Lower Flange Research Articles

Assessment of Fiber Bragg Grating sensors for monitoring induced strains on the draft tube cone of hydraulic turbines

Abstract In hydraulic turbines, several flow instabilities can take place inside the draft tube cone during off-design and transient operating conditions such as the rotating vortex rope which can severely damage the structure if sustained in time. In the frame of the AFC4Hydro H2020 research project, an extensive measurement campaign has been carried out to monitor and predict this rotating vortex rope phenomenon in a reduced scale Kaplan turbine model at the Vattenfall Research and Development facility in Älvkarleby, Sweden. The hydraulic turbine model has been operated in propeller mode with a fixed blade angle corresponding to its best efficiency point. Several sensors have been placed along the test stand to monitor vibrations, strains and pressures. Concretely, the present paper assesses the performance of using Fiber Bragg Grating sensors to measure the strains induced on the draft tube cone walls with high-spatial resolution in three different zones of influence: the upper and lower flanges and the vertical cone wall between the runner outlet and the elbow. To do so, a total of 3 arrays embedding a total of 48 Fiber Bragg Grating sensors were glued inside three grooves previously machined on these particular areas of the draft tube cone. Analysing the frequency response of the different Fiber Bragg Grating sensors, the strain patterns induced by the rotating and plunging components of the rotating vortex rope have been precisely determined. Moreover, their impacts at the different part load conditions tested have also been quantified.

Structural Behavior Castellated 2C Cold-Formed Steel Beams

This study's primary objective is to examine the structural behavior of using 2C-Cold produced. Section Castellated beams when subjected to monotonic load till failure. The experimental program testing. Seven Fabricated samples of castellated steel beams and one sample, which is a non-castellated steel beam (reference beam), were tested as supported beams under concentrated loads at two points over a clear span length (1730 mm). All castellated steel beams were similar in all properties and dimensions except the breadth of the upper and lower flanges. The current study considers the implications of modifying the width of the top and bottom flanges on how these beams behave. The findings showed that the ratio of the tested Castellated beams' ultimate load-carrying capacity to the non-castellated reference beam (R1) ranged from 99.3 to 117.2%, and the ratio of the tested beams' ultimate deflection to the same reference beam (R1) ranged from 72.6 to 103.2%. Increasing the breadth of the top and bottom flanges has a direct relationship with castellated beam stiffness and ultimate load. Finally, adjusting the flange width between the top and bottom flanges reduces castellated beam rigidity and ultimate load.

Buckling Strength Analysis of Railway Plate Girder Bridge According to the Transverse Reinforcement at the Lower Flange

Buckling Strength Analysis of Railway Plate Girder Bridge According to the Transverse Reinforcement at the Lower Flange

Shear Lag Analysis of Simply Supported Box Girders Considering Axial Equilibrium and Shear Deformation

The conventional methods used to analyze the shear lag effect in simply supported box girders assume that the neutral axis of the section coincides with the centroid, which does not strictly satisfy the axial equilibrium condition. To address this problem, this study proposes an analysis method in which three independent functions for the shear lag are employed to define the different shear lag strengths of the top slab, the bottom slab, and the cantilever slab. To fulfill the axial equilibrium condition of the box girder and to automatically locate the neutral axis position, the longitudinal displacement of the web is introduced. The shear deformation of the box girder is also considered. The governing differential equations and corresponding boundary conditions for displacement variables such as deflection and rotation of the box girder are derived through the application of the principle of virtual work. The differential equations are solved by utilizing the boundary conditions to obtain the analytical expressions of the shear lag function, longitudinal displacement of the web, rotation, deflection, and neutral axis position. Furthermore, after performing the finite element analysis, the effectiveness of the proposed method is verified by comparing the results with those obtained from conventional methods and finite element analysis. Furthermore, the influence of the axial equilibrium condition is quantified on axial force and stress difference ratios under three methods. Finally, extensive parametric analysis is carried out to investigate the effect of different parameter ratios on the ratios of the stress difference of the flanges. The results show that when the axial equilibrium condition is not considered, the axial stresses in the upper flange of the simply supported box girder are underestimated, especially at the intersection of the top, cantilever slab, and web, and the axial stresses in the lower flange are overestimated. As a result, the method in this study is able to calculate the axial stresses and deflections on simply supported box girders more accurately.

Shear Capacity of Channel Shear Connectors Applied in Composite Slabs with Profiled Steel Decking

AbstractThis paper assesses the shear capacity and the structural behaviour of channel connectors in composite slabs. Push‐out specimens were analyzed numerically by using the finite element program ABAQUS. For the studied solution, regular openings at the lower flange in the profiled decking are considered to allow the welded channel connector to pass through. The numerical model was calibrated against experimental outputs on push‐out tests found in the literature. Then, the influence of steel decking thickness on load capacity, stiffness and ductility of channel connectors in composite slabs was also assessed. In addition, it was concluded that safe predictions of load capacity could be obtained by including reduction factors in the Canadian design approach.

Improving seismic performance of fully welded connection based on truss beam segments

To enhance the seismic performance of fully welded connections (FWCs), the addition of truss beam segments to the upper and lower beam-end flanges has been investigated. This study focuses on two 2/3-scale cross-shaped substructures with an FWC and a fully welded connection with truss beam segments (FWCT). Through cyclic loading tests and detailed numerical simulations, the failure mode, hysteretic behavior, bearing capacity, ductility, strength and stiffness degradation, and energy dissipation capacity have been investigated. The results show that local cracks first appeared in the concrete slab around the column of the FWC specimen and that the lower flange at the beam root fractured eventually. Regarding the FWCT specimen, when the joint zone satisfies the shear strength requirement, a plastic hinge is formed at the beam end instead of in the joint zone, and the plastic hinge at the beam root propagates outward before eventually breaking at the beam flange. The hysteretic curves of both FWC and FWCT specimens present a spindle shape, whereas that of the FWCT specimen shows a fuller shape. The seismic performance of the FWC specimen is improved significantly by the truss beam segments. The initial stiffness, yield load, yield displacement, peak load, peak displacement, ductility coefficient, and cumulative total energy dissipation increased by 8.91%, 12.50%, 13.07%, 13.41%, 20.32%, 36.73%, and 138.53%, respectively. After the beam flange yielded, the truss beam segment and beam flange cooperated in terms of deformation and energy dissipation. When the beam flange failed, the truss beam segment continues to bear the load.

Experimental research on fire performance of U-shaped steel-concrete composite beam under uniformly distributed loading

Four U-shaped steel-concrete composite beams with channel connectors (CUSCBs) were designed and tested under the uniformly distributed vertical load and ISO-834 standard fire condition. The sectional temperature distribution, mid-span deformation development, fire resistance, and failure modes of each CUSCB under fire were investigated. The test results reveal the following facts: (1) All specimens fail flexurally; (2) The interface between the concrete flange and the U-shaped steel web remain intact and no local buckling occurs in U-shaped steel; (3) The concrete temperature decreases from the fired surface to the non-fired surface gradually; and (4) The temperature of the concrete at the corner between the lower flange and the web of U-shaped steel is higher than the concrete within the beam. Moreover, the fire resistance increases with the increase of fire protection layer thickness; and the bottom reinforcement in U-shaped steel can improve the fire resistance. The fire behavior of CUSCBs was also analyzed using the finite element program ABAQUS and the simulated temperature distributions and fire resistances were found to be in good agreement with the test results. Furthermore, the parametric analysis results show that the thickness of fire protection layer, the diameter of bottom reinforcement, the load ratio, and the thickness of U-shaped steel have significant impact on the fire resistance, while the section size and material strength have little impact. Lastly, design suggestions for the fire resistance design of CUSCBs are proposed.

Dynamic Behavior Analysis of I-Shaped RC Beams under Combined Blast and Impact Loads

The existing literature mainly focuses on the research of reinforced concrete (RC) beams under a single load such as blast or impact. In this paper, the slab–rib–slab RC beam, a new type of structure widely used in bridge structures, was taken as the research object. The explicit dynamic analysis software LS-DYNA was used to numerically analyze the dynamic response and failure behavior of I-shaped RC beams under combined blast and impact loads. For this reason, an effective numerical analysis model was obtained by carrying out experiments on I-shaped RC beams under contact explosion. The key factors affecting the dynamic response of the structure under combined loads were numerically analyzed. Numerical results showed that different load application sequences have important effects on the dynamic response of the structure. When the impact load was first applied to the structure, more severe concrete damage and deformation occured in the depth direction of the beam. However, when the blast load was first applied to the structure, the concrete at the lower flange was damaged in the span direction of the beam due to tension, and no large-scale concrete spallation occurred in the depth direction. This was mainly due to the different mechanisms of blast and impact loads. In addition, the vulnerability of the I-shaped RC beams varied with some structural parameters, including span, depth, and configuration of reinforcement. At the same time, the results showed that the structure is more sensitive to changes in structural parameters when it is first subjected to impact loads.

ОГНЕСТОЙКОСТЬ СТАЛЬНЫХ БАЛОК СТРОИТЕЛЬНОГО НАЗНАЧЕНИЯ

Приведены экспериментальные и численные исследования несущей способности стальных балок из сталей классов С255 и С355 при воздействии стандартного температурного режима пожара. Цель исследования - уточнение метода расчета предела огнестойкости изгибаемых стальных балок с учетом неравномерного распределения температуры в поперечном сечении, что позволит повысить точность расчетов и безопасность таких конструкций в практике строительства. The disadvantage of calculation and analytical methods for determining the fire resistance limits of building metal structures is the lack of practical information on the features of changes in the strength characteristics of the most common building steels at high exposure temperatures and the results of experimental studies to determine the bearing capacity of steel structures under fire exposure. For this purpose there were carried out studies of the strength characteristics of steels with rolled metal samples of C255 and C355 strength classes as well as empirical dependences of the change in the yield strength in the temperature range 20 °C < t < 700 °C were determined, which are necessary to calculate building metal structures for fire resistance. Experiments to determine the actual fire resistance of beams were carried out with class C255 rolled I-beams and class C355 welded I-beams. As controlled characteristic areas of steel temperature change there were taken the following items: the lower flange, the middle of the wall and the upper flange of the average I-section. Graphs of deformation (deflection) in the middle section of the beam under fire exposure are constructed. The calculation of fire resistance limit of bent steel beams was carried out taking into account the uneven distribution of temperature in the cross section. Comparison of experimental data and calculation results by means of the developed model, which takes into account the uneven heating of the section, showed their good agreement (up to 15 %) in terms of the loss of bearing capacity during three-sided heating under standard fire conditions.

Flexural behavior of composite beams with concrete filled steel tube flanges and honeycombed steel webs

Honeycombed beams are widely used because they are conducive to the layout of pipelines and circuits, and the traditional honeycombed beams are generally H-shaped steel beams and concrete-encased upper flange composite beams. In this paper, a composite beam with concrete-filled steel tube as both upper and lower flanges and steel plate with circular openings as web is proposed. The effective constraint of steel tube on concrete strengthens the deformation ability of concrete. In order to study the flexural behavior of composite beams with concrete filled steel tube flanges and honeycombed steel webs (SHC), 25 simply-supported SHC beams were designed to carry out the four-point bending load simulation analysis. By reasonable modeling method. The main parameters of SHC concluding the compression strength of concrete (fck), yield strength of steel (fyfk), height-to-span ratio (H/L), ratio of space to height of web (s/hw), thickness of steel tube flange (t1), thickness of web (t2) and ratio of hole to height of web (a/hw) were discussed, and the whole loading process of the beam was analyzed. The results showed that the SHC specimens could be divided into elastic stage, elastic-plastic stage and plastic stage under four-point bending load. Steel tube in the tensile zone yielded firstly before specimens failed, and the failure mode of the specimens was that the concrete at the loading point was crushed. Though the steel tube in lower flange at the support, loading point and mid-span yielded, the web did not buckle. SHC could meet the requirements of Chinese code in the normal use stage, and the cross-section deformation basically conformed to the plane assumption. Finally, based on the unified strength theory, a prediction formula of ultimate bending moment is established, which is in good agreement with experiment and can lay the foundation for the popularization and application of this kind of beams.

Blast resistance of prestressed steel-grouting composite beams under close-in explosions: Experiment and numerical analysis

To increase the blast resistance of reinforced concrete or steel–concrete composite structures with long span, an innovative prestressed steel-grouting material composite beam with a hollow web is proposed. In the beam, the flange is filled with grouting material, and an I-type steel web is used to strengthen the shear capacity, and a prestressed tendon is placed in lower flange to improve the flexure resistance. The following three specimens were designed: a double hollow tube, a double tube filled with grouting material, and a prestressed double tube filled with grouting material. The specimens were tested against close-in blast, and overpressure, deformation, and strain were recorded. In order to further understand the blast-resistant performance of the beam, a finite element model was developed by commercial software LS-DYNA. A good agreement between the numerical predictions and test data was observed. It is indicated that the proposed prestressed steel-grouting material composite beam with hollow web exhibits excellent blast-resistant performance.

Fire resistance of two types of composite beams constrained by rigid joint

To study the fire resistance of different types of composite beams in integral structures, transient state tests were performed on two-span composite beams (one span is a monolithic composite beam with a laminated slab and the other span is a composite beam with a cast-in-place slab) with rigid beam-to-column connections. The temperature distribution, displacement changes, and failure modes of the two types of composite beams were evaluated in tests mimicking the entire process of a real fire disaster. The following results were obtained in this study. Under the influence of fire, cracks of different patterns were formed on different types of composite beams. When the heating was stopped, the temperature of the steel beam experienced a sudden and sharp drop, whereas the temperature of the concrete slab rose within a short period of time. These behaviours cause the composite beam to undergo retraction in a reverse arch shape during deformation. Severe buckling occurred in the lower flange under the two ends of the steel beam as well as the web of the steel beam. During the test, the welds at both ends of the laminated-slab composite beam were cracked, whereas those at both ends of the composite beam with a cast-in-place slab remained undamaged. Finally, a method for calculating the axial force of the composite beam that considers the constraints at the beam ends is proposed in this study. The calculation results are in good agreement with the experimental test results.

Mechanical Behavior of Steel Bridge Deformed by Collision

AbstractA bridge over a highway is damaged by a truck running underneath occasionally. Typical collision damages observed in a steel girder bridge are as follows: a lower flange is deformed in the vertical direction and/or in the horizontal direction; a web plate is bent; a transverse stiffener is buckled; and a transverse stiffener is partly separated from the web. The influence of the damage on the safety of the bridge has to be judged right away. Nevertheless, it is not an easy task, since the mechanical behavior of a deformed girder has not been studied well. The first author has been involved in the evaluation of a steel girder bridge damaged by collision. Based on the data obtained from this bridge, the mechanical behavior of the deformed girder is studied numerically in the present study. To be specific, the deformation of the main girder due to collision is reproduced by the finite element analysis and the deformed steel girder is loaded to investigate its mechanical behavior. The result indicates that the damage influences the mechanical behavior of the girder, yet as far as the damage is confined to the deformation of the girder, the collision does not threaten the safety of the bridge even when the deformation is quite large. It is also clarified that the influence is mostly attributable to the configuration change and that the residual stress plays a relatively small role.

Static and modal analysis of sine-wave-shaped spar

Sine-Wave-shaped Spar (SWS) is recently involved in wing design as one of the corrugated shaped spars that highly improve the torsion and buckling resistance. SWS is an I-beam made of sine wave shaped vertical web fixed to upper and lower flanges. The current research evaluates the behavior of SWS in comparison to the traditional straight-web spar in resisting two cases of loading; static bending loading and static torsion loading. For each case, deformation and stress are analyzed. Modal analysis is also performed for the two spar configurations. For this purpose, a finite element model is developed using Ansys Workbench software for the SWS and the straight web spar. To reach a fair comparison, similar weight is considered for the two spar structures. A parametric study is performed to investigate the effect of web thickness and flange thickness on the bending and torsion deformation and stresses. The effect of thickness variation on the natural frequencies and mode shapes is also considered. The current study can be considered a base to design wing spars that combine the merits of the two spar configurations.

Temperature Rise Characteristics and Error Analysis of a DC Voltage Divider

Measurement accuracy is an important performance indicator for high-voltage direct current (HVDC) voltage dividers. The temperature rise effect for a HVDC voltage divider’s internal resistance has an adverse effect on measurement accuracy. In this paper, by building a solid model of a DC voltage divider, the internal temperature rise characteristic and error caused by the temperature rise in a resistance voltage divider were theoretically simulated. We found that with the increase in height and working time, the internal temperature of the voltage divider increased. The results also showed that the lowest temperature was near the lower flange and the highest temperature was near the upper flange in the middle of the voltage divider. The error caused by the temperature rise increased first and then decreased gradually with divider height, increasing with its working time. The measurement error caused by the internal temperature difference in steady state reached a maximum of 158.4 ppm. This study provides a theoretical basis to determine the structure and accuracy improvement for a resistive voltage divider, which is helpful for the selection of components and the optimization of the heat dissipation structure.

EQUIVALENT FLEXURAL RIGIDITY ON COMPOSITE BEAM WITH ‘REDUCED BEAM SECTION’ ON LOWER FLANGE

The Reduced Beam Section (RBS) is used as an effective method to improve deformation capacity on steel moment frames. However, study on flexural rigidity on composite beams with RBS has not been performed. This study proposes a useful method to calculate the equivalent flexural rigidity of composite beams with RBS on lower flange. The formulas were derived based on the energy method. FEM analysis was used to verify the theory. In addition, an eigenvalue analysis on a building model using the equivalent elastic beams with RBS was performed as an example.

Performance of Ultra Shallow Floor Beams (USFB) exposed to standard and natural fires

This paper investigates computationally the fire performance of a plug steel-concrete composite flooring system, the partially encased ultra-shallow floor beams (USFB). The investigation of the behaviour of USFBs exposed to standard and natural fires is crucial in determining their fire resistance and evaluating their overall performance in contemporary construction. Although the product providers usually indicate the fire resistance of USFBs based on ΕΝ1994-1-2 procedures, the response to elevated temperature effects remains yet neither well documented nor clearly understood. This analysis involves two different beams of 5 m and 8 m span. Results show that the unprotected beams experience severe temperature gradients while exposed to standard fire, as the lower flange still remains unprotected in contrast to the upper steel parts of the cross-section which are encased in concrete. Their fire resistance rating is found approximately at 40 min. Moreover, different thermal gradients are developed when the USFBs are exposed to natural fires (slow and fast burning). When the lower flange is protected with intumescent coatings, the USFBs have shown increased fire resistance and they can survive a full duration of a natural fire under realistic utilization ratios. From the parametric analyses, the optimized thicknesses for the required intumescent coating were obtained to achieve 60, 90, and 120 min of fire resistance and for surviving of natural fires exposures.

Detection of tower bolt looseness and its influence of wind level

Taking the wind turbine tower as the research object, based on the finite element software, a simplified beam-shell hybrid element model was first established; through the simulation, the phase difference between the loose position and the unloose position was compared to verify the feasibility of the phase difference detection method; Secondly, the influence of the number of loose bolts, the position of loosening, and the magnitude of the wind force on the phase of the flange bolt connection structure and the response characteristics of the system are analyzed. The research results show that the number of loose bolts, the position of loosening, and the magnitude of the wind have certain effects on the phase difference and response characteristics of the flange. With the increase in the number of loose bolts, the connection stiffness of the bolt connection continues to decrease. The linear characteristic is enhanced; the closer the loosening is to the excitation force loading position, the greater the detected phase difference; as the wind increases, the phase of the upper flange of the tower changes, and the phase of the lower flange remains unchanged, and the wind is on the flange The disc connection strength has little effect.

Flexural capacity and bending stiffness of welded hollow spherical joints with H-beams

Eight specimens were designed, and pure bending tests were completed to study the mechanical properties of welded hollow spherical joints (WHS joints) with an H-beam subjected to pure bending. Parametric analyses of the joints under pure bending were conducted in consideration of the diameter(D) and wall thickness (t) of the welded hollow sphere(WHS), and height (h) and width (b) of the H-beam to validate the numerical model. Calculation methods for the flexural capacity and bending stiffness of the H-beam WHS joints were proposed. Results revealed two failure modes of the joints under pure bending, namely, (1) concave at the connection between the WHS and upper flange and external heave at the connection between the WHS and lower flange and (2) small concave at the connection between the WHS and upper flange and tensile fracture of the welding seam at the connection between the WHS and lower flange. The joints demonstrated good ductility under pure bending. The flexural capacity and bending stiffness of the joints were positively related to the wall thickness of the WHS and to the height and width of H-beam but were negatively correlated with the diameter of the WHS. The errors between proposed formulas and FEA for calculating flexural capacity and bending stiffness are very small, indicating the formulas can be employed in structural calculation instead of FEA.

Examination of erection safety of precast beam assembly using a slanted beam section based on assembly test

ABSTRACT Assembling precast frames subjected to heavy construction loads may require a significant crane operation time when they were assembled by conventional steel joints having a straight beam cut. This study proposed a method that will provide a facile and rapid assembly of heavy precast frames, having the temporary bolting be established as noncritical path. Lower flanges of wide flange beam installed at end of precast beams were partially removed to prevent bottom flange of steel beam from running into flanges of L-shaped guide pockets when steel beam was inserted in L-shaped guide pockets. Permanent connections are made by bolting L-shaped guide pockets. Stable behavior was observed during an erection test of the proposed connection. This study also aimed to investigate an assembly safety of steel beam-column joints with a skewed beam section based on a nonlinear finite element analysis. Strain and stress analysis also demonstrated that stable structural behavior of joint elements was ensured during an assembly of precast frames.