Positive Bending Research Articles

Analytical method regarding compression-bending capacity of segmental joints: Theoretical model and verification

The flexural bearing capacity of a segmental lining structure, mainly comprising the flexural bearing capacities of segments and the compression-bending capacities of joints, is an important index for evaluating the mechanical performance of a shield tunnel. As indicated by this study, the flexural bearing capacity of a segment has a theoretical basis for the calculation, whereas that of a joint does not. Combined with the deformation characteristics of a segmental joint under compression-bending loads, concrete yielding at the joint surface is taken as the criterion of the ultimate bearing state of a segmental joint, upon which a set of theories for calculating the compression-bending capacity of the segmental joint is established in terms of the mechanical model of the segmental joint. Therefore, according to an analytical solution of compression-bending capacity of a segmental joint, the accuracy and correctness of the designed algorithm are verified through a full-scale compression-bending test of a segmental joint, and the proposed method is then applied to prototype tests of the segmental lining structure for interpretation of the test results. A comparison with the results of full-scale segmental joint tests indicates that the relative errors of the joint bending moments between the test results and the theoretically calculated results are 3% and 5.6% for positive and negative bending, respectively, which not only confirms the accuracy of the proposed theoretical model but also rationalizes the assumption that the yielding of the concrete joint surface is a sign of the joint reaching its ultimate limit state. Using the proposed method, the prototype test results of the segmental rings are interpreted and indicate that the structural failure of a straight-jointed assembly structure (STRS) is mainly caused by joint failure because most of the joints have already exceeded their ultimate bearing capacity, whereas none of the segments have reached their flexural bearing capacity. In the test results for a staggered-jointed assembly structure (STGS), both the segments and joints have reached the ultimate joint bearing capacity or are nearly yielding at the same time. The interaction between the segmental rings of an STGS not only allows both the bearing capacity of the segment and the joint to be fully exerted while the structure bears a load but also generates yielding of the two-part structure almost concurrently; thus, an STGS has better bearing performance than an STRS.

Three-dimensional analysis of effects of ground loss on static and seismic response of shafts

During the construction and use of underground structures, it is difficult to avoid ground loss. Previous studies suggested a correlation between ground loss and damage of underground structures. But the current studies are mainly focused on the two-dimensional analysis of tunnels. In the two-dimensional analysis, the simulation of ground loss is flawed, and the results cannot be applied to the shaft structures. Based on the Suzhou River deep underground drainage and storage system, this paper establishes a three-dimensional finite element model of the shaft. Voids of different depth, angle and location are set behind the shaft wall, and the effects of ground loss on static and seismic response of the shaft are analysed. It is found that the existence of ground loss leads to a stress concentration which changes the static deformation and internal force of the shaft. And large positive and negative bending moments occur in the circumference direction which may cause damage to the shafts. During the earthquake, the ground loss will increase the bending moments and reduce the axial pressure. But it has no significant effect on the response in the cross sections. This paper indicates that ground loss can change the static and seismic response of the shaft and it is a potential unsafe factor. Ground loss should be avoided as much as possible during shaft construction, and the impact of ground loss should be considered as appropriate in the design.

Development of a symmetrical four-roller bending process

In order to reduce the straight edge section and simplify process flow, a new symmetrical four-roller bending process is proposed, and its optimum forming process is determined. The main procedure composes of feeding, pre-bending, reverse roll bending, final bending, positive roll bending, unloading, and springback. It has advantages of less production procedure, small remaining straight edge, and simple equipment structure. Three methods are adopted to study the process, i.e., theoretical analysis, numerical simulation, and physical experiment. According to the theory of elastoplastic and geometric relation, the relationship between the reduction of the upper roller and the curvature radius before and after springback is established, and the reduction of the upper roller can be predicted. The symmetrical four-roller bending process is simulated by ABAQUS software. The distribution of stress and strain is analyzed, and the theoretical curvature radius and the simulated curvature radius are compared. The rolling part is obtained from simulation with an ovality of 0.43% and only 1.5 times the thickness of the remaining straight edge. The symmetrical four-roller bending machine is designed, and the ovality of the rolling part from experiment is less than 5%, and the minimum is only 1.74%. The error of most curvature radius is less than 0.5%. Numerical simulation and physical experiments both prove the feasibility of the method. The effect of the process parameters on the curvature after springback is studied by a single variable method. This process provides a new idea for pipe production and helps improve the rolling quality.

Effect of Tension at Early Age on Bearing Capacity of PC Continuous Girder Bridge

In order to study the influence of prestressed steel bundles on the bearing capacity of bridges in the early age of concrete, a new 5×20 m prefabricated continuous box girder bridge is used as the engineering background, and MIDAS/CIVIL simulation is used. When the age of precast box girder concrete is 3d (working condition 1), 5d (working condition 2), 7d (working condition 3), the steel bundle is tensioned. The ultimate state check and prestress loss analysis of the mid-span middle beam after tensioning at different ages are analyzed. The results show that the positive section bending capacity of working condition 1 and working condition 2 decreased by 13.15% and 6.51% respectively and the earlier the tensile age, the greater the prestress loss value of the steel bundle. Combined with the simulation analysis, the load test is carried out on the bridge (the actual construction is tensioning at 5d): the strain check coefficient is between 0.599 and 0.753, and the deflection check coefficient is between 0.596 and 0.705. The results show that when the concrete age is 5d, the steel bundle is tensioned, and its bearing capacity can still meet Highway Class I requirements

Effectiveness of Various Techniques Using FRP for the Strengthening of R. C. Beams with Tension Lap Splices

This paper presents an experimental program conducted to investigate the flexural performance of RC beams with tension reinforcement lap splice strengthened using externally bonded FRP different techniques in splice region. The specimens were reinforced on the tension side with four deformed bars spliced at mid span. The tested beams are of 3200 mm total length and 250*120 mm cross section, tested in positive bending. The considered parameters were splice length, type of FRP (glass or carbon), strengthening techniques in splice region (externally confine strips around cross section, Near Surface Mounted technique "NSM" stirrups, externally bonded sheets or bars on the tension face, number of GFRP strips layers (one layer, two layers, and three layers), and shape of NSM stirrups (Box or U shape). No additional anchorage mechanism or bonding methodology was applied for the FRP strips on the concrete except the epoxy adhesive. The effect of these factors on the failure of modes, the ultimate load, the bond strength and that the ductility were investigated. The results indicated that all applied strengthening techniques were efficient in improving the bond strength of the lap splices, the ductility, and the load-deflection behavior of the tested beams, especially when strips were installed over the splice region. This study approved that NSM technique gave more prominent simplicity of employ.

Symmetry selective cladding modes coupling in ultrafast-written fiber Bragg gratings in two-mode fiber.

The lower order cladding mode resonances of a fiber Bragg grating (FBG) are sensitive to fiber bending but their spectral density makes their response to bending very complex. In this work we present a simple method to reduce and control the number of low order cladding mode resonances via FBGs written in a two-mode fiber (TMF) with an ultrafast laser. Owing to the larger core size of the TMF, a slight break of the cylindrical asymmetry of the grating patterns can be induced when using femtosecond side-irradiation with a small change in the writing condition. This allows us to control the mode families coupled by the grating, and in particular to those modes that have positive or negative bending responses along certain bend directions. Experimental results demonstrate that several lower-order neighboring-cladding mode pairs coupled by the asymmetric TMFBG have antagonistic loss responses (by several dB) for different bending directions, thus allowing full 2D bending measurements with many applications in shape sensing. Finally, this device has similar advantages as tilted FBGs, i.e. temperature de-correlation and the possibility of increasing the signal to noise ratio by averaging simultaneous measurements on several pairs of resonances.

Strengthening of Composite Steel-Concrete Beams Openings by Adopting Different Reinforcement Methods

This paper presents an experimental and numerical study carried out to investigate the flexural and shear behavior of concrete-steel composite beams with circular web openings strengthened using two different techniques around openings. The experimental program conducted on nine simply supported beams which were constructed with different variables. One steel beam and eight concrete-steel composite beams were experimentally tested. The tested beams are of 1500 mm length and BFI cross section of steel beam but composite beams were BFI steel section connected with concrete slab had 300 mm width and 70 mm depth, while this connection is done by headed stud shear connector. The tested specimens subjected to positive bending were loaded by one or two line load across the width of the concrete slab. The main parameters were the type of beams, web openings effect, location of web openings, strengthening techniques around openings externally CFRP strips and vertical steel links using steel plates placed on the top and bottom surface of beams anchored with fine threads, and number of CFRP strips layers. The effect of these parameters on the failure of modes, ultimate load, first cracking load and deflection were investigated. Moreover, a finite element models were developed by ANSYS (version 14) to simulate all the tested specimens, experimental test results were compared with FE results obtained. The experimental results showed that both strengthening systems applied in this research were remarkably increased the beam strength, and the capacity retrieve of beams without openings. This study approved that steel links technique gave more prominent simplicity of use and low cost. FEM models were in good agreement with the corresponding experimental ones. However, the calculated ultimate loads were slightly higher than the experimental ultimate loads up to 10%.

Flexural behaviors and capacity prediction on damaged reinforcement concrete (RC) bridge deck strengthened by ultra-high performance concrete (UHPC) layer

Abstract Based on strengthening a damaged bridge deck in the field, this paper conducted flexural experiments on a scaled damaged bridge deck strengthened by reinforced ultrahigh performance concrete (UHPC) layer with high temperature steam and normal temperature curing; this paper investigates cracking capacity, ultimate capacity, deformation features and failure mode of RC-UHPC composites under positive bending moment and negative bending moment, respectively. Experimental results indicate that cracking and ultimate capacity of composites increased by about 2.5 and 2 times respectively with UHPC located at tension face comparing with intact RC slab; while for UHPC at compression face, no change in cracking capacity was observed and ultimate capacity was 30% higher than that of intact RC slab. Meanwhile, stiffness also obviously increased with tensile stress in steel reinforcement in RC slabs, decreasing after strengthening for all strengthened slabs; and propagation of cracks in RC slabs was restrained and delayed due to ultrahigh ductility and behavior of strain hardening of UHPC. Based on experimental results and failure mode, analytical equations for cracking and ultimate flexure capacity of UHPC-RC slabs were constructed, and applicability of equations was validated by some experimental results in this paper and other literature with good accuracy by predicted equations. Finally, the research achievements of this paper were effectively applied on the reinforcement design of damaged deck of main girder in a cable-stayed bridge.

Experimental Analysis of Shield TBM Tunnel Lining Mechanical Behaviour in an Anisotropically-Jointed Rock Mass

Jointed rock masses represent a challenging geological environment for tunnel boring machine (TBM) tunneling at great depth. Especially in the case of rock masses that have anisotropic strength and deformation characteristics, the segmental lining is susceptible to asymmetrical loading and local instabilities during tunneling. This paper presents the results of experimental tests and numerical simulations of the interaction between an anisotropic rock mass and the segmental lining of a tunnel. In the tests, we considered different lateral pressure coefficients (σh/σv), joint dip angles, and joint spacings. In the numerical simulations, different joint cohesions, friction angles, and tensile strengths were considered in order to study the effects of joint mechanical parameters on the behaviour of the liner and to evaluate quantitative trends of this effect on the liner. We studied the internal force, deformation, and fracture of the segmental lining. It was shown that, under isotropic in situ stress (σh/σv, = 1), the anisotropy of the rock masses was a major control on the deformation and damage of the liner, with the maximum positive bending moment and tensile cracks on the liner developing mainly at the direction normal to the stratification. When loaded by increasingly anisotropic in situ stress states (σh/σv > 1), the deformation of the liner and the characteristics of the damage were observed to become increasingly influenced by the major principal stress and, correspondingly, less controlled by the anisotropy of the rock structure. The smaller joint spacing tended to induce larger rock mass pressure on the liner, thereby resulting in greater internal force and deformation of the liner. According to the results of the numerical simulations, the internal force on the liner and its deformation increased markedly with decreasing joint friction angle and cohesion values. The response of the internal force and deformation of the liner to the change in the joint tensile strength was relatively small.

A Novel Separation Technique of Flexural Loading-Induced Acoustic Emission Sources in Railway Prestressed Concrete Sleepers

This study determines the effectiveness and suitability of acoustic emission in order to monitor the structural health condition of railway pre-stressed concrete sleepers since the acoustic emission sensing provides effective means for detecting cracking events and quantifying the crack density. The aim of this study is two-fold. First, we establish a novel acoustic emission source separation that offers the possibility for analyzing the content of each source separately. This study is thus the first to demonstrate that these sources can be separated from each other by employing a classification algorithm based on decision trees. Hence, a technically sound decision can be made regarding the severity of the damage and appropriate measures can be taken. Second, the paper presents a new method for compressing the essential acoustic emission information of the loaded structure for further post-processing. Data compression of 70 % with respect to the full set of features is achieved through the elimination of those acoustic emission signatures that yield the largest mutual correlation with other signatures. The reduced set of acoustic emission signatures (only two uncorrelated features) still possesses the essential information of structural health of the structure of interest at a cost of a relatively small drop in classification accuracy from around 96% to 84%. The proposed method is validated experimentally on full-scale pre-stressed concrete sleepers under positive and negative bending moment configurations under static three-point bending tests, which correspond to anticipated failure modes at rail seats by industry.

Structural analysis of classical guitar during the technological processing

The paper presents the structural analysis of the classical guitar during the mechanical processing of the neck and the guitar body. Thus, after each technological operation, the deviation from the flatness of the body and the neck of the guitar was measured, in order to explain the causes that caused the structural changes. From the point of view of the deformations recorded they were grouped in the following categories: non-deformed subassemblies; samples with deformations in 12 fret area (positive bending neck); sub-assemblies with deformations in the nut area (negative bending). From the point of view of the bending of the guitar body in the area of the bridge, it is found that all the samples have deformed top plates in the area of the bridge.

Experimental study on ferritic stainless steel trapezoidal decks for composite slabs in construction stage

The use of composite floor slabs is well established and provides an opportunity to promote the use of visually exposed composite slabs. Stainless steels, with the combination of good mechanical properties and excellent corrosion resistance, are key to this strategy, specially ferritic stainless steels, whose price is lower and more stable than that corresponding to the more widely used austenitic grades, due to their low nickel content whilst still maintaining good mechanical properties and aesthetic appeal. In addition, the emissivity of these grades contributes to lowering the heating and cooling requirements of buildings, reducing the costs associated to maintenance. Generally used as cold-formed members with high resistance-to-weight ratios, stainless steel decks are slender and highly sensitive to buckling phenomena and so the study of the structural performance of composite slabs using ferritic stainless steel decking is required due to the complex nonlinear behaviour of stainless steels, which is very different from that exhibited by carbon steel. Thus, this paper presents a comprehensive experimental programme on ferritic stainless steel trapezoidal decks for composite slabs under several structural configurations occurring during construction stage: simply supported decks under positive and negative bending moment, continuous decks and internal and end support tests. All the experimental results have been compared with the predicted ultimate loads in EN 1993-1-4, which remits to EN 1993-1-3 for carbon steel, and also with some previous tests on galvanized carbon steel decks. The paper concludes that EN 1993-1-3 provisions are applicable to ferritic stainless steels.

Analysis of the behaviour of a novel support system in an anisotropically jointed rock mass

When constructing an excavation, the segmental lining installed in an anisotropic rock mass is susceptible to asymmetrical pressure and substantial local instabilities. To promote liner stability in such cases, a support system that combines a segmental lining with a highly deformable expanded clay and rock bolts is proposed. A series of physical model tests were performed to study the effect of this support system. In the tests, different dip angles of the primary rock mass jointing, different thicknesses of the expanded clay and different lengths and spacings of rock bolts were considered. Variations in the internal forces and deformation of the segmental lining were recorded in each case. The distribution of the internal forces and deformation of the segmental lining were anisotropic due to the rock mass anisotropy; the maximum positive bending moment and positive deformation on the liner mainly developed in the direction normal to the stratification. By using a sufficiently thick deformable clay layer, the anisotropy of the load transferred to the segmental liner can be minimized. By adding rock bolts, the combined support system can take full advantage of the reinforcement effect of the rock bolts and the yielding effect of the deformable clay layer, and the effect of the rock bolts plus the yielding layer is greater than the sum of the two individual effects. Such a system can change the internal force and deformation distribution of the segmental lining to improve liner stability.

Flexural strength evaluation of concrete-filled steel tube (CFST) composite girder

The flexural strength of the concrete-filled steel tube (CFST) composite girder was investigated in this study. Firstly, simple equations to evaluate the flexural strength of the CFST composite girder under both positive and negative bending moment were derived based on the plastic stress distribution method (PSDM). A series of tests was then conducted to verify the accuracy of the proposed equation, and to investigate the effect of internal shear connectors between the steel tube and concrete infill. Further, non-linear finite element analysis for each test specimen was performed to demonstrate the failure mechanism, and to set up the verified finite element analysis model. From the results, it was found that the proposed equations provided a reasonably conservative prediction of the flexural strength of the CFST composite girder under both positive and negative bending moment, and the effect of internal shear connectors between the steel tube and concrete infill on the flexural strength was negligible. A series of parametric studies was performed to investigate the effect of the D/t ratio, compressive strength of the concrete infill, and local buckling of the steel tube on the flexural strength of the CFST composite girder. Finally, some design considerations are noted based on the results of the parametric study.

Experimental study of steel-timber composite (STC) beam to steel column joints having a flush end-plate

In recent published works, the feasibility and composite action of steel-timber composite (STC) systems have been demonstrated through push-out tests on STC joints and bending tests on STC beams subjected to sagging (positive) bending moment. However, the behaviour of STC beams subjected to negative bending moments, where the comparatively high tensile strength of the timber slab (compared to a concrete slab) can significantly increase the bending moment capacity and stiffness of STC beam-to-column joints, remains unexplored. Accordingly, this paper investigates the negative bending moment capacity, stiffness and the rotational capacity of STC beam-to-column joints with flush end-plates. Six full-scale STC beam-to-column cruciform joints were fabricated and subjected to monotonically increasing static loading up to failure. The cross-laminated timber (CLT) slab width, the connection type between the CLT panels across the column (either steel plate or gluing) and degree of composite action between the CLT-slab and the steel beam were the main variables considered in the experimental program. It is shown that the composite action between the CLT-slabs and steel beam has a minor influence on the negative bending capacity and initial stiffness of the beam-to-column connection, but the type of CLT slab-to-CLT slab connection (spline with steel plate and/or glued butt joint) has a major influence on the structural behaviour of the STC beam-to-column connections.

Force redistribution of steel moment-resisting frame retrofitted with a minimal disturbance arm damper

This paper presents an experimental investigation of a multi-span steel frame retrofitted with a minimal disturbance arm damper (MDAD). The primary objective of the paper is to analyze and verify the retrofit mechanism in terms of force redistribution. An elastic design of the MDAD, targeting the reduction of the positive bending moment at beam ends was first developed for the seismic rehabilitation of steel frames having a beam-collapse mechanism. Here, the composite beams under positive bending sustain tensile force at the bottom flanges. Its effectiveness was examined experimentally and numerically. This study also explored the effect of the MDAD on delaying the fracture of the beam ends. Particularly, the behavior of the retrofitted steel frame after the fracture of beam ends was majorly focused. By comparing the test results of specimens with and without MDAD, it was found that the MDAD successfully reduced the positive bending moment of the beam ends as intended in the proposed design equation and delayed the fracture. The retrofitted substructure did not exhibit strength deterioration even after beam end fracture because of the backup load resistance provided by the MDAD. Finally, enhancement of the collapse limit by the MDAD is discussed through numerical simulations for a moment-resisting steel frame.

Modelling and experimental validation of the effect of the elastic properties of fabrics on the durability of screen printed e-textiles

Fabrics are stiff in tension but highly compliant in compression in the plane of the textile. The effect of these differing elastic properties on the durability of electronics integrated in or on the fabric is still largely unknown because fabric properties are not easily characterised. Using a mathematical model combining classical beam theory (CBT) and Pierce’s fabric cantilever test, this paper models the bending behaviour of a woven fabric and locates its neutral axis (NA) as a basis for developing more durable printed e-textiles. The CBT model showed that the difference in the tensile and compressive moduli of a fabric reduces the bending resistance of the fabric and also moves its NA position away from the central axis on the fabric. Results obtained from a Pierce’s bending test of four different textile blends of polyester, cotton and lycra indicate textiles can have anisotropic elastic moduli with different values in their warp and weft directions. This results in different NA positions that vary depending upon the direction of the bending forces. Empirical verification of these NAs was achieved by comparing the change in resistance of a set of screen printed piezoresistive strain gauges positioned on and away from the NA during positive and negative bending with a radius of 5 mm. The gauge positioned at a 1% distance from the NA position showed approximately 0.3% change in its electrical resistance in contrast to a 37% change in its resistance when it was located at a 65% distance away from the NA.

Carbon Fiber and Structural Timber Composites for Engineering and Construction

There are environmental and potential economic advantages in using laminated veneer lumber (LVL) for building structures, but load-carrying capacity constrains uptake. Building on previous work in the field, the authors test the strategic placement of carbon fiber-reinforced polymer (CFRP) to improve the flexural strength of timber beams, investigating both positive and negative bending moments of structural assembly. The results demonstrate: unidirectional CFRP applied as a U-wrap on the tension side of beams improves load carrying by 25%, stiffness by 20%, and ductility by 30%; a combination of uni- and bidirectional CFRP mesh applied to beam-column joints with no other connectors achieves substantial structural continuity between beams. U-wrap reinforcement also shifts the mode of failure from abrupt to gradual. Another significant observation is that wood splinters appear to cause premature failure, and we consider solutions to this issue. Discussion of the outcomes for advancing the uptake of timber as a more sustainable structural material are undertaken, along with an outline of further work.

Finite Element Analysis of Weak-Axis Composite Connections Under Cyclic Loading

This paper describes a numerical study on weak-axis composite connection through the nonlinear finite element program ABAQUS. After the simulation and validation of experimental results, a total of 16 models were created to investigate the influence of the different parameters on the structural performance, and their hysteresis responses, rupture index distribution of beam flange welds were discussed in detail. The RBS connection scheme could develop extensive inelastic deformation in RBS region, thus reducing the weld rupture possibility. The thicker the concrete slab, the larger the bending moment under positive bending, and the higher the RI values at the beam bottom flange weld and also the neutral axis. The structural behavior was insensitive to the variation of the parameter reinforcement ratio as the reinforcements did not work well, and it is recommended to arrange reinforcements according to the construction requirements. Changing the weld access hole form has a little influence on the bearing capacity and rotation capacity, but the PEEQ and RI distributions are sensitive to this parameter. The design option of long access holes could provide a further means to reduce the fracture possibility of beam flange groove weld to a reasonable level, thus achieving a favorable performance of weak-axis column bending connections in a composite moment-resisting frame.

Effects of the impeller blade geometry on the performance of a turbo pneumatic separator

This paper mainly presents an analysis of the effects of the impeller blade geometry on the performance of a turbo pneumatic separator based on the CFD simulations by using Fluent 14.5.0. The simulation results indicate that the air vortex can be eliminated by using the positive bending arc blades with a remarkably small impacting angle. Furthermore, the optimum installation angle range for the positive bending arc blades was studied. The material classification experiment results show that for the positive bending arc blades with the optimum installation angles, the fishhook depth is decreased, the classification accuracy is increased, and the particle size distribution of fine powders is narrowed, especially under the design condition, compared to the straight blades. This suggestion of impeller blade geometry for the turbo pneumatic separator is the important basis for designing this type of separators and improving its classification performances.