Behavior Of Composite Frames Research Articles

Experimental and Numerical Studies on Seismic Behavior of Composite Frames with Initial Heavy Load Conditions

This study investigates the seismic behavior of composite frames with initial heavy load conditions. Two frame specimens consisting of square concrete-filled steel tube (CFST) columns and steel-reinforced concrete (SRC) deep beams were fabricated and poured using ordinary concrete and high-strength concrete, respectively. Thereafter, the two specimens were tested under cyclic loadings, and the failure models, hysteretic behavior, bearing capacity, ductility, and accumulated energy dissipation of the specimens were investigated in detail. The experimental results revealed that both of the specimens failed owing to the local buckling at the column ends. This kind of composite frame has good seismic performance and can be regarded as a high-ductility structure. Moreover, a finite element (FE) model was developed and verified by the experimental results. The effects of the typical parameters, such as the material strength and axial compression ratio, were studied using the FE model. The parametric study demonstrates that increasing the yield strength of the steel tube can effectively improve the ultimate bearing capacity of the composite frame and that decreasing the axial compression ratio is a valid method for improving the ductility of the structure.

Effect of boundary conditions on the behaviour of composite frames against progressive collapse

Boundary conditions, such as the horizontal and out-of-plane restraints, play an important role in structural resistance and deformation capacity of composite frames under column removal scenarios. Most studies only focused on interior frames with rigid horizontal and out-of-plane restraints, whereas limited data are available on the effects of weak restraints and out-of-plane rotations on the behaviour of composite frames against progressive collapse. In this study, a series of experimental tests were conducted on composite frames with different horizontal and out-of-plane restraints. Web cleat and flush end plate connections were used in the frames. Experimental results showed that when subject to in-plane loading, exterior composite frames could mobilise significant catenary action to mitigate progressive collapse and eventually column failure might occur under catenary action in bridging beams. For composite frames with out-of-plane rotation, the ultimate resistance was substantially reduced due to lateral torsional buckling of composite beams at large deformation stage. However, the flexural resistance of frames was less susceptible to boundary conditions compared to catenary action. Furthermore, bending moments at side columns were evaluated to gain insight into the behaviour of side columns under horizontal tension force at the catenary action stage. Moreover, component-based models were developed for composite frames and validated against test data. Design recommendations were provided in accordance with experimental and numerical results.

Behaviour of composite frames with castellated steel beams at elevated temperatures

The behaviour of composite frames with castellated steel beams at elevated temperatures is investigated, and the results obtained were compared with the companion results of simply supported composite castellated steel beams. Overall, it is aimed to investigate the effect of axial and rotational restraining of the steel beam via rigid connections with protected steel columns at elevated temperatures. A previously reported finite element model for the analysis of composite beams in fire was extended to perform the nonlinear analyses of composite frames at elevated temperatures. The finite element model has accounted for the frame geometries and boundary conditions, nonlinear material properties of steel, concrete, profiled steel sheeting, longitudinal and lateral reinforcement bars as well as shear connection behaviour at ambient and elevated temperatures. The thermal properties at the steel beam top flange/profiled steel sheeting and profiled steel sheeting/concrete elements interfaces were considered in the thermal heat transfer analysis that allowed the temperatures to be accurately predicted in the composite slab during fire exposure. The comparison of composite frames and composite beams behaviour has shown that if the columns were sufficiently protected and the connection maintained its rigidity during fire exposure, such that it can restrain the composite beam thermal expansions, this would result in considerable reduction in fire resistances of the composite frames compared with that of simply supported composite beams. This is attributed to the premature failure at elevated temperatures due to local buckling at the bottom flange of the steel beams in the frame connections. Furthermore, the variables that influence the fire resistance and behaviour of the composite frames comprising different load ratios during fire, different fire curves, presence of web openings and different steel grades were investigated by parametric studies. It is shown that the strength of steel and the fire scenarios have a considerable effect on the time–displacement behaviour and fire resistances of the composite frames.

Seismic analysis of CFST frames considering the effect of the floor slab

This paper describes the refined 3-D finite element (FE) modeling of composite frames composed of concrete-filled steel tubular (CFST) columns and steel-concrete composite beams based on the test to get a better understanding of the seismic behavior of the steel-concrete composite frames. A number of material nonlinearities and contact nonlinearities, as well as geometry nonlinearities, were taken into account. The elastoplastic behavior, as well as fracture and post-fracture behavior, of the FE models were in good agreement with those of the specimens. Besides, the beam and panel zone deformation of the analysis models fitted well with the corresponding deformation of the specimens. Parametric studies were conducted based on the refined finite elememt (FE) model. The analyzed parameters include slab width, slab thickness, shear connection degree and axial force ratio. The influences of these parameters, together with the presence of transverse beam, on the seismic behavior of the composite frame were studied. And some advices for the corresponding seismic design provisions of composite structures were proposed.

Nonlinear Finite Element Analysis on Seismic Behavior of Concrete Filled Square Steel Tube Planar Frames

This paper presents a nonlinear numerical analysis on the seismic behavior of concrete filled square steel tube (CFST) columns and steel beam planar frame with through bolt-endplate beam-column connection, by using the finite element analysis modeling with ABAQUS. Parametric studies were conducted to investigate the influence of axial load ratio and beam-to-column linear stiffness ratio on the seismic behavior of composite frames. The analysis results were in good agreement with the experiment results. The analysis results showed that CFST frame with through bolt-endplate beam-column connection had good seismic behavior. The increase of axial load ratio will degrade the horizontal load bearing capacity and increase the energy dissipation capability. The increase of beam-to-column linear stiffness ratio will increase the horizontal load bearing capacity and degrade the energy dissipation capability.

Nonlinear Finite Element Analysis on Seismic Behavior of Concrete Filled Square Steel Tube Planar Frames

This paper presents a nonlinear numerical analysis on the seismic behavior of concrete filled square steel tube (CFST) columns and steel beam planar frame with through bolt-endplate beam-column connection, by using the finite element analysis modeling with ABAQUS. Parametric studies were conducted to investigate the influence of axial load ratio and beam-to-column linear stiffness ratio on the seismic behavior of composite frames. The analysis results were in good agreement with the experiment results. The analysis results showed that CFST frame with through bolt-endplate beam-column connection had good seismic behavior. The increase of axial load ratio will degrade the horizontal load bearing capacity and increase the energy dissipation capability. The increase of beam-to-column linear stiffness ratio will increase the horizontal load bearing capacity and degrade the energy dissipation capability.

Seismic behavior of CFRSTC composite frames considering slab effects

This paper reports on an experimental and numerical investigation conducted on the seismic behavior of concrete-filled rectangular steel tubular columns (CFRSTC) composite frames. The experimental study was conducted by subjecting two full-scale composite frames to simulated seismic loads. Both frames were composed of CFRSTC and steel beams. One specimen was placed on a reinforce concrete (RC) floor slab and the other was not. The purpose of the test was to investigate the elasto-plastic performance of the CFRSTC composite frame system and to examine the effects of composite action on the behavior of composite frames. The test results showed that the stiffness, strength and energy-dissipating capacity of the CFRSTC frame increased significantly with the presence of the floor slab. Compared with a bare steel beam, the composite beam experienced a decrease in the rotation capacity from 0.046 rad to 0.026 rad. The shear deformation of the panel zone grew because of the composite action, which delayed the fracture of the beam. Finite element (FE) models were established to simulate the tested frames. The results of the FE model fit well with that of the test model in terms of stiffness, strength, hysteretic behavior and component deformation.

Modeling and investigation of elasto-plastic behavior of steel–concrete composite frame systems

This paper presents a mixed finite-element model combining the fibered beam and layered shell elements using the general finite-element program MSC.MARC (2005r2) based on the discussion and comparison of the previous models. The proposed modeling procedure is intended for integrated elasto-plastic analysis of fully connected steel–concrete composite frames subjected to the combined action of gravity and monotonic lateral loads. The model is verified by extensive experiments and examples, and the behavior of composite frames is also investigated intensively. The slab space composite effect and the beam–column semi-rigidity are the two critical factors influencing the structural behavior. These two factors have not been considered simultaneously in some previous models but can be both included in the proposed model. Due to the complex slab space composite effect in composite frames, the previous models with a constant-width effective flange of slab can not trace the actual nonlinear slab behavior, but the proposed model can give accurate results. Since the slip effect between the steel beam and RC slab has negligible influence on the global calculation results of the structural system verified by the calculation examples, the slip effect is neglected in the present study to simplify the modeling procedure and enhance the calculating efficiency. The proposed model possesses good accuracy and broad applicability with simple modeling procedure and high calculation efficiency, and has a great advantage for the large-scale integrated analysis of multistory and high-rise composite frames.

Finite Element Analysis on Load-Bearing Behavior of Concrete Filled Steel Tubular Composite Frames

This paper presents a nonlinear finite element (FE) analysis on the mechanic behavior of concrete filled steel tubular (CFST) composite frames. The main purpose of the FE analysis was to investigate the seismic behavior of composite frames. Three kinds of nonlinearity, namely material nonlinearity, contact nonlinearity and geometry nonlinearity, were taken into account in the FE model using MSC.Marc. The element type, connection between element, material constitutive law and boundary condition was described in detail. The elasto-plastic behavior, as well as fracture and post-fracture behavior, of the FE analysis models fitted well with those of the test specimens. The beam and panel zone deformation of the analysis models is also in good agreement with that of the test specimen. It is concluded that FE model of CFST composite frame is reliable and could be regarded as a helpful tool to expand the information on seismic behavior of CFST composite frame.

Nonlinear Analysis of CFT Composite Frame with Floor Slab

Nonlinear finite element (FE) analysis models of CFT composite frames with floor slab were established by Msc.Marc to investigate the seismic behavior of composite frames. A number of material nonlinearities and contact nonlinearities, as well as geometry nonlinearities, were taken into account, including elastoplastic properties of steel and concrete, concrete cracking and tension stiffening, steel fracture, interface slip between concrete slabs and steel beams, P-D effects etc. The elasto-plastic behavior, as well as fracture and post-fracture behavior, of the FE analysis models agreed well with those of the test specimens. The beam and panel zone deformation of the analysis models is also in good agreement with that of the test specimen. It is concluded that FE analysis is useful not only for monotonic load analysis but also for cyclic load analysis. It is a helpful tool to expand the information on seismic behavior of composite frame.

Preliminary Study on Post-Fire Behavior of Composite Frame with CFST Columns and Composite Beam

A 3-D finite element model (FEM) using ABAQUS was introduced in this paper to simulate the post-fire behavior of composite frames with concrete-filled steel tubular (CFST) columns and steel beam with reinforced concrete slab. Accurate thermal and material model, element type, and solution method were assumed in the model considering the temperature effect during the fire. Some composite joint specimen post-fire tests were modeled using the FEM. The results obtained from the FEM were verified against those experimental results. The mechanism of the composite frame was investigated based on the FEM.

Behavior of composite frames during construction

Composite construction has been widely used for building structures over the past 25 years. Initially developed for beams and girders in buildings and bridges, composite elements now also include columns and shear walls, and are frequently utilized in high-rise structures, owing to their axial load capacity and stiffness. The last few years have seen the development of the complete composite frame, where the advantages of steel and concrete are combined to provide structural systems of great strength and stiffness. The complexities of the design and construction of these frames are legion, however; in particular because the designer must consider the construction method very carefully to ensure satisfactory performance. The paper discusses the unique design considerations that must be made, including the effects of construction sequence on the overall stability and strength, and makes recommendations for design procedures.