Negative Bending Moment Research Articles

Fatigue tests on straight steel–concrete composite beams subjected to hogging moment

This paper describes the fatigue behavior of composite steel and concrete beams subjected to negative bending moment. Fatigue tests with repeated load limited to initial cracking and stabilized cracking, were performed on two steel–concrete composite beam substructures respectively. Test results indicated that when the repeated load was equivalent to the initial cracking load, the fatigue test had only limited influence on beam stiffness or crack patterns. However, when the repeated load was equivalent to the stabilized cracking load, a number of residual cracks occurred in the initial static test and the beam became less stiff as the load cycles increase. Failure of the bond between studs and surrounding concrete was confirmed in intermediate static tests; flexural stiffness of studs became smaller as the increase of load cycles. In addition, final static tests were performed on fatigue test specimens and another specimen without fatigue test. The comparison indicated that when the repeated load was larger than the initial cracking load, fatigue test could decrease beam stiffness and its ultimate load carrying capacity.

Contribution to assessing the stiffness reduction of structural elements in the global stability analysis of precast concrete multi-storey buildings

This study deals with the reduction of the stiffness in precast concrete structural elements of multi-storey buildings to analyze global stability. Having reviewed the technical literature, this paper present indications of stiffness reduction in different codes, standards, and recommendations and compare these to the values found in the present study. The structural model analyzed in this study was constructed with finite elements using ANSYS® software. Physical Non-Linearity (PNL) was considered in relation to the diagrams M x N x 1/r, and Geometric Non-Linearity (GNL) was calculated following the Newton-Raphson method. Using a typical precast concrete structure with multiple floors and a semi-rigid beam-to-column connection, expressions for a stiffness reduction coefficient are presented. The main conclusions of the study are as follows: the reduction coefficients obtained from the diagram M x N x 1/r differ from standards that use a simplified consideration of PNL; the stiffness reduction coefficient for columns in the arrangements analyzed were approximately 0.5 to 0.6; and the variation of values found for stiffness reduction coefficient in concrete beams, which were subjected to the effects of creep with linear coefficients from 0 to 3, ranged from 0.45 to 0.2 for positive bending moments and 0.3 to 0.2 for negative bending moments.

Study on the Crack in Concrete Flange of Outer-Plated Steel-Concrete Continuous Composite Beams

Static load tests were conducted on two reversed-loading simply supported and two continuous outer-plated steel-concrete composite beams to study the formation and development of cracks in such beams under negative bending moment. The test results show that based on the plane section assumption, it is an effective and economical method to calculate the cracking moment of the composite beams assuming a rectangular stress block for concrete in tension zone. Considering the structural features of outer-plated steel-concrete composite beams, the formula for calculating crack width of concrete flange of outer-plated steel-concrete composite beams is discussed and presented, and the calculated values of crack width agree well with the experimental results.

Research on Key Issues in Design of Outer-Plated Steel-Concrete Continuous Composite Beams

Based on the theoretical analysis and testing results, some key issues in design of outer-plated steel-concrete continuous composite beams are discussed. The influence of the form of steel beam upper flange on the behavior of composite beam is analyzed. The requirements about longitudinal reinforcement strength in the concrete flange of the negative moment region are given. It is suggested that the moment-shear interaction should be neglected when calculating the flexural capacity of outer-plated steel-concrete composite beams under negative bending moment. The behavior of longitudinal shear resistance at the interface between the concrete flange and web of composite beam is studied, and the related calculating formula is put forward based on the structural features of the composite beam.

Experimental investigation on inelastic behavior of composite box girder under negative moment

The mechanical behavior of negative bending moment zone in composite girder is very complex. The nonlinear characteristics due to the cracking of concrete slab need careful studies. In this experimental research, two specimens of steel-concrete composite box girder with inclined webs under hogging moment were cautiously conducted and tested. The relative slips between the steel and concrete, load-displacement relationship, the strain distribution of the steel girder, the reinforcements and the concrete slab, and the cracking behavior of the concrete slab were measured during the tests. The relatively small slips on the surfaces between the concrete slab and the top flange of the steel girder showed the full shear connection composite behavior of the girders. The initial cracking load was compared with the calculation results from linear analysis and nonlinear analysis based maximum strain. The strain of the steel web measured at different positions along the vertical direction showed the establishment of plane section assumption and the variation of neutral axis in the loading process. Moreover, shear lag effect was found in the strain distribution of the bottom flanges. The strain of concrete slab and the crack spacing showed the effect of the longitudinal reinforcement ratio on the cracking behavior of the concrete. The maximum crack width was observed in the loading process and compared with the calculation results according the design codes. The influence of reinforcement ratio on the strain of reinforcement and on the load capacity in serviceability limit state was studied in the context and it was found that the reinforcement ratio play an important role on the crack control of composite girder under hogging moment.

Mechanical Behavior of Composite Girder with Perfobond Shear Connector under Hogging Moment

The mechanical behavior of the support regions for continuous composite girders with tensile stresses in the concrete slab and compressive stresses in the lower steel profile becomes strongly nonlinear under negative bending moments. A static test on four half-scale model of a steel and concrete composite girders with different shear connectors including studs and PBL under hogging moments was conducted and observed to evaluate the influence of shear connector on inelastic behavior such as flexural stiffness reduction, crack initiation and development in concrete slab. From the test results, the flexural stiffness and loading capacity of the composite girders were improved by PBL shear connector. Higher initial cracking load and crack resistance stiffness of composite girders with PBL shear connector under serviceability limit state was obtained during crack development process. The test specimen could be assumed as full composite section until the ultimate state from load-slip relationship of shear connector. Analytical and experimental studies can serve as a basis for continuous composite bridges design.

A verification of simplified analysis method for thermal prestressing in continuous composite bridge

The use of thermal-prestressing method (TPSM) prevents the occurrence of tensile transverse crack in concrete decks located in negative bending moment regions of continuous composite bridges. An accurate representation of the structural response can be obtained by means of refined analyses using three-dimensional finite element models to carry out both heat transfer and thermo-elastic calculations. So, a simplified approach was proposed for easily using the TPSM effect in design to reduce the amount of computational work of the refined analysis, but its application to real structure was not confirmed. Therefore, in this study, the verification of a simplified analysis approach has been performed to explain TPSM effects in the analysis of continuous composite bridges. For this purpose, experimental results on 2-span thermal prestressed continuous composite bridge specimens were compared with simplified analysis and refined analysis results as well as analytical approach on 2-span and 3-span continuous composite bridges. From the verification results, the proposed simplified TPSM analysis methodology shows the good predictions of the thermal prestressing effect to apply design of TPSM applied continuous composite bridges.

Design of SFRC structural elements: flexural behaviour prediction

Practical steel fibre reinforced concrete (SFRC) applications in load-carrying structural members have yet to gain wide acceptance in design codes. This is partly explained by the lack of a unified design philosophy adapted to this material. A model based on simple and widely accepted assumptions is proposed for the analysis and the design of SFRC members subjected to bending moments. In order to evaluate the accuracy of the analytical model predictions, an extensive experimental program was conducted on 21 rectangular and T-beams of various sizes produced with five different types of SFRC. The contribution of fibres at different loading phases in bending is described in detail. The analytical model accuracy to predict maximum crack opening applicable in service conditions and at the ultimate flexural strength are compared to experimental measurements. Discrepancies observed are related to the dispersion of the material properties and the difference of fibre orientation in beams and characterization specimens. Finally, the proposed design approach is applied to the design of a realistic T-beam subjected to positive and negative bending moments.

Torsional effect on steel–concrete composite sections subjected to negative moment

This article summarizes the results of 13 push-out specimens under the effect of different loading combinations including shear, torsion and negative bending moment. The objective of the project is to record the reductions in the capacity of the stud shear connector and the change in the behaviour of the composite section when torsion is applied. An equation is presented to calculate the produced axial force in the stud shear connector for sections subject to any loading combination. Modifications are performed to the well-known exponential formula representing the load-slip relation of the studs. Finite element application is conducted to simulate the behaviour of the composite section and the stud shear connector as well. The simulation shows a very good agreement with the experimental results.

Analysis on Influence of Shield Tunnel Crossing under Intercity High-Speed Railway Station

Based on an engineering example of a certain shield tunnel passing through an intercity high-speed railway station which has been reinforced by pile-slab structure, this paper adopts finite element numerical simulation to study the influence of shield tunneling construction on the pile-slab reinforced structure and railway subgrade. The research result shows that the horizontal displacement and additional bending moment on both sides of bored piles are increasing in the process of shield tunneling, while those of the middle bored pile firstly increase and then decrease. The vertical displacement and axial force variation of the middle bored pile are more obvious than that on both sides of the bored piles. The settlement and additional bending moment of the reinforced concrete slab are relatively large in the center and midspan of both sides, the position of maximum settlement and negative bending moment is near the concrete slab just above the right tunnel, while the maximum positive bending moment is located in the very middle of the concrete slab. The pile-slab reinforced structure can effectively control the settlement and differential settlement of the intercity railway subgrade caused by shield tunneling, thus the intercity railway can keep normal operation.

The Natural Bending Vibration of the Continuous Beam and the Impact Factor of Bridge

The natural frequencies and mode shapes of 2, 3 and 4 spans continuous beam with universal cross section are calculated, and these dynamic parameters of 2 spans continuous beam model are measured. From the analysis and the model test, the locations of the maximum curvatures of the mode shapes are determined, and comparing that with the maximum bending moment of the beam under the action of uniformly distributed load, the selection of the natural frequency of the beam is discussed with the General Code for Design of Highway Bridges and Culverts as the impact factors of the beam is calculated. It is shown from the results of the analysis and the test that, for the impact factor, when the effect of positive bending moment caused by impact force is calculated, the fundamental frequency must be used as shown in the General Code, and the 2nd or 3rd frequency must be used when the effect of negative bending moment caused by impact force is calculated. The selection of the frequency should be combined with the mode shape into account for the specific circumstances.

Experimental study of retrofit solutions for damaged concrete bridge slabs

Accurate information on the actual performance of the structural system after retrofit is an essential part of a cost-effective bridge management program. This paper summarizes the results of a thorough experimental program concerning the reinforced concrete deck of a real 40year-old viaduct. The structure exhibited severe damage at the extrados mainly due to environmental agents, chemical attack and action of asphalt milling machines. Samples of the deck were cut and carried to the laboratory in order to assess the possibility of retrofit. The design of retrofit was aimed at increasing the load carrying capacity through replacement of the deteriorated concrete with a new concrete overlay and strengthening in flexure for both negative (hogging) and positive (sagging) bending moments. Experimental testing on small specimens and nondestructive techniques were carried out to identify the material properties and to evaluate the level of damage. The bonding between external reinforcement and the original or new (standard or polymer-modified) concrete was assessed through single-shear push–pull tests on 33 prismatic specimens of 100×200×500mm3 strengthened with CFRP strips. The efficiency of the retrofit techniques was checked at the structural level through four-point bending tests on eight slabs of 500×200×2000mm3. This research can contribute to guidelines for concrete patch repair of FRP-retrofitted concrete bridge decks, to ensure better long-term performance under service loads and environmental effects.

The effects of axial tension on the hogging-moment regions of composite beams

Structural parts commonly comprised of composite members such as bridge approaches, inclined parking ramps and stadium beams, can be subjected to a combination of high axial loads and bending moments. Steel–concrete composite construction is a popular solution for these types of structures due to the numerous advantages that they offer. Although, current design codes (e.g. Eurocode 4, American code AISC, Australian codes AS2327 and AS5100) provide rules for the design of composite columns subjected to flexure and axial load, however the design of composite beams, which are asymmetric in nature under the combined effects of tension and bending, is not yet fully addressed. This paper investigates the ultimate strength of composite beams under the combined effects of axial tension and negative (hogging) bending moment. An experimental programme carried out in the laboratory of the University of Western Sydney comprised of a total of six specimens representing composite beams and subjected to various levels of axial tension and bending moment. Ultimate failure modes were identified and the resulting interaction diagrams were compared to the results of sectional rigid plastic analysis. Following the tests, three-dimensional finite element models were employed using the ABAQUS finite element software to further investigate the nonlinear behaviour of the composite beams and extend the experimental observations by studying the effects of parameters such as the span length and the effect of partial shear connection. Finally, simple design rules and formulae are proposed for use in engineering practice.

Flexural responses of concrete slab over flexible girders through FEA-based parametric evaluation

The determination of flexural responses in a concrete slab over flexible steel girder, forming a composite deck has been a timeconsuming subject for the design engineers. The existing provisions of the design standards such as AASHTO or analytical solutions based on local bending or plate theory usually ignore some significant parameters affecting the deck response, such as girder flexibility, number of loaded traffic lanes and ratio between deck width and girder span. This may lead to unrealistic prediction of bridge flexural responses used in the slab design practice. Although it is well known that finite element analysis is very versatile for structural analysis, very few studies have been reported dealing with explicit determination of deck slab response. The present study investigates the transverse negative bending moment of the slab cast over a number of steel girders, subjected to traffic loads, using verified composite Shell-Frame and Plate-Frame Models. The evaluation of such response is carried out through an extensive parametric study focusing on the effect of girder flexibility due to patterns of moving loads. Based on the numerical results, empirical relationships are proposed to determine the maximum slab moments anywhere along the girder span. The application of these relationships is then compared with other references. The suggested relationships seem to give more realistic and economical values of the considered transverse slab bending moment for a wide range of deck proportions.

Slipping Effects of Simple Combination Beam under the Action of Negative Bending Moment

A numerical study on slip effect of simply supported composite beams under negative bending moment is conducted by means of finite element program of ANSYS based on the feasibility verification of ANSYS. The research contents include: slip distribution rules; slip effect on deflection in service stage and ultimate bearing capacity; relationship between slip effect and shear connection、lognitudinal percentage of reinforcement and working behavior of composite beams with partial shear connection under negative bending moment .

Three Dimensional Simulation of the Shear Property of Steel-concrete Composite Beams with an Interface-slip Model

Summary A three-dimensional finite-element (FE) analytical approach for the simulation of Shear property of steel-concrete composite beam is presents in this paper. To simulate the interfacial behavior between the steel girders and concrete slabs, an interface-slip model which has been better used in analyzing the flexural property of composite beams is applied in the simulation. Both simple-supported beam experiment at positive bending zone and negative bending moment zone in literatures are simulated respectively. The load-deflection and the slip rule between the steel girders and concrete slabs as well as the crack pattern and the contour at the ultimate load are analyzed. The results obtained from the FE analyzes match well with the corresponding experimental results. The FE analysis method is verified to be capable of simulating the shear property of steel-concrete composite beams.

Beitrag zur Entwicklung der Querschnittsgestaltung im Verbundbrückenbau

AbstractDie grafische Darstellung des Verbundquerschnittes mit einer oberen Betonplatte und einem darunter liegenden Stahlträger war seit seiner Vorstellung in den 1950er Jahren ein Symbol, das weit über die Theorie hinausging und weite Verbreitung in der Praxis des Verbundbrückenbaus fand. Seit den 1970er bzw. 1980er Jahren hat dieses Bild – bedingt durch neue und freiere Formen, Beton und Stahl miteinander zu kombinieren – seine Symbolhaftigkeit verloren. In Deutschland und Spanien wurde der Doppelverbund mit unten liegenden Betonplatten in Bereichen mit negativen Momenten eingeführt, in Frankreich werden Stahlträger auch in vorgespannten Betonquerschnitten eingebettet. Beide Ansätze haben dazu beigetragen, dass in der Gegenwart die Materialien Stahl und Beton im Verbundbau frei miteinander kombiniert werden können.On the development of sections in composite bridges. A comprehensive theory of composite construction was established in Germany by Sattler in 1953. The theoretical image of the composite section with a superior concrete slab and a lower metallic structure was shaped in addition to the analytical resolution. Theory and graphical representation were going to be known together in Europe. This figure was repeated in all theoretical and academic publications, so becoming an authentic icon of the composite section. Its translation to the bridge deck in flexion was obvious: the superior slab defines the tread platform, while the metallic structure was left off‐hook at the bottom.Nevertheless, in continuous decks the section is not optimal at all in zones of negative bending moments. But the overcoming of the graphical representation of the theory did not happen immediately. It was produced after a process in which several European countries played an active role and where different mechanisms of technological transference were developed.One approach to this overcoming is the “double composite action”, with a lower concrete slab in areas of a negative bending moment. The first accomplishments, a bridge in Orasje built in 1968 with 134 m span, as well as the publications of the system proposed by Fabrizio de Miranda in 1971 did not extend nor had continuity. Spanish bridges by Fernández Ordoñez and Martínez Calzón used double composite action for the first time in 1979. The German team of Leonhard, Andrä und partners, has used it since the end of the 1980's to solve bridges of great span. Once the technology has been well known thanks to the ASCE International Congress and the Spanish International Meetings organised by the “Colegio de Ingenieros de Caminos”, double composite action has been integrated well into the structural vocabulary everywhere.In France the approach was different. What Michel Virlogeux calls “double floor composite section” was reached as an evolution of prestressed concrete bridges. In an experimental process widely known, the external prestressing allows weight reduction by diminishing the thickness of the concrete webs. The following step, in the 1980's, was the substitution of the webs by metallic elements: stiffened plates, trusses or folded plates. A direct result of this development is the Brass de la Plaine Bridge in the Reunion Island in 2001 with 280 m span.Both approaches have contributed to a freedom of design in composite construction in steel and concrete today.

MECHANICAL BEHAVIOUR OF COMPOSITE GIRDERS SUBJECTED TO HOGGING MOMENT: EXPERIMENTAL STUDY

In continuous composite steel-concrete structures, cracking of the concrete slab in the hogging moment region decreases the global stiffness of composite steel-concrete structures and reduces the effect of continuity, thus making the structural behaviour highly nonlinear even for low stress levels, so special consideration is necessary. An experimental investigation on the behaviour of steel-concrete composite beams in hogging moment region is presented in this paper. A total of four specimens were tested under point load in the mid-span. Two of the composite beams with headed studs as the shear connectors, while the other two specimens are using Perfo-Bond Strips (PBLs) as the connection devices between the steel girder and the concrete slab. Ultimate load bearing capacity of composite sections in negative moment region was calculated and compared with experimental values. Crack formation, crack widths development process and strain distribution of the composite section before and after cracking were observed and presented in this study. Interface slip distribution was also given. Research results indicate that the current specifications such as AASHTO, JSCE, and EUROCODE-4 can provide appropriate values for ultimate strength of a composite girder under negative bending moment.

MECHANICAL BEHAVIOUR OF COMPOSITE GIRDERS SUBJECTED TO HOGGING MOMENT: EXPERIMENTAL STUDY

In continuous composite steel-concrete structures, cracking of the concrete slab in the hogging moment region decreases the global stiffness of composite steel-concrete structures and reduces the effect of continuity, thus making the structural behaviour highly nonlinear even for low stress levels, so special consideration is necessary. An experimental investigation on the behaviour of steel-concrete composite beams in hogging moment region is presented in this paper. A total of four specimens were tested under point load in the mid-span. Two of the composite beams with headed studs as the shear connectors, while the other two specimens are using Perfo-Bond Strips (PBLs) as the connection devices between the steel girder and the concrete slab. Ultimate load bearing capacity of composite sections in negative moment region was calculated and compared with experimental values. Crack formation, crack widths development process and strain distribution of the composite section before and after cracking were observed and presented in this study. Interface slip distribution was also given. Research results indicate that the current specifications such as AASHTO, JSCE, and EUROCODE-4 can provide appropriate values for ultimate strength of a composite girder under negative bending moment.

Evaluation of Flexural Ductility of Negative Moment Region of I-Girder with High Strength Steel

For continuous I-girder bridge, large negative bending moment is generated near pier region so that plastic hinge For continuous I-girder bridges, a large negative bending moment is generated near pier region so that plastic hinge is first formed at this point. Then, the bending moment is redistributed when the I-girder has enough flexural ductility (or rotational capacity). However, for I-girder with high strength steel, it is known that the flexural ductility is considerably decreased by increasing the yield strength of material. Thus, it is necessary to conduct a study for guaranteeing proper flexural ductility of I-girder with high-strength steel. In this study, the evaluation of flexural ductility of negative moment region of I-girder with high strength steel where yield stress of steel is 680MPa is presented based on the results of finite element analysis and experiment. From the results, it is found that the flexural ductility of the I-girder is significantly reduced due to the increase of elastic deformation and the decrease of plastic deformation ability of the material when the yield strength increases. In this study, the method to improve the flexural ductility of I-girder with high strength steel is proposed by an unequal installation of cross beam and an optimal position of cross beam is also suggested. Finally, the effects of the unequal installation of cross beam on the flexural ductility are discussed based on the experimental results.