Structural Systems and Industrial Applications

Introduction

Steel structures are not selected only because steel is strong. A structural system must also control deflection and vibration, resist wind and seismic actions, accommodate services and building use, permit economical fabrication and erection, and remain inspectable and maintainable throughout its life. The same steel material may therefore be arranged as a moment frame, braced frame, truss, portal frame, space structure, crane-supporting system, or long-span assembly depending on the required performance.

This chapter develops a comparative method for selecting these systems. The emphasis is on structural behaviour, load paths, preliminary sizing, construction, industrial applications, and the interaction between engineering decisions and architectural, operational, safety, and economic requirements. Final design must comply with the governing national standard, project specifications, geotechnical information, fire requirements, and a competent engineer’s review.

Learning Objectives

On completing this chapter, a student should be able to:

1. Explain the load path and principal behaviour of major steel structural systems.
2. Select moment frames, braced frames, trusses, portal frames, space structures, and long-span systems for appropriate applications.
3. Compare systems using strength, stiffness, robustness, economy, constructability, and adaptability.
4. Identify special requirements for industrial buildings and crane-supporting structures.
5. Carry out preliminary calculations for tributary load, axial force, bending, and deflection.
6. Evaluate a structural scheme at concept stage and communicate its advantages and limitations.

1. Structural-System Selection as an Engineering Decision

A structural system is a coordinated arrangement of members, joints, diaphragms, foundations, and secondary components that transfers actions to the ground. Selection begins with the building’s functional requirements rather than with a preferred member type.

Important questions include:

• What are the span, height, bay spacing, and floor-to-floor constraints?
• Are large column-free areas required?
• Will cranes, heavy equipment, impact, vibration, or thermal actions occur?
• Must the building accommodate future expansion or changing machinery?
• What are the wind, seismic, snow, fire, corrosion, and durability exposures?
• Is rapid erection more valuable than minimum material weight?
• Can the site accommodate temporary bracing, large lifts, and transportation of fabricated pieces?

A sound preliminary design establishes a clear load path:

cladding and equipment → purlins or secondary beams → primary beams, trusses, or frames → columns and bracing → foundations → ground.

Lateral loads require an additional path through roof and floor diaphragms, collectors, vertical bracing or rigid frames, and foundations. Discontinuities in this path—such as omitted bracing, weak connections, or unsupported transfer forces—are common causes of poor performance.

1.1 Evaluation criteria

The principal criteria can be organized as follows:

Material weight alone is an incomplete measure of economy. A lighter truss may require more fabrication, connections, lifting operations, and inspection than a heavier rolled beam. Whole-life cost and programme risk should be considered.

2. Principal Structural Systems

2.1 Moment-resisting frames

A moment frame resists gravity and lateral actions primarily through bending moments, shear forces, and axial forces in beams and columns. Beam-to-column joints are designed and detailed to transfer substantial moment; the frame therefore acts as a continuous mechanism.

Moment frames provide open façades and flexible planning because diagonal braces are not required in bays. They are useful in offices, commercial buildings, and structures where architectural openings or access routes conflict with bracing. Their disadvantages are relatively large member sizes, demanding connections, greater lateral drift, and sensitivity to second-order effects. Moment frames are often less economical than braced systems for tall or highly flexible buildings, although they can be advantageous where unobstructed space has high value.

For a simple beam under a uniformly distributed load, a useful preliminary relationship is:

where M_max is the maximum simply supported bending moment, w is the uniformly distributed load per unit length, and L is the span. This expression assumes a prismatic, simply supported beam, small deflection, linear elastic behaviour, and a load uniformly distributed over the span. It is not a substitute for analysis of a continuous or rigid frame.

For a simply supported beam under the same assumptions, the midspan deflection is:

where δ_max is deflection, E is Young’s modulus, and I is the second moment of area. Units must be consistent: if w is N/m, L is m, E is N/m², and I is m⁴, then deflection is in metres. The fourth-power dependence on span explains why stiffness often controls long beams before strength does.

In seismic design, moment frames may be proportioned as ductile systems with protected yielding zones and strong-column/weak-beam principles where required by the governing standard. Connections, continuity, panel zones, beam stability, and column bases are as important as member strength.

2.2 Braced frames

Braced frames resist lateral actions through axial forces in diagonal braces, columns, beams, and connections. Common forms include concentric bracing, eccentric bracing, inverted-V bracing, single diagonals, and buckling-restrained braces.

Bracing generally provides high lateral stiffness with relatively low steel weight. It is suitable for industrial buildings, warehouses, towers, and buildings where brace lines can be placed without interfering with doors, windows, or circulation. Conventional compression braces must be checked for buckling; tension-only rods require a stable load path in both wind directions and may need pretensioning or paired arrangements.

Eccentric braced frames deliberately place a short beam segment, or link, between brace intersections. The link dissipates energy through controlled shear or bending while the remaining frame members remain protected. This arrangement combines stiffness with ductility but requires careful detailing and inspection.

Bracing locations should be distributed so that torsion is controlled. A building with strong bracing on one side and little bracing on the other may twist under lateral load. Roof and floor diaphragms must transfer forces to the braced lines, and collectors must be designed where the load path changes direction.

2.3 Trusses

A truss is an assembly of straight members connected at nodes and arranged so that loads are transferred mainly through axial tension and compression. Ideal truss analysis assumes pin-jointed nodes, loads applied at nodes, straight prismatic members, and negligible bending in members. Real trusses develop secondary bending because of joint rigidity, member self-weight, eccentric connections, and loads applied between nodes.

The depth of a truss strongly influences efficiency. Increasing depth generally reduces chord forces for a given global bending moment, but increases façade height, bracing requirements, fabrication length, and architectural impact. Common forms include Pratt, Howe, Warren, bowstring, and vierendeel trusses. A vierendeel frame has rigid joints and open rectangular panels; it provides architectural flexibility but experiences significant bending and requires robust connections.

For a simply supported truss subjected to a global bending moment M, a preliminary estimate of chord force is:

where N_chord is the approximate force in one chord and h is the distance between chord centrelines. This is a conceptual estimate, not a complete member design. It neglects the distribution of force among panels, shear carried by web members, connection eccentricity, self-weight, and stability requirements.

Trusses are effective for roofs, pedestrian bridges, industrial sheds, stadiums, and transfer structures. They are less attractive where shallow depth, many service penetrations, or frequent changes in loading are required.

2.4 Portal frames

A portal frame is usually a two-dimensional rigid frame with columns and rafters connected by moment-resisting joints, often with haunches at the eaves. It is widely used for single-storey industrial, agricultural, and warehouse buildings.

Portal frames achieve economical clear spans through repeated braced bays. The rafters carry gravity actions through bending and axial compression, while the frame action resists transverse wind. Purlins, side rails, roof sheeting, and longitudinal bracing stabilize the frame and transfer longitudinal forces.

Haunches increase stiffness and resistance near the eaves, where bending moments are often high, while permitting a lighter uniform rafter elsewhere. Typical design considerations include frame sway, rafter lateral-torsional buckling, web bearing near supports, purlin restraint, connection rotation, foundation fixity, and erection stability.

Portal frames are particularly efficient when bay spacing, roof slope, loading, and geometry are repetitive. They are less suitable for irregular multi-storey layouts or buildings requiring numerous internal columns to be removed after construction.

2.5 Space structures

Space structures carry load in three dimensions. Examples include double-layer grids, space frames, geodesic domes, cable-supported grids, and three-dimensional trusses. Their depth and triangulation distribute loads among many members, allowing large column-free areas and architectural forms that would be inefficient as planar beams.

A space frame may be supported at discrete points, along a perimeter, or through a combination of supports. Support arrangement is critical: concentrated reactions can be large, and differential settlement can introduce secondary forces. The designer must consider member buckling, joint stiffness, geometric imperfections, progressive collapse, drainage, fire protection, and access for inspection.

Space structures can be prefabricated from repeated modules, reducing site work. However, the large number of nodes and members increases tolerance requirements and creates a substantial coordination task. Lightweight systems may also be vulnerable to vibration, wind uplift, and accidental damage.

2.6 Long-span solutions

Long spans are selected where columns obstruct use, such as airports, auditoria, sports arenas, exhibition halls, aircraft hangars, and industrial assembly spaces. Options include deep trusses, tied arches, arches, cable roofs, suspension systems, tensile membranes, folded plates, space frames, and composite or cellular girders.

The selection depends on span, rise or structural depth, roof weight, movement tolerance, erection method, architectural intent, and resistance to asymmetric loading. A cable or membrane system is efficient in tension but requires reliable anchorage and stabilization against wind. An arch is efficient in compression but generates horizontal thrust at its supports. A tied arch uses a tie to reduce or eliminate external horizontal thrust, transferring the force internally.

Long-span structures are often governed by serviceability and stability rather than material strength. Wind-induced oscillation, rainwater ponding, thermal movement, construction-stage instability, and fire-induced deformation require explicit assessment.

3. Industrial Buildings and Their Structural Coordination

An industrial building is an integrated system rather than a collection of frames. Its primary structure must coordinate with production lines, cranes, conveyors, tanks, pipe racks, ventilation, electrical systems, access platforms, loading areas, and fire protection.

3.1 Typical components

A steel industrial building may contain:

• primary portal frames or braced bays;
• roof trusses or space frames;
• purlins and side rails supporting cladding;
• longitudinal and transverse bracing;
• mezzanines and equipment platforms;
• crane runway beams and brackets;
• maintenance walkways, ladders, and stairs;
• expansion joints and independent blocks;
• foundations designed for vertical, horizontal, and overturning actions.

The designer should obtain equipment loads, operating temperatures, maintenance loads, impact factors, vibration limits, access requirements, and future machinery allowances early. A structure designed only for the initial static equipment weight may become unsafe when dynamic or accidental actions are introduced.

3.2 Stability and robustness

Industrial buildings commonly have large openings, interrupted cladding, flexible roofs, and localized heavy equipment. Bracing should be arranged to preserve stability if a door or service opening changes. Where practical, alternative load paths and compartmentalization can limit the consequences of local damage.

Fire engineering may require unprotected steel, intumescent coatings, board systems, concrete encasement, or active fire protection. The choice affects member sizes, connection details, inspection, and cost. Corrosive atmospheres—such as chemical plants, coastal sites, or water-treatment facilities—require a coating specification, drainage detailing, material compatibility, and a planned inspection regime.

4. Crane-Supporting Systems

Overhead travelling cranes impose actions that differ from ordinary building loads. Crane girders or runway beams receive vertical wheel loads, horizontal surge or acceleration forces, longitudinal braking forces, skewing forces, and sometimes impact effects. The crane supplier’s data should be used; nominal lifting capacity alone is insufficient.

A crane runway system typically includes crane rails, runway beams, brackets or columns, longitudinal ties, end stops, and supporting foundations. Alignment and stiffness are essential. Excessive differential deflection or misalignment can increase wheel loads, rail wear, noise, and crane maintenance.

For a simply supported runway beam under a single idealized point load P at midspan, the preliminary maximum bending moment is:

where L is the simply supported span. For two or more crane wheels, the true maximum moment depends on wheel spacing and load position; a moving-load or influence-line analysis is required. The simple equation is therefore suitable only for an initial estimate under the stated idealization.

Crane-supporting members require checks for:

• vertical bending and shear;
• lateral bending from surge and wheel flanges;
• torsion and distortion;
• local flange bending and web crippling;
• lateral-torsional buckling;
• fatigue caused by repeated crane cycles;
• weld and bolted-connection fatigue;
• rail attachment and tolerances;
• serviceability and operational alignment.

Fatigue is especially important because a stress range repeated many times can cause cracking even when the maximum stress is below yield. Weld geometry, stress concentrations, access for inspection, and a defined fatigue category must be addressed in accordance with the applicable standard.

5. Preliminary Analysis and Worked Examples

Example 1: Comparing a beam and a shallow truss

An interior roof span is 18 m. The service load on a simply supported member is 12 kN/m, including the tributary roof load and an allowance for self-weight. Compare the preliminary bending moment with the approximate chord force for a truss of 2.0 m depth.

For the beam:

M_max = wL²/8 = 12 × 18²/8 = 486 kN·m

For the truss, using the conceptual chord-force relationship:

N_chord ≈ M/h = 486/2.0 = 243 kN

The result suggests that the truss can replace a large bending action with axial chord forces, but it does not prove that the truss is economical. Web members, buckling restraint, joints, fabrication, depth, and erection must also be considered. If the truss depth were increased to 3.0 m, the approximate chord force would reduce to 162 kN, but the architectural and construction consequences could be unacceptable.

Example 2: Preliminary deflection check

A simply supported beam spans 8 m and carries a service load of 10 kN/m. Take E = 200 GPa and I = 8.0 × 10⁻⁴ m⁴. Estimate midspan deflection.

Convert the load: w = 10,000 N/m. Then:

δ_max = 5(10,000)(8⁴)/(384(200 × 10⁹)(8.0 × 10⁻⁴))

Since 8⁴ = 4096, the numerator is 204,800,000, and the denominator is 61,440,000,000. Therefore:

δ_max ≈ 0.00333 m = 3.33 mm

The numerical value must be compared with the project’s serviceability limit, which depends on cladding, finishes, drainage, occupancy, and the governing standard. The calculation assumes a uniform load, simple supports, elastic behaviour, constant stiffness, and no composite action.

6. Comparative Selection Framework

A practical concept-stage comparison can be recorded in a decision matrix. Scores should be justified rather than treated as universal rankings.

A useful selection sequence is:

1. Define geometry, use, actions, movement limits, and fire or durability exposure.
2. Establish possible load paths and locations of lateral-resisting systems.
3. Eliminate systems that conflict with access, services, clearance, or site constraints.
4. Estimate member depth, reactions, drift, deflection, and foundation implications.
5. Compare fabrication, transport, erection, temporary works, inspection, and maintenance.
6. Test abnormal, accidental, future, and construction-stage conditions.
7. Select a preferred concept and record assumptions for later verification.

7. Constructability, Digital Practice, and Sustainability

Design and construction should be considered together. Modular bay dimensions, repeated connection details, shop welding, bolted site splices, transport limits, lifting points, temporary bracing, and erection sequence can substantially reduce risk. A system that is theoretically efficient but difficult to erect safely may not be the best design.

Building information modelling can coordinate steelwork with mechanical, electrical, process, and architectural systems. Model-based checking can identify clashes, verify quantities, and support fabrication data. Digital tools do not replace engineering judgement: incorrect load assumptions or poorly controlled model revisions can produce highly precise errors.

Steel’s recyclability is an advantage, but sustainability depends on the whole life cycle. Efficient spans, reduced tonnage, reuse of existing members, bolted disassembly, durable coatings, reduced transport, and design for maintenance can improve environmental performance. Environmental product declarations and project carbon assessments may be used where reliable data are available.

Artificial intelligence may assist with option generation, clash detection, quantity estimation, and inspection-image classification. It should not independently approve structural safety. Training data, model limitations, traceability, cybersecurity, professional accountability, and independent verification remain essential.

8. Applied Case: Illustrative Manufacturing Hall

Background

A manufacturer requires a 60 m × 120 m production hall with a 20 m clear internal width, overhead cranes, large vehicle doors, and the possibility of adding a second production line. The site has moderate wind, a corrosive industrial atmosphere, and limited space for on-site fabrication.

Problem

The system must provide clear space, limit crane-induced vibration, permit future extension along the 120 m direction, and be erected rapidly without obstructing adjacent operations.

Analysis

A conventional multi-storey moment frame would provide flexibility but would introduce unnecessary complexity. A single 60 m beam would be deep and heavy. A portal frame with a 20 m transverse span and repeated longitudinal bays provides a familiar industrial solution, but crane runway forces require separate consideration. Braced bays can provide longitudinal stability, while transverse portal action resists wind and supports the roof.

The preliminary scheme uses repeated haunched portal frames at regular spacing, roof purlins, side rails, longitudinal roof and wall bracing, and crane runway beams supported on independent brackets or columns after checking compatibility of movements. Expansion joints divide the long building into manageable blocks. Crane supplier data are required before final runway design.

Approach and solution

The design team selects:

• transverse rigid portal frames for clear production bays;
• longitudinal braced bays located away from major doors;
• bolted site connections and shop-welded haunches;
• corrosion-protection systems appropriate to the atmosphere;
• removable cladding zones for future equipment access;
• foundations designed for crane longitudinal and transverse actions;
• a planned erection sequence with temporary stability bracing.

Alternative schemes—a deep roof truss and a space frame—are retained as benchmarks. The truss would reduce rafter bending but increase fabrication and lifting complexity. The space frame would distribute roof loads but provide little advantage for the repeated industrial geometry and would complicate crane clearance.

Outcome

The portal-and-bracing concept provides a balanced solution: clear space, repeated fabrication, manageable erection, and provision for extension. Its success depends on crane fatigue design, accurate runway alignment, corrosion maintenance, and preserving the identified braced bays during future alterations.

Learning points

1. The most economical primary frame may not be the best crane runway system.
2. Future expansion must be included in the initial stability and foundation concept.
3. Industrial loads are operational and dynamic, not merely static gravity loads.
4. Repetition can reduce cost, but only when connection and erection details are standardized.
5. A good concept records assumptions and identifies information still required from equipment suppliers.

9. Limitations, Governance, and Professional Responsibilities

Preliminary equations cannot replace a complete structural analysis. Actual design must consider load combinations, imperfections, frame interaction, buckling, connection behaviour, fatigue, seismic ductility, fire, accidental actions, foundation flexibility, and construction stages. Computer output should be checked against simplified calculations and engineering expectations.

Codes establish minimum requirements, but compliance is not identical to fitness for purpose. The engineer must communicate exclusions, design life, inspection requirements, tolerances, temporary conditions, and interfaces with other disciplines. Changes to equipment, openings, bracing, or crane capacity require formal review. Safety-critical decisions must be documented, independently checked where required, and approved by appropriately licensed professionals.

Chapter Summary

Structural-system selection is a multi-criteria engineering decision involving strength, stiffness, stability, robustness, economy, constructability, durability, fire performance, adaptability, and life-cycle impact. Moment frames provide open planning but rely on bending and often require substantial connections. Braced frames provide efficient lateral stiffness but can obstruct openings. Trusses transform global bending into axial chord and web forces and are effective for long spans when depth and fabrication are acceptable. Portal frames are highly effective for repetitive low-rise industrial buildings. Space structures distribute load in three dimensions and suit large column-free spaces, although their joints and tolerances are demanding. Long-span cable, arch, truss, and space systems must be assessed for movement, wind, erection, and stability as well as strength.

Industrial and crane-supporting buildings require close coordination with equipment suppliers, fatigue assessment, alignment control, impact and dynamic actions, corrosion protection, and future expansion planning. Preliminary calculations help compare concepts, but final design requires code-based analysis, connection design, stability checks, fire and durability provisions, and professional verification. The best structural solution is the one that provides a reliable load path and acceptable whole-life performance while remaining buildable and maintainable.

Key Terms

Structural system: An organized arrangement of members, joints, supports, and diaphragms that transfers actions to the ground.

Load path: The continuous route by which forces travel from their point of application to the foundations and ground.

Moment frame: A frame that resists lateral and gravity actions substantially through member bending and moment-resisting joints.

Braced frame: A frame using diagonal or other axial members to resist lateral actions.

Truss: A triangulated assembly intended to carry loads mainly through axial member forces.

Portal frame: A rigid, usually planar, frame commonly used for single-storey clear-span buildings.

Space frame: A three-dimensional framework that distributes loads among spatially arranged members.

Long-span structure: A structural system designed to bridge a large distance with few or no intermediate supports.

Diaphragm: A roof or floor component that transfers in-plane forces to vertical resisting elements.

Collector: A member or region that gathers and transfers diaphragm forces to a braced frame or shear-resisting element.

Haunch: A locally deepened portion of a rafter or beam, commonly used near a portal-frame eave.

Crane runway beam: A beam supporting rails and wheel loads for an overhead travelling crane.

Surge force: A horizontal force produced by crane acceleration, deceleration, or load movement across the runway.

Fatigue: Progressive cracking or damage caused by repeated stress cycles.

Lateral-torsional buckling: Instability involving simultaneous lateral displacement and twisting of a beam or compression flange.

Robustness: The ability of a structure to limit disproportionate consequences after local damage or abnormal action.

Constructability: The degree to which a design can be fabricated, transported, erected, inspected, and maintained safely and efficiently.

Serviceability: Performance under normal use, including deflection, drift, vibration, appearance, and operational alignment.

Life-cycle cost: The total cost of procurement, construction, operation, maintenance, alteration, and disposal or reuse.

Review Questions

Short Answer Questions

1. What is meant by a structural load path?
2. State two advantages and two limitations of braced frames.
3. Why are haunches used in portal frames?
4. Identify four actions that may affect a crane runway beam.
5. Why is material weight alone an incomplete measure of structural economy?

Long Answer Questions

1. Compare moment frames and braced frames for a medium-rise building with demanding architectural openings.
2. Explain the structural behaviour, advantages, and limitations of roof trusses.
3. Describe the principal design and construction issues in a space-frame roof.
4. Discuss how industrial equipment and future expansion influence structural-system selection.
5. Explain why serviceability, fatigue, and alignment are critical in crane-supporting systems.

Analytical / Application Questions

1. A 24 m simply supported roof member carries a service load of 9 kN/m. Estimate its maximum bending moment using M_max = wL²/8. Explain why the result cannot by itself determine whether a beam or truss should be selected.
2. A factory requires a clear 30 m span, repeated bays, overhead cranes, and large vehicle doors. Propose a structural concept and justify the positions of the primary frame, longitudinal bracing, and crane runway system.
3. A proposed space frame has low self-weight but many complex joints and concentrated support reactions. Evaluate the concept using strength, serviceability, construction, inspection, foundation, and life-cycle criteria.

Multiple Choice Questions with Answers

Question 1

Which structural system primarily resists lateral actions through axial forces in diagonal members?

A. Braced frame

B. Moment frame

C. Suspended ceiling

D. Simply supported slab

Correct Answer: A. Braced frame

Question 2

For a simply supported beam carrying a uniform load w over span L, the idealized maximum bending moment is:

A. wL²/8

B. wL/2

C. wL²/2

D. wL³/8

Correct Answer: A. wL²/8

Question 3

What is a principal advantage of a portal frame in a low-rise industrial building?

A. Repeated clear-span construction

B. Elimination of all lateral bracing

C. No need to design connections

D. Suitability only for multi-storey buildings

Correct Answer: A. Repeated clear-span construction

Question 4

In the approximate relation N_chord ≈ M/h, increasing truss depth h generally:

A. Reduces the estimated chord force

B. Increases the estimated chord force

C. Eliminates web-member forces

D. Makes the global moment zero

Correct Answer: A. Reduces the estimated chord force

Question 5

Which crane action is especially associated with repeated stress cycles and possible cracking?

A. Fatigue action

B. Thermal insulation

C. Permanent cladding weight only

D. Rainwater drainage

Correct Answer: A. Fatigue action

Question 6

Why are collectors used in diaphragm systems?

A. To gather and transfer in-plane forces

B. To provide architectural finishes

C. To prevent all member buckling

D. To replace foundations

Correct Answer: A. To gather and transfer in-plane forces

Question 7

Which system usually provides the greatest architectural freedom for unobstructed bays but may have relatively high drift?

A. Moment frame

B. Concentric braced frame

C. Simple pin-jointed truss only

D. Cable tie

Correct Answer: A. Moment frame

Question 8

A space structure differs from a planar truss because it:

A. Carries load through a three-dimensional arrangement

B. Can resist only tension

C. Requires no support reactions

D. Has no connection-design requirements

Correct Answer: A. Carries load through a three-dimensional arrangement

Question 9

For a simply supported beam with w = 10 kN/m and L = 8 m, the idealized maximum moment is:

A. 80 kN·m

B. 160 kN·m

C. 640 kN·m

D. 10 kN·m

Correct Answer: B. 160 kN·m

Question 10

Which factor is most directly associated with crane runway operational performance?

A. Alignment and differential deflection

B. Paint colour

C. Roof insulation thickness alone

D. Number of office partitions

Correct Answer: A. Alignment and differential deflection