Study of a large slab - part 2
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Examination of a reinforced concrete slab-column structure, reinforced with EPSTAL steel, in the event of a progressive catastrophe caused by the destruction of an edge column.
Purpose of research
The aim of the conducted experimental research was to determine the behavior of the edge fragment of the plate-column structure made in the scale 1: 2 in the emergency condition, which was caused by the removal of the edge support, and to indicate the influence of the amount of mechanically and adhesively retained reinforcement on the value of the breaking load. Moreover, the influence of reinforcing steel reinforcement after plasticization on the load-bearing capacity of the entire structure was checked. The scope of the conducted research includes:
- conduct a detailed observation of the behavior of the edge part of the plate-column structure evenly loaded in the emergency condition, which was caused by the removal of the edge support;
- determine the impact of the number of mechanically tensioned lower reinforcement bars on the destruction of the edge fragment of the plate-and-column structure;
- determine what mechanism of system destruction will occur after removing the support.
Research model
The research model was made as a monolithic reinforced concrete slab with dimensions of 12.3 x 12.3 x 0.1 m with heads with dimensions of 0.5 x 0.5 x 0.2 m, which was supported on 25 prefabricated supports at the site of the heads.
Three fragments of the slab with axial dimensions of 6.0 x 3.0 m at the edge of the slab were considered - marked in the drawing as: Model 1, Model 2, Model 3. In each of the distinguished areas, an identical system of span reinforcement and over-support reinforcement was used . Particular models were research fields that differed in the way of connecting the bottom reinforcement:
- test field 1 - The continuous armor, in accordance with EC2, was made in the form of two bars with a diameter of 10 mm, which were placed in the axes of the columns. The remaining bottom reinforcement is made of 8 mm diameter rods, bonded stressed in accordance with EC2 guidelines.
- test field 2 - The continuous armor, in accordance with EC2, was made in the form of two bars with a diameter of 10 mm, which were placed in the axes of the columns. The remaining bottom reinforcement is made of 8 mm diameter rods, tension stressed according to EC2 guidelines. Additionally, the joints of the 8 mm diameter rods were reinforced with additional rods 8 mm in diameter and 2lb in length.
- test field 3 - The bottom reinforcement (bars of span reinforcement Φ8 and bars in the axis of columns Φ10), in accordance with the ACI 318 guidelines, was mechanically endured in a 1.5 m wide band. The remaining bottom reinforcement made of 8 mm diameter bars bonded in accordance with ACI guidelines .
Research program
Each part of the model was tested in two phases.
Phase one:
- loading the tested fragment of the slab with the gravitational load of the value adopted to determine the reinforcement,
- removal of the edge pole to trigger an emergency state of the system,
- displacement measurements and observation of the behavior of the tested fragment of the slab under the influence of the applied load
Phase two:
- change of the method of loading the tested fragment of the slab from gravity to hydraulic load,
- measurements of displacements and observation of the behavior of the tested fragment of the slab under increasing load, up to the value at which its destruction will occur.
Below is a video showing all stages of the Model 1 study.
Obtained results
Due to the lack of information on the behavior of the slab-and-column structure in an emergency resulting from the removal of the column located at the edge of the slab, it was important to conduct research in this regard. The conducted tests allowed to determine the load-bearing capacity of the sections of the plate-and-column structure after the loss of support due to the reinforcement used and the method of its anchoring. Research has shown that:
- the reinforcement made of B500SP EPSTAL steel, calculated according to the above-mentioned standards, made it possible to safely transfer the load with the value assumed in the calculations - without leading to a progressive catastrophe, and the damage to the slab was minor;
- the use of B500SP EPSTAL reinforcement with increased ductility allowed, even in an emergency, to transfer much greater loads acting on the slab in relation to the value of the load assumed during static and strength calculations - especially in the case when most of the lower reinforcement bars were mechanically pulled.
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