Cyclic behavior of SMA slip friction damper

Shape memory alloys (SMAs) gained increasing attentions from the perspective of seismic protection, primarily because of their excellent superelasticity, satisfactory damping and high fatigue life. However, the superelastic strain of SMAs has an upper limit, beyond which the material completes the austenite to martensite phase transformation and is followed by noticeable strain hardening. The strain hardening behavior would not only induce high force demand to the protected structures, but also cause unrecoverable deformation. More importantly, the SMAs may fracture if the deformation demand exceeds their capacity under severe earthquakes. In the case of installing SMA braces (SMABs) in the multi-story concentrically braced frames (CBFs), the material failure would lead to the malfunction of SMABs and this further causes building collapse. The friction mechanism could behave as a “fuse” through capping the strength demand at a constant level. Therefore, this paper suggests connecting the SMAB with a friction damper to achieve a novel brace, i.e. the SMA-friction damping brace (SMAFDB). A proof-of-concept test was carried out on a homemade specimen and the test results validated the novel brace behaves in a desirable manner. In addition, to explore the seismic response characteristics of the SMAFDB within structures, a six-story CBF equipped with SMAFDBs was designed and compared against those incorporated with SMABs or friction damping braces (FDBs) at the frequently occurred earthquake (FOE), design basis earthquake (DBE) and maximum considered earthquake (MCE). The comparative results show the SMAFDB is superior to the counterparts. Under the FOE and DBE ground motions, the SMAFDBs successfully eliminated residual deformations as the SMABs do, and achieved identical maximum interstory drift as the FDBs. Under the MCE ground motions, the SMAFDBs not only well addressed the brace failure problem that was possibly encountered in the SMABs, but also better controlled residual deformation than the FDBs.

Download Full-text

Cyclic behavior of beams rehabilitated by reinforced concrete layers

Structural Concrete ◽

10.1002/suco.202000296 ◽

2021 ◽

Author(s):

Sabahattin Aykaç ◽

Eray Özbek ◽

Ali Tugrul Tankut

Keyword(s):

Reinforced Concrete ◽

Cyclic Behavior

Download Full-text

An enhanced damage plasticity model for predicting the cyclic behavior of plain concrete under multiaxial loading conditions

Frontiers of Structural and Civil Engineering ◽

10.1007/s11709-020-0675-7 ◽

2021 ◽

Author(s):

Mohammad Reza Azadi Kakavand ◽

Ertugrul Taciroglu

Keyword(s):

Uniaxial Tension ◽

Damage Mechanics ◽

Plain Concrete ◽

Cyclic Behavior ◽

Plasticity Model ◽

Multiaxial Loading ◽

Loading Conditions ◽

Confined Compression ◽

Concrete Damage ◽

Concrete Damage Plasticity

AbstractSome of the current concrete damage plasticity models in the literature employ a single damage variable for both the tension and compression regimes, while a few more advanced models employ two damage variables. Models with a single variable have an inherent difficulty in accounting for the damage accrued due to tensile and compressive actions in appropriately different manners, and their mutual dependencies. In the current models that adopt two damage variables, the independence of these damage variables during cyclic loading results in the failure to capture the effects of tensile damage on the compressive behavior of concrete and vice-versa. This study presents a cyclic model established by extending an existing monotonic constitutive model. The model describes the cyclic behavior of concrete under multiaxial loading conditions and considers the influence of tensile/compressive damage on the compressive/tensile response. The proposed model, dubbed the enhanced concrete damage plasticity model (ECDPM), is an extension of an existing model that combines the theories of classical plasticity and continuum damage mechanics. Unlike most prior studies on models in the same category, the performance of the proposed ECDPM is evaluated using experimental data on concrete specimens at the material level obtained under cyclic multiaxial loading conditions including uniaxial tension and confined compression. The performance of the model is observed to be satisfactory. Furthermore, the superiority of ECDPM over three previously proposed constitutive models is demonstrated through comparisons with the results of a uniaxial tension-compression test and a virtual test.

Download Full-text