Seismic Behavior of Steel Frames Equipped with Comb-Teeth Metallic Yielding Dampers

S. Garivani,A. A. Aghakouchak,S. Shahbeyk 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.4

Comb-teeth damper (CTD), is a new type of metallic yielding damper, which is made of steel plates and includes a number of teeth that dissipate energy through in-plane fl exural yielding. The behavior of individual samples of CTD have been previously studied numerically and experimentally and it has been shown that this damper has excellent energy dissipating capacity and large ductility ratio. In this paper, application of this type of damper to steel frames is studied. Sample steel frames are constructed and equipped with CTDs and tested under cyclic loading. The results show that these dampers can serve their intended duties and dissipate considerable amount of energy. Numerical modelling of the frames confi rms the experimental results and shows that by correct proportioning of the members, frame members i.e. beams, columns and braces remain elastic during lateral loading. This allows using the CTDs as a replaceable energy dissipating device. Finally CTDs are included in a reference frame and their eff ects on reducing seismic demand are studied using non-linear time history analysis. The results show that by using a smaller volume of steel in CTD dampers compared to traditional TADAS, the same level of response reduction may be achieved, while utilizing economic advantage of this type of damper.

Parametric study on probabilistic local seismic demand of IBBC connection using finite element reliability method

Mohammad Taherinasab,Ali A. Aghakouchak 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.37 No.2

This paper aims to probabilistically evaluate performance of two types of I beam to box column (IBBC) connection. With the objective of considering the variability of seismic loading demand, statistical features of the inter-story drift ratio corresponding to the second, fifth and eleventh story of a 12-story steel special moment resisting frames are extracted through incremental dynamic analysis at global collapse state. Variability of geometrical variables and material strength are also taken into account. All of these random variables are exported as inputs to a probabilistic finite element model which simulates the connection. At the end, cumulative distribution functions of local seismic demand for each component of each connection are provided using histogram sampling. Through a parametric study on probabilistic local seismic demand, the influence of some geometrical random variables on the performance of IBBC connections is demonstrated. Furthermore, the probabilistic study revealed that IBBC connection with widened flange has a better performance than the un-widened flange. Also, a design procedure is proposed for WF connections to achieve a same connection performance in different stories.

NUMERICAL INVESTIGATION OF HYDRODYNAMIC FORCE ON OUTLET GATES

AGHAKOUCHAK A.,KAVIANPOUR M.R.,SADEGHI H.R. 한국수자원학회 2005 한국수자원학회 학술대회 Vol.2005 No.1

Numerical Analysis of the Nonlinear Performance of Concentrically Braced Frames Under Cyclic Loading

M. Alipour,A. A. Aghakouchak 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.3

Concentrically braced frames (CBFs) are widely used as lateral-load resisting system in steel structures. This study examines the effects of different parameters especially those associated with connections, on the behavior of CBFs. A single bay, singlestory frame is used to evaluate the interaction between structural members. Nonlinear analyses using a detailed inelastic finiteelement model (FEM) are carried out to study the behavior of frames subjected to cyclic loading. Models are designed based on seismic codes and analyzed to evaluate the performance of both SCBFs and OCBFs. The equivalent plastic strain concept is used to determine the ductility capacity and to predict fracture and failure in these models. Results show that the seismic performance of CBFs, which are designed according to current provisions can be improved by configuring the details of gusset plate connections in a way that inelastic demands are balanced in middle of brace and gusset plate corners.

Numerical and Experimental Study of Comb-Teeth Metallic Yielding Dampers

S. Garivani,A. A. Aghakouchak,S. Shahbeyk 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.1

In this paper, a new type of metallic yielding damper called comb-teeth damper, CTD, is introduced. CTD is made of steel plates and includes a number of teeth that dissipate energy through in-plane flexural yielding. An optimum geometry of teeth is suggested, which assures uniform distribution of stress along them and prevents strain localization. Finite element modeling is used to verify the design of proposed damper and to study nonlinear behavior of the damper subjected to monotonic as well as cyclic loading. Three full scale specimens have also been made and tested under cyclic loading. In order to restrict out-ofplane buckling of damper teeth, a special clamp has been designed. A numerical study has elaborated the effects of these clamps in comparison to increasing the thickness of individual tooth. The tested samples have tolerated considerable cumulative displacement in their hysteresis cycles without any significant loss of strength.

Cyclic Behavior of Concentrically Braced Frames with Built-Up Braces Composed of Channel Sections

M. Nader Naderpour,Ali. A Aghakouchak,Amin Izadi 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.4

Concentrically braced frames are earthquake resistant systems commonly used in buildings. Seismic behavior of this type of structures is affected by their configurations, brace properties, and brace to gusset plate connections. In this paper, the results of three experiments conducted to investigate the cyclic behavior of concentrically braced frames with braces built-up of double channels are reported. Significant damage was observed in beam to column connections. Large out of plane deformation of braces caused some cracks in the connector welds; however they did not result in fracture. Although large drift was applied to the frames, no brace fracture was observed. Furthermore, experiments showed that the majority of compressive strength in post-buckling state and a noticeable portion of tensile strength originated from frame action. By choosing connector spacing as the main parameter and using finite element models, a parametric study was performed to investigate the effect of this parameter on this type of frames with two different details of brace to gusset plate connections. It is observed that reducing the connector spacing increases the inelastic strain demand in braces and decreases it in gusset plates. However, gusset plates, which accommodate 2t linear clearance, are less dependent on connector spacing, compared to those accommodating 6t elliptical clearance. It seems that the limitations of slenderness ratio of individual section, stipulated in current seismic provisions, need further study.

Experimental Investigation of Steel Frames Braced with Symmetrical Pairs of y-shaped Concentric Bracings

Sohail Majid Zamani,Abolhassan Vafaei,A. A. Aghakouchak,Chandrakant Desai 한국강구조학회 2011 International Journal of Steel Structures Vol.11 No.2

Concentric bracings composed of three members arranged in y shaped geometry have been traditionally used to provide openings in braced bays. However, simultanous occurance of compression in three braces leads to instability and out of plane buckling of braces accompanied by low hysteretic energy absorption. In order to study the behavior of y-braced frames, a research program including experimental tests was conducted at BHRC† structural engineering laboratory. Quasi-static cyclic loading was applied to specimens including four full-scale two-bay frames with y-bracings of different cross sections and connection types.The bays are braced symmetrically to have a combination of tensile and compressive braces at all loading stages. The results show that out-of-plane buckling with single curvature in braces can be substituted by in plane, double curvature buckling through appropriate detailing of cross sections and connections.Thus, hysteretic energy dissipation of ybracing is remarkably improved due to spreading of plastic strains in braces. In this paper, seismic performance of y-braced frame specimens and a reference X-braced frame are also assessed by capacity spectrum method.

Evaluation of seismic criteria of built-up special concentrically braced frames

Amin Izadi,Ali. A Aghakouchak 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.29 No.1

In this paper, seismic provisions related to built-up special concentrically braced frames (BSCBFs) are investigated under cyclic loading using non-linear finite element analysis of a single-bay single-story frame. These braces, which contain double angle and double channel brace sections, are considered in two types of single diagonal and X-braced frames. The results of this study show that current seismic provisions such as observing the 0.4 ratio for slenderness ratio of individual elements between stitch connectors are conservative in BSCBFs, and can be increased according to the type of braces. Furthermore, such increments will lead to decreasing or remaining the current middle protected zone requirements of each BSCBFs. Failure results of BSCBFs, which are related to the plastic equivalent strain growth of members and ductility capacity of the models, show that the behaviors of double channel back-to-back diagonal braces are more desirable than those of similar face-to-face ones. Also, for double angle diagonal braces, results show that the failure of back-to-back BSCBFs occurs faster in comparison with face-toface similar braces. In X-braced frames, cyclic and failure behaviors of built-up face-to-face models are more desirable than similar back-to-back braces in general.