• Journal of Korean Society of Steel Construction
• /
• v.11 no.3 s.40
• /
• pp.271-279
• /
• 1999

Recently, studies on semi-rigid beam-to-column connections have been done to develop a T-stub element with separators between column face and T-stub flange. In this paper, inelastic analyses for the improved T-stub element are performed, and their results are compared with existing experimental results. The inelastic analyses using gap elements between column face and the separator, and initial stresses at the high-tension bolts result in good agreement with experimental results. Simplified design methods estimating the initial stiffness and the strength of the semi-rigid connection for compression force are proposed.

• Steel and Composite Structures
• /
• v.28 no.2
• /
• pp.209-221
• /
• 2018

An empirical and efficient method is presented for calculating the dynamic increase factor to amplify the applied loads on the affected bays of a steel frame structure with semi-rigid connections. The nonlinear static alternate path analysis is used to evaluate the dynamic responses. First, the polynomial models of the extended end plate and the top and seat connection are modified, and the proposed polynomial model of the flush end plate connection shows good agreement as compared with experimental results. Next, a beam model with nonlinear spring elements and plastic hinges is utilized to incorporate the combined effect of connection flexibility and material nonlinearity. A new step-by-step analysis procedure is established to obtain quickly the dynamic increase factor based on a combination of the pushdown analysis and nonlinear dynamic analysis. Finally, the modified dynamic increase factor equation, defined as a function of the maximum ratio value of energy demand to energy capacity of an affected beam, is derived by curve fitting data points generated by the different analysis cases with different column removal scenarios and five types of semi-rigid connections.

• Steel and Composite Structures
• /
• v.36 no.4
• /
• pp.447-462
• /
• 2020

The paper aims to investigate the mechanical mechanism and seismic effect of stiffeners in blind bolt endplate connection to CFST column. A precise 3D finite element model with considering the cyclic properties of concrete and steel materials was established, and the efficiency was validated through monotonic and cyclic test data. The deforming pattern and the seismic performance of the unstiffened and stiffened blind bolt endplate connections were investigated. Then a parametric analysis was conducted to analyze the contribution of stiffeners and the joint working behaviors with endplate under cyclic load. The joint stiffness classifications were compared and a supplement stiffness classification method was proposed, and the energy dissipation ability of different class connections were compared and discussed. Results indicated that the main deformation pattern of unstiffened blind bolt endplate connections was the local bending of end plate. The vertical stiffeners can effectively alleviate the local bending deformation of end plate. And influence of stiffeners in thin endplate and thick endplate was different. Based on the stiffness of external diaphragm welded connection, a more detailed rigidity classification was proposed which included the pin, semi-rigid, quasi-rigid and rigid connection. Beam was the main energy dissipation source for rigid connection. For the semi-rigid and quasi-rigid connection, the extended endplate, stiffeners and steel beam would all participate in the energy dissipation.

• Structural Engineering and Mechanics
• /
• v.34 no.3
• /
• pp.351-366
• /
• 2010

A novel system identification and structural health assessment procedure of steel framed structures with semi-rigid connections is presented in this paper. It is capable of detecting damages at the local element level under normal operating conditions; i.e., serviceability limit state. The procedure is a linear time-domain system identification technique in which the structure responses are required, whereas the dynamic excitation force is not required to identify the structural parameters. The procedure tracks changes in the stiffness properties of all the elements in a structure. It can identify damage-free and damaged structural elements very accurately when excited by different types of dynamic loadings. The method is elaborated with the help of several numerical examples. The results indicate that the proposed algorithm identified the structures correctly and detected the pre-imposed damages in the frames when excited by earthquake, impact, and harmonic loadings. The algorithm can potentially be used for structural health assessment and monitoring of existing structures with minimum disruption of operations. Since the procedure requires only a few time points of response information, it is expected to be economic and efficient.

• Journal of Korean Society of Steel Construction
• /
• v.12 no.5 s.48
• /
• pp.527-535
• /
• 2000

Accurate determination of the relative restraint of beam-to-column connections is important for both the strength and the serviceability of structural frames. But steel frame analysis is carried out under the assumption that the connections are either fixed or pinned. Overestimating the connection restraint can result in underestimating lateral sway and underestimating the connection restraint can lead to underestimating forces developed in the beams and columns. This implies that the exact stiffness of connections as well as the geometric effects should be considered in the frame analysis and the overall behavior of connections could be described adequately. Therefore, the stiffness matrix which is able to consider the moment-rotation of connection was derived previously and the modified exponential model, power model and the proposed log model are adopted for modeling the semi-rigid connections. The main purpose of this study is to examine the feasibility of the derived stiffness matrix and to show the validity of log model proposed.

• Earthquakes and Structures
• /
• v.16 no.4
• /
• pp.469-485
• /
• 2019

A numerical investigation regarding local (${\mu}_L$) and story (${\mu}_S$) ductility demand evaluation of steel buildings with perimeter moment resisting frames (PMRF) and interior gravity frames (IGF), is conducted in this study. The interior connections are modeled, firstly as perfectly pinned (PP), and then as semi-rigid (SR). Three models used in the SAC steel project, representing steel buildings of low-, mid-, and high-rise, are considered. The story ductility reduction factor ($R_{{\mu}S}$) as well as the ratio ($Q_{GL}$) of $R_{{\mu}S}$ to ${\mu}_L$ are calculated. ${\mu}_L$ and ${\mu}_S$, and consequently structural damage, at the PMRF are significant reduced when the usually neglected effect of SR connections is considered; average reductions larger than 40% are observed implying that the behavior of the models with SR connections is superior and that the ductility detailing of the PMRF doesn't need to be so stringent when SR connections are considered. $R_{{\mu}S}$ is approximately constant through height for low-rise buildings, but for the others it tends to increase with the story number contradicting the same proportion reduction assumed in the Equivalent Static Lateral Method (ESLM). It is implicitly assumed in IBC Code that the overall ductility reduction factor for ductile moment resisting frames is about 4; the results of this study show that this value is non-conservative for low-rise buildings but conservative for mid- and high-rise buildings implying that the ESLM fails evaluating the inelastic interstory demands. If local ductility capacity is stated as the basis for design, a value of 0.4 for $Q_{GL}$ seems to be reasonable for low- and medium-rise buildings.

• Steel and Composite Structures
• /
• v.3 no.6
• /
• pp.451-474
• /
• 2003

Details are given of a cold-formed steel portal framing system that uses simple bolted moment-connections for both the eaves and apex joints. However, such joints function as semi-rigid and, as a result, the design of the proposed system will be dominated by serviceability requirements. While serviceability is a mandatory design requirement, actual deflection limits for portal frames are not prescribed in many of the national standards. In this paper, a review of the design constraints that have an effect on deflection limits is discussed, and rational values appropriate for use with cold-formed steel portal frames are recommended. Adopting these deflection limits, it is shown through a design example how a cold-formed steel portal frame having semi-rigid eaves and apex joints can be a feasible alternative to rigid-jointed frames in appropriate circumstances.

• Steel and Composite Structures
• /
• v.6 no.6
• /
• pp.513-529
• /
• 2006

This paper deals with the dynamic behaviour of cold-formed steel hollow frames with different connection stiffnesses. An analytical model of a semi-rigid frame was developed to study the influence of connection stiffnesses on the fundamental frequency and dynamic response of the frames. The flexibilities of the connections are modeled by rotational springs. Neglect of semi-rigidity leads to an artificial stiffening of frames resulting in shorter fundamental period, which in turn results in a significant error in the evaluation of dynamic loads. In the seismic design of structures, of all the principal modes, the fundamental mode of translational vibration is the most critical. Hence, experiments were conducted to study the influence of the connection stiffnesses on the fundamental mode of translational vibration of the steel hollow frames. From the experimental study it was found that the fundamental frequency of the frames lie in the semi-rigid region. From the theoretical investigation it was found that the flexibly connected frames subjected to lateral loads exhibit larger deflection as compared to rigidly connected frames.

• Steel and Composite Structures
• /
• v.26 no.1
• /
• pp.67-78
• /
• 2018

The application of rib stiffeners is common on steel connections, with regard to the stiffened angle connection, experimental results about the influence of stiffeners under monotonic and cyclic loading are very limited. Consequently, this paper presents the experimental investigation on four types angle connections with or without stiffener under static loading and another four type stiffened angle connections subjected to cyclic loading. The static experimental result showed that the rib stiffener weld in tension zone of the connection greatly enhanced its initial rotational stiffness and flexural strength. While a stiffener was applied to the compression zone of the connection, it had not obvious influences on the initial rotational stiffness, but increased its flexural strength. The moment-rotation curves, skeleton curves, ductility, energy dissipation and rigidity were evaluated under cyclic loading. Stiffened top-and-seat angle connections behaved as semi-rigid and partial strength, and rotation of all stiffened angle connections exceeded 0.04rad. The failure modes between monotonic and cyclic loading test were completely different and indicated certain robustness.

• Steel and Composite Structures
• /
• v.14 no.1
• /
• pp.1-20
• /
• 2013

This paper presents the formulation for a novel force-based 1-D compound-element that captures both material and second order P-${\Delta}$ nonlinearities in steel frames. At the nodal points, the element is attached to nonlinear rotational and a translational springs which represent the flexural and axial stiffness of the connections respectively. By decomposing the total strain in the material as well as the generalised displacements of the flexible connections to their elastic and inelastic components, a secant solution strategy based on a direct iterative scheme is introduced and the corresponding solution strategy is outlined. The strain and slope of the deformed element are assumed to be small; however the equilibrium equations are satisfied for the deformed element taking account of P-${\Delta}$ effects. The formulation accuracy and efficiency is verified by some numerical examples on the nonlinear static, cyclic and dynamic analysis of steel frames.