Connection Stiffness Research Articles

Numerical Behavior of Extended End-Plate Bolted Connection under Monotonic Loading

Extended end-plate connections, which act as joints providing resistance against moments between beams and columns, are commonly categorized as semi-rigid or partial-strength connections. The reason for their extensive application in steel frame constructions lies in their straightforward design, their ability to be reproduced easily, and the convenience they offer in the fabrication process. This research used the ABAQUS FE software to construct a three-dimensional finite element model (FEM) with the main objective of exploring how different geometric parameters impact the behavior of the extended end-plate bolted connection, which functions as a semi-rigid, partial-strength beam-to-column connection. Accurately determining the moment-rotation relationship and connection stiffness is of utmost importance for semi-rigid connections. The developed FEM models incorporate various factors such as geometric and material non-linearities, bolt pretension force, as well as contact and sliding between the connection elements. To establish the credibility of the numerical outcomes, the developed FEM model was meticulously calibrated and verified against experimental data obtained from previous studies available in the literature. Subsequently, using the validated finite element model, a parametric investigation was undertaken to evaluate the influence of distinct geometric parameters, namely the thickness of the end plate and column web stiffeners. This numerical model facilitates a comprehensive analysis of the extended end-plate bolted connection, encompassing critical aspects such as the moment-rotation curve and failure mode. The results demonstrated that the analyzed finite element model aligns well with experimental findings and that the use of column stiffeners is inevitable in the joint, as well as a moderated thickness of the end plate. Doi: 10.28991/HIJ-2023-04-02-04 Full Text: PDF

Dynamics modeling and flight characteristics of folded multi-body aircraft

This paper studies the dynamic modeling method of fold-able multi-body aircraft based on the dynamics theory of multi-body system. Considering the multi-body aircraft as a complete multi-rigid body system, the dynamic model for the free unfolding process of the multi-body aircraft after horizontal launch is established. On the basis of the multi-body dynamics model, the coil spring moment model and the damping moment model for the flexible connection between the flight units are added. Taking a certain type of fold-able three-section wing aircraft as an example, the numerical simulation calculation is carried out. The influence of the flexible connection stiffness coefficient between the flight unit on the dynamic characteristics of the fold-able multi-body aircraft in the free deployment process and the relationship between the stiffness of the flexible connection and the maximum initial folding angle are studied. Finally, the stability envelope between the stiffness coefficient of the flexible connection and the maximum initial folding angle is determined.

The vibration of the double-plated structure containing the inner fluid and elastic connections

Analytical studies of the vibration characteristics of double-plated structure containing the inner fluid and elastic connections have been performed. An analytical model is first derived to predict the vibration characteristics of the double-plated structure. The transverse displacements of plate and the sound pressure of inner fluid are described by the improved Fourier series. Elastic connections are regarded as springs. In order to simulate arbitrary boundary conditions, the virtual spring technology is applied along each side of the plates. The vibration and sound pressure can be obtained by the Fourier coefficients which calculated by the Rayleigh-Ritz technique. Results from the finite element method (FEM) are well consistent with ones calculated by the analytical method. The effects of parameters on vibration are studied by analytical analyses. It is found that the inner air shows well vibration isolation, while inner water acts as a short circuit in vibration transmission. The stiffness of the elastic connection has significant effects only when the inner fluid is air. When the inner fluid is water, the effect of the spring will be greatly weakened.

Performance of Beam-Column Connections with Mass Ply Lam and Steel Dowels under Cyclic Loads

A mass timber lateral force resisting system (LFRS) is proposed using a mass timber buckling restrained brace (TBRB) to improve the seismic resilience of mass timber buildings. To develop a resilient braced frame, it is essential to understand and quantify the behavior of the connections, including the possible failure modes and moment-rotation capacities. Cyclic and monotonic tests were conducted on six mass timber beam-column connections to study the response of a mass timber joint connected with slotted-in steel plates and mild steel dowels. The primary goal of the subassembly tests was to measure the maximum rotation, stiffness, ductility, and failure modes of such connections for both monotonic and cyclic loads. The tests showed that the connections with three steel dowel details reached a maximum rotation of 0.11 radians (6.3 degrees) with no loss of strength. In addition, a numerical model was developed to represent the moment-rotation relationship of the mass timber beam-column connections.

Elastoplastic Analysis of Shear Behavior of Multicell Shaped Concrete-Filled Steel Tubular Connection Based on Unified Theory

Connection between multicell shaped concrete-filled steel tube (MCFST) columns and steel beams gives full play of strength and properties of steel tube and core concrete and has many advantages in mechanical and seismic performance. Shear behavior of the connection is crucial to damage performance of special-shaped CFST structure under seismic load. However, few studies focused on shear behavior of the MCFST connection. This study investigates elastoplastic shear behavior of the MCFST connection. Nine specimens were tested under constant axial load and lateral low cyclic loading. The test results showed that as height to thickness ratio of column section increased, the plastic status of the stresses of the flange limb steel webs was obviously different from those of the web limb steel webs, and initial shear stiffness of the panel zone increased. In order to give analytical methods for shear behavior of the MCFST connection under compressive and shear force at the material level to engineers, according to unified theory the analytical model of MCFST composite material in the panel zone is equivalent to that of concrete-filled circular steel tube of web and flange limbs considering the difference of the stresses of the steel webs and interaction between the web and flange limbs. Based on the previous research and analysis of test results, migration and evolution are carried out from analytical models for shear behavior of the MCFST connection at the material level to that at the member level. The analytical expression of initial shear stiffness of the MCFST connection is derived, and the theoretical results correlate well with the experimental results. In addition, the analytical expression of shear stiffness of the MCFST connection in plastic hardening stage is obtained. The calculation formulas are proposed to predict the shear stiffness of the MCFST connection in the elastic and plastic hardening stages by geometrical parameters, material property parameters, and stress state of the steel webs.

Component method applied to base plate connections of steel racks

This paper deals with the analytical prediction of the rotational strength and stiffness of base plate connections in steel storage racks under bending moment and axial compressive force. Based on the testing prescriptions of the European Code EN15512 and on the findings of an experimental campaign on 21 full scale specimens tested at four different values of constant axial force and under two different types of connection set-up, an analytical procedure relying on the component method is proposed to estimate the rotational strength and stiffness of all load bearing components, and, by suitable assembly of the contributing parts, to obtain a prediction of the overall strength and stiffness of the connection.The aim is to contribute to the definition of improved analytical tools of possible use in the design and product development stage or in the update of existing design codes.Quantitative results are, however, still mixed. Further investigations appear to be required for the stiffness, mainly to describe the nonlinear moment rotation curves observed in the experiments. Strength results are more accurate and as well successful in predicting the failure mode and the loss of strength with increasing compression.

Analytical and experimental studies for the vibration transmission of the double-plated structure containing the inner fluid and elastic connections

The vibration transmission of the double-plated structure containing the inner fluid and elastic connections are researched by the analytical and experimental techniques. An analytical method is firstly proposed to predict vibration responses of the double-plated structure. The improved Fourier series are used to describe the transverse displacements of the plates and the sound pressure of the acoustic cavity. The elastic connections are regarded as springs. Motion equations are derived by the energy method and vibration results are gained via the Rayleigh–Ritz technique. Meanwhile, a test sample of the double-plated structure is manufactured. Four vibration isolators are utilized as the elastic connections. The inner fluid is air or water. Forced vibration tests are conducted with a random white-noise force. The results from both experiments and the finite element method (FEM) are well consistent with ones calculated by the analytical method. Then the effects of important parameters on the vibration transmission are studied by the analytical and experimental analyses, including the stiffness of elastic connections, the height of the inner fluid, the boundary condition of plates, the spring position, the inner fluid loading and the coating damping layer. It is found that the inner water acts as a short circuit in the vibration transmission, and the inner air leads to the less vibration transmission from the upper plate to the lower one. Some other new phenomena are also observed and analyzed in this paper.

Comparative study on seismic performance of prefabricated and cast-in-place underground structures under different site conditions

Since the seismic performance of prefabricated underground structures is not yet clear, they not have been constructed in high seismic intensity areas or poor sites. This paper aims to study the applicability of rectangular prefabricated (semi-rigid prefabricated, ASF, and rigid prefabricated, AMT) underground structures in soft soil sites located in high seismic intensity areas. The structures were compared with cast-in-place (CIP) underground structures. Three-dimensional soil-structure interaction advanced finite element models were established to simulate the seismic behavior of the three types of underground structures (ASF, AMT and CIP) constructed in two different sites (soft rock site and soft soil site). The pre-earthquake stress states, dynamic responses, and post-earthquake performance states of the three underground structures were systematically analyzed, considering various static and dynamic conditions. Additionally, the results of dynamic time history were compared with those of the standard procedures available in the literature. The results demonstrated that: i) site conditions have a significant effect on the structures’ static and dynamic responses, ii) the seismic response in soft soil site is much larger than that in soft rock site, but the ratio of response of prefabricated underground structures to that of CIP is almost the same for both soft soil and soft rock sites. Furthermore, as the peak ground acceleration increases, the percentage difference of inter-story displacement ratio (IDR) between ASF, AMT and CIP underground structures in soft soil site decreases, and iii) prefabricated underground structures can be used in both soft rock and soft soil sites. In addition, the seismic performance of ASF is better than that of the AMT structure, which is better than that of the CIP structure. However, when the ASF structure is built in a site with high seismic intensity and poor soil conditions, special consideration must be given to waterproofing measures for wall-slab joints or setting up tongue and groove to improve the connection stiffness and reduce the deformation.

Development of novel concave shear connector to enhance the composite behavior

In recent decades, the use of composite structures has increased in favor of their quick, simple, and cost-effective construction and shear connectors are the key to attaining this composite behavior by transferring horizontal shear from concrete to steel girder and avoiding vertical separation. The efficiency of the composite connection depends on the stiffness and strength of the shear connector. The current study proposes an innovative concave type shear connector for the composite steel beams-RCC slab structure in buildings and bridges, which is economical and easier to install compared to conventional headed studs. The push-out tests were simulated in ABAQUS software using finite element analysis to assess the connection's ductility, stiffness, and shear strength as well as the connection's ultimate slip. The numerical analysis observed an enhanced strength and stiffness of the concave shear connectors compared to conventional headed shear studs, achieving a material saving of 20% and satisfying the Eurocode ductility criteria.

Experimental Study on the Rotational Stiffness of Pocket Type Scaffolding Connection According to the Rotation Direction

The rotational stiffness of the pocket-type connection used in system scaffolding to join horizontal members and vertical members was evaluated. To investigate the rotational stiffness of connections when subjected to bending moments in the downward, upward, and lateral rotation directions, load tests were performed on 30 specimens with cantilever specimens for each rotational direction. Results showed that failure shapes of pocket-type connections were different depending on the rotation direction. Owing to the differences in the failure phenomena, the maximum moment capacity of the upwardly rotated specimens was the largest, followed by that of the downwardly rotated specimens and the laterally rotated specimens in that order. Compared to the Eurocode 3 connection classification, the pocket-type connections correspond to semi-rigid connections when the rotation direction is downward or upward, and they can be considered nominal pin connections when the rotation direction is lateral. From the moment-rotation curves, it was concluded that the rotational stiffness of the pocket-type connections could be estimated as a bilinear model.

Simulation of Load–Slip Capacity of Timber–Concrete Connections with Dowel-Type Fasteners

Quality assessment of stiffness and load-carrying capacity of composite connections is of great importance when it comes to designing timber–concrete composite structures. The new European regulation intended explicitly for timber–concrete structures has made a significant contribution to this field, considering that until today there was no adequate design standard. Due to the proposed general expressions for determining the stiffness and load-carrying capacity of composite connections made with dowel-type fasteners, which are incapable of describing most of the commonly applied fasteners, engineering, and scientific practice remained deprived of a quality assessment of the essential mechanical properties of the connection. In order to overcome this problem, this paper proposes a numerical model of the connection suitable for determining the whole load–slip curve, allowing it to estimate the stiffness and load-carrying capacity of the connection. The model was developed by considering the non-linear behavior of timber and fasteners, which is determined through simple experimental tests. For the numerical model validation, experimental tests were carried out at the level of the applied materials and on the models of the composite connection. Through numerical simulations, analysis of obtained results, and comparison with experimental values, it can be confirmed that it is possible to simulate the pronounced non-linear behavior of the timber–concrete connection using the proposed model. The estimated values of stiffness and load-carrying capacity are in agreement with the conducted experimental testing. At the same time, the deviations are much less than the ones obtained from recommendations given by the new regulation. Additionally, apart from evaluating the value and the simulation of the complete curve, it is possible to determine local effects, such as the crushing depth in timber and concrete, the fastener’s rotation, and the participation of forces in the final capacity of the connection.

厚肉溶接箱形断面部材を用いた異幅角形鋼管柱端接合部の面外曲げ剛性

In this paper, out-of-plane bending stiffness of column-end connection between square hollow section column and thick panel with different width was investigated by loading test and finite element analysis. From the results, column-end connection of corner-type under 45-degree directional force has the smallest stiffness, and of which section dose not remain plane, and proportion of bending resistance caused by partial deformation of column in column-end bending resistance is very small. Therefore, method to estimate out-of-plane bending stiffness of column-end was proposed based on deformation of diaphragm of hollow section of panel and directly above panel.

Study on Double-Resonant Characteristics of Load Simulation System for Electro-Hydraulic Servo Mechanism

The electro-hydraulic servo mechanism and engine realize thrust vector control together. Due to the low natural frequency of the engine, the dynamic characteristics of the test process show the result of double-resonance. The load simulation system can improve the efficiency of production tests and replace the actual engine in the production process. This paper fully considers the resonant problem of the engine, gives the relevant structural design scheme and parameter adjustment method to the load simulation system, and tests and analyzes the resonant characteristics. It aims at changing the resonant characteristics of the load simulation system by designing and adjusting the connection stiffness and torsional stiffness to achieve the real load condition.

Cyclic performance of fully assembled joints between H-Beam and CFST shear wall

The steel pipe of the concrete bundle shear wall is a new structural system suitable for steel structures. This study presents experimental findings of six fully assembled end-plate joints of H-beam based on high-strength bolts and one fully assembled side-plate joint of the concrete-filled steel tubes (CFST) shear wall. Two fully assembled joints of H-beam were proposed for the concrete bundle shear wall. Seven joints were subjected to low-cycle reciprocating tests in this testing program. The experimental parameters included the thickness of the end plate for H beam, the thickness of the end plate on wall, and the anchorage length of the bolts in the concrete, among which, the side-plate joints effectuated the rigid connection of unsupported frames in EC3 classification. Moreover, two fully assembled joints proposed in this study could effectuate the rigid connection of supported frames in EC3 classification. The strengthened end-plate joints significantly exceeded the rigid connection stiffness limit. The test results also indicated that the stiffness of the end-plate joint primarily depended on the thickness of the end plate for H beam and end plate on wall, while the side-plate joint mainly dissipated energy through the slip of bolts, which had excellent ductility and energy dissipation capacity, and thereby exhibiting the characteristics of low yielding load capacity and high ductility.

Seismic fragility assessment of multistory precast concrete parking structures

In this study, fragility and collapse mechanisms of multistory precast concrete parking structures were assessed. The variation of a set of structural parameters was considered, including shear stiffness and tensile stiffness of connectors, number of stories, and two orthogonal directions of the seismic action. A probabilistic analysis based on fragility curves was regarded a robust technique for assessing the influence of these parameters on the expected seismic performance. Additionally, fragility curves were obtained using the SPO2FRAG procedure. The results indicate that variation of the considered parameters significantly affects the seismic response and seismic fragilities of precast concrete parking structures.

Experimental research and theoretical analysis of novel polygon‐key assembly connections

AbstractTo improve the shear performance of assembly connections in precast RC shear wall structures, a novel polygon‐key assembly connection (PKA connection) was proposed. Shear tests were carried out to study the shear performance of the PKA connections, specimens' parameters considered in the tests consist of polygon‐key inclination angles, polygon‐key heights, and axial compression ratios. Shear capacity, stiffness, and failure modes of the PKA connections were investigated. Furthermore, theoretical analysis of the PKA connection was performed, equations of PKA connection's shear capacity were deduced, and the theoretical analysis results were verified by the test results. The results show that the polygon‐keys can effectively improve the shear capacity of assembly connection of precast RC shear wall structure. Compared with the parallel assembly connection, peak shear capacity of the PKA connection can be enhanced by more than 15%. When polygon‐key's inclination angle is within the range of 45–90°, the peak loads of PKA connections change slightly. When polygon‐key's height is within the range of 5–7 cm, the cracking load and peak load of the PKA connection change slightly. With an increase in axial compression ratio, the shear capacity of PKA connection gradually increases, and the peak displacement changes slightly. Based on the shear‐friction theory, the calculated PKA connection's peak loads are in good agreement with the test results.

Push-out test of headed stud connectors subjected to freeze-thaw cycles and artificial corrosion

To obtain the shear capacity calculation method and competition failure mechanism of headed stud connectors of steel–concrete composite structures under the influence of freeze–thaw cycles (FTCs) and artificial corrosion (AC), the material performance of concrete specimens after the FTCs and push-out tests of 36 headed stud connectors specimens were tested under the influence of FTCs and AC. The cubic compressive strength, dynamic elastic modulus, and mass loss rate of C50 concrete were obtained under different FTCs. Failure modes, load-slip curve, shear capacity, and shear stiffness of stud connectors were investigated based on push-out tests of miniaturized specimens. Based on the nonlinear fitting of test data, a formula for calculating the shear capacity reduction factor is proposed. Results show that the shear capacity and stiffness of stud connectors will deteriorate due to the deterioration of concrete performance caused by FTCs or the weakening of stud section caused by AC. The two failure modes of stud breakage or concrete cracking will change with the aggravation of FTCs and AC effect.

Tensile stiffness of perfobond rib connectors in steel–concrete composite pylon of bridges

Perfobond rib connectors (PBLs) are subjected to considerable tensile forces when used as stiffeners in steel panels and force-transfer structures in the cable anchorage zone in the steel–concrete composite pylons of cable-stayed bridges. Determining the elastic tensile stiffness of the PBLs is necessary for a structural analysis of the composite pylons. This investigation aimed to explore the critical parameters affecting the elastic tensile stiffness of PBLs and propose equations for accurately predicting the tensile stiffness of PBLs. Twelve PBL specimens were tested under pull-out load to investigate their elastic tensile stiffness. Thereafter, a parametric analysis was conducted via the finite element approach to examine the influence of the geometric characteristics of the perforated rib, transverse rebar diameter, and concrete strength on the tensile stiffness of the PBL. The results demonstrated that the elastic tensile stiffness of PBLs increased with the increase in the rib thickness, hole diameter, and concrete strength but decreased with increasing embedded depth. The perforated rib width had no influence on the elastic tensile stiffness. Additionally, the elastic tensile stiffness increased slightly as the transverse rebar diameter increased. Subsequently, a theoretical spring model was developed to predict the elastic tensile stiffness of the PBLs, considering the contribution of perforated ribs and concrete dowels. Finally, a comparative analysis was performed, which proved that the proposed equations in the present study based on the spring model were accurate in predicting the tensile stiffness of PBLs. The proposed equations are recommended for application in the structural analysis of composite pylons.

Nonlinear finite element investigations on different configurations of exterior beam-column connections with different concrete strengths in column and floor

The fast development of quality concrete production has increased the usage of high-strength concrete (HSC) in the columns of high-rise buildings where high axial column loads exist. In contrast, normal-strength concrete (NSC) is used in the floor system for economic reasons. This produces a weak concrete zone at the intersection of columns and floors. Studies focused on evaluating the performance of such connections are still limited. The current numerical study investigates the performance of such connections. The developed numerical model has been verified against the experimental test for connections with different column-to-beam strengths. The numerical model has demonstrated acceptable accuracy compared to the experimental results. Moreover, the validated model has been employed to investigate the influence of different column-to-floor strengths on connections with and without transverse beams and floor slabs. It has been found that the strength and stiffness of connections with different concrete strengths have been improved compared to monolithic connections. Furthermore, the increase in joint strength and stiffness for connections with different column-to-floor strengths is more pronounced for connections with transverse beams and floor slabs due to their contribution to achieving proper confinement conditions for the weak concrete in the joint zone. In addition, the presence of a transverse beam affects the induced stress of the beam bars, resulting in a change in the mode of failure to beam flexural failure, whereas the presence of a slab floor increases both the stiffness and flexural strength of the beam. However, connections with the floor slab suffered high damage due to the transferred equilibrium torsion. Moreover, connections with different column-to-floor strengths exhibited larger stains in their joint stirrups; hence, additional joint stirrups are recommended to avoid the brittle shear failure of the joint. The study ended by evaluating the response of such connections under high axial column loads. It has been observed that planer connections perform poorly in terms of strength and ductility, while adequate performance has been observed for connections with transverse beams or slabs. Therefore, the role of the transverse beam and slab should be taken into account in the design of the connections with different column-to-floor strengths.

Assessment of Modal Characteristics of Steel–Concrete Composite Girder Bridge with V-Shaped Piers

As the standards of bridge design and construction continue to improve, more and more combination bridges are being put into use. The public’s demand for aesthetically pleasing bridges is also increasing, making it necessary to use the special structure of steel–concrete combinations, continuous V-shaped piers, and continuously stiffened bridges. This structure has the structural and mechanical characteristics of both a continuous girder and a V-shaped pier bridge. The span can be reduced to a certain extent because the support of the V-shaped piers can be applied directly to the main girder. The spanning capacity of the bridge is generally greater than that of a combined steel–concrete girder bridge with vertical piers. The whole bridge is continuous, without expansion joints, making it more stable and safe for traffic. At present, research on this structural bridge type is not yet complete. In this paper, the structural system and dynamic characteristics of this bridge are investigated in the context of real-life engineering. Firstly, the self-vibration characteristics of the three structures were analyzed, and their effects on the self-vibration characteristics were studied by varying the height of the crossbeam at the V-shaped piers’ support, the main beam stiffness, and the V-shaped piers’ stiffness in the three structures. The results show that the increase in main beam stiffness can effectively improve the vertical stiffness of the three structures, with the most obvious effect on structure one and the least effect on structure two; the increase in V-shaped pier stiffness causes a huge improvement in the transverse stiffness of the three structures. Subsequently, a two-unit rod system model of the background bridge was established using the finite element method, and the original model was improved by calculating the equivalent shear stiffness of the shear nail group so that it could simulate the shear joints more accurately. The effects of the shear connectors on the self-vibration characteristics of the steel–concrete combined continuous beam–V-shaped piers and continuous rigid-frame bridge were investigated through theoretical analysis and finite element simulation. It was found that due to the existence of flexible shear connectors, the interface between the steel beam and concrete slab in the combined beam has a slippage effect which causes the deformation to become unsynchronized, and there is a certain difference between vibration patterns. The stiffness of the shear connectors has a certain effect on the self-vibration frequency of the bridge. The damage to the local shear connectors does not have a large effect on the self-vibration frequency of the overall structure, but the damage to the shear connectors at the beginning of the connection between the V-shaped piers and the main beam is greater than that of the other areas. Damage to shear joints should be given special consideration in comparison to other areas.