RCC design of a G+3 residential frame to IS 456 with a software check

Shubham Buildcon is building 14 identical G+3 residential blocks on one plot in Hinjawadi, Pune. Each block has 8 two-bedroom flats. The structural consultant who did the original design has left the project, and on the first two blocks the site team changed several 230 x 450 mm columns to 230 x 380 mm "to save space in the parking". Nobody re-checked the design.

The project manager wants an independent design of one typical block before the third block's footings are cast in six weeks. You will do that design.

The block is 18.0 m long (4 bays of 4.5 m) and 12.0 m wide (3 bays of 4.0 m). Floor-to-floor height is 3.0 m, the plinth is 0.6 m above ground, and the roof is accessible. Slabs are 125 mm thick, external walls are 230 mm brick and internal walls 115 mm. Use M25 concrete and Fe500 steel. The soil report gives a safe bearing capacity of 200 kN/m² at 1.5 m depth. Pune is in seismic zone III.

What you hand over: - a design basis with every load and load combination you used; - a 3D frame model in STAAD.Pro or ETABS, with a hand check of the base shear; - design calculations for one typical slab panel, the critical beams, all column groups and the footings, to IS 456 with ductile detailing where IS 13920 applies; - reinforcement drawings and a bar bending schedule for one column and one beam line; - a short report that answers the manager's real question: are the 380 mm columns acceptable, and if not, what is the fix?

The design is done when every member passes its check with the governing combination shown, and a site engineer could build from your drawings.