Semi-rigid Connections Research Articles

Performance of self-centering steel moment frame considering stress relaxation in prestressed cables

Buildings can be designed to limit the earthquake-induced damage to members that can easily be repaired. Self-centering moment-resisting frames can be used as effective structural systems for this purpose. Self-centering moment-resisting frames with prestressed cables are able to return the structure to its original position after the earthquake. The internal forces in self-centering moment-resisting frames are transferred between the beam and the column by post-tensioned cables. As a main member of self-centering connections, prestressed cables play a significant role in such systems. Cable tension decreases over time due to the effect of stress relaxation on the performance of the system. Stress relaxation is a time-dependent phenomenon causing stress reduction over time in the members prestressed at a constant strain. Therefore, the effect of stress relaxation on the performance of self-centering moment-resisting frames can be significant. In this article, after simulating and validating a moment-resisting frame with self-centering connections, stiffness and moment–rotation hysteresis diagrams were analyzed after 0, 1, 5, 10, and 20 years of cable prestressing. According to the results, two equations were presented to estimate the reduction in the connection stiffness and dissipated energy by the system based on prestressing level and the time after prestressing. The proposed equations could be used to model semi-rigid connections.

Behavior of semi-rigid steel frames under near- and far-field earthquakes

The realistic modeling of the beam-column semi-rigid connection in steel frames attracted the attention of many researchers in the past for the seismic analysis of semi-rigid frames. Comparatively less studies have been made to investigate the behavior of steel frames with semi-rigid connections under different types of earthquake. Herein, the seismic behavior of semi-rigid steel frames is investigated under both far and near-field earthquakes. The semi-rigid connection is modeled by the multilinear plastic link element consisting of rotational springs. The kinematic hysteresis model is used to define the dynamic behavior of the rotational spring, describing the nonlinearity of the semi-rigid connection as defined in SAP2000. The nonlinear time history analysis (NTHA) is performed to obtain response time histories of the frame under scaled earthquakes at three PGA levels denoting the low, medium and high-level earthquakes. The other important parameters varied are the stiffness and strength parameters of the connections, defining the degree of semi-rigidity. For studying the behavior of the semi-rigid frame, a large number of seismic demand parameters are considered. The benchmark for comparison is taken as those of the corresponding rigid frame. Two different frames, namely, a five-story frame and a ten-story frame are considered as the numerical examples. It is shown that semi-rigid frames prove to be effective and beneficial in resisting the seismic forces for near-field earthquakes (PGA = 0.2g), especially in reducing the base shear to a considerable extent for the moderate level of earthquake. Further, the semi-rigid frame with a relatively weaker beam and less connection stiffness may withstand a moderately strong earthquake without having much damage in the beams.

Seismic Behavior of the Removable Links in Eccentrically Braced Frames with Semirigid Connections

Eccentrically braced frames (EBFs) have good elastic stiffness, while semirigid joints can provide greater ductility and make all components easy to fabricate. With application of semirigid connections to EBFs, a seismic structure can be formed. After earthquake, damaged components can be easily replaced, and repair costs and maintenance time can be reduced. In order to study the seismic performance of this type of structure, four single‐story plane specimens were tested under low‐cycle cyclic loads. Also, a total of 7 EBF models were investigated through three‐dimensional, nonlinear finite element analysis. Good agreement is achieved between the simulation and experimental results. The results show that the failure modes of the EBFs with semirigid connections are the fracture at link end plate connection, and no obvious buckling deformation and cracks occur in the other components. The EBFs with semirigid connections exhibit good inelastic rotation ability, and the inelastic rotation of all specimens and models exceeds the limit of 2016 AISC specification. Due to the slip between members, the hysteretic curves of those new structures show different degrees of pinching phenomenon and it becomes more obvious with the increase of the length of links. By analyzing the strain of the bolts, it is found that the bolt strains of the joints of link‐to‐beam are the highest, while the bolt strains of the joints of beam‐to‐column and column‐to‐brace are smaller. This structure system shows higher energy dissipation capacity and good economic benefits.

A conceptual study of a self-centering semi-rigid connection with energy dissipation for wooden frames

A proposal of a semi-rigid self-centering connection for the seismic protection of wooden structures is studied. An analytical model for the characterization of the response of the connection is developed. Quasi-static tests of a wooden column with the proposed connection allowed to validate the model and calibrate its parameters, obtaining errors smaller than 6% between analytical prediction and experimental results. The self-centering capacity and the effectiveness of the connection to limit the loads transmitted to the connected elements were evidenced. Damped free vibration tests evidenced the capacity of the connection to reduce structural vibrations. It was verified that the resistance and dissipation capacity of the connection can be modified by two design parameters that can be adjusted at the assembly. The proposed connection has desirable characteristics for its use in the protection of structural wooden frames, is versatile, and its design is simple, with explicit physical parameters.

Stability Optimization of Trapezoidal Frame with Rigid Members and Flexible Joints

Stability has been an important subject in the design of a portal frame structure. Conventional stability analysis of the portal frame is normally conducted assuming that all the joints are rigid. However, the joints of a portal frame in real applications are not always rigid and semirigid connections often exist. AISC design code requires that the effect of the joint flexibility on the behavior and buckling capacity of the portal frame should be taken into account in the analysis and design procedures. To address this issue, a portal frame with flexible joints and rigid members was theoretically analyzed in the literature and closed form solution was derived for its global buckling load. However, when more parameters are involved, e.g., different leg lengths, asymmetric frame shape, and moving load, the solution to the governing equation of the stability of the frame becomes impossible. This paper presents a comprehensive parametric study on the stability of an asymmetric portal frame with flexible joints and rigid members through finite element (FE) analysis. The FE model was first validated by the existing theoretical solution in the literature. Parameters including the position of the moving load, the lengths of the two frame legs, and the span of the frame were analyzed. Design curves were developed based on the parametric study, from which the stable, unstable, and catastrophically unstable states of the portal frame were characterized. This paper contributes benchmark results for the stability optimization in the design of the portable frame of a general shape.

Effect of Random Strength Parameters of Flange Steel on Bending Resistance and Deflections of Girders with Corrugated Web

Abstract The study presents results of statistical investigations into random strength parameters of steel used to manufacture flanges of plate girders with corrugated web. In the case of plate girders with corrugated webs, flanges are manufactured from flat sheet steel S235JRG2 or S355J2+N or S275. The guaranteed yield strength Remin is determined on the basis of tests conducted on steel samples. It should be lower than yield strength of flat sheets obtained as the result of testing mechanical properties. This value at the same time should be regarded as the margin of resistance of girders. The material tests were performed on samples randomly collected from 20 girders with corrugated web and flange thickness of 15 and 20 mm, which had been already examined. Coefficients of variation of yield strength VRe =D(Re )/E(Re ) and partial factors of yield strength γm were selected on the basis of the conducted analysis of material tests. The obtained results were related to factors γm determined from the tests on thin flat sheets. The impact of yield strength and random cross-sectional area of flanges on bending resistance of girders with corrugated web was shown. Also the effect of the spread of the Young’s modulus values and semi-rigid connections on global displacements of tested plate girders with corrugated web was analyzed.

Seismic analysis of frames with semi-rigid connections in accordance with EC8

Up to date research has pointed out that most of the structural connections of reinforced concrete (RC) frames, particularly precast ones, behave as semi-rigid. Therefore, it is of great importance to develop an analysis method which takes into account the connection rigidity. For that purpose matrix formulation of the deformation method is used in this paper, and the effect of rigidity of connections on the structure response is included by stiffness matrix for semi-rigidly connected member. The elements of this matrix are functions of the fixity factors at the ends of members. The proposed method is applied in seismic analysis of the precast RC frame structure of the existing industrial hall according to Eurocode 8 (EC8).

Stiffness prediction for bolted moment-connections in cold-formed steel trusses

The purpose of this research was to study the behavior of cold-formed steel cantilever truss structures. A cantilever truss structure and bolt-moment connection were tested and verified by the 3D-finite element model. The verification results showed a good correlation between an experimental test and finite element analysis. An analytical method for elastic rotational stiffness of bolt-moment connection was proposed. The equation proposed in the analytical method was used to approximate the elastic rotational stiffness of the bolt group connection, and was also applied to the Richard-Abbott model for generating the nonlinear moment-rotation curve which modeled the semi-rigid connection stiffness. The 2D-finite element analysis was applied to study the behavior of the truss connection, caused by semi-rigid connection stiffness which caused a change of force to the truss elements. The results showed that the force in the structural members increased by between 13.62%-74.32% of the axial forces, and the bending moment decreased by between 33.05%-100%. These results strongly suggest that the semi-rigid connection between cold-formed steel cantilever truss structures should be considered in structural analysis to achieve optimum design, acknowledging this as the real behavior of the structure.

Deformation indeterminacy in global analysis of steel structures with semi-rigid joints

This paper shows the procedure for determination of deformation indeterminacy within global analysis of steel constructions with semi-rigid joints, as well as the analysis of deformation indeterminacy within the approximate deformation method. In this paper there has been a detailed comparative analysis with criteria of cinematic system stability and division on steel frame with semi-rigid connections to systems with movable and immovable joints.

Prediction of the Bending Strength of Boltless Steel Connections in Storage Pallet Racks: An Integrated Experimental‐FEM‐SVM Methodology

Due to many differences in the material, geometry, and assembly method of the commercially available beam‐end‐connectors in steel storage pallet racks (SPR), no common numerical model has been universally accepted to accurately predict the M–θ behavior of complex semirigid connections so far. Despite the fact that the finite element method (FEM) and physical experiment have been used to obtain the mechanical performance of beam‐to‐column connections (BCCs), those methods have the disadvantages of high computational complexity and test cost. Taking, for example, the boltless steel connections, this paper proposes a data‐driven simulation model (DDSM) that combines the experimental test, FEM, and support vector machine (SVM) techniques to determine the bending strength of BCCs by means of data mining from the engineering database. First, a three‐dimensional (3D) finite element (FE) model was generated and calibrated against the experimental results. Subsequently, the validated FE model was further extended to perform parametric analysis and enrich the engineering case base of structural characterization of BCCs. Based on the M–θ curve of the FE simulation, support vector machines (SVMs) were trained to predict the flexural rigidity of beam‐to‐column joints. The predictive power of the SVM algorithms is estimated by comparison with traditional ANN models via the root mean square error (RMSE), the mean absolute percentage error (MAPE), and the correlation coefficient R. The results obtained indicate that the SVM algorithms slightly outperform the ANN algorithms, although both of them are in good agreement with FEM and physical test. From the point of view of engineering application, DDM is able to provide much more effective help for structural engineers to make rapid decisions on steel members design.

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.

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

This paper performs optimization for plane steel frames with semi-rigid beam-to-column connections, in a company with fixed, semi-rigid and hinged base connections using a biogeography-based optimization algorithm (BBO), along with a genetic algorithm (GA). In this paper, Kanvinde and Grilli [1] nonlinear model is used for simulating semi-rigid base connections, where this model considers all deformations in different base connection components under the applied loads to determine the relative spring rotation for the sake of getting accurate base rotational stiffness value. In addition, Frye and Morris [2] nonlinear model is used for simulating semi-rigid beam-to-column connections. The P-∆ effect and geometric nonlinearity are considered. The stress and displacement constraints of AISC-LRFD [3] specifications, together with size adjustment constraints, are considered in the design procedure.

Experimental study and theoretical analysis of glulam-concrete composite beams connected with ductile shear connectors

Ductile shear connectors are often applied in timber-concrete composite beams. The relative interface slip of such kind of composite beams will affect the mechanical performance of the composite beams and result in structural nonlinearity. Gamma method which adopts effective bending stiffness to reflect semi-rigid connection is recommended in Eurocode 5. The effective bending stiffness is irrelevant to external loads and calculation points of the composite beam. However, actual bending stiffness distribution along the beam is variable due to that shear connectors are subjected to different shear force. In order to verify the accuracy of gamma method, four-point bending tests of a total of three glulam-concrete composite beams with lag screw connectors and one pure glulam beam were conducted in this article. The failure mode, bearing capacity, and load–deflection relationship were investigated in the experiment. Meanwhile, push-out tests of composite beams were also conducted for determination of the force–displacement relationship of ductile shear connectors. Then, numerical simulation using beam-truss model was established for investigation on the mechanism of composite beams. Finally, theoretical analysis of composite beams considering the effect of interface slip was also presented. Comparing results from gamma method with the presented method, it is shown that both methods can calculate deflection at serviceability limit state with high precision. However, non-uniform distribution of actual bending stiffness cannot be reflected by gamma method.

A Numerical Investigation of the Influence of Semi-Rigid Composite Connections on the Seismic Behavior of a Building with Steel Concentrically Braced Frames

Semi-rigid composite connections are connections which have a certain rotational stiffness and bending strength by means of the slab and its reinforcement. The use of these connections can lead to economic and structurally efficient solutions such as selecting smaller beam sections, reducing deflection and vibration problems. Additionally, they are permitted to use as a secondary lateral resisting system in regions of high seismicity. Therefore, in this study, two investigations were made in terms of seismic behavior evaluation: the influence of semi-rigid composite beam-column connections on interior frames and the influence of shear tab connections. Firstly, a 6-story building with steel special concentrically braced frames is designed according to current seismic design codes. Secondly, 3 models are created using the designed building. In Model 1, all beam-column shear tab connections are assumed as pinned connections. Model 2 and Model 1 are identical except that In Model 2, shear tab connections used in Model 1 are not assumed as pinned connections and their actual behavior is determined and included to the model. In Model 3, all beam-column connections on the interior frames are designed as semi-rigid composite connections. The interior frame sections are reselected and the exterior beam-column connections except for the ones on the braced bays are assumed the same as in Model 2. Lastly, nonlinear static analysis (pushover) is carried out and some comparisons are made with respect to the following aspects: lateral displacement and story drifts under same lateral force and lateral force under the same lateral displacement. As a result, Model 1 and Model 2 showed similar behavior due to the shear tab connections acting almost as pinned while Model 3 showed that using semi-rigid composite connections can increase the base shear capacity by %48 and decrease peak displacements and story drifts by %65.

Optimization of plane frame structure with consideration of semi-rigid connections

Beam-column connections play an important role in the load capacity of frame structures. In Vietnam, in the current design calculation standards for steel frame structures, to simplify calculations, the beam-column connections in the frame structures is considered as the two idealized extremes of either rigid connection or pinned connection. The actual behavior of beam-column connection is neglected. The paper presents the optimization calculation of steel frame structure taking into account the semi-rigid beam-column connections. The optimization problem is solved by Genetic algorithm method and the calculation procedure was implemented by Matlab programming software. Some numerical examples are conducted and from there the conclusions and recommendations of calculations and design of steel frames will be proposed.

Effect of Joint stiffness on Elastoplastic behavior of Cold-formed thin-walled Steel frames

In this paper, the first-order elastic analysis and second-order elastic analysis of cold-formed thin-wall steel frame (shelf) in practical engineering are carried out by using ANSYS and SAP2000 modeling analysis software, and the influence of semi-rigidity and second-order effect of joints on its overall performance is analyzed. At the same time, on this basis, the static elastic-plastic analysis of the shelf is carried out, and through the comparative analysis of the structural influence coefficient and displacement magnification coefficient of the shelf, the seismic performance of three kinds of beam-column connections (rigid connection, semi-rigid connection, hinged joint) is evaluated. And the structural influence coefficient of the shelf is put forward innovatively.

Study on the Static Performance of H-shaped Steel Beam to Square Tubular Column Semi-Rigid Connections Steel Frame

In order to study the overall mechanical behavior of the new H-shaped steel beam to square tubular column semi-rigid connections in steel frame, the static performance, failure characteristics and bearing mechanism of the steel frame are studied by the medium-span static load test of the full-size steel frame and finite element simulation. The results show: when the vertical concentrated force is applied to the beam span, the buckling occurs in the mid-upper flange of the beam spans, and the plastic hinge is formed at the position of the beam span, while the deformation of the joint and the column is small, so the safety factor of the frame column and the joint region is high. Due to the semi-rigidity of the joint, the force and deformation of the joint region are smaller than the span of the beam, and the rotation angle of the joint meets the requirements for normal use of the structure. Therefore, the carrying capacity mechanism of the steel frame is reasonable.

Seismic Behavior of Mid-Rise Precast Reinforced Concrete Building with Effect of Joints and Supports

Precast concrete structures are widely used in construction. It consists of prefabricated elements casted in industry and connected to each other to form a homogeneous structure. Connections function is to transfer moments and axial forces. Many engineers assume precast connection as pinned, but in reality, they are semi-rigid connections that transfer forces to other members. Lack of design and detailing of connection leads to improper behaviour of the structure, which then leads to the collapse of the building. Past earthquake studies show that many precast buildings performed poorly, and the main reasons were connections. This paper mainly focuses on understanding the seismic behaviour of mid-rise i.e seven-storey precast reinforced concrete buildings with various beam-column joints i.e rigid, semi-rigid, pinned and column-base supports i.e, fixed and hinged supports. Building is modelled and analyzed using ETABS v17 software. Rotational stiffness of precast billet connection is adopted for modelling of semi-rigid beam-column connections. Response spectrum and modal analysis are carried out. Results of displacements, storey drift, storey shear, storey stiffness, base shear, time periods and first mode shapes of models are discussed. It is observed, precast reinforced concrete building models with semi rigid connection performs better than building models with pinned connections and building models with fixed supports reduces the structural response to a great extent.

Time History Analysis on Precast Building Connections

Construction industry is one of the most important factor for the development of the country. Precast buildings are one of the major development in construction technology, this technology helps to reduce the construction time and cost. Precast building construction is widely improved at present in India. The Growth of the precast building construction improved in large scale but construction and Design faults made the Precast buildings week in seismic areas. Due to seismic effect Beam column connections are very critical in Precast buildings ,Generally precast buildings are constructed with help connecting with proper joints of prefabricated elements. Designers are assumed that Beam-column connections are hinged one but in real time execution process the connections are Different from assumption. In present study we consider the three types of Beam-columns connections such as Rigid connection ,semi-Rigid connection and Hinged connections are developed in G+20 High rise building .These High rise building analysed with help of Time history analysis of High Seismic waves, Moderate Seismic waves and Low seismic waves .It helps to Identify the behaviour of connections and The results of Top Displacements , story Drifts and Inter storey Drifts are compared for the Different connections and Different Seismic waves.

Optimal Plastic Analysis of Structures under Uncertain Conditions

In this study optimum plastic shakedown analysis of framed steel structures with semi-rigid connections (SRC) between beam and columns subjected to multi-parameter static loading presented. Since shakedown analysis does not provide information concerned with the accumulated residual displacements, complementary strain energy of the residual force (CSERF) considered as constrain to evaluate the post yield behavior of framed steel structures. The constraints on the CSERF are modelled using probabilistic and deterministic methods. To evaluate the maximum shakedown load-multipliers a numerical example is introduced, shakedown load-multipliers are calculated and safe loading domains of the framed steel structure are illustrated. The numerical results show that the constraints on CSERF, SRC and probabilistic given constraints can influence on the value of the shakedown load-multipliers.