Search

This study proposes a novel hybrid self-centering brace (HSB) with structural and nonstructural damage-control capabilities for the seismic resilience of building structures. NiTi-based shape memory alloy (SMA) U-shaped dampers and frequency-dependent viscoelastic dampers are included in HSBs to provide self-centering capacity for avoiding structural damage and velocity-proportional damping for nonstructural damage control, respectively. This study includes two major parts, i.e. component-level mechanical behaviour and system-level dynamic response evaluation of HSBs. The working principle and desired nonlinear behaviour of the HSB were first presented. Then, the preliminary design procedures were developed. After validating the efficiency of the modelling of SMA U-shaped and viscoelastic dampers using prior test results, comprehensive 3D finite element model simulations were performed to study the hysteretic responses of HSBs under cyclic loadings, where the influences of loading frequency, loading amplitude and viscoelastic damper's contribution were considered. Analysis results demonstrated that the designed HSB can attain the desired deformation mechanism and nonlinear hysteretic behaviour during dynamic cyclic loadings. Higher loading frequency and amplitude and more contributions of the viscoelastic damper can introduce higher loading and energy-dissipation capacity. Subsequent dynamic analyses of the single-degree-of-freedom systems were conducted to assess the dynamic performance and advantages of HSBs. Results showed that compared with traditional self-centering systems without velocity-proportional damping, the systems with HSBs can achieve zero residual deformations, lower base shear demands and smaller absolute acceleration responses, confirming the promising potential of HSBs in developing seismic resilient building structures by reducing structural and nonstructural damage. • A novel hybrid self-centering brace (HSB) with structural and nonstructural damage-control capabilities was proposed. • Preliminary design procedure for HSBs was proposed and validated. • Comprehensive parametric numerical simulations were conducted to investigate the mechanical behavior of HSBs under dynamic loadings. • HSBs have the unique capacities to simultaneously reduce maximum deformations, residual deformations, and accelerations. [ABSTRACT FROM AUTHOR]

This paper discusses the yielding mode of a beam-column joint and proposes a mode classification system. The yielding mode can be classified into six categories, including panel yielding, panel yielding dominated, beam yielding, beam yielding dominated, column yielding, and column yielding dominated. The mode can be determined by the column-to-panel strength ratio and the beam-to-panel strength ratio. Four beam-column joint specimens composed of wide-flange beams and square tube columns were tested. Two specimens were subjected to a high axial force, and the other two were not. The specimens were originally designed with various yielding modes. However, due to the unexpected high yield strength of the steel, the calculated strength ratio indicated that all specimens would exhibit the panel yielding dominated mode. Experimental results showed that the panels of all specimens dissipated the most energy, which is consistent with the characteristics of the panel yielding dominated mode. Despite exhibiting this mode, specimens that were subjected to high axial forces eventually failed by local buckling of the column. Moreover, one of the beam-column joint specimens developed severe column-to-diaphragm weld fractures, although the column had very small rotation. Finite element (FE) analysis was conducted on a series of beam-column joints with various strength ratios and a typical plane steel moment frame, and this approach also verified the concept of yielding mode classification. The FE analysis results indicated that the unexpected column-to-diaphragm weld fracture in one specimen resulted from the out-of-plane deformation of the extended diaphragm. • The yielding mode classification of beam-column joints composed of wide-flange beam and square tube column is proposed. • Experiment and finite element analysis were conducted to verify the concept of yielding mode classification. • The effect of high axial force on beam-column joints was examined by experiment and finite element analysis. • The reason why severe column-to-diaphragm weld fracture occurred when column only had small rotation was investigated. [ABSTRACT FROM AUTHOR]

Highlights • Ductility demand of bilinear hysteretic system with high post-yield stiffness ratio. • Ductility demand spectra computed using 742 earthquake records. • Highly accurate probabilistic ductility demand model for dual-systems. • Step-by-step structural design process based on the ductility demand model. • Illustration of the probabilistic ductility demand model and the design process via a BRBF example. Abstract A structure designed in a dual-system configuration can help to achieve a damage-control and an earthquake-resilient property. In a dual-system, the primary structural system (PSS) and the replaceable fuse act in parallel, and the entire structure exhibits a multi-stage yielding mechanism under earthquake actions. To ensure the PSS keeps elastic, the dual-system is required to have a sufficient first-yielding stage wherein the fuse yields to dissipate the input energy. Accordingly, prediction of the structural ductility demand (μ) associated with the first-yielding stage is an important issue. In the first-yielding stage, the PSS remains elastic, making the post-yield stiffness ratio (α) much larger than conventional structures. This paper focuses on the ductility demand of bilinear hysteretic systems embedded with the high- α characteristic, which represent the dual-systems behaving within the elastic and the first-yielding stages. A total number of 742 strong earthquake records (490 of them are from stiff soil according to the standard of ASCE/SEI 7-10) are adopted to compute the ductility demand of 19,200 bilinear single-degree-of-freedom hysteretic systems. These systems have different combinations of strength levels (strength reduction factor 1.25 ≤ R ≤ 5.00), post-yield stiffness ratios (0.05 ≤ α ≤ 0.80) and natural periods (0.05 s ≤ T ≤ 5.00 s). It is revealed that for α ≥ 0.30, a larger α would lead to a slightly increased μ. Therefore, improving the value of α would not alleviate the expected inelastic displacement demand associated with the first-yielding stage for a dual-system, even though a larger α could remarkably reduce the dispersion of μ. A probabilistic spectral model for μ is developed, based on which the seismic performance of a dual-system could be checked in a statistic way. A trial-and-error design process for dual-systems is given, and the design-check process of a five-story buckling-restrained-braced frame is illustrated using the spectral model of μ. This study provides instructive results for the seismic design and retrofitting of dual-systems, as the effects of α , R and T on the values of μ for dual-systems are quantified appropriately. [ABSTRACT FROM AUTHOR]

This paper presented unidirectional and bidirectional cyclic loading test results of a novel steel rocking column base. Feasibility of the column base in steel moment-resisting frames was verified through nonlinear static and time history analysis. It was found that the column base was capable of dissipating seismic energy through plastic bending deformation of the replaceable cover plates and flag-shaped hysteretic curves can be observed. Nevertheless, it is not expected to provide much energy dissipation for the whole structural system, since the plastic bending deformation of each cover plate is only in one direction. A three-dimensional simplified numerical model of the column base was developed and validated against the test results. Following that, nonlinear static and time-history analysis were conducted on prototype steel moment-resisting frames with and without the rocking column bases. In general, replacing some column bases with the rocking ones (i.e., 4/24 of all in this study) did not cause much reduction in lateral resisting stiffness and capacity. Moreover, this reduction was even slighter when the loading direction was perpendicular to the weak axis of the rocking column section. On the other hand, replacing all fixed column base with the proposed rocking column base may cause drift concentration in the ground storey, which is too radical for the prototype building. The seismic responses of modified frames were generally very close to that of the original frame with all fixed column bases. Even though the maximum drifts in the ground storey of these frames were larger than that of the original frames with fixed bases, the maximum drifts of the whole structures were not expected to be amplified. • Bidirectional cyclic loading tests on a novel steel rocking column base were conducted. • The column base showed flag-shaped hysteretic cures and dissipated seismic energy through plastic deformation of the replaceable cover plates. • Feasibility of the column base in steel moment-resisting frames was verified through nonlinear static and time history analysis. • Replacing some column bases with the rocking ones did not cause much reduction in lateral stiffness and capacity. [ABSTRACT FROM AUTHOR]

• A space-compact and cost-effective steel rocking column base is proposed. • Cyclic loading tests are conducted on three full-scale specimens, followed by three-dimensional FE analysis. • A component-based analytical model and the Yield Line Theory are employed to predict the design parameters. • Effective structural details of the column base are also discussed. This study proposed a steel rocking column base that dissipates seismic energy through a pair of replaceable steel cover plates. Three specimens of the proposed steel column base were designed and tested under static cyclic loading. Hysteretic response, failure modes, and energy dissipation of the column base were obtained and discussed. Then three-dimensional finite element model of the column base was built and validated against the test results. Later on, a component method was employed to predict the rotational stiffness and capacity of the column base. The Yield Line Theory was employed to predict the ultimate capacity of the cover plates and the demand of axial resistance of anchoring rods. It shows that the proposed column base is capable of dissipating seismic energy through the plastic bending of the cover plates. The moment resisting capacity increased with the increasing yield strength and thickness of cover plates and axial compression ratio, wherein the axial compression ratio has the most significant effect. The proposed design equations can predict the rotational stiffness of the column base and ultimate capacity of the column base with acceptable accuracy. Moreover, stiffening approaches for the column end were also presented to facilitate the practical design of the proposed column base. [ABSTRACT FROM AUTHOR]

• Numerical model which can consider elastoplastic behavior of panel zone of beam–column connection under multi-directional loadings. • Numerical model for 3D steel moment frame that comprised H-shaped beams, square hollow section columns and panels. • Comparison between loading test of cruciform frames and analysis results of proposed numerical model. • Time history response analysis of 3D steel moment frames under bidirectional ground motions. • Influence of strength ratios between structural members on energy dissipated from the plastic deformation of the beams, columns, and panels within each beam–column connection. In Japan, steel moment frames comprising H-shaped beams and square hollow-section columns with through diaphragms are often used for low- to middle-rise building structures. The column overdesign factor—strength ratio between columns and beams—is specified as ≥1.5 in Japanese seismic design code to ensure adequate energy absorption capacity against bidirectional ground motion by achieving an entire beam-hinging collapse mechanism. However, the required column overdesign factor of steel moment frames is obtained from analysis results conducted under unidirectional ground motions. Additionally, the numerical models of most previous studies considered the behavior of only beams and columns, and ignored the behavior of the panel zone of the beam–column connection. Nevertheless, the panel zone may yield with the beams and columns under severe earthquakes. In addition, the influence of panels on steel moment frames subjected to bidirectional ground motion is not completely understood, as a numerical model for panels under bidirectional shear forces and biaxial bending moments is yet to be proposed. Thus, this research proposes a novel numerical model for studying steel moment frames under multi-directional loadings to consider the 3D elastoplastic behavior of beams and columns, as well as panels. The proposed numerical model was validated by analyzing cruciform subassemblies of beams, columns, and panels, and the analysis results were compared to the experimental results from previous studies. Furthermore, a time-history response analysis was conducted for the 3D steel moment frames, and the energy dissipated from the plastic deformation of the beams, columns, and panels within each beam–column connection was discussed from the aspect of strength ratios between structural members. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a novel beam-to-column moment connection suitable for the column’s weak axis. The proposed system is developed in line with an idea to mainly utilize bolts with the number of welds minimized, thereby avoiding difficulties encountered in in situ welding. In this system, a wide-flange beam is joined to a wide-flange column by bolted splices at the top flange and newly invented hysteretic dampers at the bottom flange. The mechanical behavior of the damper and the whole connection system is described herein. The seismic performance of the proposed connection was verified through cyclic tests of six full-scale beam–column subassemblies, taking into account the effects of the geometry and arrangement of the dampers. The tests revealed that the proposed system is capable of achieving stable hysteresis behavior in a large deformation range. Yielding was limited only in the dampers while the beam and column remained essentially elastic until the ultimate state of the structure. [Copyright &y& Elsevier]

This paper presents an experimental and numerical study to examine the elasto-plastic behavior of the weak-panel type beam-column joints with RC slabs subjected to bidirectional and unidirectional loading. The effect of the RC slab on the behavior of the beam-column joints was investigated. The steel beam-column joint specimens were composed of wide-flange beams and square tube columns, and the panel zones were designed to yield before the columns and beams. The specimens failed at 0.04 rad story drift under bidirectional loading, while the specimens sustained a story drift of 0.08 rad under unidirectional loading. The existence of the RC slab led to various failure modes in this test, including the local buckling of the upper column, the weld fracture at the lower panel section, and the weld fracture at the beam bottom flange. It was worth noting that the panel-to-diaphragm weld cracks always initiated in the lower panel section and developed into severe fractures. Both the top and bottom surfaces of the slab suffered concrete crushing in the area around the column. Concrete cracks on the top surface were basically along the direction of the steel beam, while the cracks along the direction of the slab diagonal were also observed for the specimens under bidirectional loading. The RC slab increased the plastic strength of the specimens by 15%–20%. An equation was proposed to quantify the slab effect on the plastic strength of the specimens. Finite element analysis was conducted to validate the proposed equation. • Elasto-plastic behavior of weak-panel type beam-column joints with RC slabs was examined through loading tests. • Difference of behaviors of bare beam-column joints and beam-column joints with RC slabs was investigated. • The panel-to-diaphragm weld crack was found to be developed in the lower panel section due to the existence of RC slab. • An equation of the full plastic strength of weak-panel type beam-column joints with RC slabs was proposed. [ABSTRACT FROM AUTHOR]

• Benefits of installing the LVEM-isolated floor in the first story of a two-story frame. • The frame lateral stiffness is basically not weakened by the floor-isolation. • A 40% reduction in the peak inter-story drift could be obtained via a regular design. • The ambient temperature notably influences the performance of the floor-isolation system. • Peak of the floor acceleration response spectra is notably mitigated by the floor-isolation. We introduce a novel floor-isolation system for mitigating the seismic responses of steel frames. In the system, the floors are connected to steel beams by the laminated visco-elastic material (LVEM). In this paper, we present the feasibility of installing the LVEM-isolated floors in the first story of a two-story steel moment-resisting frame. Firstly, we notice that the floor-isolation decouples the composite behavior between the floors and the beams, thus weakens the stiffness of the beams. Based on a generalized frame model, it is demonstrated that such a reduction in beam stiffness only yields a tiny decrease in the global lateral stiffness of the frame. Subsequently, the dynamic analysis model is established for the frame equipped with the LVEM-isolated floor. The LVEM isolators are simulated by a refined Kelvin-Voigt model, while the entire structure is modeled by a three-degree-of-freedom system. The accuracy of the numerical approach is validated by shaking table tests. Based on the established model, a large-scale numerical computation is conducted using 136 earthquake records. The results demonstrate that the structural displacement responses could be remarkably mitigated by the floor-isolation. In general, the reduction of the peak inter-story drift gets more pronounced when a larger mass-isolation ratio and a softer LVEM isolator are applied. For a regular structural design configuration (e.g., mass-isolation ration ν = 0.7, LVEM isolator stiffness ratio κ = 0.2), a 40% reduction in the peak inter-story drifts could be obtained via the floor-isolation. The ambient temperature notably affects the performance of the floor-isolation system. In many cases, a risen temperature amplifies the benefits of the floor-isolation while a fallen temperature abates such benefits. Meanwhile, the floor-isolation alters the form and the amplitude of the floor acceleration response spectrum (FARS). The peaks of the FARS are significantly mitigated by the LVEM-isolated floors. Quantitatively speaking, we could get a 50% reduction in the peak of FARS from the LVEM-isolated floor system for regular design configurations, say, ν = 0.7, and κ = 0.2. [ABSTRACT FROM AUTHOR]

• Steel structures with floors isolated by laminated visco-elastic materials (LVEM). • Effective numerical simulating approach validated by shaking table tests. • Elastic seismic demand obtained from large-scale response history analysis. • Elastic design spectra for single-story steel structures with LVEM-isolated floor. • Quantified effect of ambient temperature on elastic structural seismic demand. The seismic demand of a structure could be reduced by isolating the floors using laminated visco-elastic materials (LVEM). Such a LVEM-isolated floor system exhibits many advantages, such as the embedded large mass-isolation ratio, the mitigation of floor acceleration, the easy-to-demolish characteristic, etc. This paper focuses on the elastic seismic performance of single-story steel structures equipped with the LVEM-isolated floor system, wherein the LVEM-isolators are made of acrylic visco-elastic materials. The numerical simulating approach and the dynamic analysis procedure are developed for the structural system. In the procedure, the LVEM isolators are simulated by the Kelvin-Voigt model. The numerical simulating approach is validated by shaking table tests. Based on the results of an extensive response history analysis, the effects of several key parameters on the elastic structural seismic demand are quantified. The considered parameters include the structural natural period (T), the mass-isolation ratio, and the stiffness of the LVEM isolators. The displacement response spectra for both the substructure and the LVEM isolators, namely, the λ S − T spectra and the λ VEM − T spectra, are developed corresponding to the ambient temperature θ = 20 °C. In the structural design, λ S is used for checking the seismic capacity of the substructure, while λ VEM is used for determining an appropriate deforming space for the LVEM isolators. The seismic demand of the substructure generally decreases as the LVEM isolators become more flexible and the mass-isolation ratio becomes larger. The effect of ambient temperature-changing on the proposed elastic design spectra is analyzed. Generally, such effect is more pronounced when the mass-isolation ratio increases and the stiffness of the LVEM isolator decreases. Analysis data is provided for quantifying the effect of ambient-temperature-changing on the λ S − T spectra and the λ VEM − T spectra. Based on the data, the structural design and evaluation could be carried out efficiently. [ABSTRACT FROM AUTHOR]

This paper aims to examine the cyclic behavior of panels in beam-column subassemblies subjected to bidirectional and unidirectional loading and to demonstrate the differences of panel behavior under two loading modes. The specimens were composed of wide-flange beams and square tube columns, and the panel zones were designed to yield before columns and beams. Experimental results showed that specimens subjected to bidirectional loading suffered severe damage, caused by the weld fracture at the corner of panel-to-diaphragm weld, and failed at 0.06 rad and 0.04 rad story drift for specimens with panel aspect ratio of 1.4 and 2.0, respectively. Specimens subjected to unidirectional loading developed a story drift of 0.06 rad without strength reduction. The panels contributed about 60%–80% story drift and dissipated approximately 80% of total input energy. Elastic stiffness of panels correlated well with theoretical values that were considered both flexural and shear stiffness. Panels with higher aspect ratio showed smaller plastic shear strength. Finite element analysis indicates that the lower plastic shear strength was resulted from flexural yielding in panels, and the effect of flexural yielding became more considerable under bidirectional loading. Moreover, the beams were found to present plastic moments 20%–50% lower than the theoretical values, which was attributed to the small panel-to-beam strength ratio. [ABSTRACT FROM AUTHOR]