Search

Axial forces are generated in the plates of ADAS-yielding dampers when subjected to lateral loading due to their boundary conditions. This on one hand can lead to an increase in strain level of the plates and accelerate the damage process, while on the other hand, the interaction of the bending moment with the tensile axial force leads to increasing strength, which is undesirable in the performance of ductile members. In this paper, a modified ADAS device (MADAS) is introduced to prevent undesirable interaction of axial forces, and its cyclic behavior is evaluated both experimentally and numerically. To this end, in the first step, two test specimens with different number of connection pins were prepared and subjected to cyclic loading in a rigid frame. Experimental and numerical results have shown that due to the removal of the constraint in the vertical direction, the level of forces produced by the damper is almost constant and the X-shaped plates have been able to tolerate significant number of cycles before crack initiation. Afterwards, the cyclic performance of ADAS and MADAS dampers was numerically compared individually and also when placed in the frame. Furthermore, in the frame equipped with ADAS damper, the increase in the level of forces produced by the damper led to the buckling of the braces, while the level of generated forces was totally in the expected range in the frame equipped with MADAS damper. [ABSTRACT FROM AUTHOR]

A variety of yielding dampers have been proposed with different materials and configurations and constructed for various structures to improve their seismic performance. ADAS dampers are considered as energy dissipation tools to experience uniform yielding according to their specific geometry. However, the damper cannot perform ideally in large deformations due to an unexpected tensile axial force. This axial force not only creates strain localization at the middle of X-shape plates but also with an unexpected increase in the level of damper force can impose damage to main members. This paper proposes a modified ADAS damper with a shape similar to ADAS dampers and boundary conditions similar to TADAS dampers. Given the geometry of the proposed damper, the generated axial force reaches the bracings through side plates instead of triangular plates, improving the operation of the damper. In order to design a suitable damper, an equation is suggested to determine the maximum shear stress by modeling the damper using the Abaqus program and parametric study. Other findings include the evaluation of the monotonic, hysteretic, and seismic performance of this damper. On one hand, the results show that the increase in force level in the nonlinear range is about 30% for MADAS damper, while it exceeds 150% for ADAS dampers. On the other hand, the maximum equivalent plastic strain in ADAS is twice that in the MADAS. In addition, the evaluations of monotonic, cyclic, and dynamic behaviors indicate that MADAS dampers have great energy dissipation in large deformations. [ABSTRACT FROM AUTHOR]

Several advantages of yielding dampers in controlling seismic energy have attracted the attention of many researchers in designing new buildings and retrofitting existing structures. In recent decades, various shapes and substances of such dampers have been used in engineering structures and their behavioral features, including the energy dissipating capacities, have been assessed. In this article, a novel method is presented to obtain the design relationship of two types of yielding elliptical dampers in terms of their selected geometric properties, i.e. distance between the shear diaphragms or virtual diameter and thickness. In addition, two different ellipticalshaped steel dampers equipped with the shear diaphragms are proposed and modeled using the finite element software ABAQUS and their performances are investigated. Then, 30 and 25 models, respectively, of the first and second types are studied using pushover analysis. The designed dampers considering the proposed relationships are used in two chevron braced steel frames placed between the bracing and the beam. Due to their desirable efficiency in energy dissipation and increase in the equivalent viscous damping of the frame, better efficiency is achieved in the modified damper with easier fabrication. [ABSTRACT FROM AUTHOR]

• Introducing a kind of all steel BRB consisting of two parallel cores. • Evaluating Ultra Low Cycle Fatigue Based on Ductile Fracture Model. • Modify Rice and Tracy's model to predict Ultra Low Cycle Fatigue. • The advantages of dual core BRB include the easy connection and high stability. While lots of efforts have been made to develop accurate numerical models for prediction of ultra-low cycle fatigue (ULCF), it still needs more studies. As it is crucial to exactly define the mechanical behavior of steel for entire range up to failure, this study first examines the required theories and presents a simple single-parameter model to predict the crack initiation. After selecting appropriate behavior models, to ensure the proper performance in numerical solution of the problem, the cyclic performance of steel coupons and two types of buckling restrained braces (BRBs) are validated comparing their local and global behaviors to experimental ones. The double core BRB consisting of two parallel steel cores is then introduced and its cyclic behavior is evaluated. Its advantages include easy connection to gusset plates, increased brace moment of inertia around the weak axis, high stability of connections under local buckling, and low impact of unpredictable defects. Finally, hysteresis curves, energy absorption rate, crack initiation and evolution, and cumulative ductility are discussed in this research. [ABSTRACT FROM AUTHOR]