Strengthening of beam-column joints

The issue with the strengthening of beam-column joints is extensively described in the draft of the Guidelines for Reparation and Strengthening of Structural Elements, Curtain Walls and Partitions edited by the Department of Civil Protection and by the ReLUIS consortium in August 2009 that highlights that the majority of failures of joints and of the requests for ductility in columns is usually localized in the exterior joints and columns, particularly those in the comers, for the following reasons  

Joints are unconflned on at least one (waU joints) or two (comer joints) sides 

Joints and columns are more subjected to the thmst action of curtain walls, especially on the comer joints, where thmst is not compensated by the presence of a curtain waU on the opposite side 

Are more subjected to larger strains due to possible torsional effects of the stmcture 

Therefore, it is recommended that the local strengthening of r.c. frames should mainly focus on perimeter joints and columns, with a priority focus on comer ones. 

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Local strengthening of beam-column joints and columns of both floors using PTMS... 

Ghobarah, A., and Said, A. (2002). Shear strengthening of beam-column joints . Engineering Structures, 24(7) 881-888. 

Fig. 14.3 ERP strengthening system details (DPC-ReLUIS Guidelines 2011) (a) SRP uniaxial system to sustain horizontal actions due to strong infills (b) L-shaped FRP laminates at beam column connection (c) Shear capacity increase of beam column joint panel (d) Column end confinement (e) Beam end FRP wrapping (f) FRP strengthened Joint...

The experimental tests clearly pointed out the potential of the recommended FRP solution to increase the seismic performances of beam-column joints designed according to non-seismic code provisions. The experimental validation of this local strengthening technique may strongly encourage the use of local interventions based on the use of FRP reinforcement to significantly increase both the local and global seismic capacity of RC structures. 

Antonopoulos CP, Triantafillou TC (2003) Experimental investigation of FRP-strengthened RC beam-column joints. ASCE J Compos Constr 7(l) 39-49... 

Ibrahim A, Mahmood M (2009) Finite element modeling of reinforced concrete beams strengthened with FRP laminates. Eur J Sci Res 30(4) 526-541. ISSN 1450-216 Johansson M (1996) New reinforcement detailing in concrete frame comers of civil defense shelters non-linear finite element analyses and experiments. Licentiate thesis, Chalmers University of Technology, Division of Concrete Structures, Gothenburg, Sweden Li B, Kulkami SA (2010) Seismic behavior of reinforced concrete exterior wide beam-column joints. J Struct Eng ASCE 136(l) 26-36... 

A wide section of the guideline focuses on the brittle failure mechanisms. In particular, according to experiences gained from examining the performances of RC structures after seismic events, a wide section focuses on the most common brittle collapse mechanisms resulting from shear failure of partially confined beam-column joints (i.e. exterior or comer joints on the perimeter of the stmcture in some cases, where frames are only in one of the plan directions, they could be also interior). The typical joint failures observed in the L Aquila post earthquake are described and a local strengthening procedure by means of FRP, steel jacketing or CAM technique is discussed. 

Engindeniz, M., Kahn, L.F., and Zureick, A.-H. (2005). Repair and strengthening of reinforced concrete beam-column joints state of the art . ACI Structural Journal, 102(2) 187-197. 

Strengthening Techniques Bridges, Fig. 3 Cap beam, Transportation (2006) beam-column joint California cap beam-column joint, and girder shear damage (Cap Department of Transportation (2003)) beam, girder shear damage California Department of... 

Strengthening method is to use external posttensioning as shown in Fig. 13a. Steel jackets bonded to the sides of the joint and anchored to the bent cap are also effective (Thewalt and Stojadinovic 1995). Finally, FRP jackets in the form of an ankle wrap have been tested (Gergely et al. 2000) and used to strengthen column to cap beam-colunm joints as shown in Fig. 13b (Pantelides et al. 2004). The nominal principal tensile stress developed in the beam-column joint is used to design the carbon FRP composite layers. When strengthening of these joints is required to improve the longitudinal response, transversely prestressed bolsters may be used. 

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