PSI - Issue 64

Ravina Sriram et al. / Procedia Structural Integrity 64 (2024) 2051–2058 R. Sriram/ Structural Integrity Procedia 00 (2019) 000–000

2056

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Figure 5: Activation of Fe-SMA bars at their free length with a blowtorch, temperature monitoring with an IR-thermometer.

4.2. Retrofitting with Fe-SMA strips The second case study focuses on the reinforcement of an underground parking garage erected in 1974. Assessment of the structure showed that both the punching strength and the flexural strength of the flat slab do not meet today’s required safety standards. To increase the shear strength of the slab “mushrooms” were built around the column underneath the slab. However, at one column the slab was still too weak in shear strength outside the “mushroom”. To this end, 3 Fe-SMA strips of 120 mm in width and 1.5 mm in thickness were added to both sides of the column and then prestressed to 54 kN. Thus, prestressing the slab in the sagging area with Fe-SMA strips lead to additional capacity of the slab, increasing its punching strength from 98% to 100% of the required value. Acting punching shear forces and resistances before and after strengthening measures are provided in Table 1. Drawings of the strengthening measures are shown in Figure 6, and photos from the construction site are provided in Figure 7.

Table 2: 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)

2040 2081

1182 2071

1517 2417

1172 2041

0.57 0.98

Column with “mushroom”

“Mushroom” + Fe-SMA strips

2081

2120

2448

2087

1.00