Cem Yalcin

Inelastic analysis of reinforced concrete columns

Abstract A computer software was developed for inelastic analysis of reinforced concrete columns under combined axial compression and monotonically increasing lateral loads. The software incorporates effects of concrete confinement, steel strain hardening, reinforcement buckling, and secondary deformations due to P – Δ effect. Hinging of column critical region and progression of hinging along column height are considered. Inelastic deformation components due to flexure and anchorage slip are included. The input consists of column geometry, material properties, and loading. The results are presented in a graphical form in terms of moment–curvature, force–displacement, and moment–anchorage slip relationships. Axial force–moment interaction diagram is also plotted as part of the output. The program was verified extensively against available experimental data.

CFRP Rehabilitation of Concrete Frame Joints with Inadequate Shear and Anchorage Details

The research presented in this study involves full-scale experimental evaluation of carbon fiber-reinforced polymer (CFRP) rehabilitation for existing beam-column joints designed for gravity load with common pre-1970s deficient reinforcement details when subjected to cyclic loading. Numerous studies have demonstrated effectiveness of externally bonded fiber-reinforced polymer (FRP) materials for retrofitting the deteriorating RC structures. Although these materials are widely used in bridges, their applications in buildings have been somewhat limited. In particular, the experimental investigations on external FRP retrofit of deficient beam-column joints have not thoroughly been investigated and they are mainly on scaled-down specimens. The failure of these subassemblies, which possess lack of shear reinforcement within the joint core and shortly embedded positive beam reinforcement, would possibly result in catastrophic collapse of reinforced concrete frame structure during an earthquake event. Recognizin...

Development of Earthquake Energy Demand Spectra

Current seismic codes are generally based on the use of response spectra in the computation of the seismic demand of structures. This study evaluates the use of energy concept in the determination of the seismic demand due to its potential to overcome the shortcomings found in the current response spectra–based methods. The emphasis of this study is placed on the computation of the input and plastic energy demand spectra directly derived from the energy-balance equation with respect to selected far-field ground motion obtained from Pacific Earthquake Engineering Research (PEER) database, soil classification according to National Earthquake Hazards Reduction Program (NEHRP) and characteristics of the structural behavior. The concept and methodology are described through extensive nonlinear time history analyses of single-degree-of-freedom (SDOF) systems. The proposed input and plastic energy demand spectra incorporate different soil types, elastic perfectly plastic constitutive model, 5% viscous damping ratio, different ductility levels, and varying seismic intensities.

Monotonic and Cyclic Bond Behavior of Deformed CFRP Bars in High Strength Concrete

Composite reinforcing bars (rebars) that are used in concrete members with high performance (strength and durability) properties could have beneficial effects on the behavior of these members. This is especially vital when a building is constructed in an aggressive environment, for instance a corrosive environment. Although tension capacity/weight (or volume) ratios in composite rebars (carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), etc.) are very high when compared to steel rebars, major weaknesses in concrete members reinforced with these composite rebars may be the potential consequences of relatively poor bonding capacity. This may even be more crucial when the member is subjected to cyclic loading. Although monotonic bond tests are available in the literature, only limited experimental studies exist on bond characteristics under cyclic loading conditions. In order to fill this gap and propose preliminary design recommendations, 10 specimens of 10-mm-diameter ribbed CFRP rebars embedded in specially designed high strength concrete (f’c = 70 MPa) blocks were subjected to monotonic and cyclic pullout tests. The experimental results showed that cyclically loaded CFRP rebars had less bond strength than those companion specimens loaded monotonically.

Sesmic investigation of heavily damaged beam column joint repaired by chemical epoxy

Özellikle Türkiye’de, 1998 öncesi yapılmış betonarme binalarda, gerek yönetmelik eksiliğinden, gerekse uygulama hatalarından dolayı çeşitli yapısal problemlerin mevcut olduğu bilinmektedir. Kolon kiriş birleşim bölgeleri deprem kuvvetleri altında yüksek kayma gerilmelerine maruz kalmaktadır. Bu da arzu edilen göçme senaryosu gerçekleşemeden binaların daha evvelden kolon-kiriş birleşim bölgelerinden ani göçmelere neden olmaktadır. Bu çalışmada eski yönetmeliklere uygun yapılmış, kolon kiriş birleşim numunelerinin sismik davranışı deneysel olarak incelenmiş ve sonra hasarlı numune kimyasal harçlar ile onarılarak tekrar teste tabii tutulmuştur. Sonuç olarak, tamir edilen numunenin Yatay yük –ötelenme davranışı, rijitlik kayıpları ve Enerji Tüketim kapasitesinde önemli derecede bir artış olduğu elde edilmiştir. It is known that, especially in Turkey, many existing reinforced concrete buildings constructed in pre 1998 era, have many structural faults, due to deficiencies both in seismic code of the time and in application process. The column-beam regions are subjected to the high shear stresses under the seismic forces. And thus causing sudden failures since the required mode of failure is not accomplished. In this research, seismic behavior of beam column joint which is designed according to the old seismic code of Turkey is investigated experimentally, and then the damaged specimen is repaired by chemical epoxy and re-tested. As a conclusion, significant improvement is obtained in lateral load-drift behavior, stiffness degradation and energy dissipation capacities of repaired specimen.