Summary
This paper presents an innovative re‐centering deformation‐amplified shape memory alloy damper (RDASD) to reduce the responses of civil structures under earthquake motions. The damper can ...amplify the displacement deformation according to actual needs and fully exploit the energy dissipation capacity of superelastic shape memory alloy materials. Cyclic tensile‐compressive tests of the fabricated RDASD are conducted to study the influence of the displacement amplitude and loading rate on the damper's mechanical properties. Additionally, a theoretical model of the RDASD that can precisely simulate the hysteretic characteristics of the damper is proposed. Finally, a nonlinear time history analysis is performed on a six‐story steel frame for three cases: no dampers, dampers without deformation amplification, and dampers with deformation amplified by a factor of 2.5. The results show that the proposed RDASD can not only effectively mitigate the displacement, acceleration, and interstory drift responses due to its efficient energy dissipation capacity but also provide superior re‐centering by amplifying the relative deflection for building structures. In practical applications, the recommended range for the deformation amplification coefficient of the damper is 2.0–3.0.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Many tower structures have collapsed during strong wind events; therefore, the objective of the present study is to estimate the strength capacity of transmission towers accurately and to identify ...all potential failure modes. An uncertainty analysis method for tower structures subjected to a wind load is presented. Subsequently, random samples of material properties and section dimensions are generated based on the Latin Hypercube Sampling technique and then used to establish uncertain finite element models for transmission towers. A static non-linear buckling analysis for structures subjected to a wind load is conducted using ANSYS software. Based on tower models incorporating uncertainty, our analysis reveals that there are six possible initial failure tower members but only one for the deterministic model, indicating that the uncertainties regarding material properties and section dimensions should be taken into account. Furthermore, a sensitivity analysis is conducted, and the results reveal that the uncertainty of material properties has a stronger influence than the uncertainty of section dimensions. Finally, the influence of wind attack angle is discussed, and the initial failure positions and corresponding probabilities for various wind attack angles are obtained. The results show that the most unfavorable wind attack angle is 0° and that the most probable failure position of the tower of interest is the middle of the tower body.
•An uncertainty analysis method for tower structures subjected to a wind load is presented.•The failure position of highest likelihood for the employed tower is the middle of the tower body.•The uncertainty of material properties has a stronger influence than the uncertainty of section dimensions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Steel rebar corrosion is one of the predominant factors influencing the durability of marine and offshore reinforced concrete structures, resulting in economic loss and the potential threat to human ...safety. Distributed fiber optic sensors (DFOSs) have gradually become an effective method for structural health monitoring over the past two decades. In this work, a strain transfer model is developed between a steel rebar and a DFOS, considering pitting-corrosion-induced strain variation in the steel rebar. The Gaussian function is first adopted to describe the strain distribution near the corrosion pit of the steel rebar and then is substituted into the governing equation of the strain transfer model, and the strain distribution in the DFOS is analytically obtained. Tensile tests are also conducted on steel rebars with artificially simulated corrosion pits, which are used to validate the developed model. The results show that the Gaussian function can be used to describe the strain variation near a corrosion pit with a depth less than 50% of the steel rebar diameter, and the strain distribution in the DFOS analytically determined based on the developed strain transfer model agrees well with the tensile test results. The corrosion pit depth and loading force in the steel rebars estimated based on the proposed model agree well with the actual values, and therefore, the developed strain transfer model is effective in detecting pitting corrosion and loading force in steel rebars.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
•Seismic fragilities of sea-crossing cable-stayed bridges are numerically analyzed.•Multi-support ground motions at different depths of offshore sites are simulated.•Effects of SSI and hydrodynamic ...added mass are systematically investigated.
As key components in the transportation networks at coastal areas, sea-crossing cable-stayed bridges play a very important role in the development of regional economy. These bridges may be subjected to severe earthquakes during their life-cycles. Owing to the lack of actual seafloor earthquake recordings and approaches in synthesizing offshore seismic motions, the onshore seismic motions are commonly utilized as inputs in the seismic design of sea-crossing cable-stayed bridges. However, this approach may lead to erroneous structural response predictions since the characteristics of onshore and offshore seismic motions are different. In this paper, the seismic performance of a sea-crossing cable-stayed bridge is comprehensively evaluated based on the fragility function methodology. A novel approach is presented to theoretically calculate the ground motion transfer function at any location within an offshore site and stochastically synthesize the offshore multi-support ground motions at different depths (MGMDDs). The OpenSees analysis platform is employed to develop the three-dimensional finite element model of the example bridge, in which the p-y, t-z and q-z elements are installed at the pile nodes to simulate the interaction between the bridge piles and surrounding soils. Moreover, the effect of seawater on the bridge seismic responses is modeled using the hydrodynamic added mass method. The seismic fragility curves of the example bridge are generated by using the synthesized MGMDDs as inputs. The influences of spatial and depth varying offshore seismic motions, soil-structure interaction (SSI) and seawater added mass on the bridge component and system fragilities are investigated and discussed. Numerical results show that the seismic fragility of the example sea-crossing cable-stayed bridge is affected by the above mentioned influencing factors with different extents. The proposed approach can rationally and effectively assess the seismic fragilities of sea-crossing cable-stayed bridges.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Summary
Pounding tuned mass damper (PTMD) is a novel type of passive damper. The PTMD utilizes collisions or impacts of a tuned mass with viscoelastic materials to efficiently dissipate the vibration ...energy of primary structures. The previous studies have verified its effective damping performance on a full‐scale subsea jumper and other structures in air. This paper presents the first‐ever experimental verification of a submerged PTMD system for vibration control of pipelike structures underwater. To facilitate the experimental studies, a vertical vibration system consisting of 4 springs and a cylindrical steel pipe was designed and set up in a water tank. Furthermore, a numerical method considering the effect of the added mass is described to estimate the natural frequencies of a submerged cylindrical pipe. Therefore, experimental results demonstrate that the PTMD system is effective and efficient to suppress the forced vibrations of the submerged cylindrical pipe at the tuned frequency and is also robust over a range of detuning frequencies.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•A multi-hazard protective frame structure with hybrid energy-dissipated devices of BRB and VD is proposed.•The effectiveness of the HDF in the vibration control against the multiple hazards of ...earthquake and wind is studied.•The multi-hazard fragility surfaces of the HDF under combined earthquake and wind loads are generated.•The optimal design schemes of the HDF under multiple hazards are suggested.
Engineering structures may inevitably be subjected to earthquakes and winds during their life cycles, furthermore, with the probability of simultaneous occurrence, the hit of combined earthquake and wind shall pose a stiffer threat to the structural functionality and safety. Passive control technique is a practical and effective method to mitigate earthquake and wind hazards for new or existing engineering structures. This paper develops a multi-hazard protective system with the hybrid energy-dissipated devices of buckling-restrained braces (BRBs) and viscous dampers (VDs), and investigates the effectiveness and optimum design parameters of different supplemental devices using the fragility function method. The OpenSees platform is employed to establish the finite element (FE) models of bare steel–concrete moment resisting frame (MRF), buckling-restrained braced frame (BRBF), viscous damped frame (VDF) and hybrid damped frame (HDF) with both BRBs and VDs. In total 120 groups of combined “earthquake-wind” events with a wide range of hazard intensities are developed using the Monte Carlo simulation, which are applied to the dynamic time history analyses of the aforementioned four frame structures. The multi-hazard fragility surfaces, which depict the exceeding probability of structures under simultaneous earthquake and wind loads, can be generated for different damage states. The numerical results indicate that the HDF is an effective structural system against the multiple hazards attacks, and the energy dissipation contributions of BRB and FVD vary with the hazard intensities of earthquake and wind. To further identify the optimum design scheme for the HDF system, the parameters of hybrid passive control devices are extensively investigated by evaluating the hazard intensities required when achieving specified damage states in the fragility surfaces. The findings can provide a practical guide for the design of structure with energy-dissipated devices against the multi-hazard scenarios of earthquake and wind.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Summary
This paper presents an innovative gear‐driven rotation‐amplified rubber viscoelastic damper (GRRVD) to reduce the seismic shift responses of beam‐column connections in frame structures. Based ...on the principle of gear transmission, the damper can amplify the rotational deformation of the beam‐column joints of frame structures according to actual engineering needs and give full play to the energy dissipation capacity of rubber viscoelastic materials. First, the design philosophy, basic construction, working mechanism, and outstanding features of this damper are introduced. Then, cyclic loading test is carried out to study the influence of rotational deformation and loading frequency on the mechanical properties of the fabricated GRRVD. Additionally, a mechanical model which can precisely simulate the hysteretic characteristics of the damper is derived and then verified by numerical simulation. Finally, a nonlinear time history analysis is performed on a six‐story steel frame for three cases: no dampers, dampers without deformation amplification, and dampers with deformation amplified by a factor of 2.5. The results show that the control effect of the damper can be improved by two to four times by amplifying the rotational deformation response at the beam‐column joint by 2.5 times.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
Integration algorithm is an important mean to solve the discrete time equations of structural dynamics in earthquake engineering. In this paper, a new model‐based explicit integration ...algorithm, featured by optimization‐based integration parameter updating, is developed for a more accurate and efficient solution of structural dynamic problems. The new integration algorithm is designed to yield minimum error and controllable numerical dispersion under the premise of stability by defining objective functions and constraints. Numerical properties of the new integration algorithm are investigated in details using the amplification matrix method for a linear elastic single degree‐of‐freedom system. Meanwhile, representative numerical examples and complex structure examples are analyzed and compared with other representative algorithms. As a result, the proposed algorithm yields comparable numerical characteristics with other methods, but exhibits pronounced superiority in controllable algorithmic dissipation, higher precision, and better efficiency. Therefore, the new integration algorithm possesses extensive application prospect in solving complicated linear and nonlinear structural dynamic problems.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
It is a novel idea to make steamed bread by adding potato flour into wheat flour considering the production and nutritional factors of potato. In this study, the influence of potato flour（0–35%） on ...dough rheology and quality of steamed bread were investigated. Potato flour addition significantly influenced the dough rheological properties and steamed bread quality, such as increased water absorption, the maximum gaseous release height, total volume of CO_2 and hardness, while decreased dough stability and specific volume of steamed bread. Moreover, correlation analysis suggested that dough height at the maximum development time, dough stability, water absorption and the phase tangent can be used for predicting the technological quality of steamed bread. Potato-wheat steamed bread had higher dietary fibre, ash content and antioxidant activity than those of wheat steamed bread. The estimated glycemic index decreased from 73.63（0%） to 60.01（35%）. Considering the sensory evaluation, the steamed bread with 20% potato flour is acceptable. In conclusion, adding appropriate quantity of potato flour to wheat flour for steamed bread production will not only maintain the technological quality, but also can improve the nutritional value of the steamed bread.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Summary
Evaluating the inelastic seismic response of structures accurately is of great importance in earthquake engineering and generally requires refined simulation, which is a time‐consuming ...process. Because the material nonlinearity generally occurs in a small part of the whole structure, many researches focus on taking advantage of this characteristic to improve the computational efficiency and the inelasticity‐separated finite element method (IS‐FEM) proposed recently provide a generic finite element formulation for solving this kind of problems efficiently. Although the fiber beam‐column element is widely used for the simulation of reinforced concrete (RC) framed structures, the inelastic deformation is often detected in a large part of the numerical model under earthquake excitation so that it is hard to achieve high efficient computation when applying the IS‐FEM to the inelastic response analysis of RC fiber models directly. In this paper, a new numerical scheme for seismic response analysis of RC framed structures model by fiber beam‐column element is proposed based on the IS‐FEM. To implement the RC fiber model for use in IS‐FEM and improve the computational performance of proposed scheme, a method of identifying the local domains with severe section inelasticity level is proposed and a modified Kent‐Park concrete material model is developed. Because the Woodbury formula is adopted as the solver, the global stiffness matrix can keep unchanged throughout the analysis and the main computational effort is only invested on a small matrix representing local inelastic behavior. The numerical examples demonstrate the validity and efficiency of the proposed scheme.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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