Seismic Retrofit Schemes with FRP for Deficient RC Beam-Column Joints: State-of-the-Art Review

Abstract

8This paper aims to review and critically assess experimental research efforts on the seismic retrofit of 9 existing reinforced concrete (RC) beam-column joints with fibre-reinforced polymer (FRP) sheets of 10 the past 20 years. The review of the literature revealed several promising features of FRP 11 strengthening schemes. FRP retrofits can be used to address a number of different deficiencies in 12 non-seismically designed RC members framing into beam-column joints. A majority of studies 13 concentrate on joint shear strengthening and strengthening in the axis of principle stress is found to 14 be most effective. Other strategies include counter-acting the weak-column/strong-beam in non-15 seismically designed specimens by means of column flexural strengthening, as well as plastic hinge 16 relocation within the beams, away from the joint. Only a limited number of studies look at combining 17 several of these retrofit objectives into a more complete retrofit of the joint sub-assemblage. In most 18 studies it is observed that simple FRP wrapping is used for anchorage, which is not always effective. 19Instead, it is shown that anchorage by means of FRP anchors or mechanical anchors is required to 20 achieve adequate strengthening in most cases. Next to the detailed discussion of the literature, a 21 database of all tested specimens is compiled and analysed. An assessment of shear strengthening 22 design equations from major design guidelines is made based on the experimental results collected in 23 this database, highlighting the need for their further improvement. Moreover, analysis of the database 24 reveals a lack of tested specimens with realistic test set-ups, including scaled specimens, testing 25 without axial load, as well lack of slab and transverse beams. It is found that these parameters heavily 26 affect retrofit effectiveness and may lead to non-conservative results. Moreover, on average, the 27 effectiveness of repairing pre-damaged specimens is found to be similar to that of retrofitting 28 specimens without damage.Reinforced concrete (RC) structures built in earthquake prone areas and designed to resist gravity 31 loads only or before the introduction of modern seismic codes (pre-1970's or 80's), typically display 32 several deficiencies resulting in inadequate behaviour under seismic loading. In particular, the 33 hierarchy of strengths around beam-column joints plays a critical role in the overall cyclic behaviour of 34 RC structures. Avoiding premature failure of said joints is hence a fundamental principle in modern 35 seismic design to allow the framing members reach full capacity (Kappos and Penelis 1996). 36Adequate energy dissipation under seismic loading also relies on an appropriate hierarchy of 37 strengths between the framing members of the joints. To achieve larger global structural 38 displacements and hence higher ductility under seismic loading, modern seismic design guidelines 39 aim to ensure beam-hinging precedes column-hinging mechanisms (Fardis 2009). 40For existing structures...

A Review of the Performance of Infilled RC Structures in Recent Earthquakes

“…They are reported due to poor and inadequate detailing of the longitudinal and transverse reinforcement and to the use of smooth bars. Some experimental studies were carried out on evaluating and retrofitting existing RC building structures designed according to codes earlier than the 1970s [6,[17][18][19][20]. Most of these studies are related to ribbed bars.…”

Effectiveness of the Novel Rehabilitation Method of Seismically Damaged RC Joints Using C-FRP Ropes and Comparison with Widely Applied Method Using C-FRP Sheets—Experimental Investigation

“…The response of beam-column joints is affected by a variety of parameters such as bond, shear load, confinement and fatigue, which are not yet well understood even independently, and they progressively reduce the joint's stiffness and strength. Therefore, the successful repair or strengthening of joints that have previously been damaged during cyclic loading caused by earthquakes is essential in order to enable the use of the affected structure again [14][15][16]. Detailed design recommendations have been introduced on the basis of the research and development of repair techniques in Europe and the United States in past decades [17][18][19][20][21].…”

“…To achieve shear strengthening, various types of FRP exterior application shapes have been investigated, such as U-shaped [48][49][50][51][52][53], X-shaped [54][55][56] and T-shaped [57]. In addition to local strengthening of the joint area, others have attempted to improve the performance of the surrounding components, such as bond enhancement of the beam's bottom reinforcement bars [58][59][60], improvement of the columns' flexural performance and column confinement [16,[60][61][62][63][64]. The most common mode of failure in FRP-strengthened specimens that were tested was the debonding of FRP composites from the concrete surface.…”

Seismic Performance of Steel Fiber Reinforced High–Strength Concrete Beam–Column Joints

“…In different designs [7][8][9][10][11][12], adding randomly distributed short fibers into the concrete matrix to improve the tensile and crack resistance is an excellent method [13][14][15][16][17][18][19]. Experiments showed that steel fiber had little contribution to compressive strength [20][21][22][23][24], but it can obviously improve the compressive behavior of stress and strain after cracking and also shows apparent toughness [25][26][27][28].…”