Mostafa Fakharifar

Rapid Repair of Earthquake-Damaged RC Columns with Prestressed Steel Jackets

AbstractIn this study, a lightweight prestressed steel jacket (PSJ) was proposed and developed for rapid and cost-effective repair of a severely damaged circular reinforced concrete column. The PSJ is composed of several prestressed strands, and a thin steel sheet is restrained by these strands, which can be manually wrapped around and jointed to form a jacket on the column as part of a 12-h repair job by two workers. The prestressed strands restrain the thin sheet from buckling, while the steel sheet in turn prevents the strands from cutting into cracked concrete and thus preserves the prestressing forces. The PSJ was validated with cyclic (reversed) testing of two large-scale columns with lap-splice deficiency under incrementally increased displacements every three cycles. The ultimate strength and displacement ductility of the damaged column were restored to 115% and 140%, respectively, of those of the as-built column. The initial stiffness of the damaged column, however, was restored to only 84% of th...

Seismic performance and global ductility of RC frames rehabilitated with retrofitted joints by CFRP laminates

This paper presents a new FRP retrofitting scheme to strengthen local beam-column joints in reinforced concrete (RC) frames. The new retrofitting scheme was proposed following a preliminary study of four different existing retrofitting schemes. A numerical simulation was conducted to evaluate the effectiveness of FRP-strengthened reinforced concrete frames by bridging behavior of local joints to the whole structure. Local confinement effects due to varying retrofitting schemes in the joints were simulated in the frame model. The seismic behavior factor was used to evaluate the seismic performance of the strengthened RC frames. The results demonstrated that the new proposed retrofitting scheme was robust and promising, and finite element analysis appropriately captured the strength and global ductility of the frame due to upgrading of the local joints.

Hybrid Jacketing for Rapid Repair of Seismically Damaged Reinforced Concrete Columns

This study proposes hybrid jacketing for rapid repair of seismically damaged concrete columns for bridge safety. The hybrid jacketing for a reinforced concrete (RC) column is composed of a thin cold-formed steel sheet wrapped around the column and its outside prestressing strands. Although the prestressing strands can prevent buckling of the confining steel sheet, the steel sheet can in turn prevent the prestressing strands from cutting into the concrete. The hybrid jacketing concept was validated with testing of a large-scale RC column with lap splice deficiency typical of pre-1970 bridge constructions in the Central United States. Results from the original and repaired columns were compared for hysteresis loops, strength, stiffness, ductility, and energy dissipation. The hybrid jacketing proved to be effective in restoring structural behavior of the damaged column to prevent bridge collapse. Such a cost-effective solution can be implemented at bridge sites in hours. Design equations to establish the lateral force–displacement relationship of the tested column to design the hybrid jacket are derived in detail.

Seismic Performance and Global Ductility of Reinforced Concrete Frames with CFRP Laminates Retrofitted Joints

Post-earthquake reconnaissance and experimental research indicate that the beam-column joint is a crucial zone in reinforced concrete (RC) moment resisting frames. Due to their exceptional mechanical properties and high strength to weight ratio, fiber reinforced polymers (FRP) are considered to be one of the most promising materials for beam-column joint retrofitting in RC structures. In this study, the efficacy of joint retrofitting in upgrading the seismic performance of RC structures is numerically investigated through displacement-based adaptive pushover and inelastic dynamic time history analyses. Four typical FRP strengthening schemes between the beam and column are investigated and the corresponding structural global ductility and seismic performance for FRP joint-retrofitted RC frames are evaluated through both the seismic behavior factor and the inter-story drift ratio. The proposed method is demonstrated by seismic behavior of an intermediate-rise RC building under earthquake forces. The numerical results indicate that the proposed retrofitting scheme can greatly improve the seismic performance and global ductility of RC buildings.

Microstructural Characteristics of Polyurea and Polyurethanexerogels for Concrete Confinement with FRP System

Due to their exceptional mechanical properties,xerogels attract increasing attention forstructural applications. In this study, the mechanical behavior of two types of polymeric xerogelsis investigated. The excellent energy-absorbing capability of those xerogelsis demonstrated by their stress-strain relations with respect to their microstructure determined withscanning electron microscopy (SEM). A pilot study on the effects of xerogellayers in an FRP system for concrete confinementis conducted.Test results clearly indicatedthat the proposed multi-layer systemcan significantly increase the ductility of confined concrete.