More safety in buildings: Experimental stress analysis of a passive reinforcement anchorage
An important aspect when designing concrete structures is the precise measurement of anchorage lengths, particularly when
they are positioned in corbels, cornices or load-bearing areas. The connection conditions are significantly improved by strong
cross-compression that runs vertically to the reinforcement bar. These radial compressions are created by concentrated loads
and reaction forces.
To investigate the anchorage node system, an experimental program was developed to enable engineers to specify the lengths for the reinforcement anchorages. The test analyzes the connection reactions, based on Compression-Compression-Tension (C-C-T) nodes.
The test
The test specimen consists of two half concrete blocks with rectangular cross-sections: Each block is 15 cm wide, 24 cm high and of variable length with a reinforcement bar in the lower section. The reinforcement bar is anchored with a screw connection in which a force transducer is integrated. A force of 1,000 kN is applied with the help of a hydraulic cylinder.
A Pentium III PC was used to automatically record the measured values in real time, together with an amplifier for data acquisition, administrated by software developed by the University.
The following are measured:
- The force at both ends of the reinforcement bar with two annular force transducers C6A/200 kN from HBM
- The force in the sub-structures with the HBM force transducer C2/100kN and three other force transducers
- The longitudinal strains in the reinforcement bar using HBM strain gage LY41-3/120, which are installed centrally in the test specimen and diametrically opposed in the reinforcement bar
- The longitudinal strains in the concrete with the aid of the HBM strain gages LY42-50/120. Three strain gages are positioned as rosettes in each block, two additional strain gages are located underneath the test specimens
- Displacement with four displacement transducers on the rear and front of the concrete blocks
In earlier tests a single longitudinal crack developed that split the test specimen vertically into two parts. This crack is due to annular tensile loading generated in the area around the reinforcement bar. The crack starts in the connection area and propagates longitudinally. Both strain gages were installed so that the exact moment of crack formation could be determined. First results show that the crack occurs just before the reinforcement bar fails. It was therefore decided not to insert further rods (brackets) in the prototype to avoid additional limiting effects.
Conclusion
A test layout was designed to enable the analysis of the connection behavior in C-C-T joints. The main advantages of this test in comparison to earlier versions where lateral pressure was applied is that here the lateral pressure acts proportionally to the tensile force of the reinforcement bar. This means that a specific inclination angle of the bar is constantly maintained as is the case when anchoring the main reinforcement bar in areas with cornices or anchorages in corbels.
In the test, the forces transmitted along the connection length in the node were measured with high accuracy so that it was possible to determine the precise length of the reinforcement bar and its anchorages.
