Positive Bending Research Articles

Highly stable flex sensors fabricated through mass production roll-to-roll micro-gravure printing system

A highly stable low cost flex sensor has been fabricated in this research work using micro-gravure mass production roll-to-roll printing system. The active layer was fabricated on PET substrate using composite of Activated Carbon with PVDF. PVDF has been added as a binding agent to improve the mechanical stability of the active layer. Protective coating of PVAc was deposited on top of active layer using the same system. The sensors’ electrical and morphological characterizations were performed to find out the surface characteristics and response of the sensors towards various bending angles. Results show promising response of both the protected and un-protected sensors towards positive and negative bending. Sensors with different lengths and widths were tested for both types and the best recorded response for protected sensors was 2.3MΩ to 3MΩ to 3.6MΩ for −120° to 0° to 120° bend while for non-protected sensors was 0.25MΩ to 0.4MΩ to 0.55MΩ for −120° to 0° to 120° bend. Protective coating caused increase in the overall sensor resistance thus reducing the operating power of the device. Also, increasing the sensor width decreases the resistance and so does reducing the length. The sensors were mounted on a glove and the results indicate stable and accurate operation.

Precast Pearl-Chain concrete arch bridges

A Pearl-Chain Bridge is a closed-spandrel arch bridge consisting of a number of straight pre-fabricated so called Super-Light Deck elements put together in an arch shape by post-tensioning cables. Several Pearl-Chain arches can be positioned adjacent to each other by a crane to achieve a bridge of a desired width. On top of the arch is a filling material to level out the surface of the above road. The filling only transfers vertical loads to the arch.The geometry and material properties of Super-Light Decks are presented, and we refer to several full-scale tests of Pearl-Chain arches where the technology was used. We also study other important components and details in the Pearl-Chain Bridge concept and review the effects of different types of loads.A theoretical case study of a circular 30m span Pearl-Chain Bridge is presented showing the influence of a number of parameters: The number of post-tensioning cables, the rise to span ratio, the height of the filling, and the height of the Super-Light Decks. We find that Pearl-Chain Bridges can be adjusted to resist specific moment loads by changing the normal force in the arch cross section by altering the above parameters. It is also found that the negative bending moment capacity starts decreasing before the positive bending moment capacity does, when the normal force in the cross section is increased. This is because of the cross section of the Super-Light Decks include a combination of normal concrete and light aggregate concrete with light aggregate concrete blocks in the bottom of the cross section.The positive bending moment capacity is therefore often larger than the negative, and that corresponds well with the required capacities when a concentrated load close to the quarter point of the span is applied. Such load is critical for arches, and gives a large positive bending moment below the load and a smaller negative bending moment in the unloaded side.When the Pearl-Chain Bridge concept is compared to other pre-fabricated arch bridge solutions we find a number of advantages when using Pearl-Chain Bridges: Straight elements, combination of normal concrete and light aggregate concrete, flexible design control, and joint details.

Fatigue behavior of GFRP and steel reinforced bridge decks designed using traditional and empirical methodologies

In this research study, experimental behavior of two full-scale bridge decks, one each reinforced with steel and GFRP, and subjected to fatigue loading is investigated. Reinforcement is provided as required by traditional (TR) and empirical (EM) design methodologies on each transverse half of each deck. The decks are subjected to load cases corresponding to an HS25 truck axle positioned for critical positive and negative bending. Measured response before, during and after the two million cycles of fatigue loading per load case is used to evaluate compliance with serviceability limits on crack-width, deflection and material stress. For the GFRP reinforced deck, results show both TR and EM are compliant with allowable limits, and that the EM load-sensor slope response is measurably less than the TR for like load cases. Similar results were found for the steel reinforced deck. Importantly, the study validates the EM design methodology for use with GFRP reinforced concrete bridge decks.

Moment redistribution of continuous composite I-girder with high strength steel

【The continuous composite I-girder should have a sufficient rotation capacity (or ductility) to redistribute the negative bending moment into an adjacent positive bending moment region. However, it is generally known that the ductility of the high strength steel is smaller than that of conventional steel, and application of high strength steel can cause ductility problems in a negative moment region of the I-girder. In this study, moment redistribution of the continuous composite I-girder with high strength steel was studied, where high strength steel with yield stress of 690 MPa was considered (the ultimate stress of the steel was 800 MPa). The available and required rotation capacity of the continuous composite I-girder with high strength steel was firstly derived based on the stress-strain curve of high strength steel and plastic analysis, respectively. A large scale test and a series of non-linear finite element analysis for the continuous composite I-girder with high strength steel were then conducted to examine the effectiveness of proposed models and to investigate the effect of high strength steel on the inelastic behavior of the negative bending moment region of the continuous composite I-girder with high strength steel. Finally, it can be found that the proposed equations provided good estimation of the requited and available rotation capacity of the continuous composite I-girder with high strength steel.】

English

The most implementable and favorable technique, used for the flexural strengthening of reinforced concrete (RC) beams is the attachment of external steel members. Attachment of external steel sections or fiber reinforced polymers is considered as a common technique used for the enhancement of flexural capacity of the existing structural elements. To investigate and evaluate the flexural capacity of reinforced concrete beams, strengthened with external steel bars, a research study was carried out and is presented in this paper. Three reinforced concrete beams reinforced with minimum reinforcement ratio were constructed and tested. Two beams were strengthened by attaching external steel bars with bottom layer of shear reinforcement and one specimen without external steel bars was tested as control sample. The area of reinforcement to be provided as external steel bars was calculated on the basis of maximum steel ratio as per the ACI (318-08) 10.3.5. Welding was used for the attachment of the external steel bars to the existing shear reinforcement. All the three beams were tested in positive bending under third point loading as per the ASTM C78/C78M-10. Test result shows that great enhancement in strength capacity and better distribution of cracks may be achieved by using this technique of flexural strengthening of beam.

Behaviour and design of composite beams subjected to sagging bending and axial compression

This paper presents an experimental and numerical study on the ultimate strength of steel–concrete composite beams subjected to the combined effects of sagging (or positive) bending and axial compression. Six full-scale composite beams were tested experimentally under sagging bending and increasing levels of axial compression. A nonlinear finite element model was also developed and found to be capable of accurately predicting the nonlinear response and the combined strength of the tested composite beams. The numerical model was then used to carry out a series of parametric analyses on a range of composite sections commonly used in practice. It was found that the sagging moment resistance of a composite beam is not reduced under low-to-moderate axial compression, while it significantly deteriorates under high axial compression. Sectional rigid plastic analyses confirmed the experimental results. The moment–axial force interaction does not change significantly between full and partial shear connection. Based on the experimental and numerical results, a sagging moment–axial compression interaction law is proposed which will allow for a more efficient design of composite beams.

Long Term Field Test on Structure Forces of Sheet-Pile Wharf with Barrier Piles

Tan, H.; Jiao, Z., and Cai, Z., 2015. Long term field test on structure forces of sheet-pile wharf with barrier piles.Based on the first engineering application of new-type sheet-pile wharf with barrier piles, the field test has been conducted for 7 years. According to the long term field testing results, the structure forces of the wharf front wall and barrier piles have been obtained in different periods. The results have showed that the new wharf structure was effective for a large harbor basin, the maximum positive bending moments for both front wall and barrier piles appeared in dredging period, and the maximum negative bending moment appeared in operation period. The rebar stress of front wall was about twice larger than that of barrier piles. In order to make full use of the potential bearing capacity of front wall and barrier piles, the optimal design was to make them in the same stress level. The modified bending moment calculation method has been proposed based on the field testing data.

Mechanical Stress Dependence of the Switching Field in Amorphous Microwires

Glass-coated magnetic microwires belong to a unique rank among materials that have high potential to be used in new technologies. We have studied the possibility to employ amorphous bistable microwires as a sensor for bending of carbon fiber composite. The measurement of switching time instead of switching field drastically increases the sensitivity of such sensors up to 380% for positive bending and 125% for negative bending. The results show that microwires applied on the surface structures of the materials can be used as sensors of mechanical stresses or bending.

Optimization of Stay Cables in the Double-Set Arch Pylon Cable-Stayed Bridge

The determination of post-tensioning cable forces is one of the most important issues for the design of arch pylon cable stayed bridge. In this paper, the optimization module implemented in MATLB, together with the commercial finite element software MIDAS, were employed to evaluate the minimum bending strain energy of the bridge. After optimizing the cable forces, the bending moment of the pylons were bigger than the values of original design. The bending moment of the main arch pylon within 55m to 70m height increased by 7280 kN•m, and the bending moment of the auxiliary arch pylon within 30m to 60m height increased by 3926 kN•m .The stress of the pylons was still far below the allowance value when the obtained cable forces were applied. However, for the girder, the difference between the maximum positive and maximum negative bending moments due to dead load can be lessened greatly by the application of the obtained cable forces. The results obtained revealed that the method presented could make full use of cable forces and lead to optimal structural performance.

Review of HL-93 Bridge Traffic Load Model Using an Extensive WIM Database

HL-93, the current bridge traffic load model used in the United States is examined here. Weigh-in-motion (WIM) data from 17 sites in 16 states containing 74 million truck records are used to assess the level of consistency in the characteristic load effects (LEs) implied by the HL-93 model. The LEs of positive and negative bending moments and shear force are considered on single- and two-lane same-direction slab and girder bridges with a range of spans. It is found that the ratio of WIM-implied LE to HL-93 LE varies considerably from one LE to another. An alternative model is proposed that achieves improvements in consistency in this ratio for the LEs examined, especially for the single-lane case. The proposed model consists of a uniformly distributed load whose intensity varies with bridge length. © 2014 American Society of Civil Engineers.

Mechanical behavior of steel-concrete composite decks with perfobond shear connectors

Exodermic deck systems are new composite steel grid deck systems which have been used in various projects during the past decade. One of the eminent features of this system is considerable reduction in the structure weight compared to the ordinary reinforced concrete decks and also reduction in construction time by using precast Exodermic decks. In this study, dynamic properties of the Exodermic deck bridges with alternative perfobond shear connectors are investigated experimentally. In order to evaluate the dynamic properties of the decks, peak picking and Nyquist circle fit methods are employed. Frequencies obtained experimentally are in good agreement with the results of the finite-element solution, and the experimental results show that the first mode is the most effective mode among the obtained modes. The first four modes are the rigid translational motion modes, and the next two modes seem to be rigid rotational motion modes around a horizontal axis. From the 7th mode onwards, modes are flexible. The range of damping ratios is about 0.5%. Furthermore, the static behavior of the Exodermic decks under a static load applied at the center of the decks was investigated. Failure of the decks under positive bending was punching-shear. The bending strength of the decks under negative bending was about 50 percent of their strength under positive bending. In addition, the weight of an Exodermic deck is about 40% of that of an equivalent reinforced concrete slab.

The Effective Width in Composite Steel Concrete Beams at Ultimate Loads

A composite section is made up of a concrete slab attached to a steel beam by means of shear connectors. Under positive and negative bending moment, part of the slab will act as a flange of the beam, resisting the longitudinal compression or tension force. When the spacing between girders becomes large, it is evident that the simple beam theory does not strictly apply because the longitudinal stress in the flange will vary with distance from the girder web, the flange being more highly stressed over the web than in the extremities. This phenomenon is termed "shear lag". In this paper, a nonlinear three-dimensional finite element analysis is employed to evaluate and determine the actual effective slab width of the composite steel-concrete beams by using theAnalysis System computer program (ANSYS 11.0). The of elements were used (SOLID65, LINK8, SHELL143, COMBIN39, TARGE170 andCONTA174) to model the concrete slab, the steel reinforcing bars, the steel girder, the shear connectors (including uplift and dowel action), and the interface between top flange of the steel girder and concrete slab, respectively. Comparisons with experimental tests have been performed to validate the finite element analysis results. In general, excellent agreement between the finite element solution and the experimental results has been obtained. The maximum difference in ultimate load is about (2.9%). Finally, parametric studies have been carried out to investigate the effect of some important parameters; these parameters include the degree of interaction, slab thickness, slab width, concrete compressive strength ( ), distribution of shear connectors, reinforcement of slab, type of loading, and boundary conditions. The effect of changing these parameters causes variety in the effective slab width and the maximum stress reaches 40.7% and 28.5%, respectively.

The Best Position to Determine the Hinge in the Cantilever Bridge

The simple-supported beam bridge is a common structure form widely used in small and medium span bridges. When the span is longer, the maximum bending moment is accordingly bigger. The maximum positive and negative bending moment numerical of beam decreases obviously because of cantilever bridge with cantilever beams to reduce the amount of materials. This article analyzes the current commonly used cantilever bridge with large span. The two-span cantilever bridge is analyzed under various loads about the internal force according to the condition of the absolute value of the maximum positive and negative bending moment being equal. It carries on the contrast and analysis about simple-supported beam bridges and obtains the best location of the hinge in the cantilever bridge. Moreover, it provides some reference for the optimum design of similar bridges and projects.

Performance of a lightweight GFRP composite bridge deck in positive and negative bending regions

This paper presents results from an experimental and analytical study of a newly developed lightweight composite bridge deck system composed of pultruded trapezoidal GFRP tubes and outer wrap. Panels with different grout materials and grouting patterns were evaluated and compared in terms of flexural stiffness. Two-span tests were performed on non-grouted and epoxy grouted panels to simulate a multi-girder bridge configuration and to evaluate their structural behavior in both positive and negative bending regions. Test results showed that the epoxy grouted panel meets the AASHTO deflection requirement (L/800) and performed well under service loads. An analytical model was developed to predict the load–deflection response of grouted and non-grouted panels at incremental load steps, even beyond the uncracked stage. The proposed model shows that shear deformation must be considered in order to accurately predict the behavior of GFRP panels in multi-girder bridges.

Nanoscale observation of surface potential and carrier transport in Cu2ZnSn(S,Se)4 thin films grown by sputtering-based two-step process

Stacked precursors of Cu-Zn-Sn-S were grown by radio frequency sputtering and annealed in a furnace with Se metals to form thin-film solar cell materials of Cu2ZnSn(S,Se)4 (CZTSSe). The samples have different absorber layer thickness of 1 to 2 μm and show conversion efficiencies up to 8.06%. Conductive atomic force microscopy and Kelvin probe force microscopy were used to explore the local electrical properties of the surface of CZTSSe thin films. The high-efficiency CZTSSe thin film exhibits significantly positive bending of surface potential around the grain boundaries. Dominant current paths along the grain boundaries are also observed. The surface electrical parameters of potential and current lead to potential solar cell applications using CZTSSe thin films, which may be an alternative choice of Cu(In,Ga)Se2.PACS number: 08.37.-d; 61.72.Mm; 71.35.-y

Flexural Resistance and Ductility Ratio of Composite Hybrid I-Girder using HSB High Performance Steel in Positive Bending

In this study, flexural strength and ductility requirements of composite hybrid steel I-girder with its HSB(high performance steel for bridge) applied to tension flanges are examined in positive bending. In AASHTO LRFD specification, flexural strength and ductility requirements of composite I-girder in positive bending are specified in terms of plastic moment and plastic neutral axis that are derived from plastic behavior of conventional steel. However, plastic zone cannot be defined clearly from the stress-strain behavior of HSB unlike the behavior of conventional steel. Therefore, through idealized stress-strain curves of HSB, the plastic moment of composite hybrid steel I-girder with its HSB applied to tension flanges is defined by assuming the plastic zone of HSB. By using the consequences of numerical analysis regarding arbitrary cross-sections that have various dimensions, ductility requirements and flexural strength of composite hybrid I-girder with its HSB applied to tension flange are proposed. Keywords - High performance steel, Positive bending, Flexural strength, Ductility ratio, Composite hybrid I-girder, HSB800

Investigation of alternative technologies for cast-in-place concrete bridge decks

Concrete bridge decks are designed using traditional methodology (TM) or empirical methodology (EM). TM models the deck as a continuous beam in flexure, and EM recognizes the compressive membrane action that aids in distributing wheel loads. An extension of membrane behavior is complete removal of reinforcement from within the deck; this is referred to as steel free deck (SF). In this research study three full-scale bridge decks are investigated, one reinforced with steel, a second is reinforced with glass fiber reinforced polymer (GFRP), and a third is SF. For each the steel and GFRP reinforced decks, the south and north sides are reinforced as required by the TM and EM, respectively. The SF deck is based on research done in Canada. Each deck is subjected to four load cases, corresponding to an AASHTO truck axle positioned for critical positive and critical negative bending on each the north and south sides. Measured response for crack width, deflection, and concrete strain is used to evaluate behavior at the service limit state.

Fixing the Energy Scale in Scanning Tunneling Microscopy on Semiconductor Surfaces

In scanning tunneling experiments on semiconductor surfaces, the energy scale within the tunneling junction is usually unknown due to tip-induced band bending. Here, we experimentally recover the zero point of the energy scale by combining scanning tunneling microscopy with Kelvin probe force spectroscopy. With this technique, we revisit shallow acceptors buried in GaAs. Enhanced acceptor-related conductance is observed in negative, zero, and positive band-bending regimes. An Anderson-Hubbard model is used to rationalize our findings, capturing the crossover between the acceptor state being part of an impurity band for zero band bending and the acceptor state being split off and localized for strong negative or positive band bending, respectively.

Preventive maintenance on welded connection joints in aged steel railway bridges

Structural repairing or maintenance technique has been a hot issue in recent years due to the increasing aging problems of old railway bridges. A strengthening method for welded joints in old steel railway bridges by integrating the rapid hardening concrete, rubber-latex mortar, and reinforcing bars is introduced in this paper. The purpose of the present study is to investigate the mechanical performance of the strengthened connection joints in old steel railway bridges. Depending on the locations of the concrete and possible loading conditions, the joint needs to sustain both negative and positive bending moment, therefore, two experimental plans were employed. The static loading tests on the steel joints before and after strengthening were performed to confirm the effects of the present strengthening method. Moreover, three-dimensional FE models were built to make a comparison study between the strengthened and original steel joints. Load versus deflection relationship and strain development process on the web of the joints were measured and compared between the original joints and the strengthened joints. Both experimental and numerical results indicate that the present strengthening method can greatly enhance the stiffness and reduce the stress levels of steel joints, resulting in the extension service life of aged steel railway bridges.

Design and Construction of Low Temperature Attachment for Commercial AFM

With the rapid advancements in the field of nanoscience and nanotechnology, scanning probe microscopy has become an integral part of a typical R&D lab. Atomic force microscope (AFM) has become a familiar name in this category. The AFM measures the forces acting between a fine tip and a sample. The tip is attached to the free end of a cantilever and is brought very close to a surface. Attractive or repulsive forces resulting from interactions between the tip and the surface will cause a positive or negative bending of the cantilever. The bending is detected by means of a laser beam, which is reflected from the backside of the cantilever. Atomic force microscopy is currently applied to various environments (air, liquid, vacuum) and types of materials such as metal semiconductors, soft biological samples, conductive and non-conductive materials. With this technique size measurements or even manipulations of nano-objects may be performed. An experimental setup has been designed and built such that a commercially available Atomic Force Microscope (AFM) (Nanosurf AG, Easyscan 2) can be operated at cryogenic temperature under vacuum and in a vibration-free environment. The design also takes care of portability and flexibility of AFM i.e. it is very small, light weight and AFM can be used in both ambient and cryogenic conditions. The whole set up was assembled in-house at a fairly low cost. It is used to study the surface structure of nanomaterials. Important perovskite manganite Pr0.7Ca0.3MnO3thin films were studied and results such as morphology, RMS area and line roughness as well as the particle size have been estimated at cryogenic temperature.