Vertical Compressive Load Research Articles

Experimental and numerical investigation on the seismic behavior of plane frames with special-shaped concrete-filled steel tubular columns

The seismic behavior of (plane) frames with special-shaped concrete-filled steel tubular (CFST) columns (SCFSTFs), H-shaped steel beams, and exterior diaphragm connections was investigated experimentally and numerically in this study. Double-bay two-story SCFSTFs with a scale ratio of 1/2 were tested under constant vertical compressive load and cyclic horizontal loads (or displacements), which is a pseudo-static experiment considering the axial compression ratio. Based on the experimental results, failure modes, bearing capacity, hysteretic curves, skeleton curves, energy dissipation, ductility, rigidity degradation, and strength degradation of SCFSTFs were investigated. As a result, a typical strong column-weak beam failure mode was observed; degradation in strength and rigidity were minimal, and the energy dissipation capacity and ductility of SCFSTFs were adequate, demonstrating excellent seismic performance. Besides, energy dissipation capacity and horizontal load bearing capacity were improved with increasing axial compression ratios within the parametric range of this test. After testing, a finite element method based on ABAQUS was carried out to further investigate the seismic performance of SCFSTFs. The numerical results of skeleton curves, stiffness, yield load, ultimate load, and stress distribution agreed well with the test results. The plastic hinge formation process and failure mode were also further investigated using the finite element method.

Biomechanical behavior of mandibular overdenture retained by two standard implants or 2 mini implants: A 3-dimensional finite element analysis

Statement of problemMini implants (<3 mm in diameter) are being used as an alternative to standard implants for implant-retained mandibular overdentures; however, they may exhibit higher stresses at the crestal level. PurposeThe purpose of this finite element analysis study was to evaluate the biomechanical behavior (stress distribution pattern) in the mandibular overdenture, mucosa, bone, and implants when retained with 2 standard implants or 2 mini implants under unilateral or bilateral loading conditions. Material and methodsA patient with edentulous mandible and his denture was scanned with cone beam computed tomography (CBCT), and a 3D mandibular model was created in the Mimics software program by using the CBCT digital imaging and communications in medicine (DICOM) images. The model was transferred to the 3Matics software program to form a 2-mm-thick mucosal layer and to assemble the denture DICOM file. A 12-mm-long standard implant (Ø3.5 mm) and a mini dental implant (Ø2.5 mm) along with the LOCATOR male attachments (height 4 mm) were designed by using the SOLIDWORKS software program. Two standard or 2 mini implants in the canine region were embedded separately in the 3D assembled model. The base of the mandible was fixed, and vertical compressive loads of 100 N were applied unilaterally and bilaterally in the first molar region. The material properties for acrylic resin (denture), titanium (implants), mucosa (tissue), and bone (mandible) were allocated. Maximum von Mises stress and strain values were obtained and analyzed. ResultsMaximum stresses of 9.78 MPa (bilaterally) and 11.98 MPa (unilaterally) were observed in 2 mini implants as compared with 3.12 MPa (bilaterally) and 3.81 MPa (unilaterally) in 2 standard implants. The stress values in the mandible were observed to be almost double the mini implants as compared with the standard implants. The stresses in the denture were in the range of 3.21 MPa and 3.83 MPa and in the mucosa of 0.68 MPa and 0.7 MPa for 2 implants under unilateral and bilateral loading conditions. The strain values shown similar trends with both implant types under bilateral and unilateral loading. ConclusionsTwo mini implants generated an average of 68.15% more stress than standard implants. The 2 standard implant–retained overdenture showed less stress concentration in and around implants than mini implant–retained overdentures.

Evaluation of Operational Loading of the Light-Rail Transit (LRT) in Capital Region, Indonesia

In 2015, the Indonesian government issued regulations to accelerate the implementation of integrated Light-Rail Transit (LRT) in the capital region and its surroundings. In order to ensure its operational safety, experimental work is required to test components’ strength of the manufactured LRT structures. Following the JIS 7105 standard test method, the strain and deflection of the structures were measured by vertical load, compression, rotation, and three-point load support test. The critical area estimated in the railroad structure were conducted according to the finite element method, in which strain gauges are installed in areas where the stress concentration exceeds nominal pressure, namely notches, bends, and junction areas. The result shows that the maximum stress on the LRT train structure occurs at the door, where maximum compressive strain value is -1082 μe » -75.74 MPa on the left and the maximum tensile strain value is 597 μe » 41.79 MPa at the right door. The results of fatigue load analysis represent the average stress (σm) and voltage amplitude (σa) at the coordinate system located in the Søderberg triangle. Meanwhile, the camber value with the full vertical load still has a positive value of 3.03 mm, which indicates a safe limit.

Effect of Hand and Rotary Instruments on the Fracture Resistance of Teeth: An In Vitro Study.

Objective: Endodontic treatment should be both conservative and effective. Endodontic instruments with a greater taper are used for coronal flaring, for proper debridement with efficient irrigation. However, increased taper of an instrument can remove a larger amount of pericervical dentin, compromising the strength of the tooth. The aim of this study was to determine the effect of hand files, ProTaper Universal, ProTaper Next, and V Taper rotary instrument systems on the fracture resistance of teeth. Materials and Methods: In total, 60 extracted human maxillary first premolars were divided into four groups—Group I (Hand Files; HF), Group II (ProTaper Universal; PT), group III (ProTaper Next; PTN) and Group IV (V Taper; VT) (N = 15). Each group was instrumented with the respective instrument system, irrigated, obturated, restored, and mounted in cold cure acrylic. A universal load-testing machine (Shimadzu, Japan) was used to apply a vertical compressive load. The maximum force was recorded in Newton. Analysis of variance (ANOVA) and Independent t-tests were applied to compare the maximum mean force required to fracture the tooth. Results: There was a statistically significant difference in fracture resistance between Group I (HF) and Group II (PT) and between Group II (PT) and Group IV (VT) (p < 0.001). Similarly, a significant difference was observed between Group II (PT) and Group III (PTN) (p < 0.01). Furthermore, a significant difference was observed between Group I (HF) and Group III (PTN), and between Group III (PTN) and Group IV (VT) (p < 0.05), too. However, there was no statistically significant difference between Group I (HF) and group IV (VT) (p > 0.05). Conclusion: Rotary files with more taper seem to remove more pericervical dentin than traditional manual and rotary files with less taper, thus altering the strength of the tooth.

STUDY OF THE STRAIN STATE AND MOVEMENTS OF A FLEXIBLE ROD WITH INITIAL CURVATURE

Abstract. Aim. The possibility of obtaining the regressive part of the elastic (regressiveprogressive) characteristic under axial loading in the initial period is studied by applying an elastic rod having an initial curvature under vertical compressive load. The objective of the study is to determine the static characteristics of such a rod without taking the resistance forces into account. Method. To solve the problem, the elliptic parameters method was used to make a comparison with a solution obtained using the finite element method in the ANSYS engineering simulation software. Results. A technique was developed for assessing the strain state and displacements of a flexible rod with initial curvature in order to study the regression-progressive characteristic of various elastic systems having initial curvature for their effective use in determining oscillations. Conclusion. The obtained technique can be used to determine the deformed state of an elastic flexible rod having initial curvature and displacement of the point of application of force. At the same time, by setting various initial parameters of the flexible rod in order to obtain a regressive-progressive characteristic, significant displacements can be obtained in the subcritical region when the axial load does not exceed the Euler force for this flexible rod

ASSESSMENT OF THE INFLUENCE OF THE ORAL ENVIRONMENT ON THE STRENGTH OF ENDODONTIC CROWNS MADE OF HYBRID CERAMICS IN THE LABORATORY

A topical issue in dentistry is the problem of restoring teeth after endodontic treatment. There are many materials available to restore them. However, each of them has its own negative properties. The purpose of this work was to determine the degree of influence of the oral environment on the strength characteristics of endocrowns made of hybrid ceramics. 30 samples from hybrid ceramics were examined. One of the groups was confirmed by thermal Cycling, and the other was not. Further, both groups on the Instron-5982 device were subjected to vertical compression load before the destruction began. According to the results of this study, it can be noted that endocorns made of hybrid ceramics perfectly distribute the occlusal load and have good elasticity, but thermal Cycling has a negative impact on the strength characteristics of this material.

Comparison of stress induced in mandible around an implant-supported overdenture with locator attachment and telescopic crowns – a finite element analysis

IntroductionOne of the principle factors for the success of implant supported/retained overdentures (IOs) is the manner in which the stresses are transferred to the surrounding bone. Hence, the aim of the present study is to compare the stress induced in the mandible around IOs, using two different attachment systems, locator and telescopic.Methods3D finite element models were prepared using Pro/ENGINEER or PTC Creo to simulate 4 clinical situations: IOs using two different attachment systems, locator and telescopic, with and without splinting. A vertical compressive load of 35N was directed toward the central fossa in the molar region of each overdenture. Non-linear static contact analysis was carried out to determine the stress distribution in various components of IOs. Then, the models were analyzed by a finite element program ABAQUS, and displayed using Von Mises stress patterns.ResultsThe contact stress values developed on the implant and attachment components were lower with locator attachment, in both splinted and non-splinted models. On the other hand, the stress distribution to the cortical bone was more with non-splinted/splinted locator attachments (3.73/4.12 Mega Pascals) when compared to the non-splinted/splinted telescopic attachments (2.66/3.7 Mega Pascals). The stresses in all the components of overdenture were greater with the splinted model compared to non-splinted, in both the attachment systems.ConclusionThe locator attachment might demonstrate superior clinical performance, as the stresses on implant and attachment components were less compared to telescopic. Non-splinted model showed better results in both the attachment types.

Frequency‐dependent dynamic behavior of a poroviscoelastic soil layer under cyclic loading

SummaryIn this study, a linear poroviscoelastic model based on the Biot theory is proposed to analyze the dynamic response of partially saturated soil. Both the flow‐dependent and flow‐independent poroviscoelastic behaviors are described in the proposed model. The compressibilities of both the constituents, including the skeleton material and porefluid, are considered, and the effective skeleton stress is determined using the linear viscoelasticity law based on the generalized spring‐dashpot model. The soil surface is subjected to two types of harmonic loading, namely, vertical compressive loading and lateral shear loading. The influences of the relaxation time, saturation degree, and soil permeability on the surface and interior dynamic responses of the soil layer are investigated. It is revealed that the amplification factor, effective stress, and pore pressure decrease as the viscous damping increases, indicating that neglecting the viscoelastic property of solid skeleton could overestimate the induced dynamic responses. Furthermore, in comparison with the viscous damping of the solid skeleton, the viscous coupling involving the viscous resisting forces between the solid skeleton and pore fluid has limited effect on the dynamic behavior of the soil layer.

Centrifuge modelling of drained pullout and compression cyclic behaviour of suction bucket

In recent years, the tripod suction bucket foundation has been considered as an option to support offshore wind turbines. In an offshore environment, a wind turbine foundation should be designed considering cyclic loading, which can lead to the permanent deformation of structures, tilting and the degradation of soil stiffness. However, there are several uncertainties in the prediction of the cyclic behaviour of the tripod foundation, since the cyclic horizontal, vertical and moment loadings applied on each bucket lead to a complicated mechanism for each bucket. In this study, the behaviour of the tripod foundation under cyclic loadings was indirectly investigated through the vertical compression and pullout tests of the bucket because the overturning moment applied to the tripod foundation presumably acts as vertical compressive and pullout loads on each bucket. A series of centrifuge model tests were performed by applying one-way (i.e. vertical compression and pullout) and two-way cyclic loadings to the single bucket. Additionally, the effects of cyclic loading level were investigated. It was confirmed that the cyclic behaviour of the single bucket is significantly affected by loading direction and level. This study highlights the importance of considering load characteristics when predicting the cyclic behaviour of the tripod.

Model tests on the bearing capacity of precast open-ended micro pipe piles in soft soil

Laboratory 1g model tests were carried out to study the bearing capacity and load transfer mechanisms of precast open-ended micro pipe piles in soft soil. The single pile, 2 × 2 and 3 × 3 pile groups were designed and tested under vertical compression, uplift and horizontal loads, respectively. A steep fall pattern occurred in the load–displacement curves of piles under vertical compression and uplift loads. The measured soil plug length and axial force indicated that the piles could be considered as fully plugged friction piles under vertical compression load. The pile groups behaved in a non-integral failure mode under vertical uplift load and a conical wedge failure mode under horizontal load. At the early loading stages under vertical compression and uplift loads, the pile shaft resistance of the upper part tended to be fully mobilised earlier than that of the lower part. At the later loading stages, the pile shaft resistance of the upper part decreased, whereas the shaft resistance of the lower part still showed a little increase. The maximum bending moment of the pile occurred at a depth of about 10Dp under horizontal load.

Experimental hydraulic fracturing of Berea sandstone under triaxial stress state

In this work, a newly designed experimental setup is used to perform in-lab fracking under controlled triaxial loading on cylindrical cores of Berea sandstone. Fracking tests are conducted at 10 MPa confining pressure, with vertical compressive loading, as well as two horizontal stresses that simulate reservoir triaxial stress state. Multiple injection scenarios are tested to investigate the effect of the pore fluid injection conditions on the fracking and failure mechanisms. In-situ micro-seismic monitoring via eight acoustic emissions sensors is used for logging the fracking events evolution with time. Post-experimental characterization included computational tomography (CT) scanning to characterize the resulting fracture patterns.

Ultimate Load Tests on Bearing Behavior of Large‐Diameter Bored Piles in Weathered Rock Foundation

Based on the vertical compressive static load test and pile mechanics test of three large diameter bored piles (one of the test piles was treated with postgrouting) in granite gneisses foundation, the bearing capacity, deformation characteristics, and influencing factors of the single pile under the limit state are analyzed and compared with the recommended values of survey report and the recommended values of current codes. By comparing the measured and theoretical values of pile axial force, the bearing capacity of cast‐in‐place pile under normal and limit conditions is analyzed. The experimental results show that the Q-s curve of large‐diameter rock‐socketed mud wall retaining bored pile with a length‐diameter ratio of 25–33 and rock‐socketed depth of 5–8 d shows a rapid growth. After grouting treatment, the ultimate compressive bearing capacity of single pile is improved, the maximum settlement is reduced by 6.6%, the rebound rate is reduced by 11.1%, and the settlement effect of controlling pile top is not significant. The bearing capacity and deformation characteristics of the three test piles are less affected by length‐diameter ratio and rock‐socketed depth. For postgrouting piles, the ratio of frictional resistance of rock‐socketed segment and the ratio of pile lateral resistance are less affected by length‐diameter ratio and rock‐socketed depth, while, for postgrouting piles, the ratio of pile lateral resistance is more affected by rock‐socketed depth. The pile end resistance ratio of the three test piles is significantly affected by the rock‐socketed depth, whether or not the pile side postgrouting treatment is carried out.

Effects of topography on dynamic responses of single piles under vertical cyclic loading

This paper describes model tests of single piles subjected to vertical cyclic compressive loading for three kinds of topography: sloping ground, level ground, and inclined bedrock. Comprehensive dynamic responses involving cyclic effects and vibration behaviours are studied under various load combinations of dynamic amplitude, mean load, frequency and number of cycles. Test results show that permanent settlement can generally be predicted with a quadratic function or power function of cycles. Sloping ground topography produces more pronounced settlement than level ground under the same load condition. For vibration behaviour, displacement amplitude is weakly affected by the number of cycles, while load amplitude significantly influences dynamic responses. Test results also reveal that increasing load amplitude intensifies nonlinearity and topography effects. The strain distribution in a pile and soil stress at the pile tip are displayed to investigate the vibration mechanism accounting for sloping ground effects. Furthermore, the dynamic characteristics among three kinds of topography in the elastic stage are studied using a three-dimensional finite method. Numerical results are validated by comparing with experimental results for base inclination topography. An inclined soil profile boundary causes non-axisymmetric resultant deformation, though a small difference in vertical displacement is observed.

Crushing Mechanism for Soil Particles

Typically, soil samples must be crushed into particles for laboratory research. Thus, an efficient mechanism to ensure a uniform particle size is essential. We previously developed a rod mill device that performs well, but video analysis indicated that the shear forces applied by the rod were more effective than the compressive forces applied by the mill. The mechanism for this phenomenon is unclear. This study focused on clarifying the relationship between compressive load and abrasion when crushing dried and hardened soil particles. Soil pellets of the same size were prepared, and model experiments were performed, where vertical compression and abrasion were applied to the pellets until they fractured. The results showed that soil pellets were fractured easily when an abrasive load was continuously applied in the circumferential direction. Additionally, the load required to fracture the soil pellets was much lower than the required vertical compressive load. The rod mill device was previously thought to fracture soil aggregates by gradually stripping soil particles away from the surface. However, our experimental results clarified that the fracture process started at the center and subsequently induced the entire pellet’s sudden failure.

Research on the Influence of The Vertical Compressive Static Load Test of The Pile by The Tidal Fluctuation

The settlement of pile top had risen continuously and stabilized difficulty during the vertical compressive static load test of single pile in the tidal fluctuation area. Based on the principle of effective stress, the phenomena can be explained that the reduction of soil effective stress caused by the rising tide level leaded to the decrease of the bearing capacity of the pile, and the reasonable suggestions are given to the designer of the pile foundation affected by the tidal fluctuation.

On the Lateral Capacity of Reinforced Masonry Members Using Combined Retrofitting Methods

Historic walls were designed in the past to withstand vertical compressive loads. However, during seismic events, walls withstand lateral loads and their response is usually unsatisfactory. Reinforcement is often needed and several retrofitting methods have been proposed in the last decades. This paper analyses and compares the strength results of several experimental campaigns, recently carried out by the authors, with the specifications and mechanical properties suggested by the new (2018) Italian Seismic Code. Two retrofitting methods are considered: grout injections, alone, and in combination with jacketing. The effect of combined retrofitting methods was also investigated in this paper with the aim at studying the limitations of the actual Italian Building Code for interventions on listed buildings. Shear tests were carried out on-site and the effectiveness of the two retrofitting methods was discussed.

Investigation of partially bonded fiber-reinforced elastomeric isolators (PB-FREIs) with nominal vertical tensile loads

Unbonded fiber-reinforced elastomeric isolators (FREIs) were initially proposed as a potential low-cost alternative to conventional steel-reinforced elastomeric isolators (SREIs). FREIs are similar to SREIs but comparatively lightweight as the steel components from SREIs have been replaced with polymer fibers in FREIs. Subsequent experimental investigations identified that unbonded FREIs have desirable characteristics for seismic isolation due to the unbonded application and fiber reinforcement. The unbonded application removes mechanical fasteners, relying on friction to transfer horizontal loads, further reducing the cost. However, the unbonded application also introduces limitations, being susceptible to slip in certain loading conditions and being incapable of resisting tensile forces. In this paper, the concept of partially bonded FREIs (PB-FREIs), a proposed solution to these limitations, is further investigated experimentally with nominal vertical tensile loads. It is shown that PB-FREIs can achieve similar properties to an unbonded FREI with a vertical compressive load.

WIND EFFECTS ON FOUNDATIONS OF SILOS AND LIGHT STRUCTURES: SOLUTION BY USE OF STEEL PILES IN DIABASIC SOIL

Wind solicitations generate horizontal, tensile, and compressive stresses on building foundations. In empty light structures, such as agricultural greenhouses and, in the specific case of silos and elevated structures such as metal water tanks, the consideration of these loads becomes important because the lack of the weight component due to the storage load significantly influences the balance of forces. This study focused on the behavior of metallic steel profiles, aiming at its application as a foundation element for the pile, considering the soil of Diabasic origin common to the Center-South region of Brazil. Load tests in real scale were carried out on three steel profiles, type I, gauge W 250 mm x 32.7 kg m-1, drilled in the ground up to 12m deep by means of a pile driver. One steel profile was submitted to lateral loading, another to vertical compressive loading, and the other to vertical tensile load. Test results determined the bearing load of the pile for each loading type, calculated the soil reaction coefficient for lateral loading, and verified the applicability of load capacity prediction methods to tensile and compressive strengths of piles, commonly used in foundation projects.

Fabrication and Characterization of Porous Bioceramic Made from Bovine Bone Powder Mixed Calcium Phosphate Glass

Bovine bone xenograft was selected bioactive material currently widespread acceptable for using as human bone void filler. In this paper we described a new porous bioceramic block fabricated from bovine bone powders mixed with calcium phosphate glass. The characterized methods were atomic absorption spectrometer, x-ray diffraction, scanning electron microscope, energy dispersion x-ray spectroscopy, diffusion test, bending test, compressive test and Archimedes’ principle. The final products showed interconnecting pores size range 100 to 500 mm, apparent porosity about 52% and mole ratio of Ca:P as 1.65. The toxic elements such as arsenic, cadmium, mercury, and lead were lower standard limits of ASTM I (American Society for Testing and Materials International). The samples had a compressive strength more than 400 kg/cm2. So, this object can be useful as an alternative choice for human bone substitute in the vertical compression load bearing area.

Cracking and Failure Mechanism of Masonry Walls Loaded Vertically and Supported by Deflecting Structural Member

The paper describes some results of tests on solid walls and walls with openings in full scale, which were built on the steel structure subjected to vertical deflection. The walls had the length of 4550 mm, the height of 2450 mm and the thickness of 180 mm and were made of silicate blocks of group 1 per PN-EN 1996-1-1 standard with mean compressive strength of 17.7 N/mm2. The specimens had thin bed joints and unfilled head joints. Solid walls (A type), walls with one door opening located unsymmetrically in relation to the vertical axis (B type), specimens with two door openings located symmetrically (C type) and walls with one door and one window opening (D type). The tests were carried out in the specially designed steel stand that allowed to test masonry full scale walls subjected to simultaneous increasing of vertical compression load and deflection of the structure which they are supported on. The vertical load of the top walls edge was realized with the use of two hydraulic jacks with range up to 500 kN. The vertical deflections of steel structure supporting the masonry wall were realized in two ways, by means of loading the top edge of wall and with use of the elements of deflection enforcement system. Apart from vertical loading and support displacements, the displacements of the masonry along the eleven sections on each surface in two fields were also measured. The measurement of changes of the measuring sections length was used for calculating the mean deformation angles of the specimen in both fields. The walls without openings were rigid enough to separate from the support even at the deflection not exceeding 1.5 mm. The walls with one door opening located unsymmetrically also crack at early stage of tests. In this case, the separation from the support of a part of the wall without opening occur and cracks appear at the end of lintels caused by rotation of parts of wall separated by door opening (at early stage of tests treated as rotations of rigid bodies). In the case of walls with two symmetrically located door openings, the first crack appeared at the ends of the lintels as a result of rotations of pillars caused by small, smaller than 3 mm support deflection. The first cracking of walls with the window and door openings took place under the window opening and in the area, where lintel was supported by external pillar adjacent to the window opening.