BACKGROUND

In 2023, the client commissioned me to prepare structural permitting plans, construction plans, and steel structural shop drawings for their new hall. The design included a two-story office and a high-ceilinged hall for storing heavy construction machinery. This version was approved, and  detailed designing began. Later a long-term tenant was secured who manufactures gas industry instruments. Due to the need for small quantities of various gases, many of which are flammable and explosive, fire protection design had to be incorporated into the planning process.

BUILDING DESCRIPTION

The hall’s structural system comprises planar steel frames with a single-span gable roof, no crane system, and cladding on all facades. The roof slope is 7 degrees. Interior height is 7.20 m, eave height is 8.20 m, and ridge height is 9.70 m. Longitudinally, the column spacing is 9×5.95 m; transversely, it spans 30.00 m. The office measures 5.95×25 m with a chamfered corner at 45 degrees. Floor heights are 3.00 m, and the parapet wall is 6.80 m high.

The hall’s primary structural elements are truss portal frames, comprising hot-rolled steel columns and planar trusses with a rising top chord and horizontal bottom chord. The frames have fixed supports. The frame corners have rigidly bolted connections. 

The office is a two-story structure with a flat slab roof. Its load-bearing system consists of columns with fixed supports connected to roof and floor beams with rigid bolted connections. 

FIRE PROTECTION REQUIREMENTS

The fire protection designer categorized the building into medium risk. Load-bearing structures, bracings, floor slabs, and stairs must meet a 30-minute fire resistance requirement, while the roof slab requires 15 minutes. Purlins, excluded from the primary bracing system, also need to meet the 15-minute requirement.

STRUCTURAL DESIGN WITH AXISVM X7

For modeling, I aimed to create a spatial model with realistic detail, incorporating both building parts, monolithic slabs, and thin-walled purlins. Simplified modeling was used only for seismic analysis.

During the design, precise load assumptions became critical, particularly due to fire protection requirements, as permanent loads lack reduction factors during fire.

The SWG enabled precise meteorological load assumptions, also accounting for snow drifts between building sections and on the office parapets. Only internal wind pressure on tall interior partitions required manual load case definitions.

The SD8 module expedited fire load definitions, automatically adapting to changing profiles during the design process. Normal temperature steel design was completed with SD1, and fire design with SD8.

With no tapered members, the program’s automatic buckling length values were mostly reliable, enabling faster design. The SC1 module proved effective for standard joint design, though some manual calculations were required. Base plate anchoring was analyzed using Fischer’s software.

The subsoil quality was average, letting us avoid deep foundations. Shallow pad footings were designed using RC4, while monolithic concrete slabs, stairs, and grade beams were designed using RC1 and RC2.

SPECIAL FIRE PROTECTION CONSIDERATIONS

My approach to fire design involves determining critical temperatures for various components and documenting them in plans and specifications. The fire-resistant product choice typically occurs post-design.

Fire-retardant coatings generally qualify from 350°C, necessitating that no element’s critical temperature falls below this threshold. Initially, round steel rod bracing was used for wall and roof planes. However, tenant function changes required replacing these with hollow steel sections and switching X-bracing to K-bracing.

Purlins were required to meet a 15-minute fire resistance. Thus, for fire design, they couldn’t be assumed to brace the trusses. This necessitated manual input for the horizontal buckling length of top chord members instead of relying on automatic values.

Purlins meeting the 15-minute requirement were certified by the manufacturer using a cable method, yielding favorable results. A substantial horizontal force (7.50 kN/m) was imposed on edge girders under fire conditions, dominating the girder’s and bracing’s design.

Fire checks on monolithic concrete structures were performed using tabulated methods, as the RC8 module was unavailable at the time.

SUMMARY

The structure was designed almost entirely using AXISVM, minimizing the need for multiple software tools, which improved efficiency and reduced error risk. No data transfers and change tracking is required this way. Despite tight deadlines and increased requirements, a cost-effective structure was achieved thanks to the software. Steel usage was 34 kg/m² for the hall and 58 kg/m² for the office (excluding purlins and lintels).

All construction and shop drawings were prepared in Tekla Structures 2017i. The steel structure’s calculated critical temperatures were included as unique parameters, enabling annotated assembly plans for ease of construction and inspection.