Strain gauge measurements on steel structure
Tech Invent has conducted strain gauge measurements on the preloaded steel structure, Operaparken, for the steel construction company, HSM Industry. Tech Invent delivered both live-monitoring measurements during installation and post-processing of the measurement data for verification of specific construction elements.
The roofing of Operaparken is an impressive steel structure manufactured by HSM Industry. The roof is supported only a few places to gain a “hovering” effect on the building inspired by Steve Jobs’ glass building. The roof is manufactured by construction steel welded with a slight vertical upward pre-bend that enables the possibility of a downward preload. The preload is temporarily executed by hydraulic cylinders until permanent tension lamellas are mounted in the structure. The stiffness of the preloaded laminas make sure that the glass fronts will not become load carrying when excited by wind, attachments etc. The principle is similar to a preloaded bolt connection.
The strain gauges are mounted on the tension lamellas in the steel structure to ensure that the preloaded lamellas carry the intended load both at ultimate limit state and serviceability limit state.
Description of the measurement system
A system is designed with 22 strain gauge measurement points on selected tensional lamellas in the steel structure. The lamellas constructed by 6 mm Super duplex stainless steel. The strain gauges are mounted in a half bridge configuration as the principle directions of the lamellas are known. This way, the temperature dependent strains are reduced significantly in the signal while the load associated strains are amplified in the signal. The strain signals are continuously used for live force calculations making us able to monitor if the tension lamellas are approaching their ultimate limit state while the hydraulic cylinders are relaxed.
Our measuring amplifier can receive 40 signals which makes it possible to design a complex while agile test setup where the individual calibration settings are saved for designated channel and several signals can be monitored simultaneously.
The strain gauge measurements shows that some tension lamellas in the structure needs further preload to encounter the design loads. This is done to a high degree of precision as we live-monitor the lamellas during the tightening. Finally, the structure is approved by the engineers.