• Journal of Korean Society of Steel Construction
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• v.27 no.2
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• pp.143-153
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• 2015

In this paper, the standard fire resistance test under load and associated numerical study were carried out to evaluate the fire resistance of unprotected partially encased beams and slimfloor beams. The temperature evolution and the deflection increase of the composite beam specimens were investigated and the effects of the key behavioral parameters including the load ratio, the reinforcement, and the fire exposure were analyzed. The test results showed that the temperature rise of the partially encased beams and slimfloor beams is considerably slow compared to the conventional H-shape composite beams. Up to at least 90 minutes, the reinforcements in the partially encased composite beams maintained below the temperature at which the cold steel strength is sustained. Unprotected partially encased beams and slimfloor beams in the experimental program achieved the fire resistance more than 2 hours according to the limiting deflection criteria. This implies that unprotected partially encased beams and slimfloor beams can be very promising alternatives to enhancing the fire resistance of steel beams. This study also conducted the fully coupled thermal-stress analysis by using the commercial code ABAQUS to the thermal and structural behaviour of composite beams in fire. The numerical predictions provide acceptable correlations with the experimental results.

• Steel and Composite Structures
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• v.38 no.6
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• pp.705-716
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• 2021

An innovative partially precast partially encased composite beam (PPECB) is put forward based on the existing research. In order to study the flexural performance of the new composite beam which has precast part and cast-in-place part, six prefabricated specimens and one cast-in-place specimen are designed with considering the influence of the production method, the steel flange thickness, the concrete strength grade and the stirrup process on the behavior of the composite beam. Through four points loading and test data collection and analysis, the behavior of partially prefabricated specimen is similar to that of cast-in-place specimen, and the casting method, the thickness of the steel flange, the concrete strength grade and the stirrup process have different influence on the crack, yield and peak load bearing capacity of the component. Finally, the calculation theory of plastic bending of partially precast partially encased concrete composite beams is given. The calculation results are in good agreement with the experimental results, which can be used for practical engineering theory guidance. This paper can provide reference value for further research and engineering application.

• Steel and Composite Structures
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• v.44 no.6
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• pp.883-898
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• 2022

A hollow-core partially-encased composite beam, named HPEC beam, is investigated in this paper. HPEC beam comprises I-beam, longitudinal reinforcement, stirrup, foam formwork, and cementitious grout. The foam formwork is located on both sides of the web, and cementitious grout is cast within the steel flange. To investigate the shear performance of HPEC beams, static loading tests of six HPEC beams and three control beams were conducted. The shear span ratio and the number of studs on the shear behavior of the HPECspecimens were studied. The failure mechanism was studied by analyzing the curves of shear force versus both deflection and strain. Based on the shear span ratio (𝜆), two typical shear failure modes were observed: shear compression failure when 1.6 ≤ 𝜆 ≤ 2; and diagonal compression failure when 𝜆 ≤ 1.15. Shear studs welded on the flange can significantly increase the shear capacity and integrity of HPEC beams. Flange welded shear studs are suggested. Based on the deformation coordination theory and superposition method, combined with the simplified modified compression field model and the Truss-arch model, Modified Deformation Coordination Truss-arch (M.D.C.T.) model was proposed. Compared with the shear capacity from YB9038-2006 and JGJ138-2016, the calculation results from M.D.C.T. model could provide reasonable predictions.

• Steel and Composite Structures
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• v.50 no.4
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• pp.419-428
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• 2024

Prefabricated partially-encased composite (PEC) structural component is widely used in construction industry due to its superior structural performance and easy assembly characteristic. However, the solid web in traditional PEC components tends to split concrete into two halves, thus potentially reduces structural integrity and requires double concrete pouring. To overcome the above disadvantages, a new PEC beam with open-web π-shaped steel is proposed in this paper. Four open-web PEC beams with varying sectional height, flange thickness and web void rate were constructed and tested under flexural loads. During experimental tests, all beams exhibited typical flexural failure modes with strong moment capacities and excellent ductility. Owing to the unique construction form of web opening, steel-concrete bonding properties were enhanced and very small relative steel-concrete slips were observed. Experimental results also showed that the flexural capacity of such PEC beams increased with the increase of the sectional height and flange thickness, while was not affected by the web void rate. At last, a flexural capacity formula of the open-web PEC beam was proposed based on the whole section plastic rule. The formula results agreed well with experimental results.

• Steel and Composite Structures
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• v.20 no.2
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• pp.251-266
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• 2016

The paper combines two distinct parts. First the behavior of welded headed studs with small diameters of 10 and 13 mm acting as shear connectors (which are not embraced in current standards) is studied. Based on standard push tests the load-slip relationships and strengths are evaluated. While the current standard (Eurocode 4 and AISC) formulas used for such studs give reasonable but too conservative strengths, less conservative and full load-slip rigidities are evaluated and recommended for a subsequent investigation or design. In the second part of the paper the partially encased beams under bending are analyzed. Following former experiments showing rather indistinct role of studs used for shear connection in such beams their role is studied. Numerical model employing ANSYS software is presented and validated using former experimental data. Subsequent parametric studies investigate the longitudinal shear between steel and concrete parts of the beams with respect to friction at the steel and concrete interface and contribution of studs with small diameters required predominantly for assembly stages (concreting). Substantial influence of the friction and effect of concrete confinement was observed with rather less noticeable contribution of the studs. Distribution of the longitudinal shear and its sharing between friction and studs is presented with concluding remarks.

• Steel and Composite Structures
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• v.18 no.5
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• pp.1119-1127
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• 2015

A finite-element model for beams with partially delaminated layers is used to investigate their behavior. In this formulation account is taken of lateral strains and the first-order shear deformation theory is used. Both displacement continuity and force equilibrium conditions are imposed between the regions with and without delamination. Numerical results of the present model are presented and its performance is evaluated for static and dynamic problems.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.4
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• pp.461-473
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• 2000

This paper deals with a numerical model for the time-dependent analysis of steel and concrete composite beams with partial shear connection. A linear partial interaction theory is adopted in formulation of structural slip behavior, and the effect of concrete creep and shrinkage are considered. The proposed model is effective in simulating the slip behavior, combined with concrete creep and shrinkage, of multi-span continuous composite beams. Finally, correlation studies and several parameter studies are conducted with the objective to establish the validity of the proposed model.

• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.143-153
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• 2003

New strengthening method based on Near Surface Mounted technique (NSM) is suggested, which can overcome the brittle nature of failure inherent to those reinforced concrete beams strengthened with FRP composite materials. The suggested technique secures ductile failure of reinforced concrete beams by having the strengthening Hybrid FRP rebars unbonded in parts. Experiments were performed in order to compare structural behaviors of strengthened beams with and without unbending along the Hybrid FRP rebars. Test results showed that only those beams strengthened by partially unbonded NSM failed in ductile manner. Theoretical expressions were derived for the minimum unbonded length of Hybrid FRP rebars with which ultimate strength of the reinforced concrete beam with partially unbonded NSM could be reached. The suggested partially unbonded NSM technique is expected to significantly improve the structural behavior of the strengthened beam with FRP composite materials.

• Journal of the Korea institute for structural maintenance and inspection
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• v.2 no.4
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• pp.177-185
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• 1998

This paper deals with the flexural behaviors of R.C beams strengthened by carbon fiber sheets. The behaviors of strengthened beams which were preloaded up to 50%, 60% and 70% of the ultimate load of unstrengthened beam are compared with that of a beam which was not preloaded. The structural behaviors of strengthened beams are compared with analytical method in terms of load-strain of concrete, load-strain of steel bar, load-strain of CFS and falilure load. Four cases of analytical method are investigated according to cracked section or partially cracked section and including strain hardening effect of steel bar or not. Comparing the results of test and analysis, both are similar in terms of load-strain of concrete, and falilure load, the results of analytical method underestimate the failure load. But each results of load-strain of steel bar, load-strain of CFS near at failure is some different, thus near at failure the composite action between CFS and upper concrete is assumed to be disturbed. Consequently, the analytical method was proved to be efficient and accurate in estimating the flexural response of CFS strengthened RC beams.

• Composites Research
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• v.30 no.6
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• pp.343-349
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• 2017

A multifield variational formulation is developed for the finite element (FE) cross-sectional analysis of composite beams. The cross-sectional warping displacements and sectional stresses are considered to be the primary variables through the application of Reissner's partially mixed principle. The warping displacements are modeled using generic FE shape functions with nonlinear distribution over the beam section. A generalized Timoshenko level stiffness matrix is derived which incorporates the effects of elastic couplings, transverse shear, and Poisson's deformations. The accuracy of the present analysis is validated for the stiffness constants and elastostatic responses of composite box beams which correlate well with the experimental data and other state-of-the-art approaches.