Faculty Publications
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Item Assessment of Cohesive Parameters Using High Dimensional Model Representation for Mixed Mode Cohesive Zone Model(Elsevier Ltd, 2019) Rao, B.; Balu, A.S.Simulation of the mechanical behavior of bonded joints using a cohesive zone model (CZM) is the most common technique to characterize the delamination process. It is usually dependent on the calculation of cohesive parameters of the traction-separation law, and the parameters are iteratively obtained with the help of simulation and experimental results. The non-availability of standard methods to obtain the parameters necessitates the iterative adjustments of simulation results to the experimental results. However, the calculations based on all individuals for the simulation are not effective as it demands high computational effort. To overcome this issue, this paper proposes a computationally efficient method using high dimensional model representation (HDMR). The cohesive parameters are determined by adopting an efficient sampling scheme within the limits of the parameters. Single leg bending (SLB) joint is tested under the influence of dominant conditions such as mode-I and mode-II to determine the equivalent parameters. The errors resulted from the comparison between the simulation, and experimental values are minimized in order to determine the optimal values. The mixed mode (MM) CZM is then established by pure mode cohesive parameters, and the same is implemented to the SLB joint under various mode mixities for analyzing the fracture process. Comparison between the numerical analysis and the experimental study proves that the proposed HDMR based approach estimates the failure mechanism exactly. © 2019 Institution of Structural EngineersItem Failure Probability of Structural Systems in the Presence of Imprecise Uncertainties(Springer, 2019) Spoorthi, S.K.; Balu, A.S.Structural reliability evaluation is considered to be the solution for modern complex engineering systems possessing uncertain parameters. Reliability estimation involves probabilistic theory when the uncertainties are defined as random variables, whereas with limited resources, it is strenuous to estimate precise parameters in the structural model. Therefore, for such cases, imprecise parameters should be treated appropriately in the design and analysis stage for the improvement of serviceability of the system. On the other side, analyses involving multi-dimensional, computationally expensive, and highly nonlinear structures are formidable in simulation-based methods in the presence of uncertainties. An efficient uncertainty analysis procedure is presented in this paper for analysing the systems with imprecise uncertainties defined as probability-box variables. The estimated bounds of failure probability for the numerical examples from structural mechanics are compared with the traditional approaches to demonstrate the efficiency of the methodology. © 2019, The Institution of Engineers (India).Item Time-dependent safety performance of reinforced concrete structures(Emerald Group Holdings Ltd., 2020) Worabo Woju, U.W.; Balu, A.S.Purpose: Performance of the structure depends on design, construction, environment, utilization and reliability aspects. Other factors can be controlled by adopting proper design and construction techniques, but the environmental factors are difficult to control. Hence, mostly in practice, the environmental factors are not considered in the analysis and design appropriately; however, their impact on the performance of the structures is significant along with the design life. It is in this light that this paper aims to perform the time-dependent performance analysis of reinforced concrete structures majorly considering environmental factors. Design/methodology/approach: To achieve the intended objective, a simply supported reinforced concrete beam was designed and detailed as per the Euro Code (EC2). The time-dependent design parameters, corrosion parameters, creep and shrinkage were identified through thorough literature review. The common empirical equations were modified to consider the identified parameters, and finally, the time-dependent performance of reinforced concrete beam was performed. Findings: Findings indicate that attention has to be paid to appropriate consideration of the environmental effect on reinforced concrete structures. In that, the time-dependent performance of reinforced concrete beam significantly decreases with time due to corrosion of reinforcement steel, creep and shrinkage. Originality/value: However, the Euro code, Ethiopian code and Indian code threat the exposure condition of reinforced concrete by providing corresponding concrete cover that retards the corrosion initiation time but does not eliminate environmental effects. The results of this study clearly indicate that the capacity of reinforced concrete structure degrades with time due to corrosion and creep, whereas the action on the structure due to shrinkage increases. Therefore, appropriate remedial measures have to be taken to control the defects of structures due to the environmental factors to overcome the early failure of the structure. © 2020, Emerald Publishing Limited.Item Time-dependent failure possibility of structures involving epistemic uncertainty(Elsevier Ltd, 2022) Worabo Woju, U.; Balu, A.S.Time-dependent failure possibility (TDFP) is the possibility of performance less than zero under fuzzy uncertainty in the given time interval. Failure possibility of structures gets accelerated by improper consideration of input variables, mathematical and structural models, and environmental factors. To explore the environmental factors in structures, the time-variant creep and shrinkage model for concrete structures, and deterioration of steel cross-section and other material properties due to corrosion, and increment of action on the structure with time are considered. A real-time data has been collected from the city of Addis Ababa, Ethiopia for the case study to substantiate the methodology presented in this paper. In this paper, identification the possible failure modes, estimation of the time-dependent performance of failure modes, generating membership function (MF) of fuzzy input and output variables, and finally, the TDFP evaluated from MF of output quantities. Because of its simplicity and frequent application, triangular MF is used to characterize epistemic uncertainty of parameters. However, the failure possibility analysis is a complex problem for practicing engineering that needs a rigorous procedure, a single-loop optimization method (SLOM) is employed to evaluate TDFP of structures involving epistemic uncertainty. The effectives of SLOM has been checked by adaptive SORM Breitung's algorithm. To enhance the validation of the proposed approach, several examples are thoroughly carried out that indicate the SLOM is bit conservative compared with SORM Breitung's algorithm in such a way that their maximum recorded percentage difference is 9.464%. © 2022 Elsevier Ltd