Failure Modes Of Connections Research Articles

Bolted end-plate tube connections subject to tension and bending

A large amount of research has been undertaken on tubular bolted end-plate connections loaded in axial tension, and considerably less on such connections in flexure. This paper studies the combined effects of these two loads and presents the first laboratory tests on these connections under combined tension and flexure. Using validated finite element models, a parametric study with 360 numerical models is performed on these connections under axial and eccentric tension loads. After screening this database of experimental tests and numerical results to isolate only connection failure modes, current design methods for predicting the connection capacity under eccentric tension are evaluated and revised. In addition, based on interaction curves, a novel approach is proposed to design these splices under combined loads. For all methods, the use of the plate ultimate and yield stress was compared for the end-plate material strength parameter. Lastly, a reliability analysis is performed for the application of the recommended design methods to Canadian practice.

Efficiency of Data-Driven Hybrid Algorithms for Steel-Column Base Connection Failure Mode Detection

Base connections join the column to the foundation, thereby providing a superstructure fixation to the foundation, and play a major role in the steel structure’s ductile behavior. Seismic damage to these connections can dramatically increase the cost of restoration and the risk of destruction. The purpose of this research was to evaluate the effectiveness of three advanced hybrid models, which combine the particle swarm optimization (PSO) algorithm, Runge–Kutta optimizer (RUN), and sparrow search algorithm (SSA) with an artificial neural network (ANN), to recognize the failure modes of the steel-column base plate (SCBP) connection. Data from prior experiments were used as inputs to the models. A comparison was performed between the results of the proposed models (PSO-ANN, RUN-ANN, and SSA-ANN) and the previous studies that utilized different machine learning algorithms, such as support vector machine and naive Bayes, for the failure mode identification of the SCBP connections. Examination of all models showed that the hybrids RUN-ANN, PSO-ANN, SSA-ANN, and decision tree perform better than the others models and can predict the failure mode with an accuracy of 95%, 92%, 90%, and 91%, respectively. The SHapley Additive exPlanation methodology is also used in this study to demonstrate the importance and contribution of the components that influence SCBP connections failure mechanism identification.

Experimental and numerical evaluation on the behavior of single-shear timber connections using lag screw

In current design procedures, the capacities of single-shear timber connections with lag screws are determined based on their governing failure modes, which are assumed to occur independently. In this study, the capacity and failure modes of single-shear timber connections with lag screws are evaluated experimentally and numerically. Six specimens of Red Meranti wood and lag screws with different penetration lengths are tested to obtain their lateral load capacities and failure modes. Nonlinear 3D finite element analyses using Abaqus are conducted to simulate the test condition. The experimental and numerical results are evaluated in terms of connection failure modes and capacities. Moreover, the result will be compared with NDS 2018 predictions. The study results show that the connection capacities between experimental tests and numerical analysis are similar if the minimum penetration requirement of NDS 2018 is satisfied. It can also be seen that the dominant failure modes, both from experimental and numerical results, match with those predicted using NDS 2018, although they are slightly combined with the other failure modes.

KEKUATAN SAMBUNGAN DUA TAMPANG PADA MDF DENGAN ALAT SAMBUNG PASAK WPC

MDF (Medium Density Fiberboard) and WPC (Wood Plastic Composite) are innovative results of using sawdust waste to overcome the problem of wood scarcity. This study used a WPC Teak dowel because it has high shear strength and does not cause rust marks. This study was conducted to determine the value of the MDF connection capacity using WPC Teak dowel connectors and to determine the connection failure mode based on the EYM (European Yield Model) theory. This study used a WPC Teak dowel with a diameter of 6 mm, 8 mm, 10 mm, and 12 mm. The type of connection is a double-shear wooden joint using MDF. The test was carried out at the Structural Laboratory, Civil Engineering Department, Tidar University using a Compression Testing Machine to get the value of the connection capacity and test failure mode based on the MDF bearing strength and WPC Teak post failure referring to ASTM D764-97a. The test results obtained an average connection capacity value WPC dowel with a diameter of 6 mm, 8 mm, 10 mm, and 12 mm, respectively, which was 1094 N; 1870 N; 2439 N; and 3462. The highest average connection capacity value at 12 mm diameter was 3462 N, and the lowest at 6 mm was 1094 N.

Brittle failure of laterally loaded self-tapping screw connections for cross-laminated timber structures

The performance of structural timber connections is of utmost importance since they control the global response of the building. A ductile failure mechanism on the global scale is desirable, especially in the design of structures in seismic areas, where dissipative components in which ductile failure modes need to be ensured are considered. Therefore, the knowledge of possible brittle failure modes of connections is crucial. The paper investigates the brittle failures of laterally loaded dowel-type connections in cross-laminated timber subjected to tensile load in a lap joint configuration through experimental investigations and analytical estimations. A set of 13 different test series has been performed with fully threaded self-tapping screws of 8 mm diameter and different lengths (40 to 100 mm) in cross-laminated timber composed of 3 or 5 layers (layer thickness range from 20 to 40 mm), giving rise to the activation of different brittle failure modes at different depths. Plug shear was among the most typically observed failure modes. A previously proposed model for the brittle capacity was applied to the tested connections at the characteristic level. As shown by the performed statistical analysis, the existing model is not reliable and mainly unconservative. A very low performance is observed (CCC = 0.299), but with a good correlation (c = 0.750) for the tests in the parallel direction. Further research work is required to improve the current model predictions and to gain a better understanding of the underlying resisting mechanisms.

Experimental study of the shear performance of H-shaped aluminum-timber composite connections

Aluminum alloy has significant advantages in reducing self-weight and improving the corrosion resistance compared with steel. The performance of the interface between timber and H-shaped aluminum alloy beams is the key to designing aluminum-timber composite beams. Twelve groups of double-shear tests were conducted in this paper to investigate the influences of glulam strength, the type and size of connectors, and the row number of connectors on shear capacity, and the failure modes of connections were evaluated. The results have shown that, compared with the specimens connected by screws, the bolt heads of the specimens connected by bolts tended to cause local crushing failure of the glulam. There is negligible difference between the shear capacities of aluminum-timber and steel-timber connection when connected by single-row screws. For the group effect of the screws, the reduction of shear capacity of aluminum-timber connections is slightly higher than that of steel-timber connections when connected by multi-row screws. The shear capacity of aluminum-timber connections with multi-row screws needs to be reduced when one plastic hinge appears in the screws (failure mode II). It does not need to be reduced when two plastic hinges appear in the screws (failure mode III), and the theoretical value has a large safety margin. The length-to-diameter ratio λ is the main factor affecting the failure modes of the screws, and the coefficient λy is introduced to discriminate the failure modes.

Seismic performance of thread-fixed one-side bolts bolted extended endplate connection to HSST column with internal strengthening components

This paper presents experimental results of the seismic performance of the Thread-fixed One-side Bolts bolted Endplate Connection to Hollow Square Steel Tube column (TOBEC-HSST) with internal strengthening components. Five specimens were tested under cyclic loading. The main variable parameters affecting the seismic behavior of specimens were the internal strengthening structure types (i.e. the polygonal steel tube without inner stiffener, or with the horizontal or vertical stiffener) and the extended endplate types (i.e. with or without the endplate stiffeners). The failure modes of connections were observed, the moment-rotation hysteretic response and the strain distribution of connections were obtained. Besides, the rotation ability and ductility, the degradation of strength and rigidity, and the energy dissipation capacity were analyzed and compared, which were affected by the strengthening measures. The introduction of the endplate stiffeners can improve the overall rigidity of the joint region and sufficiently develop the energy dissipation capacity and ductility of the connections, and the contribution from the inner stiffener in the internal strengthening polygonal steel tube can also enhance the seismic performance of the connections. In addition, the rotations at the failure of the connection were larger than 30 mrad, which satisfied the ductility limitation requirement in reference to FEMA-350, revealing a potential to the application in seismic steel structures.

Behaviour of castellated beam-to-column end-plate connection under monotonic load

The development of plastic hinges in a steel frame structure with steel beam-to-column end-plate connection joints by strengthening the end-plate area is a widely used design concept. This study explores the realization of this design concept with a beam web opening and without end-plate stiffening. The factors that impact the mechanical properties and failure modes of these joints are the end-plate thickness, opening diameter, opening position, and opening type. These parameters are tested for monotonic loading of six beam-column joints, and 220 finite element models are parametrically analysed. Additionally, the development of plastic hinge of the beam based on the development trend of maximum strain of each component section is studied. The initial rotational stiffness, ductility, bearing capacity, deformation capacity, and failure mode are used as the evaluation criteria to assess the behaviour of this joint. The research indicates that a castellated steel beam-to-column end-plate connection can realize the occurrence of plastic hinge and exhibit good ductility and load-bearing performance. This study highlights the premise that the beam web opening and end-plate thickness parameters must be within a specific range to achieve accurate results; additionally, the division method of the interval of parameters is described. The influence of end-plate thickness on the working mechanism of the connection is clarified, and the mechanical properties and failure modes of connections under different parameter intervals are studied. This study proposes a method for calculating the initial rotational stiffness of the connection to achieve good accuracy by considering the participation of the components on the beam in the rotation of the connection.

Study on tensile properties of semi grouted sleeve connectors after high temperature

In this paper, the uniaxial tensile tests of semi grouted sleeve connectors at normal temperature, 200 ℃, 300 ℃, 400 ℃ and 600 ℃ were carried out. The influence of temperature and anchorage length on the tensile properties of semi grouted sleeve connectors after high temperature was studied, and the transition process of failure mode of connection with the increasing of temperature was analyzed. The results showed that with the increasing of temperature, the failure mode of the grouted sleeve connectors changed from tension failure after steel bar yield to the pull-out failure after steel bar yield, and finally to pull-out failure before steel bar yield. The ultimate bearing capacity of the semi grouted sleeve connector decreased with the increasing of temperature. When the temperature was lower than 400 ℃, the best anchorage length of the specimen was 110 mm. The temperature was higher than 400 ℃(including 400 ℃), increasing the anchorage length can effectively increase the ultimate bearing capacity of the specimen. Finally, based on the test results, the calculation formula of the ultimate tensile force of the semi grouted sleeve connectors with the change of temperature and anchorage length was given, which provides a reference for related specification design and engineering construction.

Numerical studies on yield line patterns of thread-fixed one-side bolted endplate connection to square hollow section column under tension

Numerical analyses on yield line patterns of Thread-fixed One-side Bolts (TOBs) bolted endplate connection to Square Hollow Section (SHS) column under tension were presented. A finite element model was established and verified by test results carried out by the authors. Parametric analyses were carried out to investigate the effects of the bolt diameter and the column wall thickness on the connection behavior. Analysis results showed that the yield strength of connection increased with the increase in the bolt diameter and the column wall thickness. The relationship between the connection failure mode and the bolt diameter to the column wall thickness ratio was presented. The brittle failure of the connection could be avoided if the ratio was out of a certain range. A new dumbbell yield line pattern for connections failed by column wall yield failure was proposed and the yield strength design model corresponding to the dumbbell yield line pattern was proposed. The proposed analytical method could predict the yield strength of the TOBs bolted connection accurately.

Experimental study on seismic performance of the connection for ATLS modular house

Modular steel constructions (MSCs) have been widely used for buildings with repetitive units and a lot of research demonstrated that the overall structural performance was highly influenced by the connection between the modules. Due to the special configuration, the connection for assemble-type of light-steel modular house (ALTS modular house) was more complex than ordinary MSCs. In order to study the seismic performance of connection for ATLS modular house, three specimens were designed and tested under different axial load in this paper. The failure mode and seismic performance of the connection were evaluated and discussed in detail based on the test results. In addition, the load-transferring mechanism of the column were explored by strain monitoring. Three failure modes of connection were found. The ultimate bearing capacity, stiffness degradation, and energy dissipation of the connection were significantly influenced by the axial load. Further, a three-dimensional (3D) nonlinear finite element model (FEM) was established by the general-purpose finite element software ABAQUS. The failure mode and hysteretic curves were in good agreement with the test results and the FEM can be adopted for the analysis of the seismic behavior of the connection.

Experimental and Numerical Analysis on Full High Strength Steel Extended Endplate Connections in Fire

Full-scale experimental study and numerical analysis on behaviors and failure mechanisms of full high strength steel extended endplate connections in fire have been carried out and presented in this paper. The experimental behaviors of the connections were compared with the provisions of Eurocode 3. The test results show that the failure modes of the connections in fire are bolt failure with yielding of the flange, as same as those at ambient temperature. The failures of the bolts in fire are ductile while they are brittle at ambient temperature. The rotation capacity of the connections in fire is proved sufficient. What is more, at elevated temperature 550 °C, the plastic moment resistances of Q690 and Q960 full high strength steel endplate connections are only 40% of those at ambient temperature, while their initial rotation stiffness are 66 and 63% respectively. But the rotation capacities of Q690 and Q960 high strength steel endplate connections are 1.38 and 1.74 times of those at ambient temperature. Moreover, it is found that the component method Eurocode 3 proposed based on connections made of mild steels can be used to calculate plastic resistances and to predict failure modes of high strength steel endplate connections in fire, but it is not suitable to predict their stiffness. The suggestions about rotation capacity of connections in Eurocode 3 are found too conservative for high strength steel endplate connections in fire.

Pseudo-ductile failure of adhesively joined GFRP beam-column connections: An experimental and numerical investigation

Glass Fiber Reinforced Polymer (GFRP) I-beam-column adhesively bonded connections are tested under combined bending and shear. The special feature of the novel connection is the wrapping of the seat angles at the connection by a carbon fiber reinforced polymer (CFRP) fabric wrap.The wrap is primarily intended to alter the connection failure mode from brittle to pseudo-ductile, thus providing adequate warning of impending failure. Four moment resisting connection configurations are tested, including the reference configuration without the wrap. It is observed that the connection failure is initiated by the fracture of the adhesive, but the provision of the wrap, together with a steel seat angle, alters the failure mode from brittle to pseudo-ductile. The post-peak load deformation is achieved without a large drop in the resistance of the connection. On other hand, the connection with the wrapping and a GFRP seat angle can also change the failure mode to pseudo-ductile, but it could not be done without a large reduction in the connection resistance after the peak load.

Experimental and Numerical Studies of Failure Modes and Load-Carrying Capacity of Through-Diaphragm Connections

Shear failure in panel zones and plastic hinges in steel beams are the two major failure modes of connections between concrete-filled steel tubular (CFST) columns and steel beams. To investigate the behavior of this type of connection in both modes, two through-diaphragm connections were tested under cyclic and monotonic loadings and the load-carrying capacity, ductility, and strength of degradation of connections were discussed. Using ABAQUS software, we developed nonlinear finite-element models (FEMs) to simulate the load-carrying capacity and failure modes of the connections under monotonic loading. The finite-element (FE) analysis and test results showed reasonable agreement for the through-diaphragm connections, which confirms the accuracy of FEMs in predicting the load-carrying capacity and failure modes of connections. Based on the validated FEM, a parametric study was then conducted to investigate the influence of the thicknesses of the tube and diaphragm on the load-carrying capacity and failure modes of these connections. The results indicate that the strength, stiffness, and load-carrying capacity are influenced less by the thickness of the diaphragm, and more by the thickness of the steel tube. According to the FE analysis results, it can be found that the critical condition between the two failure modes is determined by the shear resistance and bending resistance.

Energy dissipation capacity of an unstiffened extended end-plate connection with a SMA plate

The unstiffened extended end-plate connection exhibits different behavioral characteristics and energy dissipation capacities depending on the thickness of the end-plate and the change in the gauge distance of the high-strength bolts. In particular, the energy dissipation capacity of the unstiffened extended end-plate connection is affected by the failure modes of the connection: the beam failure mode and the connection failure mode. That is, the energy dissipation capacity varies depending on the case, where the failure is caused by the occurrence of plastic hinges acting like fuses in the beam ends, and the failure results from the plastic deformation after the flexural yielding of the end-plate. This study was conducted to design and construct the connection in such a way that it could provide sufficient strength, stiffness, and energy dissipation capacity in response to the fracture of the connection that may occur in case of an emergency, by inducing a position where the plastic hinge fuse occurs in the end-plate of the connection. For the evaluation of the energy dissipation capacity of the connection, a three-dimensional nonlinear finite-element analysis of the unstiffened extended end-plate connection was performed by changing the thickness of the end-plates. The finite-element analysis results showed that the energy dissipation capacity increased when the thickness of each end-plate decreased, and that the residual deformation did not occur when an SMA end-plate was installed instead of the end-plate with the conventional SN steel applied.

Influencing factors analysis of degradation and damage and the effect on steel frame

In order to discuss the influencing factors of damage and degradation and the effect on steel frame subject to strong earthquakes, firstly, a constitutive model was proposed for 3D finite element models to calculate the seismic behaviors of steel frame more accurately. The model was proved correct and applicable due to typical quasi-static tests. Then, based on the verified model, the damage and degradation factors were discussed by parametric analyses, including the panel zone, loading history, loading amplitude, the width to thickness ratio and yield strength. The cumulative damage phenomena of steel frame connections were further studied and the degradation distribution curve was obtained. Finally, the traditional beam element model and proposed shell element model of structure were established by ABAQUS for time history analysis. The effect of damage and degradation on seismic behaviors of steel frames were compared and discussed. The tests and analysis results revealed that: panel zone strength, loading amplitude and width-thickness ratios of plates had significant impact on damage and degradation behaviors and failure modes of connections. Premature weld cracking would lead to earlier damage and degradation under “strong to weak” earthquake, which would seriously affect the overall mechanical properties of the structure. Once local buckling caused damage, the results of the beam element model and accurate shell element model were remarkably different. Beam element model without considering damage and degradation underestimated the structural deformations, which should be paid more attention for design safety.

Macroscopic strength and failure properties of flow-drill screw connections

Force–displacement responses and failure behaviour of connections using flow-drill screws to join aluminium sheets were investigated under various quasi-static loading conditions. This included single connector tests under tensile, shear and combined tensile and shear loadings, using cross test coupons in a new test set-up, and peeling and single lap-joint tests. The strength of the connection increased with the amount of shear loading, while the ductility decreased. No effect of the anisotropy of the sheets on the behaviour in the single connector tests was found. Axial crushing tests of aluminium single-hat sections joined with flow-drill screws were also performed. Two connection failure modes not observed during the single connector test were found in these tests. For comparison, equivalent single connector and component tests were carried out for self-piercing rivet connections. Similar trends with respect to the ductility, maximum force and shape of force–displacement curves were observed for the two connections, but the local failure modes were different.

Experimental Examination of the Structural Performance of Restrained HSS Steel Beams and their End Connections in Fire

This paper describes a series of full-scale tests performed in the fire research facilities of Carleton University, Ottawa, Canada. These tests are part of an experimental programme, whose objective is to investigate the structural performance of axially restrained tubular steel beams at elevated temperatures. The primary focus is to determine the effect of the beam end connections on the structural performance of the steel-frame assembly. Four unprotected steel-frame test assemblies, each composed of a hollow structural section (HSS) steel beam restrained between two HSS columns, were subjected to a standard fire while constantly loaded. The main parameters investigated were the end plate thickness and the degree of beam axial restraint. Two different end plate thicknesses were tested, 12.7 mm and 19.0 mm. The experimental results showed a considerable effect of the end plate thickness on the structural behaviour of the connection and the connected beam. Moreover, the fire tests have revealed different connection failure modes, such as excessive end plate deformations, column buckling, and bolts fracture.

Probabilistic Robustness Assessment of Pre-Northridge Steel Moment Resisting Frames

This paper investigates the robustness of moment-resisting steel frames that are typical of building construction in seismic regions before the 1994 Northridge earthquake against progressive (disproportionate) collapse. Uncertainties in the collapse demands and the resisting capacities of the connections in the frames are modeled probabilistically. The dominant connection failure mode, which involves fracture of the weld connecting the beam and column flanges under scenarios involving sudden column loss, is developed using a J-integral formulation of fracture demand and is characterized probabilistically. The connection behavior model is validated using connection test data from the SAC Project on steel frames conducted following the Northridge earthquake. The robustness of two three-story steel frames designed in the SAC Project is assessed by utilizing (a) the requirements in the new Unified Facilities Criteria (UFC), and (b) a system reliability analysis. This analysis reveals that steel moment frames with connections similar to those found in pre-Northridge building construction may not meet the UFC requirements for general structural integrity following notional column removal.

Performance of the Unified Block Shear Equation for Common Types of Welded Steel Connections

Block shear describes a steel connection failure mode in which a combination of tensile and shear failures along perpendicular planes results in a block of material being displaced from a member. This behavior has been observed to govern the design of many bolted connections and has been well researched, resulting in design equations of various forms. Certain arrangements of welded connections are also susceptible to block shear. This paper reports on the potential application of a "unified"� block shear equation, proposed by Driver et al. (2006) for bolted connections, to various welded connections. Experimental results for welded steel lap plate connections loaded concentrically in tension are examined. The results of these tests are used to describe the connection behavior and to evaluate the performance of several design equations, including the proposed "unified"� equation. The application of the unified equation to welded connections of slotted hollow structural sections (HSS) and to coped beams supported at their ends by a clip angle welded to the beam web.