How to Cite
Abstract
The subject of the Bulletin is strengthening of existing reinforced concrete corbels and the proposed thesis is that it is possible to effectively increase the carrying capacity of the corbels with embedded through-section (ETS) rods.
The main part of the dissertation is the author’s own experimental research. The study covers two categories of corbels: one with moderate shear slenderness (ac/d = 0;5÷0;6) and one with short span-to-depth ratios (ac/d ≈ 0,3). Prior to the start of the strengthening process, a force equivalent to about half of the ultimate load determined on the reference elements was applied to each corbel. All corbels were being strengthened under load. Threaded rods (M16, class 8.8) were used as addi-tional reinforcement. Some of the corbels were equipped with a steel accessory anchored to the concrete with post-installed screws. During the tests deformations on the reinforcement and the concrete surface were measured and the cracks and their width were recorded. A digital image correlation system (Aramis) was used during one of the test series. On the whole, nineteen corbels were tested: six reference and thirteen strengthened ones. Increase of load capacity of up to 64% (using embedded through-section rods only) and over 150% for the steel accessory was observed.
As a result of calculation analyses, it was found that the methods based on the strut-and-tie models correspond very well with the results of the author’s own tests for the moderate shear slenderness corbels and the post-installed reinforcement can be treated in the same way as the cast-in bars. The situation is different in the case of corbels with short span-to-depth ratios. It has been shown that the existing calculation methods lead to more conservative results if the mechanical rein-forcement ratio of the element is smaller.
Due to the different method of destruction the corbel with steel accessory (C – III) was analyzed separately. In that case the ultimate load was determined by the load capacity of anchors.
As a result of the studies and analyses it was found that corbels with moderate and high shear slenderness ac/d ≈ 0,5 and low reinforcement ratio can be effectively strengthened by embedded through-section rods.
Such reinforcement is less effective in corbels with short span-to-depth ratios ac/d ≈ 0,3.
References
ACI 318-14 Building Code Requirements for Structural Concrete and Commentary for Building Code Requirements for Structural Concrete (ACI 318R-14), Farmington Hills, 2014;
Ahmad, S. et al.: Shear Strengthening of Corbels with Carbon Fibre Reinforced Polymers (CFRP). Mater. Construcción. 60, 299, 79–97 (2010);
Assih, J. et al.: Concrete damaged analysis in strengthened corbel by external bonded carbon fibre fabrics. Appl. Adhes. Sci. 3, 1–13 (2015);
Campione, G. et al.: Flexural behaviour of concrete corbels containing steel fibers or wrapped with FRP sheets. Mater. Struct. 38, 6, 617–625 (2005);
Corry, R.W., Dolan, C.W.: Strengthening and Repair of a Column Bracket Using a Carbon Fiber Reinforced Polymer (CFRP) Fabric. PCI J. 46, 1, 54–63 (2001);
Elgwady, M.A. et al.: Strengthening of Corbels Using CFRP an Experimental Program. (2005);
El-Maaddawy, T.A., Sherif, E.-S.I.: Response of Concrete Corbels Reinforced with Internal Steel Rebars and External Composite Sheets: Experimental Testing and Finite Element Modeling. J. Compos. Constr. 18, 1, (2014);
EN 1992-1-1: Eurocode 2: Design of Concrete Structures – Part 1: General rules and rules for buildings European Commitiee For Standardization, 2008;
Feix J., Worle P. i Gerhard A.: Ein neuer Ansatz zur Steigerung der Durchstanztrag-fahigkeit bestehender Stahlbetonbauteile. Bauingenieur, April, 2012. s. 149-155;
Fernández Ruiz, M. et al.: Strengthening of Flat Slabs Against Punching Shear Using Post-Installed Shear Reinforcement. ACI Struct. J. 107, 4, 434–442 (2010).
Godycki-Ćwirko, T.: Mechanika betonu. Arkady, Warszawa (1982).
Hassanzadeh G i Sundqvist H.: Strengthenning of Bridge Slabs on Columns. Nordic Concrete Research (online, dostęp: 21.10.2003, www.itn.is/ncr/publications/pub-21.htm), 1988. str. 12.
Ivanova, I. et al.: Experimental investigation into strengthened short reinforced concrete corbels by bonding carbon fiber fabrics. J. Adhes. Sci. Technol. 29, 20, 2176–2189 (2015);
Ivanova, I. et al.: Influence of Fabrics Layers on Strengthened Reinforced Concrete Short Corbels. Int. J. Civ. Eng. 5, 11, 33–43 (2014);
Ivanova, I.: Mechanical behavior of short concrete corbels reinforced or repaired by bonding of composite materials (in French). Université De Reims Champagne-Ardenne École, Université De Technologie Chimique Et De Métallurgie (Bulgarie) (2013);
Ivanova, I., Assih, J.: Experimental study of local behavior of strengthened reinforced concrete short corbels by bonding carbon fiber fabrics. Int. J. Civ. Struct. Eng. Res. 4, 1, 148–158 (2015);
Ivanova, I., Assih, J.: Static and dynamic experimental study of strengthened reinforced short concrete corbel by using carbon fabrics, crack path in shear zone. Frat. ed Integrità Strutt. 34, 90–98 (2015);
Krawczyk, Ł.: Wzmacnianie krótkich wsporników żelbetowych zbrojeniem wklejanym. (Strengthening of short corbels with embedded through-section reinforcement), rozprawa doktorska (PhD thesis) Politechnika Łódzka (2017).
Kriz, L.B., Raths, C.H.: Connections in Precast Concrete Structures- Strength of Corbels. PCI J. 10, 1, 16–61 (1965);
Kunz J., Ruiz F., Muttoni A.: Enhanced safety with post-installed shear reinforcement. FIB Symposium Tel Awiw 22-24 April 2013, Engineering a Concrete Future: Technology, Modeling and Construction, Proceedings;
Lachowicz, M., Nagrodzka-Godycka, K.: Experimental study of the post tensioned prestressed concrete corbels. Eng. Struct. 108, 1–11 (2016);
Mast, R.F.: Auxiliary Reinforcement in Concrete Connections. J. Struct. Div. 94, 6, 1485–1504 (1968).
Model Code 2010 - Final draft, (2012).
Mohr, O.: Welche Umstände bedingen die Elastizitätsgrenze und den Bruch eines Materials? Zeitschrift des Vereins Dtsch. Ingenieure. 44, 1524–1530 (na podstawie innych prac) (1900).
Mohammed, A.A., Assi, D.K.: Behavior of reinforced concrete corbels strengthened with ferrocement sheets. GAU J. Soc. App. Sci. 6, 10, 93–102 (2014);
Nagrodzka-Godycka, K.: Badania bardzo krótkich wsporników żelbetowych. Inżynieria i Bud. 57, 6, 349–350 (2001);
Nagrodzka-Godycka, K.: Behavior of Corbels with External Prestressing Bars - Experimental Study. ACI Struct. J. 96, 6, 1033–1039 (1999);
Nagrodzka-Godycka, K.: Efekt wzmocnienia zarysowanych wsporników żelbetowych w świetle badań eksperymentalnych. Inżynieria i Bud. 52, 5, 281–285 (1995);
Nagrodzka-Godycka, K.: Wsporniki żelbetowe: badania, teoria, projektowanie. Wydawnictwo Politechniki Gdańskiej (2001);
Nagrodzka-Godycka, K.: Wzmacnianie wsporników żelbetowych. Przegląd Bud. 69, 5, 11–13 (1997).
Ozden, S., Atalay, H.M.: Strengthening of reinforced concrete corbels with GFRP overlays. Sci. Eng. Compos. Mater. 18, 1–2, 69–77 (2011);
Park, Robert and Paulay, T.: Reinforced Concrete Structures. (1975)
Randl, N.: Design recommendations for interface shear transfer in fib Model Code 2010. Struct. Concr. 14, 3, 230–241 (2013).
Randl, N., Wicke, M.: Schubübertragung zwischen Alt- und Neubeton. Experimentelle Untersuchungen, theoretischer Hintergrund und Bemessungsansatz. Beton- und Stahlbetonbau. 95, 8, 461–473 (2000)
Shadhan, K.K., Kadhim, M.M.M.: Use of CFRP Laminates for Strengthening of Reinforced Concrete Corbels. Int. J. Civ. Eng. Technol. 6, 11, 11–20 (2015);
Urban T.: Badania eksperymentalne stref ścinania wzmocnionych zbrojeniem wklejanym. XLII Konf. Nauk. KILiW PAN i KN PZITB, Krynica 1996, Tom 5, s. 149÷156;
Urban T.: Wzmacnianie konstrukcji żelbetowych metodami tradycyjnymi. Wydawnictwo Naukowe PWN, Warszawa 2015, ss. 197;
Urban T., Krawczyk Ł.: Strengthening corbels using post-installed threaded rods. Structural Concrete. 2017;18:303-315;