Oct 12  |  2015

When the Kungsholms Gate skyscraper in Stockholm was to be constructed it was required to withstand terror attacks. For Kurt Johansson of SCF Concrete AB this gave the design work in FEM-Design another dimension, to take into account the forces from an explosion.

The outrage in the USA on September 11 2001 released a shock wave around the world. Fear of being affected by similar attacks spread and Sweden was no exception. Even if it seemed unthinkable that something like that could happen here. As a result  the risk of terrorist attack is beginning to be considered for new buildings being designed in the future. One much discussed example is Kungsholms Gate in Stockholm.

”It is a completely unique project” says Kurt Johansson who is chief designer at SCF Concrete AB who carried out detailed calculations on the project.

The Kungsholms Gate development consists of two twenty storey towers with lower buildings in between; primarly intended as residential apartments. Between the towers 35 meters away is Essinge Highway. The risk of someone detonating a bomb containing two tonnes TNT on the road had to be taken into account since the massive building envelopes would have to withstand the full force of the powerful explosion. Furthermore the designers also had to add the loading to their calculations to resist terrorist attacks.

To get an idea of how these buildings behave under such large actions, Kurt carried out stabilty calculations with the help of FEM-Design.

”I calculated the effects of the imposed forces and the deformations on the frame and each element of the towers”.
Compared to the usual forces such as wind loads and eccentricities at the base, explosive forces played a majorpart in the calculations. The Underground runs beneath the east tower which means that Kurt even had to account for the vibrations in the ground.

”We set the requirement that the buildings should withstand an explosion from through traffic on the highway”.
The different forces meant that the calculations became very complicated. Kurt decided that it would not be possible to analyse the building as a whole. Each storey was different because they had separate plan layouts. It was therefore not possible to do angeneral analysis. Instead Kurt had to do the calculation floor by floor to find the true data and to get a realistic picture of how the building would deflect. Overall the structural design of the towers was an exhaustive exercise with a large number of parameters.

”Given that there was so much data for each floor, FEM-Design did the calculations satisfactorily and produced user friendly results”.

Kurt and his colleagues had to study the results carefully on this very complex project.
”We sat for many hours and analysed the information. It was important to be able to verify that the values were correct. Subsequently the data could be sent to the designers to detail the different elements.
The structural elements were dimensioned with seven inch walls reinforced with large quantities of reinforcement to withstand apossible explosion. In addition high grade concrete was used and the appropriate material properties were used into the design.

The massive structure meant that the building became substantial and very heavy. This had the advantage that it at the same time became more stable and less affected by explosions. Why did you chose to do all the calculations in FEM-Design? ”I have worked for a long time in 2D with programs from StruSoft and come to trust them” responds Kurt. ”When we needed a FE program it was natural for us to invest in their products for analysis”.

SCF Concrete AB were involved in this project in a number of ways; from calculation and analysis of data to designing the different elements and producing them. They also produced the facade which was made of polished marble. Subsequentlythe components were delivered to the site in Stockholm for assembly.

Love Janson