Concrete Encased Steel Beams Research Articles

The investigation on flexural performance of prestressed concrete-encased high strength steel beams

This paper reports an experimental on the flexural performance of prestressed concrete-encased high-strength steel beams (PCEHSSBs). To study the applicability of high-strength steel (HSS) in prestressed concrete-encased steel beams (PCESBs), one simply supported prestressed concrete-encased ordinarystrength steel beam (PCEOSSB) and eight simply supported PCEHSSBs were tested under a four-point bending load. The influence of steel strength grade, I-steel ratio, reinforcement ratio and stirrup ratio on the flexural performance of such members was investigated. The test results show that increasing the I-steel grade and I-steel ratio can significantly improve the bearing capacity of PCESB. Increasing the compressive reinforcement ratio of PCEHSSB can effectively improve its bearing capacity and ductility properties, making full use of the performance of HSS in composite beams. Increasing the hoop ratio has a small improvement on the load capacity of the test beams; setting up shear connectors can improve the ductile properties of the specimens although it does not lead to a significant increase in the load capacity of the combined beams. Then, combined with the test data, the comprehensive reinforcement index considering the location of reinforcement was proposed to evaluate the crack resistance of specimens. The relationship between the comprehensive reinforcement index and the crack resistance of specimens was given.

Experimental investigation and predictive modeling of shear performance for concrete-encased steel beams using artificial neural networks

Experimental investigation and predictive modeling of shear performance for concrete-encased steel beams using artificial neural networks

Maximum shear strength of concrete-encased steel composite beams: A novel strength model and FE verification

Due to the high load-carrying capacity and rigidity, concrete-encased steel (CES) beams are widely applied as transfer elements in heavily-loaded structures. However, the accurate shear strength prediction method is still under investigation because of the difficulty in the shear contribution decomposition of steel shape and reinforced concrete. Current design codes apply the strength superposition for CES beams, namely that their shear strength can be obtained by directly superimposing the shear strengths of RC and steel shape, which has been proven questionable by existing research. Therefore, it needs to carefully decouple the multiple shear transfer mechanisms in CES beams and explore their roles in a composite structure. In this paper, a novel shear strength model is proposed, in which a CES beam can be divided into a shear web and a composite truss consisting of RC with two steel flanges, and strain compatibility is applied to evaluate the shear contribution of these two parts. After that, an elaborate FE model is established to further quantitatively investigate the shear contribution of the composite truss and the shear web. Finally, the proposed model is verified with 61 existing specimens in the literature, and the comparison between the calculated and test results indicates that the proposed model could predict the shear strength of CES beams accurately.

Experimental and theoretical study on flexural behavior of high strength concrete encased steel beams with steel fibers

In this study, the flexural behavior of high strength concrete encased steel beams with steel fibers (HSCSBSF) under bending is investigated. The experiments of four HSCSBSF including one HSCSBSF without steel fiber (0% volume ratio of steel fiber) are carried out to investigate the effect of the volume ratio of steel fiber on the flexural behavior of HSCSBSF. All specimens fail by the yielding of reinforcement in tension zone and the crushing of concrete in compression zone. Due to the positive effect of steel fiber on the internal bonding strength of concrete, HSCSBSF with higher volume ratio of steel fiber shows higher cracking load. The bearing capacity (bending capacity) of HSCSBSF increases by 34.3% when the volume ratio of steel fiber varies from 0% to 2%. Compared with HSCSBSF with 0% volume ratio of steel fiber, the flexural stiffness of HSCSBSF with higher volume ratio of steel fiber is obviously improved and the ductility coefficient (the ratio of the displacement at failure load to the displacement at the yield load) of HSCSBSF with 2% volume ratio of steel fiber increases by 25%. Based on the material test of concrete, a value for the influence coefficient of steel fiber on the tensile strength of concrete is suggested. A model for predicting the bearing capacity of HSCSBSF is then derived from theoretical analysis of HSCSBSF. A good agreement between the proposed model and various test data is made.

Cracking behavior and energy consumption of Steel Fiber Concrete Encased Steel beams

Steel Fiber Concrete Encased Steel (SFCES) beams were subjected to bending to investigate the effect of steel fibers on the behavior of Steel Reinforced Concrete beams with or without steel reinforcement. 18 SFCES beams reinforced with steel fibers, steel reinforcement, or both were cast. The parameters considered in the experiment were (a) the volume percentage of steel fiber (0%, 1%, and 2%), (b) the shear span to depth ratio( s/d = 2.5 and 3.5), (c) the stirrups spacing (180 mm and 360 mm), and (d) the presence or absence of longitudinal reinforcement (2Φ8+2Φ10).The cracking load, crack development, energy dissipation capacity, and ductility of the specimens were investigated. The results illustrate that the cracking load F c, the total energy consumption, and the energy ductility increase with increasing steel fiber volume, and the average improvement with a steel fiber volume increase of 1% can reach 36.5%, 21.2%, and 28.67%, respectively. However, this strengthening effect of steel fibers was weakened due to the addition of steel reinforcement. The influence of the steel fiber volume and reinforcement configuration on each stage of energy consumption was mainly concentrated in the elastic ( E 1) and failure stages ( E 3). Finally, mathematical equations were proposed to predict the cracking load and crack width of the SFCES specimens, which were verified by comparing the predictions with the experiment results.

Seismic collapse resistance performance on out-jacketing frames with concrete-encased CFST columns for adding storeys

This research paper conducted a hysteretic behavior simulation on a single-span and single-storey frame composed of prestressed concrete-encased steel beams and concrete-encased concrete filled steel tube (CFST) columns. The hysteretic parameters of stiffness degradation, strength degradation and pinching behavior for members were suggested according to tested results. After that, an analytical model for corresponding out-jacketing frames with single-span and multi-storey was developed, and amounts of elastoplastic seismic response analysis were conducted for seismic fortification intensities 7 and 8 with various site-classes and design earthquake groups under rare earthquake. The results indicated that, the out-jacketing frames assigned to Intensity 7 with Site-classes I0 to III behaved perfectly in seismic collapse resistance performance, which could be designed as regular frames by using China's current codes; while referring to Intensity 8, a certain amount of out-jacketing frames assigned to Site-classes I0 to III had inter-storey collapse mechanism, and several design proposals were developed to prevent collapse failure by measurements of enhancing seismic grade.

Study on shear capacity of prestressed composite joints with concrete-encased CFST columns

Through assuming reasonable constitutive relation of materials, finite element analysis (FEA) models of joints consisting of prestressed concrete-encased steel beams and concrete-encased concrete filled steel tube (CFST) columns were established by soft ABAQUS, and the simulated results were compared with tested ones. On this basis, the nonlinear analysis on the total loading process was conducted, and the stress variation of concrete, profile steel skeleton, steel bar skeleton, and prestressing tendons were observed at yield, peak, and ultimate loads; the influence of axial compressive ratio, steel tube ratio, stirrup ratio, and prestressing level on lateral load-displacement curves at column top and shear force-shear angle in joint core were investigated, and the shear capacity formulae of joint core were developed. It could be concluded that, the lateral peak loads and shear capacity could be improved with the increase of axial compressive ratio, steel tube ratio, stirrup ratio, and prestressing levels in varying degrees, and the ductility of joints will reduce with the increase of axial compressive ratio. Additionally, the shear capacity calculated by proposed practical formula was a little lower than FEA results, which could keep the joints safety and could be used in engineering design.

Structural Behavior of Strengthened Concrete-Encased Steel Beams with Web Openings

Concrete-encased steel beams (CESB) have become one of the fundamental composite members utilized in recent years. The research aims to investigate the effect of strengthening CESB with and without openings. Eleven simply supported fully CESB beams with and without web opening under static loading using a four-point loading system were studied. Two main stages were considered; studying the effect of the presence of web opening (located in the shear zone), and the effect of applying three different strengthening materials on the flexure or the shear zone of the beams on the behavior of the CESB. Carbon fiber-reinforced polymer wraps, glass fiber-reinforced polymer wraps, and steel plates were used as externally bonded reinforcement strengthening materials. The obtained experimental results were the mode of failure, the crack pattern, load–deflection curve at mid-span, load–strain curves at different locations, first crack load, serviceability load, ultimate load, energy absorption, and ductility ratio. A Finite-Element Analysis (FEA) is performed using ANSYS release 19.0 program to simulate the 11 tested specimens. Test outcomes showed that the ultimate load and its corresponding deflection decreased by about 58.28% and 80.17%, respectively, due to the effect of the web opening. Furthermore, shear strengthening of CESB with web opening located in the shear zone is more effective than the flexural strengthening using the three different strengthening materials. Also, using a steel plate is extra effective than using carbon fiber wraps or glass fiber wraps on the performance of the tested beams. Based on the FEA, high compatibility between both FE and experimental results is achieved.

Shear behavior and shear capacity prediction of precast concrete-encased steel beams

A novel precast concrete-encased steel composite beam, which can be abbreviated as PCES beam, is introduced in this paper. In order to investigate the shear behavior of this PCES beam, a test of eight full-scale PCES beam specimens was carried out, in which the specimens were subjected to positive bending moment or negative bending moment, respectively. The factors which affected the shear behavior, such as the shear span-to-depth aspect ratio and the existence of concrete flange, were taken into account. During the test, the load-deflection curves of the test specimens were recorded, while the crack propagation patterns together with the failure patterns were observed as well. From the test results, it could be concluded that the tested PCES beams could all exhibit ductile shear behavior, and the innovative shear connectors between the precast concrete and cast-in-place concrete, namely the precast concrete transverse diaphragms, were verified to be effective. Then, based on the shear deformation compatibility, a theoretical model for predicting the shear capacity of the proposed PCES beams was put forward and verified to be valid with the good agreement of the shear capacities calculated using the proposed method and those from the experiments. Finally, in order to facilitate the preliminary design in practical applications, a simplified calculation method for predicting the shear capacity of the proposed PCES beams was also put forward and validated using available test results.

Part I: The Analytical Model Predicting Post-Yield Behavior of Concrete-Encased Steel Beams Considering Various Confinement Effects by Transverse Reinforcements and Steels.

The purpose of the work was to propose analytical model considering double confinements (provided by both transverse reinforcements and a wide flange steel section), which was verified by the nonlinear finite element analysis considering concrete-damaged plasticity. The scope of the effort and the procedures to achieve the aim of this study included the identification of the concrete confinements provided by both transverse reinforcements and a wide flange steel section based on the elasto-plastic model in tension for both rebar/steel sections and elasto-buckling for rebars in compression. The influence of rebar buckling in the compression zone on flexural moment strength was also investigated with and without considering confining effects offered by steel sections. The analytical approach predicted a post-yield behavior of composite beams based on the confining effect offered by both the shear reinforcement and wide steel flange sections. However, for beams without axial loads, the compressive zones with high and partial confinements for concrete sections at the yield and maximum load limit state were limited when compressive buckling failure was not considered, preventing the confining factors from significantly influencing the flexural load resisting capacity. An accurate flexural capacity of composite beams can be obtained when rebar was modeled with buckling in the compression zone.

Behavior of Partially Concrete Encased Steel Beams Under Cyclic Loading

This paper presents an experimental study of the behavior of partially concrete encased steel beams (PE beams) under seismic loading. The effects of a floor slab in providing lateral and torsional support to the strength and ductility of the beam are also investigated herein. One steel beam and six PE beams were tested herein. The strength development in bare steel beam was insufficient and significant lateral torsional buckling (LTB) was observed. The concrete encasement of the PE beam delayed the occurrence of LTB and hence increased the strength and ductility of the beam. The plastic rotation capacity of PE beam is enhanced by the additional lateral and torsional support provided on the top of a PE beam. For the beam tested in this study, the concrete encasement permits the beam to reach its plastic strength and have plastic rotation of at least 3.42% rad, which is larger than 2% rad required for Intermediate Moment Frames, when no lateral or torsional support is provided at the top of the beam. To satisfy the 4% rad plastic rotation limitation for special moment frames, lateral support with sufficient torsional stiffness is needed.

Effect of Intermediate Stiffeners on the Behaviors of Partially Concrete Encased Steel Beams

Partially concrete encased steel (PE) beams are composite steel beams and concrete elements that present several advantages, such as higher fire resistant, higher flexural capacity, and higher lateral torsional buckling resistant compared to bare steel beams. This paper reports an experimental study of eight PE beams under cyclic loading. The effectiveness of intermediate stiffeners, such as midspan stiffener and plastic hinge zone stiffener, in enhancing composite action and ductility of the PE beams was studied. The ductility performance of PE beams using strengthened beam‐to‐column connection and weakened beam‐to‐column connection was also investigated. The test results show that the plastic hinge zone stiffener performed well and has the potential to replace shear connectors. Strengthened and weakened beam‐to‐column connections can be implemented in PE beams to enhance the ductility of the PE beams; with the details of both strengthened and weakened beam‐to‐column connections determined by bare steel shape instead of the whole section. In addition, the suggestions to prevent premature failure of weakened beam‐to‐column connection were provide.

Experimental study on hysteretic behavior of composite frames with concrete-encased CFST columns

This paper proposed an innovative frame structure composed of concrete-encased steel beams and concrete-encased concrete filled steel tube (CFST) columns for long span building, and two one-bay and one-storey specimens were tested under lateral low cyclic loading. The testing process, such as cracks developments and failure patterns were observed, and the seismic performance such as hysteretic behavior, skeleton curves, rigidity degradation, energy dissipation, and residential deformation were investigated. Additionally, the strain variations for longitudinal bars, flanges of H-shaped steel and steel tube in potential zone of the plastic hinges of beams and columns were analyzed. The test results indicated that two specimens both behaved perfect energy dissipation and ductility even prestressed; and the initial cracks of prestressed specimen was restrained and appeared later than that of unprestressed one due to the prestressing effects; otherwise, during the whole loading the circular strains of steel tubes in the bottom of columns varies unevenly, and steel tubes in compressive zone could supply effective constraint on corresponding concrete. According to the strain variations, the sequence of plastic hinges of the two specimens presented that they occurred on the beam ends firstly and then on the bottoms of columns and mechanism of energy dissipation for beam plastic hinges and a delayed occurring of plastic hinges on column bottom were expected.

Shear performance of prestressed ultra high strength concrete encased steel beams

Due to the high compressive strength and durability properties of ultra high strength concrete, prestressed ultra high strength concrete beam was used extensively in bridge engineering, but it possessed obvious brittle behavior. Encasing structural steel into it was a good way for alleviating the problem of brittleness. The purpose of this study was to investigate shear performance of prestressed ultra high strength concrete encased steel beams. A total of fifteen prestressed ultra high strength concrete encased steel beams and seven prestressed ultra high strength concrete beams were tested to shear failure under simply supported three-point loading conditions. The primary variables of this investigation included the presence or not of structural steel, shear span-depth ratio, degree of prestress, ratio of stirrup and thickness of web. The shear performance was evaluated based on cracking pattern, load–deflection behavior and shear ductility. Test results showed that prestressed ultra high strength concrete encased steel beams had higher residual shear capacity and post-cracking stiffness as well as by far better shear ductility than prestressed ultra high strength concrete beams. In addition, influence of experimental parameters on the shear performance of prestressed ultra high strength concrete encased steel beams and prestressed ultra high strength concrete beams also was discussed and compared, respectively.

Experimental Study on Shear Splitting Failure of Full-Scale Composite Concrete Encased Steel Beams

Presented herein is an experimental study that focuses on the shear splitting failure concrete encased steel beams. Nine full-scale specimens were constructed and tested in this study. Significant horizontal cracks along the interface of steel flange and concrete, referred to as the shear splitting failure, appeared in five tested specimens. Observations from the experiments indicate that the steel flange width ratio, defined as the ratio of steel flange width to gross section width, has a dominant effect on the shear splitting failure of composite beams. The tests results reveal that the shear splitting failure occurs when the steel flange width ratio of a composite beam reaches 0.67. The test results also show that the application of shear studs has a positive effect on preventing this type of failure for beams with large steel flange ratio. In addition to the experimental study, a new method for predicting the failure mode of composite beams is proposed. The proposed method gives satisfactory predictions as compared to the test results. Finally, a new equation is derived for the design of the stirrups to prevent shear splitting failure of naturally bonded composite beams.

Experiments on the strength of reinforced and prestressed concrete beams and of concrete-encased steel joists in combined bending and torsion

Summary A series of reinforced and prestressed concrete beams and concrete-encased steel joists was tested in combined bending and torsion, with ratios of bending moment to twisting moment varying from pure bending to pure torsion. In all, 33 full-size beams were tested. Measurements of defiexions and strains due to bending and to torsion were made at selected points. The agreement between theory and experiment was generally good. The torsional strength of concrete can be augmented by suitable shear reinforcement. The resistance of the reinforced concrete beams to torsion, however, still depends on the tensile strength of the concrete; it is not therefore possible to gain an increase in strength comparable with that resulting from the addition of tension reinforcement to a plain concrete beam subject to bending. On the other hand the insertion of even a small quamity of shear reinforcement turns the abrupt torsion failure of plain concrete into a gradualfailure accompanied by considerable cracking and deformation. The torsional strength of a concrete-encased steel beam is approximately the same as that of a similar plain concrete beam. The “1” shape is fundamentally a weak one in torsion and the concrete encasement therefore results in a considerable increase in the torsional strength of the steel joist, provided that the joist is surrounded with a nominal amount of stirrup reinforcement or expanded metal to ensure that the steel and concrete act together. Very large increases in torsional strength can be obtained by prestressing, since the initial prestress in compression must be overcome before the concrete can be stressed in tension. The prestressing force, however, increases the rate at which cracks propagate during failure, which therefore tends to assume a violent character. Two distinct types of failure can be distinguished in beams subject to combined bending and torsion. A primary torsion failure occurs with a cleavage fracture normal to the direction of the principal tension. It is governed by the criterion of a constant maximum tensile stress. In bending, tension failure is prevented by the steel, and a primary bending failure therefore results in the crushing of the concrete on the compression face. In reinforced concrete and concrete-encased steel beams the addition of bending increases the resistance to torsion. The paper concludes with detailed recommendations for the design of reinforced and prestressed concrete beams and concrete-encased rolled steel joists in torsion, and in combined bending and torsion.