4 Storey hybrid office building, consisting of a combination of heavy structural steel and LSF

  • Structure had to be installed over an existing single storey building
    • Existing structure must be re-used after construction of new building
    • Foundations of new structure had to be designed in such a way that it does not influence existing structure’s foundations
  • Client Scope/ Focus points
    • Design a cost-effective steel framed 4 storey building
    • Large open plan areas required for office space
    • Aesthetically pleasing structure to showcase the use of steel
    • Speed of construction
    • Limited site access

 Designing a cost-effective solution

To reduce the overall weight of the structure, the first 3 floors were designed from heavy structural steel elements. In order to reduce overall structural weight, the top (level 4) floor was designed and constructed from LSF.

By using welded beam technology, where webs and flanges are joined together with a sub arch weld to only one side of the web and flange, we were able to design and make up our own sections. Overall dimensions of columns were kept the same, but flange and web thicknesses were reduced as overall structural loads reduced from ground floor to higher levels, as indicated on drawings.

Creating large open plan floor areas

Large open floor spaces were created by using composite action between welded beams and a 170mm thick concrete floor. The depth of the main floor beams was determined by deflection limits on the floors, rather than overall moment capacity of the beams. Again, flange and web thicknesses on the steel beams varied, depending on the moments that had to be resisted. Shear connection between steel beams and concrete floor was achieved by using Hilti Shear studs that were attached through the Bondek system into the top flanges of the steel beams.

Moment fixity was used between the columns and main floor beam connections. This ensured overall structural stability in one direction. In the other direction, vertical cross bracing was introduced

Using the above design enabled us to achieve clear spans of 14m on the floor system

Aesthetically pleasing structure

It was important to create more than just a square box that is functional, but not nice to look at. With this in mind, a staircase was designed that is supported by 2 large centre columns. Landing areas and as well as stringers were supported by small beams cantilevering from centre columns

Speed of construction

Using a steel framed building enabled erection of the heavy steel as well as placement of permanent shuttering and casting of concrete slabs in 4 weeks. Using LSF for the construction further reduced the overall construction time drastically.

Limited site access

The new office block had to be constructed between existing buildings, with a production plant on one side that must always remain operational.

Due to limited site access and the fact that the new building was almost surrounded by other structures it was not possible to use big mobile cranes on site. All these factors had to be considered when element lengths and splice positions were determined.

Conclusion

Concrete construction in Africa is normally quite expensive. By thinking outside the box and utilising different steel fabrication/ construction technologies, we were able to design, deliver and erect a cost effective and functional structure to our client. This project again showcase the advantages of steel construction and its ever-growing appeal in the office and residential space.

STRUCTURAL STEELWORK
Completion date of steelwork July 2018
Completion date of full project Dec 2018
Tons of structural steel used 28t
Structural profiles used Welded beams/ Plate girders
SA content – if this is an export project Structural steel – 100% SA content
LSFB /  LIGHT STEEL FRAME BUILDING WORK
Completion date of LSFB work Dec 2018
Completion date of full project Dec 2018
Span of trusses and Kg/m2 (if applicable) 14m
Profiles used   

Bluescope Truecore material. 0.8mm G550 – Supplied by Raincoat Roofing in Accra, Ghana

Type of cladding Combination of Standing seam roof sheeting and fibre cement wall cladding
PROJECT TEAM COMPANY
Nominator Clotan Building Systems
Client/ Developer Raincoat Roofing Systems Ltd Ghana 
Architect David Bass Architects
Structural Engineer Clotan Building Systems 
Engineer Clotan Building Systems 
Structural Detailer Steelinx Cape Town 
Quantity Surveyor Clotan Building Systems 
Project Manager Clotan Building Systems