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This study deals with the seismic behavior of old- type reinforced concrete (RC) beam-column joint and the effectiveness of an innovative application of Fiber Reinforced Concrete (FRC) as seismic strengthening solution. Two real joint subassemblies were extracted from an existing building damaged and demolished after the L’Aquila 2009 earthquake and tested in laboratory. The joints exhibited poor quality concrete and reinforcement details typical of old design practice, which are very difficult to reproduce in laboratory simulations. The joint tested in the as-built configuration showed a brittle failure with joint diagonal cracking, as commonly observed in the aftermath of recent devastating earthquakes. The FRC thin jacketing avoided the joint panel shear failure promoting a more favorable beam yielding. This resulted in a significant increase of the shear strength (until 50%) and energy dissipation (85%). The strengthening phases and the details of the proposed strengthening layout are described. A direct comparison between as-built and strengthened specimen in terms of global and local behavior is reported. Strain measurements on the FRC jacketing are also discussed as an effective design parameter.

Available capacity models for the assessment of seismic capacity of reinforced concrete columns are mainly based on experimental tests under axial load and uniaxial bending. Furthermore, experimental tests have been mainly performed on columns representative of new constructions. In order to analyze the effects of biaxial bending on the seismic performances of existing r.c. columns with design characteristics non-conforming to present day seismic codes and practices, the paper presents the results of a first stage of tests on r.c columns under both axial load and biaxial bending, which effectively simulate the seismic actions. In particular, the paper presents results of four tests on full scale square columns reinforced with plain bars, subjected to constant axial load and biaxial cyclic actions. Two different cyclic displacement paths were investigated: horizontal displacements with an inclination angle of 45or 30 with respect to the cross section principal axes. The influence of biaxial bending actions on the global behavior of existing r.c. columns in terms of stiffness, strength, and deformation capacity as well as the effects of different horizontal displacements orientation on their performances are herein investigated and discussed; the comparison with experimental outcomes provided by uniaxial bending tests on companion specimens are also presented. Experimental findings showed that biaxial bending actions affect columns rotational capacity more than strength. The rotational capacity reduction owing to biaxial bending actions, even if more significant than the flexural capacity reduction, is not currently taken into account in the available seismic guidelines related to existing r.c. buildings.

The effectiveness of externally bonded fiber-reinforced polymer (FRP) laminates for strengthening existing reinforced concrete (RC) structures is strictly related to the bond of the FRP reinforcement to the concrete substrate. Although numerous experimental studies have investigated this bond, experimental data concerning cyclic tests on both FRP sheets and plates applied on concrete specimens are still lacking. Thus, a series of single shear tests (SSTs) under both monotonic and cyclic actions, without inversion of sign, were performed on concrete prismatic specimens reinforced with carbon FRP (CFRP) sheets or plates. To evaluate and compare the influence of cyclic external actions on the bonding behavior of sheets and plate reinforcements, the results provided by monotonic and cyclic tests are reported and discussed in this paper. In particular, force-displacement relationships, axial strains, and shear stresses recorded along the FRP reinforcement are reported; the influence of the load path on the FRP debonding behavior is also examined.

Every year, several prestressed concrete (PC) bridge girders are accidentally damaged by overheight vehicles or construction equipment impact. Although complete replacement is sometimes deemed necessary, repair and rehabilitation can be far more economical, especially when the time and the installation cost of the repair system are drastically reduced. The use of fiber-reinforced polymer (FRP) composites to restore the original capacity of impacted PC girders are being increasingly considered for bridge applications due to their high strength-to-weight ratios, corrosion and fatigue resistance, their ease of transport and handling and their potential for tailorability. Experimental data on full-scale PC girders strengthened by using FRP laminates are very limited; the present paper is intended as an extension of a previous experimental work conducted by writers [as reported by M. Di Ludovico et al. ACI Struct. J. 102(5), 97–109 (2005)] on three full-scale PC specimens. In particular, tests on five full-scale (1,300 mm long, 1,050 mm high) PC I-shaped girders with RC slabs, designed according to ANAS (Italian Transportation Institute) standard specifications, are presented. One beam was used as control and the other four were intentionally damaged in order to simulate a vehicle impact by removing the concrete cover and by cutting a different percentage of tendons (17% on two specimens and 33% on the remaining two). The repair, by using externally bonded carbon FRP (CFRP) laminates installed by wet manual layup, was aimed at restoring the ultimate flexural capacity of the member, taking particular attention to the laminate’s anchoring system. Main experimental phases along with the comparison of tests results in terms of flexural capacity, deflections, strains, and failure modes are herein presented and discussed with reference to control, damaged, and CFRP strengthened specimens. The effectiveness of the adopted anchorage systems is also evaluated.

Premature brittle failures because of seismic actions strongly affect the behavior of existing reinforced concrete (RC) structural systems. They commonly involve exterior beam-column joints of structures designed without transverse reinforcement. This paper investigates the behavior of unconfined joints that do not conform to current seismic codes and the effectiveness of externally bonded fiber-reinforced polymers (FRPs) as a strengthening technique. It presents an experimental program carried out on six full-scale RC corner joints under constant axial load and transverse cyclic loading in the as-built and FRP-strengthened configuration. After describing the specimen design strategy and test setup, seismic performance is compared. Particular attention is paid to comparing the experimental capacity of as-built joints and the capacity, which can be predicted on the basis of models available in the literature. Finally, a discussion on the effectiveness of different FRP-strengthening layouts is reported.

Capacity models to assess structural safety are primarily based on experimental outcomes typical of new constructions. In order to analyze deformation and strength mechanisms of members that do not comply to current seismic codes and practices, an experimental investigation was undertaken on full-scale columns reinforced with deformed or plain rebars. The experiments involved eight tests under monotonic or cyclic actions on square or rectangular reinforced concrete columns designed according to provisions, construction practice, and material properties enforced between the 1940s and 1970s. Experimental outcomes allowed pointing out global and local behavior of RC columns typically found in existing constructions, in which both plain and deformed bars can be found. Theoretical plastic rotation capacities provided by the proposed supplement to the current ASCE standard are discussed in this paper and compared to those experimentally obtained. The results indicate that predicted plastic rotations corresponding to significant loss of lateral-force capacity are very conservative if compared with experimental outcomes. This seems especially clear in the case of columns reinforced with plain rebars. For these columns, the contribution of the base rotation on the global deformation mechanism is considerable.