Analysis Of Semi-rigid Steel Frames Research Articles

Stochastic analysis of semi-rigid steel frames using a refined plastic-hinge model and Latin hypercube sampling

This paper proposes a stochastic analysis model that combines the refined plastic-hinge analysis method with the Monte Carlo simulation to predict the realistic resistance of steel structures. The model treats the uncertainty quantifications of the material properties, geometry, and semi-rigid connections as independent random variables in the discretized stochastic fields using Latin hypercube sampling. The critical resistance of the structures in each simulation is determined using the general displacement control method and advanced analysis algorithms. The statistical approach is employed to compute the mean values and the standard deviation of the load-carrying capacity of the steel frames. The study finds that the uncertainties in material properties are the most sensitive, and the correlation of these parameters with the strength of structures is also significant. To improve the load and resistance factor design criterion, a resistance factor of 0.93 is suggested for the beam-columns in the frames under axial force, torsion, and biaxial bending moments. A stochastic response spectrum is proposed to define the boundary of strength, where a clearly defined plastic mechanism is attained. Furthermore, this study provides valuable insights into the stochastic resistance of steel frames, which are essential for practical engineering applications.

Nonlinear analysis of semirigid steel frames having nonprismatic shear-deformable members

Starting from the principle of virtual forces (PVF), one devises a flexibility-type method to obtain, based on the Timoshenko beam theory (TBT), exact expressions for the structural properties of nonprismatic frame elements. One adopts polynomials of different orders to interpolate the sectional rigidity values over the elements and employs exact Timoshenko’s shape functions for evaluating deformation-dependent structural properties, such as geometric stiffness. In this respect, we present a mathematically formal process to obtain the changes in the preexisting element forces needed to calculate geometric stiffnesses. The procedure adopted in this paper easily allows one to include higher-order nonlinear terms in the analysis. Robustness of the proposed formulation is observed by conducting geometrically nonlinear analyses of 2D semirigid steel frames possessing nonprismatic members. General nonlinear curves describing the semirigid connections may be easily incorporated into the analysis.

Nonlinear dynamic collapse analysis of semi-rigid steel frames based on the finite particle method

This paper presents a numerical procedure based on the finite particle method (FPM) for the nonlinear dynamic collapse analysis of plane steel frames with semi-rigid connections. The FPM can be used to model the plane frame with finite separated particles; in particular, geometric nonlinearity and dynamic fracture. Fictitious motion was used to consider the geometrical nonlinearity, and the explicit time integration method was used for solving the dynamic equilibrium equations. In the FPM, particles are free to separate from each other, which is advantageous in the simulation of member fracture. To simulate member fracture, the fracture criterion and fracture model of the FPM were developed. Furthermore, to simulate the rigidity of a steel beam–column connection, an independent zero-length element was adopted, which can consider the influence of nonlinear and hysteretic connection stiffness. The nonlinear response results were compared with those of existing studies to verify the accuracy of the proposed numerical procedure. Additionally, the collapse analysis of a Vogel six-story frame showed that frames with semi-rigid connections have greater anti-collapse capacity than those with rigid connections do.

Shear behaviour of stiffened double rectangular column panels: Characterization and cruciform element

The behaviour of joints exerts an important influence on the overall performance of steel and composite structures. Modern codes, including Eurocodes 3 (EC3) and 4 (EC4), have included research advances for joint modelling to be used in common practice.The method adopted in EC3 and EC4 to characterize the connections is the so-called component method. One of the most important components is the column web panel in shear, and its behaviour has been investigated thoroughly for the case of single rectangular shear panels arising when the beams have equal depths. However, the case of double column panels, formed by beams of different depths at each side of the column, has not been researched as much.The aim of this paper is the characterization of the shear behaviour of rectangular double column panels attached to beams of unequal depths. In order to isolate the shear behaviour from other components, horizontally stiffened beam to column connections with commercial sections are experimentally tested. Also, finite element modelling and analysis is carried out to compare results. A mechanical model is proposed and a parametric study is performed by means of calibrated finite element models to characterize the different components, and define the analytical expressions for the stiffness and resistance of the proposed mechanical model. In addition, a cruciform finite element that captures the behaviour of the proposed mechanical model has been developed. This general cruciform element is also suitable for semi-rigid connections and can be used for global analysis of semi-rigid steel frames.

Second-order distributed plasticity analysis of steel frames with semi-rigid connections

This paper proposes an accurately and efficiently numerical procedure for distributed plasticity analysis of semi-rigid steel frames. Both geometric and material nonlinearities are included in the proposed analysis. Geometric nonlinearities due to the large and small P-Delta effects are respectively captured using the corotational formulation and curvature-based displacement procedure. Material nonlinearities due to residual stresses and inelastic behaviour of materials are taken into account using a fibre model. The nonlinear semi-rigid behaviour of beam-to-column connections is simulated using a zero-length connection element. The validity of the present analysis is verified by comparing the obtained predictions with existing solutions. A case study of a very large-scale steel frame indicates that the present analysis is very reliable and computationally efficient and thus would be a valuable tool for daily use in office engineering design.

Dynamic Nonlinear Analysis of Semi-Rigid Steel Frames Based on the Finite Particle Method

The Finite Particle Method (FPM), based on the Vector Mechanics, is a new structural analysis method. This paper explores the possibility of the proposed method being applied in the dynamic nonlinear analysis of semi-rigid steel frames. Taking the two dimensional beam element as an example, the formulations of the FPM to calculate the dynamic and geometric nonlinear problems are derived. Spring model with zero-length is adopted to simulate the relationship between internal forces and deformations of the semi-rigid steel connections. The nonlinear strengthen spring model is used to analyze the nonlinear behavior of the semi-rigid connection. Explicit time integrations are used to solve equilibrium equations. Comparing to traditional Finite Element Method, iterations and special modifications are not needed during the dynamic nonlinear analysis, which is more advantageous in structural complex behavior analysis. Two numerical examples are presented to analyze the behaviors of rigid and semi-rigid steel frames, and behaviors of linear and nonlinear semi-rigid connections, which demonstrate the accuracy and applicability of this method in dynamic nonlinear analysis.

Shear behaviour of trapezoidal column panels. II: Parametric study and cruciform element

In recent years a considerable effort has been dedicated to improve the knowledge on the behaviour of semi-rigid steel connections by techniques such as the component method. One of the most important components of the connections is the column web under shear. This component has a well-known and defined behaviour for the case of rectangular panels, which results in internal beam to column joints with beams of equal depth. However, when the right and left beams have different depths the shear panel becomes trapezoidal, and the application of the formulation corresponding to rectangular panels produces inaccurate results. The results of different laboratory tests and finite element simulations have been shown in the companion Part I paper. Also a mechanical model was proposed to characterize its behaviour.In the present work, the results of a wide parametric study, carried out by means of calibrated finite elements models, are shown. These results form the basis to characterize the different components, and define the analytical expressions for the stiffness of the proposed mechanical model. Additionally, a cruciform finite element has been developed that captures the behaviour of the proposed mechanical model. This general cruciform element is suitable for semi-rigid connections and can be used for the global analysis of semi-rigid steel frames. Finally, this approach is applied to several practical cases and the results are shown.

Second-order elastoplastic analysis of semirigid steel frames under cyclic loading

The evolutive second-order geometry elastoplastic analysis of flexibly connected planar structures is performed to investigate their cyclic behavior under quasistatic loading conditions. The formulation is cast as a mathematical programming problem, involving so-called “complementarity” constraints. A “fictitious force” concept, that preserves static-kinematic duality, is used to describe geometric nonlinearity. A second-order approximation, deemed sufficiently accurate for practical structures, is adopted. A semirigid connection is idealized as a zero-length elastoplastic element attached to either or both ends of a beam element. Inelasticity is captured through the familiar generalized plastic hinge concept, and a piecewise linear approximation of the nonlinear plastic capacity domain is used to represent the yield condition. A number of examples concerning realistic structures and benchmark cases is provided to check the validity and applicability of the proposed method and to study the cyclic behavior of flexibly connected planar frames.

The effect of axial beam force on moment–rotation curve of top and seat angels connections

AbstractBolted top and seat angle connections are mainly designed to sustain gravitational loads of simply supported steel beams. However, the inherent flexural resistance of such connections may not be ignored when an accurate analysis of semirigid steel frames is desired. Current research aims at studying moment–rotation behaviour of this type under combined moment and axial tension force. Several refined three‐dimensional finite element models are created based on the previous experimental studies, and their accuracy is examined trough a comparison to test results from previous experimental studies. This study showed that the axial tension force reduces the connection initial stiffness and moment capacity. Based on the results obtained from analysing a series of finite element models under combined axial tension and moment loading, an equation is presented to estimate the affected moment–rotation response of such connections in terms of the connection geometrical properties, its moment–rotation response in the case of zero axial force and an expected axial tension force. Copyright © 2009 John Wiley & Sons, Ltd.

Non-discretisation formulation for the non-linear analysis of semi-rigid steel frames at elevated temperatures

This paper proposes a flexibility-based method for the analysis of steel frame structures with semi-rigid joints subjected to fire loading. The semi-analytical non-discretisation formulation is able to capture material and geometric non-linearities. The modelling of the cross-sections as comprising of elastic and inelastic domains allows for the spread of yielding to be modelled, while the geometric non-linearity included in the method allows for catenary action to develop in the heated compartment within the frame. The accuracy of the technique is verified against an independent analysis using ABAQUS as well as by analysing a rigid steel frame with 104 members.

Moment–rotation behavior of bolted top–seat angle connections

Bolted top and seat angle connections are mainly designed to sustain gravitational loads of simply supported steel beams. However, the inherent flexural resistance of top–seat angle connections may not be ignored when an accurate analysis of semi-rigid steel frames is desired. The goal of the current study is to find a new moment–rotation relation to estimate the behavior of connections of this type. Semi-analytical equations are proposed for this purpose based on the data bank, which is created using finite element simulation. Several refined 3D finite element models were created based on the previous experimental studies and their accuracy is examined through a comparison to test results from previous studies and other published numerical models. The presented new semi-analytical method covers some deficiencies of the previously proposed methods, and the accuracy of this approach is evaluated comparing its results with those of the other methods. The study is further extended, and the effect of axial force on the moment–rotation response of such connections is studied. This study shows that the axial tension load reduces the initial connection stiffness and moment capacity. The applicability of the presented method is evaluated, and it is shown that the model has the potential to estimate connection moment–rotation behavior under combined axial tension and moment loading.

Nonlinear Elastoplastic Analysis of Semirigid Steel Frames at Elevated Temperature: MP Approach

An elastoplastic analysis of semirigid steel frames subjected to elevated temperature is presented. Within the discretized structural framework, an updated Lagrangian approach is used to incorporate the nonlinear geometric effects on the equilibrium and constitutive conditions. Modeling of elastoplastic behavior is based on the generalized plastic hinge concept for beam-column elements that obey piecewise linearized yield criteria. Under the proportional temperature variation, the analysis for finite temperature increment becomes the standard form of a nonlinear complementarity problem in mathematical programming (MP) formalism. An iterative predictor–corrector scheme coupled with an MP-based method is used in the analytical procedures. Numerical studies are carried out on rigid and semirigid frames. It is found that the benefits of using a full-strength rigid connection over the semirigid one are not unlimited, particularly on the frames with fire-unprotected columns.

Hysteresis model of bolted-angle connections

This paper presents a hysteretic model of bolted-angle connections for seismic analysis of semi-rigid steel frames with bolted connections. A semi-rigid beam-to-column connection is divided into a finite number of fiber elements. Hysteretic behavior of the fiber elements under repeated tension and compression has been established using the combined experimental and analytical results. The model has been implemented into a general purpose computer program and agrees well with experimental results. The main features of the model include: (1) Parameters of the model are directly related to a connection design; (2) Hysteresis rules are developed directly from comprehensive experiments specifically designed for modeling.

Analysis of semi-rigid steel frames and criteria for their design

This paper reports studies on unbraced semi-rigid steel frames, carried out to determine criteria for their design. The analyses of the frames were performed by a computer program that uses a secant-stiffness approach to allow for the effect of semi-rigid connections on frame behaviour. A parameter entitled ‘degree of flexibility’ is introduced as a measure of the effect of semi-rigid joints on the stiffness of the frame. Within the limits of the study, it is demonstrated that second-order effects will not be significant if the semi-rigid elastic critical load exceeds ten times the design load, and the degree of flexibility is less than 50%. This last requirement was satisfied by extended end-plate beam-to-column connections. It has also been found that, under combined loading, the serviceability limit on sway is likely to control design, rather than ultimate strength.