Confinement Reinforcement of Cyclically Loaded Normal-Strength Concrete Tied Columns under High Axial Loads

Experimental observations on three reinforced concrete shear walls with small shear span-to-depth ratio (SDR) under combined high vertical axial load and horizontal cyclic loads are presented. The influence of high axial load ratio (ALR) on the failure mode, hysteretic behaviour, displacement ductility, shear strength and stiffness of the squat shear walls is investigated. In addition, a novel built-in strain gauges measuring system is employed for measuring the strain conditions in the reinforcements during the whole test process. Test results indicate that high axial load restrains the development of cracks and improves the shear load capacity, but that it also decreases ductility and energy dissipation and aggravates stiffness degradation. Concrete crush and out-of-plane buckling were observed in all specimens, resulting in the final failure of the specimens. According to the strain analysis, the section of the squat walls coincided well with the assumption of plane section under the condition of high ALR. With the increase of ALR, the depth of the compression zone of members increases, while the length of plastic hinge decreases. When the axial load is relatively small, the vertical and horizontal reinforcements provided almost equal contribution to the shear capacity of squat shear walls. However, under extremely high axial load, both vertical and horizontal reinforcements cannot provide full contribution to the shear capacity. The hysteretic behaviours of the tested shear walls were simulated by a cyclic softened membrane model (CSMM). Simulation results indicate that CSMM captured well the nonlinear characteristics of the squat shear wall under high axial load.

Premature failure of a deep-groove ball bearing used in an aeroengine governor took place during service. In this paper, the failure mode and root cause of the bearing were studied by macroscopic and microscopic examination, metallographic analysis, hardness test, calculations of contact stress and L10 life, flatness measurement and comparative experiment. The results show that the failure modes of the inner ring raceway and steel balls are contact fatigue spalling, the failure modes of the outer ring raceway are wear and contact fatigue spalling, and the failure mode of the cage is fatigue fracture. The root cause and direct cause of the bearing failure were the unqualified machining process of the spring end face and the high unbalanced axial load, respectively. The unqualified machining process induced high points of the spring end face, which caused misalignment of the outer ring and inner ring and thereby resulted in the high unbalanced axial load. The characteristic damages induced by high axial load were climbing with the morphology of metal extrusion and accumulation at the border of the raceway for the inner and outer ring, and multiple fatigue fractures with the characteristic of multi origins for the cage. The unqualified machining process can be prevented by adopting the refined grinding process and adding detection requirements of flatness.

abstractTo assess the parameters influencing the seismic performance of plastic hinge regions in Reinforced Concrete (RC) columns, eight large-scale and eight small-scale cantilevered RC columns were tested under various vertical and horizontal loading patterns. Three different axial loads were imposed on the columns: a constant moderate load, a constant high load, and a varying axial load. In addition to this, there were three lateral loading patterns: uni-directional, square, and circular. The high axial load and bi-directional loading had a significant influence on the envelope curves as well as on the damage progress. The observed damage to large-scale columns was much more severe than that observed in the small-scale columns. The equivalent viscous damping for specimens under varying axial load was between the damping of the specimens under moderate to high axial load. An increase in the number of cycles caused a rapid degradation of the envelope curve of the load-displacement history. However, no significant effect was observed on the maximum lateral load carrying capacity, peak load. Analytical FEM results such as load-displacement, moment-curvature and axial strain shortening-curvature relations, closely matched the experimental results.

Cyclic lateral load test and finite element analysis of high-strength concrete-filled steel box columns under high axial compression

During friction stir processing (FSP), the combination of rotation and movement of the tool leads to frictional heat generation and plastic deformation at the tool-material contact surface, leading to a microstructurally refined formation region. The deformation rate in the material can be altered by varying the axial load by increasing or decreasing the tool’s plunging depth. In the present study, FSP was carried out on a pure copper plate of 3-mm thickness by varying the plunge depth from 2.3 to 2.6 mm for a tool pin length of 2.4 mm. The microstructure of the processed samples was studied by optical microscopy, and the grain size was measured by the linear intercept method. Tensile testing was carried out perpendicular to the processing direction. The grain size distribution was narrower at low axial loads and wider at the higher axial loads, measured between 1 and 120 µm. At higher axial loads, microstructure consisted of bands indicative of the heterogeneity in the deformation. The formation of bands at higher axial loads leads to improved mechanical properties. The ductility of the processed materials at higher axial loads was 16%, which was four times the increase observed at lower axial loads (4%). The formation of a bi-modal microstructure (alternating layers of fine and coarse grains) at high axial load enhanced the processed materials’ strength and ductility.

Full-scale cyclic testing of slender RC columns bent in double curvature under high axial load

Determination of the differential collapse pressure rating of pipe without evaluating the effect of the internal pressure is always non conservative. The errors are highest (5 to 10 percent or greater) for thick wall pipe (API yield collapse mode) at high axial load and high internal pressure. The errors are negligible for thin wall tubulars or other applications where the axial load or internal pressure is low. The derivation of the triaxial analysis for thick wall pipe is provided. In addition, the equation is expressed on a single figure allowing the user to quickly determine the impact of ignoring the internal pressure for an application using thick wall tubulars. Adjustments are also provided for other than thick wall pipe to facilitate quick evaluation.

Recently, the development trend of turbomachinery is high capacity and high efficiency. Most of turbomachinery in the market are adopting ball bearings or air foil bearings. However, ball bearings have a limit for high speed product over 2.0×10SUP6/SUP DN(product of the inner diameter of the bearing in mm (D) and the maximum speed in rpm (N)). Air foil bearings have a limit for high axial load for high power products over 200~300 HP(horse power). Magnetic bearing is one of the solutions to overcome the limits of high speed and high axial load. Because magnetic bearings have no friction between the rotor and the bearings, they can reduce the load of the motor and make it possible to increase the rotating speed up to 5.0×10SUP6/SUP DN. Moreover, they can have high axial load capacity, because the axial load capacity of magnetic bearing depends on the capacity of the designed electromagnet. In this study, the radial and thrust magnetic bearings are designed to be applied to the 200 HP class turbo blower, and their performance was evaluated by the experiment. Based on the tests up to 26,400 rpm and 21,000 rpm under the no-load and load condition, respectively, it was verified that the magnetic bearings are stably support the rotor of the turbo blower.

BackgroundSurgical fixation for Schatzker IV tibial plateau fractures presents a clinical dilemma: achieving robust stability while avoiding impingement on the pes anserinus tendons. This study evaluated the biomechanical profile of a novel hockey-stick locking plate (NHLP), which is anatomically contoured to address this challenge by being placed anteriorly.MethodsA finite element model of a standardized Schatzker IV fracture was created. Three fixation methods were simulated: the novel hockey-stick locking plate (NHLP), the traditional T-shaped locking plate (TTLP), and the double reconstruction locking plates (DRLP). The models were subjected to four loading conditions: three physiological loads, a low axial load (500 N), a moderate combined load (1,500 N axial compression plus 150 N anterior shear force), and a high axial load (2,500 N) and a fourth “worst-case” load scenario combining a 1,700 N axial force, a 200 N anterior shear force, and a 10° varus tilt. Key biomechanical metrics, including implant stress, construct stability, fragment displacement, fracture interface mechanics and fatigue safety factor, were analyzed.ResultsUnder physiological loading, the NHLP construct demonstrated the lowest peak von Mises stress on the implant. At the high axial load of 2,500 N, the peak stress on the NHLP (159.8 MPa) was 15% lower than that on the TTLP (188.1 MPa) and 35% lower than that on the DRLP (245.5 MPa). In the “worst-case” scenario, all constructs exhibited high safety factors. In terms of stability, the NHLP provided displacement comparable to that of the TTLP, and both were substantially more stable than the DRLP construct, which exhibited the largest displacement under high load. Paradoxically, the DRLP construct consistently resulted in the highest degree of implant stress and the least stability. At the fracture interface, the NHLP maintained a stable environment across all loads, with key metrics remaining within a range conducive to bone healing.ConclusionThis finite element analysis demonstrated that the NHLP provides fracture stability while reducing peak implant stress under physiological loading. These findings support the biomechanical feasibility of its pes anserinus-sparing design, providing a strong rationale for further investigation.

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.

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

Nonlinear finite element investigations on different configurations of exterior beam-column connections with different concrete strengths in column and floor

Square seismic isolation bearings are economical to manufacture, offer the advantage of simple connection configurations and have compact geometry requiring a minimum of space for installation. To be able to more effectively utilize square bearings for seismic isolation systems, a new mechanical model for predicting the large shear deformation behavior of square elastomeric isolation bearings is presented in this paper. The new model is developed by extending to three dimensions an existing model for elastomeric isolation bearings under severe axial loads and shear deformations. The model comprises multiple shear springs at the mid‐height and a series of axial springs at the top and bottom boundaries. Static loading tests of square lead–rubber isolation bearings were performed to investigate the influence of horizontal loading direction and axial load magnitude on bearing behavior. The test results showed that the ultimate behavior is strongly influenced by loading direction, especially under large shear deformation and high axial load. To confirm the validity of the model, analyses are performed of the loading tests of the square lead–rubber isolation bearings. The results of analyses using the new model show very good agreement with the experimental results. Copyright © 2010 John Wiley & Sons, Ltd.

The skidding phenomenon, consisting of sliding and spinning may between the rolling elements and the raceways of bearings, can reduce significantly the service life. In order to early predict the arising of the skidding in angular contact bearings, a dynamic model is introduced in this paper. The centrifugal force and the gyroscopic effect are also taken into account to determine the load distribution determined by the rolling elements. The model of the rolling element orbital kinematics considers the elasto-hydrodynamic (EHD) lubrication and its contribution to the friction forces, along with the lubricant oil drag effect, the rolling element gravity and the ball-cage interactions. The fourth order Runge-Kutta integration and Newton-Raphson iteration methods are employed to calculate the load distribution, and the dynamic motion of the rolling elements and cage. The comparison between the results obtained by means of the proposed model and some experimental data shows a general good agreement. The experimental data have been obtained in a test rig equipped by an industry scale angular contact ball bearing under different axial load. Under high load, the experimental speed ratio of the cage versus the bearing inner race exceeds the pure kinematically determined value: this phenomenon is defined as over-skidding behavior and it is also simulated by the proposed model. The pure rolling state of rolling elements are also predicted by the proposed model at high axial load. The mechanism of skidding and over-skidding are also discussed based on the proposed model. In the future, the model presented will be supplemented with a temperature analysis, considering the variation of the lubricant viscosity in a full thermo- elasto-hydrodynamic (TEHD) approach.

Ex vivo biomechanical study using osteoporotic cadaveric vertebral bodies. To determine if fracture reduction could be achieved by the inflatable bone tamp (tamp) in vertebral bodies under simulated physiologic loads. Previous ex vivo biomechanical studies showed that kyphoplasty restored vertebral body height with vertebral body endplates under stress-free conditions. Simulated compression fractures were experimentally created in 18 osteoporotic vertebral bodies alternatingly assigned to one of two treatment (tamp inflation) groups: low axial load (111 N) or high axial load (222 N). Each vertebral body was then placed between two platens in a special radiolucent loading fixture and subjected to the preassigned load to simulate in vivo physiologic loading. The tamps were inflated and postreduction heights were measured fluoroscopically. The effect of applied load and condition on vertebral body height was checked for significance (P < 0.05). Comparing the experimental conditions (initial, postcompression, postinflation), there were no significant vertebral body height differences between the load groups (low load vs. high load). However, vertebral body height differences between conditions within each load group were all significant. For the low-load and high-load groups, mean postinflation heights (24.4 and 24.4 mm) were significantly greater than mean postcompression heights (21.6 and 22.5 mm) but significantly less than initial vertebral body heights (26.6 and 26.3 mm), respectively. Initial heights were fully restored in 22% (two of nine) of vertebral bodies in both groups. The inflatable bone tamp restored some of the height lost to compression fractures in vertebral bodies under simulated physiologic loads.