High Axial Load Research Articles

Analysis of a Large Database of Concrete Core Tests with Emphasis on Within-Structure Variability.

In reinforced concrete (RC) structures, the compressive strength of concrete can play a crucial role in seismic performance and is usually difficult to estimate. Major seismic codes prescribe that concrete strength must be determined essentially from in situ and laboratory tests. Mean values obtained from such tests are the reference design values when assessing existing structures under seismic actions. The variability of concrete strength can also play an important role, generally requiring that various homogeneous domains are identified in a single structure, in each of which a specific mean value should be assumed as representative. This study analyzes the inter- and intra-variability of the concrete strength of existing buildings using a very large database made up of approximately 1600 core tests extracted from RC buildings located in the Basilicata region (Southern Italy). The analysis highlighted that concrete strength variability was dependent on the structures’ dimensions as well as on the number of storeys. Moreover, the concrete strength of cores extracted from columns was found to be, on average, lower than that from beams, thus justifying the usual practice to extract cores mainly from columns, which results in a conservative approach as well as a more feasible one. Finally, some case studies were analyzed, specifically focusing on the effects of the within-storey variability. Conservative strength values, to be used especially in the case of vertical members subjected to high axial loads, are suggested.

Seismic behavior of double steel concrete composite walls

SummaryAn innovative double steel concrete (DSC) composite walls were developed to enhance constructability and lateral load resistance of buildings. In order to research the seismic behavior of DSC composite walls, experimental study was carried out. The high‐strength concrete and high axial load were considered. The failure mode, hysteresis behavior, lateral load‐carrying capacity, deformation, and energy dissipation of the composite walls under different testing parameters were observed. All specimens failed in a flexure behavior, with steel plate buckling and concrete compressive crushing in the bottom of composite walls. The pinching behavior was not significant for hysteresis loops of composite walls. Moreover, the lateral load‐carrying capacity and ductility coefficients increased significantly with spacing of constraining bolts and stiffeners decreased. In addition, the calculation method of the lateral load‐carrying capacity of DSC composite walls was proposed, with the consideration of force equilibrium and moment equilibrium. The finite element (FE) method was performed to analyze the failure process of the specimens with the cyclic load. The concrete damage plastic model was selected to simulate the damage progress of concrete. Validation of the FE models against the experimental results showed good agreement. The effect of different parameters was analyzed with FE models.

A multiscale synthesis: characterizing acute cartilage failure under an aggregate tibiofemoral joint loading.

Knee articular cartilage is characterized by a complex mechanical behavior, posing a challenge to develop an efficient and precise model. We argue that the cartilage damage, in general, can be traced to the fibril level as a plastic deformation, defined as micro-defects. To investigate these micro-defects, we have developed a detailed finite element model of the entire healthy tibiofemoral joint (TF) including a multiscale constitutive model which considers the structural hierarchies of the articular cartilage. The net model was simulated under physiological loading conditions to predict joint response under 2000N axial compression and damage initiation under high axial loading (max 7 KN) when the TF joint flexed to 30°. Computed results sufficiently agreed with earlier experimental and numerical studies. Further, initiation and propagation of damage in fibrils were computed at the tibial cartilage located mainly in the superficial and middle layers. Our simulation results also indicated that the stiffer the fibril is (higher cross-link densities), the higher the contact stress required to elicit a fibril yield and the higher the rate of yielding as a function of increased contact stress. To the best of our knowledge, this is the first model that combines macro-continuum joint mechanics and micromechanics at the tissue level. The computational construct presented here serves as a simulation platform to explore the interplay between acute cartilage damage and micromechanics characteristics at the tropocollagen level.

Impact Response of Reinforced Concrete Columns with Different Axial Load under Low-Velocity Impact Loading

Building collapses from the seismic pounding of two adjacent buildings have been found in many past earthquakes. For the two buildings with different story height, the pounding induces impact load and local stress at column mid-height where the provided column reinforcement is normally lesser than the column’s edge. This paper aims to investigate the impact responses of reinforced concrete columns with different axial load and shear capacity by using numerical simulation method. Sixteen reinforced concretes columns were subjected to an impact load created by dropping 300 kg hammer at the height of 1,200 mm above the mid-span of the column. Every specimen has an identical cross section of 220 mm by 220 mm, with 3,000 mm of clear span length. Both ends of the column were fully restrained. The magnitude of the axial load varies from 0% to 40% of the ultimate axial capacity of the concrete section. Shear reinforcement spacing varies from @200 mm to @60 mm. It is found that the axial loads have a great effect on the impact responses of the RC columns. The specimens with high axial load yield higher peak impact force value and less mid-span deflection. Shear cracks were observed on the specimens with low axial force, but the cracks were relatively decreased when increasing the axial load.

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

This paper presents an experimental study of the seismic performance of high-strength concrete-filled box columns (CFBCs) under combined axial and cyclic lateral loads. Specimens were made of high-strength SM 570 M steel (with yield strengths between 520 and 580 MPa), and concrete with compressive strength (fc') greater than 80 MPa. Three parameters that affect the seismic performance of CFBCs were investigated: the width-to-thickness (b/t) ratio of the steel column, magnitude of the axial load, and the addition of concrete infill. The specimens, which were 280–420 mm in width and 2000 mm in height, were tested under combined axial (4058–10,090 kN) and cyclic lateral loads. Experimental results indicated that the lateral displacement ductility decreases significantly with an increase in either the axial load or b/t ratio. The addition of concrete infill inside a hollow steel box column does not improve the lateral displacement ductility of CFBCs under high axial load. Although the CFBC specimens satisfied the b/t requirement of a highly ductile member, as per AISC Seismic Provisions (2016), specimens under high axial load (40%Pn) failed at 4% drift, indicating that the requirement does not guarantee that CFBCs will sustain high axial load under significant drift (i.e., >3%). The Eurocode 4 (2009), AISC Specification (2010), and Architectural Institute of Japan (2014) reasonably estimate the flexural strength of high-strength CFBCs under axial load; however, ACI 318 (2011) does not. The finite element analysis program ABAQUS can be used to estimate the hysteretic behavior of specimens before significant strength degradation.

Biomechanical Comparison of Two Pediatric Blade Plate Designs in Proximal Femoral Osteotomies

Blade plates are frequently used for internal fixation following proximal femoral varus rotational osteotomy to treat hip dysplasia in children with cerebral palsy. Recently, cannulated blade plates with the option for a proximal locking screw have demonstrated ease of insertion and low complication rates. Although there are two commonly used blade plates with a proximal screw option, no comparison of their biomechanical profiles has been undertaken. Our study sought to compare the structural properties under axial loading, as well as the biomechanical contribution of a proximal screw, of two different 90° cannulated blade plates designed for pediatric proximal femurs. Plate A has a hole distal to the blade designed to attach a plate inserter, through which a 3.5-mm non-locking cortical screw could be placed. Plate B has a threaded hole distal to the blade designed to accept a 3.5-mm locking screw. Plate A and plate B were inserted into 33 left pediatric synthetic proximal femurs. Axial loading to failure of plate A with and without a proximal screw was compared to that of plate B with and without a proximal screw. An additional 10 samples using plate B, with and without a proximal locking screw, were tested in tension to quantify the effect of the proximal screw on pullout strength. Plate B failed at a higher axial load than plate A. The addition of a proximal screw did not affect the axial load to failure for either plate. Pullout testing revealed that blade plates fixed with the proximal screw failed in tension at a significantly higher load (856.3 ± 120.9N) than those without proximal fixation (68.1 ± 9.3N, p < 0.001). Plate B failed at a higher axial load in biomechanical testing, likely related to differences in its design. The addition of a proximal screw did not increase the axial loading properties of the blade plate construct but did increase the pullout strength by a factor of 12. These results may be used to influence implant selection and post-operative rehabilitation following proximal femoral osteotomies in children.

A thermal conductivity model for microporous insulations in gaseous environments

Ceramic insulations are often used to mitigate heat losses from high temperature systems. In the case of thermal batteries, insulation is exposed to high temperatures, high axial loads, shock and vibration scenarios, and alternate gaseous environments. All of these conditions influence the effective thermal conductivity of the material and subsequently the performance of the battery. To properly balance the thermal design of these systems, a model that can capture the influence of these variables on the effective thermal conductivity is necessary. A previous publication presented the development of an effective thermal conductivity model for two common materials used for thermal batteries. This paper investigates the application of this model to Min-K TE1400 board, whose microstructure interrupts gas phase conduction to minimize thermal conductivity. This necessitates modifications to the model to accurately represent effective thermal conductivity for this type of material.Thermal conductivity was measured as a function of temperature and compression in air, helium, and partial vacuum environments using the Transient Plane Source (TPS) technique. The trends observed in the measured thermal conductivity are explained through pore size measurements of compressed samples. The effective medium model was tuned using this data and is shown to agree with experimental data. Lastly, the anisotropy of the material was evaluated using the TPS data and specific heat estimations. This showed that axial conductivity is consistently less than radial thermal conductivity, as is corroborated by X-ray CT analysis of the fiber orientations in the material. The results and implications of the anisotropic results are also discussed.

The intensity of rail failure flow

The article reveals the quantitative changes in the intensity of failure accumulations in areas with gradual introduction of high axial loads. To obtain the actual values, the authors received three-dimensional array of intensity of rail failure flow. According to the results of the research, it was discovered that the main cause of failure of the rails are the defects in the main contact-fatigue origin. The main factor that impacts the intensity of the rail failure flow is the number of transmitted tonnage. The size of the axial load and curvature of the line pours weight on this process. The proposed rail failure model is a model that can be used to optimize the track maintenance system. The authors conducted a study on the identification of quantitative changes in the intensity of accumulation of track failures in areas with high axial loads and evaluated their influence on the planning of repair and road works. On the basis of the obtained results it is possible to estimate the effect of the axial load on the intensity of changes in the state of the flow rail failure flows.

Development of a shape specification based on the waviness parameter of tapered roller bearing

Tapered roller bearings can accommodate high radial loads as well as high axial loads. The manufacturing process consists of rings machining processes and components assembly, followed by an intense quality control. In this contribution, a study of the parameters of influence in the inspection procedure has been carried out. The main objective of this work is to develop a shape specification using real parts and to optimize the process of specification development. This requires to study the influence of several parameters in the inspection and to determine how they affect the waviness specification.

Influence of Geometrical Parameters on Performance of Grouted Mortise and Tenon Joints for Application in Prefabricated Underground Structures

Prefabricated underground structures were first researched in China to address the serious social and environmental issues associated with underground construction. Five metro stations have been built on Line 2 of the Changchun Metro in China using this new prefabrication technology. The joints connecting prefabricated elements are the most critical components in such prefabricated structures. In this study, experiments and numerical simulations investigating the influences of different grouted mortise and tenon joint geometrical parameters were conducted to determine the optimal parameters and ensure proper performance. To do so, a finite element model was built with the appropriate characteristics using the experimental results, and an analysis of the influence of different geometrical parameters was conducted. The results indicate that increasing the dip angle of the tenon could improve the flexural rigidity of the joint, but its effect was relatively small compared to that of the other parameters. Increasing the width of the tenon only had a positive effect on the flexural rigidity of the joint when the width was relatively small and under small axial loads. Increasing the length of the tenon helped to enhance the flexural performance of the joint; however, this advantage was not obvious when the tenon length was relatively long. Proper indentation of the joint improved the flexural capacity under a small axial load, but was not beneficial under a high axial load. The findings of this study are of value to help researchers and engineers more effectively design prefabricated underground structures.

A Unified Approach to the Timoshenko Geometric Stiffness Matrix Considering Higher-Order Terms in the Strain Tensor

Abstract Nonlinear analyses using an updated Lagrangian formulation considering the Euler-Bernoulli beam theory have been developed with consistency in the literature, with different geometric matrices depending on the nonlinear displacement parts considered in the strain tensor. When performing this type of analysis using the Timoshenko beam theory, in general, the stiffness and the geometric matrices present additional degrees of freedom. This work presents a unified approach for the development of a geometric matrix employing the Timoshenko beam theory and considering higher-order terms in the strain tensor. This matrix is obtained using shape functions calculated directly from the solution of the differential equation of the problem. The matrix is implemented in the Ftool software, and its results are compared against several matrices found in the literature, with or without higher-order terms in the strain tensor, as well as the Euler-Bernoulli or Timoshenko beam theories. Examples show that the use of the Timoshenko beam theory has a strong influence, especially when the structure has small slenderness (short members). For high axial load values, the consideration of higher-order terms in the strain tensor results in larger displacements as expected.

Shear behavior of short square tubed steel reinforced concrete columns with high-strength concrete

Six shear-critical square tubed steel reinforced concrete (TSRC) columns using the high-strength concrete (fcu,150 = 86.6 MPa) were tested under constant axial and lateral cyclic loads. The height-to-depth ratio of the short column specimens was specified as 2.6, and the axial load ratio and the number of shear studs on the steel shape were considered as two main parameters. The shear failure mode of short square TSRC columns was observed from the test. The steel tube with diagonal stiffener plates provided effective confinement to the concrete core, while welding shear studs on the steel section appeared not significantly enhancing the seismic behavior of short square TRSC columns. Specimens with higher axial load ratio showed higher lateral stiffness and shear strength but worse ductility. A modified ACI design method is proposed to calculate the nominal shear strength, which agrees well with the test database containing ten short square TSRC columns with shear failure mode from this study and other related literature.

Correlation between shear and normal strength for brittle reinforced concrete member considering internal stress condition of concrete

Formulas used to predict shear strength of reinforced concrete in different standards do not always correspond to each other due to the complexity of the shear transfer mechanism. Currently there is no generally accepted method of shear strength pridiction, however, traditionally, shear strength anticipation of a structural concrete elements is performed differently on members with or without shear reinforcement. These empirical approches tend to predict the shear strength too conservatively; alternatively, shear strength of concrete can be easily predicted by Mohr-Coulomb theory. In case of high-axial load and low shear reinforcement, the strength is likely to be determined by the concrete's shear crack. Therefore, a method to predict the strength of concrete with Mohr-circle has been proposed but the circles crossed the boundary and could not evaluate the strength correctly. Mohr circle can be used for prediction of diagonal tension failure strength but the circle cannot be evaluated. In this paper, Mohr circles were investigated considering all steps of cyclic loading until shear crack occurred. It also investigates a correlation between shear strength and normal strength through recognition of the Mohr-Coulomb failure criteria for each specimen.

Clinical relevance between anatomic features of sustentaculum tali and intra-articular calcaneal fractures

The calcaneus is the most commonly fractured tarsal bone, calcaneal fracture comprises 2% of all fractures, the primary mechanism of injury involves a high energy axial load. To get a better outcome, the literature review recommends the use of Open Reduction and Internal Fixation (ORIF) for this kind of injury. Sustentaculum tali is a triangular projection from the medial surface of the calcaneus, it possesses strong trabecular structure and thick cortex, and it's thought to remain tightly bound to the talus by ligaments and muscle tendons nearby, that's why it′s often used as a constant fragment to which other fracture fragments are reduced to restore congruity of the subtalar joint. Hence, it's important to understand the anatomic features of sustentaculum tali. In this article, we describes the anatomic measurements of the sustentaculum tali including the size, angle and soft tissue nearby, and described the correlation between these anatomic features and intra-articular calcaneal fractures. We are hoping that we can provide theoretical reference to the clinical treatment of calcaneal fractures. Key words: Calcaneus; Anatomy; Intra-articular fractures; Surgical procedures, operative

Experimental cyclic response of RC walls with setback discontinuities

After the 2010 Maule, Chile, earthquake (Mw 8.8), several reinforced concrete (RC) buildings presented damage in some walls (crushing of concrete, buckling and fracture of steel reinforcement). These buildings had been designed according to the up-to-date seismic standards in the country and were not expected to suffer damage as severe as what was observed. Common features of the damaged walls were: little or no confinement at the wall ends; relatively high axial load; narrow thicknesses (below 200 mm); and discontinuities in height. Slender RC walls are often used in Chile and commonly, due to architectural constraints, the length of the walls changes between floors designated for parking use and the upper floors, creating a setback in the lower levels. These types of walls are commonly called “flag walls”. The problem of discontinuity has not been investigated experimentally and therefore it is necessary to observe its impact in RC walls. Four structural wall specimens were designed, one with no discontinuity and the other three with different sizes of the setback. They were tested under a nominal constant axial load of 0.1f'cAg and cyclic lateral loads increasing at specific drift levels. Conventional instrumentation and photogrammetry were used to monitor the tests. The experimental results show that the impact of the setback, for the sizes tested, is not significant for the strength but it is relevant for the strength degradation and deformation capacity. Strains in the extreme fibers, curvature and principal strains are studied using photogrammetry. It is found that the plastic hinge length increases with drift, but it remains constrained to the setback region. Another discontinuity is found around the reinforcement of the setback where large concentration of strains can cause premature failure of the wall.

Experimental and Numerical Analysis of Large-Scale Circular Concrete-Filled Steel Tubular Columns with Various Constructural Measures under High Axial Load Ratios

To investigate the effect of constructional measures (including horizontal and vertical stiffeners, rebar cages, embedded steel tubes, and cavity welded steel plates) under high axial load ratios on the seismic performance of concrete-filled steel tubular (CFST) columns, quasi-static tests for six large-scale CFST columns with various constructional measures are performed. All specimens are subjected to identical axial forces. The failure mode, hysteresis characteristics, bearing capacity, stiffness degradation, ductility, and energy dissipation of specimens are analyzed. The study shows that the horizontal stiffener delays the occurrence and severity of column base buckling, the vertical stiffener improves the bending resistance capacity and initial stiffness of the member, the rebar cage improves the ductility, and the embedded circular steel tube significantly improves the member’s bearing capacity, ductility, and energy dissipation. When an internal circular steel tube and cavity welded steel plate are applied in tandem, the section steel ratio increases by 4.42% and the bearing capacity improves by 42.72%. A finite element model is created to verify test results, and simulation results match the test results well.

Finite element analysis of surface indentation on turbo-drill thrust ball bearing

ABSTRACT In harsh drilling conditions (e.g. abrasive drilling fluid), turbo-drill thrust ball may suffer from raceway surface indentation under the high axial load. The indentation can cause early failure of the bearing components. This paper establishes a micro-scale finite element model (FEM) to discuss the raceway surface indentation resulted from solid particle. For the sake of simplicity, the interaction between steel ball and solid particle as the latter is pressed into the raceway surface was depicted by axial and circumferential displacements. The distribution of stress and strain in solid particle and raceway surface was obtained from the finite element analysis. Through the discussion on solid particle ellipticity and the effect of friction coefficient on indentation features, it is learned that the variation in ellipticity has a slight impact on indentation depth, but a marked effect on raceway surface deformation; the friction coefficient has a significant impact on indentation edge shape and bottom centre of indentation. The simulation results provide a valuable reference for prevention of bearing raceway indentation.

In-Process Measurement for the Process Control of the Real-Time Manufacturing of Tapered Roller Bearings.

Tapered roller bearings can accommodate high radial loads as well as high axial loads. The manufacturing process consists of machining processes for ring and component assembly. In this contribution, the parameters of influence on the measurement procedure were studied. These parameters of influence were classified as environmental, process, and machine parameters. The main objective of this work was to optimize the process using real-time measurements, which required the study of the influence of several parameters on the measurement uncertainty and how to correct their effects.

Experimental study of rectangular multi-partition steel-concrete composite shear walls

Multi-partition composite shear walls have the strong points, such as high load-carrying capacity, good ductility, excellent energy dissipation capacity and fast construction speed. Even if they were used in the buildings, there was a little research work on this kind of composite shear walls. To study the axial behavior and cyclic behavior of multi-partition composite shear walls, six axially loaded specimens were tested, and two specimens were tested under horizontal cyclic load. Through testing of specimens, the damage progression, failure mechanism, stiffness and energy dissipation of composite shear walls were investigated. The experimental results showed that this kind shear walls under axial load had high load-carrying capacity and good ductility. The steel section could confine the core concrete, whose capacity was higher than that the summation capacity of steel section and core concrete. The shear walls exhibited excellent energy dissipation ability under high axial load ratio. Because of the confinement of steel section, the specimen showed higher energy dissipation capacity with the increasing of axial load ratio. However, the ductility of the specimen under cyclic load decreased with the increasing of axial load ratio. The experimental results were compared with the calculated results calculated by EC4, AISC and CECS. The results showed that all design codes underestimated the axial compressive capacity of the specimens. For specimens subjected to cyclic load, the results based on EC4 were the nearest to the experimental results.

Injury Risk of the Human Leg Under High Rate Axial Loading

This paper proposes a new risk function for lower limb fractures from high rate axial loading, such as that expected in under vehicle explosions. The aim is to improve the prediction of such fractures based on the loads measured by an Anthropomorphic Test Device (ATD) during blast testing. This function has been created by combining data from six different peer-reviewed post mortem human subjects (PMHS) studies. The work, which led to the risk function, considered proximal tibia force as the primary indicator of fracture, with age, sex and body mass considered as covariates. Previous studies considered age as a linear covariate to allow the elderly PMHS population results to be mapped onto a younger population. The literature review as part of this study found, however, that bone strength varies non-linearly with age. Extrapolating bone strength linearly may therefore overestimate the strength of younger populations’ lower limbs. This study uses a non-linear variation of bone strength with age and optimised parameters within this function to produce a Weibull risk curve with a minimum spread. The function described is for loads on the human; for it to be applicable in vehicle testing, there is a need to account for the response of the ATD.