Metal structural work for the brick industry
The engineering of the steel structure behind a steel cover
The load-bearing structure of a steel roof is the key element for the safety and durability of any industrial building. Unlike concrete or wood solutions, steel provides consistent, predictable and constant behavior over time, as long as the design takes into account all structural and environmental factors. A well-designed metal roof must resist loads, absorb thermal expansion and resist corrosion, without losing stability or geometry.
Functions and requirements of steel roof support structure
An industrial steel roof must simultaneously meet static, functional and maintenance requirements. The design must integrate these three levels into one coherent model. Specifically:
- Static function: distribute loads (snow, wind, plants, maintenance) evenly without excessive deformation.
- Protective function: ensuring waterproofness, insulation and resistance to external agents.
- Management function: enable inspection, cleaning and maintenance without risk to operators.
The longevity of a load-bearing steel structure depends on the integration of these factors, not on the individual component. A well-designed system can last over fifty years without substantial intervention.
Load analysis and static behavior
The calculation of the load-bearing structure follows the principles of the Technical Standards for Construction (NTC 2018) andEurocode 3. Each roof is subject to permanent, variable and accidental loads. The main elements to consider are:
- Permanent loads: own weight of the structure, mantle and anchored systems (photovoltaics, conduits, lifelines).
- Accidental loads: snow, wind, inspection and maintenance loads.
- Thermal and rheological effects: expansion, shrinkage, and differential deformation.
The overall behavior of the roofing must ensure that deformations do not impair the functionality of the membrane or drainage systems. The allowable deflection of main beams is generally limited to L/250, with more restrictive local verifications at purlins and roof joints.
Structural configurations for a steel roof and selection criteria
Types of frames and trusses
The geometry of the supporting structure depends on span, loads and constraints. The most commonly used configurations include:
| Type | Maximum light | Key Features | Applications |
|---|---|---|---|
| Portal frame | 20-30 m | Simple, quick to assemble, inexpensive | Standard sheds, warehouses |
| Reticular truss | 25-40 m | Low weight, excellent load distribution | Light structures, sports buildings |
| Box beam | > 40 m | High torsional stiffness, consistent thicknesses | Large industrial roofing |
Bracing and overall stability
Steel braces, arranged in the shape of a St. Andrew’s cross or with round profiles, provide transverse and longitudinal stability. In integrated systems, the roofing membrane cooperates as a rigid diaphragm. In Mantiero’s designs for industrial load-bearing structures, structural verifications and design according to NTC standards take these interactions into account, ensuring a consistent response of the entire system.
Choice of materials and surface treatments
The material crucially affects the service life of the cover. S275 or S355 structural steel is the standard for main beams, while exposed or wet-zone components can be made of AISI 304 or 316 stainless steel. The environmental factor is decisive: a coastal area requires different materials and thicknesses of protection than a dry inland environment.
Surface treatment is an integral part of the design. A hot dip galvanizing provides mechanical and chemical protection, but must be complemented by painting or metallization if the environment is classified C4 or C5 according to ISO 12944. In many Mantiero realizations, combined zinc + epoxy + polyurethane cycles are applied with durability of more than 40 years.
| Environment | ISO Class | Recommended solution | Durability |
|---|---|---|---|
| Dry interior | C2 | Epoxy primer + acrylic enamel | 10-15 years |
| Urban environment | C3 | Hot dip galvanizing + polyurethane paint | 25-30 years old |
| Marine environment | C5-M | Metallization + polyurethane top coat | 40-50 years old |
Construction details and connections
The connections represent the most delicate points of the entire structure. They can be bolted, welded or mixed. The designer must define construction details so as to avoid stress concentrations and ensure proper water runoff.
Bolted connections are preferred in prefabricated structures and modular industrial halls: they allow quick assembly and partial replacement. Welded joints, which are stiffer, require magnetoscopic or radiographic inspections. In Mantiero’s designs, the combination of the two techniques makes it possible to optimize stiffness and maintainability.
Roofing and thermal behavior
Steel roofs are subject to significant temperature variations. Linear thermal expansion can reach 1 mm per meter length per 100 °C excursion. It is therefore essential to provide expansion joints and flexible connections between the structure and the mantle.
Sandwich panels with polyurethane or mineral wool insulation reduce transmittance and improve indoor comfort. A well-designed roof can achieve U values ≤ 0.30 W/m²K. The combination of insulation material and natural cavity ventilation ensures the absence of condensation and prolongs the life of galvanizing.
In the case of roofs with integrated photovoltaic systems, it is essential to verify the thermal compatibility between panel and structure. Mantiero structures for photovoltaic systems adopt fastening systems with compensated expansion that avoid localized stresses.
Maintenance and periodic checks
A well-designed steel roof is an investment that will stand the test of time only with proper maintenance. The control plan should include:
- Annual inspection of beams, bolts and drainage points;
- Cleaning of gutters and runoff channels at least twice a year;
- Triennial verification of the condition of protective coatings;
- Static control after exceptional events (high wind, heavy snow, earthquakes).
Preventive maintenance helps to avoid hidden degradation and ensure operational continuity. It is good practice to keep a documentary record of interventions and detected conditions.
Technical reference tables
| Parameter | Indicative value | Unit of measurement | Remarks |
|---|---|---|---|
| Steel elastic modulus | 210 000 | MPa | Constant across grades |
| Steel density | 7,85 | t/m³ | For calculation of own loads |
| Thermal expansion coefficient | 12×10-⁶ | 1/°C | Dilatation 1.2 mm/m for 100 °C |
| Yield Strength Limit S355 | 355 | MPa | Basis for static calculation |
Design verification checklist of a steel roof support structure
- Analysis of climatic and static loads completed according to NTC 2018;
- Choice of material consistent with ISO 12944 environmental class;
- Strain testing and global stability;
- Definition of drainage and slopes according to rainfall zone;
- Specifications of surface treatments and thickness controls;
- Preparation of expansion joints;
- Drafting the maintenance plan and inspection log.
Technical conclusion
A well-designed steel supporting structure is an investment in time. Every detail-from the profile to the galvanizing, from the bolt to the paint contributes to durability. Design should not be limited to static calculation, but include environmental, maintenance and construction aspects. In this way, the roof becomes a reliable system that can withstand stress and maintain performance for decades.
The difference between an aging cover and one that lasts is not in the materials, but in the method by which they are chosen and protected. It is a lesson that engineering teaches every day, and one that those who make corrosion-resistant steel structures know well: