Stiffness Ratio Research Articles

Association of Abnormal Lung Function and Its Subtypes With Arterial Stiffness: A Longitudinal Cohort Study.

Prior studies have reported the cross-sectional relationship between lung function and arterial stiffness, while the longitudinal association remains unclear to date. This study aimed to investigate whether abnormal lung function and its subtypes at baseline are associated with increased arterial stiffness using a cohort. This was a secondary analysis extracting 2461 participants from Beijing Health Management Cohort as baseline and annually followed for development of arterial stiffness. Abnormal lung function was defined by forced expiratory volume in 1s <80% of the predicted value, forced vital capacity of the predicted value, or forced expiratory volume in 1s/forced vital capacity ratio <70%. Increased arterial stiffness was determined by brachial-ankle pulse wave velocity ≥1400 cm/s. Cox proportional hazards model was used to calculate the hazard ratio and population attributable fraction. The mean age was 42.8±8.1 years, and 444 (18.0%) cases developed increased arterial stiffness during a median follow-up of 3.0 years. The adjusted hazard ratio (95% CI) of arterial stiffness was 1.47 (95% CI, 1.10-1.96) for abnormal lung function, with a population attributable fraction of 3.9% (95% CI, 0.8-7.1). Of subtypes, only obstructive ventilatory dysfunction was significantly associated with arterial stiffness (adjusted hazard ratio, 2.06 [95% CI, 1.27-3.36]), not restricted ventilatory dysfunction (adjusted hazard ratio, 0.95 [95% CI, 0.54-1.65]). Consistent results were observed on multiple sensitivity analyses. Our study indicated a longitudinal association of abnormal lung function with increased arterial stiffness using a large cohort, especially for the obstructive ventilatory dysfunction.

Study on seismic behavior and collapse risk of super high-rise braced mega frame-core tube structural system

The braced mega frame-core tube (BMFCT) structure could provide an efficient lateral-force resisting (LFR) system for high-rise or super high-rise buildings, especially for those higher than 500 m. The BMFCT structure is a dual LFR system, including the outer braced mega frame and the inner core tube. The seismic behavior and design method of this structural system is not clear. In this study, a parametric study based on collapse risk-targeted analysis is conducted to clarify seismic mechanism and performance and to make clear means of matching reasonable stiffness and setting energy-dissipation components. Five comparable BMFCT structures with different mega brace stiffness proportions and frame-tube stiffness ratios are designed. An efficient elasto-plastic modeling method is introduced to establish the accurate FE models. The corresponding collapse risks are calculated through Incremental Dynamic Analysis and fragility theory. The results show that the structural collapse risk increases with the increased frame-tube stiffness ratio. Therefore，the stiffness and bearing capacity of peripheral frames should be strengthened to ensure the structural collapse margin. On the other hand, the collapse resistance capacity gradually decreases with the increasing of the mega brace stiffness. Thus, the stiffness proportion of mega braces should be recommended to meet the basic lateral stiffness requirements, which shall not exceed 35 % of the overall structural stiffness. Moreover, the distribution feature and ideal arrangement of the energy dissipation components are proposed. The seismic design recommendation based on the uniform collapse risk is also proposed for the BMFCT system, which serves a reference for the structural design of super high-rise buildings.

Development and optimization of a novel response‐amplified friction damper with different friction pairs

AbstractIn order to improve the efficiency of friction dampers, a shear‐type response‐amplified friction damper (RAFD) was proposed, which utilized a lever mechanism to amplify the shear displacement and increase the sliding distance of friction pairs. Cyclic loading tests were conducted on 12 RAFD specimens to evaluate the effects of machining processes, friction materials, loading protocols, and bolt pretension on the mechanical performance of the specimens. The results showed that the RAFD specimens with NAO and brass friction pads exhibited plump hysteresis loops, and the bearing capacity, effective stiffness, energy dissipation, and equivalent viscous damping ratio all met the stability requirements of FEMA 356 for the friction damper. Reducing the clearance between pins and holes and strengthening the hole edges shortened the plateau near zero resistances of the hysteresis loops by 75%–90%. Furthermore, combined with rotational analysis of the lever, a design methodology for the RAFD specimen was developed. Based on the response amplification factor R, key mechanical indices such as bearing capacity and equivalent friction coefficient were derived, and a theoretical hysteresis model for the RAFD was constructed, which matched well with experimental results.

Influence of slab structure on the behavioral analysis of hybrid outrigger system

SummaryOutriggers are internal structural systems used to enhance the stiffness and strength of high‐rise structures. This research investigates the efficacy of a hybrid outrigger system (HOS) which consists of one conventional and one virtual outrigger at two distinct floor levels in high‐rise RCC buildings. A non‐dimensional quantity, ϒ, defined as the relative stiffness ratio between the core and the diaphragm is used to describe variations in the stiffness of the building's core, stiffness of floor diaphragm, breadth, and height of the structure, in the behavioral analysis of the HOS. To investigate the efficacy and optimum locations of the hybrid outriggers, static and dynamic analysis are carried out on models with four‐story heights of 140, 210, 280, and 350 m under static wind loading, uniform wind loading, equivalent static earthquake loading, and dynamic earthquake loading. Results are assessed based on the responses from roof displacement (Disptop), base bending moment, roof acceleration (Acctop), fundamental period, and absolute maximum inter‐story drift ratio (ISDabs.max). Based on the minimum responses of the aforementioned dependent parameters under wind and earthquake excitations, the corresponding optimum locations of hybrid outriggers are investigated. To investigate the impact of the slab on the functionality of the HOS, the behavior of shell stress variation in the tension and compression side of the slab at the outrigger floor level and the force transmission through the column at the outrigger level is analyzed. Also, the optimum location of the hybrid outriggers based on the ideal performance index (IdealPI) is investigated. IdealPI is defined as a parameter that considers the combined response of Disptop, Acctop, and ISDabs.max and the criteria required for the structure under wind and seismic loads. From the behavioral analysis results, it is found that an increase in the stiffness of the slab showed an improved performance of the HOS compared to an increase in the stiffness of the core, and HOS performance can be maximized by increasing both thickness of the slab and outrigger arm length. The findings of the optimum location analysis could serve as a guide for structural engineers when selecting suitable positions for hybrid outriggers in high‐rise structures.

TEST RESULTS OF REINFORCED CONCRETE CROSS-RIBBED MODEL OF SPAN STRUCTURE OF THE BRIDGE AND THEIR ANALYSIS

Presentation of samples of basic experimental data from research of spatial work of large-scale (scale 1: 4) reinforced concrete model of cross-ribbed span structure of the bridge and separate beams similar in structure to model beams, as well as methodological features and results of their analysis. During the tests, the model and separate (reference) beams were loaded with concentrated force, alternately at the intersections of the longitudinal and transverse ribs of the model. Deflections in the same nodes and support reactions of longitudinal beams were measured. A new methodological feature of this research was the determination of experimental bending moments in the model beams by direct comparison of the deflections of the model beams with similar deflections of separate (reference) beams. Depending on the location of the external load and the stiffness ratio, the load on the beams of the model is different. Taking into account an elastic-plastic stage of their work, the method of calculation of the maximum bending moments in the most loaded beams is offered in this paper.

Study on influencing factors of hysteretic performance of cantilever fully-bolted prefabricated beam-column joint

In order to improve the construction efficiency and integrity of prefabricated RC frames, a cantilever fully-bolted prefabricated beam-column joint is proposed. Through the reciprocating loading test, the change rules of rotation characteristics, mechanical properties and stiffness degradation of this type of joint were obtained. The failure mode of the joint is found: the steel plate in the connection area undergoes a slight flexural deformation, the concrete on the outside of the connection area forms a plastic region of about 1/3 beam length, the concrete crack develops obliquely from horizontal cracking with the increase of stiffness, and the damage characteristic develops from bending damage to shear damage. The initial stiffness of the precast joint is about 1.5 times that of the cast-in-place joint, the yield load is increased by 31 %, the peak load by 52 % and the ductility coefficient by a maximum of 96 %, with significantly better mechanical properties than the cast-in-place joint. Parametric analysis was carried out based on the tests. When the flexural stiffness ratio of the cantilevered section to the reinforced concrete beam section is less than 0.5, it is a weak connection. Damage to the section cantilever section occurs, and the stiffness degrades significantly. It is recommended that the joint be designed for a strong connection, with a stiffness ratio of around 0.6. The cantilever section's length greatly influences the joint's stress transfer. It is recommended that the length be taken to be about 0.6 and no greater than 0.75 for the width of the precast reinforced concrete beam. The design process of a prefabricated RC frame is given on this basis. A research basis has been laid for the engineering application of this new type of connection.

Prediction of acute rejection in renal allografts using shear-wave dispersion slope.

To evaluate the role of shear-wave dispersion slope for predicting renal allograft dysfunction. We retrospectively reviewed 128 kidney transplant recipients (median age, 55years [interquartile range, 43-62years]; male, 68) who underwent biopsy for allograft evaluation from November 2022 to February 2023. Cortex and renal sinus fat stiffness and shear-wave dispersion slope were obtained at shear-wave elastography (SWE). Cortex-to-sinus stiffness ratio (SR) and dispersion slope ratio (DSR)-related clinical and pathologic factors were evaluated using multivariable linear regression analysis. We conducted univariate and multivariate analyses for multiparametric ultrasound (US) parameters for identifying acute rejection and calculated the area under the receiver operating curve (AUC) values. Of 128 patients, 31 (24.2%) demonstrated acute rejection. The SR value did not differ between patient groups (1.21 vs. 1.20, p = 0.47). Patients with acute rejection demonstrated a higher DSR than those without rejection (1.4 vs. 1.21, p < 0.01). Interstitial fibrosis and tubular atrophy grade (IFTA; coefficient, 0.11/grade; p = 0.04) and renal transplant and biopsy interval (coefficient, 0.00007/day; p = 0.03) were SR determinant factors, whereas only IFTA grade (coefficient, 0.10/grade; p = 0.01) for DSR. Multivariate analysis revealed mean resistive index (odds ratio [OR] 1.08, 95% confidence interval [CI] 1.02-1.14, p = 0.01) and DSR value (OR 16.0, 95% CI 3.0-85.8, p = 0.001) as independent factors for predicting acute rejection. An AUC of 0.74 for detecting acute rejection was achieved by combining the resistive index and DSR value. Shear-wave dispersion slope obtained at SWE may help identify renal allograft dysfunction. Acute rejection in renal allografts is a major cause of allograft failure, but noninvasive diagnosis is a challenge. Shear-wave dispersion slope can identify acute rejection non-invasively. • The interstitial fibrosis and tubular atrophy grade was a determinant factor for stiffness ratio and shear-wave dispersion slope ratio between cortex and renal sinus fat. • Shear-wave dispersion slope ratio between cortex and renal sinus fat could identify acute rejection in renal allografts. • A shear-wave dispersion slope has a potential to reduce unnecessary renal biopsy for evaluating renal allografts.

Stress analysis of assembled concrete structures with application of finite element modeling

Abstract In the paper, the finite element model of the assembled concrete structure is constructed based on the finite element method combined with ABAQUS software, including the specific definition of the model material, the boundary condition and contact setting, the analysis step and loading setting, and the validity of the constructed finite element model is verified. In order to deeply explore the stress changes of the assembled concrete structure, four aspects were analyzed, namely, concrete strength grade, load-mid-span displacement curve, stress of tensile and compressive reinforcement, and stress changes of frame combination beams respectively. The results showed that the larger the concrete strength grade, the relative stiffness ratio at the peak point gradually decreased from 0.44 to 0.27, and the specimen of concrete structure with higher steel content reached the maximum load at the mid-span displacement of 12.5 mm. The reinforcement at the end of the steel frame reaches the yield stress only when the lateral displacement is 25.8 mm, while the RC frame reaches the yield stress when the lateral displacement is 16.1 mm. When the load of the assembled concrete structural frame combination beams does not exceed 0.5 times the ultimate load, the stress change is elastic, which can ensure the stability of the assembled concrete structural building. Using the finite element model to model the assembled concrete structure numerically analyzes its stress change, which can better grasp the development of its structural stress during the actual casting process so as to ensure the safety of the building structure.

Shear stability and resistance design of novel vertically-flexible stiffened steel plate shear walls

Steel plate shear walls (SPSWs) have been widely employed in practical engineering projects. The steel plates inevitably endure axial loads due to the gravitational forces and structural settling. However, vertical pre-compressive loads have detrimental effects on the buckling behavior and shear resistance of the steel plates. Instead of strengthening the SPSWs to resist the vertical loads, a new type of vertically-flexible stiffened steel plate shear wall (VFS-SPSW) is proposed to minimize these adverse effects. The incorporation of hollow steel tube reduces the vertical compressive stiffness of the VFS-SPSW, leading to a decrease in the proportion of axial compressive loads transmitted to the steel plate wall from the boundary frame. Consequently, this feature facilitates the installation of VFS-SPSW without the necessity of awaiting the completion of the upper structure. In this paper, finite element (FE) analysis is conducted to obtain a threshold out-of-plane bending stiffness ratio for the stability of the VFS-SPSW. Subsequently, a formula for threshold out-of-plane bending stiffness ratio is proposed, including parameters of the ratio of torsional to bending stiffness and aspect ratio of the subpanel. Then, the anchoring mechanism of hollow steel tube to the tensile field of the steel plate is investigated. The threshold in-plane anchor stiffness ratio is defined to ensure the full development of the tension field in the steel plate. A formula for predicting this ratio is proposed by theoretical and numerical analysis. Finally, the reduction factor of vertical compressive stiffness for the VFS-SPSW at the threshold in-plane anchor stiffness ratio is calculated. The results indicate that the vertical compressive stiffness of the VFS-SPSW, which meets the threshold stiffness design requirements, can be decreased to below 50% of the traditional stiffened SPSW, while ensuring that the reduction in ultimate shear stress remains within the limit of 5%.

Seismic performance of high-strength steel plate-concrete composite shear walls

The application of high-strength steel plate-concrete composite shear walls in super high-rise frame-core tube structure can significantly increase the bearing capacity, reduce the dimensions of the core tube and the frame part, and harmonize the stiffness ratio of frame and core tube, therefore improve the economic efficiency. In order to study the seismic performance of the high-strength steel plate-concrete composite shear walls, pseudo-static tests on three composite shear wall specimens with an aspect ratio of 1.43 were conducted, the failure mechanism, strength, ductility and energy dissipation capacity of specimens with Q355B, Q460B, Q550B steel were studied. Experimental results showed that the crushing of concrete and the failure of vertical reinforcement at the corner leaded to the flexural failure of specimens; hysteresis curves of specimens showed good energy dissipating capacities without pinching phenomena; with the increase of the steel strength, the yield strength, yield displacement, peak strength and ultimate displacement of specimens increased, while ductility decreased. Finite element analysis was conducted using OpenSees, the modeling method had been proven accurately simulate the performance of the specimens, and was subsequently used for parametric study to investigate the impact of axial compression ratio, thickness of the embedded steel plate, and aspect ratio (height to width) on the performance of high-strength steel plate-concrete composite shear walls.

The Influence of Box-Strengthened Panel Zone on Steel Frame Seismic Performance

During the Northridge earthquake, extensive brittle failures on the weld zones of the beam bottom flanges in the rigidity connection of steel special moment frames (SMFs) were detected. One of the primary reasons is the high-tensile strain demand created at the beam bottom flange zones due to positive bending. The weak panel zone of the I-section column exhibits more shear deformation, which promotes and accelerates the brittle fracture of the beam bottom flange weld zones. A box-strengthened panel zone can minimize the shear deformation of the panel zone of the I-section column, which may also reduce the inter-story displacement of steel SMFs and enhance their seismic behavior. In order to investigate this fact, in this research we carried out a model test of a steel frame with a box-strengthened panel zone to examine SMFs’ seismic performance and inter-story displacement, as well as testing the contribution of panel zone shear deformation to inter-story drift. Numerical methods were then used to investigate the influence of the axial compression ratio and beam-to-column linear stiffness ratio on the effect of shear deformation on the box-strengthened panel zone. Design recommendations are given based on the research results.

Dissimilar Pile Raft Foundation Behavior under Eccentric Vertical Load in Elastic Medium

Pile raft foundation (PRF) is a common foundation type for buildings and bridge piers which has been commonly subjected to eccentric vertical load in engineering applications. Dissimilar PRF is often adopted to reduce the excessive settlement and differential settlement of superstructures. The behavior of dissimilar PRF under eccentric vertical load is a significant issue and investigated with the boundary element method in this paper. In this method, the dissimilar pile–soil system is decomposed into extended soil elements and fictitious pile elements. The second kind of Fredholm integral governing equation of the axial force of fictitious piles is established based on the compatibility condition of axial strain between the extended soil and fictitious piles. An iterative procedure is adopted to analyze the average settlement w and rotation slope θ of raft stemming from the settlement compatibility condition of the top of each element and the equilibrium condition of the raft. Furthermore, the axial force and settlement of each element along its depth can be predicted. The corresponding results agree well with a reported case and the finite element method. The characteristics of 3 × 1 and 3 × 3 dissimilar PRFs under eccentric vertical load, including non-dimensional vertical stiffness N0/wEsd, differential settlement wd and the load sharing ratio of typical elements Ni/N0, are systematically investigated by considering different eccentricity e, length/diameter ratios of pile l/d and pile–soil stiffness ratio Ep/Es conditions. The N0/wEsd increases with l/d, while the load sharing ratios of the raft Nraft/N0 and wd decreases with l/d. The eccentricity e has a significant effect on wd and Ni/N0 and a neglect effect on N0/wEsd and Nraft/N0. The N0/wEsd, wd and Ni/N0 are significantly increased with Ep/Es. This research is expected to provide insights to the practitioners into the dissimilar PRF design under eccentric vertical load.

Neural Metamaterial Networks for Nonlinear Material Design

Nonlinear metamaterials with tailored mechanical properties have applications in engineering, medicine, robotics, and beyond. While modeling their macromechanical behavior is challenging in itself, finding structure parameters that lead to ideal approximation of high-level performance goals is a challenging task. In this work, we propose Neural Metamaterial Networks (NMN)---smooth neural representations that encode the nonlinear mechanics of entire metamaterial families. Given structure parameters as input, NMN return continuously differentiable strain energy density functions, thus guaranteeing conservative forces by construction. Though trained on simulation data, NMN do not inherit the discontinuities resulting from topo-logical changes in finite element meshes. They instead provide a smooth map from parameter to performance space that is fully differentiable and thus well-suited for gradient-based optimization. On this basis, we formulate inverse material design as a nonlinear programming problem that leverages neural networks for both objective functions and constraints. We use this approach to automatically design materials with desired strain-stress curves, prescribed directional stiffness and Poisson ratio profiles. We furthermore conduct ablation studies on network nonlinearities and show the advantages of our approach compared to native-scale optimization.

Microporous Polyurethane Elastomer’s Comprehensive Properties Affected by Flame Retardant EG/APP

The mechanical characteristics, creep resistance, fatigue resistance, and other comprehensive properties of flame retardants/microporous polyurethane elastomers (FRs/MPUE) have not been systematically researched. Because of this, we used expandable graphite (EG) and ammonium polyphosphate (APP) to conduct this study on FRs/MPUE composites. The thermal degradation and flame retardant characteristics, tensile strength, compressive creep, and dynamic and static stiffness ratio of FRs/MPUE were studied. The findings demonstrated that the optimum synergistic flame retardant effect occurred when the ratio of EG to APP was 2:1. The LOI of MPUE reached 30.5%. The vertical combustion grade achieved V-0. The stage of thermal decomposition was the most stable. However, compared with pure MPUE, the tensile strength was slightly decreased, and the compressive creep and dynamic and static stiffness ratio were slightly increased. The MPUE’s LOI value was more than or equal to 26% when the EG to APP ratio was 2:1 to 1:2. The tensile strength was basically the same as that of pure MPUE. The compression creep was less than 5%, which met the B1 flame retardant requirements and creep resistance performance indicators of floating floor vibration-damping pads.

Flexural rigidity of pressurized model notochords in regular packing patterns

The biomechanics of embryonic notochords are studied using an elastic membrane model. An initial study varying internal pressure and stiffness ratio determines tension and geometric ratios as a function of internal pressure, membrane stiffness ratio, and cell packing pattern. A subsequent three-point bending study determines flexural rigidity as a function of internal pressure, configuration, and orientation. Flexural rigidity is found to be independent of membrane stiffness ratio. Controlling for number and volume of cells and their internal pressure, the eccentric staircase pattern of cell packing has more than double the flexural rigidity of the radially symmetric bamboo pattern. Moreover, the eccentric staircase pattern is found to be more than twice as stiff in lateral bending than in dorsoventral bending. This suggests a mechanical advantage to the eccentric WT staircase pattern of the embryonic notochord, over patterns with round cross-section.

A Low-Frequency Vibration Isolator with Cross-Ring Structure

Low-frequency vibration isolation is essential for ultra-precision manufacturing and measurement equipment. Low stiffness is beneficial for low-frequency isolation, while leading to a degradation of the load capacity of the isolator. To tackle the problem, a nonlinear isolator is proposed with a cross-ring structure, composed of a circular ring and a semi-circular ring. Experimental studies validate that the isolator is applicable to different payload mass, and a cut-off frequency of 1.1[Formula: see text]Hz is achieved for an effective isolation. The isolator is theoretically investigated to reveal the mechanism leading to the low-frequency isolation performance. An elliptic integral method is adopted to characterize the stiffness characteristics of the ring structures under compression. The whole compression process of a semi-circular ring is divided into five stages according to the deformed shapes, exhibiting quasi-linear stiffness, stiffness-softening, negative stiffness, and stiffness-hardening characteristics in sequence. Together with the stiffness-softening circular ring, the cross-ring structure demonstrates a growing high-static-low-dynamic-stiffness (HSLDS) characteristic in a wide load range, and the result is verified by a restoring force measurement test. A harmonic balance analysis is performed to predict the frequency responses of the proposed isolator. It is shown that a low-frequency isolation can be achieved with the structure compressed to the HSLDS region by the payload, and an ultra-low-frequency isolation is achieved with the dynamic-to-static stiffness ratio below 0.1. A numerical investigation is performed to further reveal the frequency responses of the isolator with lightweight/overweight payloads and excessive excitation amplitudes. Jump phenomena are presented. This work provides a prototype and the theoretical basis for low-frequency vibration isolation via a cross-ring structure.

Experimental Investigate on Seismic Performance of RC Hill-Side Stilted Buildings Affected by Vertical Stiffness Irregularity

ABSTRACT In this study, the ratio of lateral stiffness of the stilted story to that of the second story was proposed as the story stiffness ratio (SSR) to quantify vertical stiffness irregularities of hillside stilted buildings. A quasi-static experiment was conducted on a plane stilted frame with an SSR of 40 in the slope direction. Experimental results were compared with those of a stilted frame with an SSR of 1.01. The results show that SSR is an important factor influencing seismic failure modes of stilted buildings. As SSR decreases, structural ductility and deformation capacity improve, and stiffness degradation decelerates.

Reverse time migration and genetic algorithms Combined for Reconstruction in Transluminal Shear Wave Elastography: An In Silico Case Study

A new reconstruction approach that combines Reverse Time Migration (RTM) and Genetic Algorithms (GAs) is proposed for solving the inverse problem associated with transluminal shear wave elastography. The transurethral identification of the first thermal lesion generated by transrectal High Intensity Focused Ultrasound (HIFU) for the treatment of prostate cancer, was used to preliminarily test in silico the combined reconstruction method. The RTM method was optimised by comparing reconstruction images from several cross-correlation techniques, including a new proposed one, and different device configurations in terms of the number and arrangement of emitters and receivers of the conceptual transurethral probe. The best results were obtained for the new proposed cross-correlation method and a device configuration with 3 emitters and 32 receivers. The RTM reconstructions did not completely contour the shape of the HIFU lesion, however, as planned for the combined approach, the areas in the RTM images with high level of correlation were used to narrow down the search space in the GA-based technique. The GA-based technique was set to find the location of the HIFU lesion and the increment in stiffness and viscosity due to thermal damage. Overall, the combined approach achieves lower level of error in the reconstructed values, and in a shorter computational time, compared to the GA-based technique alone. The lowest errors were accomplished for the location of HIFU lesion, followed by the contrast ratio of stiffness between thermally treated tissue and non-treated normal tissue. The homologous ratio of viscosity obtained higher level of error. Further investigation considering diverse scenarios to be reconstructed and with experimental data is required to fully evaluate the feasibility of the combined approach.

Fire research of joint between special-shaped CFST column and U-shaped composite beam

The steel-concrete composite joint plays an important role in the building structure of transmitting load and maintaining structural stability, and the research on fire performance of composite joints is significant. The special-shaped concrete-filled steel tube (SCFST) column and U-shaped steel-concrete composite beam (USCB) have good fire resistance which is proved by authors' previous fire tests. Therefore, the fire performance of the joint between SCFST column and USCB, the temperature distribution, failure mode, fire resistance, and internal force distribution of the joint under fire are investigated based on the fire tests results of column and beam component. The results showed that the temperature of the joint zone is lower than that of the non-joint zone, which ensured that the strength and stiffness of the joint zone are higher than that of the non-joint zone (beam and column). Then the two failure modes including beam failure and column failure occurred in the composite joint in fire conditions. Furthermore, the internal force analysis indicated that internal force redistribution happens during the elevated temperature. The parameter analysis expressed that fire resistance decreases with the increase of load ratio and the beam-column moment ratio and increases with the increase of the beam-column stiffness ratio and the fire protection layer thickness. Finally, the high-temperature calculation formula for the bearing capacity of beam-column joint was proposed.

Vibration reduction performance for the novel grounded inerter-based dynamic vibration absorber controlling a primary structure under random excitation

This paper investigates the control performance of a novel grounded inerter-based dynamic vibration absorber (GI-DVA) for random vibration reduction. First, the dynamics equations of the coupled system are written and the transfer function is obtained based on the Laplace transform. Then, assuming that the primary structure is under random white noise excitation, the displacement variance of the primary structure is calculated based on the exact definition of the H2 norm, by solving the Lyapunov equation. By imposing that the partial derivatives of the response variance of the primary structure with respect to the system parameters are simultaneously equal to zero, the optimum design values of the H2 optimized GI-DVA were derived numerically for given different mass ratio. It can be found that the optimal design parameters as the inerter-to-mass ratio, the stiffness ratio and the damping ratio increase, while the frequency ratio decreases with the increase in the mass ratio. Under the optimal conditions, the response analysis showed that the primary structure response controlled by the H2 optimized GI-DVA can decrease with the increase in the mass ratio, but is less sensitive to large mass ratios, and can be robust to the mistuning on the optimum design parameters. Then, the control performance evaluation is first performed in the frequency domain, which reveal that the dynamic response reduction capacity of the H2 optimized GI-DVA are significantly 62% and 48% superior to the H2 optimized classic DVA (CDVA) and high-performance passive nontraditional inerter-based DVA (NIDVA-C4), respectively. Furthermore, for the root mean square response evaluation (H2 performance), the H2 optimized GI-DVA can provide significantly H2 performance 58% and 50% than the H2 optimized CDVA and NIDVA-C4, respectively. To obtain more realistic results, the time domain simulation is performed, which showed that the GI-DVA can provide significantly performance for random vibration reduction.