Dr. Kazuaki Suzuki, Chief Manager, Construction Products Development Division at Nippon Steel, on continuing to create sustainable buildings using steel
As part of a series of Q&As, constructsteel is interviewing experts within the construction sector on aspects of steel’s performance and sustainability in the built environment.
Japan is one of the most earthquake-prone countries in the world. Having experienced the Great Hanshin-Awaji Earthquake in 1995 and the Great East Japan Earthquake in 2011, we have been promoting the construction of buildings that are resistant to earthquakes and tsunamis. We believe that we are working towards a sustainable society by constructing buildings that are resistant to earthquakes and tsunamis and, even if destroyed, can be easily repaired and continued to be used after the disaster. In addition, the recent climate change has led to an increase in the number of disasters on a scale larger than previously anticipated, such as giant typhoons, torrential rains, river insurgencies, and landslides. The demand for disaster-resistant buildings is continuously increasing amid efforts to make Japan’s social infrastructure sustainable.
We, steel manufacturers, have been striving to realise a sustainable society (infrastructure) by developing and providing high-performance steel materials for disaster-resistant, steel structural buildings, as well as design and construction technologies for utilising such materials.
To improve earthquake resistance, we have developed steel materials for earthquake-resistant building structures and standardised to JIS, including requirements to set upper and lower limits for strength specifications and ensure those yield ratios do not exceed 80% to ensure high plastic deformation capacity and energy absorption performance. We have often seen damage sustained in major earthquakes cause rupture at welded joints at the ends of steel beams, leaving the buildings unusable. Therefore, we have created and issued guidelines that clearly define the required performance of welds and steel materials for column-beam joints. Our newly generated idea suggests preventing damage to columns and beams by incorporating energy-absorbing dampers into the building frames. The steel material for dampers (low-yield-point strength steel) developed for this purpose has high fatigue strength and seismic energy absorption performance and helps reduce damage to buildings. In this way, various efforts have been made to ensure the seismic performance, quality, and safety of steel structures.
Japanese steel-framed buildings are not entirely made of steel but often have composite structures that combine concrete and steel. For example, most columns in Japanese skyscrapers are CFT columns. CFT columns are constructed by pouring concrete into circular or square steel tubes to form columns. By combining the strengths of concrete and steel, which are resistant to compression and tension, respectively, the columns achieve high bearing capacity and deformation performance with small cross-sectional areas, resulting in a large living space. In addition to high-strength, thick-walled, large-section steel tubes for CFT columns, we also provide high-strength, high-toughness steel for welded box section columns, which are widely used in Japan, as well as steel for electro-slag welding with high heat input. Used in CFT columns, these high-strength steels can reduce the cross-sectional size and steel weight of the columns, thereby helping to reduce CO2 emissions.
Used for flooring structures, composite floor beams combine concrete flooring and steel beams. This method is widely used worldwide, although the design approach differs slightly depending on the environment and design requirements of each country. Therefore, it is necessary to review existing design standards and technologies and develop new technologies to maximise the performance of composite floor beams. The year before last, we began providing rolled wide flange beams with a height of 1200 mm. This product helps streamline the production of built-up H-section beams, which are conventionally assembled by welding. The rolled wide flange beams can be used along with the technology that utilises the combined effect with concrete floor slabs to increase the buckling resistance of steel beams, helping to reduce steel beam weight and CO 2 emissions.
The development of composite structures combining steel and concrete, which maximise the performance of the materials and create a synergistic effect, makes it possible to achieve a rational structure that fully utilises resources. This mechanism applies not only to steel and concrete but also to steel and timber. Aiming to optimise and maximise structural efficiency by combining different materials will help reduce the materials used and achieve sustainability. We believe that aiming to optimise structures by utilising these materials is one way to reduce CO2 emissions by driving sustainability.
Nippon Steel Corporation