Monotonic Loading Research Articles

Bond behaviour of steel rebar in polyethylene engineered cementitious composites under various load conditions

Engineered Cementitious Composites (ECC) are a special type of ultra-ductile fiber-reinforced concrete that uses microfibers. The bond strength of Polyethylene ECC with steel reinforcement was found to be not well investigated in the literature under both monotonic loading and cyclic loading conditions. This study aims to investigate the bond strength properties of Polyethylene ECC with steel reinforcement under monotonic and cyclic loading conditions and to evaluate the effect of embedment length, loading rate, and the cover on bond strength experimentally. The beam-end test was selected for this experiment since it is a relatively simple test, yet it produces a realistic stress field. The results indicated that ECC's main failure mode is splitting-pullout, with high slippages occurring. Furthermore, increasing the cover thickness from 3db to 4db enhanced the bond strength by 91%, while raising the anchorage length from 5db to 7db improved it by 105%. Increasing the load rate from 0.01 mm/s to 32 mm/s resulted in a significant 63% improvement in bond strength. Moreover, ECC performed exceptionally well under cyclic loading, displaying increased peak loads by an average of 76.8% compared to monotonic loading. The study findings are expected to guide the formulation of development length equations and finite element models incorporating ECC.

Autoclaved aerated concrete masonry wallettes strengthened using TRC overlay under out-of-plane load

The objective of this study is to assess the out-of-plane flexural responses of autoclaved aerated concrete (AAC) masonry wallettes externally strengthened with textile reinforced concrete (TRC) overlay. This method can be applied as a retrofitting technique for existing AAC masonry walls or as a constructive technique for new constructions. Sixteen AAC masonry specimens (shear span ratio = 5) were subjected to monotonic four-point bending loads. The design variables were the textile types and number of textile layers (reinforcement ratio). The load–deflection responses and corresponding flexural performances of specimens were assessed to quantify the influences of different test parameters. Results showed that the higher tensile strength of TRC would change the failure mode of AAC masonry wallettes from bending to shear. Finally, according to the different failure pattern observed in the tests, flexural and shear models available in the literatures were examined to assess their applicability to predict the load-carrying capacity of AAC masonry wallettes strengthened with TRC.

Grouped rubber-sleeved studs–UHPC pocket connections in prefabricated steel–UHPC composite beams: Shear performance under monotonic and cyclic loadings

Prefabricated steel–ultra-high-performance concrete (UHPC) composite beams (PSUCBs) with grouped stud–UHPC pocket connections (GSUPCs) are a successful attempt of UHPC in bridge engineering, which offers significant advantages in accelerating on-site construction, enhancing structural performance, and improving environmental benefits. However, the uneven steel–concrete interfacial shear stresses distribution caused by the insufficient deformability of ordinary studs (OSs) in UHPC may result in the premature stud failure in large interfacial slippage regions. To address this issue, rubber-sleeved studs (RSSs) that wrapped rubber-sleeves around the stud roots were introduced to improve ductility and reduce the stiffness of connectors. However, the shear performance of grouped RSSs embedded in UHPC remains unclear, which hinders their application in practices. Against this background, systematic experimental and numerical studies were conducted to investigate the monotonic and cyclic shear performance of grouped RSSs–UHPC pocket connections. The results indicated that wrapping rubber-sleeve could increase the ultimate slip capacity and remained sufficient shear resistance, demonstrating great potentials of grouped RSSs–UHPC pocket connections in PSUCBs. Increasing the rubber-sleeve thicknesses and height effectively improved the ultimate slip capacity and deformation recovery, but led to the significant plastic deformation accumulation and cyclic stiffness degradation. Finally, design recommendation on rubber-sleeve configuration rationalization, ultimate shear resistance and load–slip relationship predictive models were provided.

Elastoplastic constitutive model of gravelly soil and its validation through numerical analysis of the Kobe Port Island liquefaction

The liquefaction of gravelly soil has been demonstrated in many earthquakes, but the constitutive model to predict its liquefaction behavior is limited. The dilatancy equation plays an important role in establishing elastoplastic models of geotechnical materials. Recognizing the unique dilatancy characteristics of gravelly soil, this study introduces an improved nonlinear dilatancy equation into the generalized plasticity model. Consequently, a unified elastoplastic constitutive model is proposed, aimed at accurately predicting both the monotonic and cyclic behaviors of saturated gravelly soil under diverse drainage conditions. A series of drained and undrained triaxial tests of gravelly soil under monotonic and cyclic loadings are carried out to validate the model performance. In addition, the model performance is also examined through monotonic and liquefaction tests of gravelly soil obtained from prior publications. Furthermore, the proposed model is implemented into the nonlinear finite element program GEODYNA and applied to the numerical simulation of the Kobe Port Island liquefaction to better validate the capabilities of the proposed model. From the comprehensive analysis of triaxial tests and numerical simulations, the proposed model performs well in predicting mechanical behavior of gravelly soil and can provide a powerful tool for seismic liquefaction analysis of gravelly soil sites.

Critical loss of primary implant stability in osteosynthesis locking screws under cyclic overloading

Primary implant stability, which refers to the stability of the implant during the initial healing period is a crucial factor in determining the long-term success of the implant and lays the foundation for secondary implant stability achieved through osseointegration. Factors affecting primary stability include implant design, surgical technique, and patient-specific factors like bone quality and morphology. In vivo, the cyclic nature of anatomical loading puts osteosynthesis locking screws under dynamic loads, which can lead to the formation of micro cracks and defects that slowly degrade the mechanical connection between the bone and screw, thus compromising the initial stability and secondary stability of the implant. Monotonic quasi-static loading used for testing the holding capacity of implanted screws is not well suited to capture this behavior since it cannot capture the progressive deterioration of peri‑implant bone at small displacements. In order to address this issue, this study aims to determine a critical point of loss of primary implant stability in osteosynthesis locking screws under cyclic overloading by investigating the evolution of damage, dissipated energy, and permanent deformation. A custom-made test setup was used to test implanted 2.5 mm locking screws under cyclic overloading test. For each loading cycle, maximum forces and displacement were recorded as well as initial and final cycle displacements and used to calculate damage and energy dissipation evolution. The results of this study demonstrate that for axial, shear, and mixed loading significant damage and energy dissipation can be observed at approximately 20 % of the failure force. Additionally, at this load level, permanent deformations on the screw-bone interface were found to be in the range of 50 to 150 mm which promotes osseointegration and secondary implant stability. This research can assist surgeons in making informed preoperative decisions by providing a better understanding of the critical point of loss of primary implant stability, thus improving the long-term success of the implant and overall patient satisfaction.

Effect of strengthening by carbon fiber reinforced polymer sheets on the flexural behavior of reinforced self-compacting concrete beams under repeated loads

This study investigates the effect of strengthening self-compacted concrete (SCC) beams using CFRP sheets on flexural behaviour subjected to repeated loads. During the experiment, six rectangular reinforced SCC beams were evaluated; two were reference beams without strengthening, while the remaining four were strengthened with CFRP sheets. The beam’s length, depth, and width are 2100 mm, 300 mm, and 200 mm, respectively. A monotonic load was applied to one of the reference beams, while repeated loads were applied to the remaining (compression cyclic loads). The main parameters studied in this experimental work were the type of loading (monotonic and repeated), the positions of strengthening and the dimensions of CFRP sheets. The flexural behaviour of these beams was investigated through experimental examination by recording the ultimate load and maximum deflection. Meanwhile, the cracks’ pattern and failure modes were observed. The findings of the present study demonstrated that the limited cycles of repeated loads have marginal effect on the flexural behaviour of the beams. This results in an ultimate load reduction of no more than 11%. It was also noted that SCC beams strengthened using CFRP sheets subjected to repeated loads significantly affected the flexural behaviour of these beams. Consequently, the ultimate load of the strengthened beams was improved by up to 18%. Besides, the maximum deflection of the strengthened SCC beams was reduced by 45% compared to those without strengthening. Using strengthening throughout the beams’ entire width and length that are subjected to repeated loads improved their ultimate load to surpass that of non-strengthened beams under monotonic loads by as much as 7%.

EXPERIMENTAL STUDY OF THE LATERAL RESISTANCE OF CFS SHEAR WALLS

AbstractIn recent years, the attention grew toward sustainability issues. This led to the popularity of residential buildings made of cold formed steel profiles. In these systems the lateral bracing is provided by the shear walls. Their complex response calls for the design by testing approach. At the University of Trento an experimental study is in progress of the shear wall response under monotonic and cyclic loading. Five shear wall configurations differing in the steel skeleton and sheathings type are comprised in the programme. The paper presents the main features of the testing set‐up and the preliminary results related to two shear wall configurations. The key role of sheathing‐to‐steel framing connections is pointed out.

Combined anisotropic and cyclic constitutive model for laser powder bed fusion fabricated aluminum alloy

This study presents new methods to effectively model the anisotropic yielding and hardening behavior of laser powder bed fusion fabricated aluminum alloy under both monotonic and cyclic loading conditions. The proposed model combines the yield surface-interpolation method to accurately describe the anisotropic hardening rates in various directions, with the Chaboche kinematic hardening rule to precisely reflect the cyclic characteristics. For numerical implementation of the combined anisotropic and cyclic constitutive model, a fully implicit stress integration algorithm based on return mapping method is provided. Moreover, the multiple parameters associated with the model are categorized and identified in an uncoupled manner. The isotropic and cyclic hardening parameters are determined by an inverse method, and the stability of the optimization outcomes is validated by applying different starting points for the parameters. Particularly, the back-stress effect on the identification of anisotropic parameters associated with the stress invariant-based Hill48 yield function is considered for the first time. This consideration leads to an improved prediction accuracy compared to the identification of anisotropic parameters without considering back-stress effect. The combined anisotropic and cyclic constitutive model, along with the calibrated parameters, are proven capable of accurately reproducing the intricate deformation behavior of laser powder bed fusion fabricated AlSi10Mg.

Elastic-viscoplastic behaviors of polymer-blend geocell sheets: Numerical and experimental investigations

Polymer-blend geocell sheets (PBGS) have been developed as substitute materials for manufacturing geocells. Various attempts have been made to test and predict the behaviors of commonly used geogrids, geotextiles, geomembranes, and geocells. However, the elastic-viscoplastic behaviors of novel-developed geocell sheets are still poorly understood. Therefore, this paper investigates the elastic-viscoplastic behaviors of PBGS to gain a comprehensive understanding of their mechanical properties. Furthermore, the tensile load-strain history under various loading conditions is simulated by numerical calculation for widespread utilization. To achieve this goal, monotonic loading tests, short-term creep and stress relaxation tests, and multi-load-path tests (also known as arbitrary loading history tests) are performed using a universal testing machine. The results are simulated using the nonlinear three-component (NLTC) model, which consists of three nonlinear components, i.e. a hypo-elastic component, a nonlinear inviscid component, and a nonlinear viscid component. The experimental and numerical results demonstrate that PBGS exhibit significant elastic-viscoplastic behavior that can be accurately predicted by the NLTC model. Moreover, the tensile strain rates significantly influence the tensile load, with higher strain rates resulting in increased tensile loads and more linear load-strain curves. Also, parametric analysis of the rheological characteristics reveals that the initial tensile strain rates have negligible impact on the results. The rate-sensitivity coefficient of PBGS is approximately 0.163, which falls within the typical range observed in most geosynthetics.

Method of exact solutions code verification of a superelastic constitutive model in a commercial finite element solver

The superelastic constitutive model implemented in the commercial finite element code ABAQUS is verified using the method of exact solutions (MES). An analytical solution for uniaxial strain is first developed under monotonic loading. Numerical simulations are then performed, and simulation predictions are compared to the exact analytical solutions. Results reveal the superelasticity model agrees with the analytical solution to within one ten-thousandth of a percent (0.0001%) or less for stress and strain quantities of interest when using displacement-driven boundary conditions. Full derivation of the analytical solution is provided in an Appendix, and simulation input files and post-processing scripts are provided as supplemental material.

Analysing the influence of ground granulated blast furnace slag and steel fibre on RC beams flexural behaviour

This study examines the effect of Ground Granulated Blast Furnace Slag (GGBS) and steel fibers on the flexural behaviour of RC beams under monotonic loading. Various percentages of GGBS were used to substitute cement, namely 0%, 20%, 40%, 60%, and 80% and fibers were added to the concrete mix as 0%, 0.5%, 1%, and 1.5% of the volume of concrete. The load–deflection behaviour of GGBS-incorporated RC beams with fibers was compared with the control RC beam. Beams were tested under load control for 28 days and 180 days. The ultimate load of the GGBS-incorporated RC beam up to 40% cement replacement was found to higher than that of the control beam. The strength of concrete is reduced by 28% and 19% when cement was partially replaced by 80% of GGBS at 28 and 180 days, respectively, compared to control concrete without fibres. Further, the analytical load–deflection response of GGBS-incorporated RC beams was determined by using several codes of practice, namely, ACI 318-11(2011), CSA A23.3-04 (2004), EC-04 (2004), and IS 456 (2000). The Codal provisions were primarily based on the effective moment of inertia, Young’s modulus, and modulus of rupture, stiffness, and cracking. Average load–deflection plots obtained from experiments were compared with the computed load–deflection of analytical studies. It was found that the analytically predicted load–deflection behaviour is comparable with the corresponding average experimental load–deflection response. Moment curvature relations were also developed for RC beams.

Effect of variations in concrete quality on the crack width in rigid pavement

Cracks pose a significant issue in rigid pavement, leading to substantial damage. The manual mixing and casting of road pavement concrete underscore the importance of concrete quality as a critical parameter. This study investigates crack behavior by varying concrete quality. Loading is performed statically using line loads, shedding light on the impact of concrete quality on crack development. The concrete to be used has a quality fc' of 15 MPa, 25 MPa, and 35 MPa. The fine aggregate used in this study was Lumajang black sand, while the coarse aggregate used was machine crushed stone, and Portland Composite Cement (PCC) was used in all concrete mixes. The reinforcing steel used had a quality fy of 480 MPa, with a reinforcement ratio of ρ=0.010, which was converted to 5-D16 reinforcement. The subgrade density used to support the specimens had a CBR value of 10 %. Specimen dimensions were 2×0.6×0.2 m for length, width, and thickness. Pavement plates, 30 cm thick, were placed on leveled subgrade soil in a steel box set to achieve a 6 % CBR reading. Hydraulic jacks, monitored by a load cell, applied monotonic static loading with 2 kN intervals, reaching a maximum load of 200 kN. Steel tension and plate settlement were measured using a tension sensor and Linear Variable Differential Transformer (LVDT), respectively. A data logger recorded readings, and crack widths were captured by a digital microscope with 0.01 mm accuracy. Experimental results show that low concrete compressive strength values result in larger crack widths, and vice versa. Cracks also occur at earlier loading of concrete quality fc' 15 MPa. In addition, experiments show that the reinforcement stress value has a significant influence on crack width in specimens with low concrete quality

Experimental study of the static and hysteretic performance of grouted steel beam-column inter-connections for modular integrated construction

Modular Integrated Construction (MiC) has gained prominence as a construction method, and the integrity of its structural connections plays a critical role in ensuring the overall stability and safety of buildings. This paper presents an experimental investigation into the static and hysteretic performance of grouted steel beam-column inter-connections designed for MiC. The study examines eight full-scale specimens subjected to both monotonic and cyclic loading conditions, with a focus on failure characteristics, deformation behavior, loading-displacement curves, loading-strain curves, skeleton curves of hysteretic loops, stiffness degradation, and energy dissipation. Key findings of the study include the observation of weld cracking between beam flanges and columns in all specimens, highlighting the necessity of welding quality control to prevent such issues. Grouted connections exhibited superior integrity, with no gap opening or misalignment between upper and lower columns. Additionally, it was found that grouting could enhance the stiffness of certain connections. Removal of diagonal stiffeners significantly decreased peak bearing capacity, emphasizing their importance. The composite action brought about by bolts connecting ceiling and floor beams also proved influential. According to Eurocode 3, all grouted specimens fall under the classification of semi-rigid connections, with a distinction made for partial and full-strength connections. This research contributes valuable insights into the static behavior and hysteretic performance of grouted steel beam-column inter-connections for MiC, providing essential knowledge for the structural design and safety of buildings utilizing this innovative construction method.

Shear performance of high-strength bolt-epoxy bonding composite connector in steel-concrete composite structure

To clarify the shear mechanism of high-strength bolt-epoxy bonding composite connectors in prefabricated steel-concrete composite structures, twenty-one direct shear specimens and six double shear specimens were carried out in this study. The pretension force, interface type, epoxy curing time and loading pattern were considered. Results revealed that the main failure mode of high-strength bolt-epoxy bonding composite connectors was that the large area of epoxy matrix was separated from the steel plate, and the bolt was sheared off. The load-slip curve of composite connector specimens included the elastic stage, epoxy failure stage, frictional slip stage, bolt force transmission stage and failure stage. Compared to the specimens with a bolt connector under recommended pretension, the average initial slip load of composite connector specimens was 437.7% higher. Additionally, the average initial slip load of specimens with 1-day epoxy curing time was 24.4% lower than 7-day curing time, but the average ultimate load and ultimate slip were 12.4% and 29.4% higher, respectively. When the pretension ratio decreased from 1.0 to 0.6, the average initial slip load of specimens with a bolt connector was significantly decreased by 33.0% and the average ultimate slip of composite connector specimens was increased by 18.1%. The average initial slip load and ultimate load of composite connector specimens were comparable under cyclic loading compared to monotonic loading. Upon the experimental results and existing formulas, some equations were proposed for predicting the initial slip load and bearing capacity of steel-concrete composite structures with composite connectors.

BOUNDING SURFACE COUPLED FINITE ELEMENT CONSOLIDATION ANALYSIS OF NORMALLY AND OVERCONSOLIDATED CLAYS

The radial mapping version of the bounding surface plasticity model is implemented in a computer program to predict the response of cohesive soils. The eight-noded isoparametric element and Biot’s theory are used in this study for analyzing soil consolidation problems. The model has been used in the analysis for two classes of problems. The first involves the comparison of model predictions with the results of laboratory tests in compression and extension for normally and overconsolidated clays. The second class involves using the model to predict the results of one- and two-dimensional finite element problems of soil consolidation. The comparisons with experiments demonstrate that the model, through its simplicity, can describe realistically the soil response under different monotonic loading conditions at any overconsolidation ratio. The comparison between the bounding surface plasticity model with the classical modified Cam clay model shows considerably different rates and magnitudes of settlement, and different pore pressure behavior during the consolidation process.

Low-high-low cyclic performance of screw connections for fibre-polymer composites

This study examines the cyclic performance of screw connections for joining fibre polymer composite members. Cyclic tensile experiments were conducted on connection specimens consisting of a flat panel (FP) and a square hollow section (SHS) at a right angle. A low-high-low (LHL) cyclic loading program was employed, consisting of seven varying-amplitude loading sequences spanning over 10,361 cycles, in order to simulate wind actions according to relevant standards. Four types of specimens, connected using screws or/and adhesive bonding, were examined, under three load amplitude levels corresponding to 50%, 80%, or 100% of the monotonic ultimate load. All specimens loaded under the LHL amplitude levels of 50% and 80% of the monotonic ultimate load survived after all LHL cycles. These survived specimens were subsequently loaded to determine their retention capacity. The results revealed that no less than 89% of the monotonic strength was preserved. In the LHL loading process, the specimens with adhesive bonding showed more severe degradation of stiffness than their screw-only counterparts, due to the initiation of delamination near the bonded side edges on the FP in the early stage of cycles, with further propagation as the number of cycles increased. The screw-only specimens also demonstrated comparable retention capacity in comparison to the adhesively-bonded specimens.

Fatigue behavior investigation of artificial rock under cyclic loading by using discrete element method

In numerous engineering projects, such as tunnel construction, underground gas storage in caverns, and the impact of earthquakes, rock materials experience cyclic loading. However, the response of rock materials to cyclic loading, which may vary in terms of waveform, frequency, and amplitude, is not uniform. Consequently, comprehending the mechanical attributes and fatigue behavior of rocks holds significant importance in engineering designs. This study focuses on subjecting a collection of cylindrical concrete specimens, categorized into three groups with distinct mechanical properties, to both monotonic and cyclic loading within a laboratory environment. Three groups of cylindrical concrete samples with different mixing designs are prepared to evaluate the effect of the mechanical strength of the samples on the fatigue response of the rock. In such a way that: The first group (G1) with Uniaxial Compressive Strength (UCS): 19 MPa, the second group (G2) with (UCS): 49 MPa, and the third group (G3) with (UCS): 71 MPa. In addition, the discrete element method is utilized to simulate uniaxial cyclic compression tests under various loading conditions, such as monotonic and cyclic loading. The resulting fracture propagation patterns and geometries are then analyzed. Numerical and experimental results show that the cyclic uniaxial compressive strength, due to the presence of damage and fatigue phenomena, has decreased relative to the monotonic tests. Also the cyclic elastic modulus values (Ec) have decreased by 53 %, 25 %, and 11 % relative to the monotonic elastic modulus (Em) for the three groups of G1, G2, and G3, respectively. The Stress-life (S-N) model is used to express the fatigue behavior of rock, and the final equation for the S-N model is expressed.

Experimental study on RC beams shear‐strengthened with composite polymer mortar and steel strands wire mesh

AbstractThis paper presents an experimental investigation of the use of composite polymer mortar (CPM) and steel strands wire mesh (SSWM) to strengthen reinforced concrete (RC) beams in shear. In order to maximize the shear resistance of the steel strands, a new type of anchor device called wedge‐shaped steel plate hoops (WSSPHs) was developed. And the study aimed to examine the effect of shear‐to‐span ratio and prestressing level on the mechanical properties of the beams. A total of nine beams were constructed and tested under four‐point bending monotonic load, comprising three control beams and six strengthened beams. The study analyzed the damage modes, load‐deflection curves, strength, stiffness, and ductility of the beams. The test results indicated that (1) the mechanical properties of the strengthened beams were improved, with the shear capacity improving by 38.47%–71.37% after strengthening. (2) It was observed that SSWM could be utilized more effectively in high shear‐to‐span ratio beams among the strengthened beams with the same prestressing level. (3) Additionally, the larger prestressing level was found to change the design damage mode of the test beams, with RB‐2.5‐0.5 failing in bending. Finally, a model was proposed to predict the shear capacity of the test beams based on the specification GB 50011‐2010. The model considered the effect of the initial prestressing of the steel strands.

Behavior of Reinforced Concrete Corbels Strengthened with CFRP Strips Subjected to Monotonic and Repeated Loading

Concrete corbels are short cantilevers subjected to monotonic and repeated loads. Repeated loads generally negatively affect the concrete structural members' strength as they decrease the resistance to external loads. To increase these loads, strengthening with carbon fiber reinforced polymer (CFRP) strips as an externally bounded technique is used. This paper studies the behavior and strength of strengthened corbels subjected to monotonic and repeated (constant and incremental) loads. The experimental program included the casting and testing of twelve double-concrete corbels. All specimens have been kept constant for corbel dimensions and main and secondary reinforcement. Nine were strengthened with CFRP strips using different patterns, while the others were left un-strengthened as control corbels. The results showed that both repeated loads' types, i.e., constant and incremental, affected the ultimate load capacity of corbels. Compared to monotonic loading, a reduction occurred in ultimate load and ultimate deflection for corbels subjected to five repeated loading cycles. For corbels strengthened by externally bounded CFRP strips under any applied loads, the ultimate load significantly increased, while the ultimate deflection decreased compared to un-strengthened at the same applied load. All corbels failed by de-bonding the CFRP strips.

A new p-y model for soil-pile interaction analyses in cohesionless soils under monotonic loading

The most widely used analysis method for the laterally loaded pile problem is the Winkler spring approach. Although researchers have proposed nonlinear formulations for the p-y curves, the contribution of the soil nonlinearity has not been thoroughly studied. The main drawback of the current approach is the use of a single stiffness in the p-y formulation. This study investigates the laterally loaded pile problem by employing the pressure-dependent hardening soil model with small-strain stiffness (HS-Small Model), where the degree of soil nonlinearity is better integrated. The parametric analyses are performed on the verified model for various pile and soil properties. A new p-y model is proposed for pile behaviour under monotonic loading based on the numerical analysis results. The model includes the initial stiffness, ultimate soil resistance, and degree of nonlinearity parameters. The validity of the proposed model is demonstrated by simulating a centrifuge and two field tests from the literature. The proposed model accurately accounts for soil nonlinearity and significantly improves the estimation of lateral displacements.