PSI - Issue 64

5

Author name / Structural Integrity Procedia 00 (2019) 000–000

Ravina Sriram et al. / Procedia Structural Integrity 64 (2024) 2051–2058

2055

4.1. Retrofitting with Fe-SMA bars The first case study focuses on an existing three-story building at Zurich Airport, erected in 1984, which is currently used as a mail sorting facility. A new X-ray machine has been installed on the 1 st floor, which is a typical flat slab supported by columns. Due to increased loads on the slab, there is a bending issue above the column G3 and the upper reinforcement in the y-direction above the column begins to yield. To retrofit the slab, 14 Fe-SMA bars ( Ø 12mm), each 2.5 meters long, were installed on both sides of the column and prestressed to a force of 35 kN. By prestressing the reinforcement above the column, the concrete is subjected to increased compression, which, in turn, also enhances the slab's shear resistance. The strengthening measures are illustrated in Figure 4. Before installation, the concrete surface was roughened. The Fe-SMA bars were laid out and anchored/embedded on both sides in Sika MonoTop 452 high-strength mortar. Once the mortar achieved a compressive strength of > 35 N/mm², they were heated with a gas burner to prestresses the bars (see Figure 5). Following this, the entire reinforcement was embedded in Sika MonoTop-452 mortar.

Table 1: Acting punching shear force and resistance before and after strengthening measures.

State of Column

Acting Punching Shear Force V d [kN]

Resistance of first concrete compression diagonal V Rd,cc0 [kN]

Resistance of concrete and steel components in the support area V Rd,cs0 [kN]

Resistance of concrete outside punching shear reinforcement V Rd,c1 [kN]

Compliance [-]

As-is (Evaluation)

2437 2502

2153 2776

1940 2711

2121 2731

0.80 1.09

Strengthened

Figure 4: Reinforcement details of Fe-SMA bars over the slab, layout (left) and cross-section (right)