A luxurious residential building in Metro Manila is being built with 700 tonnes of HISTAR® 460 sections produced by ArcelorMittal Europe – Long Products’ mill in Differdange. Called the Imperium, this building is not only earthquake resistant but will contain everything you could dream of:  pool, fitness facility, recreation room, mini theater…

HISTAR®: Smaller, Faster, Lighter

Manila is located in one of the most severe seismic zones on the globe, and steel - especially HISTAR^® steel - is an increasingly chosen answer for adding building stiffness and ductility while keeping column sizes reasonable. Where space optimisation and speed of construction are key, HISTAR^® steel can allow for smaller and lighter pieces over conventional steel or concrete-only solutions.

The American structural engineering firm of Magnusson Klemencic Associates (MKA) from Seattle conceived the lateral-force resisting structure of the Imperium using a methodology called “Performance-Based Seismic Design” (PBSD).  Don Davies, President of MKA, explains:  “By using PBSD and nonlinear modeling techniques, we are able to better simulate the behavior of a structure under strong seismic ground motions or strong winds. This allows us to better predict how a building will perform and propose solutions that put materials where they are more efficient for their intended purpose.”

The lateral force-resisting system for the Imperium is a central concrete core with outrigger* bracing to perimeter columns for increased tower stiffness (Picture 2). HISTAR^® steel rolled shapes are utilised in the composite outrigger columns and result in increased column strength and stiffness in both tension and compression. The use of embedded HISTAR^® steel allowed the column sizes to be reduced by as much as 50% compared to the initially considered all-concrete columns for the project (Picture 3). This column size reduction increased the floor efficiency ratios and useable square footage of the units, offsetting other first costs and leading to true value-optimised design for the owner.

Another key factor for buildings located in highly seismic zones is ensuring strong column–weak beam behavior and the ability to dissipate energy absorbed from an earthquake in a ductile and predictable way.  MKA engineers specified the use of Buckling Restrained Braces (BRB) as the outrigger bracing elements connecting the core to the perimeter outrigger columns.  BRBs are like reliable giant fuses that are able to absorb a huge amount of energy during large earthquakes while protecting other structural elements in the tower. These BRBs engage through connection plates directly to the HISTAR^® steel shapes within the perimeter columns, providing for a robust and efficient connection.

King of the Block

The Imperium is a 63-storey residential high-rise building designed by the global architecture firm CallisonRTKL. It features an architectural design with vertical lines and a circular form recognisable from afar. The Imperium is shifted forward with angled windows that ensure unobstructed views of the horizon and the nearby Capitol Commons Park. This appearance emphasises the building’s majestic positioning as "King" of the block, hence its Imperial name.

Expected to be completed by 2018, the Imperium will soon become a new landmark in Capital Commons, the new dream city in Metro Manila.

 
*Outrigger systems are structures designed to improve a building’s stability and strength by connecting the building core or spine to distant columns, much in the way an outrigger can prevent a canoe from overturning. (Source CTBUH)

Text: ArcelorMittal Europe Communication

Pictures:
1. ©CallisonRTKL, Design Consultant for the Project
2.+3. ©Courtesy of Magnusson Klemencic Associates

The Chinese company Broad Sustainable Buildings BSB is revolutionising the construction of high-rise buildings by using a modular construction technique with steel. For the construction of the 57-storey Mini Sky City in a record-breaking 19 days, ArcelorMittal supplied 10,345 tonnes of rolled HISTAR® steel sections.

Broad Sustainable Building (BSB) has been in the headlines around the world for constructing  a tower in the Chinese city of Changsha in less than 3 weeks, at the equivalent rate of three storeys per day. For its structure, 10,345 tonnes of HISTAR® sections were used, produced at ArcelorMittal Europe’s long products plant in Differdange, Luxembourg.

ArcelorMittal was involved in the project providing the best-suited steels for the structure and counselling Broad Sustainable Building to use rolled sections instead of built-up sections in order to speed up the fabrication of the individual columns, the so called “steel trees”. The use of innovative, high resistance HISTAR® steels contributed to the speedy fabrication of the vast amount of steel "trees" required to construct the building’s core.

The skyscraper is built with 90-percent, factory-produced, LEGO-like blocks, using a modular construction technique which won BSB a CTBUH Innovation Award in 2013.

This modular technique not only contributes to the speed of construction and its cost-efficiency, the structures have also proved structurally safe in earthquake testing and are highly energy efficient. According to BSB, the quadruple-paned glass façade together with 20 cm wall insulation and exterior sun shading make the buildings up to 5 times more energy efficient than conventional buildings of this type.

On 80,000 m2 the high rise building Mini Sky City will provide 800 apartments and office space for 4,000 people.

Broad Sustainable Building realized their first public prototype in 2010, a six-storey building erected in a single day for the Shanghai Expo. More than 30 buildings have been completed since then, among them a 15-storey hotel in six days and a 30-storey hotel in 15 days.

HISTAR® steels

HISTAR® steels are quenched and self-tempered (QST) steels with market-leading weldability and ductility. Supplied in several different grades, these ArcelorMittal steels have been used in skyscrapers worldwide, including the Freedom Tower in New York and the World Financial Center in Shanghai.

“Time is money and the modular construction is going to change the way small and tall buildings are constructed all over the world”, said Jacques Braun, a general manager at ArcelorMittal. “The combination of recyclable high-strength steel and rolled sections in HISTAR® is ideal for achieving the fastest, safest and most economical structures”.

The aspect of sustainability is playing an increasingly important role in building. However, this concept is not just restricted to ecological issues but also comprises economic and socio-cultural aspects. Only structures which fulfill all this criteria are permanently successful and therefore sustainable.

In this instance, constructional steelwork certainly has an advantage over other constructive forms thanks to structural steel which spares resources when manufactured and is infinitely reusable. Moreover, the increasing usage of high strength steels enables the possibility to further optimise sustainability of the steel or composite construction.

Modern steels such as Histar® 460, for example, demonstrate an outstanding weldability thanks to thermomechanical rolling and subsequent QST treatment in addition to high strength owing to carbon equivalent.

Principally, the use of high strength steels is worthwhile if tension problems are decisive when measuring structural components. This is often the case with compound girders, comprehensive roof supporting frameworks, trusses or heavily burdened supports. The somewhat higher price per tonne is by far and away exceeded through savings on material, processing, transport and assembly.

Histar® for Car Park Ceiling Girders

In the meantime, one sector in which high-strength steels have been enforced is car park ceiling girders. A span of approx.16m is usually required. An example can be seen in Table 1. With the use of Histar 460 the assessment usually results in an IPE 500 profile as opposed to an IPE 600 when using an S235JR+M. In this way, the component weight can be reduced by 24%. This leads to a cost saving of 17% for the pre-finished structural component.

Apart from the considerable economic advantage through use of the high-strength steels, a contribution to environmental sustainability is made at the same time.

Quintessentially, this is calculated for a car park with a capacity for 1000 vehicles. 250 ceiling girders are used in such a building. If trusses are used according to variant 2, a total of 127 tonnes of steel will be saved. Consequently, in addition to the lower emissions in the manufacturing process, seven journeys to the construction site by lorry can be spared for the ceiling girders alone.

Along with this, there are still savings through shorter supports, shorter lift shafts and stairwells, more favourable arrangements for ramps and a reduced façade area. Moreover, the reduced headroom leads to a lower overall height of the building – for example, a six-storey car park can be built 60 cm smaller.

Reducing Surfaces & Costs

High strength steels also have great advantages when used in industrial construction and multi-storey buildings. Reduced dimensions of roofs or roof girders, for example, lead to decreased building heights.

For this reason, the exterior surface area of the building can be reduced. Apart from saving on construction costs for wall and façade areas, one can also save on regular costs for heating and air-conditioning respectively.

Finally it can be determined that the use of high strength steels in the building industry is generally recommended for constructions in which use of tension is relevant to building specifications. With the use of Histar® 460 as opposed to the S235JR+M, approximately 25% of component weights and approximately 15 – 20% of component costs are saved in everyday applications.

In an extreme case – e.g. with comprehensive timber work construction – saving may even amount to 50%. Apart from economic advantages, a contribution to environmental sustainability is also made. In order to fully benefit from the advantages described, it is important that high strength steels are already included early on in the planning phases for the components in question.