Commercial Structural Framing: Steel, Concrete, and Wood Systems

Commercial structural framing is the load-bearing skeleton of any non-residential building — the engineered system that transfers gravity loads, lateral forces, and dynamic stresses from the roof and floors down to the foundation. This page covers the three dominant framing material categories used in US commercial construction (structural steel, cast-in-place and precast concrete, and heavy timber/mass timber), the code and regulatory frameworks that govern their design and inspection, and the classification boundaries that determine which system applies to a given occupancy and building height. The selection of a structural framing system is among the most consequential early decisions in any commercial project, with downstream effects on fire resistance ratings, span capability, schedule, cost, and seismic or wind performance.

• Definition and scope
• Core mechanics or structure
• Causal relationships or drivers
• Classification boundaries
• Tradeoffs and tensions
• Common misconceptions
• Checklist or steps
• Reference table or matrix
• References

Definition and scope

Structural framing in commercial construction refers to the integrated assembly of primary members — columns, beams, girders, joists, shear walls, and diaphragms — that collectively resist and transfer all applied loads to the foundation system. The governing document for structural design across nearly all US jurisdictions is the International Building Code (IBC), published by the International Code Council (ICC) and adopted with local amendments in all 50 states. The IBC does not independently set material-specific design rules; instead, it incorporates by reference the material standards published by bodies including the American Institute of Steel Construction (AISC), the American Concrete Institute (ACI), and the American Wood Council (AWC).

Framing systems are subject to structural engineering of record (EOR) review, stamped design documents, and phased inspections by the authority having jurisdiction (AHJ). For projects of substantial scale, special inspection programs under IBC Chapter 17 apply mandatory third-party verification for high-strength bolting, welding, concrete placement, and masonry grouting. The scope of "commercial structural framing" spans structures from a 5,000-square-foot single-story retail shell to a 60-story office tower — meaning that no single system dominates the full range of application.

The commercial building listings on this authority reflect the diversity of framing approaches across occupancy types, regions, and building heights encountered in the national market.

Core mechanics or structure

Structural steel framing relies on hot-rolled wide-flange (W-shape) sections, hollow structural sections (HSS), and built-up plate girders. Steel members carry load primarily through bending, shear, and axial compression or tension. Connections are achieved through bolted moment or shear connections and full-penetration or fillet welds, designed per AISC 360 (Specification for Structural Steel Buildings). Lateral resistance is provided by moment frames, concentrically or eccentrically braced frames (CBF/EBF), or steel plate shear walls. The yield strength of A992 wide-flange steel is 50 ksi (50,000 pounds per square inch), which governs most standard beam and column design.

Concrete framing operates through two distinct subsystems. Cast-in-place (CIP) concrete uses formwork erected on-site, with reinforcing bar (rebar) placed and concrete poured to form monolithic frames, flat-plate slabs, or shear wall cores. Precast concrete involves factory-manufactured elements — double-tees, hollow-core planks, inverted-tee beams, and precast columns — delivered to site and assembled under PCI MNL-120 (PCI Design Handbook). Post-tensioned slabs, common in parking structures and long-span office floors, introduce high-strength steel tendons stressed after the concrete reaches design strength, allowing thinner slabs over longer spans. Concrete's compressive strength in commercial framing typically ranges from 4,000 to 8,000 psi, specified at 28-day cylinder test.

Mass timber and heavy timber framing uses large-format solid or engineered wood elements: glued-laminated timber (glulam), cross-laminated timber (CLT), nail-laminated timber (NLT), and dowel-laminated timber (DLT). Design is governed by the AWC National Design Specification (NDS) for sawn and engineered lumber. The 2021 IBC introduced Type IV-A, IV-B, and IV-C construction types specifically for tall mass timber buildings, allowing mass timber up to 18 stories under certain encapsulation and sprinkler requirements — a direct expansion from the previous 6-story limit.

Causal relationships or drivers

The selection of a structural framing system is not arbitrary; it is driven by a hierarchy of constraints operating simultaneously.

Occupancy and height represent the first filter. The IBC's Table 504.3 and Table 504.4 govern maximum building heights and stories by construction type. A Type I-A building (protected noncombustible — primarily steel or concrete with fire-resistive coatings) carries no maximum height restriction under the IBC base code, while a Type III-A structure (protected combustible — wood framing with noncombustible exterior) is limited to 65 feet in most occupancy groups.

Seismic Design Category (SDC) drives lateral system selection. Buildings assigned to SDC D, E, or F — concentrated in the western United States, Pacific Northwest, and portions of the central US — require special moment-resisting frames or special concentrically braced frames designed and detailed per ASCE 7 (Minimum Design Loads and Associated Criteria for Buildings and Other Structures) and AISC 341 (Seismic Provisions for Structural Steel Buildings). Concrete systems in high SDC buildings must comply with ACI 318 Chapter 18 requirements for special reinforced concrete moment frames.

Span requirements and live loads dictate the structural depth and material choice at the floor and roof framing level. Warehouse and industrial occupancies routinely carry floor live loads of 250 to 500 pounds per square foot (psf) for rack storage, while office occupancies are designed to 50 psf per ASCE 7 Table 4.3-1. Long-span framing — exceeding 40 feet between columns — generally favors steel wide-flange girders, prestressed concrete double-tees, or glulam beams depending on fire rating requirements.

Schedule and site logistics create practical pressure. Steel framing erects rapidly once fabrication is complete, but lead times for structural steel fabrication commonly run 16 to 26 weeks from order to delivery. Precast concrete components require factory production time but reduce on-site formwork labor. CIP concrete is schedule-intensive due to forming, pouring, curing, and stripping cycles.

For context on how framing decisions interact with overall project delivery, the commercial building directory purpose and scope page outlines the project categories where these systems appear.

Classification boundaries

IBC Chapter 6 establishes five construction types (Types I through V), each subdivided into A (protected) and B (unprotected) variants, creating 8 distinct construction type classifications. These types directly map to required fire resistance ratings for structural elements:

• Type I-A: Columns require 3-hour fire resistance; beams, 2.5-hour; floors, 2-hour. Used for high-rise buildings and large-occupancy structures.
• Type I-B: Columns require 2-hour fire resistance; beams, 2-hour; floors, 2-hour.
• Type II-A/B: Noncombustible materials with reduced or no fire resistance requirements. Steel framing is common; occupancy heights are restricted.
• Type III-A/B: Noncombustible exterior walls; interior elements may be combustible (wood framing). Common in mid-rise mixed-use under 65 feet.
• Type IV-HT (Heavy Timber) and IV-A/B/C (Mass Timber): Large-dimension wood structural members with prescriptive minimum sizes. IV-A allows up to 18 stories with specific encapsulation.
• Type V-A/B: Any materials, including conventional wood framing. Limited to low-rise structures.

Material-specific design standards create a parallel classification layer. Structural steel systems are further classified by AISC as ordinary moment frames (OMF), intermediate moment frames (IMF), or special moment frames (SMF) based on seismic detailing requirements. Concrete systems are classified as ordinary, intermediate, or special reinforced concrete moment frames under ACI 318. These classifications carry enforcement weight at the structural design review stage.

Tradeoffs and tensions

The structural framing decision involves genuine engineering and economic tradeoffs that do not resolve to a universal optimum.

Steel versus concrete for mid-rise commercial: Steel framing typically allows faster erection — a 10-story steel frame can advance 2 to 3 floors per week once steel arrives — but requires fireproofing application (spray-applied fire-resistive material, or SFRM) that adds cost and schedule. CIP concrete is inherently fire-resistive but requires forming and curing time that constrains floor-to-floor cycle time. On a 200,000-square-foot office building, the cost differential between structural steel and post-tensioned concrete can range widely based on local steel fabrication capacity, concrete labor rates, and site constraints — there is no fixed national cost advantage for either.

Mass timber versus steel for low-to-mid-rise: Mass timber appeals to occupants and developers seeking measurable embodied carbon reductions. The Carbon Leadership Forum's Embodied Carbon in Construction Calculator (EC3) documents significantly lower global warming potential (GWP) for mass timber structural elements compared to structural steel or CIP concrete. However, mass timber requires precise dimensional tolerances, is sensitive to moisture during construction, and requires careful connection detailing to achieve fire performance equivalent to Type I construction.

Special inspection program scope: IBC Chapter 17 mandates special inspections for high-strength concrete, welding, high-strength bolt installation, and soil conditions. Project owners and contractors sometimes treat this as an administrative burden rather than a risk-control mechanism, leading to gaps in inspection coverage that surface during permit closeout or building department audits.

Hybrid systems: Many commercial buildings — particularly mid-rise multifamily, mixed-use, and podium-style structures — use steel or concrete for the podium floors and wood framing above. This creates regulatory complexity at the construction type transition level, requiring careful coordination between the EOR and the AHJ regarding fire separation, lateral load transfer, and code interpretation.

The how to use this commercial building resource page covers how framing-related contractor specializations are organized within this reference.

Common misconceptions

Misconception: Steel is always stronger than concrete.
Structural steel has superior tensile and flexural strength per unit weight. Reinforced concrete, however, exceeds steel in compressive strength per unit volume for columns and bearing walls, and CIP concrete moment frames can achieve equivalent lateral stiffness with smaller floor-to-floor heights in certain configurations. Strength comparisons require specifying load type, orientation, and application.

Misconception: Mass timber cannot be used in buildings over 6 stories.
The 2021 IBC explicitly permits mass timber up to 18 stories under Type IV-A construction, provided the structural members are encapsulated with Type X gypsum board and the building is fully sprinklered per NFPA 13. This represents a codified change from earlier IBC editions.

Misconception: Fire-resistive ratings mean a structural element will not be damaged in a fire.
Fire resistance ratings, as defined by ASTM E119 testing protocols, measure the time a structural assembly can sustain a standard fire exposure and maintain structural integrity and fire barrier performance — not permanent immunity to fire damage. Steel members that reach temperatures above 1,100°F lose approximately 50% of yield strength, which is the underlying basis for SFRM thickness requirements.

Misconception: Structural framing is finalized during schematic design.
Framing system selection often undergoes significant revision through design development and construction document phases as foundation conditions, mechanical coordination, cost estimates, and long-lead procurement realities are integrated. Structural framing is typically at 60% or greater design development before final system commitment.

Misconception: Precast concrete is only for parking structures.
Precast elements — including architectural precast panels, precast shear walls, and prestressed double-tees — are used in warehouses, industrial facilities, schools, and data centers. The PCI Design Handbook (9th Edition) documents precast applications across 11 structural system configurations.

Checklist or steps

The following sequence represents the structural framing decision and execution process as it occurs across a standard commercial project. This is a descriptive process map, not prescriptive design advice.

Phase 1 — Programming and System Feasibility
- Confirm IBC occupancy classification and applicable construction type options (IBC Table 504.3 / 504.4)
- Identify Seismic Design Category per ASCE 7 site analysis
- Establish basic wind speed and exposure category per ASCE 7 Chapter 26
- Determine maximum span requirements from program (column grid, bay spacing)
- Assess site conditions affecting foundation type and structural depth

Phase 2 — Structural System Selection
- Evaluate 2–3 structural framing alternatives against height, fire rating, and SDC requirements
- Review local fabrication and erection contractor availability for each system
- Confirm fire resistance assembly options per IBC Table 601 and UL assembly listings
- Identify long-lead procurement items (structural steel mill order windows, precast production schedule)

Phase 3 — Design Development
- Structural engineer of record (EOR) completes preliminary member sizing and lateral system layout
- Coordinate structural grid with MEP penetration requirements
- Identify special inspection program scope per IBC Chapter 17
- Confirm construction type assignment with AHJ if mixed or hybrid system

Phase 4 — Construction Documents and Permitting
- EOR issues stamped structural drawings and specifications
- Structural calculations submitted to AHJ for plan review
- Special inspection agreement executed between owner, EOR, and approved special inspection agency (SIA)
- Shop drawing review process initiated for steel fabrication, precast production, or engineered wood components

Phase 5 — Construction and Inspection
- Pre-construction conference with SIA to confirm inspection hold points
- Foundation and anchor bolt inspections completed before erection
- Structural steel: bolt installation inspection (pre-installation verification, snug-tight, and final torque per AISC 360 Table J3.1)
- Concrete: batch ticket review, slump/air testing, cylinder sampling per ACI 318 and project specifications
- Mass timber: moisture content verification, connection hardware inspection, encapsulation installation confirmation
- EOR field observation at key structural milestones

Phase 6 — Closeout
- Special inspection final report submitted to AHJ
- EOR letter of structural compliance (where required by jurisdiction)
- As-built drawing reconciliation for any field modifications

Reference table or matrix

Structural Framing Systems: Key Comparison Matrix