Signature Structures, LLC requested our partnership for a practice facility of a Philadelphia Football team facility that needed replacement of outer fabric and inner liner fabric for a steel frame supported tensioned fabric structure (measurements: 200 ft wide by 280 ft long, with 26 ft tall sidewalls and an arched roof). For logistical and scheduling reasons, the inner liner replacement was done first, and before the new liner was installed, new fiberglass insulation was placed in the cavity. The existing fabric system for both the liner and outer fabric was a large panel system, tensioned with pipes and pockets. The customer requested color stripes every 20 ft up and over the roof for the outer fabric.
There was already an existing system in place
The liner was replaced re-using the existing system. The outer fabric existing system required access from the inside, impractical with new insulation and a new liner already in place due to the scheduling requirements. Therefore an alternate system was proposed for the outer fabric replacement, using smaller panels with keder edges which allowed installing and tensioning the fabric from the outside.
Solution: Individual keder panel
The design team proposed to leave the old outer fabric in place, which helps with weather protection during fabric replacement. The first preparatory step was to screw new keder track into the top chords of the steel trusses, sandwiching the old fabric between the keder track and rectangular HSS steel chords. Then individual keder panels could slide between the keder rails. Because the fabric is at all times connected to the frame through the keder edges, this made the installation schedule less dependent on the weather. Having a functional facility at all times also allowed the customer to schedule events during the install period, requesting specific dates that no install work would take place in between install days.
Find the system that would work best
The chosen tensioning system in any fabric replacement project is dependent on many factors. In this case the system needed to accommodate the lack of access on the inside, work with a steel frame that cannot be moved to create side-tension in the fabric panels, retain a functional facility during install and preferably place the fabric with warp direction in the direction up and over, so that the color stripes can run in the warp direction, for efficiency of manufacturing and aesthetic effect, avoiding cross seams that can collect dirt more easily.
The system that was utilized uses a specially shaped keder track, with a second extrusion in the shape of a hat channel. The hat channel is bolted down after the fabric panels are installed on both sides of the keder track, with bolts and nuts that grab in the keder track flanges. It pushes the fabric panel down and the resulting elongation of the fabric creates side-tension (see fig 1). The chosen fabric was Serge Ferrari Precontraint fabric, style 702, specifically made for the project. The unique Precontraint system results in balanced stretch properties between warp and fill. This allowed the use of the hat channel to tension the keder panels sideways. If the fabric would have more stretch in the fill direction, the limited geometrical elongation in the keder-to-keder direction would not have generated enough prestress and forced the use of cross-seams to be able to utilize the fabric in the warp direction as main load carrying direction or alternatively, a different tensioning system.
While the Precontraint system utilized by Serge Ferrari is beneficial in almost any tensioned fabric application, this project shows a unique combination of requirements where the Precontraint benefits really shine. The customer was very pleased with the end result, seeing the aesthetics that they wanted to be combined with an install schedule that met their very unique requirements.