High Initial Stiffness Research Articles

Numerical modeling of seismic behavior of ellipse and peanut-shaped auxetic steel plate shear walls

This study proposes a new auxetic-shaped steel plate shear walls (simply referred to as ASSPSWs) consisting of boundary members and built-in perforated infill plates. The connection type between the boundary members is a hinge joint. The hole forms on the infill plates include orthogonal ellipse-shaped (ASSPSW-OE) and orthogonal peanut-shaped (ASSPSW-OP). This paper studied the hysteretic performance of two steel plate shear walls’ types based on the finite element analysis method. Within the study context, a parametric analysis was carried out to investigate the influence of various factors, such as hole size and hole distance, on the seismic performance of steel plate shear walls (SPSWs). The results indicated that reducing the the ratio of the ligament thickness to ellipse major axis (t/D) in orthogonal ellipse-shaped SPSWs can effectively increase the porosity while reducing the bearing and energy dissipation capacities. Under the condition with the t/D unchanged, increasing the ratio of the major to minor axis of the ellipse (d/D) raises the porosity and does not significantly reduce the bearing capacity and energy dissipation capacity of the SPSWs. For orthogonal peanut-shaped SPSWs, the holes’ geometrical parameters significantly influence the hysteretic performance. Particularly, with the increase in the radial ratio of large to small circles in a peanut-shaped hole (R/r), the spacing between cells decreases. When drift exceeds 2%, the equivalent viscous damping ratio decreases sharply. Unlike the orthogonal ellipse-shaped SPSWs, changing the arrangement angle of peanut-shaped cells has no significant effect on orthogonal peanut-shaped SPSWs. However, the larger the angle, the greater the out-of-plane buckling of orthogonal ellipse-shaped SPSWs; thus, the energy dissipation capacity is reduced. The similarities lie in that the larger cell arrangement angle will make the steel plates have a complete stress field, and the bearing capacity will be slightly improved. When the cell arrangement angle (θ) is 45°, the SPSWs can develop high initial stiffness.

Experimental study on frictional behavior of different structural materials

Friction dampers were widely applied to the beam-column connections to dissipate earthquake energy. The damage of buildings under earthquake could then be reduced obviously. To ensure the good performance of the friction dampers, the appropriate selection of the materials for the friction pads was important. This paper investigated the coefficient of friction of different materials under cyclic loading. Four types of materials which included steel, galvanized steel, brass, and aluminum were chosen. The studied variables were the surface cleaning process, the bolt pretension, and the loading protocols. The test results showed that the shot blasting process significantly enhanced the coefficient of friction and the energy dissipation ability. Friction dampers with friction pads made of these four materials offered high initial stiffness. They could provide the needed stiffness for the structures. The coefficient of friction was largely affected by the bolt pretension and the loading protocols. Except for the friction damper with friction pads made of aluminum, the other three friction dampers exhibited satisfactory energy dissipation ability without obvious strength degradation. Mathematical models were proposed to predict the variation of the coefficient of friction for different materials. Good agreement was found between the prediction and the test data.

All-metal enhanced members with extreme dissipation capacity for vibration suppression of grille structures

Marine structures are supposed to simultaneously possess high stiffness bearing high loadings and large damping dissipating dynamic energy. Structural impact protection and stiffening approach is achieved via assembling a pre-compressed negative stiffness component and linear members, which not only exhibits high initial stiffness but also dissipation capacity approaching the theoretical limit under small deformation. The effects of design parameters on the energy dissipation characteristics are investigated by the combination of quasi-static, dynamic and finite element analysis. For potential applications, the dynamic responses and vibration suppression of a representative grille structure optimized by the novel design are studied via FE simulations.

Poly(ethylene glycol)-Norbornene as a Photoclick Bioink for Digital Light Processing 3D Bioprinting.

Digital light processing (DLP) bioprinting is an emerging technology for three-dimensional bioprinting (3DBP) owing to its high printing fidelity, fast fabrication speed, and higher printing resolution. Low-viscosity bioinks such as poly(ethylene glycol) diacrylate (PEGDA) are commonly used for DLP-based bioprinting. However, the cross-linking of PEGDA proceeds via chain-growth photopolymerization that displays significant heterogeneity in cross-linking density. In contrast, step-growth thiol-norbornene photopolymerization is not oxygen inhibited and produces hydrogels with an ideal network structure. The high cytocompatibility and rapid gelation of thiol-norbornene photopolymerization have lent itself to the cross-linking of cell-laden hydrogels but have not been extensively used for DLP bioprinting. In this study, we explored eight-arm PEG-norbornene (PEG8NB) as a bioink/resin for visible light-initiated DLP-based 3DBP. The PEG8NB-based DLP resin showed high printing fidelity and cytocompatibility even without the use of any bioactive motifs and high initial stiffness. In addition, we demonstrated the versatility of the PEGNB resin by printing solid structures as cell culture devices, hollow channels for endothelialization, and microwells for generating cell spheroids. This work not only expands the selection of bioinks for DLP-based 3DBP but also provides a platform for dynamic modification of the bioprinted constructs.

Development and investigation of an innovative shape memory alloy cable‐controlled self‐centering viscoelastic coupling beam damper for seismic mitigation in coupled shear wall structures

AbstractTo improve the seismic performance of coupled shear walls in high‐rise buildings and to eliminate the problems of large residual deformation and relatively small initial stiffness and damping properties of the traditional viscoelastic coupling beam damper (TVCBD), an innovative shape memory alloy (SMA)‐cable‐controlled self‐centering viscoelastic coupling beam damper (SVCBD) with energy dissipation and self‐centering capabilities was designed and investigated in this study. The construction form and operating principles of the SVCBD were proposed, relevant material performance tests of the cables were performed, and good results were obtained. Finally, the contribution of the SVCBD to seismic mitigation of a 10‐story reinforced concrete coupled shear wall structure was verified by seismic time‐history analyses. The results indicated that compared with TVCBD, SVCBD possesses fuller hysteretic curves, showing stronger energy dissipation capacity, higher initial stiffness, and much smaller residual deformation. The initial strain and cross‐sectional area of the SMA cables and the shear area of the viscoelastic plates affect the energy dissipation and self‐centering performance of SVCBD significantly. The seismic response and post‐earthquake residual deformation of the coupled shear wall structure and the plastic damage of the main components can be effectively controlled by utilizing the proposed SVCBD.

Evaluation of slip behaviour of self-locking modular steel connection

Modular steel building (MSB) is an exceptional substitute for traditional on-site steel construction. Bolt hole tolerance is provided in inter-modular connections (IMC) to allow positioning of modules which causes a higher initial slip of bolted connection. This study proposes a new connection with a four-stage assembly procedure that omits the need for excess hole tolerance in bolted connections and provides higher initial stiffness. The performance of this proposed connection is evaluated using finite element analysis, which has been validated against the existing experimental data from the literature. An analytical study is conducted on two variants of the proposed connection, the first variant with bolts and the second variant with dowel pins, to evaluate the shear force-slip behaviour. The force-displacement curve of the proposed connection is compared with existing models of bolted connections. Results show that the connections with pretension force applied on bolts had good agreement with the traditional four-stage model for bolted connection. Equations provided by established design codes can predict the initial stiffness in IMCs.

Investigation of equal strength mild steel tenons as displacement restraining devices for long-span railway arch bridges

In this paper, Equal Strength Mild Steel Tenons (ESMSTs) have been developed as a candidate for displacement restraining device of long-span railway arch bridges. They are made of a cheap and easily fabricated material, low carbon mild steel. The geometry is designed according to the principle of equal strength beam to make full use of the ductile deformation of mild steel, increase the energy dissipation capacity and alleviate damage concentration. To begin, the design concept of ESMST is given followed by the derivation of the theoretical formula of the mechanical properties with the vertical free mechanism which is of no vertical load to guide the design. A pseudo-static experiment program is then presented for two full-scale 2.5 m tall ESMSTs. Besides, a rigorous 3D numerical model was developed in ABAQUS to reproduce the behavior of ESMSTs to guide the design of ESMST in future application. Finally, a case study is presented for the application of ESMST in one of typical long-span railway arch bridges to evaluate its efficiency and effectiveness. The test results indicate that the tested ESMSTs can meet the demands of the long-span railway arch bridges for high initial stiffness, energy dissipation and deformability under strong earthquake action. It was also found that the ESMST had good fatigue performance. In addition, the developed numerical model in ABAQUS can accurately reproduce hysteretic behavior of the ESMST and hence can be used with confidence in the future to guide the design of ESMSTs. Results from the case study show the ESMSTs can work effectively and efficiently in reducing the response of long-span railway arch bridges without imposing much additional demand on the substructure. Findings of this study can provide guidance on the design of ESMSTs as well as support for the application of the ESMSTs in long-span railway arch bridges.

Silver Sintering of Packaged GaN-Devices on Printed Circuit Board

Abstract Despite the higher thermal conductivity and the higher lifetime offered by silver sintering technologies, most packaged GaN devices are attached using solders due to technological difficulties in the sintering process. In this work, a silver sintering process for a packaged GaN power transistor on a printed circuit board (PCB) was successfully developed. Different sintering paste types were examined regarding their suitability for this application. Electrical measurements, shear tests, and metallographic cross sections were used for the evaluation. Numerical analyses were used to study the internal stress distribution in the GaN package after sintering depending on the paste structure. In the final sintering process, a shear strength of 20 MPa for sintering at 15 MPa and 240°C, for 300 s with electrical functional devices could be obtained by using nanoscale sintering paste. The authors contribute this to the high initial stiffness of the silver layer, which is obtained much earlier in the sintering process compared with the stiffness of a microscale silver paste. This high initial stiffness counteracts the semiconductor device deflection from the applied sintering pressure and reduces the stresses inside the semiconductor.

Chondroitin Sulfate Promotes Interstitial Cell Activation and Calcification in an In Vitro Model of the Aortic Valve.

Calcific aortic valve disease (CAVD), has been characterized as a cascade of cellular changes leading to leaflet thickening and valvular calcification. In diseased aortic valves, glycosaminoglycans (GAGs) normally found in the valve spongiosa migrate to the collagen I-rich fibrosa layer near calcified nodules. Current treatments for CAVD are limited to valve replacement or drugs tailored to other cardiovascular diseases. Porcine aortic valve interstitial cells and porcine aortic valve endothelial cells were seeded into collagen I hydrogels of varying initial stiffness or initial stiffness-matched collagen I hydrogels containing the glycosaminoglycans chondroitin sulfate (CS), hyaluronic acid (HA), or dermatan sulfate (DS). Assays were performed after 2 weeks in culture to determine cell gene expression, protein expression, protein secretion, and calcification. Multiple regression analyses were performed to determine the importance of initial hydrogel stiffness, GAGs, and the presence of endothelial cells on calcification, both with and without osteogenic medium. High initial stiffness hydrogels and osteogenic medium promoted calcification, while for DS or HA the presence of endothelial cells prevented calcification. CS was found to increase the expression of pro-calcific genes, increase activated myofibroblast protein expression, induce the secretion of collagen I by activated interstitial cells, and increase calcified nodule formation. This study demonstrates a more complete model of aortic valve disease, including endothelial cells, interstitial cells, and a stiff and disease-like ECM. In vitro models of both healthy and diseased valves can be useful for understanding the mechanisms of CAVD pathogenesis and provide a model for testing novel therapeutics.

Research on the specially-shaped corrugated steel plate shear walls with horizontal corrugation

A specially shaped corrugated steel shear wall (S-CSSW) system was proposed for the application of steel residential buildings. The proposed shear wall system featured a main shear wall with small section concrete filled steel tube (CFST) boundary columns and horizontally corrugated shear plates and side short pier CSSWs in the perpendicular direction. Quasi-static cyclic tests were performed on the S-CSSWs with and without reinforcing beams to investigate the shear strength, failure modes and hysteretic responses. Finite element simulations were introduced to further study the shear bearing mechanisms of S-CSSWs for a comparison with traditional flat plate shear walls with similar wall configurations. An additional parametric simulation was performed to investigate the influence of the corrugated plate width on failure modes. Results indicated that the proposed S-CSSWs possessed good ductility. Compared with the flat plate shear walls, the proposed shear walls had higher initial stiffness and elastic shear strength. The width of the corrugated shear panels was an important factor influencing the failure modes and lateral bearing abilities and needed to be carefully controlled to avoid early buckling occurring ahead of the shear yielding mode. Some design remarks are concluded regarding the design of the corrugated shear panels and stiffening beams.

PERFORMANCE OF SQUARE REINFORCED CONCRETE COLUMNS CONFINED WITH INNOVATIVE CONFINING SYSTEM UNDER AXIAL COMPRESSION

Several structural failures occur in the columndue to the lack of confinement. The circular column is not popular for regular buildings. The use of circular spiral is only familiar tothe circular column. Many design engineers usesquare columns with hoops and cross tiesas confinement. As far as the authors’ knowledge, therewasonly a study carried out on square columnswith circular spirals as confinement. For this reason, the authors propose and introduce a new type of innovative confinement system for square columns using square spiralsas confinement and a combination thereof, which has never been carried out in the previous studies. No code’s provision is also applicable tothis type of confinement.This research was conducted to investigate the performance of each of these new confinement systems as a promising option in the future instead of the traditional confinement. To achieve the objective of the research, a two-phase study was conducted. The first phasewas to analyze the potential, design, formation, and assemblyof the new confinement systemconsisting of a combination of square and circular spirals (SPIL), a combination of octagonal and square spirals (SS8I), an interlocking among square spirals (SPIP), and a plain concrete specimen (PC) as a benchmark. The second phasewas an experimental program that involvesa mix-designof the concrete, preparation of the column specimens with various confinement systems, and the compression tests of the column specimens using a 3500-kN UTM. The test results indicate that the SPIP specimen has higher initial stiffness, peak stress, and strain ductility compared with others.

Seismic design of innovative steel frames with partially‐prefabricated infill walls

AbstractHybrid steel and concrete seismic‐resistant systems made by steel frames with reinforced concrete infill walls (SRCWs) have potential advantages over structural solutions made only by steel or reinforced concrete (RC). In fact, the high initial stiffness of concrete is useful to minimize the damage of non‐structural elements under frequent (low to moderate) earthquakes while the ductility and dissipative capacity of the steel allow good performances under rare (high‐intensity) events. Eurocode 8 considers SRCW systems to behave essentially as RC walls. However, numerical analyses on SRCWs, designed according to the Eurocodes, pointed out an unsatisfactory seismic behaviour with discrepancies between the behaviour assumed in the design and the simulated response under seismic actions. Indeed, the idea of stiffening a steel frame with a RC infill leads complex mechanisms that are difficult to control as being affected by many variables. In this study, some of the recent developments made for innovative SRCW are transferred to hybrid steel and concrete walls with partially‐prefabricated infills. Numerical models are analysed to understand the global behaviour of the considered SRCWs and to provide a preliminary validation of the proposed structural solution.

Ethylene Propylene Diene Monomer (EPDM) Effect on Asphalt Performance

The asphalt industry is increasingly developing with greater focus on sustainability. This study focuses on the benefits of a binder modification of stone mastic asphalt (SMA) by adding a rubber—ethylene propylene diene monomer (EPDM)—into a class 320 bitumen. This study observes the advantages that occur for the rutting and fatigue performance of the samples. The binder modification was made by incorporating 0, 2, 4 and 6% binder weight into each sample. The tests performed on the samples were the wheel-tracking test and the four-point beam bending test. The results revealed varied outcomes, with the four-point beam bending test showing the 6% sample having the highest initial stiffness and modulus of elasticity but the lowest cycle to failure. Therefore, the best performer was determined as the 4% sample, which performed consistently throughout, having the highest cumulative dissipated energy and second-highest initial flexural stiffness, modulus of elasticity and cycle to failure results. There was a clear indication of the best performer for the wheel-tracking test, with the 4% sample having the lowest rut depth, although there were signs of further improvement to be achieved within the 4–6% range. In addition, drain-off tests were conducted on the mixtures, and the addition of EPDM significantly reduced the SMA drain-off values. Overall, the best improvements through binder modification for an SMA mix with EPDM concerning fatigue and rutting resistance came from a 4% incorporation.

Axial capacity and stiffness of post-heated circular and square columns strengthened with carbon fiber reinforced polymer jackets

The exposure of reinforced concrete (RC) columns to elevated temperatures is detrimental to its axial capacity and stiffness. Selecting the proper strengthening technique to repair heat-damaged RC columns is critical to ensure that the axial capacity and stiffness are restored. This paper examines the performance of different strengthening schemes using carbon fiber reinforced polymer (CFRP) jackets and near-surface mounted (NSM) steel bars in repairing circular and square RC columns damaged due to the exposure to high elevated temperature. The tested columns were divided into three categories, un-heated and un-strengthened columns, post-heated and un-strengthened columns, and post-heated and strengthened columns. The heated columns were exposed to 600 °C for 3 h. Two strengthening schemes were evaluated. The first strengthening scheme consisted of unidirectional CFRP strips in combination with NSM steel bars. The second scheme consisted of strengthening with unidirectional CFRP strips only. All the columns were tested under axial compression until failure. The test results showed that exposure to elevated temperatures caused a reduction in the load-carrying capacity of 38% in circular columns and 29% in square columns. Both strengthening schemes were effective in restoring and exceeding (by approximately 16%) the initial load-carrying capacity of heat-damaged RC columns. The use of CFRP strips in combination with NSM steel bars was more effective in restoring the initial stiffness of the post-heated columns compared to using CFRP strips alone. The initial stiffness recovery was more pronounced in circular columns compared to square columns. Circular columns exhibited 15% higher initial stiffness when compared to the control columns before heat-exposure. For square columns, the initial stiffness was equivalent to the initial stiffness of the control RC columns before heat-exposure.

Some Aspects of Shear Behavior of Soft Soil-Concrete Interfaces and Its Consequences in Pile Shaft Friction Modeling.

This paper examines the stiffness degradation and interface failure load on soft soil–concrete interface. The friction behavior and its variability is investigated. The direct shear tests under constant normal load were used to establish parameters to hyperbolic interface model which provided a good approximation of the data from instrumented piles. Four instrumented piles were used to obtain reference soil–concrete interface behavior. It was found that the variability of the friction characteristics is the highest for organic clays and the lowest for organic silts. The intact samples exhibit lower shear strength than reconstituted ones. The adhesion varies significantly depending on interface and soil type, which can result in high scatter of the skin friction prediction. The analysis of parameters variability can be used to determine the upper and lower bound of friction behavior on the interface at constant normal load condition. The backward shearing results in decrease in shear strength up to 40% of the precedent forward phase but higher initial stiffness by a factor of between 2 and 3. Presented research provides basic shear and stiffness parameters for four soft soils (organic clay, organic silt, peat, and silty loam) and gives information about variability of interface characteristics.

Experimental Testing and Analytical Modeling of Glulam Moment Connections with Self-Drilling Dowels

An experimental and analytical study on rotational behavior of glulam beam-column moment connections with self-drilling dowels (SDDs) is conducted. Connection properties including strength, stiffness, ductility, and energy dissipation were experimentally evaluated by testing seven full-scale connection specimens with and without self-tapping screw (STS) reinforcement along timber perpendicular to grain. All the connections showed high initial stiffness and high moment capacity when compared with the test results of bolted connections reported in the literature. The unreinforced connections had relatively low ductility due to timber splitting despite the increased fastener edge distance. The STS reinforcement effectively reduced the timber splitting tendency and encouraged the yielding of more SDDs, leading to slightly increased moment capacity, but significantly improved ductility. A modified analytical model (MAM) is then proposed to predict strength and rotation of the SDD moment connections based on force and moment equilibrium of the glulam members. Improved prediction accuracy is achieved for the SDD moment connections when compared with the past analytical methods.

Cyclic behavior of an innovative braced ductile thin shear panel

This study aimed to investigate the cyclic behavior of an innovative braced ductile thin shear panel (BDSP) component consisting of a concentric rectangular thin shear panel, a surrounding flange plate, and X-shaped brace segments. A total of eight BDSP specimens at a one-third scale were designed, considering the influence of shear panel thickness, shear panel dimension, and stiffening rib space. The tests were performed by applying a reversed cyclic lateral load. All specimens exhibited a high initial lateral stiffness and stable cyclic behavior and failed in the shear panel region. The adoption of stiffening ribs reduced the ductility of test specimens but enhanced the lateral strength and energy dissipation. Pinching of the lateral force versus drift ratio was observed for the BDSP specimens without stiffening ribs, which exhibited considerably high deformability and limited energy dissipation. Additionally, the specimens without stiffening ribs experienced elastic shear buckling behavior and developed a tension field mechanism in the shear panel region along the main diagonal direction. The overstrength factor (RΩ) value of 1.4 was conservatively recommended for the BDSP specimens without stiffening ribs.

Parametric analysis and failure mode of steel plate shear wall with self-centering braces

A steel plate shear wall with self-centering energy dissipation braces (SPSW-SCEDB) is developed and tested. The SPSW-SCEDB is prefabricated and replaceable. The effects of various design parameters on the hysteretic behavior of the SPSW-SCEDB without the effects of the frame are investigated. The experimental results show that the residual deformations of the wall plate are eliminated by the restoring force of braces, and the SPSW-SCEDB exhibits high initial stiffness, stable post-yield stiffness, and good energy dissipation capability. The SPSW-SCEDB with a thicker and wider wall plate has better energy dissipation capacity and higher post-yield stiffness. The wider wall plate reduces the lateral force contribution of the braces to the SPSW-SCEDB, resulting in the weakening of the overall strength of the SPSW-SCEDB. The SPSW-SCEDB has a good self-centering capability when the ratio of the horizontal restoring force of the braces to the compressive force of the wall plate is larger than 1.3. Compared with the size of the wall plate, the effect of the friction force on the SPSW-SCEDB is relatively small. The destructive test results demonstrate that the SPSW-SCEDB maintains stable lateral force resistance, energy dissipation and self-centering capabilities, even though the lateral drift is 4% and many wrinkles that cannot be smoothed out occur on the wall plate. In addition, the test results highlight the assembly capability and the replaceability of the components of the SPSW-SCEDB.

A novel design of printable tunable stiffness metamaterial for bone healing

A tunable stiffness bone rod was designed, optimized, and 3D printed to address the shortcomings of existing bone fixation devices, such as stress shielding and bone nonunion in the healing of fractured bones. Current bone plates/rods have constant and high stiffness. High initial stiffness prevents the micromotion of newly formed bone and results in poor bone healing. Our novel design framework provides surgeons with a ready-for-3D-printing, patient-specific design, optimized to have the desired force-displacement response with a stopping mechanism for preventing further deformation under higher-than-normal loads, such as falling. The computational framework is a design optimization based on the multi-objective genetic algorithm (GA) optimization with the FE simulation to quantify the objectives: tuning the varied stiffness while minimizing the maximum von Mises stress of the model to avoid plastic and permanent deformation of the bone rod. The computational framework for optimum design of tunable stiffness metamaterial presented in this paper is not specific for a tibia bone rod, and it can be used for any application where bilinear stiffness is desirable.

A homogenization‐based state‐dependent model for gap‐graded granular materials with fine‐dominated structure

AbstractGap‐graded granular soils are common natural soils composed of cohesionless granular matrix and rock aggregates. Since they are widely used as construction materials worldwide, their deformation behavior is crucial for the design of civil infrastructures. There have been rare constitutive models reported for gap‐graded granular soils in the literature. This study presents a homogenization‐based state‐dependent model within the elastoplastic framework. The model features a homogenization equation with a structure parameter and a novel state‐dependent dilatancy function to describe the behavior of granular matrix. Simulations of the model reveals that the initial stiffness and peak shear strength of gap‐graded soils rely on both the coarse fraction and the initial density of granular matrix. The structure parameter is related to the internal structure of gap‐graded soils, and it varies with the particle shape, and particle size distribution of rock aggregates. A higher value of the structure parameter indicates a more distinct coarse fraction effect of rock aggregates, that is, higher initial stiffness, higher peak shear strength, and higher residual shear strength. For a given coarse fraction, the critical states can be well fitted by a straight line through the origin, and the critical state strength parameter Mm increases with the rising rock fraction. A practical method is further proposed for the critical state line of gap‐graded granular soils in e‐p′ compression plane. The proposed model is validated by using experimental data from the literature, including the soils with various densities of sand matrix, different particle size, and particle size distribution of rock aggregates. Comparison between measured data and model predictions indicates that the proposed model can well reproduce the stress‐strain relationship and volumetric deformation behavior of sand‐gravel mixtures and soil‐rock mixtures.