• Steel and Composite Structures
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• v.16 no.4
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• pp.417-436
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• 2014

During an earthquake, steel frame columns can be subjected to high axial forces combined with inelastic rotation demand resulting from story drift. Generally, the whole beam or component can be represented with one element. In elasto-plastic analysis, subdivision is necessary if the plastic deformation occurs within two ends of beams. If effects of the joint panel are necessarily considered in the analysis, the joint panel should be represented with an independent element. It is a special element to represent the shear deformation of the joint panel in the beam-column connection zone. Several analytical models for panel zone (PZ) behavior exist, in terms of shear force-shear distortion relationships. Among these models, the Krawinkler PZ model is the most popular one which is used in the AISC code. Some studies have pointed out that Krawinkler's model gives good results for the range of thin to medium column flanges thickness. This paper, introduces a new model to estimate the response of shear force-shear distortion for the PZ including column axial force. The model is applicable to both thin and thick column flange. To achieve an appropriate PZ mathematical model first, the effects of PZ strength and stiffness on connection response are parametrically studied using finite element models. More than one thousand and four-hundred beam-column connections are included in the parametric study, with varied parameters; then based on analytical results a simple mathematical model is presented. A comparison between the results of proposed method herein with FE analyses shows the average error especially in thick column flange is significantly reduced which demonstrates the accuracy, efficiency, and simplicity of the proposed model.

• Steel and Composite Structures
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• v.26 no.4
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• pp.463-471
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• 2018

The bolted end-plate beam-column connections have been widely used in steel structure and composite structure because of its excellent seismic performance. In this paper, the end-plate bolted connection is applied in the concrete structure, A new-type of fabricated beam-column connections with end-plates is presented, and steel plate hoop is used to replace stirrups in the node core area. To study the seismic behavior of the joint, seven specimens are tested by pseudo-static test. The experimental results show that the new type of assembly node has good ductility and energy dissipation capacity. Besides, under the restraint effect of the high-strength stirrup, the width of the web crack is effectively controlled. In addition, based on the analysis of the factors affecting the shear capacity of the node core area, the formula of shear capacity of the core area of the node is proposed, and the theoretical values of the formula are consistent with the experimental value.

• Steel and Composite Structures
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• v.9 no.3
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• pp.191-208
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• 2009

Observations from experiments and real fire indicate that restrained steel beams have better fire-resistant capability than isolated beams. Due to the effects of restraints, a steel beam in fire condition can undergo very large deflections and the run away damage may be avoided. However disgusting damages may occur in the beam-to-column connections, which is considered to be mainly caused by the enormous axial tensile forces in steel beams resulted from temperature decreasing after fire dies out. Over the past ten years, the behaviour of restrained steel beams subjected to fire during heating has been experimentally and theoretically investigated in detail, and some simplified analytical approaches have been proposed. While the performance of restrained steel beams during cooling has not been so deeply studied. For the safety evaluation and repair of steel structures against fire, more detailed investigation on the behaviour of restrained steel beams subjected to fire during cooling is necessary. When the temperature decreases, the elastic modulus and yield strength of steel recover, and the contraction force in restrained steel beams will be produced. In this paper, an incremental method is proposed for analyzing the behaviour of restrained steel beams subjected to cooling. In each temperature decrement, the development of deformation and internal forces of a restrained beam is divided into four steps, in order to consider the effect of the recovery of the elastic modulus and strength of steel and the contraction force generated by temperature decrease in the beam respectively. At last, the proposed approach is validated by FE method.

• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.617-624
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• 2008

Well-designed steel moment connections will undergo local buckling before they exhaust their available rotation capacity, and inelastic post-buckling deformation plays a major role in defining the connection rotation capacity. An approximate analytical method to model strength degradation and failure of beam plastic hinges due to local buckling and estimation of the seismic rotation capacity of fully restrained beam-column connections in special steel moment-resisting frames under both monotonic and cyclic loading conditions is proposed in this study. This method is based on the plastic mechanism and a yield line plastic hinge (YLPH) model whose geometry is determined using the shapes of the buckled plastic hinges observed in experiments. The proposed YLPH model was developed for the improved WUF-W and RBS connections and validated in comparison with experimental data. The effects of the beam section geometric parameters on the rotation capacity were discussed in the companion paper (parametric studies).

• Structural Engineering and Mechanics
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• v.18 no.4
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• pp.389-410
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• 2004

In this study, theoretical and experimental results are presented which were obtained during an investigation of the influence of the $P-{\Delta}$ effect that was caused by the simultaneous changing of the axial load P of the column and the lateral displacement ${\Delta}$ in the external beam-column joints. The increase or decrease of ${\Delta}$ was simultaneous with the increase or decrease of the axial compression load P and caused an additional influence on the aseismic mechanical properties of the joint. A total of 12 reinforced concrete exterior beam-column subassemblies were examined. A new model, which predicts the beam-column joint ultimate shear strength, was used in order to predict the seismic behaviour of beam-column joints subjected to earthquake-type loading plus variable axial load and $P-{\Delta}$ effect. Test data and analytical research demonstrated that axial load changes and $P-{\Delta}$ effect during an earthquake cause significant deterioration in the earthquake-resistance of these structural elements. It was demonstrated that inclined bars in the joint region were effective for reducing the unfavourable impact of the $P-{\Delta}$ effect and axial load changes in these structural elements.

• Journal of Korean Society of Steel Construction
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• v.27 no.3
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• pp.289-298
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• 2015

The steel tube of Concrete-Filled Tube(CFT) confines the concrete and the concrete restrains the buckling of the tube, The objective of this study is to investigate the influences of the opening shape of the through diaphragm in case of the rectangular CFT column-to-beam connection through the structural experiment. The experiment results are compared with analysis results obtained by using the FEM program. These results are shown that strength of the rectangular CFT column-to-beam connection have similar structural performance regardless of the opening shape if opening areas of the through diaphragm are same. Also in case the connection area/shape of the through diaphragm and the flange of H-beam are similar, it was ascertained that the bending stress occurred at the beam can be transferred to the column through the diaphragm.

• Structural Engineering and Mechanics
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• v.57 no.5
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• pp.785-808
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• 2016

An innovative Reduced Beam Section (RBS) connection, called Tubular Web RBS connection (TW-RBS), has been recently introduced and its performance has been numerically investigated in some earlier studies. The TW-RBS connection is a kind of accordion-web RBS connection in which part of the flat web of the beam is replaced by a steel tube at the expected region of the plastic hinge. This paper presents experimental results of three TW-RBS connections under cyclic loading. Obtained results indicated that TW-RBS reduces contribution of the beam web to the whole moment strength and creates a ductile fuse far from components of the beam-to-column connection. Besides, TW-RBS connection can increase story drift capacity up to 9% in the case of shallow beams which is much more than those stipulated by the current seismic codes. Based on the experimental results, the tubular web in the plastic hinge region improves lateral-torsional buckling stability of the beam such that only local buckling of the beam flange at the center of the reduced section was observed during the tests. In order to achieve a better understanding, behavior of all TW-RBS specimens are also numerically investigated and compared with those of experimental results.

• Journal of Korean Society of Steel Construction
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• v.10 no.1 s.34
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• pp.25-35
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• 1998

A moment connection of H beam-to-rectangular tube column with external stiffeners was proposed. A formula to predict the ultimate strength of the connection was derived based on the yield line mechanism. Experimental investigation was performed to determine the applicability of the connection type and the strength formula. The ultimate strengths computed by the formula agreed well with the experimental values.

• Structural Engineering and Mechanics
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• v.23 no.4
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• pp.387-407
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• 2006

A Genetic Algorithm (hereinafter GA) based optimum design algorithm and program for plane steel frames with partially restrained connections is presented. The algorithm was incorporated with the refined plastic hinge analysis method, in which geometric nonlinearity was considered by using the stability functions of beam-column members and material nonlinearity was considered by using the gradual stiffness degradation model that included the effects of residual stress, moment redistribution by the occurrence of plastic hinges, partially restrained connections, and the geometric imperfection of members. In the genetic algorithm, a tournament selection method and micro-GAs were employed. The fitness function for the genetic algorithm was expressed as an unconstrained function composed of objective and penalty functions. The objective and penalty functions were expressed, respectively, as the weight of steel frames and the constraint functions which account for the requirements of load-carrying capacity, serviceability, ductility, and construction workability. To verify the appropriateness of the present method, the optimum design results of two plane steel frames with fully and partially restrained connections were compared.

• Structural Engineering and Mechanics
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• v.44 no.4
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• pp.539-569
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• 2012

The behaviour of beam-to-column connections plays an important role in the analysis and design of steel structures. A computer-based method is presented for nonlinear steel frames with semi-rigid connections accounting for shear deformations. The analytical procedure employs transcendental stability functions to model the effect of axial force on the stiffness of members. The member stiffness matrix, and the fixed end forces for various loads were found. The nonlinear analysis method is applied for three planar steel structures. The method is readily implemented on a computer using matrix structural analysis techniques and is applicable for the efficient nonlinear analysis of frameworks.