Cyclic Loading Sequence Research Articles

Influence of precast microbial reinforcement on lateral responses of monopiles

Microbially Induced Calcium Carbonate Precipitation (MICP) provides an environmentally friendly solution for reinforcing large diameter monopiles for offshore wind turbines (OWTs). This study presents an investigation into the lateral responses of monopiles with precast microbial reinforcement using a low-pH one-phase method. Both static and cyclic loading tests were carried out. The results of static loading tests show that the failure mode of the bio-reinforced monopile was an overall overturn failure. The lateral bearing capacity was increased by 50% and the bending moment was reduced by about 25% with the bio-reinforcement. Further investigation was conducted on the secant stiffness, damping ratio, and accumulated deformation of the bio-reinforced monopile under various cyclic loadings. With the bio-reinforcement, the accumulated deformation under one-way cyclic loading can be reduced by 30%–60%. The influences of cyclic loading parameters and loading sequence on pile stiffness were clarified. The growth ratio of pile stiffness due to bio-reinforcement under one-way loading was between 1.65 and 2.82, and decreased with increasing load amplitude. The ratio was smaller under two-way loading. Three competing factors on pile stiffness were identified: cyclic compaction of the unreinforced sandy soil, weakening of the bio-reinforced soil and soil subsidence around the bio-reinforced soil.

Topology optimization of the flat steel shear wall based on the volume constraint and strain energy assumptions under the seismic loading conditions

In structural engineering systems, shear walls are two-dimensional vertical elements designed to endure lateral forces acting in-plane, most frequently seismic and wind loads. Shear walls come in a variety of materials and are typically found in high-rise structures. Because steel shear walls are lighter, more ductile, and stronger than other concrete shear walls, they are advised for usage in steel constructions. It is important to remember that the steel shear wall has an infill plate, which can be produced in a variety of forms. The critical zones in flat steel shear walls are the joints and corners where the infill plate and frame meet. The flat infill plate can be modified to improve the strength and weight performance of the steel shear walls. One of these procedures is Topology Optimization (TO) and this method can reduce the weight and also, increase the strength against the cyclic loading sequences. In the current research paper, the TO of the infill steel plate was considered based on the two methods of volume constraint and maximization of strain energy. Four different volumes (i.e., 60%, 70%, 80%, and 90%) were assumed for the mentioned element in the steel shear wall. The obtained results revealed that the topology configuration of CCSSW with 90% volume constraint presented the highest seismic loading performance. The cumulated energy for this type of SSW was around 700 kJ while it was around 600 kJ for other topology optimization configurations.

Experimental Investigation of Seismic Vulnerability of Braces under Hazard Consistent loading sequences

AbstractIn the last ten years, Chile and Japan have experienced several subduction earthquakes that lasted for extended periods of time. These occurrences have emphasized the need for a thorough examination of how the duration of ground motion impacts the performance of the components of the lateral load resisting system. In the present study, three large‐scale experiments were conducted on the wide‐flange brace member to evaluate the seismic vulnerability of the braces under the hazard consistent loading protocol. The loading sequences consider in the study are standard symmetric cyclic loading sequences, collapse‐consistent loading sequences representing subduction zone tension dominated and collapse‐consistent loading sequences representing subduction zone compression dominated. The subassemblage test‐set‐up was taken in the study to consider the effect of the end‐protect zone on the seismic assessments of the brace members. The evolution of strain at the mid‐section of the brace member is observed to be higher in case of the standard loading sequences as compared to the subduction zone loading sequences. The post yielding stiffness and the collapse resistance of the brace member under the subduction zone earthquake are present. The damage state of the open section brace member and evolution of the local bucking at the mid of the brace member were discussed. It is observed that open section delays the accumulation of strain at brace member and delay the fracture initiation. The ductility of the different brace members is compared to highlight the influence of the cross‐section properties of the brace on the ductility of the braced system.

An advanced t-z curves method using cyclic shaft friction degradation for the design of piles in sand

A calculation model including an original cyclic t-z method is proposed for the analysis and the design of piles subjected to cyclic axial loads both in terms of displacements and resistance. This model allows the assessment of pile displacement and axial force distribution with depth for each load increment. The cyclic effects and especially the decrease of the shaft friction are accounted for by considering the current state of stress at the pile-soil interface. The approach is based on the ‘ABC’ method developed by the Imperial College. A procedure is developed to combine this method with t-z cyclic curves. Comparisons are made between the numerical results obtained from this cyclic t-z model and the experimental data of tests which were carried out during the project GOPAL (Grouted Offshore Piles For Alternating Loadings) and the French National Project SOLCYP (SOLlicitations CYlcliques sur Pieux): four cyclic loading sequences are considered for both driven and bored piles. The reliability of the proposed model is evaluated according to the loading level and the number of cycles. The use of this model also leads to the construction of cyclic stability diagrams.

Durability of Buckled Composites Using Virtual Crack Closure Technique Fatigue -Curve Implementation

Composite structures have become popular in modern aircraft because they help reduce weight and increase durability. In addition, hat-stiffened panels provide the stability that the airframe skin needs. However, they can be subject to delamination in the postbuckling regime. Progressive damage analysis methods can help predict interlaminar and intralaminar failure events. Many aircraft structures are subject to cyclic loading in the postbuckling regime. Hence, fatigue life prediction becomes essential for design and sustainment purposes. Under the NASA Advanced Composites Project, composite panels stiffened with single- and multiple-hat stringers were subject to a cyclic loading sequence from a prebuckling state to a postbuckling state. This work uses the Abaqus virtual crack closure technique with enhanced capabilities through an empirical method to integrate fatigue effects (different from the ) into the Paris law. This was accomplished via a user-defined subroutine to simulate the fatigue response of these panels. This novel method captured the fatigue life predictions within 5% of the test results.

A multiscale model for multiaxial inelastic behavior of elastomeric particulate composites

This article addresses the problem of the multiscale constitutive representation of the multiaxial inelastic behavior of elastomeric particulate composites. A fully three-dimensional model is proposed within a micromechanical treatment to describe the multiaxial inelastic response in relation to the reinforcement mechanisms. A network decomposition based on the tube confinement theory is used to consider the combined effects of multiaxiality and inelasticity. The near-field direct interactions between the particles and the rubber networks are physically described using the Eshelby inclusion theory. The capabilities of the microstructure-based model are evaluated for different modes of deformation over a wide range of filler concentrations. It is found being able to successfully reproduce the significant features of the multiaxial macro-response upon monotonic and cyclic loading sequences. Important insights about the effective role of the reinforcement mechanisms on the multiaxial dissipation are revealed.

Functional Interaction of the Cruciate Ligaments, Posteromedial and Posterolateral Capsule, Oblique Popliteal Ligament, and Other Structures in Preventing Abnormal Knee Hyperextension

Background: The ligaments and soft tissue capsular structures of the knee joint that provide a resisting force to prevent abnormal knee hyperextension have not been determined. This knowledge is required for the diagnosis and treatment of knee hyperextension abnormalities. Purpose: To determine the resisting moment of knee ligament and capsular structures that resist knee hyperextension. Hypothesis: The combined posteromedial and posterolateral capsular structures function to provide a major restraint to prevent abnormal knee hyperextension. The anterior and posterior cruciate ligaments resist knee hyperextension but function as secondary restraints. Study Design: Descriptive laboratory study. Methods: A 6 degrees of freedom robotic system determined intact laxity limits in 24 cadaveric knees from 0° to 100° of knee flexion for anteroposterior limits at ±135 N, abduction-adduction limits at ±7 N·m, and external-internal limits at ±5 N·m. One loading method (n = 14 knees) used a static loading sequence with knee hyperextension to 27-N·m torque while maintaining all other degrees of freedom at zero load during sequential soft tissue cutting. The second method (n = 10 knees) used a cyclic loading sequence to decrease viscoelastic effects with soft tissue cutting at 0° of extension, followed by knee hyperextension to 27-N·m torque and cycled back to 0°. Selective soft tissue cuttings were performed of the following: oblique popliteal ligament, fabellofibular ligament, posterolateral capsule, posteromedial capsule with posterior oblique ligament, cruciate ligaments, lateral collateral ligament, popliteus, anterolateral ligament and iliotibial band, and superficial plus deep medial collateral ligaments. The sequential loss in the restraining moment with sectioning provides the function of that structure in resisting knee hyperextension. Results: The median resisting force to knee hyperextension, in descending order, was the posteromedial capsule and posterior oblique ligament (21.7%), posterorolateral ligament and fabellofibular ligament (17.1%), anterior and posterior cruciate ligaments (13% and 12.9%, respectively), superior and deep medial collateral ligament (9.6%), oblique popliteal ligament (7.7%), and lateral collateral ligament (5.4%). The combined posterior capsular structures provided 54.7% and the anterior and posterior cruciate ligaments 25.3% of the total resisting moment to prevent knee hyperextension. Conclusion: Diagnosis of abnormal knee hyperextension involves a combination of multiple ligament and soft tissue structures without 1 primary restraint. The posteromedial and posterolateral capsular structures provided the major resisting moment to prevent knee hyperextension. The cruciate ligaments produced a lesser resisting moment to knee hyperextension. Clinical Relevance: This is the first study to comprehensively measure all of the knee ligaments and capsular structures providing a resisting moment to abnormal knee hyperextension. These data are required for diagnostic and treatment strategies on the pathomechanics of abnormal knee hyperextension in patients after injury or developmental cases.

Seismic performance of steel chevron braced frames designed according to Japanese practice

Six steel braced-frame specimens and nine isolated brace specimens were tested to examine the seismic behavior of steel chevron braced frames designed and constructed according to the current Japanese practice. The braced-frame specimens placed a pair of braces in a “chevron” arrangement, in a single-bay, single-story moment-resisting frame. The braces had either a round-HSS or I section. The bracing connections adopted either slip-critical bolted connections as is the norm in Japan or a field-welded connection following U.S. recommendations. The specimens were subjected to a cyclic loading sequence that is similar in severity to the protocol specified for steel moment-resisting frames in the U.S. seismic provisions. The test results suggest that chevron braced frames with compact braces and using moment-resisting beam-to-column connections can safely develop large story drifts exceeding 0.03 rad. The force unbalance between the tension and compression braces led to large beam deflection and, in some cases, torsion, which in turn limited the tensile axial forces in the braces. The lateral resistance at key limit states matched the strength computed based on plastic analysis.

Influence of stress history on the cyclic behavior of compacted soils in the frozen state: Deviator stress history

Observation of the cyclic behavior of compacted soils in a frozen state is required for assessing the dynamic stability of subgrades or embankments induced by earthquakes or traffic in cold regions, in which the compacted frozen soils have often experienced deviator stress history before applying cyclic stress. Therefore, strain-controlled monotonic triaxial tests followed by stress-controlled cyclic triaxial tests were carried out on compacted frozen soils to investigate the influence of deviator stress history on the cyclic behavior of such soils. The results shows that nonlinear and accumulated behaviors are represented in the stress-strain response of frozen soils regardless the amounts of residual strain induced by stress history. Although the volume fluctuations along with the general path are observed in the cyclic loading sequence, the general path seems consistent with volume changes during the monotonic loading stage, which potentially indicates that the plastic flow characteristics of this frozen soil are independent of the axial loading models (monotonic or cyclic loading). Moreover, an increase in the residual strains induced by stress history led to a decrease in the axial strain accumulation rate and to an increase in cyclic stiffness due to strain hardening induced by preloading. A previously proposed model for predicting the changes in the accumulated strain with the cyclic loading process was found to be applicable to compacted frozen soils regardless of the amounts of residual strain induced by stress history.

Characterization of a soil-rough structure interface using direct shear tests with varying cyclic amplitude and loading sequences under a large cyclic testing cycle condition

Characterization of a soil-rough structure interface using direct shear tests with varying cyclic amplitude and loading sequences under a large cyclic testing cycle condition

Material and Size Effect on Fatigue Damage of Concrete for Pavement Application

Highway pavements need to withstand repeated and varying traffic loads due to which they may fail at a stress level lower than their strength called fatigue. Fatigue is the progressive damage due to propagation of cracks and is considered to be the primary cause of structural failure in concrete pavement. The propagation of cracks in concrete is resisted by the fracture toughness, which is a material property. Stress intensity factor is used to express the fracture toughness which depends upon the present state of crack tip stress, strength and geometry of the structural component. Material fracture toughness and the applied stress ratio influence the progressive damage and the fatigue life of concrete. This paper investigates analytically the progressive damage of concrete due to cyclic loading based on a stress intensity factor based fatigue damage prediction model. The effects of material property and specimen size have found to affect the propagation of cracks and the incremental damage. The varying sequence of cyclic loading has found to influence the progressive damage and fatigue life of concrete significantly.

Evaluation of local friction and pore-water pressure evolution along instrumented probes in saturated clay for large numbers of cycles

To investigate local friction mobilization along piles subjected to cyclic axial loadings, a calibration chamber experiment is presented based on the implementation of instrumented probes in specimens of saturated clay. Typical results obtained with a piezo-probe are presented, allowing not only tip resistance and local friction to be measured, but also the local pore-water pressure developed on the probe shaft. In addition, specific piezometers installed in the clay specimen allow a good picture to be obtained of the pore-water pressure field around the probe during installation and loading. After installation of the probe, a succession of monotonic and cyclic displacement-controlled loading phases is applied. Upon displacement-controlled cyclic loading of the piezo-probe up to a very large number of cycles (105 cycles), an initial degradation of local friction is observed followed by a subsequent reinforcement, which continues until the end of the cyclic sequence. The friction evolution is related to the evolution of the pore-water pressure measured during cyclic loading. In particular, the influence of the cyclic loading sequence on the post-cyclic static friction resistance is evaluated. A comparison is finally made with the results obtained with another type of probe, showing a good consistency between both types of results.

A simplified damage evolution relationship and deformation character¬istics of a pozzolanic lime mortar when subjected to unloading-reloading cycles in the pre-peak region

Two series of uniaxial and triaxial compression tests including unloading-reloading cycles were performed under different confining press­ures, in order to study the stress-strain and the deformation behavior of a pozzolanic lime mortar subjected to cyclic loading. Each test included a cyclic loading sequence using five loops in the pre-peak region. The experi­ment­al results showed that the specimens exhibit a strain-softening behavior for uniaxial and low pressure triaxial tests and a strain-hardening behavior for higher triaxial compression tests. The mortar specimens subjected to triaxial compressive cyclic loading at higher confining pressures failed along a single or conjugate shear planes accompanied by considerable lateral ex­pansion. The marked Young’s modulus degradation behavior in the pre-peak region is related to damage that occurs in each specimen.

Fatigue resistance of ultrathin CAD/CAM ceramic and nanoceramic composite occlusal veneers

ObjectiveThe fracture resistance of different ultrathin occlusal computer-aided design/computer-aided manufacturing (CAD/CAM) veneers was investigated under cyclic mechanical loading to restore combined enamel-dentin defects. MethodsEighty-four molars were reduced occlusally until extensive dentin exposure occurred with a remaining enamel ring. Twenty-four molars were ground flat for examination of highly standardized specimens, of which 8 were treated with uniformly flat 0.3mm IPS Empress CAD and 0.3 and 0.5mm IPS e.max CAD restorations. Sixty-four molars were anatomically prepared until dentin exposure and were restored using occlusal veneers with fissure/cusp thicknesses of 0.3/0.5mm from 3 different dental CAD/CAM materials: IPS Empress CAD, IPS e.max CAD and Lava Ultimate CAD/CAM. Teeth were etched with 37% phosphoric acid, and occlusal veneers were bonded using an adhesive luting system (Syntac Primer, Adhesive, Heliobond and Variolink II). Specimens were placed under cyclic mechanical loading in a chewing simulator (1 million cycles at 50N) and were examined for cracks after each cyclic loading sequence. The anatomical 0.3/0.5mm IPS e.max CAD specimens experienced an additional 1 million cycles at 100N. Kaplan–Meier survival curves and log-rank tests were used for data analysis. ResultsAll highly standardized and 0.3/0.5mm IPS e.max CAD specimens tolerated cyclic loading. One anatomical Lava Ultimate CAD/CAM and 10 IPS Empress CAD specimens showed cracks. SignificanceUltrathin occlusal veneers of lithium disilicate ceramic and nanoceramic composite showed remarkably high fracture strength under cyclic mechanical loading. These veneers might be a tooth substance preserving option for restoring combined dentin–enamel defects.

Centrifuge modelling of a helical anchor under different cyclic loading conditions in sand

Helical foundations used in transmission towers, wind turbines, solar panel systems and other similar structures must exhibit adequate performance under cyclic loading. Although a number of studies on the cyclic behaviour of helical anchors has increased, the available observations are still incomplete in terms of providing conclusive recommendations for practical applicability. To address this need, cyclic and monotonic axial tensile load tests were conducted on a single-helix model anchor in very dense dry sand in a centrifuge. The cyclic tests were carried out with different load amplitudes and with the number of cycles varying between 1000 and 3000. After the cyclic tests, the post-cyclic tensile capacity was evaluated by way of monotonic loading tests. Two different displacement regimes were observed during cycling, with a noticeable development of cumulative permanent displacements in the first approximately 100 cycles. In most of the tests, a stable cyclic response and a slight reduction in the post-cyclic capacity were observed. Additionally, the effect of the cyclic loading sequence was evaluated by way of two additional tests in which the cyclic loading was applied with different amplitudes in different orders. The results indicated that the order of the cyclic sequences influences the displacement response and the losses in the post-cyclic capacity.

Evaluation of the healing potential of asphalt mixtures based on a modified semi-circular bending test

Since the semi-circular bending (SCB) test has been widely used to evaluate the fatigue properties of asphalt mixtures, it has been modified in this paper by adding a certain length of rest period in each cyclic loading sequence to evaluate the healing potential of different asphalt mixtures. The digital image correlation (DIC) method was utilized to characterize the tensile strain at the bottom of specimens during the healing-based cyclic SCB test. The influence of notch depth of the specimen (0 mm, 15 mm and 25 mm) and the length of the rest period (0 s, 0.4 s, 0.8 s and 1.2 s) on the fatigue and healing behaviour were carefully evaluated. The fatigue life (Nf), total dissipated energy (Gsum), secant modulus (Ms), average deformation growth rate (Dr) and average tensile strain (εr) during the cyclic load with or without rest period were analysed. Test results show that the inserted notch reduces the fatigue life and deformation of specimens, while can hardly change the load-sensitivity and secant modulus of the specimen. Most performance recovery happens within the rest period of 0.8 s. So it is better to conduct the healing-based cyclic test with non-notched SCB specimen and 0.8 s rest period. Additionally, it is found that asphalt mixtures with modified binder present both better fatigue and healing properties than asphalt mixtures with neat asphalt, while the stone matrix asphalt mixture presents similar fatigue property but much better healing potential than one dense graded mixture with the same binder.

Effects of cyclic axial loading sequences on piles in sand

The cyclic axial behaviour of piled foundations in sand is studied using centrifuge tests. Model piles are partially jacked in flight. Loads are applied to identify cyclic tension loading effects in stable and meta-stable zones on pile behaviour and physical failure. Failure occurs with larger displacements than those achieved during monotonic loading tests. Sequences of 200 cycles with three different amplitudes are applied in different orders. With the same total amount of cycles, final displacements are different and potentially lead to failure. The order of the cyclic sequences significantly affects pile behaviour; however, this is not taken into account or even mentioned in standards.

OPERATING ELEMENTS DAMAGE OF TOOLS CONNECTED WITH THE PLASTIC DEFORMATION OF HARDENED ORGANIC COMPOUNDS

Purpose. Most of the freight traffic in Ukraine is made by railway transport. Government statistics of annual railway freight traffic (January-November) records the following data: 2011 - 468 million tons (108.2% to 2010); 2012 – 421.5 million tons (98.5% to 2011); 2013 – 441.8 million tons (96.6% by 2012). Despite the annual decrease of freight traffic volumes, a significant contribution during the freight traffic belongs to transportation in tanks. That is why the term of their service life extension is very topical today at the operation of tanks. Modern ideas about the accumulation of fatigue damages in the details of railway vehicles are based on models that assess the service life of metallic systems, depending on the load conditions. These models with sufficient accuracy let carry out an assessment of softening of metallic systems in high-cycle fatigue conditions and at the presence of elastic deformation. At the same time, peculiarities of counterbodies′ behavior these models do not take into account. The purpose of this paper is to construct a mathematical model to evaluate the durability of the operating tools, which are used in the purification of solidified organic cargo of tank cars. Methodology. With the use of modern approaches of deformed solid body mechanics the parameters impact of organic substances structure on the service life of heavy structural elements was analyzed. We present the interaction of damages ratio in this article. It relates mainly to those elements of the tool structure, which due to the influence of broadband Gaussian random loadings oscillate with their resonant or near-resonant frequencies. Findings. The influence of the fatigue loads features on the structure durability was studied. Thus, the obtained results suggest the increase of damages that are entered with low-amplitude cycles of strain, because of the nonlinear effect of the interaction between instrument operational elements with organic material. For the given example durability with fatigue which, according to an updated assessment, had been reduced by 10...15% was calculated. A decrease of 10% corresponds to the maximum amplitude of the voltage , and a decrease of 15% - the maximum amplitude . Originality. It is analytically shown that parameters of the metallic systems softening are connected with the kinetics of fatigue damages that accumulate in the metal structures under external loads. Practical value. Authors have proposed correlation that allows estimating the residual life of the part in conditions of a given sequence of multilevel cyclic loading.

Α Hybrid Device for Anchoring FRP Sheets Aimed to Enhance the Flexural Capacity of RC Elements

Abstract: The potential of externally applied FRP (fiber-reinforced plastic) sheets, being employed in retrofitting schemes aimed to repair and strengthen RC (reinforced concrete) structural elements damaged by prototype strong earthquakes, is presented and discussed in this study. The limitation of the debonding mode of failure of these FRP sheets is highlighted and the necessity to develop efficient anchoring devices for these FRP sheets is underlined. The behavior of such a novel HAD (hybrid anchoring device), capable of anchoring CFRP (carbon fiber reinforcing plastic) sheets to RC structural elements, is presented and discussed. The behavior of the device itself was studied through a 3D non-linear numerical simulation at the preliminary design stage in order to establish certain desired features such as the ductile behavior of the device itself as well as the satisfactory performance of the FRP sheets wrapped around this device. This HAD was next applied as part of a strengthening scheme aimed to upgrade the flexural capacity of an RC bridge-type pier specimen subjected to a cyclic seismic-type loading sequence. The obtained results demonstrated an increase in the specimen’s flexural capacity by 100% as well as a similar increase in its capability of dissipating energy in a ductile manner during the cyclic load sequence. Moreover, the employed 3D non-linear numerical simulation yielded reasonably good agreement between the measured and the predicted cyclic response of this specimen strengthened by CFRP layers, which were anchored by the novel HAD. The successful behavior of this novel HAD, which has been patented with No. WO2011073696, is currently being tried with a number of other retrofitting schemes employing FRP sheets externally attached on RC structural elements.

Fracture of a ridged multi-year Arctic sea ice floe

Abstract As part of the 1994 Sea Ice Mechanics Initiative experimental program, fracture experiments were carried out on an 80 m diameter ridged multi-year (MY) ice floe in the Beaufort Sea. An edge cracked, quasi-circular ridged floe was subjected to both cyclic and ramp loading sequences using a steel flat jack. Load, crack opening displacement, acoustical and seismic measurements were made during the experiments. The objective was to gain further insight into the fracture and constitutive properties of MY sea ice. Accurate predictions of the strength of MY sea ice and the forces developed during interactions between MY sea ice and floating or fixed structures are sought. Such interactions include MY ice floe collisions with offshore structures and ships. The fracture resistance of MY ice is determined to be within the range 23