Load-displacement Relationship Research Articles

Effect of the Size of Multiple Perforations on the Performance of Long Reinforced Concrete Shear Walls

This paper investigates the effect of the size of multiple openings on the behavior of shear walls. In this study, the wall span is 24 m, the wall depth is 4 m, and is 0.3 m thick. The work involves the discussion of the three main kinematic and strength indicators that influence the shear wall performance. They are the load displacement relationship for the wall top edge, the equivalent concrete stress flow within the body of the wall, and the bending stress gradient at the bottom of the wall. The wall is constructed of reinforced concrete. A nonlinear finite element push over analysis has been carried out using Ansys software. The element Solid65 presented by Ansys effectively simulates the true behavior of concrete. The steel reinforcement has been modeled by link180 element. Primarily a finite element model for the solid bearing RC shear wall has been constructed and analyzed. The primary step has involved calibration and validation of the finite element model. Thereafter, pushover analysis has been performed for four perforated walls of various opening sizes. The study has indicated that when the percentage of the sum of the perforations’ areas to the total wall area surpasses 8.35%, the shear wall load carrying capacity starts to degrade. When the percentage of the sum of perforations surpasses 16.7% of the total wall area, the shear wall behavior starts to convert to that of two coupled shear walls. The larger the opening size is, the higher the stresses are, and the less the wall load carrying capacity is. When the percentage of the sum of the perforations’ areas to the wall total area surpasses 25%, the behavior of the shear wall converts to that of a frame. The study recommends that further future studies should be carried out on the effect of providing CFRP sheets on the edges of the openings, especially at lower stories in order to control concrete cracks at the edges of the perforations resulting from the developed large concrete equivalent stresses.

Cyclic Behavior of Multiple Hardening Precast Concrete Shear Walls

Precast Concrete (PC) shear walls are becoming popular in building structures. With “wet” connection techniques, PC shear walls often behave like conventional cast-in-place walls, where hardening occurs after yielding. In this study, two PC shear walls assembled by the “dry” connection technique, and one cast-in-place shear wall, were tested by means of quasi-static cyclic loading. The main purpose of the experiment was to systematically investigate the cyclic response of PC shear walls with varying types of vertical connection in the form of a friction-bearing device. The results showed that vertical bearing in devices, which mainly stems from the longitudinal elongation of PC wall panels, could enlarge the axial force of end column so that it provided an additional resistance moment. The PC shear wall with weak connection achieved ductile failure and second ascending branches on load-displacement relationship, i.e., secondary hardening, and the wall with strong vertical connection performed great moment capacity as well as tertiary hardening. Compared to cast-in-place walls, the peak load and cumulative hysteretic energy of PC shear walls increased by about 60% and 100%, respectively. A conceptual analysis of the multiple hardening phenomenon is presented based on experimental results.

Parameter identification of hysteresis model of reinforced concrete columns considering shear action

It is necessary to determine the load-displacement hysteresis relationship of the reinforced concrete (RC) columns to accurately predict the nonlinear dynamic response of RC columns during earthquakes. In this paper, 17 rectangular RC columns were tested under horizontal cyclic loading and the hysteresis characteristics of RC columns considering shear action were obtained. Then, the influences of Bouc-Wen-Baber-Noori (BWBN) restoring force model parameters on the hysteresis loops of RC columns were analyzed. Based on the quasi-static test data of rectangular RC columns failed in flexural-shear and shear collected from the PEER-Structural Performance Database and the tests in this paper, a parameter identification method for the BWBN model of RC columns was proposed. After that, the probability distribution and the statistical value of the major influencing parameters of BWBN model for shear-dominated RC columns were calculated. The results show that the BWBN model can accurately predict the hysteresis loops of RC columns under cyclic loading and describe the hysteresis characteristics of shear-dominated RC columns, such as strength, stiffness degradation, and pinch effect. The proposed method can identify BWBN model parameters for shear-dominated RC columns well, and the main distribution range of strength degradation parameter δv, stiffness degradation parameter δη, and pinch effect parameter ζs increase gradually with the failure mode of RC columns from flexural-shear failure to shear failure, indicating that the degradation and pinch effect of RC columns failed in shear is more significant than that of flexural-shear. The presented approach is also appropriate for other components or structures, which lays a foundation for further seismic dynamic response analysis.

Thermal-mechanical dynamic interaction in high-speed motorized spindle considering nonlinear vibration

The neglection of thermal-mechanical interaction of the high-speed motorized spindle system may lead to modeling errors of thermal and dynamic characteristics. In this work, the thermal-mechanical interaction mechanism is analyzed, and a closed-loop iterative modeling method for thermal and dynamical characteristics is proposed to improve the modeling accuracy. The nonlinear dynamic model with thermal effects of the spindle system under unbalanced magnetic pull and unbalanced mass excitation is established to evaluate its transient dynamic behavior. A multi-node thermal resistance network model of the motorized spindle system considering the nonlinear vibration of the spindle system is established to evaluate transient thermal behavior. Based on the load-displacement relationship, the nonlinear stiffness and restoring force model of bearing considering thermal effects and nonlinear vibration is established. The heat generation of the bearing and the built-in motor are calculated by Palmgren's formula and the equivalent circuit model of the induction motor, respectively. The bearing heating is improved considering the comprehensive effects of lubricant viscosity change, bearing thermal expansion, and nonlinear dynamic load. The mechanical power loss of the motorized spindle is analyzed to calculate the electrical parameters required to study the spindle dynamics and motor heat generation. The accuracy and effectiveness of the proposed theoretical method are experimentally verified. Numerical simulations show that the thermal and mechanical effects in the motorized spindle system exhibit a non-negligible dynamic interaction.

New approach for predicting the load-displacement curve of axially loaded piles in sand

A relationship to predict the load-displacement curve for axially loaded piles in sandy soil is presented by using the tri-linear softening model to describe the shaft load-displacement relationships, as well as a bi-linear model is adopted to characterize the unit end resistance-displacement reaction in the region of the pile's tip soil. Subsequently, an analytical mathematical approach to a single pile-surrounding soil interaction relation is provided as a nonlinear analysis to obtain the load-displacement curves. The mechanical response of piles under compression loading was analysed, and thus, an analytical method is developed to establish a solution for the entire compression process of the piles. A combination of the prementioned models with the pile response under compression loading was employed to establish a fully analytical approach. Furthermore, additional analytical approaches and field-tested pile loading history cases were utilized to prove the degree of exactness of the suggested method by comparing the experimental load-displacement curves with the ones founded by the proposed theoretical method in this work. The results of this study illustrate that the proposed method could be considered as an analytical mathematical technique for utilizing both the tri-linear softening model and the bi-linear elastic-plastic model for the purpose of predicting the load-displacement curves of the axially loaded pile with a 98% degree of accuracy compared to field load tests results.

Seismic performance of GFRP tube concrete-encased steel composite columns under axial compression

A glass fiber-reinforced polymer (GFRP) tube concrete-encased steel (GTCES) composite column is a novel column type comprising an outer GFRP tube containing a concrete core and an encased steel section. Although previous studies have examined the static performance of GTCES columns, their seismic performance has not yet been investigated. Therefore, in this study, six GTCES columns with different steel ratios, GFRP tube thicknesses, and axial compression load ratios were tested under combined reversed cyclic lateral loading and static axial compression conditions. The results were used to investigate the influences of these parameters on the failure mode, hysteretic behavior, skeleton curve, ductility coefficient, stiffness, energy dissipation, and strength degradation of GTCES columns. They were found to exhibit favorable seismic performance with excellent ductility and energy dissipation. The steel ratio had a considerable influence on the energy dissipation and carrying ability of the column, and the axial compression load ratio increased its lateral load capacity. Finally, a simplified hysteretic restoring force model for the load-displacement relationship of GTCES columns was established and verified.

Experimental and numerical studies on compressive behavior of steel–concrete–steel composite walls considering local buckling and post-buckling effect

In this study, the axial compressive performance of steel–concrete–steel​ composite walls (SCSCWs) with novel dumbbell-shaped connectors (DSCs) was investigated. Six specimens were designed and tested, and the study parameters included the physical dimensions and arrangement schemes of DSCs. The failure mode, axial displacement, steel strain, and bearing capacity of the specimens were analyzed. The external steel plates exhibited local buckling, and the internal concrete was crushed. The variation in the physical dimensions of the DSC had little effect on the failure modes, and increasing the number of connectors improved the bearing capacity of the specimens. The axial load–displacement relationships of the SCSCWs were calculated considering the effects of local buckling and post-buckling behavior of steel faceplates in the constitutive relationship. The theoretical curves were in good agreement with the experimental results. A simplified formula for the bearing capacity was proposed, and the average ratio of the experimental to theoretical peak loads was 0.98, indicating that the simplified formula had high accuracy. ABAQUS software was used to simulate the axial behavior of SCSCWs. The simulated results were similar to those of the experiments, and the average ratio of the experimental bearing capacity to the corresponding simulated value was 0.99. Based on the benchmark model, further parameter analyses were conducted to study the effects of material strength and physical dimensions on the axial behavior of SCSCWs. Increasing the material strength and sectional thickness could increase the bearing capacity, and the failure mode was not affected. The theoretical initial stiffness of the SCSCWs was calculated, and the accuracy of the formulas was verified using the simulated results.

Utjecaj duljine kritičnog područja na nosivost armiranobetonskih greda

This study investigated seismic analysis of the behavior of reinforced concrete beams with various shear spans, stirrup shapes, and tightening zone lengths using the Seismo-struct 2020 program. The load–displacement relations of 24 reinforced concrete beams with different conditions were modeled analytically. The analytical model used in the study was validated by comparing it with the experimental data from the literature. It was found that increasing the length of the tightening zone, particularly in beams with a high shear span, is essential for earthquake safety. In addition, the backbone curve of each beam was extracted, and comparison graphs were analyzed. The results obtained demonstrated that the length of the tightening zone limits the effect of stirrup shape and diameter on beam behavior.

Fracture simulation of welded RHS X-joints using GTN damage model

A welded rectangular hollow section (RHS) X-joint exposed to tension loading has three typical fracture-related failure modes: Punching shear failure (PSF), Brace failure (BF), and Chord side wall failure (CSWF). Prediction of these failure modes by finite element (FE) simulations requires modelling of the material damage. An appropriate damage model accurately predicts the behaviour of the fracture zone and provides the necessary information to improve design rules for welded high-strength steel (HSS) RHS X-joints based on parametric studies using validated model. In this paper, the parameters of the Gurson-Tvergaard-Needleman (GTN) damage model are calibrated for the base material (BM) and the heat-affected zone (HAZ) of butt-welded cold-formed RHS connections, no fracture appeared in the weld. A computational homogenisation analysis is carried out using representative volume element (RVE) models to calibrate the pressure-dependent yield surface parameters of the GTN damage model, considering the different combinations of the accumulated initial hardening strain and the void volume fraction (VVF) due to a varying stress triaxiality. The critical and final VVFs are calibrated against tensile coupon tests. Finally, the GTN damage models calibrated for BM and HAZ are used in the fracture simulation of nine welded cold-formed RHS X-joints in monotonic tension. The FE model successfully predicts the experimental load-displacement relationships and fractured zone, indicating the calibrated GTN models could effectively be used in parametric study of welded cold-formed RHS X-joints. Finally, possible improvements to the used FE model are outlined for future studies.

Centrifuge performance of LCSM wall reinforced pile-supported wharf subjected to yard load-induced marine slope soil movement

Lattice cement soil mixing (LCSM) walls are constructed to relief the marine slope soil movement that will trigger failure of the pile-supported wharf, the structural performance and pile-soil interactions after the LCSM implementation are major concerns. This paper investigated motion modes, load-displacement relations, soil and pore pressures, and bending moments of pile-supported wharfs with LCSM walls subjected to yard load-induced slope soil movement via centrifuge modeling. Results showed that the LCSM wall tilted to compress the soil and pile, inducing the tilting of the wharf. The lateral structural displacement was effectively restricted by the LCSM wall compared with that of a nonreinforced wharf, but the LCSM wall was not superior to the other lattice wall type with legs in limiting the lateral structural displacement, and the deep LCSM wall worked better at larger soil movement. The rear piles were evidently affected by slope soil movement and were compressed in the middle part. Soil pressures generally increased with increasing yard loads, whereas their distributions were deeply affected by different LCSM wall depths. Pore pressures were greater around the tilting LCSM wall because of larger soil shear areas but dissipated when soil movement stopped. Bending moment distributions indicated evident waterside curvatures in rear piles, whereas waterside curvatures occurred in the upper part and landside curvatures occurred in the lower part in front and middle piles, the effects of LCSM wall types and depth on bending moment distributions were tremendous.

FRP Stay-in-Place Formworks for High Performance of Concrete Slabs

Stay-in-Place (SiP) formworks obviate the transportation, placement, removal and storage requirements of conventional formworks. Fibre Reinforced Polymer SiPs (FRP-SiP) have additional advantages, such as corrosion resistance, high specific strength and durability. This paper discusses an experimental instigation consisting of two sets of slabs having varying span-to-depth ratios cast on an FRP-SiP. Control specimens with conventional steel bar reinforcements were also cast. Several treatments for improving interfacial bonds at the interface between concrete and FRP-SiP have been investigated. Cyclic flexural tests were performed to evaluate their structural performance. Load-displacement relationship and load capacity are presented. Failure envelopes and energy absorption capacity were evaluated. It was found that the load capacity of FRP-SiP was around 107% greater than the conventional steel rebar specimens. Bond treatment on the FRP-SiP specimens increased the load capacity by around 215% over the untreated specimens. The load-deflection behaviour and the failure modes of the FRP-SiP specimens were distinctly different from those of the conventional specimens. The flexure and shear provisions in American Concrete Institute Standards (ACI 440) were found to be conservative in comparison to the present results. This study demonstrates that FRP-SiPs improve both the structural performance and construction efficiency of concrete slabs, however, new standards would be necessary to be able to utilize their improved capacity.

Experimental study on the effect of grouting volume on the tensile performance of offset semi-grouted couplers

Research results have shown that the mechanical properties of sleeve grouting connections are related to the diameter of the rebar, the sleeve, the grout, the temperature and the loading method, but research on the factor of grout volume needs to be further developed. Therefore, this paper considers the effects of three grouting volumes (50%, 75% grouting and 100% full grouting) on the tensile properties of the joint under the offset condition of the rebar. A total of 22 uniaxial tensile tests on semi-grouted steel sleeve connection specimens were carried out, mainly to study the damage morphology, load-displacement relationship, stiffness and the strain change law on the surface of the rebar and the sleeve under different grouting amount, etc. The stress mechanism of the specimens in the tensile condition was analysed, and the effective bond length calculation model was proposed with reference to the steel-concrete bond strength research theory, and the formula for calculating the maximum bond stress related to the effective anchorage length was obtained. Studies have shown that the grouting amount affects the load bearing capacity and stiffness, and that the quality of the specimen joint is reliable when the grouting volume reaches more than 75% of the design grouting volume.

Effects of Early-Age rheology and printing time interval on Late-Age fracture characteristics of 3D printed concrete

• Fracture of 3D printed concrete is strongly affected by rheology and printing process. • Increasing printing time interval changes rheology and decreases fracture toughness. • Time effect is stronger on fracture characteristics of interlayers than filaments. • Dynamic oscillation sweep method reveals time-dependent storage modulus and viscosity. • Novel fracture experiment using DIC measures and visualizes process zone growth. Concrete additive manufacturing, also known as 3D printing, opens tremendous opportunities in the construction industry, architectural design, defense and space exploration. As concrete is a quasi-brittle material and prone to fracture, it is crucial to understand the effect of the layer-by-layer manufacturing process, such as the variation in printing time intervals and the introduction of printing interlayers, on the fracture behavior of 3D printed concrete. This study elucidated the effects of early-age material rheology, printing time interval and printing path on the late-age load versus crack mouth opening displacement relation, fracture process zone, fracture toughness and fracture energy of 3D printed concrete materials with notch locations at interlayers vs filaments. A dynamic oscillation stress sweep method was used to reveal the time-dependency of early-age rheological parameters. A novel fracture experiment was designed to integrate a digital image correlation system to enable closed-loop control, measurement, and visualization of crack tip parameters during the rapid fracture processes along the printing interlayers or filaments. The results revealed that the fracture characteristics of 3D printed concrete are strongly influenced by its rheology and time-dependency of rheology, which is fundamentally different from normal cast concrete. Increasing the printing time interval increases the storage modulus, yield stress and complex viscosity of 3D printed concrete materials at different shear stress levels, consequently increasing the likelihood of imperfections, and thus decreasing the maximum process zone size developed at the crack tip, fracture toughness and fracture energy of 3D printed concrete. Such effects were found to be stronger on the fracture characteristics of printing interlayers than filaments.

THE IMPACT OF A POLYUREA LAYER ON CRACKING AND PERFORMANCE OF REINFORCED CONCRETE BEAMS UNDER BREAKING LOAD

The paper discusses the results of laboratory experimental studies on reinforced concrete components (beams) with an outer polyurea layer. The important part of the study is the comparison of the results concerning the load-displacement relation for the reference beams (without the polyurea layer on their external surfaces) and those with the polyurea layer. The main conclusion from this part of the research is that the beam elements covered with a polyurea layer are protected against corrosion processes even in an emergency state. The occurrence of scratches, even of large size, is neutralized by the coating that effectively bridges them.

Bending deformation and self-restoration of submicron-sized graphite cantilevers

Van der Waals (vdW)-stacked materials exhibit unique mechanical properties owing to their strong in-plane atomic bonds and weak interlayer vdW interactions. In this study, we experimentally demonstrate that submicron-sized graphite cantilevers can accommodate large out-of-plane deformations without fracturing and undergo self-restoration upon unloading. Submicron-sized cantilever beam specimens were fabricated from highly oriented pyrolytic graphite using the focused ion beam method and subjected to in situ transmission electron microscopy-based bending tests. The cantilevers exhibited a nonlinear load–displacement relationship, and their deformation was almost completely restored upon unloading, even though a large hysteresis loop was observed during the loading–unloading process. Moreover, similar loading–unloading curves were obtained during the repeated loading of the same specimen, indicating that the mechanical properties were restored by unloading even in the case of large nonlinear deformations. For larger deformations, plastic deformation occurred, and the self-restoration property was lost. However, no clear fracture was observed in the cantilevers even when they were deformed to a deflection angle of 62°. Even in this case, the deformation could be restored by electron-beam irradiation. Based on the obtained results, we propose a mechanism to explain the nonlinear and fully reversible deformation behavior of the specimens.

Full-Scale Experimental Study on Prefabricated Greening Ecological Retaining Walls

Prefabricated walls are frequently utilized as retaining structures in different applications. A new type of prefabricated greening ecological retaining wall (PGERW) is proposed in this research. Full-scale tests and numerical simulations were conducted to investigate the stress characteristics of the PGERW. To this end, the load–stress relationship, load–displacement relationship, and crack development of the retaining wall columns were carefully evaluated. It was found that when the load acting on the 3 m high column reached the ultimate load-bearing capacity (about 150 kN), an “arc + 7”-shaped crack pattern emerged. A V-shaped crack composed of bolt–chamfer cracks formed when the load applied to a 2.5 m high column reached the ultimate load-bearing capacity (about 335 kN). The design of hollow thin-walled columns can effectively reduce the amount of concrete used and, as a consequence, reduce its carbon emissions, while meeting the design strength requirements of the retaining wall. The PGERW addresses the challenges of improving the extent of greening and drainage performance of traditional prefabricated retaining walls. It has excellent applicability to highway slope construction and therefore can be applied in several contexts.

Flexural strengthening of RC columns with EB-CFRP sheets and NSM-CFRP rods and ropes

Externally bonded (EB) and near-surface-mounted (NSM) systems have been investigated in the literature to be used in flexural strengthening of reinforced concrete (RC) columns. Research has shown that NSM-FRP systems are preferred in most cases over the use of EB-FRP systems especially in flexural strengthening RC columns against lateral loads. However, limited studies have been conducted to accurately compare the behavior of columns strengthened with EB-FRP or NSM-FRP systems. In this study, six specimens were fabricated and tested. To add to the novelty of this investigation, CFRP ropes were used for the first time in flexural strengthening of RC columns against cyclic lateral loads. Two of the columns were strengthened with NSM-CFRP ropes, one with NSM-CFRP rods, one with EB-CFRP sheet, and one with CFRP lateral confinement only. The results showed that both EB-CFRP and NSM-CFRP techniques can improve the flexural resistance of RC columns. The percentage of enhancement in lateral resistance ranged from 35% to 60%. Limited slippage of NSM-CFRP rods was an advantage and led to a more ductile response. Finally, theoretical analyses were performed to predict the lateral response of strengthened RC columns. The predicted load–displacement relationships had good agreement with the experimental results.

A modified strain gradient beam constraint model

The objective of the present paper is to develop a modified strain gradient beam constraint model (MSGBCM) to improve the modeling accuracy of small‐scale compliant mechanisms. First, a simple nano/micro flexure beam under the effect of end loads is considered. The virtual work principle is employed to formulate the nonlinear load–displacement behavior of the system, based on the modified strain gradient theory. It is observed that as the size of the structure becomes smaller, the elements of the elastic stiffness and load stiffening matrices severely deviate from their corresponding values in the beam constraint model (BCM). A closed‐form nonlinear strain energy expression is also derived for nano/micro flexure beams in terms of their tip displacements. This energy expression is utilized to model the nonlinear load–displacement relationships of small‐scale parallelogram (P) flexures. Moreover, analytical formulas are derived for the axial, transverse, and rotational stiffness values of P‐flexures. The most important observation is that in the small‐scale P‐flexures, the axial stiffness loss of small‐scale P‐flexures resulted from the movement of the stage in the transverse direction, may be seriously overestimated by BCM. The developed MSGBCM can be easily extended for investigating the static and dynamic behavior of more complicated micron and submicron size flexures.

A universal similarity method and design procedure for buckling assessment of stiffened plates under compression load on real ships

The geometric and material nonlinearity make it difficult to provide reliable prediction on the buckling behaviors of ship structure theoretically. Experimental tests are thus still indispensable for the evaluation of the structural safety of ships. In experimental studies, the similarity methods are essential to guide the design of scale-down models for the lab testing, yet the existing similarity methods are either difficult to provide precise similarity or focused on idealized structures. The aim of this paper is to put forward a universal similarity method and ensure the scale-down models designed by the corresponding similarity method can better reproduce the whole buckling process of large stiffened plates from real ship structures. The similarity method and corresponding design procedure for T-bar and angle-bar stiffened plates were derived based on buckling process analysis. Results show good agreements between the real ship structures and scale-down models in terms of buckling mode, load–displacement relationship and ultimate loading capacity. This could be regarded as the first step towards filling the gap between precision and practical application in the field of experimental assessment of ship structural safety.

Effect of Fiber Wrapping on Bending Behavior of Reinforced Concrete Filled Pultruded GFRP Composite Hybrid Beams.

The application of pultruded fiber reinforced polymer (FRP) composites in civil engineering is increasing as a high-performance structural element or reinforcing material for rehabilitation purposes. The advantageous aspects of the pultrusion production technique and the weaknesses arising from the 0° fiber orientation in the drawing direction should be considered. In this direction, it is thought that the structural performance of the profiles produced by the pultrusion technique can be increased with 90° windings by using different fiber types. This paper presents experimental studies on the effect of FRP composite wrapping on the flexure performance of reinforced concrete (RC) filled pultruded glass-FRP (GFRP) profile hybrid beams with damage analysis. The hybrid beams are wrapped fully and partially with Glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) composites. Hybrid beam specimens with 0° to 90° fiber orientations were tested under three- and four-point bending loads. Based on the experimental load–displacement relationship results, initial stiffness, ductility, and energy dissipation capacity were compared. The experimental findings revealed that the maximum load-carrying capacities of beams produced with pultrude profiles increased by 24% with glass wrapping and 64.4% with carbon wrapping due to the change in the damages. A detailed damage analysis is provided. Similarly, significant increases were observed in structural performance ratios such as initial stiffness and ductility ratio.