Improvement In Load Carrying Capacity Research Articles

Effects of GFRP Stirrup Spacing on the Behavior of Doubly GFRP-Reinforced Concrete Beams

This study investigates the impact of varying glass fiber-reinforced polymer (GFRP) stirrup spacing on the performance of doubly GFRP-reinforced concrete beams. The research focuses on assessing the behavior of GFRP-reinforced concrete beams, including load-carrying capacity, cracking, and deformability. It explores the feasibility and effectiveness of GFRP bars as an alternative to traditional steel reinforcement in concrete structures. Six concrete beams with a cross-section of 300 mm (wide) × 250 mm (deep), simply supported on a 2100 mm span, were tested. The beams underwent four-point bending with two concentrated loads applied symmetrically at one-third of the span length, resulting in a shear span (a)-to-depth (h) ratio of 2.8. The experimental findings reveal that altering the GFRP stirrup spacing along the longitudinal axis of the beams, from 200 mm (equivalent to the effective depth (d)) to 50 mm (equal to (d⁄4)), altered the mode of failure from flexure-shear to flexure-compression. However, when the spacing was equal to or less than (d⁄3), there was no significant improvement in load-carrying capacity, as the contribution of GFRP bars in resisting shear loads was limited. Under service loads, the GFRP-reinforced beams exhibited wider cracks, but reducing the stirrup spacing helped restrain crack widening. Incorporating GFRP bars in the compression zone had a positive effect on reducing crack width in the tension zone. Additionally, using GFRP stirrups with spacing varying between (d) and (d⁄2) in the pure bending region increased the deflection ductility indexes. To enhance the ductility of GFRP-reinforced concrete beams, it is recommended to use GFRP stirrups in the pure bending region with spacing greater than the spacing between GFRP stirrups in the shear spans. The study highlights that the current ACI code overestimates the shear capacity provided by GFRP stirrups, particularly when the spacing is less than or equal to (d⁄3). Doi: 10.28991/CEJ-2024-010-02-011 Full Text: PDF

Maintenance of crack with infilling polymer modified mortar for shear deficient of reinforced concrete beam

Being a developing country, Pakistan needs sustainable and cost-effective strengthening/ retrofitting solution to be adopted/ practiced in the construction industry. The research reported in this paper was aimed to study the effectiveness of PMM, an indigenous product, for repairing reinforced concrete beams, resulting more effective and cost benefiting repair and strengthening for restoration of pre-cracked RC structures. This article presents the research results of experimental investigation conducted for repairing of cracks in shear deficient reinforced concrete (RC) beams with locally available novel material polymer modified mortar (PMM). A total of 6 beams; divided in three groups i.e. short beams, medium beams and deep beams with varying depths and same mix design were tested to four point loading under monotonic loading conditions until failure loads. Afterwards, these beams were repaired with PMM and cured with water for 72 h for retesting until failure. Load at first crack and at failure, crack pattern and deflections were recorded for all specimens during testing. Results from the experimental investigation indicate that load carrying capacity of the repaired beams was significantly restored in comparison to the control specimens. However, repaired specimens of medium group showed more improvement in load carrying capacity as compared with those of repaired specimens of short and deep group. The specimens of medium group restored up to 90% of their original load carrying capacity. The ductility is improved significantly for all shear critical repaired RC beams up to opening of cracks. Sudden brittle failure was observed after opening of repaired cracks. The contribution of PMM to load carrying capacity was found more significant for medium beams as compared to short and deep beams. The results of this study indicated that application of polymer modified mortar is effective technique for repairing of cracks in shear deficient RC beams.

Use of recycled waste plastic bottles in a ground engineering technology

Previous studies have investigated internal reinforcing of granular columns to further improve the loading, settlement and deformation characteristics of these columns which are popular for improving load carrying capacity, reducing settlement, mitigating liquefaction and improving drainage. This research expanded on past studies where reinforcement materials, generated from the recycling process of waste polyethylene terephthalate (PET) bottles, were used to improve the engineering characteristics of granular columns so as to potentially generate more sustainable construction technologies which is in line with the Sustainable Development Goals of the United Nations. A series of laboratory tests were undertaken on single columns which were installed in a steel cylindrical tank and subjected to a vertical compression load; the reinforced granular columns were improved with PET bottles in the form of flakes. The load-settlement characteristics were electronically recorded and a physical model of the deformation of each column was built using a paste of plaster of Paris. Modelling of the deformed columns was necessary to establish the maximum bulging diameter and the position at which it occurred along the length of the column. The results obtained showed that the highest improvement in vertical applied load was 143% and it was recorded for a test which was conducted on a column installed in the wetter silt bed, with a flakes concentration of 5.6%. In terms of settlement, a drastic reduction in settlement was observed with the inclusion of the flakes in the columns for tests on the wetter silt. The lowest settlement of 13 mm was obtained in the test with the wetter silt bed and flakes content of 5.6%. Additionally, inclusion of the flakes also reduced the extent of lateral bulging, depending on the testing conditions.

Effect of bond length on bond behavior between basalt fiber-reinforced polymer sheet and concrete

Many reinforced concrete structures are always damaged due to material aging during service life. Reinforced concrete structures can be retrofitted by fiber-reinforced polymer (FRP) sheets to improve load carrying capacity and extend the service life. The bond behavior between the FRP sheet and concrete is important for assessing the load carrying capacity of reinforced concrete structures retrofitted with FRP sheets, and the effective bond length is often used in determining the bond behavior. Basalt FRP (BFRP) has excellent properties, such as light weight and high tensile strength. Although the effective bond length between carbon FRP sheets and concrete has been studied, study on the effective bond length between BFRP sheets and concrete remains lacking. The effect of bond lengths on the bond behavior between BFRP sheets and concrete was investigated in the present study. The results revealed that: (1) the failure load between the BFRP sheets and concrete increased with the increase of the bond length when the bond length was not beyond the effective bond length; (2) the effective bond length of the interface between BFRP sheet and concrete was not beyond 80 mm obtained from the failure load; (3) the effective bond length of the interface between BFRP sheet and concrete was obtained from the bond stress; and (4) models for the failure load and the effective bond length were established.

Improving the load capacity of journal bearings with chevron textures on the shaft surface

The manufacturing of texture patterns on the surfaces of lubricated bearings proved to be an interesting way of improving the tribological behavior in such systems. Depending on the adopted texture geometry, one can achieve significant reductions in friction or an improvement of the load-carrying capacity. In the case of journal bearings, the adoption of textures in the static surface of the contact (bearing casing) usually reduces the friction coefficient with the cost of increasing rotor eccentricity (an indication of a lower load capacity). In this work, we investigate the effects of texturing the rotating surface of the journal bearing’s lubricated contact. In this case, by adopting a chevron texture pattern, one can improve the bearing load-carrying capacity with the cost of increasing the bearing friction (opposite effect). The hydrodynamic lubrication is modeled by the Reynolds equation considering mass-conserving cavitation, whose solution is obtained using a moving multigrid algorithm due to the moving nature of the textures on the shaft. The results show that the improvement in load-carrying capacity is caused by a localized pumping effect of the lubricant towards the centerline of the bearing. In addition, the optimization of the texture geometry for different operating conditions leads to a general design guideline for such textures in journal bearings.

Experimental studies on use of bamboo mat as stone column encasement in clayey soils

With the rapid urbanization and industrialization; scarcity of useful land is experienced for the infrastructure projects particularly in the urban areas. This has resulted in the use of sites with weak soil deposits such as soft clayey soils. Numerous problems are associated with these soils are high volumetric changes, heave, low bearing capacity, etc. So as to minimize the constructional difficulties associated with the soils; ground improvement techniques are practiced quite frequently on the sites. Stone column provision is one such approach used widely in the fields to enhance the properties of the weak soils. The stone column installation involves partial replacement of 10–35% of weak soils by gravelly materials to form stiffer composite mass.In the present study, an experimental program was undertaken to observe the improvement in strength properties of soft clayey soils collected from Nagpur area, Maharashtra State, India on insertion of stone column. Stone columns were placed single and in group with triangular arrangement. Effects of varying length (L) to diameter (D) ratios (i.e. L / D ratio) of stone columns on the strength properties were analyzed.As an attempt towards sustainable construction; demolition aggregates was used as partial replacement to the natural aggregate while preparing the stone columns. To increase the stiffness of stone column, cement was attempted in small quantity (4% by weight of aggregate) while preparing the specimen. Further, the use of bamboo mat as encasement was planned to study further improvement in load carrying capacity of stone column by increased lateral confinement.The experimental observations depict overall improvement in the load carrying capacity of clay beds on insertion of stone columns. Laboratory testing confirms the possibility of use of demolition waste in stone column construction, as the observed strength (uni-axial compressive strength) is 60–75% of the natural aggregate stone column. Use of bamboo as encasement is effective and shows noticeable improvement in the load carrying capacities (nearly 35–60%) and reduced settlement. Further, study illustrate that the use of single stone column is more effective.

Nanoparticle lubricant additives applied in a CNC lathe ball screw component for improving the quality of machined workpieces: A case study

A lathe ball screw is a mechanical actuator that translates rotational motion to linear motion. These machine elements are lubricated to reduce friction and wear since they can affect dimensions of the machined workpiece, measured by Cp and Cpk process capability indicators, and the number of equipment shutdowns. In this work, different nanoparticles (NPs) were added to a commercial lubricant for machine tool slideways with the purpose of reducing coefficient of friction (COF) and wear. NPs of SiO2, CaCO3 and montmorillonite clay (MMT) were added to the lubricant in concentrations on 0.01 and 0.05 wt%. Four ball tests performed under scuffing conditions showed that the best concentration was 0.01 wt% for all NPs, with improvements in load-carrying capacity of 13–15%. Higher concentrations resulted in agglomeration and these large NP clusters were not able to infiltrate the contact area to reduce friction and wear. Block-on-ring tests showed that 0.01 wt% MMT reduced wear and COF by 83% and 81%, respectively. Finally, machining tests were performed in a CNC lathe with the 0.01 wt% MMT nanolubricant for the ball screw component. Improvement was measured by keeping track of the dispersion of the workpiece dimensions, the process capability indicators Cp and Cpk and the number of equipment shutdowns for adjustments. The addition of MMT NPs to the lubricant improved Cp and Cpk by 34% and 52%, indicating a lower variation on the work piece measurements. Furthermore, equipment shutdowns were reduced by up to 50%, improving the process efficiency and lowering manufacturing costs.

Shear Strengthening of RC Beams Using Fabric-Reinforced Cementitious Matrix, Carbon Plates, and 3D-Printed Strips

Existing reinforced concrete (RC) structures suffer from degradation in their structural capacity. These structures require strengthening and retrofitting to integrate sustainability and improve their serviceability and durability. RC members strengthened with fiber-reinforced polymer (FRP) composites usually suffer from FRP debonding; therefore, researchers proposed several types of sustainable materials to overcome the shortcomings of FRP composites. Limited experimental studies have been conducted for shear strengthening of RC beams using sustainable fabric-reinforced cementitious matrix (FRCM) composites; moreover, the application of 3D-printed strips in strengthening RC beams has never been established. The current research experimentally investigates the efficiency of FRCM composites, 3D-printed sheets (CD), and CFRP plates (CP) in strengthening RC beams that are weak in shear. Various strengthening configurations were adopted, including vertical, oblique, zigzag, and several-slanted layouts. Eight simply supported beams were prepared to find the most efficient shear-strengthening configuration and material for RC beams. Test results showed that FRCM and CP are both efficient for shear strengthening in terms of maximum load capacity, initial stiffness, and ductility. However, CD showed a limited effect on enhancing the performance of shear-strengthened beams. The best shear enhancement was found in the beam strengthened with vertical CP, with improvements in load-carrying capacity, stiffness, and ductility of 43%, 23%, and 23%, respectively. The vertical and oblique strengthening configurations were more efficient than the zigzag and several-slanted layouts. The ACI 440.2R-17 model yielded accurate predictions with an average (Vc, test/Vc, ACI 440) of 1.11.

Enhancing the ability of the square footing to resist positive and negative eccentric-inclined loading using an inclined skirt

Laboratory model tests were performed to investigate the behavior of shallow and inclined skirted foundations placed on sandy soil with R.D%=30 and the extent of the impact of the positive and negative eccentric-inclined loading effect on them. To achieve the experimental tests it was used a box of (600*600)mm cross-sectional and 600mm in height and a square footing of (50*50)mm and 10mm in thickness attached to the skirt with Ds=0.5B and various an angle of (10°,20°,30°). The results showed that using skirts leads to a significant improvement in load-carrying capacity and decreased settlement in addition when the skirt angle increased, the ultimate load improved. load-carrying capacity decreased with increasing eccentricity and load inclination For load inclination (Beta) 15° when the eccentricity changed from e=0.15B to e=0.05B the load improvement percentages were (323.2% to 263%) and (214% to 220%) and settlement reduction factor was (83% to 78%) and (62% to 58%) for positive and negative eccentric-inclined loading, respectively also the result showed the effect of positive on the reduction of soil-bearing capacity is more than negative. Increasing eccentricity increases the improvement percentage for positive eccentric-inclined load and decreases for the case of negative eccentric-inclined load. Increased skirt angle will increase the Improvement factor (IR) When the skirt angle increased from 10° to 30° for an improved foundation with load angles of 5°, 10°, and 15° the improvement factor (IR) increased from (2.53, 2.51, 2.4) to (3.45, 3.65, 3.97) and (2.43, 2.58, 2.54) to (4, 4.63, 5.3) for both negative and positive eccentric-inclined load respectively and settlement reduction factor for load angle 15° and skirt angle increase from 10° to 30° were 34% and 27% for positive and negative eccentric-inclined load respectively. the (IR) for positive eccentric-inclined load is more than the negative eccentric-inclined load for all cases, in addition, the skirt angle of 30° showed a significant improvement in the improvement factor (IR).

Behaviour of carbon fiber reinforced polymer strengthened and retrofitted RC beams

This paper deals with an experimental investigation on self-compacting concrete (SCC) reinforced concrete beams of size 150x150x700mm with externally bonded carbon fiber reinforced polymer (CFRP) composites for flexural and shear strengthening. In general, strengthening techniques aims to improve load carrying capacity. Mix proportion for M30 grade concrete was arrived by Nan Su method. The strengthening techniques included are of four types such as Beam strengthened at tension face (BST), Beam strengthened at tension face extending to half depth on two sides of the beam (BSHU), Beam strengthened with four numbers of U-strips (BSUS) and Beam strengthened with two number of U-strips with CFRP inserted in hole (BSUR). Further the failed control beams were retrofitted by similar application as adopted for strengthening and were tested for load–deflection behaviour. The results indicate that among the four configurations, the beam strengthened at tension face (BST) has better flexural response compared with beam strengthened at tension face and extended to half depth at two sides of beams. Beam strengthened with 50 mm wide U-strips with CFRP inserted in a hole exhibited significant increase in toughness. Correlation equations have been developed by using regression analysis and coefficient of correlation obtained are in the range of 0.98 to 0.99 for various applications.

A numerically investigate of the improvement of load carrying capacity of square footings utilizing micropiles

This paper is aimed to address an actual case study on the use of micropile technology for improving the bearing capacity of an old building. The numerical simulation results show that the load-carrying capacity of square footing utilizing micropiles is notably increased. The improvement of the bearing capacity of the foundations depends on the strengthening methods, such as inclination angle ((), length (L), and distance of micropile from the edge of footings (S). Specifically, with the same length value of pile used, the bearing capacity reaches the largest magnitude at the S/B ratios of (0.5(0.75). The use of inclined piles yields a larger magnitude of bearing capacity than the vertical ones, these obtained results are contributed to the contribution of the “confining effects” of soil mass underneaths the footing as subjected to vertical loads. Additionally, if the soil mass below the footing has a high bearing capacity (firm to stiff clayey soils, medium to dense sandy soils…) , the design value of L/B ratio in the strengthening method should be in range of (2.0÷3.0), chosing beyond that optimal range is uneconomical since the improvement of bearing capacity is insignificant. In other words, the relationship between stress bulb in soil under the footing and the length of micropile should be taken into consideration to achieve a higher economic efficiency of the strengthening method.

An Experimental Study on Corex (Steel) Slag Reinforced with Terrazyme Treated Clay for Improvement of Soft Soil

Stability and settlement problems are common for foundations constructed on soft soils. In major parts of the world, ground improvement techniques have been used to mitigate these challenges. This research aims to stabilize the soft soils using corex steel slag blended with terrazyme treated clay. The corex steel slag is an industrial waste formed during the extraction of steel from ores through the corex process. The corex slag of sand size in the form of columns have been used to improve the load-carrying capacity of the soft soils and to control the settlement. To increase the stiffness of the corex slag columns, the terrazyme treated clay was mixed with the corex slag. The terrazyme is an eco-friendly and sustainable organic liquid and it is fully soluble in water. To prepare the terrazyme-processed clay gel 0 to 3 % of terrazyme dissolved in water was used. Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) for terrazyme treated clay were determined through the compaction tests. Appropriate proportions of corex slag and terrazyme treated clay with a suitable curing period were obtained from unconfined compression tests. A series of laboratory model plate load tests for 3 foundation shapes were performed on soft soil, stabilized with a blend of corex slag and terrazyme treated clay. Improvement in the MDD with a reduction in OMC was noticed when terrazyme was added to soft soil. Unconfined Compressive Strength (UCS) value for corex slag increased with an increase in the content of terrazyme treated clay. Model plate load tests showed significant improvement in the load-carrying capacity of soft soil.
 HIGHLIGHTS
 
 Stability and settlements are the major problems for foundation constructed on soft soil
 Corex (Steel) slag blended with terrazyme treated clay is utilized to stabilize the soft soil
 The specimens prepared with corex steel slag and terrazyme treated clay demonstrate remarkable improvement in UCS value at 21 to 28 days of curing
 The soft soil stabilize with specimens in group reveled remarkable improvement in load-carrying capacity of soft soil
 
 GRAPHICAL ABSTRACT

Repair and retrofitting of external RC beam-to-column joints using the hybrid NSM + EBR method

In this study, the repair and retrofitting of external reinforced-concrete (RC) beam-to-column joints using FRP composites is investigated by performing experimental tests. The seismic design detailing for the panel zone is not considered in the design of the tested joints. The test program was performed in three stages. At the first stage, the specimens were loaded until reaching different levels of damage. Subsequently, the damaged specimens were repaired and retrofitted by the NSM and hybrid EBR + NSM methods using FRP composites. Finally, the retrofitted joints were loaded cyclically until their failure. This study is intended to investigate the influence of the utilized retrofitting methods on improving load carrying capacity, stiffness, and ductility of damaged RC joints. For this purpose, eight RC beam-to-column joints, including seven non-seismically designed (NS) and one seismically designed joint (S), were cast and tested. The attained experimental results for the load-carrying capacity, stiffness reduction, and the cumulative dissipated energy of NS specimens were compared with the S specimen. The results showed the proposed hybrid retrofitting methods can recover the lost capacities of joints and even increase their capacities to levels higher than the seismic control specimen. In addition, it is found that according to Park and Ang damage index, the tested specimens are repairable up to 2.6% drift ratio.

Performance of PSGWC-Bars and other rebars reinforced columns

In comparison to earlier concrete structures, recent decades' structures have experienced early deterioration. The majority of the time, this is due to the severe corrosion found in today's ribbed rebars. The adoption of PSGWC-bars, which have a plain surface and a gentle wave-type configuration, can extend the life of concrete structures by several times by reducing the rate of rebar corrosion. Beams strengthened with PSGWC-bars performed significantly better in tests conducted at several colleges. To establish its viability as a replacement for traditional rebars in columns, the load carrying capacity of PSGWC bars and other rebars must be tested. In this paper an attempt has been made to improve load carrying capacity of column with rebars. The impact of plain bars, epoxy coated plain bars, galvanised plain bars, PSGWC-bars of five different types, ribbed bars, epoxy coated ribbed bars, and ribbed bars with galvanising on the performance of sustainable columns was examined in this paper. It has been discovered that the use of PSGWC-bars increases load-carrying capacities in concrete columns as well.

Experimental Study of the Fatigue Performance of the Bonding Surfaces and Load-Bearing Capacity of a Large-Scale Severely Damaged Hollow Slab Strengthened by CFRP

In recent years, carbon fiber reinforced polymer (CFRP) has been widely used in bridge repair, retrofitting, rehabilitation and strengthening to improve the bearing capacity. Although many studies have been conducted to explore the strengthening efficiencies of CFRP, the test specimens were small and the results were difficult to apply to full-scale bridges. Investigations into the strengthening effects of CFRP on real life structures rely on field load tests (without damaging the structures), making it difficult to understand actual improvements in load carrying capacity and strengthening effect. Moreover, there have been few experimental studies on the fatigue performances of CFRP-strengthened structures, especially on the large-scale structures with real wheel moving loads. In this study, the feasibility and efficiency of CFRP strengthening and repair was investigated on a large-scale, prestressed concrete hollow slab decommissioned from a real-life concrete bridge. The hollow slab was first put through a destructive test to test the ultimate load-bearing capacity. Then, CFRP strips were installed on the surface of the severely damaged slab to repair and strengthen it. Fatigue load test—including the moving load test and single point sinusoidal load—and load-bearing capacity tests were conducted on the CFRP-strengthened hollow slab after the destructive test to evaluate the strengthening performance. This study could help us to understand the actual load-bearing capacities of severe damaged concrete structures strengthened by CFRP, reduce waste, save resources and improve the utilization of our infrastructures.

Thermal Analysis of Journal bearing with controlled slip/no-slip boundary condition and Non-Newtonian Rheology of lubricant

This paper discusses the combined effect of Non-Newtonian rheology of lubricants and slip boundary condition on the static performance characteristics of finite hydrodynamic journal bearings. A modified JFO model with an adiabatic energy equation has been used for calculating the variation of performance parameters. It has been observed that shear-thinning lubricant with slip effect on partial circumferential region shows a significant percentage of improvement in load-carrying capacity and coefficient of friction. Further, For eccentricity ratio of less than 0.2, these lubricants give maximum tribological performance as compared to Newtonian lubricants under conventional boundary condition.

Momentless design of variable stiffness composite cylindrical vessels with elliptical heads

Membrane stress state is favorable for pressure vessels to resist internal pressure since the stress through shell thickness is constant. However, bending stresses resulted from bending moments of pressure vessels will destroy the favorable membrane stress state leading to nonuniform stress through shell thickness. Thus, suppressing bending moments in pressure vessels will be an efficient way to achieve improvement of load carrying capacity. A momentless design of variable stiffness composite cylindrical vessels with elliptical heads which are widely used in engineering has been presented in this study. The momentless governing equations concerning both the elliptical head and junction region of the pressure vessels under uniform pressure are derived. Numerical analyses are carried out on the pressure vessel models with different configurations. The variable angles of fiber orientations over these models are explicitly provided. The stress resultants and deformation behaviors together with the curvature changes of these models have been checked and compared. Results show that based on the variable fiber angles over the structure obtained from the presented mathematical design methodology, the bending moments are successfully suppressed in the variable stiffness composite pressure vessels. The momentless design method will ensure the pressure vessels to service in an efficient membrane state.

Susceptibility of strain-hardening cementitious composite to curing conditions as a retrofitting material for RC beams

Strain-hardening cement-based composites (SHCC) have recently been developed as repair materials for the improvement of crack control and strength of flexural members. This work focuses on strengthening and flexural enhancement using SHCC layer in tensile regions of flexural members under three different curing conditions. The curing conditions simulate the effect of different environmental conditions prevailing in the central and coastal regions of the Arabian Peninsula on the properties of SHCC as a retrofitting material. In this investigation, beams with SHCC layer were compared to control beams. The beams with SHCC layer of 50-mm thickness were cast. The results revealed that the flexural behavior and the load-carrying capacity of the normal concrete beam specimens under hot and dry environmental conditions were significantly reduced, lowering the ductility of the section. However, compressive strength is comparatively unaffected. Similarly, the hot curing conditions have also led to a notable reduction in the loading capacity of the beam with SHCC layer with a slight effect on its stiffness. On the other hand, steam-curing conditions have shown improvement in load-carrying capacity and a reduction in section ductility of the beam with SHCC layer. It was found that the structural unit retrofitted with SHCC layer was a curing-regime dependent as the tensile and strain-hardening properties of SHCC are highly sensitive to the alteration in the cement hydration process. A normal curing regime was found effective and satisfying the practical, cost, and performance requirements. Accordingly, a normal curing regime could be implemented to retrofit reinforced concrete (RC) beams with SHCC layers as recommended in the study.

A Study on Effect of Steel Tube in Axial Behavior of CFST Stubs

Concrete filled steel tubular (CFST) columns are becoming popular due to its advantages from both steel and concrete in resisting loads. CFST members are made up of steel hollow section of rectangular or circular sections filled with plain or reinforced concrete. CFST columns can be used effectively in high raised structures and in bridges. The reduced cross sections of columns can be achieved by the composite action of steel and concrete. The steel tube provides confinement to the concrete and helps to improve load carrying capacity. The concrete core offers higher resistance to axial compression. The inward buckling of steel tube will be avoided due to concrete and the out buckling resistance may be improved due to higher stiffness of the column due to higher gross moment inertia with combined effect of steel and concrete. This experimental work made an attempt to understand the effect of thickness of steel tube in behavior of CFST stubs.In the present experimental study, a total of 24 cylindrical concrete filled steel tube specimens were prepared to evaluate the uniaxial compressive behavior and to understand the effect of thickness and aspect ratio (h/D) on the compressive strength. Two different thickness of steel tubes 3 mm and 5 mm and four aspect ratios (h/D) 1, 2, 3 and 4 are considered in the present study. M30 grade of concrete is used. From this study, as the aspect ratio increases the buckling loads decreases. The decrement is up to 37% in aspect ratio 4 when compared to aspect ratio1.

A Novel Planetary Thread Roller Bearing: Design and Analysis of Load Characteristic

Abstract A novel planetary thread roller bearing (PTRB) was proposed in this paper based on the Hertz theory combined with multiple principles (e.g., equivalent steel ball, multi-point meshing, and power dividing). A significant improvement in load-carrying capacity, compared with existing bearings, was achieved and thus providing a new option for the advanced equipment with high thrust-to-weight ratio requirement. The newly proposed PTRB exhibited a 83% increase in dynamic axial load rating while a comparable static axial load rating comparing with the thrust ball bearing with a comparable size. Furthermore, the working efficiency of the new PTRB was constantly higher than 97%. A self-degradation operation was achieved by the system when some thread rollers were stuck, which improved the system fault tolerance. Finally, friction torque tests were performed on the self-developed test instrument. The results showed a good agreement with the theoretical analysis.