Dynamic vulnerability assessment and damage prediction of RC columns subjected to severe impulsive loading

Masoud Abedini,Chunwei Zhang 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.77 No.4

Reinforced concrete (RC) columns are crucial in building structures and they are of higher vulnerability to terrorist threat than any other structural elements. Thus it is of great interest and necessity to achieve a comprehensive understanding of the possible responses of RC columns when exposed to high intensive blast loads. The primary objective of this study is to derive analytical formulas to assess vulnerability of RC columns using an advanced numerical modelling approach. This investigation is necessary as the effect of blast loads would be minimal to the RC structure if the explosive charge is located at the safe standoff distance from the main columns in the building and therefore minimizes the chance of disastrous collapse of the RC columns. In the current research, finite element model is developed for RC columns using LS-DYNA program that includes a comprehensive discussion of the material models, element formulation, boundary condition and loading methods. Numerical model is validated to aid in the study of RC column testing against the explosion field test results. Residual capacity of RC column is selected as damage criteria. Intensive investigations using Arbitrary Lagrangian Eulerian (ALE) methodology are then implemented to evaluate the influence of scaled distance, column dimension, concrete and steel reinforcement properties and axial load index on the vulnerability of RC columns. The generated empirical formulae can be used by the designers to predict a damage degree of new column design when consider explosive loads. With an extensive knowledge on the vulnerability assessment of RC structures under blast explosion, advancement to the convention design of structural elements can be achieved to improve the column survivability, while reducing the lethality of explosive attack and in turn providing a safer environment for the public.

Strengthening of the panel zone in steel moment-resisting frames

Abedini, Masoud,Raman, Sudharshan N.,Mutalib, Azrul A.,Akhlaghi, Ebrahim Techno-Press 2019 Advances in computational design Vol.4 No.4

Rehabilitation and retrofitting of structures designed in accordance to standard design codes is an essential practice in structural engineering and design. For steel structures, one of the challenges is to strengthen the panel zone as well as its analysis in moment-resisting frames. In this research, investigations were undertaken to analyze the influence of the panel zone in the response of structural frames through a computational approach using ETABS software. Moment-resisting frames of six stories were studied in supposition of real panel zone, different values of rigid zone factor, different thickness of double plates, and both double plates and rigid zone factor together. The frames were analyzed, designed and validated in accordance to Iranian steel building code. The results of drift values for six stories building models were plotted. After verifying and comparing the results, the findings showed that the rigidity lead to reduction in drifts of frames and also as a result, lower rigidity will be used for high rise building and higher rigidity will be used for low rise building. In frames with story drifts more than the permitted rate, where the frames are considered as the weaker panel zone area, the story drifts can be limited by strengthening the panel zone with double plates. It should be noted that higher thickness of double plates and higher rigidity of panel zone will result in enhancement of the non-linear deformation rates in beam elements. The resulting deformations of the panel zone due to this modification can have significant influence on the elastic and inelastic behavior of the frames.

Residual capacity assessment of post-damaged RC columns exposed to high strain rate loading

Masoud Abedini,Chunwei Zhang 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.3

Residual capacity is defined as the load carrying capacity of an RC column after undergoing severe damage. Evaluation of residual capacity of RC columns is necessary to avoid damage initiation in RC structures. The central aspect of the current research is to propose an empirical formula to estimate the residual capacity of RC columns after undergoing severe damage. This formula facilitates decision making of whether a replacement or a repair of the damaged column is adequate for further use. Available literature mainly focused on the simulation of explosion loads by using simplified pressure time histories to develop residual capacity of RC columns and rarely simulated the actual explosive. Therefore, there is a gap in the literature concerning general relation between blast damage of columns with different explosive loading conditions for a reliable and quick evaluation of column behavior subjected to blast loading. In this paper, the Arbitrary Lagrangian Eulerian (ALE) technique is implemented to simulate high fidelity blast pressure propagations. LS-DYNA software is utilized to solve the finite element (FE) model. The FE model is validated against the practical blast tests, and outcomes are in good agreement with test results. Multivariate linear regression (MLR) method is utilized to derive an analytical formula. The analytical formula predicts the residual capacity of RC columns as functions of structural element parameters. Based on intensive numerical simulation data, it is found that column depth, longitudinal reinforcement ratio, concrete strength and column width have significant effects on the residual axial load carrying capacity of reinforced concrete column under blast loads. Increasing column depth and longitudinal reinforcement ratio that provides better confinement to concrete are very effective in the residual capacity of RC column subjected to blast loads. Data obtained with this study can broaden the knowledge of structural response to blast and improve FE models to simulate the blast performance of concrete structures.

The Effect of Intravenous Paracetamol on Postoperative Pain after Lumbar Discectomy

Mohammad Shimia,Masoud Parish,Naghi Abedini 대한척추외과학회 2014 Asian Spine Journal Vol.8 No.4

Study Design: A randomized, double-blinded controlled trial. Purpose: Postoperative pain relief especially using analgesic drugs with minimal side effects has considerable clinical importance. This study aimed to examine the effect of intravenous paracetamol on pain relief after lumbar discectomy as a major surgery. Overview of Literature: Patients undergoing lumbar discectomy experience a high degree of lumbar pain. Some authors emphasize the use of intravenous paracetamol to improve postoperative pain and increase patients’ satisfaction following this surgery Methods: Fifty-two patients scheduled for lumbar discectomy were randomly allocated into two groups: a group that received intravenous paracetamol (1 g/100 mL normal saline) within the last 20 minutes of surgery as the case group (n=24) and a group that received sodium chloride 0.9% 100 mL as the control group (n=28). Postoperative pain was assessed at 1, 6, 12, 18, and 24 hours after surgery by a visual analogue scale (VAS). The dosage of the administered opioid (morphine), as well as drug-related side effects within the first 24 hours after surgery were also recorded. Results: The mean VAS score was significantly lower in the paracetamol group than the controls for all of the assessed time points. Although the dose of the administered morphine was numerically lower in the paracetamol group, this difference was not statistically significant (5.53±4.49 mL vs. 7.85±4.17 mL). Conclusions: Intravenous paracetamol as a non-opioid analgesic can relieve postoperative pain in patients undergoing lumbar discectomy; however, its use alone may not represent the best regimen for reducing the needed dose of opioids after operation.

Application of Lagrangian approach to generate P-I diagrams for RC columns exposed to extreme dynamic loading

Zhang, Chunwei,Abedini, Masoud Techno-Press 2022 Advances in concrete construction Vol.14 No.3

The interaction between blast load and structures, as well as the interaction among structural members may well affect the structural response and damages. Therefore, it is necessary to analyse more realistic reinforced concrete structures in order to gain an extensive knowledge on the possible structural response under blast load effect. Among all the civilian structures, columns are considered to be the most vulnerable to terrorist threat and hence detailed investigation in the dynamic response of these structures is essential. Therefore, current research examines the effect of blast loads on the reinforced concrete columns via development of Pressure- Impulse (P-I) diagrams. In the finite element analysis, the level of damage on each of the aforementioned RC column will be assessed and the response of the RC columns when subjected to explosive loads will also be identified. Numerical models carried out using LS-DYNA were compared with experimental results. It was shown that the model yields a reliable prediction of damage on all RC columns. Validation study is conducted based on the experimental test to investigate the accuracy of finite element models to represent the behaviour of the models. The blast load application in the current research is determined based on the Lagrangian approach. To develop the designated P-I curves, damage assessment criteria are used based on the residual capacity of column. Intensive investigations are implemented to assess the effect of column dimension, concrete and steel properties and reinforcement ratio on the P-I diagram of RC columns. The produced P-I models can be applied by designers to predict the damage of new columns and to assess existing columns subjected to different blast load conditions.