Punching Behavior of RC Slabs Retrofitted with FRP Sheets
Mohamed Sahab Mohamed Mohamed Seliem;
Abstract
Flat slabs of existing structures may require strengthening due to a variety of reasons: to accommodate the increase in acting loads as a result of changing building usage; improve the performance of already existing concrete that did not satisfy the required design recommendations; and/or to fortify void-cut areas within the column vicinity. The punching shear capacity – at the slab-column connection of flat slabs whether in original form or strengthened – serves as a governing factor to the overall capacity of the existing element. Nonetheless, the performance of strengthened flat slab-column connections, using the various available techniques, demands further observation in terms of slab ultimate capacity, stiffness and ductility.
In this respect, an experimental program has been conducted where the effectiveness of using carbon fiber reinforced polymer (CFRP) sheets in punching shear strengthening of slab-column connections has been examined. The program consists of a total of six square slabs with overall dimensions and thickness of 1800x1800x150 mm, respectively; loaded concentrically onto a reinforced concrete stub of dimensions 150x150x150 mm. one slab was strengthened using the regular indirect shear technique. The remaining slabs were installed using an innovative stitching technique. The obtained results for the strengthened samples were normalized according to the control specimen ; where failure strength and ductility were obtained/calculated. Experimental results were compared to the punching shear equations provided in various codes and guideline (ACI-318, BS-8110, EURO code-2). The slabs were designed to guarantee a punching- stress failure. Results showed a substantial increase in the punching shear capacity in the direct strengthening technique (stitching) ranged from 23% to 50% and an increase in ductility ranged from 38% to 161% while the indirect strengthening technique showed a slight enhancement in the punching capacity equal to 6.2% and an increase in ductility equal to 7% and this is proving that the newly developed stitching technique – where holes are drilled in the column territory and filled with CFRP and epoxy – yields superior results to conventional CFRP sheet-bonding to slab bottom. Experimental results – for the punching shear capacity were compared to predictions using ACI 318, BS 8110 and Euro code 2 provisions. On average, all codes/provisions underestimated the punching shear capacity by values of 22%, 12.7% and 4%, respectively. In turn, Euro-code2, yields the most accurate prediction values.
Keywords: Punching Strengthening; Flat slab; FRP sheets; Stitching; Reinforced Concrete.
In this respect, an experimental program has been conducted where the effectiveness of using carbon fiber reinforced polymer (CFRP) sheets in punching shear strengthening of slab-column connections has been examined. The program consists of a total of six square slabs with overall dimensions and thickness of 1800x1800x150 mm, respectively; loaded concentrically onto a reinforced concrete stub of dimensions 150x150x150 mm. one slab was strengthened using the regular indirect shear technique. The remaining slabs were installed using an innovative stitching technique. The obtained results for the strengthened samples were normalized according to the control specimen ; where failure strength and ductility were obtained/calculated. Experimental results were compared to the punching shear equations provided in various codes and guideline (ACI-318, BS-8110, EURO code-2). The slabs were designed to guarantee a punching- stress failure. Results showed a substantial increase in the punching shear capacity in the direct strengthening technique (stitching) ranged from 23% to 50% and an increase in ductility ranged from 38% to 161% while the indirect strengthening technique showed a slight enhancement in the punching capacity equal to 6.2% and an increase in ductility equal to 7% and this is proving that the newly developed stitching technique – where holes are drilled in the column territory and filled with CFRP and epoxy – yields superior results to conventional CFRP sheet-bonding to slab bottom. Experimental results – for the punching shear capacity were compared to predictions using ACI 318, BS 8110 and Euro code 2 provisions. On average, all codes/provisions underestimated the punching shear capacity by values of 22%, 12.7% and 4%, respectively. In turn, Euro-code2, yields the most accurate prediction values.
Keywords: Punching Strengthening; Flat slab; FRP sheets; Stitching; Reinforced Concrete.
Other data
| Title | Punching Behavior of RC Slabs Retrofitted with FRP Sheets | Other Titles | سلوك البلاطات الخرسانية المدعمة بالبوليمرات المسلحة بالاليف تحت تأثير القص الثاقب | Authors | Mohamed Sahab Mohamed Mohamed Seliem | Issue Date | 2015 |
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