The structural research team at the Universitat Politècnica de Catalunya (UPC), Barcelona, Spain, has developed tests to determine the stresses in concrete beams that are used in construction.
The tests, that have taken the past two years to develop, focus on the use of externally reinforced carbon fiber laminate to reinforce the concrete beams.
The use of carbon fiber laminates (CFRP) has increased over the past several years. CFRP characteristically has its fibers running in one direction to provide a semi-rigid structure with high modulus when bonded with an epoxy adhesive.
The laboratory tests were undertaken to simulate varioustypes of failures that can commonly occur. These include:
- Removal of a concrete roof
- Removal of the end laminate interfacial
- Detachment of the laminate interfacial induced by the fracture
- Shear failure in concrete
The tests undertaken by the Laboratori per a la Innovació Tecnològica d'Estructures i Materials (LITEM) involved fitting the beams with 24strain gages of type 1-LY41-6/350. These were pasted in position using HBM adhesive X280. Strain gages were placed under the beam and along the CFRP strips with two at each side on position L/4 for linear displacement. In addition two laser sensors were placed – one on either side at the center of the beam – for triangulation displacement measurements.
The signals were captured using HBM’s MGCplus with three AP815i modules for the strain gages while an AP801 module was used for the laser sensors. Load and displacement signals were detected by a 250 kN actuator. HBM’s catman®APdata acquisition software was used to analyze the results.
Traditional beam theory was used to calculate the reinforced beam bending forces and these were subsequently compared with the data obtained from the tests. This enabled the general equation for doubly-reinforced concrete beams and beams reinforced with external laminates such as fiber-reinforced polymers to be modified to give more accurate estimations for deformationεdb (deformation blast-off).
Future tests may also utilize gages attached to the laminated embedded on the tension face of beams.