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    Cyclic displacement model for reinforced concrete columns
    (John Wiley and Sons Ltd, 2023) Biçici, Erkan; Sezen, Halil
    Reinforced concrete (RC) structures in low to moderate seismic regions and many older RC structures in high seismic regions include columns with steel reinforcement details not meeting the requirements of modern seismic design codes. These columns typically fail in shear or in a brittle manner and their behavior must be accurately captured when RC structures are modeled and analyzed. The total lateral displacement of a low ductility or shear critical RC column can be represented as the sum of three displacement components: (1) flexural displacement, (2) displacement due to slippage of the reinforcing bars at column ends, and (3) shear displacement. In this study, these three displacement components are separately modeled and then combined together following a proposed procedure based on the expected overall behavior of the column and its failure mechanism. A simplified slip model is proposed. The main objective of this research is to develop an easy-to-apply method to model and capture the cyclic behavior of RC columns considering the shear failure mechanism. The proposed model is validated using the available data from RC column and frame experiments.
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    Cyclic shear displacement model for reinforced concrete columns
    (Elsevier, 2021) Biçici, Erkan; Sezen, Halil
    Lateral response of reinforced concrete (RC) columns can be modeled and simulated considering three displacement components: flexural displacement, displacement due to slippage of longitudinal bars at column ends, and shear displacement. The incorporation of shear displacement in a computational model is essential for accurate calculation of lateral load–displacement relationship. The contribution of shear displacement can be significant for RC columns with low displacement capacity or ductility. An easy-to-apply shear displacement model is proposed in this study, and implemented in the open source software, OpenSees. The proposed model is based on a pre-defined envelope or monotonic model and does not require updating of modeling parameters during each cycle. The model is validated using experimental data. New rules are developed for the cyclic model to capture the effects of cracking and change in stiffness and strength during the loading and unloading cycles. Comparison of the calculated and measured shear displacements indicates that the cyclic shear response can be captured by the proposed model.
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    Effect of size and slenderness on the axial-compressive behavior of basalt FRP-confined predamaged concrete
    (American Society of Civil Engineers (ASCE), 2021) Ma, Gao; Chen, Xiaohuang; Biçici, Erkan; Hou, Chunxu; Sezen, Halil
    To investigate the size and slenderness effect on the axial-compressive behavior of basalt fiber-reinforced polymer (BFRP)-confined predamaged concrete, five groups of concrete cylinders with different sizes and slenderness ratios were designed and tested. The cylinders were axially preloaded to three predamage levels, then repaired using BFRP, and reloaded. The results showed that the concrete predamage had an adverse effect on the ultimate strength and initial elastic modulus of BFRP-confined concrete. Except for the smallest specimens affected by the wall effect, the initial analysis found that the ultimate strength of BFRP-confined concrete decreased with an increase in size and slenderness ratio, and the size and slenderness effect decreased with an increase in BFRP confining pressure, while these increased with the severity of concrete predamage. However, there was no obvious size or slenderness effect on the ultimate strain of BFRP-confined concrete. Through multifactorial analysis, it was confirmed that the ultimate strength of BFRP-confined undamaged and predamaged concrete was influenced by the slenderness. Considering the effect of size, slenderness, and predamage, monotonic and cyclic models were developed for BFRP-confined concrete. Finally, a uniaxial material object was added into OpenSees to provide an effective numerical material model for theoretical analyses and engineering applications. © 2021 American Society of Civil Engineers.
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    Interface slip model for reinforced concrete columns strengthened with concrete jacketing
    (Pontificia Universidad Catolica de Chile, 2020) Çağlar, Naci; Sichko, Alexander; Sezen, Halil; Biçiçi, Erkan; Demir, Aydın; Farah, A. Farhan
    Retrofit and strengthening of columns can be an effective solution to improve the capacity of reinforced concrete (RC) structures when the structural details and strength are insufficient to resist extreme loads. When concrete jacketing is used by enlarging the existing RC column cross section, the main concern is the performance loss between new and old concrete due to potential interface slip. There are three major options to improve slip resistance at the interface including surface roughening, dowels, or both. In this study, these methods are evaluated and parameters are proposed to model the load transfer along the interface between the existing and new concrete. The response of reinforced concrete jacketed columns is simulated using the proposed numerical models. The effectiveness and need for surface roughening, dowels, or their combination are investigated. A slip coefficient is proposed to model the friction between new and old concrete materials based on comparison of the experimental data and numerical simulations.
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    Reinforcement slip model considering corrosion effects
    (Elsevier, 2020) Zhang, Yixin; Biçici, Erkan; Sezen, Halil; Zheng, Shansuo
    A new bar slip model is developed to account for the contribution of reinforcement anchorage slip to thetotal displacement of corroded reinforced concrete (RC) members. An analytical procedure is proposed tomodel the distribution of the reduced bond stress along the corroded steel bar to predict the reinforce-ment slip in the anchorage area. The reinforcement slip is formulated using an existing model and by newgoverning equations defined for different bond regions. The possibility of having an insufficient embed-ment length is also considered, and a corresponding failure criterion is defined. The bar model is validatedby comparing the available data from single bar pullout experiments and an existing bar force-slip model.The proposed column model is implemented using a fiber element model to capture both the monotonicand cyclic behavior of corroded columns. Pseudo-static test data from corroded column specimens areused to validate the proposed column model. Overall, the proposed model captures the slip of a singlecorroded bar reasonably well to accurately simulate the total lateral displacement of columns with cor-rosion damage.