Semi-rigid Connections Research Articles

Specificity of strength calculation for glued-in steel rods in LVL with unidirectional veneer

Design of joints of LVL elements with glued-in steel rods and metal connectors is considered as semi-rigid connection and requires taking of account the compliance. A comparative analysis of the test results of the beams with a metal connector and glued-in steel rods as well as solid beams is made in the paper. Design method of glued-in rods in LVL is proposed and taken into account failure mode. It allows reducing the distance between the axes of the rods as well as the distance from the rod axіs to the edges in the cross section of the beam and increasing the joint strength.

Sub-assemblage low damage connection incorporating blind-bolts and RBRFs subjected to cyclic loading

The Christchurch earthquake has given a renewed impetus to the development and use of low damage connections within moment-resisting frames in New Zealand. When using a low-damage technology, the building is designed to be easily repairable after a severe earthquake and is hence expected to be more resilient and cost-effective. This paper reports on a sub-assemblage test that investigates the behaviour of a newly proposed low damage connection between a steel beam and composite column. The connection incorporates blind-bolts, curved T-stubs and replaceable buckling restrained fuses (RBRFs). The RBRF is the only element which is allowed to yield when the earthquake level is higher than the design-based earthquake, so the establishment of a suitable strength hierarchy is vital to the success of the design. Two loading protocols have been applied using the same sub-assemblage but with a new RBRF at the start of each test; i.e. the RBRF was replaced after each test. The contributions of the connection, beam, and column to the total rotation have been summarised. The results show that a semi-rigid connection can be achieved by using this type of connection. Furthermore, an analytical approach has been proposed to predict the behaviour of this type of connection.

Steel-timber composite beam-to-column joints: Effect of connections between timber slabs

Studies of steel-timber composite (STC) connections and STC beams under sagging bending have been reported elsewhere in the literature using push-out and four-point bending tests respectively. However, the structural behaviour of STC beam-to-column connections under hogging bending moments (with the prefabricated timber slabs in tension) have hitherto not been investigated. In particular, the connection between the two prefabricated timber slab panels (across the column) has a major influence on the structural performance of a STC beam-to-column connection and is the focus of the current study. Eight full-scale STC beam to steel column cruciform specimens with different connections (half lap, single and double surface spline with timber and/or steel plate) for the timber slabs were fabricated and tested under a monotonically increasing downwards displacement, and these are described in this paper. The bending moment capacity, rotation capacity, failure mode, stiffness and ductility of the STC connections are evaluated and discussed. The composite steel-timber system exhibits both appreciable ductility and rotation capacity which fulfil the existing design requirements for semi-rigid composite connections in Eurocodes EC3 and EC4. Furthermore, the negative bending moment capacity of STC connections is significantly higher than that of bare steel connections without a timber slab.

An Equivalent Single-Degree-of-Freedom System to Estimate Nonlinear Response of Semi-fixed Flexural Members Under Impact Load

A quick and reliable method to estimate the nonlinear dynamic response of a structure is replacing it with an equivalent single-degree-of-freedom system. To analyze the equivalent system, determination of the load and mass transformation factors is essential. So far, these factors have been calculated just for elements with completely fixed or hinged supports. However, so many supports and connections behave as semi-fixed or semirigid and the assumption of being fully fixed or hinged does not comply with current practical conditions. The purpose of this study is to determine load and mass factors, ultimate resistance and nonlinear dynamic response for one-way flexural members with semi-fixed supports or a member of a frame with semirigid connections under impact (blast) load. The results of the proposed model are verified with available codes and references. Also, the importance of considering the members with semi-fixed supports in obtaining accurate responses is demonstrated.

An investigation of the behavior of header end-plate connections under monotonic loading

In seismically active regions such as Turkey, the context of the nonlinearity provided by a building is based on the behaviors of structural components; beams, columns and their connections constituting the seismic force resisting system of the structure. Of these members, beam-to-column connections can play a considerably important role even if they have a capability of limited stiffness and flexural strength. Structural steel connections are mainly classified as a pinned or a moment connection. However, some beam-to-column connections having limited stiffness and flexural strength, which are called semi-rigid connections such as header end-plate connections designed so as to transmit only shear forces, can be characterized by moment-rotation relationship. This paper investigates the behavior of header end-plate connections using finite element (FE) modeling. The FE models include material, geometrical and contact nonlinearities. FE modeling technique was first verified through the test results of the experimental research performed by Aggarwal (1990). Then the effect of header end-plate thickness upon moment-rotation relationship was investigated. According to the analyses results, in addition to shear stresses, axial tensile stresses have been observed to occur in the bolts at the tension side and thickness of the header end-plate and beam web play a governing role in the development of initial rotational stiffness and the flexural strength of header end-plate connections.

Development of frame finite element model for truss structures with semi-rigid connections

Development of frame finite element model for truss structures with semi-rigid connections

Stability Analysis of Frame Having FG Tapered Beam–Column

This study focuses on the analysis of the tapered beam–column having functionally graded section. By using two different methods, the substantial effects of the coupling–extensional bending of this structure are considered. Both second-order effects and flexibility of connections are considered in the analysis. The suggested exact stiffness matrix is very general and suitable for analyzing any plane frame, which has non-prismatic members and various types of connections. By using this formulation, the frame stability analysis of the FG beam with power function will be performed. Furthermore, the effects of semi-rigid connections and supports on the buckling load of 2D frames will be studied. Finally, comparing the new responses with the available solutions shows the accuracy, efficiency and capabilities of the proposed stiffness matrix. In addition, some new problems, including 2D frame, especially gabled frame, are solved using authors’ schemes.

Beam-end stiffness identification for a structural health monitoring-oriented finite-element transmission tower model using effective optimization techniques

As an important issue for establishing structural health monitoring–oriented finite element models for large steel pylons, identification of beam-end stiffness draws the attention of the engineering circle. Since the methods adopted by other researchers for parameter identification are impracticable, a beam-end stiffness identification method which combines in situ measurements for the structure’s global dynamic properties with effective multi-variable optimization methods is utilized to improve the accuracy of established finite element models. A 131-m-high large transmission tower is employed as a case study to validate the method. In situ measurements for the tower’s global dynamic characteristics are performed, and identifications of Young’s modulus for 20 semi-rigid connections distributed along each of the tower’s four main chords are undertaken utilizing three multi-variable optimization methods, that is, the first-order method, the subproblem approximation method, and the response surface method. Static numerical simulations on two detailed connection models prove that multiple uncertain parameters can be correctly and simultaneously identified when appropriate optimization techniques are chosen. Finally, the influence of beam-end stiffness identification on the structural health monitoring–oriented structural safety assessment is revealed by calculating the wind-induced dynamic structural responses for the single tower and the transmission tower-line system, which indicates that identification of the correct beam-end stiffness and updating the structural health monitoring–oriented finite element model are indispensable procedures for reliable structural health monitoring.

Dynamic Mechanical Behavior of Aluminum Alloy Mortise-and-Tenon T-Joints

An experimental investigation was conducted on aluminum alloy mortise-and-tenon T-joints (MT-joints) under dynamic cyclic loading. The MT-joints strengths, stiffness, failure characteristics, hysteresis curves, skeleton curves, restoring force models and energy dissipation curves of the joints have been reported. It’s shown from the experiment that main failure modes of the MT-joints are plastic deformation of squeezing area and tenon divorced from joint. And MT-joints structure is a typical semi-rigid connection that can withstand both rotation and bending moment.

Second-order Stiffness Matrix and Loading Vector of a Tapered Rectangular Timoshenko Beam-column With Semirigid Connections

The second-order stiffness matrix and loading vector of a linearly tapered Timoshenko beam-column with rectangular cross-section, constant width and generalized end conditions subject to a constant axial load is derived. The proposed model includes the simultaneous effects of: (1) axial load (tension or compression) applied at both ends; (2) transverse load; (3) generalized end conditions; (4) bending and shear deformation along the member; (5) shear stress correction factor induced by the tapering of the cross section; and (6) the shear force induced by the applied axial load as the member deflects laterally using two different approaches, those by Engesser and Haringx which are proportional to the total slope (dy/dx) and to the angle of rotation (θ) along the span of the member, respectively. The governing differential equations are solved by the power series method. The concept of fixity factor of tapered Timoshenko beam-columns with semirigid end connections is introduced. The proposed method and corresponding equation are capable of determining the static and stability behavior of elastic framed structures made of tapered beam-columns with semi-rigid connections using a single segment per element. Three comprehensive examples are presented that show the accuracy and validity of the proposed method and the calculated results are compared with those obtained using ABAQUS.

Structural reliability analysis of steel plane frames with semi-rigid connections

Abstract The design codes for structural design traditionally establish the adoption of partial safety factors to deal with uncertainties. These standards do not allow one to know the real probabilities of failure of a structure. What is needed, from a practical and scientific point of view, is a more consistent approach, based on reliability theory. This article addresses an initial attempt at determining the safety levels of structures based on advanced analysis and design with structural reliability theory. In this context, the authors consider the effects of the geometric nonlinearity and flexibility of connections in the reliability analysis, which aims at setting a certain displacement as the service limit state. For this purpose, a computer program was written called Structural Reliability Module. This program uses a First Order Reliability Method to analyse reliability. To carry out the structural analysis of steel structures, this study uses the program Computational System for Advanced Structural Analysis. Validating the Structural Reliability Module involved comparing the results from other authors with those generated by the program. Results for the structures under study indicate the efficiency of the implemented measures. Results suggest that, when a certain displacement is set as a service limit state, the reliability of the structures under analysis are only slightly influenced by geometric nonlinearity but considerably so by semi-rigid connections.

Dynamic Instability in Shallow Arches under Transversal Forces and Plane Frames with Semirigid Connections

Structural engineering demands increasingly lighter systems, which can cause instability problems and compromise performance. A high slenderness index of a structural element makes it susceptible to instability. It is important to understand the problem, the limits of stability, and its postcritical behavior. An example that can occur in collapsed arches under a cross load is the dynamic snap-through behavior, where the structure in a given equilibrium condition jumps to a new remote equilibrium setting, causing usually sudden curvature. The semirigid connections are a source of physical nonlinearity and can influence the overall stability of the structural system, in addition to the distribution of stresses in the same system. Conventional approaches make use of static considerations. However, instability problems are inherently evolutionary processes, so a transient analysis is necessary for a complete description of structural behavior. The present work evaluates the geometrically nonlinear dynamic behavior of collapsed arches subjected to transverse force and plane frames with semirigid connections. The time domain responses, via Newmark's Method and positional formulation of the Finite Element Method, were obtained in terms of displacements, velocities, acceleration, and phase diagrams.

Seismic response and energy dissipation of 3D complex steel buildings considering the influence of interior semi-rigid connections: low- medium- and high-rise

A numerical investigation regarding the seismic behavior of complex-3D steel buildings with perimeter moment resisting frames (PMRF) and interior gravity frames (GF) is conducted. The interior connections are assumed to be first perfectly pinned (PP) and then semi-rigid (SR); the two model responses are compared. Three steel building models representing low-, medium- and high-rise buildings, and several strong motions are used. The relative stiffness of SR connections is calculated according to the Richard Model and the Beam Line Theory. The Ruaumoko Computer Program is used to perform the required step-by-step nonlinear seismic analysis. Results indicate that interstory shears and interstory displacements at PMRF may be significantly reduced when interior connections are modeled as SR. Average reductions of up to 20, 46 and 11% are observed for interstory shears, for low-, medium-, and high-rise buildings, respectively. The corresponding reductions for interstory displacements are about 14, 44 and 15%. The contribution of GF to the lateral resistance is considerable, which significantly increases when the connections are modeled as SR; relative contributions larger than 80% are observed. The dissipated energy (DE) at PMRF is larger for the buildings with PP than for the buildings with SR connections indicating that damage at PMRF is reduced. Thus, the effect of the stiffness and the DE at interior connections should not be ignored. However, the design of some elements, particularly columns of the GF, has to be revised; these members may not be able to support the loads produced by the neglected lateral contribution if they are not properly designed.

Cyclic Experimental Behavior of CFST Column to Steel Beam Frames with Blind Bolted Connections

This paper aims to investigate the seismic behavior of blind bolted end plate composite frames between square or circular concrete filled steel tubular (CFST) columns and steel beams. Two composite frames were tested under a constant axial load on the CFST columns and a lateral cyclic load on the frame. Each specimen composed of CFST columns and steel beams was selected to represent a plan frame in an assembly building. Failure pattern of the type of frames was analyzed to comprehend the structural response. The seismic resistance ability of the blind bolted CFST frames was also estimated in terms of hysteretic curves, ductility and energy dissipation etc. The effect of column section type and end plate type on the type of semi-rigid CFST frames was studied. The test results showed that at the same steel ratio of the column section, the bearing capacity and energy dissipation of square CFST frame were higher than those of circular CFST frame at ultimate state. Strain response of main members in each CFST frame was also estimated. The internal force analysis of the test CFST frames with semi-rigid connections was discussed and evaluated the effect of the bending moment distribution. It was concluded that the novel typed CFST frames exhibited excellent seismic performance and structural internal force redistribution. The experimental studies will be useful for design and application of the blind bolted CFST frames in fabricated steel structure building.

Lateral performance of a semi-rigid timber frame structure: theoretical analysis and experimental study

Semi-rigidness of the joint connections is one of the main characteristics of timber structures. The pin-joint assumption for the semi-rigid joint connections might be not conservative in the timber structural design. In this paper, structural analysis was conducted on a semi-rigid timber portal frame; the formulas were derived in terms of the internal force and the lateral stiffness, and the influence of the semi-rigid connections was discussed. Moreover, experimental tests were performed on three full-scale timber portal frames and five bolted timber connections to study the lateral performance of the frames and the moment resistance of the connections. For consistency, the connections from the portal frames and the connections for bending tests were of the same configuration. Finally, a calculation flowchart of the lateral performance on a semi-rigid frame was presented to verify the derived formulas and to show a framework of the lateral structural design process.

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.

Optimizing Structures with Semi-Rigid Connections Using the Principle of Virtual Work

In this paper, the virtual work optimization method (VWOM) has been generalised to consider structures with semi-rigid connections. The VWOM is an automated method that minimizes the mass of a structure with a given geometry, multiple deflection criteria and load cases, while adhering to Design code requirements. In the optimization process, members are selected from a discrete database to meet all strength and stiffness criteria. Connections are modelled using rotational springs, allowing some moment transfer. The rotational stiffness of each connection can be varied form rigid to pinned. The example of a pitched roof frame is used to explain the method. Two case studies are considered: (i) a three-storey two-bay and (ii) a four-storey three-bay office building. The VWOM produced results up to 26.7% lighter than results in the literature. Furthermore, the structures were optimized for a range of rotational stiffness, where all connections in the structure were assumed to have the same rotational stiffness. Characteristic jumps in the optimized mass versus rotational stiffness were observed.

Rotational Stiffness of Precast Beam-Column Connection using Finite Element Method

Current design practice in structural analysis is to assume the connection as pinned or rigid, however this cannot be relied upon for safety against collapse because during services the actual connection reacts differently where the connection has rotated in relevance. This situation may lead to different reactions and consequently affect design results and other frame responses. In precast concrete structures, connections play an important part in ensuring the safety of the whole structure. Thus, investigates on the actual connection behavior by construct the moment-rotation relationship is significant. Finite element (FE) method is chosen for modeling a 3-dimensional beam-column connection. The model is built in symmetry to reduce analysis time. Results demonstrate that precast billet connection is categorized as semi-rigid connection with Sini of 23,138kNm/rad. This is definitely different from the assumption of pinned or rigid connection used in design practice. Validation were made by comparing with mathematical equation and small differences were achieved that led to the conclusion where precast billet connection using FE method is acceptable.

Behavior of Semi-Rigid Steel Connection For G+3 Symmetrical Structures Under Consideration of Seismic Forces Civil Engineering Department

Behavior of Semi-Rigid Steel Connection For G+3 Symmetrical Structures Under Consideration of Seismic Forces Civil Engineering Department

JOINTS OF LVL ELEMENTS WITH GLUED-IN STEEL RODS AND METAL CONNECTOR

The joints of the LVL elements with glued-in steel rods and metal connectors are considered as semi-rigid connection and requires taking of account compliance. In this study gives an analysis of the results of tests LVL beams with a metal connector on glued-in steel rods and solid LVL beams. Model of the destruction of rods in LVL is proposed, and allows for reduction the distance between the axis of the rods and from the axis of the rod to the edges in the cross section of the beam. This proposing is based on the analysis of the carried out investigations.