One of the proposed options to increase the LHC luminosity is the replacement of the existing inner triplets at the interaction regions with new low-beta larger aperture quadrupoles operating at the same gradient. Lawrence Berkeley National Laboratory (LBNL) is carrying out preliminary studies of a large-bore Nb3Sn quadrupole. The mechanical design presents a support structure based on the use of keys and bladders without self-supporting collars. This technology has been proven effective in several successful common coil Nb3Sn dipoles built at LBNL, and it is for the first time applied to a cos(2ϑ) design. In this paper, we present a detailed analysis of the quadrupole mechanical behavior, demonstrating the possibility of delivering, through this method, well-controlled coil pre-compression during assembly, cool-down and excitation. The study has been performed with the finite element program ANSYS.