Concrete Composite Structures Research Articles

Collapse risk-targeted seismic design of concrete-filled steel tube frame-RC core tube structures

The concrete-filled steel tube (CFST) frame-reinforced concrete (RC) core tube composite structure is a widely-used structural system of high-rise buildings due to its high compressive strength, good plasticity, and convenient construction. The cross-sectional dimensions and bending stiffness of CFST frames are smaller than those of RC frames with the same vertical load-bearing capacity. Since the seismic forces are distributed in proportion to stiffness for components, the assigned seismic forces of CFST frames are smaller, which may result in CFST frames not meeting the minimum load-bearing capacity requirement for the frame part in a dual system. If the CFST frame-core tube structure is designed adopting the dual system seismic design method which is applicable to RC frame-core tube structure, forcefully increasing the design seismic force of the frame, this will significantly increase the amount of material consumed and reduce the available area of the building. In this study, the CFST frame-RC core tube structure is designed according to different seismic design methods and compared through incremental dynamic analysis-based (IDA) fragility analysis. Then, an improved collapse risk-targeted seismic design method is proposed. The study results indicate that the structure designed according to the proposed method can achieve the excellent collapse resistance capacity, low collapse probability, and less material cost, which may provide a reference for seismic design of CFST frame-RC core tube composite structures.

Seismic Evaluation of Building having Steel Concrete Composite Columns and RC Beams

Abstract: Steel concrete composite structures are gaining popularity due to the advantages they offer over the conventional reinforced concrete and steel structures like the ease and speed of construction. In the light of this, it becomes essential to understand the behaviour of this type of structures when used in buildings. This study mainly focuses on the use of building frame consisting of steel-concrete composite column section with the reinforced concrete beams. To achieve this objective, the seismic analysis of the buildings was chosen for evaluating the performances of the buildings designed and analyses using Indian standards. The building selected for the study was rectangular in plan andhad an elevation of 30 meters with no plan or vertical irregularity present. The gravity loads considered for the building are in compliance with the IS 875 Part 1 and IS 875 Part 2. However, the gravity loads used in case of both buildings were kept to be same as the prime focusof the study was seismic analysis. The materials used for the design of the building with respect to Indian standards are E345 grade of steel and M30 grade of concrete. Various codes of practices including IS 456, IS 11384, IS 1893 and IS 13920 have been used throughout the study in case of the building designed and analysed with respect to Indian standards. The assumptions regarding the seismic characteristics of the buildings are also selected of the same nature for both the buildings. A finite element modellingbased software ETABs is used to carry out the design and analysis for the buildings. The buildings were designed with respect to the selected gravity loads and the seismic loads to obtain the section details to be used for seismic analysis. The building with finally obtainedsection sizes is used for carrying out the nonlinear analysis. This includes both the nonlinear static and nonlinear dynamic analysisas they both have their respective advantages in predicting the behaviour of the structure. For carrying out nonlinear analysis both material as well as geometric nonlinearity is considered. In case of the nonlinear dynamic analysis, the ground motions with respect to the guidelines of FEMA P695 and ASCE 7-16 were selected and scaled to perform the analysis. A total of 11 time histories were considered for NLTHA to have a thorough analysis. Various factors such as thecapacity curves, story displacements, base shears and story drifts were considered for evaluation of the seismic performance of both the buildings. The results obtained from the analysis of both thebuildings are represented in the form of tables and graphs, and are compared with each other to study the differences observed. It can be concluded that the buildings designed composite columns offers a better ductility and thus is more earthquake resistant

Experimental residual capacity of steel-reinforced concrete-filled steel tubular stub columns after fire exposure

Technological advances in the development of steel–concrete composite structures have led to the introduction of novel types of sections in the sought of higher load-bearing capacities. Particularly for composite columns, the axial capacity of concrete-filled steel tubular (CFST) sections may be enhanced by the introduction of an open steel profile embedded within the concrete infill, forming the so-called steel-reinforced concrete-filled steel tubular (SR-CFST) columns. An important aspect that should be revised, in order to safely use these sections in design, is their performance after a fire. In this experimental program, six SR-CFST stub columns are tested in the post-fire situation. Two series of columns comprising three circular and three square sections with the same steel usage are tested for comparison purposes. The size of the inner steel profile is varied in order to investigate its effect over the post-fire capacity of the columns. The specimens were initially exposed to elevated temperatures inside an electric furnace, and then cooled to ambient temperature; afterwards compressive axial load was applied gradually until failure, to ascertain their residual capacity. The experimental results show the high ductility of the SR-CFST stub columns after heating, with the circular specimens reaching higher post-fire peak loads than their square counterparts. This load increases with the size of the embedded steel profile. The post-fire capacities of the columns are evaluated through the Residual Strength Index, showing similar values for both circular and square SR-CFST columns. Finally, a design equation is proposed to facilitate the evaluation of the post-fire compression resistance of SR-CFST columns, as an extension of the existing room temperature design equation in Eurocode 4 Part 1–2 for CFST columns, accounting for the degradation of the steel and concrete after fire exposure through the corresponding residual factors.

Flexural stiffness characterization of the corrugated steel–concrete composite structure for tunnel projects

Corrugated steel–concrete (CSC) composite structures are increasingly used in tunnel and culvert projects due to their good mechanical properties. The design of CSC composite structures is often governed by deflection limits in service, hence it becomes crucial to evaluate accurately their flexural stiffness. In this work, the deflection deformation mechanism of CSC composite structure is studied by experimental and numerical methods, and a simplified formula for calculating the flexural stiffness is established. In addition, the deflection results obtained by different methods are compared and analyzed. It is found that: (1) the flexural stiffness of the CSC composite structure is constant only when the load is small, and after the bending moment exceeds a certain value, the flexural stiffness will gradually become smaller as the bending moment increases. (2) The value of the bending moment corresponding to the end of the elastic stage of the bending moment-deflection curve increases with the increase of the axial force in the composite structure. (3) As the axial force of the composite structure increases, the flexural bearing capacity of the structure increases first and then decreases.

Simulation of Load–Slip Capacity of Timber–Concrete Connections with Dowel-Type Fasteners

Quality assessment of stiffness and load-carrying capacity of composite connections is of great importance when it comes to designing timber–concrete composite structures. The new European regulation intended explicitly for timber–concrete structures has made a significant contribution to this field, considering that until today there was no adequate design standard. Due to the proposed general expressions for determining the stiffness and load-carrying capacity of composite connections made with dowel-type fasteners, which are incapable of describing most of the commonly applied fasteners, engineering, and scientific practice remained deprived of a quality assessment of the essential mechanical properties of the connection. In order to overcome this problem, this paper proposes a numerical model of the connection suitable for determining the whole load–slip curve, allowing it to estimate the stiffness and load-carrying capacity of the connection. The model was developed by considering the non-linear behavior of timber and fasteners, which is determined through simple experimental tests. For the numerical model validation, experimental tests were carried out at the level of the applied materials and on the models of the composite connection. Through numerical simulations, analysis of obtained results, and comparison with experimental values, it can be confirmed that it is possible to simulate the pronounced non-linear behavior of the timber–concrete connection using the proposed model. The estimated values of stiffness and load-carrying capacity are in agreement with the conducted experimental testing. At the same time, the deviations are much less than the ones obtained from recommendations given by the new regulation. Additionally, apart from evaluating the value and the simulation of the complete curve, it is possible to determine local effects, such as the crushing depth in timber and concrete, the fastener’s rotation, and the participation of forces in the final capacity of the connection.

Prediction of long-term durability of unidirectional/multidirectional basalt fiber- and hybrid fiber-reinforced polymer profiles under concrete environment

Recently, concrete composite structures based on a fiber-reinforced polymer (FRP) profile, which serves in the corresponding alkaline concrete environment have been widely used. Unlike FRP bars, the long-term durability of FRP profiles in concrete remains unclear, particularly for those with multidirectional (MD) or hybrid fibers, whose internal structure differs from that of FRP bars. This study focused on the tensile strength degradation of FRP profiles exposed to an artificial concrete environment solution at various ambient temperatures. Three types of FRP specimens were considered, including unidirectional (UD) basalt FRP (BFRP), MD BFRP and MD basalt-carbon hybrid FRP profiles. The results show that the alkaline environment of the concrete caused a decrease in the tensile strength of the FRP profiles, and the rate of degradation in strength significantly accelerated as the ambient temperature increased; however, the environment had no apparent effect on the elastic modulus. In addition, the strength degradation of MD FRP profiles was more significant than that of UD FRP profiles after corrosion due to insufficient impregnation of the fibers by the resin, which results in initial defects as well as increased intrusion of external moisture and corrosive media. Scanning electron microscopy (SEM) was employed to analyze the morphology and degradation mechanism of FRP profiles in a concrete environment. Moreover, a long-term prediction method for tensile strength retention of three types of FRP profile in arbitrary ambient temperatures is proposed based on the Arrhenius equation.

Numerical investigation of the effects of symmetric and eccentric earthquake-induced pounding on accelerations and response spectra for two-storey structures

This paper examines the effect of symmetric and eccentric earthquake-induced pounding between adjacent two-storey structures on acceleration times histories and response spectra. The numerical investigation benefits from experimental data issued from an extensive shake table campaign involving two-storey steel–concrete composite structures and slab-to-slab contacts. It is shown that the high frequency branch of the floor response spectra is only related to the maximum impulse acceleration spike during time, characterized by its impulse value, contact duration and time-history shape. In order to numerically reproduce such characteristics, three-dimensional detailed models are set up by modeling the slab with shell elements or hexahedral elements. Previously developed explicit time integrator, the CD-Lagrange scheme, based on non-smooth contact dynamics approach, is employed for ensuring the contact conditions expressed in terms of velocity and impulse, without requiring any contact parameters such as contact stiffness, local damping and restitution coefficient. The eccentric pounding between slabs is simulated by introducing a small defect in the parallelism of the colliding slabs, as measured in experience. The results of eccentric and symmetric pounding, assuming elastic behavior for the steel and concrete materials, are compared with the experimental data in terms of acceleration time-histories and pseudo-acceleration response spectra. It is concluded that symmetric pounding predicts an acceleration spike with a more abrupt increase to the peak and a shorter contact duration in comparison to experimental data, leading to an overestimation of the high frequency branch of the response spectra. On the contrary, eccentric pounding achieves to reproduce the experimental acceleration time histories as well as response spectra up to 400 Hz. Finally, the robustness of the proposed numerical approach is underlined by changing the time step size of the CD-Lagrange scheme as well as by prospecting different relevant choices concerning the Rayleigh damping.

Pullout performance of headed anchor studs in Engineered Cementitious Composites (ECC) with Polyvinyl Alcohol fibers

To study the pull-out resistance of headed anchor studs in Engineered Cementitious Composites (ECC) for steel-ECC composite structures, pull-out tests were carried out on 9 scenarios of ECC specimens. The failure modes, load–displacement curves, peak load (Nu), initial stiffness (K0.3), and ultimate displacement (Du) of studs in Polyvinyl Alcohol fiber (PVA)-ECC under different stud sizes (d = 13 mm and 16 mm), stud embedment depths (hef = 40 mm, 60 mm, and 80 mm) and fiber content (Vf = 2.0% and 2.5%) were obtained. Failure modes include (ductile) concrete cone failure, cone-splitting combined failure, and steel failure. For the specimens with concrete cone, either increasing d or hef increases K0.3, Nu, and Du, and Nu shows the greatest improvement. Increasing fiber content (Vf) exerts a significant enhancing effect on Nu, but exerts little effect on K0.3 and Du. Through the comparisons to the pull-out resistance of studs in high-strength concrete (HSC), the studs in ECC show evident advantages in ductility, toughness, and Nu. Based on the experimental results, the applicability of the original CCD model and two modified CCD models from literature to studs in ECC is discussed. The modified CCD model including the effect of stud size and specimen size presents the best accuracy in predicting Nu of studs in ECC. Overall, ECC is a promising material for steel–concrete composite structures, considering it evidently improves the pull-out performance of studs, thus the anchorage between steel and ECC.

Dispersion characteristics of surface wave in SCCS: theoretical analysis, numerical simulation and MASW-based NDT

To fully validate the feasibility of multichannel analysis of surface waves (MASW)-based interfacial debonding detection for steel–concrete composite structures (SCCS), dispersion characteristics of surface waves in SCCS are systematically investigated using theoretical analysis and elaborate 3D numerical simulations. First, the influences of material strength and thickness of concrete core, steel plate thickness on the dispersion figures are analyzed based on the theoretical dispersion characteristic of Rayleigh wave. Scientific layering strategy, including single steel plate, double-layer, and three-layer medium assumptions, is investigated using the theoretical dispersion analysis of Lamb wave. Besides, the dispersion characteristics of surface wave in circular steel pipes are calculated to determine the appropriate theoretical dispersion curves for MASW measurement. Finally, the stress wave propagation processes in SCCSs with various internal structures, including stiffeners, studs, and diaphragms, as well as the debonding width, are simulated using 3D numerical simulation to validate the research finding of theoretical analysis and detectability of MASW-based non-destructive testing on interfacial debonding defects in rectangular and circular concrete-filled steel tubulars. Finally, the dispersion characteristics corresponding to displacement, velocity, and acceleration of surface waves are comparatively discussed. The research findings of this study are the cornerstone of experimental study and essential theoretical support for identifying interfacial debonding and bond-slip damage of SCCS components utilizing MASW method.

Review on Analysis of Structure and Design of Steel Bridge Using Staad Pro Software

Abstract: In this study the T-beam bridge is to be analysis on the staad pro sofware. A T-beam bridge is composite concrete structure which is composed of slab panel, longitudinal girder and cross girder. This project looks on the work of analysis and design of bridge deck and beam on software the specific bridge model is taken of a particular span and carriageway width the bridge is subjected to different IRC loadings like IRC Class AA, IRC Class 70R tracked loading etc. in order to obtain maximum bending moment and shear force. From the analysis it is observed and understand the behavior of bridge deck under different loading condition and comparing the result. The different codes of design will be use in this project are IRC 5-2015,IRC 6-2016, IRC 112-2011, IRC 21-2000.

Experimental study on the elastic-plastic dynamic response of shallow-buried corrugated steel-plain concrete composite structures under long-duration plane blast wave loading

To study the elastic-plastic dynamic response characteristics of shallow-buried corrugated steel-plain concrete (CSPC) composite structures under long-duration plane blast loads, a series of tests were conducted in a large confined blast-resistant test facility using the plane charge explosion technique (PCET), and the dynamic response and deformation laws of CSPC arches, reinforced concrete (RC) arches and plain concrete (PC) arches under different blast loads were comprehensively compared and analyzed. The test results show that under this test condition, the plane air shock wave overpressure peak with the increase in charge is basically a linear growth, but the shock wave pressure duration of action and impulse growth rate gradually decreased, the test device simulated by the explosion shock wave pressure duration of the maximum action time of more than 340 ms. Comparing the differences in the dynamic response of the three structures, it was found that when the peak long-duration shock wave overpressure acting on the structure reached 0.09 MPa, the PC model had plastic deformation, and the combined reinforced concrete and CSPC structure exhibited fully elastic deformation. When the peak shock wave overpressure reaches 0.238 MPa, the RC model begins to show plastic deformation. When the peak shock wave overpressure increased to 0.315 MPa, all models produced significant plastic deformation. The deformation resilience of the CSPC composite structure under the above-mentioned blast shock wave load is greater than that of RC and PC structures, which have good deformation recovery ability and can effectively reduce the damage to the structure by blast shock. On the contrary, the peak structural vibration acceleration caused by the blast shock wave is greater in the CSPC combined structure than in the RC and PC structure, and the deformation rebound and oscillation of the corrugated steel plate is the main way of impact energy dissipation. The results of the study provide an experimental basis for the simulation of long-duration plane blast waves and the optimal design of CSPC blast-resistant structures.

Bond-slip effect in novel steel box-concrete composite structures part Ⅰ: Short-term loading

Steel box-concrete composite beam (SBCCB) is a novel type of steel–concrete composite structure. The concrete part at compressive zones is enclosed by the steel box without shearing studs at the interface between concrete and steel plates. Bond-slip effect on structural performance of SBCCBs needs to be quantitatively analyzed. In this study, the negative influence of bond-slip effect in SBCCB on stress redistribution and additional deflection is investigated. The differential equations of the bond-slip in SBCCB are established according to force equilibrium and compatibility deformation of micro unit and bond-slip strength of square concrete-filled steel tubular (CFST). To validate the feasibility of proposed theoretical equations, finite element models of SBCCB are constructed using spring elements to simulate the bond-slip mechanism between concrete and steel plates. Analytical solutions of deflection and stress agree well with numerical simulation results and experimental measurement. The research findings in this study can provide essential theoretical foundations for the structural design of practical SBCCB.

Tensile behaviour of transverse reinforcement with different connection methods in single steel-plate concrete composite structures

Transverse reinforcement is key to the single steel-plate concrete composite (SSC) structure when subjected to out-of-plane shear and impact load. This research focuses on the tensile behaviour of two connection methods between transverse reinforcement and steel plate in SSC structure, namely the tie bar interlocked with the J-hook connector (TBIJC) and the tie bar overlapped with the headed stud (TBOHS), which are much more convenient in construction compared to direct welding connection. Pull-out tests are carried out on 10 groups of specimens with different detail parameters to verify their reliable performance. Various types of failure modes and corresponding experimental phenomena are observed and recorded. The interfacial slip between the tie bar and concrete was measured to reflect the load–deflection characteristics. Parametric studies are carried out on the tensile performance considering connector shape and dimensions, end-anchor form of the tie bar and concrete strength. Plastic limit analysis is performed based on twin shear strength criterion for concrete, and an analytical model is developed to predict the ultimate tensile resistance. The accuracy of the proposed model is validated against the test results. Finally, based on the test results, design suggestions are proposed for the tie bar connection details considering both mechanical performance and construction efficiency.

Seismic response mitigation of prefabricated industrial equipment structural frames through a hybrid isolation system

For reducing the excessive acceleration response of the critical equipment in a type of industrial equipment structural frames under strong earthquakes, a hybrid isolation system (HIS), incorporating linear natural rubber (LNR) and lead rubber (LR) bearings, is proposed. The efficiency and reliability of the HIS are verified through a series of full-scale shaking table tests on two prefabricated industrial moment resisting frames (MRFs), with respect to a corresponding fixed-base system (FBS). The structural dynamic characteristic and seismic performance of the two types of MRFs, i.e., reinforced concrete structure (RCS) and composite concrete-filled steel tube structure (CCFSTS), are examined both with the HIS and FBS subjected to a range of seismic intensities. The test results demonstrate the superior performance of the HIS in controlling transient acceleration response under near-fault, far-field and artificial ground motions. The average peak acceleration reduction coefficients (PARCs) of the HIS range between 75.60% and 79.51% in the two considered MRFs along two horizontal directions, with a strict satisfaction on the peak acceleration response for normal operation of the critical equipment. Also, the hysteretic behavior of the HIS is stable and controllable during the earthquake excitations. The peak transient displacement of the HIS is satisfactory, and the residual deformation is negligible even under the maximum considered earthquake (MCE) excitations. Besides, components of the two MRFs are undamaged during the whole test. Thus, with the capacity of protecting the acceleration-sensitive equipment and structural components, the proposed HIS possesses a great prospect in enhancing the structural resilience.

Push-out test of headed stud connectors subjected to freeze-thaw cycles and artificial corrosion

To obtain the shear capacity calculation method and competition failure mechanism of headed stud connectors of steel–concrete composite structures under the influence of freeze–thaw cycles (FTCs) and artificial corrosion (AC), the material performance of concrete specimens after the FTCs and push-out tests of 36 headed stud connectors specimens were tested under the influence of FTCs and AC. The cubic compressive strength, dynamic elastic modulus, and mass loss rate of C50 concrete were obtained under different FTCs. Failure modes, load-slip curve, shear capacity, and shear stiffness of stud connectors were investigated based on push-out tests of miniaturized specimens. Based on the nonlinear fitting of test data, a formula for calculating the shear capacity reduction factor is proposed. Results show that the shear capacity and stiffness of stud connectors will deteriorate due to the deterioration of concrete performance caused by FTCs or the weakening of stud section caused by AC. The two failure modes of stud breakage or concrete cracking will change with the aggravation of FTCs and AC effect.

Analysis of the explosion resistance of an I-shaped steel‒concrete composite structure under contact explosion

Reinforced concrete and steel structures are commonly used in bridge construction; thus, researchers have conducted relatively comprehensive analyses of their dynamic responses and damage mechanisms under blast loads. However, for a new type of I-shaped steel‒concrete composite structure with various structural performance advantages, there remains a lack of effective experiments and analyses of damage modes. In this paper, three I-shaped steel‒concrete composite specimens are designed and fabricated, and explosion experiments under different explosion scenarios are performed. The experimental results show that under the support of an I-shaped steel plate, the structure has a strong ability to withstand the blast load. The concrete damage area on the rear blast surface is small, and the I-shaped steel plate does not yield under a small explosive equivalent. Based on the experimental results, the dynamic response and failure behavior of the I-shaped steel‒concrete composite structure are numerically evaluated using Autodyn explicit dynamic analysis software. By considering different working conditions and by taking the deformation and damaged areas of the structure as the damage index, the key explosion resistance factors of the structure under contact explosion are studied. Some important structural parameters greatly influence the explosion resistance of the structure, including the thickness of the I-shaped steel plate; however, increasing the strength of concrete does not significantly improve the explosion resistance of the composite structure.

Experimental investigation of mechanically laminated straight or curved-and-tapered bamboo-concrete T-beams

This study echoes the rising demand for bio-based material in concrete composite structures in the race to accelerate carbon neutrality in construction. Noticing that most previous studies are focused on straight timber or engineered bamboo-to-concrete composite beams, this study developed straight or curved-and-tapered mechanically laminated bamboo-concrete (LBC) T-beams. Six layers of 26 mm thick laminated bamboo panels were glue laminated together to form the bamboo beams. The curved bamboo beams have three different rises of arch: 50 mm, 100 mm and 150 mm. All specimen beams were tested by four-point bending tests to evaluate their structural performances of the curved and straight LBC T-beams. To monitor the flange-to-web interface shear transfer, a novel interface shear slip calibration method that captures the longitudinal after-slip strain redistribution was developed and validated by strain gauge measurements. This study also highlights the interlayer shear bonding strength of laminated bamboo as the thresholding parameter that determines the composite beams' overall flexural strength, evidenced by detailed failure mode analysis. The proposed interface shear slip calibration method can be extended to the other types of shear connectors such as screws, nails, shear plates and notched connections.

Analysis and Assessment of Prestressed Reactive Powder Concrete Box-girder Bridge with Corrugated Steel Webs

Prestressed concrete box girder bridge with corrugated steel webs is a new type of bridge which uses corrugated steel webs to replace the traditional concrete webs. Compared with the traditional box girder bridge, it has certain advantages and has been widely used in bridge engineering. Combined with the characteristics of prestressed concrete box girder bridge with corrugated steel webs and reactive powder concrete theory, this paper puts forward the concept of new prestressed corrugated steel webs reactive powder concrete box girder bridge. By improving the material properties, structural design and construction methods of prestressed concrete composite structure with corrugated steel webs, its bearing capacity can be improved, so as to improve its construction efficiency and economic benefits. The research shows that the prestressed reactive powder concrete box girder with corrugated steel webs has the advantages of light structure and convenient construction, and has superior mechanical properties and obvious economic benefits when it bears the equivalent external load of prestressed corrugated steel web concrete composite girder.

Development of hybrid models for shear resistance prediction of grouped stud connectors in concrete using improved metaheuristic optimization techniques

Shear connectors are essential in ensuring a composite action in steel–concrete structures. An accurate estimation of the shear resistance of group stud connectors (GSC) is crucial for the design of steel–concrete composite structures. Overfitting problems arise when the artificial neural network (ANN) is trained using traditional optimization algorithms. However, metaheuristic algorithms maintain the equilibrium between exploitation and exploration in solving this problem. This study combines metaheuristic optimization algorithms, including classical particle swamp optimizer (PSO) and novel improved eliminate particle swamp optimizer (IEPSO) with ANN. The proposed algorithms was used to simulate the shear resistance of GSC. A total of 232 data points of push-out test results were collected. The results show that the ANN-IEPSO with simpler architectures outperforms ANN-PSO and traditional optimization algorithms. The efficacy of the metaheuristic algorithms was benchmarked against four existing design codes, including AASHTO, EC 4, JSCE, and GB50017. The global sensitivity analysis visualizes the relationship between the six predictors and target shear resistance and shows the interaction between the two predictors. The number of studs, stud diameter, and stud spacing are the most critical parameters in predicting the shear resistance of the GSC.

Experimental and analytical study on the mechanical properties of U-shaped steel-encased composite beams

The U-shaped steel-encased composite beam is a new type of steel–concrete composite structure comprising concrete filled in a variable U-shaped steel structure. The steel and concrete are combined by shear connectors arranged on the web and bottom plate. Compared with traditional composite beams, this beam better utilises the steel, exhibits superior mechanical performance, and is more suitable for constructing composite structures. To study the mechanical behaviour of this type of beam under static load, four small-scale simply supported specimens were tested. Their main parameters were height, thickness of the encasing steel plate, and length of the shear span. The failure modes, load–displacement curves, distribution of strain along the section height, and slip of the encasing steel plate were investigated. The specimens exhibited typical failure modes such as oblique section shear failure, mixed bending failure, and longitudinal slip failure. Based on the simplified plastic theory and the experimental results, formulae for calculating the flexural bearing capacity of the composite beam under a positive bending moment, bearing capacity considering slip, and shear bearing capacity of the oblique section were derived. This paper presents experimental research and a theoretical analysis for the engineering application of U-shaped steel-encased composite beams.