1. Classification by Structural System
1.1 Moment-Resisting Frames
Moment-resisting frames use beam-to-column connections and member stiffness to resist bending moments and lateral forces.
Unlike a simple gravity frame, the connections in a moment-resisting system are designed to transfer significant moments between beams and columns. This can allow the frame itself to contribute to the building's lateral stability.
Moment-resisting frames can be used in a range of building types, particularly where architectural requirements or other constraints limit the use of diagonal bracing.
1.2 Braced Frames
Braced frames use diagonal structural members to provide lateral resistance.
Depending on the structural arrangement, braces can efficiently transfer horizontal forces to the foundations while reducing the amount of bending required in the primary frame.
Braced systems are commonly used in industrial and multi-story buildings, although the appropriate arrangement depends on building geometry, openings, architectural requirements, and the applicable design criteria.
1.3 Truss Systems
Steel trusses use interconnected members arranged in a triangulated configuration to carry loads primarily through axial forces.
Trusses can provide efficient solutions for relatively large spans and are commonly found in roofs, halls, industrial buildings, and other structures where a large unobstructed space is required.
The choice between a truss and a conventional beam or frame depends on factors such as span, structural depth, architectural requirements, fabrication, transportation, and erection.
1.4 Portal Frames
A portal frame is a specific framing arrangement commonly used for single-story buildings such as warehouses, workshops, and industrial facilities.
Portal frames typically rely on rigid or moment-resisting behavior at the beam-to-column connections to transfer loads and provide lateral stability.
They are particularly common in buildings with relatively large clear internal spaces. Their suitability depends on factors such as building width, eaves height, loads, spacing, wind conditions, and foundation requirements.
For a more detailed comparison of framing systems, see Portal Frame vs Truss System in Steel Structures.
2. Classification by Span and Bay Arrangement
2.1 Single-Span Buildings
A single-span building has one primary clear span between its main supports.
This arrangement can provide a relatively simple structural layout and is commonly used where the building width and internal space requirements can be satisfied without intermediate columns.
2.2 Multi-Span Buildings
Multi-span buildings use multiple structural bays across the building width or length.
Additional columns or frames divide the building into several spans, which can make it possible to cover wider buildings while balancing structural efficiency, material use, and interior space requirements.
Multi-span arrangements are common in industrial and commercial buildings where different functional areas need to be accommodated within one overall structure.
2.3 Long-Span Structures
Long-span structures are designed to create large unobstructed spaces with limited internal supports.
They may use portal frames, trusses, space frames, arches, or other structural systems depending on the required span and building form.
Large-span design places particular emphasis on factors such as deflection, stability, connection behavior, wind effects, and erection sequence.
Therefore, long-span is best understood as a description of the structural geometry and performance requirement rather than a single structural system.
3. Classification by Building Function
3.1 Industrial Buildings
Factories, workshops, and manufacturing facilities may require large clear spans, overhead cranes, equipment support, heavy-duty floors, or provisions for future expansion.
See Steel Structure Applications for a broader overview.
3.2 Warehouses and Distribution Centers
Warehouses generally prioritize efficient storage space, clear internal circulation, loading operations, and compatibility with racking systems.
The structural design may need to account for storage loads, large openings, handling equipment, and future changes in the building layout.
3.3 Agricultural Buildings
Agricultural structures include equipment storage buildings, farm workshops, livestock buildings, and agricultural storage facilities.
In these projects, durability and environmental exposure can be particularly important because moisture, condensation, chemicals, and other conditions may affect corrosion risk.
3.4 Commercial and Other Public Buildings
Steel can also be used for offices, retail buildings, hotels, exhibition halls, sports facilities, and other public or commercial buildings.
These applications may place greater emphasis on architectural integration, flexible floor layouts, large openings, fire protection, and long-span spaces.
The structural requirements vary considerably between building types, so the functional category alone does not determine the final structural system.
4. Classification by Construction Approach
4.1 Prefabricated Steel Construction
Many steel components can be fabricated in a controlled manufacturing environment before being transported to the construction site.
Fabrication may include cutting, drilling, welding, fitting, surface preparation, and coating.
This approach can reduce the amount of fabrication required on site and allow fabrication and foundation or site preparation work to proceed in parallel.
4.2 Modular Steel Construction
Modular construction takes prefabrication further by producing larger assemblies or building modules that can be transported and installed on site.
The feasibility of modular construction depends on transportation limits, module dimensions, lifting capacity, site access, connection details, and project requirements.
4.3 Pre-Engineered Building Systems
The term "pre-engineered building" is commonly used for standardized or systemized steel building solutions in which design, fabrication, and component selection are coordinated around a defined structural system.
These systems can provide efficient solutions for certain building types, particularly single-story industrial and commercial buildings.
However, pre-engineered does not mean that engineering is unnecessary. The system still needs to be designed and checked for the project's actual loads, dimensions, location, and applicable codes.
5. Materials and Connections: Important Design Characteristics
5.1 Structural Steel Grades
Different steel grades provide different combinations of strength, ductility, weldability, and other properties.
The appropriate grade depends on factors such as structural requirements, applicable standards, fabrication processes, environmental conditions, and project specifications.
For more information, see Structural Steel Grades for Buildings.
5.2 Bolted and Welded Connections
Steel structures commonly use bolted connections, welded connections, or combinations of both.
Connection selection affects load transfer, stiffness, ductility, fabrication, erection, inspection, and maintenance.
The appropriate connection method therefore depends on the structural design and construction requirements rather than representing a separate type of steel building.
See Bolted vs Welded Connections in Steel Buildings for a detailed comparison.
6. How These Classifications Work Together
The different classification methods should not be viewed as competing ways to label a building. They describe different aspects of the same structural project.
For example, a building could be described as:
| Classification |
Example |
| Building function |
Steel structure warehouse |
| Structural system |
Portal frame |
| Span arrangement |
Multi-bay |
| Construction approach |
Prefabricated steel construction |
| Connections |
Bolted and welded connections |
| Steel material |
Structural steel grade selected for the project |
Each description answers a different question.
The structural system explains how loads are resisted. The span arrangement describes the building geometry. The functional category explains how the space will be used. The construction approach describes how the structure will be fabricated and assembled.
Considering these characteristics together provides a much clearer description of the actual building than using a single classification alone.
7. Factors That Influence Structural System Selection
7.1 Structural Loads
The structure must be designed for the loads relevant to its location and use, including dead loads, live loads, wind loads, snow loads, seismic actions, equipment loads, and other project-specific actions.
See What Is Load Combination in Steel Structure Design? for a related explanation.
7.2 Span and Space Requirements
The required clear span, building width, column spacing, ceiling height, and internal layout can strongly influence the choice of structural system.
A portal frame may be suitable for one industrial building, while a truss or another long-span system may be more appropriate for a larger unobstructed space.
7.3 Construction Conditions
Transportation, site access, lifting equipment, fabrication capabilities, erection sequence, and connection methods can all affect the practicality of a structural solution.
A structurally efficient system is not necessarily the best choice if it is difficult or impractical to fabricate and erect at the project site.
7.4 Future Expansion
If future extensions or changes in building use are expected, these possibilities should be considered during the initial structural design.
The structural grid, foundations, connections, and reserve capacity may all need to account for potential future requirements.
