The completed office expansion – exterior view. One last service platform still in place at the outermost end.
Last year I presented the thoughts behind Hi-Cons office expansion in Hjallerup, and the first small steps in the actual building process. Hi-Con main office expansion. Now, finally, we are ready to move into the new offices and enjoy the light and spacious rooms of the floating modular CRC i2® building!
It has been an interesting process to produce the elements and erect the building – many processes have been tried for the first time, and we have been required to make constant adjustments and develop solutions as difficulties arose, in both design, production and installation.
The biggest obstacle has been the complexity of the elements themselves - especially the façade elements. Each façade element is comprised of a load carrying inner wall in light-colored CRC® i2, including integrated reinforced ribs in areas with increased internal loads, a middle layer of PIR insulation (fire improved version of Polyurethane foam) and a thin front plate of dark grey CRC i2® with a broken-stone imprint pattern. See the images below.
Completed facade element for the outermost cantilevered box module in the production hall.
The reason for the complexity was, that in order to clearly demonstrate the capacity of the CRC i2® structures, dimensions have been kept to an absolute minimum, based on iterative optimization of stresses, deflections and eigenfrequency using an advanced FEM model of the load carrying parts of the entire building:
FEM model with support conditions indicated by green arrows (top). Resulting stress distribution (bottom). The model is comprised of the load carrying inner walls of the modules and the columns, with the insulation, outer plates, windows, floor etc. added as distributed loads, together with the dimensioning live load combinations.
Consequently, very little space was left to arrange the reinforcement, and in general low tolerances were required in all aspects of the production process.
But the result is, that the load carrying facades have a thickness of only 230 mm with a U-value of 0,15 W/m²·K of the normal section and an average for the entire element of 0,2 W/m²·K when including all border effects of ribs, window frames etc. The corresponding thickness of a conventional element using mineral wool would be between 460 and 500 mm depending on the exact configuration – or double thickness. This means that an extra ~25 cm, corresponding to a total of 12.5 m² extra interior space (app. 10%) is available with the same exterior dimensions.
The insulation value can of course be optimized with slightly larger dimensions if so required – the roof and floor demonstrate this with an effective average U-value of 0.1 W/m²·K including the effect of ribs etc. for each 36.5 m² element.
Also, the minimal dimensions ensured that the weight of the modules was kept low enough to enable the building to “float” on the asymmetrically arranged inclined CRC i2® columns while exerting very limited forces on the existing office building – this was not designed to support significant extra transverse loads.
The minimal dimensions and small tolerances also made the erection process difficult, and required that everything was checked, double checked and triple checked in the design phase to make sure that the elements and connections actually could be assembled in the required order. In the first blogpost I showed an animated assembly sequence that was made as part of this control process.
But now finally the real time-lapse sequence can be shown:
As the video shows, we included a test loading of the outermost module that is cantilevered from the building – a maximum applied load of 22.6 tons corresponded to app. 1.2 × dimensioning load, which in Denmark is considered the required load for a full documentation testing. The test was made both to document and quality assure all connections, and, to measure the deflections for comparison to the calculated values of the full-building FEM model:
FEM simulation result of the deflection at full dimensioning load level – the expected short term deflection of the end of the cantilevered outer box module is app. 5 mm.
An actual deflection of 10 mm was registered, with an elastic recovery of 4 mm when the load was removed – very close to the expected 5 mm. The difference in initial deflection of 5 mm is attributed to compression of all the various connections in the building (almost 200 individual connection points ensure the elements work together in the intended way). The main reason that some movement in the connection points was possible is, that the connections are designed to allow both each individual module to be decoupled and moved separately, or to completely disassemble the modules into their original elements again, should it be desired to move the building or to reuse its components in another location or context. Consequently, some tolerances remained in the connections until full force was applied.
Interior view during the construction phase showing the ribs in roof and floor, cut-outs in the PIR insulation to make the connections accessible, and the load carrying beams of the internal cross walls across the aisle that are hidden in the roof and floor build-up of the final building.
After the erection of the elements was completed and all connections verified, craftsmen moved in to install windows, fire insulation on roof and floor, electricity, heating, ventilation units, etc. to complete the interior. The result is a light and open interior space with raw light-colored CRC i2® walls:
Interior view of the almost completed building – the separating glass walls and glass panel at the end of the aisle still needs to be installed. Upper left: Office cubicle from the aisle, upper right: View through the aisle, lower left: An internal joint between the two outermost box modules, lower right: View from a cubicle to the aisle towards the existing office building.
We are now finally moving in and look very much forward to experiencing our new CRC i2® offices in day-to-day work. It has been hard work and at times a serious challenge, but I think it has been worth the journey – from imagining the vision of the building, through innovating the solutions to realize it in cooperation with our advisors, suppliers and craftsmen, to now finally showing the impressive result to the world.
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Bendt Kjær Aarup Group Material Development Manager