St Martins Place is a 17-story mixed-residential building located in Broad Street, Birmingham. The project commenced in January 2019, with the concrete frame construction being carried out by Clark Mulhern with Colmore Tang as the Main contractor.
BONDED POST-TENSION SLABS AND BEAMS
Interspan carried out the design and execution of bonded post-tension slabs and beams. For levels 1-2, there were 9m span residential slabs. At level 3 a transfer beam and slabs support the remaining precast floors. The transfer structure on Level 3 consisted of beams with a thickness range from 775mm to 1000mm and slabs ranging from 350mm to 500mm.
The design of the level 3 structure limited the deflection after the precast slab installation to 6mm.
The variance in slab thickness meant that both 12.9mm and 15.7mm strand configurations were adopted in the design of the structure. With the focus on buildability, a 15.7mm strand configuration was adopted for the transfer level 3 to maximize the spacing between tendons to ease the congestion associated with thicker beams and slabs. The level 1 and 2 slabs adopted a conventional 12.9mm strand configuration in the tendons to provide the client with an efficient design solution.
ST MARTINS PLACE CORES
The structure had 3 cores. On Levels 1 and 2, all cores were separated with temporary movement joints. However, Level 3 only had 2 cores which were separated with a temporary movement joint due to precast arrangement, which could not be separated with a joint.
The project was executed using 6 pours per level, with the post-tensioning works taking place over a 28-week period.