Build a full 3D multi-story RC frame in ETABS. Define story heights, bays, columns, beams, and slab dead/live loads. This is the core model you'll use through Day 10.
A 2D beam or portal is easy to verify by hand. A 3D multi-story frame with 5 floors, 4 bays, and lateral loads is not — you need software. But you also need to know when the software is wrong.
A multi-story frame is a stacked series of one-story frames, but columns are now continuous elements that carry gravity from every floor above and must also resist lateral loads.
Build a 3-bay × 3-bay × 3-story frame (4 m bays, 3 m stories) with 300×500 beams, 400×400 columns, and 150 mm slabs.
File → New Model → Grid Only. Set X: 3 bays @ 4 m, Y: 3 bays @ 4 m, Z: 3 stories @ 3 m. Total building: 12×12×9 m.
Create beam section B300×500, column section C400×400, slab section S150 (shell). Assign beams along X and Y grid lines, columns at intersections, slabs to each floor.
Select all ground-floor column base nodes → Assign → Joint → Restraints → Fixed. This is standard for RC building frames.
Select all slab elements per floor → Assign → Shell Loads → Uniform. DEAD: self-weight (auto) + superimposed 2 kN/m². LIVE: 3 kN/m² (office, per BNBC Table 6.2.1).
1.4D or 1.2D + 1.6L (take the larger). Run linear static. Check column axial forces — ground floor should be highest.
Before adding lateral loads on Day 8, verify your gravity model.