The effects of beam-column connections on behavior of buckling-restrained braced frames

Mohammad Ali Hadianfard,Fateme Eskandari,Behtash JavidSharifi 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.3

Buckling Restrained Braced (BRB) frames have been widely used as an efficient seismic load resisting system in recent years mostly due to their symmetric and stable hysteretic behavior and significant energy dissipation capacity. In this study, to provide a better understanding of the behavior of BRB frames with various beam-column connections, a numerical study using non-linear finite element (FE) analysis is conducted. All models are implemented in the Abaqus software package following an explicit formulation. Initially, the results of the FE model are verified with experimental data. Then, diverse beam-column connections are modeled for the sake of comparison from the shear capacity, energy dissipation and frame hysteresis behavior points of view until appropriate performance is assessed. The considered connections are divided into three different categories: (1) simple beam-column connections including connection by web angle and connection by seat angle; (2) semi-rigid connection including connection by web and seat angles; and (3) rigid beam-column connections by upper-lower beam plates and beam connections with web and flange splices. Results of the non-linear FE analyses show that these types of beam-column connections have little effect on the maximum story drift and shear capacity of BRB frames. However, the connection type has a significant effect on the amount of energy dissipation and hysteresis behavior of BRB frames. Also, changes in length and thickness of the angles in simple and semi-rigid connections and changes in length and thickness of plates in rigid connections have slight effects (less than 4%) on the overall frame behavior.

Effect of Acupuncture on Pain and Quality of Life in Patients with Lumbar Spinal Stenosis: A Case Series Study

Mohammad J. Hadianfard,Ali Aminlari,Arghavan Daneshian,Ali R. Safarpour 사단법인약침학회 2016 Journal of Acupuncture & Meridian Studies Vol.9 No.4

Lumbar spinal stenosis (LSS) is a major cause of debilitation in adults, and acupuncture is a recommended treatment. We assessed the effect of acupuncture on pain and quality of life in patients with LSS. Twenty-four patients with LSS who had symptoms of neurogenic claudication were randomly selected and underwent 10 sessions of acupuncture. Pain and quality of life were evaluated before and immediately after the intervention and 6 weeks later using a visual analogue scale and Short Form-36 Health Survey. Paired t tests and repeated measure tests were used to analyze the data. The mean age of the patients was 48.2 ± 10.8 years. The mean visual analogue scale scores before and immediately after intervention (7.9 ± 1.3 and 4.3 ± 2.1) were statistically different (p < 0.001), as was the mean score (3.08 ± 2.3) 6 weeks later (p = 0.01). Five aspects of the Short Form-36 Health Survey score were associated with significant improvements immediately after acupuncture (p < 0.05). Comparisons of the scores before and 6 weeks after intervention showed significant improvements in emotions, vitality, general health, bodily pain, and physical well-being. Therefore, acupuncture had a significant short-term effect on pain and quality of life in patients with LSS.

On the effect of steel columns cross sectional properties on the behaviours when subjected to blast loading

Hadianfard, Mohammad Ali,Farahani, Ahmad,B-Jahromi, Ali Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.44 No.4

For buildings subjected to blast loading, structural failure can be categorized into local failure (direct blast effects) and progressive collapse (consequential effects). In direct blast effects, the intensive blast pressures create localized failure of structural elements such as exterior columns and walls. Columns, and their behaviour, play a key role in these situations. Therefore investigating the behaviour of columns under blast loading is very important to estimate the strength, safety and reliability of the whole structure. When a building is subjected to blast loading, it experiences huge loading pressures and undergoes great displacement and plastic behaviour. In order to study the behaviour of an element under blast loading, in addition to elastic properties of materials, plastic and elastic-plastic properties of materials and sections are needed. In this paper, using analytical studies and nonlinear time-history analysis by Ansys software, the effects of shape of column sections and boundary conditions, on behaviour and local failure of steel columns under blast load are studied. This study identifies the importance of elastic-plastic properties of sections and proposes criteria for choosing the best section and boundary conditions for columns to resist blast loading.

Case study on the effects of retrofitting on changing structural dynamic characteristics by microtremor measurements and finite element analysis

Mohammad Ali Hadianfard,Ramin Rabiee,Azad Sarshad 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.55 No.5

Determination of dynamic parameters of a structure such as predominant frequency and damping ratio is one of the most important subjects in dynamics of structures. Different methods are used to determine predominant frequency. These methods are different in the cost, implement accessibility, accuracy, speed, applicability in different conditions, simplicity of calculations and required data accessibility. Calculation of damping ratio by using common experimental procedures is very difficult and costly, then it is assumed as a constant value in most calculations. Microtremor measurements and using spectral ratio method to determine the predominant frequency and damping ratio of structure is of interest in recent years. In this paper, as a case study, the effects of retrofitting on structural dynamic parameters of two four-story buildings by using microtremor measurements and also finite element analysis, is investigated. The results of this study show that microtremor measurements can be utilized to assess the improvement of dynamic behavior of the retrofitted structure and the effectiveness of the method of retrofitting.

On the effect of steel columns cross sectional properties on the behaviours when subjected to blast loading

Mohammad Ali Hadianfard,Ahmad Farahani,Ali B-Jahromi 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.44 No.4

For buildings subjected to blast loading, structural failure can be categorized into local failure (direct blast effects) and progressive collapse (consequential effects). In direct blast effects, the intensive blast pressures create localized failure of structural elements such as exterior columns and walls. Columns, and their behaviour, play a key role in these situations. Therefore investigating the behaviour of columns under blast loading is very important to estimate the strength, safety and reliability of the whole structure. When a building is subjected to blast loading, it experiences huge loading pressures and undergoes great displacement and plastic behaviour. In order to study the behaviour of an element under blast loading, in addition to elastic properties of materials, plastic and elastic-plastic properties of materials and sections are needed. In this paper, using analytical studies and nonlinear time-history analysis by Ansys software, the effects of shape of column sections and boundary conditions, on behaviour and local failure of steel columns under blast load are studied. This study identifies the importance of elastic-plastic properties of sections and proposes criteria for choosing the best section and boundary conditions for columns to resist blast loading.

Inelastic buckling and post-buckling behavior of gusset plate connections

Mohammad Ali Hadianfard,Ali Reza Khakzad 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.2

In this study, by using finite element non-linear static analysis and comparing it with experimental models, the buckling and post-buckling behavior of bracing gusset plates has been investigated. The effects of such parameters as dimension and thickness of the gusset plate and the influence of position of the bracing member on the behavior of gusset plate have been examined. The results of the analyses clearly suggest that capacity, buckling and post-buckling behaviors of gusset plates depend on the position of the bracing splice plate with respect to the free bending line as well as on the size and thickness of the gusset plate. Also, with respect to numerical analysis results, some practical graphs for the calculation of buckling capacity of gusset plate connections are presented. For steel structures, the proposed method is apparently more accurate than available code procedures.

Investigation of welded top and seat angle connections under column removal event

Mohammad Ali Hadianfard,Mahboobe Namjoo,Morteza Boroumand,Sareh Akbarpoor 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.40 No.1

A structure undergoes progressive collapse when a primary structural element fails, leading to damage of either a large part or even the entire structure. Beam-column connections are one of the major contributing structural elements which significantly affect the performance of the structure. Undesirable performance and damage to these connections can result in local failure and, in turn, lead to progressive failure. In the present research, behaviors of some beam-column connections were empirically and numerically assessed subject to column removal scenario. A number of tests were performed on some welded top and seat angle connections. Then, numerical models were created and validated by the experimental results. It was observed that the results of finite element analyses very well correspond to the test results. Moreover, parametric studies were done using finite element analysis. Behavior, failure limit states, and formation of the catenary action were investigated. Results demonstrate that adding a web plate or a web angle could be an appropriate method for upgrading the connection behavior. Furthermore, an increase in the angle thickness and length of the angle leg attached to the column can result in higher resistance to progressive collapse.