Shell-based support structures for Nb$_{3}$Sn accelerator quadrupole magnets

Shell-based support structures are being fabricated and tested as part of the development of large-aperture Nb$_{3}$Sn superconducting quadrupoles for future upgrades of the LHC Interaction Regions. These structures utilize water pressurized bladders for room-temperature pre-load control, and rely on a pre-tensioned aluminum shell to deliver a substantial part of the coil pre-stress during cooldown. The coil final pre-load is therefore monotonically approached from below, without overstressing the strainsensitive conductor. This method has been adopted by the US LARP collaboration to test subscale racetrack coils (SQ series), 1 m long cos-theta coils (TQS series), and 4 m long magnets (LRS and LQS series). We present recent progress in the development of shell-based support structures, with a description of the principles of operations and the future plans.