Effect Of Loading Patterns Research Articles

Effect of loading patterns on in-plane flexural hysteretic performance of CHS X-connections

This paper presents an experimental investigations to study the hysteretic behavior of circular hollow section (CHS) X-connections which widely applied in various tubular structures. Cyclic in-plane bending moment (IPBM) loading patterns and geometric parameter of brace-to-chord diameter ratio (β) were varied in testing four connection specimens, to evaluate the influence of load patterns on the hysteretic behavior of the connections. Test results shown that regardless of load patterns and connection details, all specimens showed plump and no pinching effect for the hysteresis curve before cracking occurred, all specimens shared similar final failure modes (the chord wall near the intersection teared) and similar energy dissipation modes (mainly rely on the plastic deformation of the chord wall near the intersection). However, the influence of loading patterns on the hysteretic behavior of the X-connections with varied β is different. For the CHS X-connections with large β, it developed higher flexural strength, better ductility and more energy dissipation performance under synchronized down and up IPBM (SDUI) loading pattern than that under take turns to align clockwise and counterclockwise IBPM (TCCI) loading pattern; while for the X-connections with small β, it is opposite. This experimental observation result was further affirmed by a simplified analytical model and FE analysis results. The test results also indicated that regardless of the load patterns, increasing β trend to significantly improve the strength, ductility ratio and energy dissipation behavior of CHS X-connections under cyclic IPBM, and the current specification trend to give conservative prediction on the in-plane flexural strength of the X-connections.

Influence of Waveforms on Fatigue Crack Growth Characteristics of Tire Tread Rubber using Finite Element Analysis

ABSTRACT Rubber products are typically subjected to cyclic fatigue loading in service. During prolonged exposure to cyclic loading, damages initiate at intrinsic defect sites at microscopic levels and subsequently propagate, leading to catastrophic failure. Therefore, the material that offers better resistance to fatigue crack growth (FCG) is suitable for a durable product. FCG characteristics of rubber compounds depend on many factors, such as constituent material (rubber, filler, etc.), environment, and operational conditions (loading amplitude, loading pattern, etc.). To simulate the realistic service condition of a product, the choice of loading pattern is a key factor and has emerged as a very important research topic in recent times. The present work focuses on the effect of loading pattern on FCG characteristics of tire tread rubber compounds. In the present study, FCG characteristics of a 100% natural rubber (NR) compound were measured on a tear and fatigue analyzer (TFA, Coesfeld, Germany) using double edge notched pure shear specimen. Fatigue loading was applied using sinusoidal and pulse waveforms over a wide range of tearing energy levels. Pulse mode recorded a very high crack growth rate (∼2 times) compared to sine mode at equivalent peak energy levels. In order to understand the mechanics of the higher crack growth rate in pulse mode, finite element analysis (FEA) of a pure shear specimen was performed wherein FCG experimental conditions were used as boundary conditions. FE analyses were carried out using both linear and nonlinear viscoelastic material models. Nonlinear viscoelastic FEA results revealed that viscous energy dissipation at the crack tip is much lower in the case of pulse mode, which is in support of higher the FCG rate in pulse mode as observed in the experiments.

Combined Effect of Loading Pattern, Pulse Duration, and Stress Level on the Cyclic Creep Test of Asphalt Mixture

AbstractIn this research work, based on the permanent strain mechanisms, the behavior of asphalt mixture under different loading conditions was examined in a cyclic compression creep test. This research study was conducted with three loading patterns at three pulse durations and stress levels. The results show the following: (1) the permanent strain mechanisms are strongly affected by stress level, pulse duration, loading patterns, and their interactions; (2) the rate of change in permanent strain from stress at a low stress level is significantly higher than that at a high stress level; (3) asphalt specimens with higher initial strain will show a lower rate of rutting progression as the number of load applications increases; (4) at a pulse duration corresponding to low speed, the asphalt specimen shows permanent strain over a shorter period of time, but at high speed this condition is dependent on stress level; (5) cumulative permanent strain is not linearly proportional to stress level for all loading c...

Effect of Load Pattern in the Generation of Higher Harmonic Amplitude in Concrete Using Nonlinear Ultrasonic Test

Effect of Load Pattern in the Generation of Higher Harmonic Amplitude in Concrete Using Nonlinear Ultrasonic Test

Performance of reinforced concrete columns under bi-axial lateral force/displacement and axial load

Accurate and realistic assessment of the performance of columns in general and those in critical locations that may cause progressive failure of the entire structure, in particular, is significantly important. This performance is affected by the load history, pattern and intensity. Current design code does not consider the effect of load pattern on the load and displacement capacity of columns. In the study reported here, monotonic material models, cyclic rule, and plastic hinge models have been utilized in a fiber-based analytical procedure, validated against experimental data. Comparison of the analytical predictions and experimental data, through moment–curvature and force–deflection analyses, confirmed the accuracy and validity of the analytical algorithm and models. The analytical model was then used in a parametric study considering the effects of axial load variation and lateral force/displacement paths on the flexural strength and energy dissipation capacity of reinforced concrete columns.

Effect of loading pattern and deck configuration on the progressive collapse response of cable-stayed bridges

Effect of loading pattern and deck configuration on the progressive collapse response of cable-stayed bridges

Effect of Loading Pattern and Deck Configuration on the Progressive Collapse Response of Cable-Stayed Bridges

In the cable stayed-bridges, sudden loss of cables is usually associated with material as well as geometrical non-linearities that may trigger progressive collapse of the entire bridge. Accordingly, in this paper detailed 3D finite element models of a hypothetical cable-stayed bridge is developed and analysed with material and geometrical non-linearities included. A parametric study is undertaken and effect of cable loss scenarios (symmetric and unsymmetric), deck configurations (steel box girder and open orthotropic deck) and number of lost cables on the progressive collapse response of the bridge is investigated. With regard to the results of parametric study, it is concluded that the deck configuration has a minor influence on the progressive collapse response of cable-stayed bridges. Also, it is shown that localised yielding of steel may occur following loss of more than one cable, however, such localised plastic strains cannot trigger the progressive collapse of the entire bridge. During cable loss scenarios, the reduction in post-tensioning stress and subsequently stiffness of the remaining cables (reflected in Ernst’s modulus) is found to be around 10% that warrants effect of geometrical non-linearities within the cables being considered.

Lateral-torsional buckling of laterally unsupported single angle sections loaded along geometric axis

Equal-leg single angle section (SAS) members were analyzed for flexural loading patterns along the geometric axis. Uniform, triangular, double-curvature and parabolic bending moment were produced using loading patterns over the span of member. Variations in orientation as well as in local and global slenderness ratio were considered to plot normalized moment rotation curves. Both material and geometrical nonlinearities with imperfections in member were also incorporated. These curves were compared with the existing provisions of AISC specification to verify the validity of the upper limit on Cb, which accounts for the effect of loading patterns on the elastic critical buckling moment of SAS members. Design specifications of Indian Standard (IS 800: 2007) for lateral-torsional buckling (LTB) of doubly and mono-symmetric sections were used to develop the design guidelines for limit state of LTB of SAS members. Moment capacity curves from proposed guidelines were compared with the AISC specification and were found to be safe and conservtive.

Effect of Loading Pattern on Performance of FRP-HSC-Steel Double Skin Tubular Columns

This paper reports on part of an ongoing experimental program at the University of Adelaide on FRP-concrete-steel double-skin tubular columns (DSTCs). The main emphasis of the study reported in this paper was to investigate the influence of loading pattern on the axial compressive behavior of DSTCs. To this end, 12 hollow and concrete-filled DSTCs were manufactured and tested under monotonic or cyclic axial compression. All of the specimens were manufactured using high-strength concrete (HSC). The results of the experimental study indicate that that concrete in cyclically loaded hollow DSTCs exhibits slightly larger strength and strain enhancement ratios than concrete in companion monotonically loaded DSTCs. The results also indicate that concrete in filled DSTCs exhibit slightly larger strength enhancement ratios than and similar strain enhancement ratios to concrete in monotonically loaded DSTCs.

Effects of loading patterns on seismic behavior of CHS KK-connections under out-of-plane bending

This paper deals with experimental investigations to study the seismic behavior of circular hollow section (CHS) KK-connections used in steel tubular structures. Cyclic out-of-plane bending (OPB) loading patterns were varied in testing two full-scale specimens in order to evaluate their effect on connection behavior. Test results indicated that the strength efficiency of these connections significantly depended on the loading patterns. CHS KK-connections under alternate opening and closing out-of-plane bending (AOCO) developed more satisfactory levels of ductility and energy dissipation than that under alternate clockwise aligned and counter-clockwise aligned out-of-plane bending (ACCO), although the final failure modes for both showed similar fracture initiated from the chord wall. This observation was further verified by the proposed simplified analytical model results. Finite element (FE) analyses were performed to simulate the experimental behavior and facilitate the interpretation of the important test observations. Additionally, it was found that the energy dissipation due to the ductile chord crack propagation could be utilized effectively to some extent for earthquake resistance.

Performance-based seismic design of a continuous bridge

Performance-based design (PBD) provides an insight into the expected performance of a designed structure during an earthquake. Over recent decades, considerable development on the PBD of buildings has taken place, but studies regarding the PBD of bridges are limited. This paper examines the estimated performance of a three-span continuous bridge designed using a codal procedure for the site-specific design response spectrum. A three-dimensional model of the bridge was developed using non-linear modelling of the piers. The response of the bridge was estimated using non-linear static and dynamic procedures. The effect of loading patterns and the accuracy of different pushover analysis methods were examined, and Fema-356 performance levels compared with limit states defined by Kowalsky. The performance of the bridge was studied for different values of the response reduction factor used in the design. The paper also discusses the advantages of PBD and pushover analysis.

Effect of load pattern on solar-boosted heat pump water heater performance

The performance of a solar-boosted heat pump water heater (HPWH) operating under full load and part load conditions was determined in an outdoor experimental study. The system utilised flat unglazed aluminium solar evaporator panels to absorb solar and ambient energy. Absorbed energy was transferred to the water tank by means of the heat pump and a wrap around condenser coil on the outside of the tank. The system COP was found to be in the range of 5–7 under clear daytime conditions and 3–5 under clear night-time conditions. Using part load testing of the HPWH system it was found that concentrating the coils in the lower portion of the tank could increase the efficiency of the condenser coil. It was also shown that there exists a generalised linear relationship that can be used to describe the system COP in terms of the temperature difference between the water in the storage tank and the ambient air.

Stiffened steel box columns. Part 2: Ductility evaluation

The purpose of this study is to evaluate the ultimate strength and ductility capacity of stiffened steel box columns failed by local and overall interaction instability under a constant compressive axial force and cyclic lateral loading. In a companion paper, a finite element formulation accounting for both geometrical and material non-linearity was developed to obtain cyclic hysteretic behaviour of such columns. In this paper, the effect of loading patterns on the cyclic inelastic behaviour is first studied; then, a parametric study is carried out to investigate the effects of flange plate width–thickness ratio parameter, column slenderness ratio parameter, stiffener's equivalent slenderness ratio parameter, magnitude of axial load, and material type of stiffeners on the strength and ductility of the columns. Last but not least, empirical formulae of both the ultimate strength and ductility capacities are proposed for stiffened steel box columns, and the limit values of various parameters for the required ductility demand are also discussed. Copyright © 2000 John Wiley & Sons, Ltd.

Effects of loading patterns on the pressure-sinkage relation of dry loose sand

The pressure-sinkage relation of dry loose sand is one of the main problems considered for a vehicle to drive in desert. It is affected by loading patterns. Based on plate-sinkage tests. the effects of two different loading patterns on the pressure-sinkage relation of dry loose sand are studied. One is that the plate is horizontal with the angle of load relative to the plate normal varying from 0 to 30 degrees. The other is that the load is perpendicular to the plate with the angle of the plate relative to sand surface varying from 0 to 30 degrees. The results indicate that the pressure -sinkage relations of dry loose sand in both the above mentioned cases are different from that in the horizontal plate-vertical load case and that if the sinkage-pressure relation under the horizontal plate-inclined load case is used to determine the normal stress distribution under the tire, a precise prediction of the tractive properties of a wheel can be obtained.

Effect of loading pattern on flow of porous materials under biaxial deformations: Y.A. Panfilov et al, Poroshkovaya Metallurgiya, No 7, 1992, 14–17. (In Russian)

Effect of loading pattern on flow of porous materials under biaxial deformations: Y.A. Panfilov et al, Poroshkovaya Metallurgiya, No 7, 1992, 14–17. (In Russian)

Parametric Study of Continuous Prestressed Composite Girders

The technique of prestressing has been used successfully to improve the performance of existing concrete structures. However, very few applications of this technique can be found in steel structures. Prestressing by means of high‐strength cable or bar can be used to effectively increase the working load and the ultimate capacity of composite steel‐concrete girders. The benefits of prestressing the steel wide flange section in composite construction can be achieved in strengthening of existing structures as well as in the design of new structures. In this paper, the elastic behavior of continuous, prestressed, composite girders with straight and draped tendon profiles is examined. The effects of design variables such as the prestress force, tendon eccentricity, and tendon length on the working load and deflection of girders are studied. The results show that the allowable load of girder increases proportionally with increase in prestress force and eccentricity. The effect of load pattern on the change in t...

Effect of loading pattern on elastic-plastic fatigue crack growth behavior under varying loadings.

Load-controlled fatigue crack growth tests were carried out on two kinds of steels, S35C and SM50A, under repeated two-and three-step loadings in the post-yield region. Crack closure was investigated using the minicomputer-aided unloading elastic compliance method. Crack closure and plastic deformation under varying loadings were found to be affected by load variation and load sequences. However, fatigue crack growth rate under varying loadings where both one-directional and cyclic plastic deformation were observed remarkably, could be well predicted by the linear summation rule of crack growth by using ΔJ* is the J-integral range-pair taking into account one-directional deformation under low-level loadings.

The effect of loading pattern on the growth rate of a stress corrosion crack at high stress levels

Earlier work by the present author has focused on the determination of the growth rate of a stress corrosion crack at high stress levels under constant load conditions, in situations where the J integral increases as the crack extends.The basis of the approach is to correlated the crack-tip-opening angle with the crack growth rate, using the experimentally determined linear elastic fracture mechanics (LEFM) relation between the crack tip stress intensity K and growth rate, and to assume the same correlation is valid when LEFM conditions are not operative. In the present paper the earlier work is extended by analysis a particular case where J decreases rather than increases during crack growth: a crack with line the forces applied to its faces. The results are compared with those for the cases where J increases, enabling some general conclusions to be drawn regarding the effect of loading pattern on the stress corrosion crack growth rate at high stress levels. The theoretical results highlight the importance of the gradient of J, as distinct from J itself, in affecting the growth rate.

The transition between stress corrosion crack growth and plastic fracture—II. The effect of loading pattern

The paper addresses the problem of predicting the onset of plastic fracture at the tip of a growing stress corrosion crack, using data from laboratory fracture mechanics tests. A theoretical analysis for a particular model: namely that of the place strain deformation of a solid with two symmetrically situated deep cracks, and with tension of the small remaining ligament, shows that plastic fracture occurs at a J value that is not constant, but depends on whether the loading is load or displacement control. This result, which is valid for materials for which the onset of crack extension and unstable fracture are coincident in a rising load fracture mechanics test, provides valuable support for the view that great care must be exercised when using fracture mechanics procedures to predict the transition between stress corrosion crack growth and plastic fracture in such materials.

The effect of loading pattern on crack growth instability under small-scale yielding conditions

A theoretical analysis shows that if a plane strain crack is stable up to a certain J level ( J ST ) under small-scale yielding conditions and the displacement control loading conditions that are characteristic of a machine loaded specimen, then unstable fracture under load control conditions cannot occur at J levels that are appreciably less than J ST . The results, therefore, give added confidence to the use of linear elastic fracture mechanics data, for assessing the integrity of cracked engineering structures with regard to catastrophic fracture.