Load-displacement Relationship Research Articles

Mechanical properties of fast-growing poplar glulam columns reinforced with steel plate

Fast-growing poplar with characteristics of fast growth, convenient processing, and strong adaptability is widely planted all over the world, but it is difficult to be directly used as structural timber due to its loose fibers and low strength. In order to enhance mechanical properties of fast-growing poplar, a new type of steel plate reinforced glulam fast-growing poplar is developed. Nine columns are tested including one fast-growing poplar column, two glued-laminated timber (glulam) columns and six steel plate reinforced glulam columns. The influencing factors include the steel plate thickness and eccentricity. Based on test results, axial stiffness, failure mode, load-displacement and load-strain relationships were investigated. Test results indicate that ultimate load and axial stiffness of steel plate reinforced glulam columns were respectively increased by 134.5–177.5% and 168.5–244.1% compared to fast-growing poplar column. With the increase of steel plate thickness and decrease of eccentricity, ultimate load increased by 10.9–18.3% and 27.2–92.3%, respectively. It was found that steel plate thickness and eccentricity have great impacts on bearing capacity of steel plate reinforced glulam columns. In addition, bearing capacity equation for steel plate reinforced glulam columns was established and test results coincide quite well with calculated results with difference of less than 5%.

Modeling of load-displacement relationships for corrugated cardboard containers

This article discusses the nonlinear behavior of the corrugated packaging during compression. The model of this behavior is a load-displacement curve with an ascending branch, a peak point and a descending branch. In some cases, the descending branch shows signs of plastic transition and/or loss of stability of the container walls. The purpose of this work is to predict the transition point of a corrugated container into a plastic (or pseudo-plastic) state. This condition is unacceptable because there are residual deformations that reduce the quality of the container. The article proposes and implements an approach based on the joint application of the well-known equation of the dependence of the load on displacement and the differential fracture criterion. The simulation results are consistent with experiments known from the literature. The conducted research makes a certain contribution to the creation of new tools, the use of which expands the possibilities of analyzing the mechanical behavior of corrugated cardboard containers for the purpose of rational use of resources in accordance with the concept of sustainable development.

Large-scale test of a 3D steel moment-resisting frame with composite slab subject to penultimate interior column loss

This paper investigates the structural behavior of a typical three-dimensional steel frame-concrete slab substructure (3D composite floor subassembly) subject to a penultimate interior column removal scenario. A two-by-two bay composite floor subassembly is one-third downscaled and quasi-statically pushed down to failure by a specially designed twelve-point loading tree in displacement control mode. Unlike the previous studies where progressive collapse propagates vertically, the current study reveals the possibility of horizontal progressive collapse of 3D composite floor structures that characterized by losing stability of the exterior column. The load-displacement relationships, failure modes, deformation pattern and beam end rotations of the test specimen are presented in detail. Based on the test results, the three load-transferring mechanisms, including flexural action, catenary action and tensile membrane action, are determined and discussed. Besides, the test results are compared with previous test results subject to interior column, edge column and corner column removal scenarios, based on which a structural design and analysis strategy of normal composite buildings against progressive collapse are recommended in this study.

FINITE ELEMENT ANALYSIS ON THE NONLINEAR BEHAVIOR OF THE RC SHEAR WALL WITH REGULAR OPENINGS INFLUENCED BY HIGH-STRENGTH STEEL

This paper presented a nonlinear finite element analysis of lateral loading RC shear walls with regular openings using the 3D-NLFEA program. The RC shear walls model was generated from the available test results in the literature. To model the concrete under a complex stress state, a multi-surface plasticity model which combines compression failure surface with tension cut-off failure surface was used. The model was intended to look at the load-displacement relationship and the crack pattern between the model and the numerical model. In addition to the numerical model verification, parametric studies were carried out to investigate the use of high-strength steel (HSS) of the two different grades (grades 100 and 120) to replace all the normal-strength steel (NSS) or only some of it. The parametric studies found that the shear wall with the NSS bar demonstrated higher stiffness and achieved higher lateral load with the lowest extent of damage (compared to the RC shear wall with the HSS bar). On the other hand, using the HSS bar resulted in lower stiffness, lower lateral load, and higher damage region, which was expected as more strain is required to yield the HSS bar.

Numerical and Experimental Study on Large-Diameter FRP Cable Anchoring System with Dispersed Tendons

Based on a previously designed variable-stiffness load transfer component (LTC), a novel dispersed-tendon cable anchor system (CAS) was developed to increase the anchoring efficiency of large-diameter basalt-fiber-reinforced polymer (BFRP) cables. The static behaviors of the CAS are then numerically evaluated by a simplified three-dimensional finite-element (FE) model and implemented in a full-scale BFRP cable. The FE results indicated that the accuracy of the simplified dispersed-tendon model could be effectively ensured by dividing the revised compensation factor. The anchor behavior of the dispersed-tendon CAS was superior to that of the parallel-tendon CAS when the same cable was applied. The radial stress and tensile stress difference can be reduced by decreasing the tendon spacing. The testing and simulated results agreed well with the load–displacement relationship and axial displacement. All tendons fractured in the testing section, and the LTC suffered minimal damage. The ultimate force of the cable with 127 4-mm-diameter tendons was 2419 kN, and the corresponding anchoring efficiency was 93%. The cable axial tensile strain in the anchoring zone decreased linearly from the loading end to the free end. The cable shear stress concentration at the loading end can be avoided by employing a variable-stiffness anchoring method.

Static performance of non-through one-side bolted end-plate joint for floor-by-floor assembled steel structures

The static performance of non-through end-plate joint with one-side bolts for floor-by-floor assembled steel structures was investigated by means of tests and finite element simulations. A total of six monotonic static loading tests were carried out on the column-end and beam-end joints individually. The stiffness, strength characteristics and failure mechanism were obtained. A partial numerical model of the thread-fixed one-side bolted connection was established. It was proposed that the corresponding mechanical properties could be simplified to a trilinear load–displacement relationship and applied to the overall joint models. The tests and numerical simulations of the specimens were compared and analyzed. The results showed that the failure mode of the column-end joints was the tearing of the bottom welds after the yielding of cross web, while the failure modes of the beam-end joints were the failure of the threads or bolts. The influences of the thickness of cross web and flange of the column-connection, the thickness of beam end plate and the depth of threads on the failure modes and mechanical properties were studied with the test and finite element models. According to the force mechanism of the column-end and beam-end joints, the bearing capacity calculation formulae of the non-through one-side bolted end-plate joint were proposed finally.

Experimental and Theoretical Research on the Bearing Mechanism of Group Anchors in Sand

To investigate the bearing mechanism and efficiency of group anchors in sand, upward pulling tests of model group anchors were carried out for different conditions of the sand density, anchor burial depth ratio, and anchor spacing. The results show that the load-displacement relationships for group anchors is similar to that for single anchors, both being nonlinear for the same relative density and embedment ratio. The load-carrying capacity of group anchors is not a simple superposition of the capacities of two single anchors, but has a clear superposition effect, depending on the relative density, embedment ratio, and anchor spacing. The load carrying capacity increases with the anchor spacing up to a limiting critical value. The bearing mechanism of group anchors was qualitatively analyzed and quantitatively characterized using the strain field and shear stress field obtained through the digital image correlation. Adopting the test data and theoretical derivation, a critical anchor spacing equation is proposed and the relationship between critical anchor spacing, embedment ratio, and relative density is quantitatively characterized. Theory is proposed for predicting the group efficiency of group anchors with different configurations. Comparisons between the results of the developed model and experimental results reported in the literature show good agreement.

Experimental and numerical investigation of shear strength at dapped end beams having different shear span and recess corner length

The geometric properties of the support region of dapped end beams (DEBs) cause a significant change in the ratio of the distance between the support and suspension reinforcement (a) to the effective depth (d). This ratio is effective in the shear capacity of DEB. In addition, in the ratio of the distance of the load on the beam from the support (av) to the depth of the beam (deff) is also effective on the behavior of the beam under vertical loads. For the first time in the literature, the combined effects of these two ratios on the shear capacity of DEBs was investigated by experimental and numerical methods in this study. Firstly, an experimental study was carried out having 1/1 cross-sectional scale six different DEBs. In the experimental study, while the a/d ratio was kept constant as 1.8, the av/deff ratio was varied between 0.75 and 3. The experiments results indicate that towards increasing the av/deff ratio, the DEBs failed by flexure. The strength of DEBs decreases with an increase in the av/deff ratio. With smaller av/deff, the DEBs show greater stiffness and ultimate load. Numeric finite element models by using ABAQUS were verified by the load–displacement relationships and damage modes obtained from these experiments. After that, at the parametric stage of the study numeric models were also constructed in order to further investigate the effect of different a/d ratios and av/deff on the strength of DEBs. According to all test and numeric results, it is recommended that DEBs should be placed on the supporting member by considering the minimum a/d ratio. Otherwise, the capacity of the DEBs will be significantly reduced since the damage in the thinned zone will occur at lower load levels. At the end of study, considering the combined effects of a/d and av/deff, a shear capacity reduction coefficient based on these parameters has been proposed. The shear capacity, which is reduced using the proposed coefficient, approaches the numerical results, which converge to a great extent with the experimental data by 92.46%.

Axial mechanical behavior of innovative inter-module connection for modular steel constructions

Modular steel construction (MSC) is a construction mode where volumetric modules are prefabricated in a factory and assembled on-site to form permanent buildings. Inter-module connections are critical to the integrity and robustness of modular steel constructions (MSCs). In this paper, the mechanical behavior of a typical corner inter-module connection under axial tensile and compressive loads was investigated. A tensile test of the inter-module connection was carried out to investigate their axial tensile behavior. The refined numerical model was established, calibrated against the test results and then used to simulate the axial tensile and compressive mechanical behaviors of the inter-module connection. The effects of key design parameters on the axial load-displacement responses of the connection, including the bolt gasket thickness, the bolt diameter and the preload were investigated. The inter-module connection was shown to exhibit excellent load-carrying capacity under axial compression and adequate performance under tension. In terms of tensile resistances, the bolt gasket thickness and the bolt diameter were shown to be the critical parameters, while the section size of the modular columns dominated the compressive load-carrying capacity. Through geometrical parameters correlation analysis, a simplified piecewise polynomial axial load-displacement model with different stiffnesses in tension and compression was employed for predicting the axial load-displacement relationship. The proposed model was shown to be capable of accurately capturing the axial resistance characteristics of the connection while maintaining simplicity, and is therefore recommended for use to represent the axial behavior of the inter-module connection in global frame modelling.

Shape optimization of Hourglass-shaped damper using Fe-Mn-Si-Based alloy considering target Load-displacement relationship and target fatigue characteristics

To reduce the response of buildings during earthquakes, the use of various hysteresis dampers for passive control is increasing. For effective application to buildings, these dampers must meet both load displacement relationship and fatigue property requirements. In this study, shape optimization of an Fe-Mn-Si-based alloy damper was conducted to improve the fatigue property while maintaining the target load displacement relationship, and the obtained optimized damper was examined. First, shape optimization was conducted using the modal iterative error correction (MIEC) inverse analysis method. Subsequently, a loading test on the damper fabricated based on the optimized shape was conducted, and its effectiveness was confirmed. As a result, it was confirmed that the optimized shape of the damper, which improves the fatigue performance while maintaining the load displacement relationship, was successfully searched using the MIEC inverse analysis method. In addition, it was confirmed that the fatigue performance of the test specimen based on the optimized shape was improved compared to that of the initial-shape.

Seismic performance of lap-spliced pre-damaged and intact concrete columns strengthened or retrofitted with UHPC and NSM

Reinforced concrete (RC) columns with deficient lap splice details such as short lap splice length and widely spaced stirrups were vulnerable to earthquakes. In the present study, to evaluate the effectiveness of an innovative retrofitting technique using the combination of ultra-high performance concrete (UHPC) and near surface mounted (NSM) technique on the seismic performance of RC columns with deficient lap splices details, cyclic loading tests were performed on four large-sized RC column specimens. Two RC columns were strengthened with UHPC or the combination of UHPC and NSM, and the other two were retrofitted with the combination of UHPC and NSM after the lateral strength decreased to 85% peak strength during the pre-damage cyclic tests. The load–displacement relationship, stiffness degradation, energy dissipation, and residual displacement of RC columns are evaluated. The test results showed that the peak strength and ductility of RC columns with deficient lap splice are significantly improved after strengthening or retrofitting with the combination of UHPC and NSM. The seismic performance of severely damaged RC columns due to deficient lap splice details can still be effectively restored after retrofitting with the combination of UHPC and NSM. Considering the adverse effect of pre-damage, a design method is proposed to predict the flexural capacity of RC columns retrofitting with UHPC or the combination of UHPC and NSM. The proposed method is also applied to predict the flexural capacity of RC beams strengthened with UHPC. The proposed method predicted well the test results of this study and existing tests.

A unified method to estimate J-resistance curve of thin-walled metallic tube containing axial cracks

Fracture toughness of thin-walled metallic tubes is an important mechanical property index to ensure their safety in service. Because of the particularity of geometric structure, the fracture toughness test of thin-walled metallic tubes cannot be carried out using traditional standard specimens. In this work, the expressions of load–displacement relationship and J-integral of thin-walled tube specimens containing bilateral axial cracks are proposed based on the energy density equivalence principle, in which the effect of material and specimen geometry has been considered. Through three-dimensional finite element simulation analysis, the relevant parameters of the expression are obtained and validated, and then a fracture toughness test method for thin-walled metallic tubes is established. The method is applicable to the fracture toughness measurement of thin-walled metallic tubes with different sizes and materials. Finally, the fracture toughness tests of two thin-walled alloy tubes were completed by the new method, and the J-resistance curves were obtained.

Fatigue failure mechanisms and probabilistic S-N curves for CFRP–steel adhesively bonded joints

In this study, fatigue tests were conducted on a series of carbon fiber reinforced polymer (CFRP)–steel double lap shear joints. The fatigue failure mechanisms were investigated based on the failure modes, load–displacement relationships, and stiffness degradation. Inherent scatter characteristics of the fatigue life were discussed using probabilistic S-N (P-S-N) curves based on four statistical models (ISO 12107, ASTM E739-91, two-parameter Weibull, and Gumber models). The results indicate that the fatigue life decreased dramatically with the increase of the load level, and interface debonding is the primary failure mode of fatigue joints. Stable debonding and accelerated debonding of the bonded interface are initiated when the joint stiffness degrades to approximately 98% and 82–86% of the initial stiffness, respectively. The S-N curve based on the mean bond stress range shows a better fit than that based on the local bond stress. Based on the comprehensive evaluation of the performance of the P-S-N curves, the two-parameter Weibull model is recommended for fatigue life design as it can well-constrain fatigue data without excessive safety redundancy.

Shear behavior of I-section steel with circular web opening and novel reinforcement

For reinforcement of circular web opening in I-section steel beams, half-ring plates of novel configuration were proposed considering the economy and structural performance. To verify the proposed method, cyclic loading tests were conducted for cantilever beams with a single web opening and low shear-span ratio. The test parameters were opening diameter-to-beam depth ratio and degree of reinforcement. The test results showed that the shear behavior of I-section steel was significantly affected by web opening of standard and small diameters (= 50% and 33% of the beam depth, respectively). On the other hand, properly designed ring plates strengthened the perforated beams to exhibit the plastic capacity of solid I-section, restraining the double-curvature flexural mode of web opening (i.e., the Vierendeel mechanism). The proposed ring plates were effective not only in enhancing the flexure-shear strength of the perforated beams, but also in ensuring large inelastic deformation, irrespective of design parameters. The test results, such as the overall load-displacement relationships and buckling modes, were successfully captured by finite element analysis using Abaqus. An existing analytical model for the flexure-shear interaction capacity of the circular web opening was modified to account for the proposed reinforcement method. The predictions conservatively estimated the test strengths.

Mixed-mode fracture of compacted tailing soils. I: Fracture toughness

Mine tailings are man-made soils and leftovers from the mineral processing that share the similar geotechnical properties with natural soils. In areas with abundant mineral reserves and developed mining industries, tailings could be utilized as an alternative of natural soils for subgrade materials of pavement and adobes for building and construction constructions. The tailing soils are also the based materials for tailing dams. The compacted tailing soils might thus be subject to combined opening or shearing deformations that were unexplored in the current academic society. In this paper, a test configuration called asymmetric semi-circular bending (ASCB) was adopted to investigate the mixed I/II mode fracture properties of the compacted tailing soils. First, the load–displacement relationships of the SCB specimens for different notch depths and span ratios were presented. The mode I and II fracture toughness components were then calculated by referring to the theoretical solutions derived from classical fracture mechanics. The fracture envelope from mode I and II fracture toughness components were presented. Meanwhile, the mixity parameter was introduced to evaluate the mode mixity of the ASCB specimens. Finally, the crack initiation angles of the SCB specimens were measured through experimental tests and compared to the theoretical results obtained from generalized maximum tangential stress criterion (GMTS). Results show that the mode I fracture toughness component of the compacted tailing soils increased with the span ratio, while the mode II fracture toughness component increased with the decrease of span ratio. The mode mixity and crack initiation angles of the SCB specimens under mixed mode loading conditions increased with the decrease of span ratio.

Modeling and Simulation of Electric Thrust Reverser Actuator Control Based on Simulink

According to the structural characteristics and working principle of the electric actuator system of the aircraft thrust reverser, the mathematical control model of the thrust reverser actuator is proposed for a certain type of electric thrust reverser actuator system. The model is established and simulated by the modular modeling method based on Simulink software. The actuator’s load force, transmission, displacement, and velocity relationship are analyzed. The simulation results show that the model can simulate the deployment and stow of the actuator under different conditions and provide a platform for the control logic design, force analysis, and fault diagnosis of the electric thrust reverse actuator system.

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.