جستجوی مقالات مرتبط با کلیدواژه « hysteresis curve » در نشریات گروه « عمران »

In the present paper, the retrofitting of welded moment connections with welded flange plate (WFP) in Double-I built-up columns with overall cover plate is discussed by presenting the design method and retrofitting details. The problems of above-mentioned connection include the unfavorable quality of groove weld with full penetration at the connection of the flange plate and the column cover plate, or in worse conditions, using one-sided fillet weld with insufficient strength, the out-of-plane buckle of the column cover plate at the level of the beam-to-column connection, and as a result, its inappropriate seismic performance and its partially restrained behavior. Thus, it was tried to evaluate the advantages of strengthening this defective connection with the help of T- stiffeners using analytical and experimental studies. For this purpose, the experimental test and the finite elements model were made based on the proposed design method, and its cyclical behavior, rupture potential of weld connection, and failure mode under cyclical load were compared with the defective sample. The results indicated that the proposed design, while being classified in the group of fully restrained connections, has the necessary strength and ductility to accept the conditions of the special moment-resisting frame according to the AISC. By performing a sensitivity analysis on the T- stiffener by changing its dimensions and examining the damage indices, the accuracy of the proposed design method was proved. The examinations indicated that the aforementioned retrofitting method is a proper method for the introduced defective connection.

By examining the results related to the Northridge earthquakes in 1994 and other destructive earthquakes, it was observed that strengthening the structural members and increasing the length of the welding line of beam-to-column connections in steel structures did not have a suitable seismic performance. After that, to prevent the brittle failure of the connections, the way of forming the plastic joint outside the connection area was investigated and beams with a reduced cross-section were proposed. But less attention has been paid to the use of absorbers in bending frames. The proposed pin-fuse connection, (pin-fuse SBC), is one of the connections that can absorb the incoming forces near the connection through sliding and friction. When an earthquake occurs, the pin-fuses acts through the rotational sliding of the steel surfaces towards each other, the presence of friction between the fuse plates will cause the consumption of the earthquake energy. Frames equipped with pin-fuses, this frame has the ability to absorb high energy through said fuses, it can be used in areas with strong seismic activity. In the model proposed in this research, the intended connection of a real joint near the beam-to-column connection is designed with bean-shaped holes that can rotate and move after reaching an anchorage lower than the connection moment. Therefore, the experimental results of the proposed model under cyclic loads have been investigated and compared with the numerical results of finite elements. These results show that the pin fuse connection after reaching the required limit and due to the removal of the contribution of the web from the bending resistance and the absence of torsional buckling in the beam web and by creating a safe fuse away from the connection of the beam and the column, in addition to the resistance of the fuse pin connection and plasticity has increased by 11% and 6%, respectively, it has been able to reach a relative displacement of up to 9%, which is more than the regulation limit in special bending frames.

In this study, hysteresis behavior and energy absorption rate of steel shear walls in reinforced sheets CFRP, GFRP and the effect of grooves with different patterns under cycling have analyzed using the finite element method. For this purpose, the accuracy of the responses obtained from the software is compared with the experimental model. Sensitivity analysis is then performed on the dimensions and types of elements used in the analysis. All models are subjected to cyclic loading in according with ATC-24 code. After simulating each of the models in the ABACUS, the results of analysis include shear capacity, energy absorption and the maximum of these parameters were evaluated during the analysis of the models and compared with each other. The best model also in two parts of reinforcement and groove, under four different earthquakes, behavior seismic has been studied. The results show that the reinforced polymer sheets on the shear wall have a direct effect on the seismic performance and the pattern of stress distribution is directly related to how grooves. Also among the models, the use of CFRP with horizontal alignment has the best seismic performance.Key words: Steel shear wall, Reinforced polymer sheets, Energy absorption, Hysteresis curve, Performance improvement

In this study, a novel hybrid self-centering system is introduced. This system consists of self-centering systems and Pall friction dampers. The design methodology of hybrid self-centering systems is developed and some examples of the designed hybrid self-centering are presented. Hybrid self-centering systems not only have the capability of dissipating energy but can also remove or arrange residual drifts of structures. In fact, hybrid self-centering systems can maintain design target residual drifts (zero or any) during lateral loading similar to the pure self-centering system and have the benefits of high capacity energy dissipation of Pall friction dampers. The hybrid self-centering system is developed for seismic resilience in terms of economic benefits, ready-to-use after the earthquake event, and practical fabrication. To evaluate the proposed design method, different low- to high-rise (3-, 6-, 9- and 12-story) buildings are selected from the literature, redesigned based on the proposed method, and then subjected to cyclic loading. Results are presented in terms of the cyclic response, residual drift and energy dissipation capacity of structures. Results indicate that the proposed design equations precisely meet the target structural performance (target residual drift) of the hybrid self-centering system and this system is obviously a superior system compared to the pure self-centering or Pall system.

Rotational friction dampers are a specific type of friction dampers which have several advantages. Dampers are used to improve the cyclic behavior of structures against forces caused by wind and earthquake. These types of dampers will cause energy dissipation by its rotating and rerotating. However, complete and comprehensive researches have not been performed on the effect of rotational friction dampers and their effect on the bearing capacity of steel frames. In this research, the behavior of concrete-filled steel tube (CFT)  in two cases frame braced with rotational friction dampers and frame braced without rotational friction dampers is investigated. For verification, the results obtained from finite element method software, ABAQUS, were compared with that of experimental studies for test samples used in a building with a height of 300m in Osaka, Japan. The hysteresis curves of the modeled samples are in good agreement with the experimental results. In order to investigate the performance of steel composite frame (with CFTs) braced with rotational friction dampers towards to steel composite frame (with CFTs) braced without rotational friction dampers  under the effect of three earthquake Far-field records, the structure was modeled, designed and analyzed in ETABS software. The use of bracing with rotational friction dampers has caused a decrease in the displacement of the roof’s center of mass for each record mentioned above which modeled in ETABS software. It decreased by 13 to 49 % for 9 records and increased by 2 to 17 % for 2 records. The use of bracing along with rotational friction damper modeled in ABAQUS software under the effect of each record has caused a decrease in base shear. The extent of these reductions was different for each record mentioned above. In each record modeled in ETABS software, the base shear of the structure has not reduced similarly; however, in some cases, the base shear has increased. It had a decrease of 11 to 37% for 7 records and an increase of 3 to 26% for 4 records.  Then a Single-storey frame with single-span With the same materials and specifications introduced in ETABS software in ABAQUS software Has been modeled. For lateral loading of columns, the lateral loading protocol based on ATC-24 and the instructions for using dampers in the design and reinforcement of buildings have been used.  According to Regulation No. 766 of the Program and Budget Organization, the loading cycles introduced in ETABS software with a frequency of 1.15T have been used in the ABAQUS Limited Components Software to move. The use of rotary braces and crankshafts in the ABAQUS limited component software under the influence of each of the discussed records has reduced the displacement of the structure relative to the structure without braces and without rotational friction dampers of the structure mentioned above was exerted under the record effect of the same earthquake in ABAQUS software The use of bracing along with rotational friction damper modeled in ABAQUS software under the effect of each record has caused a decrease in base shear. The amount of energy reduction for records understudy was not equal and varied from 8% to 34.7%. The hysteresis curves of base shear of braced structures with and without dampers are well presented.

The Buckling Restrained Brace (BRB) is a type of high energy dissipation damper. The damper includes a thin steel core, a concrete cover designed to maintain the steel core and prevent it from buckling under axial compression, and a middle layer that prevents unwanted interactions between the steel brace core and the concrete sheath. Braced frames that use the BRB are known as buckling restrained braced frames, which have many advantages over conventional braced frames. In this study, the effect of geometric shape and number of holes on the core of the buckling restrained brace has been investigated by numerical simulation with finite element method. Six brace core types with rectangular and circular shaped with equal area with and without holes. The holes are placed one, three and five with full details in ABAQUS software and results in terms of failure modes, severity of damage and Hysteresis curve have been studied. To verify the modeling method and assumptions, an experimental sample is verified. The results of this study indicate the significant effect of more holes and the use of circular rather than rectangular holes on the cyclic performance of buckling restrained brace.

In this study, the effect of steel damper with vertical slits on chevron braced frames with the number of different stories is investigated and pushover and cyclic analyses are performed . To evaluate and compare the results, a parametric study is carried out on a steel damper with and without slit. Eight model frames such as a single-story in ordinary moment frame, braced frame, chevron braced frame with gusset plate, chevron braced frame equipped by a damper with vertical slits, chevron braced frame with silt damper and three-story chevron braced frame equipped by a damper with vertical slits, five-story chevron braced frame equipped by a damper with vertical slits, eight-story chevron braced frame equipped by damper with vertical slits are modeled and analyzed by finite element method in Abaqus software. The results showed that the braced frame equipped by a damper with vertical slits by its ductile behavior, dissipated a large amount of earthquake input energy and reduced the base shear. The hysteresis curves were stable and without any loss, indicating high energy absorption by chevron braced frame equipped by a damper with vertical slits. In all the chevron braced frame equipped by a damper with vertical slits, the plastic hinges are not formed in the members of structures, and the failure mechanism is concentrated in the damper. The damper with vertical slits reduced the elastic stiffness, secondary stiffness and carrying capacity, which in addition to controlling the drift of the structure, increased the energy absorption capability. The chevron braced frame equipped by a damper with vertical slits had more ductility than other specimens, and according to the results, damper with vertical slits had good seismic performance.

Steel plate shear walls (SPSWs) have been considered as a lateral resisting system in recent years. The reasons for openings in SPSWs include architectural requirements and non-structural considerations, e.g. passing installation systems. The present study analyzed twelve SPSWs with a circular opening by considering cross stiffeners with and without openings. To this end, cross stiffener-reinforced SPSWs with openings were studied. To validate the finite element (FE) modeling results, they were compared to those of an experimental model. It was concluded that a large thickness and reinforcement of an SPSW enhanced its strength and stiffness, but reduced its out-of-plane buckling. The results revealed that a cross stiffener had a large contribution to the enhancement of the shear capacity and stiffness of the system. Moreover, cross stiffener reinforcement was observed to have a proper performance in controlling out-of-plane displacements and stress distribution in the wall filler plate.

Buckling Restrained Braces are typically made of a steel core that is encased in a steel sheath filled with concrete. The steel core is designed based on axial strength with the potential for compressive and tensile yields, regardless of fracture, and provides steel and concrete sheaths of sufficient axial and flexural strength to prevent overall buckling of the braces. In this study, the effect of geometric shape and steel material of connection plate on cyclic performance of buckling restrained brace is investigated using finite element simulation. 6 types of rectangular and curved connection plates are modeled ST37 and ST52 with and without holes in with finite element ABAQUS software and the results are presented in the form of damage modes and the force-displacement hysteresis curves are studied and compared. In this study, in order to confirm the modeling method and used assumptions, an experimental specimen buckling restrained brace is tested in finite element ABAQUS software. The results of this study indicate the considerable effect of geometric shape of the connection plate and its steel material on the cyclic performance of frames with buckling restrained braces.

During the recent past decade, semi-supported steel shearwalls (SSSW) have been introduced as an alternative tothe traditional type of steel plate shear walls (SPSW).In this system, the shear wall does not connect directlyto the main columns of the building frame, instead, itis connected to a pair of secondary columns that do notcarry gravity loads. However, a SSSW system, comparedto the corresponding SPSW system in which thein ll plate is connected to the main frame columns, has alower span width (or lower in ll plate width) and, thus,lower strength, stiness,energy dissipation capability.To oset these eects, one eective,practical approachis the use of ber-reinforced-polymers (GFRPs)for strengthening the steel in ll plate. GFRP laminatescan be easily attached to one or both sides of the in llplates by the use of adhesive. In this paper, the behaviorof semi-supported steel shear walls reinforced byglass- ber-reinforced-polymers (GFRPs) is studied usingthe nite-element method,compared with thecorresponding systems without the reinforcement. Anumber of semi-supported steel shear walls with differentplate aspect ratios, plate thicknesses, secondarycolumn pro les,with,without opening of varioussizes is considered for this research. Both pushoverand cyclic analyses are performed. The adequacy ofthe nite-element modeling approach for representingthe pushover,cyclic responses of SPSWs is veri edthrough comparisons with experimental results. Resultsshow that the use of GFRP laminates, especially for thesystem with thinner in ll plate thickness, can signi -cantly increase the system strength, initial stiness, andenergy dissipation, while it partially decreases the systemductility. In turn, the improvement of the systemstrength,energy dissipation capability is mainly dueto the improvement of the SSSW in ll plate behavior. Infact, the use of GFRP laminates does not aect much thehysteresis,pushover behavior of the SSSW frames.

Due to disadvantages of seismic behavior in conventional braces in term of low plasticity and asymmetric hysteresis curve in tension and compression and pinching which reduces the energy dissipation rate, Buckling Restrained Braces (BRBs) have been proposed as a new generation of bracing system. This paper examines specific type of these braces with steel core and concrete sheath. The effects of core distancefrom confining concrete of these braces haven been discussed using Finite element analysis method. The results show that buckling mode and energy absorption of this system have largely depend on the distance, and 2 to 4 mm distance causes the most energy dissipation.

This paper investigates the impressions of gypsum panel and fiber cement board sheathing on seismic performance of CFS stud walls. For this purpose, five 3600 in 3000 millimeter (length in height) specimens which three of them were strapped diagonally have been tested under cyclic loading. The hysteresis diagram, failure modes and ductility coefficient, were extracted for each specimen and compared. The experiments showed the nonstructural sheathing boards such as gypsum panel and fiber cement cladding would improve the lateral performance of the CFS walls – with or without the strap brace – by 40 percent in average.