Rigid Connection Research Articles

Experimental investigation of rigid khorjini connections using reduced beam sections with diagonal and horizontal-vertical stiffeners

Steel structures with khorjini beam–column connections, used to be a popular construction practice in Iran. This paper presents a new rigid khorjini connection with reduced beam sections (RBS) for earthquake-resistant steel structures. In rigid khorjini connection, two beams pass next to the column faces without interruption and are connected to the column by vertical plates. In this research, Rigid khorjini connections with Reduced beam sections were investigated. RBS method has some disadvantages such as web local buckling and lateral torsional buckling. Therefore, to prevent these weaknesses and improve the performance of khorjini connections with reduced beam sections, web stiffeners were employed. Four different specimens were constructed and tested using IPE 140 profiles for beams: one without an RBS (KHORJINI), one with reduced beam section (KRBS), and two with RBS and web stiffeners (KRBS-HVS and KRBS-DS). Through these experimental tests, it was revealed that all specimens sustained the interstory drift angle greater than 0.06 rad without any significant loss of strength, which indicates that the Rigid khorjini connection with reduced beam sections for IPE140 profiles can perform acceptably under the conditions of AISC regulations and the use of Diagonal and Horizontal-Vertical stiffeners increased the energy dissipation and plastic rotation capacity of connections.

Improving cable-stayed bridge longitudinal aseismic capability via fluid viscous damper parametric optimization and experimental investigation

The seismic vulnerability of Cable-stayed Bridges (CSBs) in high-earthquake intensity areas can be of significant concern to structural safety and resilience. A promising design practice for CSBs depends on decoupling the girder from the girder-pylon connection and involving energy dissipation devices such as fluid viscous damper (FVD) to mitigate the seismic responses. However, the parametric damper optimization algorithm and experimental validation on the FVD of a longitudinal aseismic system for CSB is still limited. In this study, three longitudinal aseismic systems (a semi-floating system with an elastic or damper connection, and a pylon girder consolidation system with a rigid connection) were investigated and compared based on the actual bridge Xigu Yellow River CSB erected in Lanzhou, China. The non-linear time history methodology was implemented to analyze the pylon and girder’s displacement and internal force responses, and the fluid viscous damper (FVD) aseismic system was the optimal choice considering the oval seismic performances. The optimal damping parameters were obtained by conducting parametrical analysis based on qualitative analysis and non-linear multi-function optimization in the pylon-girder and auxiliary pier-girder connections. A full-scale FVD model was designed and manufactured to conduct low velocity, constitutive law, and damping efficiency tests. The experimental results indicate that FVD achieved good energy dissipation capability and stability. FVD damping parameters were deduced according to the constitutive law test. The optimal analytical FVD damping parameter agreed well with the experimental results. Furthermore, the optimization was implemented in the final bridge design, referencing longitudinal aseismic systems for CSBs.

High performance rocking timber wall with innovative low-damage floor connections

While mass timber structures are gaining more share of the new build structures considering their well-known advantages, rocking timber walls have been particularly popular with engineers and researchers due to their reliable and efficient seismic performance. With the current conventional approach of using rigid bracket plates and fasteners on rocking timber walls, not only floors and connections are prone to damage, but also the rocking motion is compromised. This paper proposes an innovative wall-to-floor and wall-to-beam mechanism that eliminates bulky rigid bracket connections and allows safe transfer of lateral loads, while dissipating seismic energy without damage as well as providing full self-centring. Numerical results present a few key advantages of this system, such as reduced drifts and seismic base shear and an increase in damping and seismic energy dissipation. The findings of this study demonstrate the significant potential of the proposed system for further developments and application in real structures.

The influence of hinged and rigid connections on the seismic behaviour of “Inverted Y” bracing systems

AbstractThe present paper intends to illustrate the seismic behaviour of different configurations for a ten storeyed “inverted Y” eccentrically braced frame provided with rigid and/or pined beam/column and diagonal/column connections. Four configurations were analysed for the “inverted Y” braced frame, sized for the forces produced by the same code seismic base shear force. In the first configuration, rigid connections were used for all kind of structural elements. The second configuration had hinged beam/column and diagonal/column connections. In case of the third configuration, rigid connections were used among all kind of structural elements and additional potentially plastic zones with reduced cross‐sections (resembling the “dog‐bone” detail) were considered along the girders and braces, near the member ends connected to the columns. The fourth configuration had hinged diagonal/column connections and additional potentially plastic zones were considered only along the frame girders, near the girder ends connected to the columns. The behaviour of each frame configuration during static and dynamic nonlinear analyses was observed. The extreme values for deformations and member forces were compared. The steel consumption was estimated for each of the four considered configurations.

Deadbeat-Direct Torque and Flux Control of a Brushless Axial-Flux Magnetic-Geared Double-Rotor Machine for Power-Splitting HEVs

A deadbeat-direct torque and flux control (DB-DTFC) for brushless axial-flux magnetic-geared double-rotor machines (AMGDRMs) is presented in this paper. The AMGDRM is employed as a power-splitting component in hybrid electric vehicles (HEVs) to enable speed decoupling between the internal combustion engine (ICE) and load. Since the rigid connection between the ICE and the drive train is replaced by the AMGDRM, fast torque control of the AMGDRM is required for the ICE speed regulation. Furthermore, the ICE torque contains abundant harmonics, inevitable sinusoidal components are introduced to the modulating rotor torque for torque balance, and further to the PM rotor torque owing to the magnetic-gear effect. Since both the PM rotor of the AMGDRM and the traction motor contribute to the hybrid electric system total torque output (i.e., torque coupling), the cascaded traction motor should compensate the PM rotor torque ripple actively to guarantee smooth total output torque. However, proportional-integral (PI) regulator suffers from limited bandwidth and thus could not realize accurate torque decoupling. Therefore, DB-DTFC, where torque and flux linkage are decoupled and respectively achieve their reference commands within two sampling periods, i.e., deadbeat responses, is proposed to enable a faster and more robust ICE speed control and accurate torque decoupling. The DB-DTFC law is derived and discrete-time close-loop current and flux linkage observers of the AMGDRM are developed. The proposed scheme and its superiorities are experimentally validated on an AMGDRM prototype test bench.

Numerical Assessment of The Robustness of a Corner‐supported Modular Steel Building

AbstractThis paper investigates the robustness of a 6‐storey corner‐supported Modular Steel Building (MSB) under notional ground floor corner column removal (i.e. alternate path method). The robustness assessment investigates the following structural effects that were frequently ignored for the sake of simplicity in existing numerical modelling approaches: (1) semi‐rigidity in the beam‐to‐column connections, and (2) initial out‐of‐straightness (geometric imperfection) in the compression members. Commonly, the welded connections between the beams and square hollow section columns are modelled as fully rigid, however, this may overestimate the actual robustness of MSBs as fully rigid connections often have a higher energy absorption capacity. Similarly, modelling a perfectly straight column could overestimate the actual robustness of MSBs. Comparing the model with semi‐rigid connections to that with fully rigid connections, an additional 30% vertical displacement was observed at the point of removal. However, geometric imperfections in the columns and diagonal braces did not cause any increase in building displacement/drift after removal. This highlights the importance of modelling the semi‐rigidity in the connections especially when the connections involve joining hollow sections.

Stability Analysis of Prefabricated Underground Granary Composite Silo Walls

The prefabricated steel plate-concrete composite silos have been recently used for underground granaries. As the buried depth and diameter-thickness ratio of underground silos increase, the calculation of elastic stability, which takes into account the effects of prefabricated joints, becomes a primary consideration in the design of the silo walls. In the present study, the equation to estimate the elastic critical pressure of double-layer heterogeneous cast-in-situ silos under uniform external pressure was proposed first. The theoretical solutions were then compared with the numerical results and the accuracy of the equation was verified. To derive the critical pressure of prefabricated steel plate-concrete silo walls, an equivalent joint design method was proposed and verified by a series of numerical analyses for different models. The results indicate that if the bending stiffness ratio of the joint is larger than the bending stiffness of the composite silo wall section, the prefabricated double-layer composite silo walls are equivalent to cast-in-situ double-layer composite silo walls, and the equation to evaluate the elastic critical pressure of double-layer heterogeneous cast-in-situ silo walls under uniform external pressure could be used to derive the critical pressure of prefabricated steel plate-concrete silo walls. The bending tests of the full-scale steel plate-concrete composite silo wall models with and without joints were conducted and the experimental results indicate that the assumption of a rigid connection between the steel plate and concrete was reasonable, and the equivalence of prefabricated composite silos to cast-in-situ composite silos to obtain the elastic critical pressure is feasible and the result is reliable.

Reliability of super-slope rack railway under bridge pier settlement

Bridge pier settlement always occurs on the super-slope rack railway, which has serious impact on reliability and stability of rack-bridge system. Aiming at this issue, a coupled dynamic model of the super-slope vehicle-rack(track)-bridge system under pier settlement is established considering gear-rack nonlinear meshing behavior, wheel-rail nonlinear contact behavior and pier settlement. On this basis, the mechanical characteristics of gear-rack system induced by pier settlement are studied. Then, the dynamic influences of two common gear-rack connections (rigid connection and elastic connection) on the adaptability and safety of this system are discussed. Finally, the safety control value of pier settlement of the large-slope railway in mountainous areas is proposed. Results show that pier settlement potentially leads to fracture of gear-rack fasteners under multi-loads such as gear-rack meshing and wheel-rail contact. When the rack and the sleeper are rigidly connected, the maximum shear stress of the fastener is 346.43 MPa when the settlement is 10 mm, which seriously exceeds the standard limit (235 MPa). When they are elastic connected, the maximum shear stress of the fastener is 262.80 MPa, slightly exceeding the limit value. The structural stress of rack is far less than the tensile strength of rack. Under the two connection modes, the maximum deformation of the rack is 14.02 mm and 11.08 mm respectively, which is about 140% and 125% of the pier settlement. The main frequencies of the vibration of the rack are located at 70 ∼ 80 Hz and 65 ∼ 70 Hz respectively. Pier settlement has a significant effect on the stress of the fastener and the deformation of the rack, but has little effect on the vibration and stress of the rack railway.

Initial lateral stiffness of plate-type modular steel frame structure with semi-rigid corner connections

The plate-type modular steel frame buildings with semi-rigid corner connections are assembled structures, whose prefabricated plate-type modules are constructed in the factory and assembled on site. Owing to the assembly of different plate-type modules, this self-bearing building forms a double-beam and multi-column structure. To calculate the initial lateral stiffness of the plate-type modular steel frame structure with semi-rigid corner connections, based on the modified displacement method, the lateral amplification effect caused by semi-rigid connections between upper and lower modules was transferred to the lower beam of the upper module; according to the concept of superposed beam, the structure can be simplified into the form of single beam and multiple columns; in addition, by using the combination method of multiple columns with different corner connections, the theoretical formulas of the initial lateral stiffness of the semi-rigid connected plate-type modular frame structure were derived. Compared with the plate-type modular frame with rigid connections, the lateral amplification coefficients of regular plate-type modular frames with semi-rigid connections were derived and the influence of the number of spans and stories on the lateral amplification coefficient were investigated. The theoretical values of the initial lateral stiffness of the plate-type modular steel frame with semi-rigid connections were in good agreement with the experimental values and FEM evaluations.

Management of bridge with non-rigid connectors in cases with pier abutments

The type of denture bridge with pier abutments where there are stand-alone abutment teeth between the abutment terminals, requires the dentist to pay special attention. One crown is attached to a natural tooth, and the other crown is attached to a dental implant or other type of abutment, known as the pier abutment that can become a class I fulcrum if restored using a 5-unit bridge with rigid connectors, which can cause excessive force to be received by the retainer at the abutment terminal, leading to debonding of the retainer or even damage to the periodontal tissues of the abutment teeth. In addition to these problems, long-span bridges have a poor prognosis due to the mobility difference between the anterior and posterior teeth, which may cause excessive stress on the connector. The use of a non-rigid connector can overcome this problem, as it can be a stress breaker by allowing micro-movements in the connector. The design of semi-rigid bridge with pier abutments must consider factors such as span length, anticipated occlusal load, and mastication factor. Proper consideration of these factors ensures the safety and longevity of the bridge.

Effects of beam-column connection rigidities and soil-structure interaction on seismic performance of steel frames

Structures can be exposed to non-linear deformations under earthquake effects. However, linear methods are mostly preferred for designs because of their simplicity and facility. The inelastic behavior of the structure is approximately taken into account by using some coefficients. However, it is possible to make more realistic and economical designs by using methods that consider the inelastic behavior of the structure. In this context, the displacement-based design method is becoming increasingly popular. This study evaluates the seismic performance of steel frames resting on elastic foundations with different beam-column joint stiffnesses using the static pushover analysis method. Static pushover curves, plastic deformations, performance points, and base shear forces were compared. The results show that the base condition greatly affects the seismic performance of the building.

Wildly ramified rigid G2$G_2$‐local systems

AbstractIn earlier work of the author, rigid irregular connections with differential Galois group and whose slopes have numerator 1 were classified and new rigid connections were constructed. The same construction can be carried out for ‐adic local systems in the setting of positive characteristic. In this article, we provide the results that are needed to obtain the classification of wildly ramified rigid ‐local systems whose slopes have numerator 1. The overall strategy of the classification is very similar but the methods needed to obtain some invariants differ.

Undrained capacity of two rigidly connected rectangular foundations under general V-H-M loading

Analytical and numerical solutions of the undrained load-carrying capacity of shallow foundations are mainly available for single foundations. This paper investigates the undrained limit states of two-spaced rectangular foundations with rigid connections. Three-dimensional finite-element analyses are carried out to systematically examine the coupled interaction of foundation spacing and degree of soil strength heterogeneity on the load-carrying capacity of the foundation systems under general loading. Results are presented in the form of ultimate limit states under pure vertical (V), horizontal (H), and moment (M) loads, and the failure envelopes under combined V-H, V-M, H-M and V-H-M loading. Soil failure mechanisms obtained from the finite-element analyses are shown for the representative loading paths of the two-foundation systems. Based on the failure mechanisms, the methods are established for calculating the undrained load-carrying capacity of the two-foundation systems to assist the foundation design in practice.

Relationships between vibrations of main device and mechanical network in a classical vibration control system

For a classical vibration control system consisting of a main device, an auxiliary device and a mechanical network, two major results are obtained. The first major result is analyzing the effect of adjusting the main device vibration on the vibration of the mechanical network. The second major result is establishing the upper and lower bounds of the amplitude–frequency curve of the mechanical network when the amplitude–frequency curve of the main device is fixed. For theoretical research, the first conclusion can be used to predict the variation trend of the vibration of the mechanical network when the vibration of the main device is further suppressed. For engineering applications, the second conclusion can be used to evaluate whether the vibration suppression performance indicators can be achieved. Then, to demonstrate the effectiveness, these two major results are applied to wind turbine load mitigation. A 7-DOF onshore wind turbine model including nacelle relative displacement is established. By replacing the rigid connection between the nacelle and the tower top with a mechanical network, the tower top relative displacement is reduced under both wind loads and seismic waves. Finally, a theoretical explanation of the simulation results is provided using the two major results above.

Experimental and numerical investigations of tensile behavior of slip-critical blind bolts anchored in concrete-filled steel tubes

This paper presents experimental and numerical investigations of a Concrete-Anchored Slip-Critical Blind Bolt (CASCBB) system, which can be used to connect a steel beam to a concrete-filled steel tube column to form a rigid moment connection. A series of pull-out tests of CASCBBs embedded in concrete-filled steel square hollow section (SHS) is conducted with varying parameters such as with or without concrete infill, types of bolts, threaded or non-threaded anchor stud, tube thickness and bolt edge distance. A connection with a sufficiently thick SHS flange benefits significantly from its direct contribution to the total resistance even well before the anchorage failure. If the tube flange is too thin, the connection will possess no ductility as the concrete cone failure mode governs and dominates. A finite element methodology that resolves the difficulties of modelling the behaviour of infill concrete housing an anchored bolt is able to closely replicate the experimental responses. It is found from the finite element analysis that the contribution of the steel tube’s flange is independent of its thickness-to-width ratio but is a function of its thickness and the bolt edge distance. Placing the anchored bolt close to the SHS web can double the stiffness compared to placing it in the middle of the flange due to the greater contribution of the steel tube. It can also increase the maximum load-carrying capacity significantly. The finite element analysis results suggest that threading the anchor stud does not have noticeable effects on the anchorage failure load and the connection’s stiffness, in contrast to the apparent test results. In order to enable the plate separation to take place (at a load slightly higher than the bolt pretension), the column wall must be sufficiently thick. The wall thickness controls the maximum tensile capacity, the elastic stiffness and the ductility, but does not affect the initial stiffness.

Research on Digital Modeling Method of Triaxial Vibration System

To meet the demand of providing basis for improving triaxial vibration system, it is necessary to extract the overall Frequency Response Function (FRF) matrix of triaxial vibration system from its digital model. The mechanical parts of triaxial vibration system is connected tightly which satisfy rigid connection assumption. The Jetmudsen FRF method is used to construct the overall frequency response function matrix of triaxial vibration system. The electrodynamic shaker (referred to as the shaker) is an important component of the three-axis vibration system, and its function is to provide the test bench with an excitation force in a certain direction. Therefore, it is necessary to define a large number of internal nodes on the shaker. The FRF matrix of shaker (including origin FRF matrix of internal nodes and joints, cross-point FRF matrix of internal nodes and joints) should be obtain to carry out the construction of overall FRF matrix of triaxial vibration system. It is difficult because the size of FRF matrix of shaker is too large. So a way to simplify the distributed loads exerting on the structure into multi-point concentrated loads is proposed, it can be used to obtain the simplified digital model of the electrodynamic shaker. Based study above, the overall frequency response function matrix of the triaxial vibration system is obtained, and the digital modeling of the triaxial vibration system is completed.

Effect of non-rigid connector on the stress distribution of tooth-implant supported fixed prostheses using different implant length and diameter: A comparative 3D finite element study.

To investigate the significance of the connector type on stress dissemination within the tooth-implant-supported fixed dental prostheses in the mandibular posterior region with different combinations of implant diameter and length by means of finite element analysis (FEA). Six models of different designs for tooth-implant fixed dental prosthesis (FDPs)were simulated and divided into two main groups. Implant lengths were 10, 11.5, and 13mm while implant diameters were 3.7, 4.7, and 5.7mm. The main difference between the groups was the connector type. Models were evaluated using 3D FEA (Solidworks Premium 2018 × 64 Edition). Group A tooth-implant FDPs (5.7mm × 10 mm) had a mesial and distal rigid connector while group B tooth-implant FDPs (3.7mm × 10mm, 3.7mm × 11.5mm, 3.7mm × 13mm, 4.7mm × 10mm and 5.7mm × 10mm) had a mesial non-rigid connector in their design between the pontic and the tooth. Models were analyzed to determine the magnitude of von Misses Stresses at six specific zones (fixed dental prosthesis, bone around distal implant, bone around tooth, cementum, periodontal ligament, implant) under vertical occlusal loading of 100 N after meshing and assigning the material properties. Stress values around the supporting bone were significantly higher in Group B (tooth-implant FDP with non-rigid connection) when compared to Group A (tooth-implant FDP with rigid connection). Also, the stresses measured at the FDP level showed that the rigid connection group (5.7 mm × 10mm) exhibited 26% lower stress values when compared to the non-rigid group (5.7 mm × 10mm). Implant-tooth FDPs with rigid connector design using the combination of implant diameter and length (5.7mm × 10mm) demonstrated a better design modality thus predicting a higher success rate and more longevity than using the non-rigid connection option.

Analysis of a Bending-Stressed Pile in Interaction with Subsoil

This study explored reinforced concrete piles located in a flexible half-space and loaded with external loads, considering various contact elements and the connection between the pile and the ground massif. Piles are mainly solved as axially loaded elements stressed by a vertical force. However, there are also several cases in the construction industry where a pile is stressed by a horizontal force or by a bending moment, producing a bending loaded pile. A static model of a pile and the surrounding subsoil was constructed using software based on FEM. The pile was modelled from 3D finite elements that were rotationally symmetric around the vertical axis of the pile. Additionally, the flexible half-space was modelled from 3D elements that were rotationally symmetrical around the piles. The boundary conditions were applied on the surfaces around the perimeter and at the bottom of the ground massif. The flexible half-space was modelled up to the area where there was zero deformation. The presented analysis focused on the description of different types of contact elements between the surface of the reinforced concrete pile and the surrounding ground mass. This interaction was modelled as a fixed connection or as point-to-point contact, and a contact surface. In the next part, different boundary conditions on the pile bottom were considered. Floating piles, supported by joints or firmly woven into the ground massif, were considered. All these outputs based on FEM were compared with the analytical solution of the bent pile that was published in the 1980s. The deformations and internal forces during different modelling of the contact between the edge of the concrete pile and the surrounding ground mass were compared. The higher values of the studied quantities were for rigid connections, which is logical. For contact elements, the property of the contact was considered. This property introduces less stiffness, and thus, the resulting values were lower compared to those for a fixed connection. The presented analysis of the FEM analytical and numerical solution is also very valuable for engineers working in construction.

Pier Abutment: Non-Rigid Stress Breaker Appliance -A Case Report

Nonrigid connector (NRC) in a fixed partial denture having pier abutment increases the life of the prosthesis. Rigid connectors though most commonly use they result in early failure of the prosthesis such as debonding as well as put adverse effects on the abutments when have been used in the case of pier abutment. This case report presents with the missing first premolar and first molar rehabilitation on the maxillary left arch using non-rigid connector.

Structural performance of rigid shear connectors in concrete encased steel composite columns

Concrete encased steel (CES) composite columns possess a wide variety of advantages in constructing concrete-steel composite frames. In order to achieve the composite behaviour of these columns, it is necessary to transfer the force between steel and concrete, effectively. Therefore, shear connectors should be used on the contact surface between concrete and steel. In this research, behaviour of the rigid shear connectors in CES composite columns is numerically studied. The results – obtained from the finite element analysis – were validated against the experimental results. Afterwards, parametric studies were conducted to investigate the effective parameters on the behaviour of the rigid shear connectors. The results show that the length, the thickness and the penetration depth of the shear connector, the compressive strength of concrete and the thickness of concrete cover have a noticeable effect on the strength and stiffness of the shear connector. Moreover, increasing the length and the penetration depth of the shear connector, and the thickness of the concrete would increase the residual strength level. In general, the rigid shear connector is mobilized under a much smaller slippage (between concrete and steel), as compared to the stud shear connector, and provides greater stiffness and strength. Moreover, due to being encased in reinforced concrete, it can also provide sufficient ductility. Finally, based on the parametric studies, a formula is suggested to predict the ultimate shear capacity of the rigid shear connector in the CES composite columns.