Steel Industrial Building Design — Pre-Engineered Buildings, Rigid Frames

Steel industrial buildings span a wide range of structures from pre-engineered metal buildings to custom rigid-frame structures. This guide covers design provisions per MBMA, AISC 360, and AISI S100.

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Core calculations run via WebAssembly in your browser with step-by-step derivations across AISC 360, AS 4100, EN 1993, and CSA S16 design codes. Results are preliminary and must be verified by a licensed engineer.

Frequently Asked Questions

PRELIMINARY — NOT FOR CONSTRUCTION. All results are for educational and reference use only. Must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) before use in any project.

What is a pre-engineered metal building (PEMB)? A PEMB uses a factory-designed and fabricated rigid steel frame with tapered built-up columns and rafters. Per MBMA (Metal Building Manufacturers Association) standards: (1) Primary frames — rigid moment frames with tapered I-sections optimized for each load condition, (2) Secondary members — cold-formed Z or C purlins and girts, (3) Bracing — rod or cable X-bracing in roof and walls, (4) Typical spans — 40-200 ft (12-60 m), bay spacing 20-30 ft (6-9 m). PEMBs are economical for low-rise industrial, warehouse, and agricultural buildings.

How are rigid frame industrial buildings designed? Rigid frame industrial buildings use moment-resisting connections between columns and rafters. Design considerations: (1) Frame analysis — second-order (P-Δ) analysis required per AISC 360 C2, (2) Haunched connections — deeper sections at the knee (column-rafter intersection) where moments are highest, (3) Tapered sections — variable depth to match moment envelope, (4) Stability — out-of-plane bracing at purlin and girt locations, (5) Crane loads — vertical (wheel loads + impact) and lateral (surge + traction) must be included for crane bays.

What are the design loads for industrial buildings? Per ASCE 7-22 and IBC 2021: (1) Roof live load — 20 psf (0.96 kN/m²) minimum, reducible per Section 1607.13, (2) Roof snow — ground snow load based on location with drift accumulation at steps and parapets, (3) Wind — MWFRS and C&C per ASCE 7-22 Chapters 27-30, (4) Seismic — importance factor Ie=1.0 for standard occupancy, (5) Crane loads — vertical impact 25% of max wheel load (CMAA 70), lateral surge 20% of lifted + trolley weight, (6) Fire — fireproofing typically required for 1-2 hour rating depending on building type.

How are crane runway beams designed in industrial buildings? Crane runway beams are among the most fatigue-critical elements in industrial buildings, supporting moving overhead cranes that deliver millions of stress cycles over the building life. Per CMAA 70 and AISC 360: (1) Wheel loads — each crane end truck typically has 2-4 wheels. A 20-ton capacity bridge crane (CMAA Class C) with 4 wheels per end truck: maximum wheel load = (crane weight + lifted load)/wheels per side = (40,000 + 20,000)/4 = 15,000 lb. With 25% impact factor per CMAA 70 Section 3.3.1: P_design = 15,000 × 1.25 = 18,750 lb per wheel. (2) Lateral loads — crane surge = 20% of (lifted load + trolley weight) applied at the rail. For our example: lateral = 0.20 × (20,000 + 8,000) = 5,600 lb total, distributed to 4 wheels = 1,400 lb lateral per wheel. (3) Crane beam selection — a 40 ft span crane beam with the wheel configuration above (wheels at 12 ft axle spacing) produces Mmax ≈ 200 kip-ft. Using a W27×94 (Sx = 243 in³): fb = M/S = 200 × 12/243 = 9.88 ksi. Fb = 0.66Fy = 0.66 × 50 = 33 ksi. Ratio = 0.30 — OK. However, deflection controls: Δ_max = 18,750 × (3 × 480³ - 4 × 144² × 480) / (24 × 29,000,000 × 2,700 × 2) = 0.58 inches. L/800 = 480/800 = 0.60 inches — marginally OK.

Purlins and Girts — Secondary Framing Design

Secondary members in industrial buildings transfer loads from the cladding to the primary frames and provide lateral bracing to the compression flanges of rafters and columns.

Purlin design (roof). Purlins span between roof rafters, typically at 5-8 ft spacing. For a building with 25 ft bay spacing and purlins at 6 ft centers: (1) Loads — dead load (metal roof + insulation = 3 psf, purlin self-weight = 2 psf), roof live load (20 psf), wind uplift (varies by location, typically 25-40 psf uplift for wall zones). (2) Tributary width = 6 ft. w_u = 1.2(5 × 6/1,000) + 1.6(20 × 6/1,000) = 0.228 kips/ft for gravity. (3) M_max = wL²/8 = 0.228 × 25²/8 = 17.8 kip-ft. Using a C-section purlin (Z or C shape per AISI S100), S_req = 17.8 × 12/(0.9 × 50) = 4.75 in³. A typical Z8×2.5×0.060 purlin (S_eff ≈ 5.2 in³) works. (4) Wind uplift check: for 35 psf uplift, w_u = 1.6(35 × 6/1,000) = 0.336 kips/ft upward. M_max_uplift = 0.336 × 25²/8 = 26.3 kip-ft. Check the bottom flange in compression — requires lateral bracing from the metal roof diaphragm. (5) Purlin bracing: bridging lines at 5 ft spacing (typically 1.5 inch diameter pipe or 1×3 angle), with anchor braces at the frame lines. Per AISI S100 Section D3.2.2, bridging must resist 2% of the compression flange force.

Girt design (wall). Girts span between columns horizontally. For 25 ft bay spacing with girts at 6 ft vertical spacing: (1) Wind load: 20 psf design wind pressure for the interior zone (ASCE 7-22 Chapter 30). (2) w = 20 × 6/1,000 = 0.120 kips/ft. M_max = 0.120 × 25²/8 = 9.38 kip-ft. A C8×1.5×0.060 girt (S_eff ≈ 3.0 in³) provides: fb = 9.38 × 12/3.0 = 37.5 ksi — marginal. Use Z8×2.5×0.075 (S_eff ≈ 4.0 in³): fb = 9.38 × 12/4.0 = 28.1 ksi — OK. (3) Sag rods: at midspan between frames, 5/8 inch diameter round bar sag rods are typical, designed to support the girt weight between frames.

Worked example — frame design for 100 ft span industrial building. A rigid frame with 100 ft span, 25 ft eave height, 6:12 roof slope: (1) Design loads: DL = 10 psf on roof, LL = 20 psf, wind = 25 psf (MWFRS). (2) Frame spacing = 25 ft. (3) First-order analysis: for DL+LL, the ridge moment is approximately wL²/20 = (0.75 × 100²)/20 = 375 kip-ft, and the knee (haunch) moment is approximately wL²/12 = (0.75 × 100²)/12 = 625 kip-ft. (4) Second-order (P-Δ) amplification: B2 = 1/(1 - P/P_e). For P_total = 150 kips (dead + roof live) per frame, P_e = π²EI/(KL)² = 4,630 kips for a W30×99 rafter section. B2 = 1/(1 - 150/4,630) = 1.033 — 3.3% second-order amplification. (5) Haunch design: the knee requires a deeper section — typically a haunch extending 10-15% of the span (10-15 ft) from each column. A haunch depth of 48 inches at the column face tapering to 30 inches at the end (matching the rafter depth) is typical for a 100 ft span. (6) Column base: for H = 25 ft, the maximum column shear from wind is approximately 20 kips per column. Each column base must resist: uplift (from wind) = 15 kips, shear = 20 kips. With 4-7/8 inch diameter A36 anchor rods: φT_n = 0.75 × 0.75 × 58 × 0.601 × 4 = 78.4 kips > 15 kips — OK.

Mezzanine design in industrial buildings. Mezzanines within industrial buildings add usable floor area without expanding the building footprint. Per IBC 2021 Section 505: (1) Maximum area — 1/3 of the room area for fire areas without sprinklers, 1/2 if sprinklered. (2) Load path — mezzanine loads must be transferred directly to the main frame columns or to the building foundation, not the existing floor slab unless verified for the additional load. (3) A 5,000 sq ft mezzanine at 100 psf LL: total mezzanine vertical load = 500 kips, requiring 4 columns (W10×33 each, φcPn = 265 kips each, 4 × 265 = 1,060 kips > 500 kips). (4) Deflection criteria: L/360 for LL, L/240 for total load. Connection to the existing building: sliding connections at main frame columns to avoid unintended diaphragm forces.

Fire protection for industrial buildings. Per IBC 2021 Table 601 and 602: (1) Type IIB (unprotected) — most industrial steel buildings, no fireproofing required except for exit enclosures and shaft walls. (2) Type IIA (protected) — requires 1-hour fire rating for primary frames. Spray-applied fire resistive material (SFRM) at 0.5-1.5 inch thickness provides 1-2 hour ratings depending on the W/D ratio of the member. (3) For crane buildings, the crane runway beam typically does not require fireproofing (classified as movable equipment area).

Use the beam capacity calculator to verify frame member sizes and the column buckling calculator for column stability under gravity plus crane loads.

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Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice. All results must be independently verified by a licensed Professional Engineer.

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Frequently Asked Questions

What is the recommended design procedure for this structural element?

The standard design procedure follows: (1) establish design criteria including applicable code, material grade, and loading; (2) determine loads and applicable load combinations; (3) analyze the structure for internal forces; (4) check member strength for all applicable limit states; (5) verify serviceability requirements; and (6) detail connections. Computer analysis is recommended for complex structures, but hand calculations should be used for verification of critical elements.

How do different design codes compare for this calculation?

AISC 360 (US), EN 1993 (Eurocode), AS 4100 (Australia), and CSA S16 (Canada) follow similar limit states design philosophy but differ in specific resistance factors, slenderness limits, and partial safety factors. Generally, EN 1993 uses partial factors on both load and resistance sides (γM0 = 1.0, γM1 = 1.0, γM2 = 1.25), while AISC 360 uses a single resistance factor (φ). Engineers should verify which code is adopted in their jurisdiction.