Search Results (16)

As a common large-scale civil engineering structure, cable-supported photovoltaic (PV) arrays are typically designed with a 25-year service life, with their primary structural system composed of beam-column frames, pre-tensioned cables and modules. Cable-supported photovoltaic arrays are susceptible to large-amplitude wind-induced vibrations (WIV), threatening structural safety and serviceability. This study investigates interference effects on an eight-row array that employs aeroelastic wind tunnel tests, focusing on how tilt angle and sag-to-span ratio influence vibration characteristics and interference mechanisms. Results show coupled vertical–torsional vibrations with amplitudes increasing with wind speed and that are more intense under wind suction than under wind pressure. Reducing tilt angle and sag-to-span ratio effectively suppresses vibrations and raises critical flutter speed. For interference effects, mean response demonstrates clear shielding with amplitudes decreasing leeward. In contrast, fluctuating response behavior depends on tilt angle: 5° tilt angle produces a shielding effect, while 25° tilt angle causes an amplification effect with periodic fluctuations. The 25° tilt angle shows greater sensitivity to wind speed, evidenced by decreasing interference coefficients from the second to eighth windward rows with increasing wind speed. Although reducing the sag-to-span ratio most effectively suppresses vibrations in the first windward row and consequently affects downstream interference coefficients, it does not alter the fundamental trends governed by tilt angle. Full article

The storage conditions of multi-floor grain warehouses change frequently during grain circulation. This paper investigates the effects of various storage conditions on the seismic performance of multi-floor grain warehouses. The numerical results indicate that the higher the storage material distribution position, the greater the damping ratio of the structural model and the more obvious the contribution of storage material movement to the damping of the structure. The intensity of earthquake action and the spatial height of the floor where the storage material is located are negatively correlated with the acceleration response of the structure. Under full-silo conditions, when the peak ground acceleration (PGA) is 0.4 g, the acceleration amplification factor at the top of the structure is 69.7% of the corresponding parameter at 0.1 g. The discontinuity in the storage space of the structure results in a torsional effect on the structure. When PGA = 0.22 g, the peak inter-story displacement angle of the first floor differs by nearly 1.7 times under different operating conditions, and the peak inter-story displacement angle of the second floor during an earthquake with PGA = 0.40 g differs by about 1.5 times under different operating conditions. The lateral pressure of the silo wall at different burial depths under earthquake action shows a highly nonlinear distribution trend, and the overpressure coefficient at the same burial depth of the warehouse wall is proportional to the PGA of the earthquake action. During 0.1 g, 0.22 g, and 0.40 g earthquakes, the maximum overpressure coefficients at the bottom of the warehouse wall on different floors are 1.13, 1.21, and 1.66, respectively. Full article

The establishment of a linear seismic response analysis model that considers ground rotation effects and eccentric torsion informed the investigation of the linear response characteristics of coupled lateral–torsional vibration, considering eccentricity and ground rotation, after which the lateral–torsional coupling linear response pattern of special-shaped column structures is examined. The results show that the torsion angle of a floor is equal to the sum of the interlayer torsion angle caused by eccentric torsion and the pure torsion angle caused by ground rotation, respectively. The natural vibration frequency of the structure considering ground rotation effects is a function of relative eccentricity; the period ratio of translation to torsion caused by ground rotation; and the period ratio of translation to torsion when considering only eccentric torsion. When the translation to torsion period ratio, considering eccentric torsion, is greater than 1.0, the torsional amplitude increases remarkably, but the first-order participation mode is considerably higher under the same conditions. The natural vibration characteristics, translational response, torsional response, and seismic force distribution are obtained for special-shaped columns by conducting the shaking table test on steel-reinforced concrete (SRC) frame structures. After comparative analysis, the maximum ratio of the maximum torsional displacement of the bottom layer of the structure to the horizontal displacement in the X direction is 0.0007. The maximum ratio of the base shear force to the theoretical base shear force of the structure without considering coupling is 0.93. The maximum ratio of the measured shear force of the special-shaped column to the theoretical shear force without considering coupling is 0.65. This indicates that ground rotation has a significant amplification effect on structural response. The research results provide a reference for the seismic design of special-shaped column structures. Full article

A shaking table test of a 1/60 scale cross-fault bridge model considering the effects of soil–bridge interactions was designed and implemented, in which the bridge model was placed in two individual soil boxes to simulate the bridge across a strike-slip fault. Three seismic ground motion time-histories with permanent displacements were selected as input excitations to investigate the influence of seismic ground motions with different frequency characteristics on the seismic response of the testing soil–bridge model. The one-side input method was used to simulate the seismic response of bridges across faults. The seismic responses of the soil and bridge in terms of acceleration, strain, and displacement were analyzed. The test results show that the one-side input method can simulate the seismic response of the main girder displacements well and the displacements and strains of piers and piles of the bridge structure spanning a fault. The strain responses at near-fault pile foundations are much larger than those farther away from the fault. Compared with other bridges, the cross-fault bridge is more prone to torsional and displacement responses during earthquakes. Surface fault rupture can lead to permanent inclination of the bridge piers, which should be paid more attention to in the practical engineering design of the bridges. Soil–bridge interactions can suppress the amplification effect of soil on ground motions. The test results can provide a reference for future research and the design of cross-fault bridges. Full article

Mutual dislocation of seismogenic faults during strong earthquakes will result in a large relative displacement on both sides of the fault. It is of great significance to explore the influence of the collision effect between the main beam and the transverse shear key on the seismic response of the bridge under fault dislocation. In this paper, a series of cross-fault ground motions with different ground permanent displacements are artificially synthesized using a hybrid simulation method. Based on the contact element theory, the Kelvin–Voigt model is used to simulate the lateral collision effect. The effect of lateral collision on the seismic response of the continuous girder bridge is compared from the two aspects of fault dislocation position and fault dislocation degree. On this basis, the analysis of lateral collision parameters is carried out with the aim of reasonably regulating the seismic response of the structure. The results show that, compared with the near-fault bridge, the influence of lateral collision on the cross-fault bridge is stronger. The amplification of the bending moment of the central pier and the limitation of the bearing displacement are five times and two times, respectively, for the near-fault bridge. When the fault has a large dislocation, the weak point of the structural damage is the bending failure of the pier bottom and the residual torsion after the earthquake. The collision parameters of conventional bridges will aggravate the bending moment demand of the pier bottom of cross-fault bridges and limit their bearing displacement too much. Therefore, by appropriately reducing the collision stiffness and increasing the initial gap, the internal force and displacement response distribution of the cross-fault bridge structure can be more reasonable. The study in this paper has reference significance for seismic analysis of cross-fault bridges with transverse shear keys. Full article

The flexibility of insect wings should be considered in the design of bionic micro flapping-wing aircraft. The honeybee is an ideal biomimetic object because its wings are small and possess a concise vein pattern. In this paper, we focus on resilin, an important flexible factor in honeybees’ forewings. Both resilin joints and resilin stripes are considered in the finite element model, and their mechanical behaviors are studied comprehensively. Resilin was found to increase the static deflections in chordwise and spanwise directions by 1.4 times and 1.9 times, respectively. In modal analysis, natural frequencies of the first bending and first torsional modes were found to be decreased significantly—especially the latter, which was reduced from 500 Hz to 217 Hz—in terms of resilin joints and stripes, closely approaching flapping frequency. As a result, the rotational angle amplitude in dynamic responses is remarkable, with an amplification ratio of about six. It was also found that resilin joints and stripes together lead to well-cambered sections and improve the stress concentrations in dynamic deformation. As resilin is widespread in insect wings, the study could help our understanding of the flexible mechanism of wing structure and inspire the development of flexible airfoils. Full article

Stability calculation is the main objective during the analysis of domes. To investigate the effects of the initial defect, geometric nonlinearity, and material nonlinearity on the stability performance of different dome structures, 60 m numerical models were built and optimized by an iterative force-finding APDL program. Then, linear buckling analysis, geometric nonlinear stability analysis, geometric nonlinear stability analysis with initial defects, and dual nonlinear analysis with initial defects were discussed to compare the stability performance of ridge-beam cable domes (RCDs), suspen-domes, and conventional cable domes via finite element analysis. The results show that the buckling loads all follow the order of initial defect + dual nonlinear analysis < initial defect + geometric nonlinear analysis < geometric nonlinear analysis < linear buckling. The addition of ridge beams improves the overall stability and transforms the instability modes from local concave instability to overall torsional buckling. The ultimate load amplification coefficients of the RCD are close to those of the suspen-dome, while the vertical displacements of the RCD are more than those of the conventional cable dome, so the RCD has sufficient stiffness to reduce local displacement. Under 2–3 load combinations, internal ridge beams change from a tensile-bending state to a compressive-bending state, causing the entire instability of the RCD afterwards. Full article

Single-column elevated station structures are irregular structures with long-span cantilever beams and individual pier columns in the transverse section. The uneven mass and stiffness in the horizontal and vertical planes necessitate research on the seismic performance of these structures. This study performed a nonlinear response-history analysis (NRHA) of a single-column elevated station structure using the finite element program MSC.MARC and analysed its seismic performance under different seismic intensities. The stress states of the primary components were evaluated, and the effect of vertical earthquake motion on the seismic performance of the structure was considered. The torsional behavior caused by the uneven mass and stiffness in both horizontal and vertical directions should be considered, and energy dissipation measures should be taken to reduce the internal force and deformation of the bottom-pier columns and second-floor columns in the process of designation to improve the seismic performance of the structure. A bidirectional pushover analysis (BPA) was applied. The load amplification factor was adjusted to optimize the BPA results. The results of the modified BPA were similar to those of the NRHA, indicating the computational reliability of the modified BPA. The modified BPA method was accurate, applicative, and efficient. The BPA can improve computational efficiency compared to NRHA and can be widely applied in the structural design process for practical engineering applications. Full article

This paper aims at giving structural designers guidance on how to transform seismic demand on a building structure from two-dimensional (2D) to three-dimensional (3D) in an expedient manner, taking into account amplification of the torsional actions. This paper is to be read in conjunction with either paper #3 or #4. Torsional amplification of the drift demand in a building is of major concern in the structural design for countering seismic actions on the building. Code-based seismic design procedures based on elastic analyses may understate torsional actions in a plan of asymmetric building. This is because the inability of elastic analyses to capture the abrupt increase in the torsional action as the limit of yield of the supporting structural walls is surpassed. Nonlinear dynamic analysis can provide accurate assessment of torsional actions in a building which has been excited to respond in the inelastic range. However, a 3D whole building analysis of a multi-storey building can be costly and challenging, and hence not suited to day-to-day structural design. To simplify the analysis and reduce the scale of the computation, closed-form expressions are introduced in this paper for estimation of the ${\mathsf{\Delta }}_{3D}/{\mathsf{\Delta }}_{2D}$ drift demand ratio for elastic conditions when buildings are subjected to moderate-intensity ground shaking. The drift demand of the 3D model can be estimated as a product of the 2D drift demand and the ${\mathsf{\Delta }}_{3D}/{\mathsf{\Delta }}_{2D}$ drift demand ratio. In dealing with higher-intensity ground shaking causing yielding to occur, a macroscopic modelling methodology may be employed. The estimated ${\mathsf{\Delta }}_{3D}/{\mathsf{\Delta }}_{2D}$ drift demand ratio of an equivalent single-storey building is combined with separate analysis for determination of the 2D drift demand. The deflection profile of the multi-storey prototype taking into account 3D effects, including torsional actions, is hence obtained. The accuracy of the presented methodologies has been verified by case studies in which drift estimates generated by the proposed calculation procedure were compared against results from whole building analyses, employing a well-established computer software. Full article

This paper is in the field of elastic flexural-torsional buckling of steel beam-columns of bisymmetric narrow-flange and wide-flange I-section shape. Investigations are focused on the derivation of the strain components and the energy equation, based on the displacement-field formulation in the deflected configuration. At the same time, a review of analytical solutions based on the classical and refined energy-equations are summarized, presented and discussed. The relationship between the maximum in-plane bending moment and the compressive force of beam-columns is the main objective of this research investigation. Simple boundary conditions of end-sections free to deflect and to warp are considered, together with an arbitrary loading-pattern. The principle of superposition and the moment amplification rule for considering the second-order effects are widely used. The main conclusions are drawn in relation to the flexural-torsional resistance-evaluation design of steel beam-columns in modern design codes for steelwork. Full article

Spacetime torsion is known to be highly suppressed at the end of inflation, which is called preheating. This result was recently shown in (EPJ C (2022)) in the frame of Einstein–Cartan–Brans–Dicke inflation. In this paper, it is shown that a torsionful magnetogenesis in QED effective Lagrangean drives a torsion damping in order to be subsequently amplified by the dynamo effect after the generation of these magnetic fields seeds. This damping on amplification would depend upon the so-called torsion chirality. Here, a cosmic factor $gkK$ is present where K is the contortion vector and k is the wave vector which is connected to the inverse of magnetic coherence length. In a second example, we find Higgs inlationary fields in Einstein–Cartan gravity thick domain walls (DWs). Recently, a modified Einstein–Cartan gravity was given by Shaposhnikov et al. [PRL (2020)] to obtain Higgs-like inflatons as a portal to dark energy. In the case of thick DW, we assume that there is a torsion squared influence, since we are in the early universe where torsion is not so weak as in the late universe as shown by Paul and SenGupta [EPJ C (2019)] in a 5D brane-world. A static DW solution is obtained when the inflationary potential vanishes and Higgs potential is a helical function. Recently, in the absence of inflation, domain wall dynamos were obtained in Einstein–Cartan gravity (EC) where the spins of the nucleons were orthogonal to the wall. Full article

This study aimed to evaluate the soil–structure interaction of three historical buildings at the University of Catania using ambient noise. The results point out the different oscillation modes of Villa Cerami and Palazzo Boscarino buildings sharing a side. They also show different damping values, which are probably linked to the different rigidities of the structures, since one is a masonry building and the other is a reinforced concrete building without earthquake-resistant design. Villa Zingali Tetto, a reinforced concrete building without earthquake-resistant design, showed significant torsional effects, which may be related to the geometrical and material irregularities of the structure. Comparison of the buildings’ fundamental periods and site frequencies did not show potential soil–structure resonance effects. Modelling of the local seismic response confirms the obtained experimental site frequencies, suggesting that there are no important amplification factors. On the other hand, from both of the computed Spectral and Peak Ground Accelerations for an Mw 7.3 earthquake, intensity values were estimated for which Villa Cerami could suffer heavy structural damage, and Palazzo Boscarino and Villa Zingali Tetto very heavy non-structural damage. Additional engineering investigations, aimed at reducing seismic vulnerability, are necessary to improve the safety of these heritage buildings considering they are also used for educational purposes. Full article

Squeezing light is a critical resource in both fundamental physics and precision measurement. Squeezing light has been generated through optical-parametric amplification inside an optical resonator. However, preparing the squeezing light in an optomechanical system is still a challenge for the thermal noise inevitably coupled to the system. We consider an optically levitated nano-particle in a bichromatic cavity, in which two cavity modes could be excited by the scattering photons of the dual tweezers, respectively. Based on the coherent scattering mechanism, the ultra-strong coupling between the cavity field and the torsional motion of nano-particle could be achieved for the current experimental conditions. With the back-action of the optically levitated nano-particle, the broad single-mode squeezing light can be realized in the bad cavity regime. Even at room temperature, the single-mode light can be squeezed for more than 17 dB, which is far beyond the 3 dB limit. The two-mode squeezing light can also be generated, if the optical tweezers contain two frequencies, one is on the red sideband of the cavity mode, the other is on the blue sideband. The two-mode squeezing can be maximized near the boundary of the system stable regime and is sensitive to both the cavity decay rate and the power of the optical tweezers. Full article

Buildings possessing an asymmetrical arrangement of structural elements are torsionally unbalanced and can be vulnerable in a seismic event. Building codes of practices typically recommend the use of three-dimensional dynamic analysis to determine the seismic demands of a multi-storey building. Whilst most design practices are well equipped with commercial software for undertaking such analyses, designers often find it difficult to verify results. Much of the published technical articles present findings for buildings based on an idealised single-storey model. As a result of challenges in dealing with real multi-storey buildings, there has been very limited uptake of research findings in design practices. This article presents a three-tiered approach of estimating the displacement behaviour of the building in term of 3D/2D displacement ratio. The estimate can be used for verifying results reported from a computer package conveniently. The quick method provides predictions of the 3D/2D ratio and only requires the gross plan dimensions of the building to be known. The refined method requires knowledge of the torsional stiffness properties to be known, whereas the detailed method requires the eccentricity properties to be known as well. The proposed methodology is robust and reliable, as is demonstrated by case studies undertaken on six real multi-storey buildings. Full article

This article presents the findings of a study on assessment of the increase in building’s response due to accidental torsion when subjected to seismic forces. Critical stiffness and geometrical parameters that define buildings torsional response are examined including: (1) the ratio, Ω, between uncoupled torsional frequency ω_θ to uncoupled translation frequencies in the direction of ground motion ω_x or ω_y, (2) floor plan aspect ratio, b/r, which is a function of the floor dimension and radius of gyration. The increased response is assessed on symmetric multi-storey buildings using both static and dynamic analysis methods specified by ASCE-7 and considering parameters affecting the torsional response. It was concluded that static and dynamic analysis procedures predict different accidental torsion responses. Static analysis based on the Equivalent Lateral Force (ELF) method predicts more conservative accidental torsions responses for flexible structures with Ω < 0.7~0.80, while the responses are less conservative for stiffer buildings. The conservativism in static analysis method is attributed to the response amplification factor, Ax. Floor plans and their lateral support system having frequency ratio Ω = 1 will also have a torsional radius equal to radius of gyration, and will experience drop in torsional response relative to more torsionally flexible buildings. This article presents a procedure to overcome the shortcomings of static and dynamic analysis procedures in terms of estimating accidental torsion response of symmetric building structures. Full article