spanning the 90 ft between the auditorium's side walls. In the transverse direction, two pairs of steel trusses, also 10 ft, 6 in. deep, would pick up the load of the timber trusses at third points, effectively reducing the span of each timber truss to 30 ft.

The construction team implemented the design in the summer of 1996 as one of the earliest phases of the program. Using a derrick mounted on the stage house roof, workers needled steel sections no longer than 20 ft through three 10x4-ft access hatches. "Each piece needed to be field measured, detailed and manufactured to get it through the access holes," says Eugene Grossi Sr., CEO and president of erector Samuel Grossi & Sons Inc., Bensalem, Pa.

Working inside the cramped attic directly above the fragile plaster ceiling, erectors assembled the trusses with bolts instead of welds because of the threat of fire. "The wood is so dry that a high-speed drill could ignite it," says D'Antonio.

To give workers space to assemble the trusses, the engineer designed temporary work platforms suspended between each pair of timber trusses. The tired wood could still support the platforms because of the absence of snow loads during the summer, says Doukakis.

Although the design of these platforms would typically have been the responsibility of the contractor, because of the project's complexity "we couldn't just say 'there is the attic; here is the design for the trusses; go build them,'" says Doukakis. "We worked as a team, devising solutions together."

The stage house phase of the work was the most time consuming. The phase was originally scheduled to run concurrently with restoration of the auditorium ceiling in 1998, but it soon became apparent that the 120-day summer window would not be enough to complete the required work, which included removal of the old rigging, demolition of the stage house roof and timber trusses, construction of a new steel deck and concrete roof, and installation of the mechanized rigging. Driscoll decided to postpone the phase until completion of the nearby Kimmel Center for the Performing Arts (ENR 10/26/ 01 p. 26). The orchestra's move to that facility last December gave the construction team almost six months for the stage house work.

SUPPORTING ROLE Proscenium truss was temporarily hung from two girders. (Photo courtesy of L.F. Driscoll Co.)

One of the challenges of this last phase was protecting the stage floor once the old roof was removed. To keep the rain out, Driscoll built a temporary plywood and rubber roof supported by scaffolding. Around three sides of the roof's perimeter, approximately 29 hatches allowed insertion of the new rigging components from a crane located in the street below. The temporary roof required a constant vigil for incoming storms since lifting the hatches and putting them back in place took almost an hour for each operation. "Our superintendent knew the weather better than the forecasters," says D'Antonio.

The final phase also included the project's heaviest structural member, a 45,000-lb, 12-ft-deep truss, located directly behind the proscenium wall, that spans 86 ft from stage right to stage left and carries more than half of the stage house roof. Erectors lifted the bottom chord first and temporarily suspended it from two plate girders that had been installed a decade earlier to pick up the load of the subsequently demolished stage house timber trusses. The remainder of the truss was assembled in sections in the street and lifted into place.

With the current project complete, the academy is considering changes to the lighting system and the addition of the new speaker clusters. Says Nan Gutterman, project manager for Philadelphia-based architect Vitetta: "The academy is a project that is forever."