Behaviour Of Semi-rigid Connections Research Articles

System reliability-based design of composite frames with concrete – filled steel plate shear walls

Nowadays, many high-rise buildings are constructed from concrete-filled steel tubular (CFST) columns and concrete-filled steel plate (CFSP) shear walls due to their superior merits. However, these composite buildings are still designed by traditional load and resistance factor design (LRFD) approach which is conservative and impossible to explicitly capture the complex behaviour of CFST structures. Hence, this paper develops an efficient framework for the system design of CFST structures utilizing nonlinear simulation and reliability analysis. Firstly, a C+ + source code for a new material model is developed in OpenSees to capture the behaviour of semi-rigid connections. This material is implemented into the numerical model of CFST structures. Secondly, a framework based on subset simulation is developed for the reliability analysis. This code rigorously considers uncertainties of variables such as numerical model, geometric and material properties or applied loads of both American (US) and Australian (AS) standards. Finally, case study and parametric study are conducted by using the developed framework to propose resistance reduction factors for the investigated frames. The results of the study show that the resistance reduction factor can be taken as 0.8 for both AS and US codes. This proposed factor can be a great source of reference for the system design of CFST buildings with composite shear walls.

Constitutive model for rotation behaviour of semi-rigid steel beam-to-column joints

This study proposed a generalised and concise model consisting of spring-slider elements to characterise the nonlinear bending moment-rotation relationship of semi-rigid steel beam-to-column joints. First, the density function of the constitutive model was constructed based on the rotational characteristics of the joints. Second, the mathematical expression for the moment-rotation relationship of the constitutive model was derived. A method was developed to identify the parameters. Finally, after a discretisation method of the model was derived based on the strategy of evenly divided stiffness, the discrete model was applied to the numerical simulation of the rotation of the semi-rigid steel beam-to-column joints. It is observed that the proposed model accurately describes the rotation behaviour of semi-rigid connections in the entire rotation domain while reducing the degrees of freedom of the contact interfaces to improve the computing efficiency. There are six parameters in the model with a clear physical definition, which can be directly identified through macroscopic experiments. A high level of accuracy can be achieved by numerically calculating a discrete model using only five Jenkins elements.

Effect of Semi-Rigid Joints on Design of Steel Structure

Abstract: Limit state design method has presented a new era of safe and economic construction for steel structures. New standard IS 800:2007 for design of steel structures has provided an opportunity for modern design philosophy, design specifications and provisions as per Limit State Method of design in our country. In design of steel structures, steel connections are important elements for controlling behaviour of structure. It is essential that to understand behaviour of steel frame, connectors are required to develop full or a little higher strength compared to members being joined in order to achieve a safe and an economical design. A connection rotates through angle Or caused by applied moment M. This is angle between beam and column from their original position. Several moment-rotation relationships have been derived from experimental studies for modelling semi-rigid connections of steel frames. These relationships vary from linear model to exponential models and are nonlinear in nature. Connections possess semi rigid end conditions in actual behaviour. In the present dissertation, the effect of semi rigid joints on design of steel structures is studied. The behaviour of semi rigid connections and its modelling is discussed. The analysis of the frames is done using ANSYS 2016 and the comparative results of rigid, semi rigid and pinned end conditions has been presented in graphical form. From the results of analysis the design of various semi rigid connections is carried out. Further buckling analysis of stepped columns has been carried out in order to obtain effective length parameters for semi-rigid connections. The design examples has been solved using AISC and IS 800-2007. The comparison is done for fixed, semi rigid and pinned end condition. Keyword: semi-rigid joint, frame analysis, rotational stiffness, buckling length, genetic algorithm.

Component-based model of semi-rigid connections for nonlinear analysis of composite structures

In order to achieve better mechanical performance and construction efficiency, the outrigger bracket with a “through type” interior diaphragm (OBTID) connection is proposed for application in semi-rigidly connected composite structures. The mechanical behaviour of OBTID connections in two frame tests under lateral cyclic loads is investigated to reveal the failure mechanism. Based on the test observations, a component-based model is proposed to analyse the nonlinear behaviour of semi-rigid connections by decomposing the connection components and putting forward the constitutive law of each component. Furthermore, the proposed model is implemented in a general commercial finite element package and a program for nonlinear analysis of semi-rigidly connected composite structures is developed by combining the component-based model with the previous fiber beam-column model. Then, a comparison between the numerical results and experimental results in both connection level and frame level indicates that the proposed component-based model can predict the complex nonlinear behaviour of semi-rigid connections with good accuracy. Additionally, the contribution of bolt slip to connection rotation is analysed to clarify the pinching effect, and the semi-rigidity of OBTID connections are compared with provisions of Eurocode 3 and that of other similar semi-rigid connections.

Seismic behavior of steel space truss connections to reinforced concrete supporting columns

Roof joint is a critical connection in space truss structures, which connects the upper steel space truss roofs and reinforced concrete structures. Because of its simple structural detailing and easy construction, a typical kind of roof joint is comprised of four embedded anchor rods, a mortar layer, a base plate, and stiffeners are popular in small- to medium-span space truss structures. Among them, base plates with slotted bolt holes are commonly used to release the deformation caused by temperature change or earthquake input. The roof joints were considered either as pinned or rigid connections in the design. In this paper, quasi-static tests investigating the influence of the applied axial force and the shape of bolt holes on the shear resistance and seismic behavior of roof joints were performed. The roof joints exhibited semi-rigid connection behavior and two types of initial resistance mechanisms, sliding and overturning, were observed. With the increase of applied axial force, the behavior of roof joint changes from sliding to overturning. Finally, effective methods to determine the initial resistance mechanism and calculate the ultimate shear strength of roof joints are proposed. These findings and analyses may provide guidelines for roof joint design practice for space truss structures.

In situ assessment of the timber structure of an 18th century building in Madrid, Spain

The timber structural members of a seven-story building from the end of the 18th century were evaluated following a procedure based on previous research works. The structure consisted of timber-framed brick walls and heavy timber floors with mortar filling. Non-destructive measurements were taken in 13 sampling areas of the floors and framed walls. Detailed measurements of at least 3 pieces in each sample were taken (stress wave Time-of-Flight and probing tests). Mean density and modulus of elasticity values and characteristic values of bending and compression strength were estimated. On-site load tests were carried out on three floor slabs to deduce their actual bending stiffness and compare it with estimation by NDT. They behaved more rigidly than expected, which is explained by floor screed stiffness, the transverse stiffness effect and possible semi-rigid connection behaviour at the supports. Structural verification determined the required strength of the critical members to compare this with the estimated strengths, showing a correct safety level.

Shape optimization of braced frames for tall timber buildings: Influence of semi-rigid connections on design and optimization process

With the recent development of timber as a viable structural material for high-rise structures, glulam braced frames have been recently introduced in lateral load-resisting systems of timber buildings. Based on a simple shape optimization problem of a braced frame, this paper explores one of the specificities of timber structures: the influence of semi-rigid connections on their overall structural behavior and design. Dowel-type connections are first studied to obtain a simplified relation between joint stiffness and axial load-carrying capacity. Then, the established local behavior law is introduced in the shape optimization process and design of a discrete braced frame subject to lateral drift constraint under wind load. The problem is solved by a COBYLA optimization method, combined with Optimality Criteria (OC) member sizing techniques. Solutions are then evaluated and compared with classical steel/concrete design. The semi-rigid behavior of connections finally leads to a significant increase in the volume of timber but also affects the optimal shape and topology of the X-braced frame compared with classical results.

A Calculation Method for Interconnected Timber Elements Using Wood-Wood Connections

Wood-wood connections, widely used in the past, have been progressively replaced by steel fasteners in timber constructions. Currently, they can be manufactured and implemented more efficiently thanks to digital fabrication techniques. In addition, with the emergence of new timber plate engineered products, digitally produced wood-wood connections have been developed with a strong focus on complex free-form geometries. The gained knowledge through research and building implementations have pushed the development of more standardized structural elements. As a result, this work presents a new concept of building components using through tenon connections based on the idea of transportable flat-packs directly delivered and assembled on site. The main objective of this research is to develop a convenient calculation model for practice that can capture the semi-rigid behavior of the connections and predict the effective bending stiffness of such structural elements. A case study is used as a reference with three large-scale slabs of a 8.1 m span. Bending and vibration tests are performed to study the mechanical behavior and assess the proposed calculation method. The results show the high influence of the semi-rigid behavior of connections on the bending properties and, therefore, on the serviceability limit state. The model is in good agreement with the test results, and further improvements can be made regarding the local behavior of the connection. This study demonstrates the feasibility of the proposed construction system and the applicability of the developed calculation model to design practice.

Plastic-zone advanced analysis – Formulation including semi-rigid connection

A new numerical formulation includes the behavior of the semi-rigid connection into plastic-zone finite element model for steel plane frames. This Bernoulli-Euler formulation is an expansion and generalization of the slice technique with updated Lagrangian co-rotational system, presented before. Only one spring is placed in the finite element end node to allow the study of plasticity inside the member. The connection semi-flexibility factor eta controls this spring. It is defined for the beam length and can classify the connection as rigid or flexible. The eta effects on the vertical displacement function, the generality of the proposed model and the corresponding stiffness matrices are shown. The usage of another eta based on the finite element length is also explained. The advantages of semi-rigid connection behavior are discussed. Several answers were obtained, considering the connection stiffness and the inelastic behavior. This technique is applied to solve three benchmarked examples, applying connections of constant stiffness and semi-rigid curves from an existing data bank. The semi-rigid connection economy on beams, its appearing improvement of columns capacity, and the reduction of portal frame limit load justify this research. These examples are minimum requirements to develop the advanced direct analysis, which power is explored in the last one.

Mechanical behaviour of semi-rigid connections coupling two concrete segmental linings

This paper describes the use of segment joints in shield-driven tunnel linings. The opening of segment joints due to the application of a bending moment under different levels of axial stress is studied. The main focus is the mechanical behaviour of the joints, which are considered to be semi-rigid, and the moment-rotation behaviour of the joint. A physically based mathematical model is proposed based on the joint dimensions and material properties. Considering joints connected by two long curved bolts as an example, the model parameters are evaluated, and the moment-rotation curves for the joint are presented. The model distinguishes joint behaviour before and after opening, and agrees well with the real mechanical behaviour of the joints. A comparison with previous experiments on segment joints and with Janssen's and Gladwell's models is provided, and the proposed model is found to be accurate and universal.

Seismic behavior of semi-rigid steel joints—Major axis T-stub and minor axis end-plate

Due to its cost-effective nature and satisfactory seismic performance, semi-rigid steel frame is often considered as an alternative to conventional fully rigid steel frames. To date, the seismic behavior of semi-rigid connection has typically been documented in two dimensions. To fill this gap, an experimental investigation was made to study the behavior of the internal semi-rigid joints through spatial quasi-static tests with loads applied to the ends of the columns from both the major and minor axes. In our newly proposed semi-rigid joint, the minor beam is attached to the column web by an end-plate connection and the major one attached to the column flange by a T-stub connection, where the loading effect from the minor direction on the major direction of semi-rigid joints was considered. Results show the major beams failed with T-stub fractures and the minor beams failed with substantial bending deformations at the end-plates, which are easy failures to repair. In addition, the initial rotational stiffness and angular ductility coefficient of the minor beam decreased with increases in the thickness of the end-plate. Compared with the semi-rigid steel joints with T-stub connections in both axes, the major beams of our proposed joints exhibited obviously increased bending resistances, equivalent viscous damping coefficients and equivalent energy dissipations.

Behaviour of top-seat double web angle connection produced from austenitic stainless steel

Beam-to-column connections are regarded as one of the critical elements in structures, especially in the case of bare metallic frame construction, as the overall structural performance is highly influenced by the connection behaviour. Significant research on stainless steel members has been reported in the recent past, but research on beam-to-column connections is still scarce. This paper presents an experimental and numerical investigation on the moment-rotation (M-φ) behaviour of a top-seat with double web angle (DWA) connection produced from austenitic stainless steel. A comprehensive investigation on the elasto-plastic deformation patterns observed in individual connection elements has been reported to gain in-depth knowledge in assessing overall stiffness, strength and rotational capacity of the considered connection type. Beam and column sections, as well as the connecting angles and fasteners used in the experiment, were produced from austenitic stainless steel AISI 316 L (equivalent to EN 1.4301). Significant strain hardening, as characterised by stainless steel, was observed throughout with the top angle experiencing most significant deformations. 3D finite element (FE) model was developed to replicate the observed experimental behaviour, and good agreement was observed between numerically obtained results and experimental observations. Based on the experimental and numerical results, semi-rigid connection behaviour was recognized for stainless steel alloy to lay a foundation for the development of the top-seat DWA connection. The observed behaviour for the considered stainless steel connections was compared with those obtained analytically for equivalent carbon steel connections; this comparison demonstrated enhanced ductility and significantly higher plastic moment for stainless steel connections.

Design optimization of semi-rigid space steel frames with semi-rigid bases using biogeography-based optimization and genetic algorithms

This paper performs for the first time a simultaneous optimization for members sections along with semi-rigid beam-to-column connections for space steel frames with fixed, semi-rigid, and hinged bases using a biogeography-based optimization algorithm (BBO) and a genetic algorithm (GA). Furthermore, a member\'s sections optimization for a fully fixed space frame is carried out. A real and accurate simulation of semi-rigid connection behavior is considered in this study, where the semi-rigid base connections are simulated using Kanvinde and Grilli (2012) nonlinear model, which considers deformations in different base connection components under the applied loads, while beam-to-column connections are modeled using the familiar Frye and Morris (1975) nonlinear polynomial model. Moreover, the P-∆ effect and geometric nonlinearity are considered. AISC-LRFD (2016) specification constraints of the stress and displacement are considered as well as section size fitting constraints. The optimization is applied to two benchmark space frame examples to inspect the effect of semi-rigidity on frame weight and drift using BBO and GA algorithms.

On the Nonlinear Transient Analysis of Planar Steel Frames with Semi-Rigid Connections: From Fundamentals to Algorithms and Numerical Studies

Abstract This paper presents the fundamentals for prediction of a more realistic behavior of planar steel frames with semi-rigid connections under dynamic loading. The majority of the research in this area concentrates on the nonlinear static analysis of frames with semi-rigid connections. Indeed, few studies have contributed to the nonlinear dynamic and vibration analyses of frames. Therefore, this article first describes the frames’ semi-rigid connection behavior under monotonic and cyclic loads, and presents the independent hardening technique adopted to simulate the joint behavior under cyclic excitation. In a finite element context, this paper presents an efficient numerical methodology that is proposed in algorithmic form to obtain the nonlinear transient response of the structural system. The paper also presents, in algorithmic form, a complete description of the adopted connection hysteretic model. Satisfying the equilibrium and compatibility conditions, and assuming only the connection’s rotational deformation due to bending as variable, this work obtains the tangent stiffness and mass matrices of the beam-column element with semi-rigid connections at the ends. The study concludes by verifying and validating the proposed numerical approach using four structural steel systems: a L-frame, a two-story frame, a six-story frame, and a four-bay five-story frame. The analyses show that the hysteresis of the semi-rigid connection has a strong effect on the frames’ responses and is an important source of damping during the structural vibration.

A shear-deformable beam model for stability analysis of orthotropic composite semi-rigid frames

In this paper, a shear deformable beam model for nonlinear stability analysis of frames made of composite materials is presented. Each wall of the cross-section is assumed to be orthotropic in such a way that normal stress does not cause shear strains to occur. The incremental equilibrium equations for a straight thin-walled beam element are derived within the framework of updated Lagrangian formulation and the nonlinear displacement field of cross-sections, which accounts for the restrained warping and the large rotations effects. Timoshenko’s theory for non-uniform bending and modified Vlasov’s theory for non-uniform torsion are applied to include the shear deformation effects. The coupled bending-torsion shear deformation effects occurring at the asymmetric cross-section are also included in the model. To account for the semi-rigid connection behaviour, the hybrid finite element is introduced through the special transformation procedure. Several benchmark examples are demonstrated for verification purposes. The obtained results indicate that the proposed model can be classified as shear locking-free one.

Demands and distribution of hysteretic energy in moment resistant self-centering steel frames

Post-tensioned (PT) steel moment resisting frames (MRFs) with semi-rigid connections (SRC) can be used to control the hysteretic energy demands and to reduce the maximum inter-story drift (γ). In this study the seismic behavior of steel MRFs with PT connections is estimated by incremental nonlinear dynamic analysis in terms of dissipated hysteretic energy (EH) demands. For this aim, five PT steel MRFs are subjected to 30 long duration earthquake ground motions recorded on soft soil sites. To assess the energy dissipated in the frames with PT connections, a new expression is proposed for the hysteretic behavior of semi-rigid connections validated by experimental tests. The performance was estimated not only for the global EH demands in the steel frames; but also for, the distribution and demands of hysteretic energy in beams, columns and connections considering several levels of deformation. The results show that EH varies with γ, and that most of EH is dissipated by the connections. It is observed in all the cases a log-normal distribution of EH through the building height. The largest demand of EH occurs between 0.25 and 0.5 of the height. Finally, an equation is proposed to calculate the distribution of EH in terms of the normalized height of the stories (h/H) and the inter-story drift.

System reliability evaluation of steel frames with semi-rigid connections

This paper presents an accurate and efficient numerical procedure for evaluating the system reliability of steel frames with semi-rigid connections. The ultimate strength and behaviour of the frame were predicted using a refined plastic hinge model due to its computational efficiency, whilst the nonlinear behaviour of semi-rigid connections was captured using a three-parameter power model. The statistical properties for the three parameter power model were obtained based on available experimental results. The sensitivity of reliability to the model error was also studied. Monte Carlo simulation was used to estimate the probability of failure and the reliability index of a system. Two example frames subjected to combined gravity and wind loads were examined and their system reliability indices for both strength and serviceability limit states were evaluated based on the randomness in loadings, material and geometric properties and semi-rigid connections. The results indicate that the frame reliability is strongly affected by semi-rigid connections.

Finite element formulation for semi-rigid beam-to-column connections using potential energy approach

This paper presents the behaviour of semi-rigid connections in steel frame analysis by utilizing the total potential energy principal. A finite element model is proposed to consider the behaviour of the semi-rigid connection. The proposed finite element method is compared with the existing method proposed by other researchers. Both linear and non-linear analyses are performed to acquire the solution of steel frame under elastic condition. The results of comparison agreed well with other method proposed by other researchers. The results of the proposed finite element method is also compared with the available experimental results and found that the linear analysis agrees well with the experimental results. Therefore, it is concluded that the behaviour of the semi-rigid connection is steel framing can be predicted using potential energy approach.

A beam formulation for large displacement analysis of composite frames with semi-rigid connections

This paper presents a geometrically non-linear beam formulation for large displacement analysis of composite beam type structures with semi-rigid connections. Within the framework of updated Lagrangian incremental formulation and the nonlinear displacement field of thin-walled cross-sections, which accounts for restrained warping and the second-order displacement terms due to large rotations, the equilibrium equations of a straight beam element are firstly developed. Due to the nonlinear displacement field, the geometric potential of semitangential moment is obtained for both the internal torsion and bending moments, respectively. To account for the semi-rigid connection behaviour, a special transformation procedure is developed. The laminates are modelled on the basis of classical lamination theory. In order to illustrate the application of the proposed formulation, several numerical examples are presented.

Design and analysis of non-linear space frames with semi-rigid connections

Semi-rigid connections are the actual behavior of beam-to-column connections in steel frames. However, the behavior of semi-rigid connections is not taken into account for the simplicity in the conventional analysis and design of steel frames. A computer-based analysis and design has been studied for the three-dimensional steel frames with semi-rigid connections. The nonlinear analysis which includes the effects of the flexibility of connections is used for this study. It is designed according to the buckling and combined stress constraints under the present loading after the joint deformations and the member end forces of the space frame are determined by the stiffness matrix method. The semi-rigid connection type is limited to the top and bottom angles with a double web angle connection. The Frye-Morris polynomial model is used to describe the non-linear behavior of semi-rigid connections. Various design examples are presented to demonstrate the efficiency of the method. The results of design and analysis of unbraced semi-rigid frames are compared to the results of unbraced rigid frames under the same design requirements.