Load Transfer Capacity Research Articles

Influence of aggregate gradation on hma mixes stability

Abstract The load transfer capacity of pavements is to a great extend influenced by aggregates. About 85% of the total volume of hot mix asphalt (HMA) mixtures consists of aggregates; thus, they are greatly influenced by aggregate properties like angularity (shape), roughness (texture), and gradation. Aggregate gradation controls the structure of voids. Current specifications for aggregate properties in HMA pavements require the aggregate blend to fall within a specified range of gradation values. Although the abovementioned requirement has ensured the construction of high quality HMA pavements, the properties are largely empirical and they are not based on performance-related tests. Marshall Stability is in principle the resistance to plastic flow of cylindrical specimens of a bituminous mixture loaded on the lateral surface. It is the load carrying capacity of the mix at 60oC. Aggregates with different gradations from the broader area of Xanthi, Northern Greece, have been used to prepare specimens for stability testing of hot asphalt mixtures in the laboratory. The research focused on the evaluation of the influence of aggregates in the overall stability characteristics of the mixtures. The maximum stability value has been obtained with an open-graded mixture having 5% asphalt and aggregate size 2.36 mm. However, the stability of the dense graded mixture is higher than this maximum value.

Effect of Cyclic Heat, Humidity, and Joining Method on the Static and Dynamic Performance of Lightweight Multimaterial Single-Lap Joints

This experimental study investigates the effect of environmental loading and joining methods on the static and dynamic performance of lightweight multimaterial single-lap joints (SLJ). Joint adherend material combinations are divided into two groups; namely, composite-based and steel-based materials that include glass fiber reinforced polymer (GFRP), steel (St), aluminum (Al), and magnesium (Mg). A commercially available adhesive is selected for the study. Investigated joining methods include bonding-only, bolting-only, and hybrid bonding-and-bolting. Static performance is assessed by the load transfer capacity (LTC) of SLJ after they have been subjected to heat cycling at ambient level of relative humidity, or after heat cycling at high relative humidity. Dynamic performance is measured by durability life (in cycles) of SLJ test samples under a fixed dynamic load ratio in a tensile–tensile fatigue test, after they have been subjected to heat cycling and humidity. The cyclic test load fluctuated between 67.5% and 75% of the static LTC at ambient condition. Sample finding includes the significant effect of heat cycling at an ambient humidity level; it has tripled the LTC of bonded-only composite-to-composite SLJ, relative to their baseline LTC at ambient conditions. Detailed discussion of the results, observations, and conclusions are presented in this paper.

Effect of Adhesive Nanoparticle Enrichment on Static Load Transfer Capacity and Failure Mode of Bonded Steel–Magnesium Single Lap Joints

An experimental procedure and test setup are used for investigating effect of using nanoparticle additives to the adhesive on the load transfer capacity (LTC) of bonded magnesium (Mg)–steel (St) single lap joints (SLJ). Investigated variables include the nanopowder material (alumina versus silica), particulate size (20 nm versus 80 nm), and concentration in the adhesive (2.5 wt.% versus 5.0 wt.%). Two different levels of surface roughness on the bonded area are used, namely, sanding the bond area with G60 or G180 sand paper. Test data and scanning electron microscopy (SEM) failure mode analysis are provided.

Using carbon nanotubes to improve strengthening efficiency of carbon fiber/epoxy composites confined RC columns

The effectiveness of using carbon nanotubes (CNTs) to enhance the strengthening efficiency of carbon fiber/epoxy composites confined reinforced concrete (RC) columns was investigated. A total of fourteen large scale rectangular RC columns were prepared and tested under concentric axial loading. The incorporation of CNTs within the carbon fiber/epoxy composites was achieved by modifying the epoxy resin using CNTs and/or coating the carbon fiber with CNTs enriched sizing agent. The failure modes, axial load–displacement responses, and microstructures of unwrapped, fully wrapped, and partially wrapped specimens were analyzed. Experimental results showed that using CNTs modified epoxy or CNTs enriched sizing agent improved the load carrying capacity and toughness of RC columns confined with carbon fiber/epoxy composites. Scanning electron microscopy (SEM) characterization showed that CNTs could improve the adhesion at the carbon fiber/epoxy interface and concrete/epoxy interface leading to improvement in the load transfer and load carrying capacity.

Optimization of the fully grouted rock bolts for load transfer enhancement

The purpose of this study is to investigate the role of bolt profile configuration in load transfer capacity between the bolt and grout. Therefore, five types of rock bolts are used with different profiles. The rock bolts are modeled by ANSYS software. Models show that profile rock bolt T3 and T4 with load capacity 180 and 195kN in the jointed rocks, are the optimum profiles. Finally, the performances of the selected profiles are examined in Tabas Coal Mine by FLAC software. There is good subscription between the results of numerical modeling and instrumentation reading such as tells tale, sonic extensometer and strain gauge rock bolt. According to the finding of this study, the proposed pattern of rock bolts, on 7+6 patterns per meter with 2 flexi bolt (4m) for support gate road.

Joint Load-Transfer Prediction Model Considering Dowel-Bar Position Deviation in Rigid Pavements

A double-layer structure model of pavements that considered interlayer contact status was established to manage the dowel-bar position deviation problem in rigid pavements. The deviation effect of three-dimensional positions, such as horizontal angle, vertical angle, and embedded depth, on joint load-transfer capacity was analyzed. A load-transfer capacity prediction model that considered dowel-bar position deviation was established via ternary nonlinear regression. The load correction factor and its range were also proposed. This prediction model can effectively reflect the joint load-transfer capacity during dowel position deviation after verification via falling weight deflectometer testing. The horizontal angle of the dowel bar minimally affected joint load-transfer coefficient. By contrast, the joint load-transfer coefficient decreased almost linearly as the vertical angle increased. The coefficient reduced by approximately 12% when the vertical angle was 15°. Meanwhile, the load-transfer coefficient was maximized when a dowel bar was embedded in the middle of a surface. The coefficient would decline either upward or downward. The coefficient particularly decreased by 10% when the position was 2 cm downward.

Effect of CuO nanostructure morphology on the mechanical properties of CuO/woven carbon fiber/vinyl ester composites

The effect of CuO nanostructure morphology on the mechanical properties of CuO/woven carbon fiber (WCF)/vinyl ester composites was investigated. The growth of CuO nanostructures embedded in the surface of woven carbon fibers (WCFs) was carried out by a two-step seed-mediated hydrothermal method; i.e., seeding and growth treatments with controlled chemical precursors. CuO nanostructural morphologies ranging from petal-like to cuboid-like nanorods (NRs) were obtained by controlling the thermal growth temperature in the hydrothermal process over a growth time of 12h. The Cu2+/O− ratio and the rate of reaction greatly influenced the formation of CuO nanostructures as self-assembled shapes on the crystal planes in the order L[010]>L[100]>L[001]. Morphological variations were analyzed by scanning electron microscopy, X-ray diffraction, and Brunauer–Emmett–Teller surface area analysis. The impact behavior, in-plane shear strength, and tensile properties of the CuO/WCF/vinyl ester composites were analyzed for different CuO NR morphologies at various growth temperatures and molar concentrations. The CuO/WCF/vinyl ester composites had improved impact energy absorption and mechanical properties because the higher specific surface area of CuO NRs grown as secondary reinforced nanomaterials on WCFs enhanced load transfer and load-bearing capacity.

Influence of interfaces on the mechanical behavior of SiC particulate-reinforced Al–Zn–Mg–Cu composites

In particulate-reinforced metal matrix composites (MMCs), geometrically necessary dislocations (GNDs) form in the vicinity of reinforcement/matrix interfaces. In this study, the hardness distribution across the interface was studied using nanoindentation with high spatial resolution, for composites treated under different aging conditions. The size of the GND punched zone, as determined from the hardness measurement, was found to be in agreement with that estimated by transmission electron microscopy (TEM). Mechanical characterization of bulk composites revealed a reduction in failure strain with decreasing punched zone size, while the strength of the composites was found to depend more on the intrinsic strength of the matrix alloy. These observations were interpreted in terms of the load transfer capacity between the matrix and reinforcement through the interface.

Geogrid and Soil Displacement Observations During Pullout Using a Transparent Granular Soil

Current practice to quantify the load transfer capacity between soil and geosynthetic reinforcement materials in the anchorage zone of a wall, slope, or embankment is to carryout laboratory pullout tests. In a recent paper, the authors described a novel large pullout box with a transparent bottom. Geogrid specimens up to 2000 mm in length were embedded in a transparent fused quartz soil and the specimens subjected to constant rate-of-displacement in-air testing and in-soil pullout testing under a range of normal stress. Displacement–time histories over the entire area of each reinforcement specimen were measured using the digital image correlation (DIC) technique applied to sequential images captured by a row of cameras located directly below the test apparatus. Opaque particles were also mixed with the transparent soil particles so that horizontal displacement of the soil in the planes immediately above and below the geogrid specimens could be tracked. The difference in horizontal displacement response corresponds to the relative shear displacement between the soil and geogrid that is responsible for load transfer during pullout. These results demonstrate the utility of the experimental methodology using the transparent fused quartz material as a successful analog to a natural sand soil for the investigation of granular soil–geogrid interaction. The example data is a necessary precursor to the development of interface shear models for load transfer in the anchorage zone of geogrid reinforced soil structures.

Improvement of rock bolt profiles using numerical method

Current developments in numerical modelling techniques are presented to investigate the load transfer between the steel bolt surface and grout. Underground measurements of steel bolt performance indicate that amongst many parameters bolt profile configuration play an important role in load transfer capacity between the bolt and grout. This study proposes a new numerical solution to predict displacement, shear stress and shear strain of a fully grouted rock bolt intersected by single rock joint. The main characteristics of the numerical solution, consider the bolt profile and joint movement under pull test condition. In this paper, five types of rock bolts are used with different profiles. The rock bolts are modelled by ANSYS software. Profile rock bolt T3 and T4 with load capacity 180 kN and 195 kN in the jointed rocks, were choices as the optimum profiles. The results showed that there is a promising agreement between numerical and experimental methods.

Comparison of load transfer index (U<SUP align="right">*</SUP>) with conventional stress analysis in vehicle structure design evaluation

The load transfer index (U*), is a relatively new concept compared to its counterpart of structural stress analysis. The U*index characterises the internal stiffness distributions, which indicates the load transferring function of the prospective structure. Although the U* index and stress values have been proven to be useful indices in design, a systematic comparison between the conventional stress analysis and the loads transfer analysis (based on U*index) is lacking. In this study, using a component of the parcel rack from multiple passenger vehicles as an example, we demonstrate the unique capability of U*, indicating the load transferring function. We further show how the combination of the load index U* and the stress distributions provides a comprehensive understanding of the structure's response to various loading conditions. More importantly, we will discuss how the U* can provide unique guidelines for structure design with the purpose of improving the load transfer capacity and reducing the weight.

Effectiveness of R/C jacketing of substandard R/C columns with short lap splices

The effectiveness of a retrofitting method for concrete columns with particular weaknesses is experimentally evaluated and presented in this paper. Structural deficiencies namely the inadequacy of transverse reinforcement and short length of lap splices are very common in columns found in structures built prior to the 1960s and 1970s. Recent earthquakes worldwide have caused severe damages and collapses of these structures. Nevertheless, the importance of improving the load transfer capacity between the deficiently lap-spliced bars is usually underestimated during the strengthening procedures applied in old buildings, though critical for the safety of the residents\' lives. Thus, the seismic performance of the enhanced columns is frequently overestimated. The retrofitting approach presented herein involves reinforced concrete jacketing of the column sub-assemblages and welding of the lap-spliced bars to prevent the splice failure and conform to the provisions of modern design Codes. The cyclic lateral loading response of poorly confined original column specimens with insufficient lap splices and the seismic behavior of the retrofitted columns are compared. Test results clearly demonstrate that the retrofitting procedure followed is an effective way of significantly improving the seismic performance of substandard columns found in old buildings.

Analysis profile of the fully grouted rock bolt in jointed rock using analytical and numerical methods

The purpose of this study was to investigate the effect of bolt profile on load transfer mechanism of fully grouted bolts in jointed rocks using analytical and numerical methods. Based on the analytical method with development of methods, a new model is presented. To validate the analytical model, five different profiles modeled by ANSYS software. The profile of rock bolts T3 and T4 with load transfer capacity, respectively 180 and 195kN in the jointed rocks was selected as the optimum profiles. Finally, the selected profiles were examined in Tabas Coal Mine. FLAC analysis indicates that patterns 6+7 with 2NO flexi bolt 4m better than other patterns within the faulted zone.

Introducing aggregate into grouting material and its influence on load transfer of the rock bolting system

A fully grouted bolt provides greater shear load capacity for transmitting the load from the rock to the bolt, and vice versa. When grout fills irregularities between the bolt and the rock, a keying effect is created to transfer the load to the bolt via shear resistance at the interface and within the grout. Previous research has revealed that the mechanical properties of the grout had a great impact on the load transfer capacity of the rock bolting system. This paper presents a method to enhance the rock bolting strength by introducing metal granules into the grouting material. Experimental results suggest that both the average peak load of pullout tests and the total energy absorption of the system will increase if some metal granules are mixed into the resin.

Stress Analysis for Cement Concrete around Joint Dowel after Loosing

The stress concentration will appear in cement concrete around joint dowel set in contraction joint of cement concrete pavement with repeated loads. And concrete around joint dowel will damage gradually.In this paper, the stress of concrete around joint dowel and deflection of concrete slab are analyzed when joint dowel loosing. It is indicated that the shear stress is key to damage of concrete around joint dowel. when the loosing width reaches certain extent. With loosing width increasing, load transfer capacity will decrease gradually. And it is shown that the load transfer capability will lower rapidly when the loosing width comes in 4cm.

Optimal design for the mortar-filled glass fibre-reinforced polymer tube dowels

Use of mortar-filled glass fibre-reinforced polymer (GFRP) tubes is considered as an alternative of steel dowel bars in concrete pavement. The mortar-filled GFRP tubes have two major advantages over conventional steel dowels: its stiffness is comparable to that of concrete and it has a high corrosion resistance. In the present study, five different types of mortar, made with different concrete materials and mix proportions, were used to fill up a given GFRP tube. The mechanical properties, such as flexural and shear strength, of these mortar-filled GFRP tubes were investigated. One mortar-filled GFRP tube was then selected and used as dowels in field pavement. The field performance of the mortar-filled GFRP tube dowels was evaluated. The results indicate that the GFRP tube dowels have sufficient load transfer capacity and the overall performance of the GFRP tube dowels is comparable to that of steel dowel.

Analytical study of steel bolt profile and its influence on bolt load transfer

The load transfer capacity of fully grouted steel bolts has been the subject of research for the past three decades. Experimental studies have confirmed that the bolt surface profile plays an important role in load transfer of fully grouted rock bolting systems. This research work seeks to lay the foundation for the role of the bolt profile in rock bolting mechanisms. A shear failure surface which is parallel to the bolt surface has been assumed and investigated using stress analysis. The stress field within the resin introduced by the axial load of the bolt has been formulated based on the half space theory, and the influence of the bolt profile configuration on rock bolting failure is identified under Mohr–Coulomb's failure criterion. Parametric studies show that bolts with smaller rib face angles or smaller profile height to length ratios are favourable to transfer load radially. Hence, they should be used in hard rock environments. On the contrary, bolts with large rib face angles and higher rib height to length ratios will transfer the major part of axial load into the resin in a direction parallel to the bolt surface. Thus, they should be used in soft rock conditions.

Fracture Behavior of Dowel Joint of Concrete Slab Track

최근 콘크리트궤도 공법이 증가함에 따라 인접한 슬래브를 연결하는 방법에 대한 관심이 높아지고 있다. 슬래브의 연결부는 효과적인 하중전달, 변형 연속화, 응력 분산을 위해서 다웰 시스템이 다수 적용된다. 본 연구에서는 콘크리트 슬래브 다웰연결부를 효율적으로 이상화할 수 있는 연결부의 집중 전단스프링 (Lumped shear spring) 모델을 제안한다. 전단 스프링 모델의 강성은 다웰바의 강성과 유격을 고려하였으며, 강도는 연결부의 전단파괴에 근거한 Concrete Capacity Design(CCD) 방법에 의해 산정되었다. 해석모델의 타당성을 검증하기 위하여 다웰로 연결된 슬래브 실험체를 제작하고 재하실험을 수행하였다. 제안된 해석모델은 다웰과 콘크리트 간의 유격으로 인한 초기 비선형성 및 콘크리트 재료 비선형성을 합리적으로 반영하고 있는 것으로 분석되었다. 따라서 향후 슬래브 다웰 조인트로 연결된 콘크리트궤도의 파괴 시까지의 비선형 거동을 합리적으로 예측함으로써 철도 궤도의 설계 시 효과적으로 활용될 수 있을 것이다. Recently, an interest on joint behavior between adjacent concrete slab tracks has increasing due to large application of such track system. Dowel bars are widely used to improve load transfer capacity across the joints. Dowel bars reduce the deflections and stresses by transferring the load between the slabs. This study proposes the lumped shear spring model to efficiently model dowel joints of adjacent slabs. This model includes bearing stiffness between dowel bar and concrete as well as dowel gap. Strength of the proposed spring model is evaluated based on Concrete Capacity Design method under the assumption of shear failure mode in the joints. Experiments are also performed up to failure to evaluate the accuracy of the proposed model. It has been observed that the proposed model is able to predict initial nonlinearity due to dowel gap, and capture material nonlinearity of the test slabs. Thus, it is recommended that the proposed model can be effectively applied to the dowel joints of concrete slab track.

A Study on the Working Performance of Dowel Bars with Horizontal Installation Errors

AbstractUsing the pullout test on dowel bars with different surface treatment modes and position deviations, the present paper draws the conclusion that plastic-spraying treatment on different surface treatment modes can meet the maximum setting requirements for dowel bars and that the angular deviation of the dowel bar is the main reason for the cracking within 50 cm on both sides of the cement concrete pavement joint. Using the bending fatigue test, the present paper evaluated the attenuation law of the joint load transfer capacity under different horizontal installation error conditions (0°, 5°, 10°, and 15°) and found that the initial joint load transfer capacity showed fast downward trend with increase in dowel bar deviation angle and that the performance during the entire working period became increasingly worse. When the angular deviation of dowel bar along the horizontal plane was not more than 5°, juncture load transfer capacity can still remain on the medium level, which will not have too much i...

Shaping scaffold structures in rapid manufacturing implants: A modeling approach toward mechano‐biologically optimized configurations for large bone defect

Large segmental bone defects remain a clinical challenge. Titanium lattice-structured implants in combination with laser sintering technology promises to be an alternative to bone grafting in the treatment of critical sized bone defects. Laser sintering allows the rapid manufacturing of patient specific 3D-structured scaffolds with highly interconnected macroporous networks and tunable mechanical properties. Unknown remains to what degree the mechanical properties of these implants could be tuned, without leading to mechanical failure but still providing adequate mechanical stimuli for tissue ingrowth. The aim of this study was to evaluate various implant designs for their mechanical potential towards (a) optimized safety against stress failure and (b) optimal intrastructural straining for bone ingrowth. Finite element analyses of several lattice-structured configurations were performed. Results illustrated a strong influence of the configuration on the load carrying capacity of the constructs. The likelihood of mechanical failure was predicted to be highly dependent on structure configuration with little influence of implant porosity. Increasing porosity did not result in an increase in the implant intrastructural straining in all configurations; however, the lattice configuration was the determinant factor for implant load transfer capacity. This study provides a framework for the design of effective implants with open pore structures to ensure mechanical stability as well as promote mechanical stimulation and encourage in vivo osseointegration.