Light Steel Frame and Reinforced Concrete
Steel and concrete are fundamental materials for the construction sector, but how do they compare when used in residential buildings?
The World Steel Association, Framecad and Saint-Gobain commissioned this independent comparative study of Light Steel Frame (LSF) and Reinforced Concrete (RC) in a residential building.
The University of Coimbra’s Institute for Sustainability and Innovation in Structural Engineering was assigned to provide unbiased information for use by the construction sector. This piece of research identified strong and weak aspects of various structural solutions that employ different materials within the scope of low-rise residential buildings.
The LSF building was made from cold roll-formed galvanised steel strip of less than 3mm thickness. Located in Luanda, Angola, the building has a footprint of 360m2, comprising four two-bedroom apartments spread over four floors. The results of the study are based solely on load-bearing members such as columns, beams, walls, floor systems, roof materials and foundations.
The statistics below are all in the context of comparison with an RC solution for the load-bearing components within an identical building structure.
For all buildings, the floors and foundations represent a significant part of their overall weight. The LSF building has a much lower weight per unit area which impacts directly on the foundations as lower loads are transmitted.
The LSF solution is 55% lighter than an RC equivalent, requiring -700 tonnes less materials. This difference is even more pronounced when constructing in areas with high seismic activity.
The percentage weight increase when accounting for potential earthquake activity in the design of a residential building is higher in the RC solution. This is due to reinforced concrete having a higher mass, greater rigidity and less capacity for energy absorption.
As a result, in areas of high seismic activity, the LSF solution is 60% lighter, requiring -1000 tonnes less materials.
Sustainability is becoming an increasingly important aspect of design considerations for construction projects. Here LSF solutions can offer a range of benefits when compared with RC alternatives.
As the LSF solution is lighter, less concrete is required for the foundations.
The LSF solution requires -60% less concrete or -800 tonnes less, which includes -55 tonnes less water and -240 tonnes less sand, as well as less cement and aggregate. Again, this is more pronounced when accounting for areas with high seismic activity, with the LSF solution here requiring -66% less concrete or -1000 tonnes less, which includes -70 tonnes less water and -320 tonnes less sand.
When considering all life cycle emissions, from extraction through to manufacture and construction, while adjusting for end of life, the LSF solution produces -26 tonnes less CO2, which is -10% less than the RC alternative.
Increased speed of construction has impacts across the entire project. LSF is faster due to lighter foundations and offsite prefabrication. The is also no need for time-consuming formworks or propping. As a result, LSF construction time is -23% less, or -90 days fewer.
Craning costs are directly proportional to the duration of construction which means that costs are -20% lower in the LSF solution.
Since LSF is lighter, lower material quantities are required which reduces the need for transport. Prefabricated LSF solutions are also modular and as a result are usually nestable, leading to more efficient transportation.
This means that, when compared with a reinforced concrete solution, a LSF residential building project requires -60 fewer trucks. Again, this is more pronounced in high seismic areas, resulting in -85 fewer trucks being needed.
Fire and acoustic compliance
In addition to its other benefits, up to 180mins fire protection can be achieved in a LSF solution through the use of specialist gypsum boards. Other solutions include sprayed plaster, while intumescent paints that activate when heated are also used to achieve fire protection on structural steel.
Superior acoustic solutions for walls, ceilings and floors can be achieved by combining LSF with high performance acoustic insulation and gypsum board. This can deliver on demanding performance requirements and provide high comfort for building occupants.
Light Steel Frame buildings perform well across three key sustainability criteria.
First, from an economic perspective, LSF offers the lightest solution, with significant costs savings from its foundations and high levels of off-site prefabrication that result in a shorter construction schedule. This means higher productivity rates and a more cost-effective product.
From a social perspective, the flexibility of dry construction methods offers demountability, re-adaptabilty and re-use, as well as increasing the safety of the workforce. In addition, the modularity and pre-fabrication of LSF enhances the development of technology and provides the opportunity for higher paying jobs. Offsite prefabrication also results in better quality control.
LSF’s environmental aspects, include steel being 100% recyclable, as well as its re-usability and adaptability. It also has lower life cycle emissions and lower waste due to reduced use of concrete and higher levels of prefabrication. Finally, LSF reduces demand for on-site resources and generates less waste.
This independent comparative study showcases the range of benefits LSF offers when deployed in low-rise residential buildings.