What Structural Drawings and Calculations Are
Structural drawings show the building's load-bearing skeleton: foundations, columns, beams, slabs, shear walls, and connections. Structural calculations are the engineering analysis that demonstrates the structure can safely carry all applied loads — dead load (self-weight), live load (occupants and equipment), wind load, and seismic load. Together, they are the structural safety evidence base.
Structural Design Certificate
Licensed Structural Engineer
Project Name
Proposed 10-Storey Commercial Building
Design Code
BNBC 2020 (Part 6: Structural Design)
Seismic Zone
Zone II (Dhaka) per BNBC
Soil Type / Investigation
Type SD (Stiff Soil) / SPT Report attached
Foundation Type
Pile Foundation (RCC bored cast-in-situ)
No. of Floors
G+9 with 2 basement levels
Design Wind Speed
210 km/h (3-second gust)
Engineer Name / Registration
Engr. [Name] / IEB Reg. No. XXXX
Structural Drawing Set Contents
| Drawing | Shows | Key Information |
|---|---|---|
| Foundation plan | Foundation type (pile, raft, isolated footing), layout, depths | Bearing capacity, pile lengths, soil type assumed |
| Column layout | Column positions, sizes, reinforcement schedules | Column sizes, rebar diameters and spacing, concrete grade |
| Beam layout | Beam spans, sizes, reinforcement details | Span lengths, load-bearing vs non-load-bearing |
| Slab details | Slab thickness, reinforcement, openings | Design live load (kN/m²), slab type (one-way, two-way, flat) |
| Shear wall details | Location, thickness, reinforcement of lateral load-resisting walls | Seismic resistance contribution |
| Staircase details | Structural design of stairs including landings | Fire escape staircase structural integrity |
| Retaining walls | Basement wall design, earth pressure resistance | Waterproofing, drainage provisions |
Key Structural Design Parameters
| Parameter | Typical Value (Office) | Standard |
|---|---|---|
| Concrete compressive strength | 25–40 MPa (cylinder) / 30–50 MPa (cube) | ACI 318, BNBC |
| Reinforcement yield strength | 415 MPa (Grade 60) or 500 MPa | ASTM A615, BDS |
| Design live load — office | 2.4 kN/m² (50 psf) | BNBC Table 2.2.3, ASCE 7 |
| Design live load — corridor | 4.8 kN/m² (100 psf) | BNBC, ASCE 7 |
| Design live load — storage | 6.0–12.0 kN/m² (125–250 psf) | Depends on storage type |
| Seismic zone factor (Dhaka) | Z = 0.20 (Zone II per BNBC 2020) | BNBC 2020 |
| Wind speed (Dhaka) | 195 km/h (3-second gust) | BNBC 2020 |
What to Check During Due Diligence
- Design code: Which code was the structure designed to? BNBC 1993, BNBC 2006, BNBC 2020? Older codes had lower seismic requirements.
- Design loads: Does the design live load match the intended use? A building designed for 2.4 kN/m² (office) cannot safely support 6.0 kN/m² (storage) without structural verification.
- As-built vs design: Were the structural drawings followed during construction? Common deviations: smaller rebar, lower concrete grade, missing shear walls.
- Modifications: Any post-construction structural modifications (core-cutting, column removal, additional floors)?
- Condition: Signs of structural distress — cracks, spalling, exposed rebar, settlement, deflection.
Bangladesh Context
- Missing structural drawings: Many older Dhaka buildings were built without formal structural engineering. Some have no drawings at all.
- Code evolution: BNBC 1993 → 2006 → 2020. Each increased seismic requirements. Buildings designed to BNBC 1993 may be under-designed for current seismic requirements.
- Construction quality: Gap between design and execution is common. Specified 30 MPa concrete may have been poured at 20 MPa. Core testing can verify actual strength.
- Rana Plaza lesson: The 2013 Rana Plaza collapse (1,134 deaths) was caused by structural overloading, poor construction quality, and unauthorised floors. Structural document verification is a life-safety issue.
References
- ACI 318 — Building Code Requirements for Structural Concrete
- BNBC 2020 — Part 6: Structural Design (Chapter 6.1–6.9)
- ASCE 7 — Minimum Design Loads for Buildings
- ASTM E2018 — Property Condition Assessment
Insights & Guidance
- Structural drawings show the load-bearing skeleton; calculations prove it can safely carry all loads.
- Key parameter: design live load — office (2.4 kN/m²) vs storage (6-12 kN/m²). Using a building beyond its design load is dangerous.
- Dhaka seismic zone factor: Z = 0.20 (BNBC 2020 Zone II). Buildings designed to BNBC 1993 may be under-designed.
- Many older Dhaka buildings lack structural drawings entirely — a critical due diligence red flag.
- Gap between structural design and construction quality is common in Bangladesh — core testing can verify actual concrete strength.
Structural failure is the most catastrophic building failure — it kills people. The Rana Plaza collapse (2013, 1,134 deaths) demonstrated what happens when structural integrity is not verified. Structural drawings and calculations are the only way to verify that a building can safely carry its loads. Without them, no one can confirm the building is structurally adequate for its use — and no responsible organisation should occupy it without verification.
- Structural overload — using building beyond design capacity (e.g., heavy storage on floors designed for office use).
- Seismic inadequacy — older buildings designed to outdated codes with lower seismic requirements.
- Construction defects — lower concrete grade than specified, missing reinforcement, honeycombing.
- Unauthorised modifications — column removal, core-cutting through beams, additional floors.
- Complete structural drawing set (foundation, column, beam, slab, shear wall details)
- Structural design calculations (load analysis, member design, seismic/wind analysis)
- Soil investigation report (used for foundation design)
- Concrete test reports (cube/cylinder test results during construction)
- Any structural assessment reports (post-construction)
- Visible cracks — pattern, width, location (structural vs cosmetic)
- Spalling concrete or exposed reinforcement
- Signs of settlement — uneven floors, tilting, door frame distortion
- Evidence of structural modifications — filled openings, new columns, patched areas
- Water damage near structural elements — corrosion risk
- Are structural drawings and calculations available?
- What design code was used? (BNBC version)
- What is the design live load per floor?
- Have any structural modifications been made since construction?
- Has a structural assessment been conducted? When?
- Structural assessment — licensed structural engineer for load capacity verification.
- NDT testing — non-destructive testing firm for concrete strength (rebound hammer, core testing).
- Seismic assessment — structural engineer with seismic expertise for vulnerability analysis.