PSI - Issue 84

Ahmed Amir Khalil et al. / Procedia Structural Integrity 84 (2026) 1031–1038

1035

Special detail is designed at columns with added steel plates, K-12c, K-15d and J-15d. Here scarfing of a small thickness of the column’s flanges and additional strengthening with additional steel plates is necessary to install shaped charges and guarantee a certain margin of safety, for details see Analysis results. 3.2. Reinforced concrete stack An overview of the 3D AEM model of the reinforced concrete stack is shown in Figure 2. The reinforced concrete outer shell is represented with the effective geometry reducing the thickness through the height and implementing all the openings. Even the FRP internal liners are explicitly modeled together with the supporting steel platforms. Diffused reinforcements and trimmer rebars are implemented in the model with the effective position, length and diameter. The demolition scenario provides the weakening of the outer reinforced concrete shell through removal of specific portion of concrete towards the fall direction. Then a saw cut was provided flush to the ground in the opposite direction, to minimize the resistance to the rotation for a total length of about 36 m along the stack circumference. The collapse is triggered by charges located in the outer shell in the direction of failure. The blast area presents a height of 7 m and a development along the circumference for about 55% of the length. To facilitate the collapse of the structure, on top of the blast area, the outer shell is further weakened with five vertical lines of explosive intended to remove concrete only. This demolition plan is optimized thanks to the simulation results, in fact initially the 65% of the outer shell was expected to be blasted, furthermore additional reinforcement of the construction opening at the backside with five steel props installed (steel columns W14x257 imperial size – H beam 40 cm x 40 cm) is provided to reduce the risk of premature failure. Figure 5 shows an overview of the demolition scenario implemented. As for the boiler unit, the demolition scenario is implemented by stages. Initially the portions of concrete shell are removed, then the saw cut is implemented and finally the blasted parts are removed to initiate the collapse. The modelling of the weakening and the explosion permit evaluating the safety of the different cutting stages, analyzing the load redistribution in the new configuration.

a

b

Outer shell weakening

6 m

4.5m

3m

Blast area

7m

Fig.5 Demolition scenario implemented in the stack model (a) Plan view, (b) elevation view looking to the blast area

4. Analysis results 4.1. Boiler unit

In the ELS software analysis, stresses and displacements are monitored throughout the cutting stages. Results indicate a reduced safety margin, with vertical stresses reaching approximately 190 MPa—close to the 250 MPa yield