Structural Steel Frame Design For A 4-Story Hotel in Papua New Guinea

 

Location: Papua New Guinea

Seismic Zone: Seismic intensity of 8 degrees (equivalent to PGA ≈ 0.3g based on ASCE 7 or similar local codes)

Wind Load: Basic wind speed = 120 km/h (~33.3 m/s)

Snow Load: None

Building Use:

Level 1: Parking garage (height = 3.8 m)

Levels 2–4: Hotel guest rooms (floor-to-floor height = 3.7 m, 3.7 m, and 3.4 m respectively)

Roof Type: Single-slope roof (assumed slope = 2% for drainage)

Exterior Walls: Non-structural hollow concrete blocks (locally constructed; not load-bearing)

Floor System: Composite steel deck with cast-in-place concrete topping (to be specified)

 

 

Total Building Length: 80 m

Plan Configuration:

East Wing: 55.6 m (L) × 27 m (W)

West Wing: 25 m (L) × 41.7 m (W)

Note: The plan is non-rectangular, likely L-shaped or stepped. For structural analysis, the building is treated as two connected blocks with possible expansion joint or rigid connection depending on seismic detailing.

Typical Bay Sizes: Assume column spacing of 7.5 m longitudinally and 6.0 m transversely (adjustable per architectural input).

 

 

Primary Code: AISC 360-16 (Specification for Structural Steel Buildings)

Seismic Design: ASCE 7-16 (or equivalent – adapted for PNG seismicity)

Wind Load: ASCE 7-16, Chapter 27 (Directional Procedure)

Material Standards: ASTM A992 (beams/columns), ASTM A36 (plates, secondary members)

 

 

 

Component	Load (kN/m²)
Steel Deck + 125 mm Concrete Slab (ρ = 24 kN/m³)	0.25 + (0.125×24) = 3.25
Ceiling, MEP, Finishes	0.5
Roofing (metal deck + insulation)	0.3
Hollow Block Wall (non-structural, but applied as line load on beams)	~3.0 kN/m (per meter height)

 

 

Level	LL (kN/m²)	Reference
Level 1 (Parking)	2.5	ASCE 7
Levels 2–4 (Hotel)	1.9	ASCE 7 (residential)
Roof	0.5	Maintenance load

 

 

Basic wind speed: V = 33.3 m/s

Exposure Category: C (assuming suburban/urban terrain)

Gust factor: G = 0.85

Pressure coefficient (Cp):

Wall (windward): +0.8

Wall (leeward): –0.5

Roof (single-slope): –0.9 to –0.3 (depending on zone)

Using ASCE 7 Eq. 27.3-1:
[ q_z = 0.613 K_z K_{zt} K_d V^2 I ]
Assuming (K_z = 0.85) at mid-height (~7 m), (I = 1.0), (K_{zt} = 1.0), (K_d = 0.85):
[ q_z ≈ 0.613 × 0.85 × 1.0 × 0.85 × (33.3)^2 × 1.0 ≈ 0.613 × 0.7225 × 1109 ≈ 490 Pa ≈ 0.49 kN/m² ]

Design wind pressure:
[ p = q_z G C_p ≈ 0.49 × 0.85 × C_p ]
→ Max wall pressure ≈ 0.33 kN/m² (windward), suction ≈ –0.21 kN/m² (leeward)

Note: Due to low rise (<15 m), wind governs lateral stability but seismic may control due to high seismicity.

 

 

Spectral Response: For 8-degree zone, assume S_DS = 1.0, S_D1 = 0.6 (conservative estimate per local adaptation of ASCE 7)

Risk Category: II

R-factor (steel moment frame): R = 8 (for Special Moment Frame – SMF)

Importance Factor: (I_e = 1.0)

Approximate Fundamental Period:
[ T_a = C_t h_n^x = 0.028 × (14.6)^{0.8} ≈ 0.028 × 8.5 ≈ 0.24 s ]
(Total height (h_n = 3.8 + 3×3.7 – 0.3 = 14.6) m approx.)

Seismic Base Shear:
[ V = \frac{S_{DS}}{R/I_e} W = \frac{1.0}{8} W = 0.125 W ]
→ 12.5% of total weight - significant.

 

 

Floor area ≈ (55.6×27) + (25×41.7) ≈ 1501 + 1043 = 2544 m²

3 occupied floors + roof ≈ 4 levels

Avg. DL + LL per floor ≈ (3.75 + 1.9) ≈ 5.65 kN/m²

Total weight (W ≈ 2544 × 5.65 × 4 ≈ 57,500 kN

Base shear (V ≈ 0.125 × 57,500 ≈ 7,200 kN

→ Seismic governs over wind for lateral design.

 

 

Lateral Force Resisting System (LFRS):

Special Concentrically Braced Frames (SCBF) or Special Moment Frames (SMF)

Given architectural flexibility and need for open parking, SCBF preferred for efficiency and ductility in high-seismic zones.

Gravity System:

Composite beams (W-shapes with shear studs + metal deck + concrete slab)

Columns: HSS or W-sections continuous from foundation to roof

Bracing: X-bracing in both directions at stair/elevator cores and perimeter where possible

Roof: Single-slope supported by sloped roof beams or tapered frames; purlins on top.

 

 

6.1 Floor Beams (Typical Interior)

Span: 7.5 m

Load: (w = (3.25 + 1.9) × 6.0 = 30.9 kN/m)

Max moment: (M = wL^2/8 = 30.9 × 7.5^2 / 8 ≈ 217 kN·m)

Required section modulus: (Z_x ≥ M / (0.9 F_y) = 217×10⁶ / (0.9×345) ≈ 700×10³ mm³)

Trial Section: W410×60 (Zₓ = 773×10³ mm³, OK)

6.2 Edge Beams (with wall load)

Additional wall load: 3.0 kN/m × 3.7 m = 11.1 kN/m

Total w ≈ 30.9 + 11.1 = 42.0 kN/m

M ≈ 295 kN·m → W460×74 (Zₓ = 942×10³ mm³)

6.3 Columns (Interior, 4 stories)

Tributary area: 7.5 m × 6.0 m = 45 m²

Axial load per floor: (3.25 + 1.9) × 45 = 232 kN

Total P ≈ 4 × 232 = 928 kN

Add 20% for seismic axial effects → P_u ≈ 1,115 kN

Effective length (K L ≈ 0.8 × 3700 = 2,960 mm)

Trial: W250×73 (A = 9,290 mm², r = 119 mm → KL/r ≈ 25 → φPₙ ≈ 0.9×345×9290 ≈ 2,880 kN >> 1,115 kN → OK)

Use W250×67 or HSS203×203×9.5 for economy

6.4 Bracing Members (SCBF)

Assume bracing at 2 bays per direction

Seismic story shear per bay ≈ 7,200 / (number of braced frames)

Assume 4 braced frames in each direction → ~900 kN per frame

Diagonal force: (F = V / sinθ); θ = 45° → F ≈ 900 / 0.707 ≈ 1,270 kN

Required A_g ≥ 1,270,000 / (0.9×345) ≈ 4,090 mm²

Trial: HSS152×152×9.5 (A = 5,200 mm², OK for tension/compression with slenderness check)

 

 

Metal Deck: Conform® 2.0 or Bondek® (profile depth = 60 mm)

Concrete Slab: 125 mm thick, f'c = 25 MPa

Shear Studs: 19 mm diameter × 100 mm height, spaced at 300 mm o.c. along beams

Composite Action: Full interaction assumed per AISC 360 Chapter I

 

 

Soil Report Required – assume moderate bearing capacity (150 kPa)

Column Reactions: Max ~1,200 kN → footing size ≈ √(1,200 / 150) ≈ 2.8 m × 2.8 m isolated footing

Seismic Anchorage: Anchor rods designed for uplift and shear per ACI 318

 

 

Beam-to-Column: Bolted end plates or welded moment connections (if SMF used)

Brace-to-Gusset: Whitmore section method per AISC Seismic Provisions

Deck Support: Simple bearing on beam top flange

 

 

Item	Specification
LFRS	Special Concentrically Braced Frames (SCBF)
Gravity Beams	W410×60 (interior), W460×74 (edge)
Columns	W250×67 or HSS203×203×9.5
Braces	HSS152×152×9.5
Floor Deck	60 mm deep composite metal deck + 125 mm concrete
Seismic Base Shear	~7,200 kN (governs design)
Wind Pressure	~0.33 kN/m² (non-governing)
Roof Slope	2% single slope, supported by sloped rafters

 

 

Engage local geotechnical engineer for soil report.

Coordinate with architect to locate braced frames without obstructing parking or rooms.

Use corrosion-resistant paint system (C4 environment per ISO 12944 – coastal PNG).

Provide movement joints if east/west wings are significantly offset.

Perform detailed 3D structural analysis using software (e.g., ETABS, SAP2000) including P-Δ effects.

 

 

 

This steel tonnage estimate covers the primary and secondary structural steel elements required for the gravity and lateral load-resisting systems of the 4-story hotel, including:

Columns (from foundation to roof)

Floor and roof beams (composite design)

Bracing members (Special Concentrically Braced Frames – SCBF)

Roof framing (sloped rafters and purlins)

Connections (estimated as 5% of main member weight)

Excluded:

Metal deck (considered non-structural cladding/slab support)

Anchor rods, base plates (included in connection allowance)

Stairs, railings, miscellaneous steel

 

 

Building plan consists of two connected blocks:

East Block: 55.6 m × 27 m

West Block: 25 m × 41.7 m
→ Total footprint ≈ 2,544 m²

Typical column grid: 7.5 m (longitudinal) × 6.0 m (transverse)

Number of columns:

East block: (55.6/7.5 ≈ 8 bays → 9 lines) × (27/6 ≈ 4.5 → 5 lines) = 45 columns

West block: (25/7.5 ≈ 3.3 → 4 lines) × (41.7/6 ≈ 7 → 8 lines) = 32 columns

Deduct overlap at junction (~5 shared columns) → Total columns ≈ 72

Floors: 4 levels (including roof)

Braced frames: 2 per direction per block → 8 total braced bays

Roof slope: 2%, supported by sloped beams; no trusses

 

 

Given the project's nature as public residential housing, we decided to strengthen the entire structural system to create a robust building with a service life exceeding 100 years. To achieve this, we replaced conventional columns with box-section steel columns and filled them on-site with concrete, significantly enhancing the overall structural strength.

 

 

Section: Box type 400X400x12x12mm (mass = 146.2 kg/m)

Height per column:

Level 1: 3.8 m

Levels 2–3: 3.7 m each

Level 4: 3.4 m
→ Total height = 14.6 m

Total column length = 72 × 14.6 = 1,051 m

Column weight = 1,051 m × 146.2 kg/m = 153,656 kg ≈ 153.7 tonnes

Note: Ground floor columns may be heavier; this is an average.

 

 

Interior Beams: WH500X290X10X16mm (mass = 109.6 kg/m)

Span: 7.5 m

Number per floor:

East block: 5 transverse lines × 8 longitudinal bays = 40

West block: 8 transverse lines × 3 longitudinal bays = 24
→ 64 interior beams per floor

Total for 3 floors + roof framing = 4 × 64 = 256 beams

Length = 256 × 7.5 = 1,920 m

Weight = 1,920 × 109.6=210,432 kg

Edge/Perimeter Beams: WH600X200X12X12mm (mass = 92 kg/m)

Perimeter length per floor ≈ 2×(55.6+27) + 2×(25+41.7) – overlap ≈ 290 m/floor

Assume edge beams every 6 m → ~48 edge beams per floor

Total = 4 × 48 = 192 beams, avg. span = 6.0 m

Length = 192 × 6 = 1,152 m

Weight = 1,152 × 92=105,984 kg

Total Beam Weight = 210,432 + 105,984 = 316,416 kg ≈ 316.4 tonnes

 

 

Section: HSS152×152×9.5 (mass = 42.5 kg/m)

Braced bays: 8 total (4 in E-W, 4 in N-S)

Each bay has 2 diagonals per story → 4 stories × 2 = 8 diagonals per braced frame line

Total diagonals = 8 frames × 8 = 64 braces

Avg. diagonal length (for 7.5 m × 3.7 m bay at 45°):
( L = \sqrt{7.5^2 + 3.7^2} ≈ 8.4 m )

Total brace length = 64 × 8.4 = 538 m

Brace weight = 538 × 42.5 = 22,865 kg ≈ 22.9 tonnes

 

 

Main roof rafters follow single-slope profile; use W310×45 (45 kg/m)

Spacing: 3.0 m o.c. (to support purlins)

Total roof area = 2,544 m² → rafter length ≈ building width (max 41.7 m)

Number of rafters ≈ 80 m / 3.0 ≈ 27 lines

Avg. rafter length = 35 m (weighted avg. of east/west widths)

Total rafter length = 27 × 35 = 945 m

Rafter weight = 945 × 45 = 42,525 kg

Purlins: C200×20×2.5 (5.5 kg/m), spaced 1.5 m o.c.

Total purlin length ≈ (2,544 m² / 1.5 m spacing) × 1.0 m = 1,696 m

Weight = 1,696 × 5.5 = 9,328 kg

Total Roof Steel = 42,525 + 9,328 = 51,853 kg ≈ 51.9 tonnes

 

 

Standard practice: 5% of total main member weight

Main members total = 153.7 + 316.4 + 22.9 + 51.9 = 533.9 tonnes

Connections = 0.05 × 533,900 = 27,245 kg ≈ 27.3 tonnes

 

 

Component	Weight (tonnes)
Columns	153.7
Floor & Edge Beams	316.4
Bracing (SCBF)	22.9
Roof Framing (Rafters + Purlins)	51.9
Connections (5%)	27.3
Total Estimated Structural Steel	572.2 tonnes

 

 

Total floor area = 2,544 m²

Steel per unit area = 572.2 t / 2,544 m² = 225 kg/m²

This is reasonable for a 4-story seismic-resistant steel building with braced frames in a high-seismic region.

 

 

Optimization Potential: Use of larger bays or reduced bracing could lower tonnage, but seismic demands in PNG limit reductions.

Local Fabrication: Consider standard section availability in PNG or Australia (common sections like W-shapes and HSS are assumed).

Corrosion Protection: All steel to receive hot-dip galvanizing or duplex paint system due to coastal tropical environment.

Contingency: Add 5–10% for design development, architectural changes, or detailing inefficiencies → Final budget estimate: ~615–700 tonnes. If add some staircase and structure for lifts, overall will be around 650~750 tonnes in final.

Prepared by: Hangzhou Xixi Building Co., LTD.
Date: January 16, 2026
Basis: AISC 360-16, preliminary layout, ASCE 7-16 seismic assumptions