Blind Bolted Joints Research Articles

Fire and post-fire performance of blind-bolted concrete-filled steel tubular joints with restrained steel beams: Experiment and simulation

Blind-bolted connection is a type of new developed prefabricated beam-column connection, which can be used to connect the concrete filled steel tubular (CFST) columns and the steel beams easily. The static and dynamic performance of CFST column to steel beam joints with blind-bolted connections have been well explored, but limited research has been conducted to investigate the fire and post-fire performance of this type of composite joint. In this paper, a series of reversed T-shaped joint fire tests were conducted to investigate the fire and post-fire performance of blind-bolted CFST joints with axially restrained steel beams. The influence of restrained effect from adjacent members in the entire frame structure on the response of blind-bolted joints in and after fire could be reasonably considered by the reversed T-shaped joint fire test. The joint temperature, failure modes, beam and column displacements and temperature internal force development during the entire loading and fire stage were recorded and discussed. The test results indicated that the blind-bolted connections showed very good working performance in and after fire, and no bolt shank fracture or bolt pull-out failure was observed. Finite element analysis (FEA) models were established to simulate the fire and post-fire performance of blind-bolted CFST T-shaped joints with axially restrained steel beams, and the joint moment versus relative rotation angle relationship curves of the blind-bolted joints during the entire fire and loading process were extracted and discussed based on the FEA models. The results indicated that the joint negative moment generated by the axially restrained beam boundary in the heating and cooling phases could go up to around 1.4 times the joint negative moment at ambient temperature.

Hybrid simulation test and seismic assessment of CFDST moment resisting frame

Concrete filled double skin steel tubular (CFDST) moment resisting frame is an effective structural system owing to the higher strength to weight ratio and better fire performance compared with traditional concrete filled steel tubular (CFST) structures. This paper aims to analyze the seismic response of assembled CFDST moment resisting frame with blind bolted joints by the hybrid simulation test and numerical approaches. A prototype CFDST moment resisting frame was designed and its numerical model was established by Opensees software. After the validation of the numerical model, typical failure modes and dynamic response of the CFDST moment resisting frame observed from the hybrid simulation test were detected and discussed under maximum-considered earthquake (MCE) and 2MCE levels (2 times MCE level), respectively. Detailed behavior of the columns and joints were analyzed for the prototype building. It verified that a large portion of energy was dissipated by the joints under seismic loads. Subsequently, parametric analyses were performed to study the influence of joint stiffness on the global behavior of CFDST moment resisting frames by the endurance time method. The energy dissipated by the columns and joints were investigated in detail, indicating that the energy dissipated by the joints was more than 70% of the total hysteretic energy of the frame under earthquakes. It indicated that decreasing the joint stiffness was beneficial for the joint to dissipate more energy and for protecting the column from being damaged. It also generalized that decreasing the joint stiffness had a positive contribution to the uniform story drift distribution and would not always increase the maximum story drift. The analysis results verified that the CFDST moment resisting frame exhibited excellent seismic behavior and activated the application of CFDST moment resisting in engineering practice.

Further analysis on mechanical behaviors of blind-bolted T-stub connections to CFDST columns

The mechanical behavior of blind-bolted T-stub connections between concrete-filled double steel tubular (CFDST) columns and steel beams was investigated by cyclic loading tests and numerical simulations. Five bolted joints were tested to evaluate the bending moment (M)-rotation (θ) hysteretic behavior, and the numerical results agreed well with experimental data including the failure mode, initial stiffness, and bending resistance. Results proved that T-stubs with different stiffeners deformed in three modes; the internal force-transferring behavior of blind-bolted joints was different from that of the through-bolted joint, especially the stress response of inner tubes; blind-bolted joints hold a similar bending resistance as the through-bolted joint, but the ductility and energy dissipation capacity were improved significantly. The bending resistance of blind-bolted T-stub connections was predicted based on the tensile T-stub model, and the accuracy of the proposed formula was verified in comparison to both test and numerical results since all the calculation errors were within 9.3%. Parametric study showed that installing stiffeners on the T-stub was the most effective way to enhance the bending resistance, the effect of thickening the T-stub flange ranked second, and the growth rate of ultimate bearing capacity slowed down with the bending stiffness increase of the T-stub. Lastly, the optimum strength matching range of the T-stub flange was suggested.

Component based moment-rotation model of composite beam blind bolted to CFDST column joint

This paper aims to explore the mechanical behavior and moment-rotation model of blind bolted joints between concrete-filled double skin steel tubular columns and steel-concrete composite beams. For this type of joint, the inner tube and sandwiched concrete were additionally identified as basic components compared with CFST blind bolted joint. A modified moment-rotation model for this type of connection was developed, of which the compatibility condition and mechanical equilibrium were employed to determine the internal forces of basic components and neutral axis. Following this, load transfer mechanism among the inner tube, sandwiched concrete and outer tube was discussed to assert the action area of the components. Subsequently, assembly processes of basic coefficients in terms of their stiffness and resistances based on the component method by simplifying them as assemblages of springs in series or in parallel. Finally, an experimental investigation on four substructure joints with CFDST columns for validation purposes was carried out to capture the connection details. The predicted results derived from the mechanical models coincided well with the experimental results. It is demonstrated that the proposed mechanical model is capable of evaluating the complete moment-rotation relationships of blind bolted CFDST column composite connections.

Moment-rotation model of endplate blind bolted joints with CFST column

The moment-rotation curves can directly reflect the performance of H-shaped beam to concrete filled steel tube (CFST) column joints, which should be fully considered in structure analysis and design of such joints. However, the current determination of moment-rotation curves is mainly fitting results of experiments or simulations, which results considerable consumption of human and material resources. Hence, this paper proposes a new three-parameter exponential model for this type of joint to forecast the moment-rotation relation curve. Considering possible failure modes, a calculation method of ultimate bending moment for joints is proposed. An analysis model of initial rotational stiffness for joints is established according to component method. Based on the research results of this paper, the ultimate bending moment and initial rotational stiffness can be calculated straight by measurement factors and material properties. The values of the shape parameter for two kinds of the joint are derived by fitting the existing experimental data. Based on the established prediction model of moment-rotation, an accurate calculation method of ultimate bending moment, and analysis model of initial rotational stiffness, the prediction results are in good agreement with experimental results according to the comparison. The established moment-rotation model may be applied to the design of composite frames to predict the behavior of the joint with endplate and blind bolts simply and accurately. Moreover, it can save the workload of experiments and simulations.

Seismic performance of blind-bolted joints for square steel tube columns under bending-shear

In this study, a plug-in plate blind-bolted joint and double-splint blind-bolted joint are proposed for square steel tube columns. The seismic performance of joints under bending-shear combination was studied via experiments and finite element simulations. Four test specimens of plug-in plate blind-bolted joint and double-splint blind-bolted joint were studied by varying the numbers of bolts used in the connection. Additionally, eleven joints with different thicknesses of the plug-in plate, the double-splint, and the column wall were compared via finite element simulation. The strength of the test specimens increased till the loading was stopped at 0.05 rad. This suggests that the specimens had good ductility and rotation ability. The effect of the number of bolts, thickness of the plug-in plate and double-splint on the rotational stiffness, slip resistance, ductility performance, energy dissipation capacity, ultimate load-bearing capacity, and yielding mechanism of the joint were analyzed. Additionally, simplified equations were derived for slip resistance and yield strength of the joints. The values obtained using these equations agreed well with that of the experiment and finite element analysis. Furthermore, four frames with the plug-in plate blind-bolted joint and double-splint blind-bolted joint for square steel tube columns were subjected to cyclic loads. Their seismic performance was found to be better than that of the frame without the column joint. The proposed blind-bolted joints can be used for splicing a column at mid-height.

Seismic experiment on blind-bolted joint in concrete-filled double steel tubular structure

In this study, blind-bolted joints were designed for use between steel beams and concrete-filled double steel tubular (CFDST) columns to utilize the structural advantages offered by double steel tubes. Six joint specimens were tested under a constant axial load and lateral cyclic load for a CFDST column. The seismic behaviors of these blind-bolted joints were estimated in terms of the hysteretic curves, ductility, and energy dissipation. The effects of a T-plate section type and steel beam-type on the semi-rigid joints were studied. The test results showed that the failure of the joints began with the yielding of the T-plates, and that the final failure mode was plastic deformation at the steel beam ends. The obtained hysteretic curves were complete, and the energy dissipation ability of the bolted joint was strong. The bearing capacity and energy dissipation of ribbed joints were higher than those of unribbed joints. Based on a steel volume comparison, the installation of stiffening ribs proved to be considerably more effective than the thickening of the T-plate flanges. The strain response of the inner tube in each CFDST column was also estimated. It was concluded that the blind-bolted joints exhibit excellent deformation capacities and structural internal force redistributions. The results of this experimental research could be helpful for the application of blind-bolted joints in fabricated CFDST structures.

Experimental and Analytical Behavior of Square CFDST Column Blind Bolted to Steel Beam Connections

In recent years, steel or composite beam-column connections adopting blind fasteners have drawn increasing praise due to the rapid development of assembled steel structures. However, limited researches have paid attention to the experimental and analytical behavior of concrete filled double-skin steel tube (CFDST) column blind bolted joints. For investigating the structural performance and seismic behavior of this type of connection, cyclic tests on blind bolted joints to square CFDST columns were carried out to explore the effects of column hollow ratio and end plate type. Finite element analytical modelling of the semi-rigid joint was performed considering complex contact interactions and material models. Good agreement between the test and analytical results was observed in terms of the failure modes and the hysteretic behavior. Substantial parametric analyses were conducted on typical CFDST column connections to observe the influence of parameters including strength of steel tube, column hollow ratio and bolt pretension force. Furthermore, certain constructional measures commonly employed in engineering practice were also discussed. It was concluded that the CFDST column blind bolted to the steel beam joint has favorable seismic behavior and is feasible for application in high-intensity earthquake regions.

Seismic evaluation and calculation models of CFDST column blind bolted to composite beam joints with partial shear interaction

With the purpose of investigating the seismic performance and failure mechanism of the concrete filled double skin steel tubular (CFDST) column blind bolted to composite beam joint with partial shear interaction, an experimental campaign was carried out to assert the effects of end plate type and column hollow ratio. Each specimen was tested subjected to cyclic lateral loads. Typical failure modes of this novel joint in conjunction with the application of partial shear interaction were examined. Based on the experimental results, the crack patterns of steel bar truss deck (SBTD) concrete slabs and hysteretic performance were also estimated. Shift of the beam neutral axis was evaluated by the analyses of the strain distributions. Furthermore, calculation models of the blind bolted composite connections to circular CFDST columns with partial shear interaction were developed based on the component method, where the sagging and hogging moments were both incorporated. For partial shear joints, the shear connector was identified as an important component to estimate its influence on the initial stiffness and moment resistance. In addition, the lower bound of the degree of shear connection was proposed to avoid the shear connector fracture under sagging moment. The predicted results from the proposed component-based models were validated by the experimental data, which demonstrated that the derived calculation models were capable of evaluating the initial stiffness and moment resistances of the CFDST column blind bolted joints to composite beams with partial shear interaction. The experimental and analytical results provide a reference for the analysis and design of blind bolted composite joint to CFDST column with partial shear interaction in engineering practice.

The Effect of Fastener Type on the Connection Performance of Bolted Joints in Composite Laminates

An experimental investigation was conducted to determine the effect of fastener type on the connection performance of double lap-type single bolted composite joints. The joints with blind bolts and high lock bolts were tested separately by static tests and dynamic tests. ASTM D 5961 was adopted by static tests, and tension-compression reversed force/stress ratio, R=-1, was selected to evaluate the fatigue tests. The appropriate levels of fatigue stress were determined by the ultimate bearing strength of the fastener structure obtained from the static tests. The bearing stress and the fatigue life (S-N) date of different fastener types of specimen were presented and the relationship between fastener types and fatigue life were obtained. The experimental results showed that the connection performance of the blind bolted joint was better than that of the high-locking bolted joint. The ultimate bearing strength of the blind bolted joints was 1.9% higher than that of the high lock bolted joints, and the fatigue life of the blind bolted joints was 1-2 orders of magnitude higher than that of the high-locking bolted joint under the same cyclic stress.

An Experimental Investigation on Dynamic Performance of Interference-fit Composite Joints with Blind Bolt and High Lock Bolt

The experimental investigation were conducted in order to study the dynamic strength of the mechanically fastened composite joints, involving interference-fit joints with blind bolt and sliding-fit joints with high lock bolt. The joint type of the specimens researched was single-bolt, double-lap, which was a standard test configuration in ASTM for composite joints. Experimental results showed that the fatigue performance of the blind bolted joint was better than that of the high-locking bolted joint. The fatigue life of the blind bolted joints was 10-100 times higher than that of the high-locking bolted joint under the same cyclic stress, and the limit fatigue strength of the blind bolted joints was over 50MPa higher than hat of the high-locking bolted joints.

Fire performance of blind bolted composite beam to column joints

Blind bolts can be used to connect steel beams to concrete filled steel tubular (CFST) columns, and the obtained composite joints have relatively high initial stiffness, flexural resistance, and ductility at ambient temperature. However, very limited research has been conducted on the fire performance of the blind bolted composite joints. In this paper, eight full-scale blind bolted joints were tested to study their fire performance. The test parameters include: (a) whether fire protection is applied to the steel beam or not; (b) beam load ratio (0.25 and 0.5); (c) type of steel used for the column (stainless or carbon steel); and (d) with or without binding bars in the connection region. The test results indicated that the joint failure was mainly dominated by flexural failure of the steel beam near the panel zone. In general, the blind bolted joints demonstrated very good performance in fire, and no bolt shank fracture or bolt pull-out failure was observed in any joint test. The beam protection or reduction of the beam load significantly increased the fire resistance of the joint, whereas the presence of the binding bars or the type of the steel tube had only moderate influence on the fire resistance.

Seismic performance assessment of blind bolted steel-concrete composite joints based on pseudo-dynamic testing

This paper aims to investigate seismic behavior and dynamic responses of semi-rigid composite joints composed of steel-concrete composite beams and concrete-filled thin-walled steel tubular (CFTST) columns. A range of pseudo-dynamic tests (PDTs) was performed on two full-scale blind bolted end-plate joint specimens, including one flush and one extended end-plate typed joint. The input ground motion adopted for the PDTs was Ispara seismic acceleration record and scaled to represent various seismic hazard levels. Using Ispara earthquake record with different peak ground accelerations (PGAs), a lot of useful data about hysteresis behavior, stiffness degradation and energy dissipation capacity was obtained. The data was also estimated in detail to characterize the seismic performance of this kind of composite joints. Dynamic responses of beam-to-column joint including displacement and acceleration responses, and dynamic magnification factor were discussed. The experimental results indicated that the structural responses of the test joints under seismic actions coincided with the desired performances analyzed for varying damage levels. The study affirms that the blind bolted end-plate composite joints to CFTST columns possess good energy dissipation seismic performance, so they can provide sufficient ductility and adequate strength to satisfy the seismic design requirement.

Experimental and numerical analysis of blind bolted moment joints to CFTST columns

Experiments and numerical analysis were conducted to investigate the mechanical behavior of the blind bolted end plate joints to concrete-filled thin-walled steel tubular (CFTST) columns. Four blind bolted end plate joints to CFTST columns subjected to the monotonic loading were tested. Then, finite element analysis (FEA) modeling of the tested specimens was developed, and the results obtained from FEA modeling were verified against those from the test results. Parametric studies were conducted to investigate the influence of end plate thickness, axial load level, steel ratio and slenderness ratio etc. on moment-rotation curves of composite joints. Some methods of effective provisions were proposed and discussed in order to enhance the connection behavior. The test and numerical analysis results indicated that the typed joints to CFTST columns behaved in a semi-rigid and partial strength manner. The proposed innovative blind bolted joint using reliable and effective solutions could be applied in the mid- and low-rise buildings.

Seismic behavior of blind bolted end plate composite joints to CFTST columns

The seismic behavior and failure mechanism of a novel type of composite joints are presented in this paper. These composite joints are composed of composite steel-concrete beams and square concrete-filled thin-walled steel tubular (CFTST) columns. The steel beams are connected to the CFTST columns using end plates with blind bolts, while the cast-in-situ RC slabs are attached to steel beams with shear connectors. Some quasi-static tests were performed on flush and extended end plate joints and horizontal cyclic displacements at the column ends were experienced during the test. A detailed account of the results and observations from the cyclic tests are investigated, and the main behavioral aspects are discussed. The seismic performance of the blind bolted composite joint to CFTST column is estimated in terms of the hysteretic behavior, strength and stiffness degradation, ductility, and energy dissipation capacity, etc. The results of this study show that the novel composite joints exhibit adequate ductility and energy dissipation, whilst they behave in a semi-rigid manner according to the EC3 specification.

Cyclic behaviour of novel blind bolted joints with different stiffening elements

Because of the difficulty of accessing the interior of structural hollow sections, emerging technology using blind bolts has been recently developed for fabricating connections to concrete-filled steel tubular (CFST) columns. However, two issues limit the structural benefits of this joint system including the limited transfer of hogging moment and high susceptibility of the steel tube to local failure. Therefore, the authors proposed four methods to enhance the CFST column’s stiffness in the connection region, namely, using inner binding bars, welding two internal rings, externally welding two C-shaped channels, and internally embedding a short segment of I-section in the steel tube. A total of 6 joints were tested under cyclic loading accordingly. The experimental results are analysed in this paper to evaluate the efficiency of different stiffening methods. It indicates that the C-shaped channels and embedded I-section are very effective in enhancing the performance of the joint, and the joint’s strength and deformation capacity can be significantly improved with large bending deformation developed in the end plate. In contrast, welding binding bars or internal rings has only moderate influence on the joint performance.

Comparative Study on Static and Fatigue Performances of Pultruded GFRP Joints Using Ordinary and Blind Bolts

AbstractBolted connections are often used in pultruded glass fiber reinforced polymer (GFRP) structures. Blind bolts, which require installation from one side only, become convenient when access is limited to tighten the ordinary bolts, especially for tubular GFRP sections. This paper presents the results of a comparative study on pultruded GFRP double-lap joints using ordinary bolts and blind bolts. Static experiments were conducted on pultruded GFRP double-lap joints with two columns of bolts, whereas the number of rows varied by one, two, and three. The static behaviors of ordinary bolted and blind bolted joints were compared in terms of load-displacement response, failure modes, and failure load. Then, constant amplitude fatigue tests were carried out on the double-lap joints with two bolts in a row. The maximum fatigue load varied from 30 to 80% of the static failure load of the corresponding joint. The fatigue life of each specimen was recorded and S-N curve was obtained. It was found that the stati...

Experimental Study of Blind Bolted Joints to Concrete-Filled Thin-Walled Steel Tubular Columns under Cyclic Loading

This paper discusses results of experiments on blind bolted end plate joints to concrete-filled thin-walled steel tubular (CFTST) columns. Four exterior joints to CFTST columns subjected to cyclic loadings. A feature of this novel joint is the use of the blind bolts and extensions to these bolts into the concrete-filled square steel tubular column. Failure modes, moment-rotation hysteretic curves and energy consumption of the connections were analyzed. Further, the connection rigidity and ductility were also elevated by present specifications. The test results showed that the end plate type and the steel tube thickness affect the seismic behaviour of the typed blind bolted end plate joints. The proposed joint has reasonable strength, stiffness and ductility by taking reasonable end plate type, steel tube thickness and blind bolt anchorage; its ultimate connection rotation satisfies the ductility design requirements, and could be reliably and safety used in low-layer or multi-layer composite frames.