Maximum Axial Load Research Articles

Experimental Investigation of Concrete Filled PVC Tube Columns Confined By Plain PVC Socket

This paper presents results of an experimental study for concrete column filled poly vinyl chloride (PVC) tubes confined by plain socket with 5.8 & 6.8 mm thicknesses, 102 mm diameter and 100 mm depth. The total of five concrete filled columns using PVC tubes (CFT PVC) was tested to investigate the columns’ behaviour. The column is 700 mm height, 100 mm external diameter and 3.5 mm tube thickness with different thickness of plain socket. The results presented include maximum axial load, plain socket confinement effect, the mode of failure, and lateral PVC strain. The axial load enhancement of PVC-concrete columns confined using plain socket shows an increment of 21.3% up to 55.2% and axial strain from 21% to 40% compared with displacement for control composite columns at 192 kN ultimate load.

Fatigue Failure of Electronic Unit Pumps Used in Truck Diesel Engine

Several electronic unit pumps (EUPs) used in the truck diesel engine failed during the trial tests. All the failures occurred at the same location, the fifth thread root on the outer diameter of oil-outlet of EUP. Two typical failed EUPs were analyzed to assess failure causes. Fractographic investigation shows that the fatigue fracture was the dominant failure mechanism of two EUPs. Crack origins of the failed EUPs initiated from the fillet root of the step in the internal hole of oil-outlet and propagated toward the fifth thread root on the outer diameter of oil-outlet. Over-small radius of the root fillet caused a high notch effect, and the presence of porous structure and network nitrides on the nitrided internal hole surface created a “metallurgical stress concentration.” Under the action of the great contact force between the plug and the side wall of internal hole of oil-outlet resulting from the press-fitting the plug, the crack initiated easily at the fillet root. The fillet root of step in the internal hole was almost in the same level with the fifth thread root on the outer diameter of oil-outlet. The fifth thread on the outer diameter of oil-outlet was just corresponding to the first engaged thread inside the nut of oil-pipe matched with the threaded portion of the outer diameter of oil-outlet. This resulted in a maximum axial tensile load on the fifth thread due to pre-tightening the nut of oil-pipe. The crack propagated rapidly toward the fifth thread on the outer diameter under the great axial tensile load to lead to premature fatigue failure of EUP.

Active buckling control of an imperfect beam-column with circular cross-section using piezo-elastic supports and integral LQR control

For slender beam-columns loaded by axial compressive forces, active buckling control provides a possibility to increase the maximum bearable axial load above that of a purely passive structure. In this paper, the potential of active buckling control of an imperfect beam-column with circular cross-section using piezo-elastic supports is investigated numerically. Imperfections are given by an initial deformation of the beam-column caused by a constant imperfection force. With the piezo-elastic supports, active bending moments in arbitrary directions orthogonal to the beam-column's longitudinal axis can be applied at both beam- column's ends. The imperfect beam-column is loaded by a gradually increasing axial compressive force resulting in a lateral deformation of the beam-column. First, a finite element model of the imperfect structure for numerical simulation of the active buckling control is presented. Second, an integral linear-quadratic regulator (LQR) that compensates the deformation via the piezo-elastic supports is derived for a reduced modal model of the ideal beam-column. With the proposed active buckling control it is possible to stabilize the imperfect beam-column in arbitrary lateral direction for axial loads above the theoretical critical buckling load and the maximum bearable load of the passive structure.

Preload variation due to temperature increase in double nut ball screws

Ball screws are robust and economic linear positioning systems that are widely employed in high speed and high precision machines. Due to precision and stability requirements, the preload force has been considered one of the main parameters in order to define the axial rigidity and the maximum axial load capacity of ball screw feed drives. In high speed motions, thermal effects are also considerably relevant regarding positioning precision and dynamic stability of the machine. The temperature increase and the thermal gradient between the screw, the balls and the nuts led to a variation in the contact geometry and consequently in the preload force. This paper presents an experimental analysis of the preload variation due to the temperature increase. The study has been performed for several initial preload forces and linear speeds in a preloaded double nut ball screw. The heating of the system results in a decrease of the preload force, where a maximum decrease of 60 % has been observed for a temperature increase of 28 K in the test bed of the study. Regarding the consequences of the loss of rigidity, the first eigenvalue decreased by only 5 % for a preload drop of 33 %.

Validation of a steel dual-core self-centering brace (DC-SCB) for seismic resistance: from brace member to one-story one-bay braced frame tests

A steel dual-core self-centering brace (DC-SCB) is an innovative structural member that provides both energy dissipation and self-centering properties to structures, reducing maximum and residual drifts of structures in earthquakes. The axial deformation capacity of the DC-SCB is doubled by a parallel arrangement of two inner cores, one outer box and two sets of tensioning elements. This paper presents cyclic test results of a DC-SCB component and a fullscale one-story, one-bay steel frame with a DC-SCB. The DC-SCB that was near 8 m-long was tested to evaluate its cyclic behavior and durability. The DC-SCB performed well under a total of three increasing cyclic loading tests and 60 lowcycle fatigue loading tests without failure. The maximum axial load of the DC-SCB was near 1700 kN at an interstory drift of 2.5%. Moreover, a three-story dual-core self-centering braced frame (DC-SCBF) with a single-diagonal DC-SCB was designed and its first-story, one-bay DC-SCBF subassembly specimen was tested in multiple earthquake-type loadings. The one-story, one-bay subassembly frame specimen performed well up to an interstory drift of 2% with yielding at the column base and local buckling in the steel beam; no damage of the DC-SCB was found after all tests. The maximum residual drift of the DC-SCBF caused by beam local buckling was 0.5% in 2.0% drift cycles.

Evaluation of the maximum axial force on a cylindrical shell structure in terms of stability and strength using fuzzy quantities of chosen geometric parameters

The paper deals with the application of the fuzzy sets theory for determining the maximum axial load of a pin-supported smooth cylindrical shell surface. It takes into account the stability and strength criteria, using fuzzy shell radius and plate thickness data. The formulated optimisation problems relate to fuzzy chance-constrained programming (CCP) models. A Monte-Carlo simulation modelling algorithm is proposed. Computational experiments were performed as part of the study. The proposed method can be used for designing and assessing the load-bearing capacity of structures such as bridges and railroads when faced with incomplete or time-varying input data.

A Comparison between cutting and folding modes of an extruded aluminum alloy tube during impact using ductile failure criterion

Thin-walled structures like crash boxes may be used as energy absorbers in the automotive chassis. There have been lots of investigations about the behavior of these parts during frontal crashes. Previous researches show that thin-walled circular tube has the highest energy absorption among different structures. In this study, cutting and folding modes of extruded aluminum tubes (EN-7018 T6) with 50 mm diameter, lengths of 300 and 400 mm and thicknesses of 2, 2.5 and 3 mm are compared when axial impacts with velocities of 6, 8 and 10 m.s-1 are applied to them. Cutting tools of 4 and 6 blades are used to provide the cutting mode. Effective parameters of energy absorbers including crush force efficiency, specific energy absorption and maximum axial load are modeled numerically with the help of Hooputra’s ductile damage criterion and are compared to each other for three cases of aluminum tube folding between two rigid plates and tube rupture by using 4 and 6 blades cutting tools. The analyses show that the tube rupture by the 6 blades cutting tool is better than the other two in the case of energy absorption. Furthermore, the results demonstrate that tube cutting with the help of multi-blades cutting tools is more stable, controllable and predictable than tube folding.

Drilling the near cortex with elongated figure-of-8 holes to reduce the stiffness of a locking compression plate construct.

To compare the stiffness of locking compression plate (LCP) constructs with or without drilling the near cortex with elongated figure-of-8 holes. 24 synthetic bones were sawn to create a 10-mm gap and were fixed with a 9-hole 4.5-mm narrow LCP. In 12 bones, the near cortex of the adjacent holes to the LCP holes was drilled to create elongated figure-of-8 holes before screw insertion. The stiffness of LCP constructs under axial loading or 4-point bending was assessed by (1) dynamic quasi-physiological testing for fatigue strength, (2) quasi-static testing for stiffness, and (3) testing for absolute strength to failure. None of the 24 constructs had subcatastrophic or catastrophic failure after 10 000 cycles of fatigue loading (p=1.000). The axial stiffness reduced by 16% from 613±62 to 517±44 N/mm (p=0.012) in the case group, whereas the bending stiffness was 16±1 Nm2 in both groups (p=1.000). The maximum axial load to catastrophic failure was 1596±84 N for the control group and 1627±48 N for the case group (p=0.486), whereas the maximum bending moment to catastrophic failure was 79±12 and 80±10 Nm, respectively (p=0.919). Drilling the near cortex with elongated figure-of-8 holes reduces the axial stiffness of the LCP construct, without compromising its bending stiffness or strength.

Lower Leg Injury Reference Values and Risk Curves from Survival Analysis for Male and Female Dummies: Meta-analysis of Postmortem Human Subject Tests

Objective: Derive lower leg injury risk functions using survival analysis and determine injury reference values (IRV) applicable to human mid-size male and small-size female anthropometries by conducting a meta-analysis of experimental data from different studies under axial impact loading to the foot–ankle–leg complex.Methods: Specimen-specific dynamic peak force, age, total body mass, and injury data were obtained from tests conducted by applying the external load to the dorsal surface of the foot of postmortem human subject (PMHS) foot–ankle–leg preparations. Calcaneus and/or tibia injuries, alone or in combination and with/without involvement of adjacent articular complexes, were included in the injury group. Injury and noninjury tests were included. Maximum axial loads recorded by a load cell attached to the proximal end of the preparation were used. Data were analyzed by treating force as the primary variable. Age was considered as the covariate. Data were censored based on the number of tests conducted on each specimen and whether it remained intact or sustained injury; that is, right, left, and interval censoring. The best fits from different distributions were based on the Akaike information criterion; mean and plus and minus 95% confidence intervals were obtained; and normalized confidence interval sizes (quality indices) were determined at 5, 10, 25, and 50% risk levels. The normalization was based on the mean curve. Using human-equivalent age as 45 years, data were normalized and risk curves were developed for the 50th and 5th percentile human size of the dummies.Results: Out of the available 114 tests (76 fracture and 38 no injury) from 5 groups of experiments, survival analysis was carried out using 3 groups consisting of 62 tests (35 fracture and 27 no injury). Peak forces associated with 4 specific risk levels at 25, 45, and 65 years of age are given along with probability curves (mean and plus and minus 95% confidence intervals) for PMHS and normalized data applicable to male and female dummies. Quality indices increased (less tightness-of-fit) with decreasing age and risk level for all age groups and these data are given for all chosen risk levels.Conclusions: These PMHS-based probability distributions at different ages using information from different groups of researchers constituting the largest body of data can be used as human tolerances to lower leg injury from axial loading. Decreasing quality indices (increasing index value) at lower probabilities suggest the need for additional tests. The anthropometry-specific mid-size male and small-size female mean human risk curves along with plus and minus 95% confidence intervals from survival analysis and associated IRV data can be used as a first step in studies aimed at advancing occupant safety in automotive and other environments.

Concrete-Filled Steel Tube Columns Encased with Thin Precast Concrete

An experimental study was performed to investigate the axial-flexural load-carrying capacity of concrete-filled steel tube columns encased with thin precast concrete (PC). Six eccentrically loaded columns and one concentrically loaded column were tested. To prevent the premature failure of the concrete encasement, various reinforcement details such as studs, steel fiber, welded wire mesh, and cross ties were used. The maximum axial loads of the specimens agreed with the strengths predicted by current design codes, although in some specimens, the load-carrying capacity decreased immediately after the peak strength owing to early spalling of the concrete encasement. On the basis of the test results, the use of fiber-reinforced concrete is recommended to increase the ductility of columns by restraining the spalling of the concrete encasement.

The Performance of Double Sheathed Composite Walling Made from Profiled Steel Sheeting and Dry Board

This paper presents the performance of an emerging prefabricated composite system made from profiled steel sheeting and dry board. Six full-scale wall specimens were prepared and tested under axial load. The results of the experimental investigation showed that the performance of the composite walls is governed by the strength of profiled steel sheeting while the dry board performed as a wall sheathed. A partial interaction between the profiled steel sheeting and dry board was achieved by using self-drilling screws. The maximum axial load capacity is 1329kN for the double sheathed wall. The failure behavior of single and double sheathed composite wall exhibited similar pattern such as global buckling and cracking. The developed composite wall system was found the great potential in prefabricated and modular construction in Malaysia.

Kinematic internal forces in deep foundations with inclined piles

SummaryThis paper presents a parametric study that looks into the influence of pile rake angle on the kinematic internal forces of deep foundations with inclined piles. Envelopes of maximum kinematic bending moments, shear forces and axial loads are presented along single inclined piles and 2 × 2 symmetrical square pile groups with inclined elements subjected to an earthquake generated by vertically incident shear waves. Inclination angles from 0° to 30° are considered, and three different pile–soil stiffness ratios are studied. These results are obtained through a frequency–domain analysis using a boundary element–finite element code in which the soil is modelled by the boundary element method as a homogeneous, viscoelastic, unbounded region, and the piles are modelled by finite elements as Euler–Bernoulli beams. The rotational kinematic response of the pile foundations is shown to be a key factor on the evolution of the kinematic internal forces along the foundations. Copyright © 2015 John Wiley & Sons, Ltd.

Axial Load Performance of Circular CFT Columns with Concrete Encasement

콘크리트피복 충전강관의 휨-압축 성능을 평가하기 위한 편심압축실험을 수행하였다. 기둥 주철근의 국부좌굴을 구속하고 콘크리트피복의 조기파괴를 방지하기 위하여 U형 띠철근 상세를 제안하였다. 주요 실험변수는 축하중 편심거리, 띠철근 간격, 그리고 콘크리트피복 여부이다. 실험결과 얇은 콘크리트피복에 수직균열이 조기에 발생하였지만 실험체의 최대강도는 콘크리트 피복의 기여도를 고려한 예측강도를 만족하였다. 또한, 내부 원형강관으로 인하여 제안된 콘크리트피복 충전강관은 우수한 변형능력을 나타냈다. 실험체의 휨-압축 강도 및 휨강성을 현행 설계기준과 비교하여 분석하였다. An experimental study was performed to investigate the axial-flexural load-carrying capacity of concrete-encased and-filled steel tube (CEFT) columns. To restrain local buckling of longitudinal bars and to prevent premature failure of the thin concrete encasement, the use of U-cross ties was proposed. Five eccentrically loaded columns were tested by monotonic compression. The test parameters were axial-load eccentricity, spacing of ties, and the use of concrete encasement. Although early cracking occurred in the thin concrete encasement, the maximum axial loads of the CEFT specimens generally agreed with the strengths predicted considering the full contribution of the concrete encasement. Further, due to the effect of the circular steel tube, the CEFT columns exhibited significant ductility. The applicability of current design codes to the CEFT columns was evaluated in terms of axial-flexural strength and flexural stiffness.

Axial dynamic analysis of marine riser in installation

In this paper, the riser is regarded as continuous system with infinite degrees of freedom and the mechanical model to analyze its axial dynamic characteristics during installation has been established according to the basic principle of vibration mechanics. The model has taken the influence of damping on vibration into consideration, and the axial vibration differential equation has been deduced. The equation has been solved on the basis of boundary conditions and initial conditions. Besides, the variations of water depth, riser size, weight of Blowout Preventers (BOPs) on axial vibration natural frequency and axial vibration load have been discussed. Results show that axial vibration is given priority to the first order vibration mode and the maximum vibration load point located at the riser top. With the increase of water depth and riser wall thickness, the natural frequency increases gradually. The natural frequency decreases with the increase of weight of BOPs. However, the maximum axial vibration load decreases with the increase of the above mentioned factors. What's more, the riser bottom trends compression when the water up to a certain depth. The study has shed some light on safe and quick installation of marine riser.

Development of cross-anchored dual-core self-centering braces for seismic resistance

The steel dual-core self-centering brace (SCB) is an innovative structural member that provides both energy dissipation and re-centering properties to structures, reducing the residual drift of braced structures in earthquakes. The axial deformation capacity of the brace is doubled by using two inner cores and one outer box and by serial axial deformations of two sets of parallel tensioning elements. The original dual-core SCB that used E-glass fiber tendons or T-700 carbon fiber tendons as tensioning elements exhibited good self-centering and energy dissipation up to an interstory drift of 2.5%. The new cross-anchored dual-core SCB halves the work required to apply the initial post-tensioning forces to tendons. The potential use of high-strength steel tendons as tensioning elements is studied herein, and the effects of the number of cycles on the brace behavior, energy dissipation, and durability of the steel tendon-anchorage system are also examined. First, the mechanics and cyclic behavior of the new brace are explained; a 7950mm-long cross-anchored dual-core SCB is then tested six times. The cross-anchored dual-core SCB exhibits excellent self-centering property up to a drift of 2.5% and a maximum axial load of 1700kN. No damage to the steel tendons, anchors or bracing members is found after three cyclic loading tests with increasing displacement amplitudes and 60 low-cycle fatigue tests. Finite element analysis further confirms the hysteretic responses and mechanics of the cross-anchored dual-core SCB in the cyclic test.

Behaviour of masonry wallettes made from a new concrete formulation under compression loads at ambient temperatures: Testing and modelling

This paper presents an experimental investigation and analytical simulation which aim to assess the behaviour of a new type of masonry wallette under conditions of an axial compression load at ambient temperature. Two different masonry wallettes were produced using two types of lightweight concrete blocks, the first incorporating expanded clay and the second using by-product materials which consisted of recycled waste glass and metakaolin. Both vertical and lateral deformations were measured at different positions on the wallette specimens. The load-bearing capacity was also determined. The measured results obtained were compared with analytically simulated results produced by the Abaqus/Standard finite element package.The experimental results showed that the maximum axial loads at failure were 474 kN and 558 kN for the reference and modified wallettes respectively implying corresponding bearing capacities of 7.1MPa and 8.3MPa. The critical path of the failure mode was similar for all of the wallettes tested and normally began underneath the load point, then passed through the concrete blocks and head joint to reach the wallette toe.The most influential factors on the analytical model are the value of penalty stiffness and imperfect wallette construction. A close agreement between the measured and simulated results has been observed, suggesting that finite element analysis provides a reliable alternative to further laboratory measurements.

Full-Scale Tests of Slender Concrete-Filled Tubes: Interaction Behavior

AbstractThis paper presents selected results from an experimental and computational evaluation on the behavior of slender concrete-filled steel tubes (CFTs) under combined axial compression and biaxial flexure. A complex loading protocol was used in the experimental program, including monotonic and cyclic loading that allowed detailed evaluation of the complete beam-column response. This paper principally addresses the experimental determination of the maximum stable axial load–bending moment (P−M) interaction strength. The experimental P−M interaction strengths extracted at incipient instability shows that for very slender specimens, the bilinear interaction diagram proposed in the current design provisions of the AISC is somewhat unconservative. This experimental observation is also confirmed by detailed computational results. However, the results also indicate that current AISC provisions provide an accurate and conservative approach for evaluating axial load–flexural interaction for most practical CFT...

Thermal-hydro-mechanical coupling stress intensity factor of brittle rock

A new calculation formula of THM coupling stress intensity factor was derived by the boundary collocation method, in which an additional constant stress function was successfully introduced for the cracked specimen with hydraulic pressure applied on its crack surface. Based on the newly derived formula, THM coupling fracture modes (including tensile, shear and mixed fracture mode) can be predicted by a new fracture criterion of stress intensity factor ratio, where the maximum axial load was measured by self-designed THM coupling fracture test. SEM analyses of THM coupling fractured surface indicate that the higher the temperature and hydraulic pressure are and the lower the confining pressure is, the more easily the intergranular (tension) fracture occurs. The transgranular (shear) fracture occurs in the opposite case while the mixed-mode fracture occurs in the middle case. The tested THM coupling fracture mechanisms are in good agreement with the predicted THM coupling fracture modes, which can verify correction of the newly-derived THM coupling stress intensity factor formula.

Eccentric Axial Load Test for Concrete-Filled Tubular Columns Encased with Precast Concrete

In this paper, concrete-filled steel tubular columns encased with precast reinforced concrete were studied. Four eccentrically loaded columns and a concentrically loaded column were tested to investigate the axial load-carrying capacity. The test parameters were the use of fiber reinforcement for cover concrete, eccentricity, column length, and lateral reinforcement. The maximum axial loads of the specimens agreed with the nominal strengths predicted by KBC 2009. However, in some specimens, the load carrying capacity quickly decreased after the peak strength due to spalling of the cover concrete.

The effects of tine coupling and geometrical imperfections on the response of DETF resonators

This paper presents a two-degree-of-freedom analytical model for the electromechanical response of double ended tuning fork (DETF) force sensors. The model describes the mechanical interaction between the tines and allows investigation of the effect of a number of asymmetries, in tine stiffness, mass, electromechanical parameters and load sharing between the tines. These asymmetries are introduced during fabrication (e.g., as a result of undercut) and are impossible to completely eliminate in a practical design. The mechanical coupling between the tines induces a frequency separation between the in-phase and the out-of-phase resonant modes. The magnitude of this separation and the relative intensity of the two modes are affected by all the asymmetries mentioned above. Two key conclusions emerge: (i) as the external axial compressive load is increased, the in-phase mode reaches zero frequency (buckling) much faster than the out-of-phase (i.e., operational) mode, resulting in a device with a decreased load range. (ii) During the operation, balanced excitation is essential to guarantee that the out-of-phase mode remain significantly stronger than the in-phase mode, thus allowing sharp phase locked loop locking and hence robust performance. The proposed model can be used to assess the magnitude of asymmetries introduced by a given manufacturing process and accurately predict the performance of DETF force sensors. For the specific sensor characterized in this study, the proposed model can capture the full dynamic response of the DETF and accurately predict its maximum axial compressive load; by contrast, the conventional single-DOF model does not capture peak splitting and overpredicts the maximum load by ∼18%. The proposed model fits the measured frequency response of the electromechanical system and its load-frequency data with coefficient of determination (R2) of 95.4% (0.954) and 99.2% (0.992), respectively.