Results Of Cyclic Tests Research Articles

Influence of Alkali Treatment of Jatropha Curcas L. Filler on the Service Life of Hybrid Adhesive Bonds under Low Cycle Loading

The aim of this research was to evaluate the effect of untreated and 5% aqueous NaOH solution-treated filler of the plant Jatropha Curcas L. on the mechanical properties of adhesive bonds, especially in terms of their service life at different amplitudes of cyclic loading. As a result of the presence of phorbol ester, which is toxic, Jatropha oilseed cake cannot be used as livestock feed. The secondary aim was to find other possibilities for the utilization of natural waste materials. Another use is as a filler in polymer composites, that is, in composite adhesive layers. The cyclic loading of the adhesive bonds was carried out for 1000 cycles in two amplitudes, that is, 5-30% of the maximum force and 5-50% of the maximum force, which was obtained by the static tensile testing of the adhesive bonds with unmodified filler. The static tensile test showed an increase in the shear strength of the adhesive bonds with alkali-treated filler compared to the untreated filler by 3-41%. The cyclic test results did not show a statistically significant effect of the alkaline treatment of the filler surface on the service life of the adhesive bonds. Positive changes in the strain value between adhesive bonds with treated and untreated filler were demonstrated at cyclic stress amplitudes of 5-50%. SEM analysis showed the presence of interlayer defects in the layers of the tested materials, which are related to the oil-based filler used.

Prediction of foundation stiffness and damping ratio under horizontal translation and rocking motion

In this paper, the results of snapback, cyclic and forced-vibration tests performed by laboratory and full-scale facilities are collected and analysed to investigate the nonlinear response of shallow foundations. The outcomes of tests on a full-scale soil-foundation-structure prototype, performed during the EU-research project SISIFO, were exploited to fill the lack of data on foundation damping and stiffness associated with the translation motion and enrich the database relevant to low-amplitude rocking motion. Predictive equations are calibrated to estimate the nonlinear variation of the foundation stiffness and damping ratio with the increasing amplitude of the foundation translation and rocking motions. In the latter case, the availability of numerous experimental data allows differentiating the predictive damping equation according to the so-called ‘critical foundation-soil contact area’, which is the most influencing factor on the energy dissipation capacity of the foundation. To prove the reliability of the proposed approach, two different applications with an increasing level of complexity are discussed. First, simplified analytical formulas are employed to calculate the fundamental period and damping ratio of the prototype tested during the SISIFO project. Then, a flexible-base model of the same structure is calibrated to simulate the experimental forced-vibration tests. The outcomes of both applications successfully match the experimental measurements.

Restoring force characteristic model for bending moment–rotation angle relationship of concrete‐filled square steel tube beam‐columns

AbstractThis paper proposes a new simplified restoring force characteristic model of the bending moment–rotation angle relationship for square concrete‐filled steel tube (CFT) beam‐columns to estimate the elastoplastic flexural‐shear behavior from short to slender beam‐columns. The square CFT beam‐column model incorporates a reduction in strength after the ultimate strength. The proposed simplified model is multilinear and involves a cracking strength point, a yield strength point, an ultimate strength point, and strength reduction points. In the proposed model, each flexural strength is calculated by a general superposed strength method, and new empirical expressions for each rotation angle are proposed from the results of previous experimental cyclic and monotonic loading tests. The proposed model for the bending moment–rotation angle relation is found to agree approximately with experimental results up to large rotation angles.

Investigation the temperature-dependent surface mechanical properties of PolyJet printed samples by cyclic indentation testing in a DMA system

Tools and products used in everyday life are regularly exposed to dynamic, cyclical stress. These stresses are particularly significant in the case of polymers, as their viscoelastic behavior means that creep can be considerable even at room temperature. Therefore, polymer components are often tested for maximum deformation rather than for maximum load-bearing capacity. Basic material testing methods are tensile, compression, and flexure tests, which are excellent for determining the material properties of the bulk material. However, in some cases, it is more appropriate to investigate surface mechanical properties. The ideal method for this is the depth-sensing indentation test. This method has been widely applied to polymers in the last ten years, but cyclic tests are rare, and creep is not considered in this type of indentation test. In the case of cyclical tests, temperature dependence is not fully examined, either. This paper presents the results of cyclic indentation tests on photopolymer specimens produced by additive manufacturing with the use of a dynamic mechanical analyzer with a unique indentation clamp. We performed the tests at three temperatures to investigate the influence of temperature on cyclic indentation tests. The test results show the variation of deformation between cycles and the significant effect of temperature.

Seismic Response Analysis of Steel–Concrete Composite Frame Structures with URSP Connectors

The uplift-restricted and slip-permitted (URSP) connector is a new type of connector used in steel-concrete composite structures that has been proven to improve the structural performance of negative moment regions. Since this connector changes the interface restraint between the slab and steel beam, there is an imperative to study the seismic performance of steel-concrete composite frame systems with this new type of connector. In this study, the dynamic behavior of composite frame structures with URSP connectors under seismic loads was numerically investigated. First, a beam-shell mixed model was used and complex interfaces of different connectors were considered while establishing a numerical model to conduct elasto-plastic time history analysis under various seismic loads. This numerical model was validated with the frame sub-assemblage experimental results of quasi-static cyclic tests. Second, the model analysis results of structures with URSP connectors were obtained and compared with those of traditional structures. Third, dynamic response results including roof displacement, inter-story displacement, and the distribution and failure modes of plastic hinges were analyzed and compared. The comparisons indicated that the arrangement of full-span URSP connectors had a non-negligible influence on the dynamic behavior of the systems. The arrangement increased the maximum inter-story displacement by 31.5% and induced adverse effects in certain cases, which is not suggested in the application of URSP connectors. The partial arrangement of URSP connectors had little influence on the dynamic behavior of the systems, and the frame systems still showed a good seismic performance, which was the same as the traditional composite structural system. These findings may promote the application of URSP connectors in composite structures.

Uniaxial tensile response and tensile constitutive model of ultra-high performance concrete containing coarse aggregate (CA-UHPC)

To establish the tensile constitutive model of ultra-high performance concrete containing coarse aggregate (CA-UHPC), monotonic and cyclic uniaxial tensile tests for CA-UHPC with fiber volume fractions of 2.5% and 2.0% were conducted. Test results showed that CA-UHPC exhibits approximately linear stress-strain relation up to the tensile strength, and tensile softening response composed of the smeared- and localized-cracking stages, regardless of the tested fiber contents. Based on the monotonic test data, the tensile stress-crack opening model of CA-UHPC was established, and the model was further simplified into tri-linear relation. Based on the cyclic test results, tensile damage evolution laws according to the strain equivalence principle and the energy equivalence principle were developed, respectively. Finally, the proposed tensile constitutive model and the calibrated tensile damage evolution laws were demonstrated to effectively predict the mechanical response of CA-UHPC members under both monotonic tension and cyclic tension through numerical simulations.

Quasi-static cyclic tests on a half-scaled two-storey steel frame equipped with Crescent Shaped Braces at both storeys: Experimental vs. numerical response

This paper discusses the results of quasi-static cyclic tests performed on a half-scaled two-storey one-bay steel pendular frame equipped with Crescent Shaped Braces (CSBs) at both storeys. The same steel pendular frame was previously tested with only one CSB device located at the first storey to validate the structural response of a single device when inserted into a realistic frame. The CSB seismic design procedure and the experimental results of this first configuration were presented and discussed in a companion paper which proved that the experimental behaviour of the single CSB matched the theoretical predictions and that the effect of connection plates was not negligible. Here the attention is focused, for the first time, on a structure fully braced along the height by CSBs as in a realistic building configuration. During the tests, the global and local responses of the structure were monitored by means of inductive displacement transducers, strain gauges and Digital Image Correlation technique. Non-linear Finite Element models were also developed to provide an in-depth interpretation of the experimental results. The objective is twofold: (i) the experimental assessment of the global performances of the braced structure in terms of stiffness, strength, ductility and energy dissipation, and (ii) the comparison between the experimental and the numerically-simulated response of the structure, with specific focus on the response of the two CSBs and on the effects of realistic connections (parasitic bending moments and bolt slippage). In conclusion, the results of the experimental test carried out on a two-storey building structure fully braced with CSBs proved that the CSB seismic design procedure is effective and the use of CSBs as diagonal braces could represent a feasible solution for buildings to achieve multiple seismic performance objectives.

Overturning effects on seismic performance of the hybrid friction-based seismic isolation system

The safety and reliability of the double-deck variable-depth composite truss bridge (DDVD-CTB) during earthquakes can be ensured by a hybrid friction-based seismic isolation system (HFBSIS). However, the overturning effects on seismic performance of HFBSIS is a significant concern, as it can induce vertical actions of isolation bearings. In this study, a single-degree-of-freedom (SDOF) system was first employed to describe the isolation system with the consideration of overturning effects. Following the nondimensionalization of motion equation, it indicated that the ratio of total axial load variations of spherical bearings to deadweight of the girder (γ) was a good indicator for the overturning effects on seismic performance. Then, the finite element (FE) model of SDOF system was developed and verified by the quasi-static cyclic test results. Finally, parametric sensitivity analyses were carried out to evaluate the degree of overturning effects on the seismic performance of the isolation system under different design parameters. Therefore, the maximum value γ of was less than 5 × 10−7 degree in the engineering practice. The nondimensionalization of motion equation considering overturning effects was approximately the same as that neglecting overturning effects, suggesting that overturning effects could be neglected when designing the HFBSIS in DDVD-CTB.

Development and verification of model predictive control strategy for selective catalytic reduction with rapid prototyping

The International Maritime Organization has set forth strict regulations about the NOx emission limit of ships to address the pollution problem in the transportation sector. Selective catalytic reduction (SCR) is the most effective post-engine means to reduce emission, and the control of urea spray critically affects the SCR performance. This paper developed a predictive control strategy of the SCR system based on the state space model. Specifically, the block model of the SCR reactor was established based on the reaction mechanism of the SCR system, and the unknown model parameters were identified. Rapid prototyping of the SCR system was carried out using the dSPACE real-time simulation platform to optimize the control under steady-state conditions. The catalyst ammonia coverage was set as the control target to maximize the NOx conversion rate while maintaining the NH3 escape at the outlet less than 10 ppm. The cyclic test results showed that the control strategy can quickly respond to external disturbance and modify the control target to keep the ammonia coverage rate within the target range, to thus achieve high NOx conversion rate while maintaining the required ammonia escape.

DSS tests on marine clays for offshore windfarm foundation design

This technical note presents results of a series of monotonic and cyclic DSS laboratory tests performed on five intact marine clays offshore China. The laboratory program aimed to determine the cyclic shear strength and soil deformation properties for offshore foundation design. Various cyclic contour diagrams are provided, including cyclic shear strength and average and cyclic shear strains for different number of cycles. Results of the five clays are discussed and compared with an existing database on static and cyclic strengths of clays. In general, the test data fits well with the database and OCR plays an important role in the cyclic behaviour of the marine clays. The provided cyclic strength parameters for the tested clays can be used as references for similar clays offshore. The purpose of this study is to provide a realistic reference for research and practice offshore China where very few cyclic test results are available for offshore wind energy industry.

Pore-water pressure accumulation during closely spaced earthquakes: Fundão Tailings Dam

ABSTRACT This paper focuses on pore-water pressure accumulation in loose sandy tailings during three (3) earthquakes within four minutes and the accompanying decrease in effective stress to assess the dynamic stability of the Fundão Tailings Dam, which failed on 5 November 2015. Results of laboratory cyclic direct simple shear tests are used to illustrate the accumulation of pore-water pressures with closely spaced low-level cyclic events. The seismically-induced pore-water pressures in the loose sands below the left abutment downstream slope and setback area are used to estimate the decrease in factor of safety with time until failure occurred within 20–30 minutes of the earthquakes. Field cone penetration and standard penetration test conducted prior to the failure are used to calculate the factor of safety against liquefaction to estimate pore-water pressures generated during the fore, main, and aftershocks in the sandy tailings. The effective stress stability analyses utilise a liquefied shear strength ratio for the sand tailings below the left abutment downstream slope and toe of the plateau because the sand tailings reached the critical state condition due to a reduction in the effective stress. SITE LOCATION: 20.206500°S, 43.467111°W

Seismic Response of GFRP-RC Interior Beam-to-Column Joints under Cyclic Static Loads

A total of nine specimens were constructed and tested under cyclic loads to investigate the differences in seismic behavior between glass fiber-reinforced polymer (GFRP)-reinforced concrete (RC) joints and RC beam-to-column joints. The experimental parameters included stirrup ratios, axial pressure ratios and concrete strength of the beam-to-column joints. The cyclic loading test results showed that the GFRP-RC beam-to-column joints can withstand significantly high lateral deformations without exhibiting brittle failure. Moreover, the RC beam-to-column joint exhibited significantly higher energy dissipation and residual displacement than the GFRP-RC beam-to-column joint by 50% and 60%, respectively. Finally, a shear capacity calculation method for the core zone of this kind of joint was proposed, which agreed well with the experimental results.

Strength characterization of cohesionless soil treated with cement and polyvinyl alcohol

Lime, cement, and bitumen are well-known traditional binders for improving the bearing capacity of soils. However, the production of these binders results in a massive impact on the environment due to the emission of greenhouse gases, such as carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). In this study, a novel cement–polyvinyl alcohol (PVA) mixture is proposed to fabricate strong composite geomaterials. The advantage of the proposed materials is that they can increase the unconfined compressive strength (UCS) and, combined with cement hydration, producing PVA glue, can be used to fill up the soil pores. Laboratory tests indicate a threefold increase in UCS with the cement–PVA-combined mixture compared to a cement-stabilized one. The results of scanning electron microscope (SEM) observations suggest that the cement–PVA composite can ameliorate the pore structure that is more solid than the cement-stabilized one. Moreover, by curing at 80 °C, the strength of the cement–PVA stabilized soil decreases by threefold, plateauing at the same strength as the non-PVA stabilized soil. In addition, the results of cyclic thermal exposure tests suggest that, with the increase in the number of heating/cooling cycles, the UCS gradually decreases compared to the initial one. However, the loss of UCS is less than 25 % under the three cycles of exposure. Thus, these composites have the potential to promote urban renewal projects in an ecofriendly manner.

The Reactive Element Effect

Rationalizing the reactive element effect operative in alumina- and chromia-forming alloys upon oxidation under oxidizing hot gas atmospheres, referring to investigations on zirconium oxide-coated test samples for gas turbine alloys. This retrospective study uses the results of cyclic furnace lifetime tests conducted at 1100 °C on ZrO2-coated Ni-base alloys with Y− or Y+ Hf-doped bond coats and correlates them with the parabolic oxidation rate constant at 1100 °C of binary NiAl alloys doped with Y, Zr, or Hf. Parallel results at higher temperatures allow the respective oxidation processes during the cyclic lifetimes to be assigned to cation-dominated or anion-dominated transport processes. The correlations document the close interrelationship betweenthe refractory element content (Mo, Re, Ta, W) in the substrate alloythe total content of the two reactive elements Y and Zr in the mixed zone of the scale, representing a Me3+ iso-valence valueindividual relative lifetime parameters in pct for EBPVD thermal barrier coating systems associated with cation-dominated transport processes.

Resilient modulus of crushed stone material reinforced with geogrids

Unbound base layers can be stabilized with geogrids that reduce lateral movement of granular material thus improving its stiffness through particle interlocking inside geogrid openings. Good particles-geogrid interlocking depends significantly on the ratio of geogrid aperture size to the average soil particle size. This paper describes testing of a resilient modulus and a permanent deformation of geogrid reinforced granular material. Biaxial and triaxial geogrids made with 3D printer were used in which geogrids were of different aperture sizes and rib thickness. It was thus possible to test parametrically the effect of geogrid geometry and rib stiffness on the resilient behaviour and permanent deformations. Experiments were conducted on cylindrical specimens of 160 mm diameter and 320 mm height and were reinforced with one or several layers of geogrids. The results of cyclic triaxial tests for unreinforced and reinforced specimens with created geogrids are presented in the paper, as well as the results of the previous research on commercially available geogrids. It is observed from the presented results that resilient behaviour of the tested granular material was not improved with the use of geogrids, while geogrids gave certain improvement with respect to permanent deformations. Presented research is a part of the ongoing project at the University of J.J. Strossmayer in Osijek and the Slovenian National Building and Civil Engineering Institute.

Evaluation of Cyclic Resistance and Postliquefaction Volumetric Strains of Intermediate Soils

Postshaking soil volumetric strains of liquefiable soils are of technical interest because they cause a relevant part of the total settlements experienced by the site of interest. In the case of liquefiable intermediate soils, such as sandy silts or silty sands, reconsolidation volumetric strains are affected by the amount of fines. The technical note reports the results of laboratory cyclic undrained tests carried out to study liquefaction resistance and postliquefaction volumetric behavior of sand-silt mixtures reconstituted with increasing amount of nonplastic fines [0<fines content (FC)<20%]. The test outcomes indicate that the equivalent granular void ratio (e*) can be successfully adopted to quantify the volume reduction of sand-silt mixtures as long as the soil matrix is ruled by the grains of sand. An analytical relationship between e* and the volumetric strain is finally proposed to be of technical help in predicting the effects of reconsolidation in intermediate soils.

Seismic application of steel rocking column bases with replaceable cover plates in steel MRFs

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

Design and cyclic testing of bolted end plate connections between steel link beams and cross-laminated timber for coupled shear walls

Coupled cross-laminated timber (CLT) wall systems with ductile steel link beams offer an efficient, high-capacity lateral load resisting system for buildings in earthquake-prone regions. This study proposes a type of beam to CLT wall connection using a bolted end plate in a notched CLT panel edge to create a semi-rigid joint. A simplified analytical method is proposed to predict the connection strength and is compared against the results of full-scale experiments. The experimental strength values were all greater than the predictions from the proposed method. Therefore, the strength method seems conservative and is suitable for the capacity design of similar connections in coupled wall systems. The final specimen in the test programme was capacity designed and its cyclic test results demonstrated adequate connection strength and relatively high stiffness were achieved for a 200 mm-deep wide flange link beam. The specimen’s link beam yielded at an applied shear load of 180kN and reached a maximum strength of 278kN while dissipating a large amount of energy through steel yielding. The bolted end plate connection appears to be a practical solution for application in coupled CLT shear walls.

Electrospun Benzimidazole-Based Polyimide Membrane for Supercapacitor Applications.

A benzimidazole-containing diamine monomer was prepared via a simple one-step synthesis process. A two-step procedure involving polycondensation in the presence of aromatic dianhydrides (4,4′-oxydiphthalic anhydride, ODPA) followed by thermal imidization was then performed to prepare a benzimidazole-based polyimide (BI-PI). BI-PI membranes were fabricated using an electrospinning technique and were hot pressed for 30 min at 200 °C under a pressure of 50 kgf /cm2. Finally, the hot-pressed membranes were assembled into supercapacitors, utilizing high-porosity-activated water chestnut shell biochar as the active material. The TGA results showed that the BI-PI polymer produced in the two-step synthesis process had a high thermal stability (Td5% = 527 °C). Moreover, the hot-press process reduced the pore size in the BI-PI membrane and improved the pore-size uniformity. The hot-press procedure additionally improved the mechanical properties of the BI-PI membrane, resulting in a high tensile modulus of 783 MPa and a tensile strength of 34.8 MPa. The cyclic voltammetry test results showed that the membrane had a specific capacitance of 121 F/g and a capacitance retention of 77%. By contrast, a commercial cellulose separator showed a specific capacitance value of 107 F/g and a capacitance retention of 49% under the same scanning conditions. Finally, the membrane showed both a small equivalent series resistance (Rs) and a small interfacial resistance (Rct). Overall, the results showed that the BI-PI membrane has significant potential as a separator for high-performance supercapacitor applications.

Behavior of deformation joints of RC utility tunnels considering multi-hazard conditions

Utility tunnels have been widely constructed worldwide to accommodate the lifeline infrastructure and ever-expanding municipal needs caused by fast population concentration and urbanization in recent years. Typical reinforced concrete utility tunnels consist of tunnel segments no longer than 30 m in length and deformation joints between adjacent segments. Although extensive research has been carried out on the seismic behavior of utility tunnels using shaking table testing and numerical method, little progress has been made in the understanding of the mechanical behavior of deformation joints under differential settlement and earthquake ground motion. Engineering practice has demonstrated that the deformation joints also play an important role in ensuring the functionability and durability of utility tunnels. In this research program, two groups of eight test models of utility tunnel deformation joints with shear dowel bars were constructed and tested under monotonic and reversed cyclic loading respectively, aiming to simulate the responses of the deformation joints subjected to differential settlement and earthquake excitation. Both ends of each shear dowel bar were inserted into adjacent segments for certain length, where one end is bonded with the segment concrete while the other debonded to allow for potential longitudinal movement due to temperature change. Concrete strength, dowel bar amount, insert length and layout were considered as the test variables. Test results indicated that concrete strength has little influence on the shear capacity of deformation joints. Placing dowel bars only at two vertical sides of the tunnel box-section can improve the deformation capacity and avoid concrete cracking at the bottom slab of the deformation joints. The reversed cyclic loading test results showed great seismic performance of the test models with great load bearing capacity, ductility, energy dissipation and stiffness. Although arranging all dowel bars at side walls can reduce the cracking of bottom slabs, the ductility and energy dissipation capacity are less favorable compared with placing dowel bars all around the box-section. In addition, although 10d is sufficient for the dowel bar insert length, it is suggested that use of 15d can help prevent severe concrete damages. The numerical analysis verified the test results and can be used for further study of the deformation joints of utility tunnels.