High Axial Load Research Articles

Tailoring of the bearing stiffness to enhance the performance of gas-lubricated bump-type foil thrust bearing

This study aims to tailor the bearing stiffness for enhancing the load-carrying capacity of foil thrust bearings. New architectures for the bump foil are introduced with structural stiffness tailored in the radial and circumferential directions to ensure a converging gas film under high axial loads while maintaining a reasonable bearing compliance to accommodate thermal as well as mechanical distortions. The structural stiffness of the bearing is calculated with an analytical method previously introduced by the authors, and the flow in the gas film is modeled with 2-D compressible Reynolds equation. The Couette Approximation technique is used to calculate the temperature distribution in the gas film and the small perturbations method is used to calculate its dynamic force coefficients. Enhanced load capacity could be obtained with the introduced bump foil designs.

Pushover Analysis of Reinforced Concrete Shear Wall Subjected to High Axial Load Using Fiber Slices and Inelastic Shear Spring

Reinforced concrete shear walls are effective for resisting lateral loads imposed by wind or earthquakes. Observed damages of the shear wall in recent earthquakes in Chile(2010) and New Zealand(2011) exceeded expectations. Various analytical models have been proposed in order to incorporate such response features in predicting the inelastic response of RC shear walls. However, the model has not been implemented into widely available computer programs, and has not been sufficiently calibrated with and validated against extensive experimental data at both local and global response levels. In this study, reinforced concrete shear walls were modeled with fiber slices, where cross section and reinforcement details of shear walls can be arranged freely. Nonlinear analysis was performed by adding nonlinear shear spring elements that can represent shear deformation. This analysis result will be compared with the existing experiment results. To investigate the nonlinear behavior of reinforced concrete shear walls, reinforced concrete single shear walls with rectangular wall cross section were selected. The analysis results showed that the yield strength of the shear wall was approximately the same value as the experimental results. However, the yielding displacement of the shear wall was still higher in the experiment than the analysis. The analytical model used in this study is available for the analysis of shear wall subjected to high axial forces.

A novel FRP–dual-grade concrete–steel composite column system

This paper presents an experimental study that was designed to investigate the compressive behavior of a new type of fiber reinforced polymer (FRP)-concrete–steel composite column system. This composite column system has recently been developed by the author as a special form of double-skin tubular columns (DSTCs), with the column manufactured using two different grades of concrete (referred to as dual-grade concrete (DGC) DSTCs in this paper). In this system, the annular section of the column (i.e. the section between FRP and steel tubes) is filled with normal-strength concrete (NSC) and the core section inside the steel tube is filled with a higher grade concrete mix. Based on the understanding that confinement demand of concrete increases with its strength, the system was designed to maximize the effectiveness of the composite column. To establish the performance levels of this new column system with respect to those of the conventional DSTCs manufactured with normal- and high-strength concrete (NSC and HSC), a comprehensive experimental investigation was undertaken where 28 circular and square DSTCs were tested under concentric compression. Results of the experimental program indicate that the proposed DGC DSTC system exhibits a superior compressive behavior compared to those of the conventional NSC and HSC DSTCs. It is observed that both circular and square DGC DSTCs exhibit extremely high axial load and deformation capacities, which in turn results in a much higher system and concrete ductility compared to those in companion single-grade concrete DSTCs. The results also show that companion square and circular DGC DSTCs can be designed to develop similar axial load capacities under the same level of FRP confinement. It is found that, under these conditions, the axial deformation capacities of square DGC DSTCs exceed those of their circular counterparts.

Effect of axial compression on ductility design of RC walls

Reinforced concrete (RC) structural walls can render excellent lateral stability and ductility to medium to high-rise buildings, but are generally subjected to very high axial compression loading, which can reduce the inherent ductility. A comprehensive statistical analysis with 474 sets of experimental data was conducted to evaluate and quantify the effect of the axial compression ratio (ACR) on the structural performance of RC structural walls. The stipulated limits on the ACR and the methods of evaluation used in various design codes were compared. Provisions on the limits of the ACR stipulated in various design codes were compared, and the expected attainable ductility factors for RC walls designed to different codes were evaluated. It was found that the provisions on ACR limits in Eurocode 8 generally satisfy the target ductility level but a distinction needs to be made between non-squat and squat walls due to their different structural behaviours.

High Axial Loads While Walking Increase Anterior Tibial Translation in Intact and Anterior Cruciate Ligament–Deficient Knees

To evaluate the effect of high axial loading (AL) on anterior tibial translation (ATT) according to the increase in knee flexion and the effect of valgus stress (VS) and internal rotation (IR) combined with high AL in intact and anterior cruciate ligament (ACL)-deficient knees according to the increase in knee flexion. We used 10 fresh-frozen, human cadaveric knees. Different loading conditions (134-N anterior drawer, 1,000-N AL, 10-Nm VS, and 5-Nm IR) were sequentially combined, and ATT was measured at 0°, 15°, 30°, 45°, and 60° of flexion in the intact and ACL-deficient knees. ATT increased significantly by adding high AL in intact knees (P= .001) and ACL-deficient knees (P< .0001) according to the change in flexion angle (P < .0001). Under high AL, ATT in the ACL-deficient knees was significantly larger than that in the intact knees for all loading conditions, and it also increased gradually according to the increase in knee flexion (P= .0001). ATT increased significantly after adding IR or VS with high AL in intact knees (VS, P= .002; VS/IR, P= .03) and ACL-deficient knees (VS, P= .0004) at some of the flexion angles. The added high AL increased ATT in intact and ACL-deficient knees from 0° to 60° of flexion. The effect of high AL on ATT became greater in ACL-deficient knees than in intact knees, and ATT also gradually increased according to the increase in knee flexion from 0° to 60°. In both the intact and ACL-deficient knees, ATT increased significantly after valgus stress or IR from 0° to 60°. ATT during weight bearing increases stress to the ACL, which worsens with valgus stress and/or IR forces. This finding should be considered when one is studying ACL injury mechanisms, as well as prescribing rehabilitation after ACL surgery.

The Study of Thermal Raising and Transmission Torque of High Speed Ball-Screw Lubricated by Different Greases

Ball screw is a high-precision and high performance linear drive of mechanical elements. The frictional heat of internal components what is very significant impact for platform transmission in high speed and the high axial load and causes the thermal expansion of element. In this research , the influence of different greases on ball screw is investigated in thermal rising of nut and driving torque in high speed and high axial load. A vertical motion platform was used for driving performance test. Thermal rising of nut of ball screw and the variance of transmission torque whose lubricated by high viscosity base oil grease is significant larger than the lower one. High viscosity grease is not easy to carry out the friction heat generated at ball and raceway contact area due to the bad flowing properties. It also has more serious wear occurred at contact area and high friction force, whose causes the large variance of transmission torque.

Friction Stir Welding of Al-Cu Bilayer Sheet by Tapered Threaded Pin: Microstructure, Material Flow, and Fracture Behavior

The fracture behavior and intermetallic formation are investigated after friction stir welding of Al-Cu bilayer sheets performed by tapered threaded pin. To do so, temperature, axial load, and torque measurements during welding, and also SEM and XRD analyses and tensile tests on the welds are carried out. These observations show that during welding from Cu side, higher axial load and temperature lead to formation of different kinds of Al-Cu intermetallics such as Al2Cu, AlCu, and Al4Cu9. Also, existence of Al(Cu)-Al2Cu eutectic structures, demonstrates liquation during welding. The presence of these intermetallics leads to highly brittle fracture and low strength of the joints. In samples welded from Al side, lower axial load and temperature are developed during welding and no intermetallic compound is observed which results in higher strength and ductility of the joints in comparison with those welded from Cu side.

Comparison of the seismic response of reinforced auger pressure grout and concrete columns

Despite the wide use of grout as a structural material due to easy construction and cost-effectiveness, its seismic performance has rarely been evaluated experimentally. In particular, reinforced grout columns which may experience significant lateral deformation need experimental evidence to validate their adequacy. This paper summarizes findings from a relevant experimental study, which consists of five cyclic tests and one hybrid simulation test conducted at the University of California, Berkeley. The results show that reinforced auger pressure grout columns under cyclic lateral load and high constant axial load can provide ductile and reliable behavior in flexure, comparable to that of similarly configured reinforced concrete (RC) columns. Therefore, these reinforced grout columns can be considered as an adequate alternative to RC columns subjected to medium to high compressive axial loads in regions of high seismicity.

Characteristics and displacement capacity of reinforced concrete walls in damaged buildings during 2010 Chile earthquake

About 2 % of reinforced concrete (RC) buildings taller than nine stories suffered important structural damage during 2010 Chile earthquake. The typical structural configuration of residential buildings is characterized by a large number of RC structural walls which provides high lateral stiffness and strength. The first objective of this paper is to obtain global geometric and design parameters of RC structural walls in damaged buildings and correlate their values with the observed damage. The second objective is to compare the roof displacement capacity with the roof displacement demand in critical walls, and hence, try to explain the observed damage. The wall parameters were obtained from five representative damaged structural wall buildings; these are: wall thickness, aspect ratio, axial load, reinforcement ratios, and the ratio between horizontal reinforcement spacing and the vertical bar diameter. The roof displacement capacity is obtained using a plastic hinge approach, and the ACI 318-08 approach, since both methods are proposed in the current Chilean seismic code. The displacement demand is estimated from ground motions recorded in the vicinity of the buildings. It is found that values of wall parameters correlate well with the observed damage. The structural walls were subjected to relatively high axial loads, and some walls included a large amount of vertical reinforcement to provide the required strength, but had inadequate transverse reinforcement thus compromising ductility. Findings from this research suggest that the plastic hinge approach is inadequate to estimate the roof displacement capacity and lacks correlation with the observed damage. Moreover, the use of the ACI 318-08 approach to estimate the roof displacement capacity is also inadequate, but leads to better predictions of wall displacement capacity. As shown by the results of response history analysis, the failure of walls was triggered by high axial loads rather than flexural deformation.

アンカーボルトと鉄筋を併用して接合した鉄骨コンクリート露出型柱脚の復元力特性

We confirmed the mechanical behavior of exposed type column bases in steel concrete composite columns through the structural tests. The experimental parameters were as follows, axial load level and method of connecting the column of steel concrete member to the footing beam of reinforced concrete member. Total nine specimens were tested, and the ultimate failure mode of eight specimens excluding one specimen under the high axial load failed in flexure at the column base. The structural tests make it clear that the hysteresis curve changes greatly depending on the kind of the connecting bar at column base, and ultimate flexural strength can be evaluated to super posed strength method, in which the ultimate flexural strength of the section of anchor-bolts, reinforcements and concrete below the baseplate. Moreover, proposed evaluation method of restoring force characteristics matches the test result well.

Experimental research on seismic behavior of +-shaped columns reinforced with high-strength steel bars under cyclic loading

500MPa steel bar is a new type of high-strength reinforcing bar applied in China. To investigate the feasibility of using this type of reinforcement in specially shaped column structure, six +-shaped column specimens varying in axial compression ratio and stirrup spacing were tested under cyclic loading. Behaviors in failure mode, shear crack width, bearing capacity, displacement ductility and energy dissipating capacity are studied to evaluate the seismic resistance performance of the columns. Test results show that 500 MPa steel bars can be effectively used as longitudinal reinforcement and provide more significant confinement to core concrete as transverse reinforcement. It is demonstrated by the observed results that expected oversize flexure-shear crack width can be prevented through an appropriate design procedure following the current building codes in China. Reducing stirrup spacing provides better performance in member ductility, crack behavior, cumulative damage and energy dissipation capacity, but has little influence on the bearing capacity; high axial load can offer advantages in bearing capacity, energy dissipating capacity and shear crack behavior, but reduce the member ductility. To predict the behavior of test specimens under cyclic loading, analytical model are implemented in program OpenSees using flexural fiber beam-column element with the consideration of the shear effect. Analytical results have an acceptable agreement with the test results.

Post-buckling dynamics of Timoshenko microbeams under axial loads

The nonlinear buckling and post-buckling dynamics of a Timoshenko microbeam under an axial load are examined in this paper. The microbeam is assumed to be subject to an axial force along with a distributed harmonically-varying transverse force. As the axial load is increased, in the absence of the transverse load, the stability of the microbeam is lost by a super-critical pitchfork bifurcation at the critical axial load, leading to a static divergence (buckling). The post-buckling state, due to a sufficiently high axial load, is obtained numerically; the resonant response over the buckled state, due to the harmonic transverse loading, is also examined. More specifically, Hamilton’s principle is employed to derive the equations of motion taking into account the effect of the length-scale parameter via the modified couple stress theory. These partial differential equations are then discretized by means of the Galerkin scheme, yielding a set of ordinary differential equations. The resultant equations are then solved via a continuation technique as well as a direct time-integration method. Results are shown through bifurcation diagrams, frequency-responses, and force-response curves. Points of interest in the parameter space in the form of time histories, phase-plane portraitists, and fast Fourier transforms are also highlighted. Finally, the effect of taking into account the length-scale parameter on the buckling and post-buckling behaviour of the system is highlighted by comparing the results obtained through use of the classical and modified couple stress theories.

Pilon fracture: a case report of a 45-year-old dental technician.

Pilon fractures are complex and difficult-to-treat fractures of the lower extremity that account for about 1% of all lower extremity fractures and up to 10% of tibial fractures. The injury is caused by high energy axial load either from motor vehicle accidents or a fall from height. The treatment of these fractures has caused controversy among surgeons due to mixed outcomes. Here we report a case of pilon fracture in a 45 year old male patient who has sustained the injury as a result of a fall from a height of approximately 12 feet. We describe why it is absolutely crucial that the patient is treated with external fixation initially and evaluate its merits and drawbacks as well as ways to minimize the complications associated with external fixation of open intra-articular distal tibial fractures.

Friction Torque Measurement in Partial Hybrid S-C Angular Contact Ball Bearings

To monitor the friction torque evolution in tandems of angular contact ball bearings, a new testing device is developed. New partial hybrid bearings from 7206C series are obtained by combining 8 steel balls with 4 silicon nitride balls of the same diameter equally spaced in the cage, these bearings being denoted hereafter as 8S-4C type. For comparison, tests are carried-out also on conventional all-steel bearings and hybrid bearings with all the steel balls replaced by silicon nitride balls. The equilibrium temperature of the all-steel, hybrid and 8S-4C ball bearings is determined by tests. At high speed and light axial load, the 8S-4C ball bearings withstand to an oil shut-off test of one minute, while the similar all-steel bearings seized. The 8S-4C partial hybrid ball bearings can be an advantageous solution comparative to more expensive all hybrid bearings, avoiding the scuffing due to the self-healing effect induced by the higher hardness of the silicon nitride balls.

Hysteretic behavior of multi-cell T- Shaped concrete-filled steel tubular columns

Several multi-cell improvement methods for solving existing problems of conventional T-shaped concrete-filled steel tubular (T-CFST) columns and for determining steel׳s optimal distributions for increasing the strength and ductility of the columns are presented. An experimental study with eight multi-cell T-shaped concrete-filled steel tubular (MT-CFST) columns and one conventional T-CFST column under low frequency cyclic loading was conducted. Effects of the multi-cell layout and the concrete strength on the hysteretic behavior of the specimens were investigated. Experimental results showed that the lateral load-displacement hysteretic curves of the columns were generally saturated with a slight pinching effect. Owing to the asymmetry of the T-shaped cross section, the hysteretic behavior of the composite columns is asymmetrical in different loading directions. The improved MT-CFST columns showed better seismic behavior due to high load bearing capacity, ductility and energy dissipation capacity. Furthermore, the non-linear finite element analysis was performed to simulate the hysteretic behavior of the specimens and the numerical results agreed well with the test results. In conclusion, with an increasing axial load ratio, the ultimate lateral load in the pushing direction gradually decreases and is reached earlier, whereas the ultimate lateral load in the pulling direction increases slightly under low axial ratio and decreases under high axial load ratio.

Analytical investigation of the cyclic behavior and plastic hinge formation in deep wide-flange steel beam-columns

This paper investigates the cyclic behavior of deep wide-flange sections, used as columns in steel Special Moment Frames (SMFs), through detailed finite element (FE) analysis. A wide range of wide-flange sections is subjected to symmetric cyclic lateral loading combined with different levels of constant compressive axial load ratios representing the loading conditions of interior steel columns in SMFs. The FE simulations demonstrate that wide-flange beam-columns, with web and flange slenderness ratios near the current compactness limits of seismic design provisions (AISC 341-10), experience rapid cyclic deterioration in flexural strength under high axial load ratios. It is also found that deep wide-flange slender sections shorten axially to about 10 % of their length due to severe flange and web local buckling. Based on the FE simulations, for bottom story columns, where axial load ratios are in the range of 20–35 %, a reduction to about two thirds of the current compactness limit for highly ductile members would achieve a 4 % chord rotation while maintaining a flexural strength larger than 80 % of the expected plastic flexural strength of a steel column. The FE simulation results also suggest that the pre-capping rotation predicted by current modeling recommendations for steel components (PEER/ATC 72-1) is overestimated for sections with high web and flange slenderness ratios undergoing monotonic and/or cyclic lateral loading combined with high axial load levels.

Identification of suitable process parameters for friction surfacing of mild steel with AA6063 aluminium alloy

The present study is aimed at identifying suitable process parameters for friction surfacing of IS2062 mild steel with AA6063 aluminium alloy and obtain relationships between the input parameters and the process response that can be used for sound coating with adequate strength and ductility. Factorial experimental design technique was used to investigate and select the parameter combination to achieve adequate strength and ductility. Mechatrode rotational speed, axial load and substrate traverse speed were observed to be the most significant factors on the process response. Based on the results, it was observed that (i) lower axial load and traverse speed with high rotational speed and (ii) higher axial load and traverse speed with lower rotational speed produced sound coatings. It has also been observed that sound coatings could be obtained in a narrow set of parameter range as the substrate-coating materials are metallurgically incompatible and have propensity to form brittle intermetallics.

Accelerated corrosion investigation of axially loaded reinforced concrete elements

Purpose – This paper aims to present results of an experimental investigation on a series of scaled reinforced concrete column elements which were subjected to chloride exposure under accelerated conditions under a concurrent service axial load, over a period. In the presence of an axial load, directed microcracks of increasing density and width are introduced in the concrete mass, depending on the axial load level. Such cracks are believed to enhance the intrusion rate of chlorides in the concrete, relative to what is obtained in the normally performed unloaded specimen tests. Design/methodology/approach – Eighteen column specimens were tested over two chloride exposure periods, of duration up to a maximum of six months. Three different service axial load levels were considered, namely, none, 22 per cent and 43 per cent of the normalized axial load capacity of the columns. Findings – The results indicate that the specimens loaded to the higher axial load, which closely resembles actual service situation of such type of elements, exhibited up to ten times faster rates of induced current flow under a constant applied voltage of 500 mV, compared to the unloaded and less loaded specimens. Practical implications – It is proven that the presence of axial load influences the rate of chloride ingress in columns and, therefore, should be taken into account in estimating the concrete cover of such elements in durability design. Originality/value – The influence of axial loading on corrosion rate has not been considered in published experimental and analytical studies of chloride ingression. These studies have typically so far considered the accelerated corrosion of unloaded column specimens.

Effect of axial loads in the seismic behavior of reinforced concrete walls with unconfined wall boundaries

About 2% of Reinforced Concrete (RC) buildings taller than nine stories suffered serious damage in structural walls during the 2010 Chile earthquake. The observed damage involved mostly crushing of concrete, buckling of vertical reinforcement, and opening of the horizontal reinforcement. This damage is attributed to poor concrete confinement in the web and boundaries, inadequate horizontal reinforcement detailing, and high axial loads. This research aims to reproduce the observed damage and evaluate the influence of axial loads in the seismic behavior of RC walls with unconfined boundaries. To achieve these objectives, three identical wall specimens were tested. The wall specimens were designed with characteristic wall detailing obtained from data of five damaged buildings. These wall specimens were tested under equal lateral displacement cycles and subjected to different axial load ratios. The flexural-compressive failure mode exhibited by damaged walls during the earthquake was reproduced in these tests. Experimental results indicate that high axial load has a significant effect on the seismic performance and failure mode of RC walls. Indeed, it triggers a dangerous brittle concrete crushing failure which occurs immediately after spalling of the concrete cover.

Experimental study on the mechanical behaviour of a heat exchanger pile using physical modelling

This study aims to provide knowledge on the thermo-mechanical behaviour of heat exchanger piles, through a laboratory scale model. The model pile (20 mm in external diameter) was embedded in dry sand. The behaviour of the axially loaded pile under thermal cycles was investigated. After applying the axial load on the pile head, the pile temperature was varied between 5 and 30 °C. Seven tests, corresponding to various axial loads ranging from 0 to 70 % of the pile estimated bearing capacity, were performed. The results on pile head displacement show that heating under low axial load induced heave and cooling induced settlement; the pile temperature-displacement curve was found to be reversible and compatible with the thermal expansion curve of the pile. However, at higher axial loads, irreversible settlement of the pile head was observed after a few thermal cycles. The axial load profile measured by the strain gauges evidenced that the pile head load was mainly transferred to the pile toe. Nevertheless, thermal cycles modified significantly the mobilised skin friction along the pile. The total pressure measured at various locations in the soil mass was also slightly influenced by the thermal cycles.