Tensile behaviour of double headed anchored blind bolt in concrete filled square hollow section under cyclic loading

doi:10.1016/j.conbuildmat.2018.12.089

Construction and Building Materials

Volume 200, 10 March 2019, Pages 146-158

https://doi.org/10.1016/j.conbuildmat.2018.12.089 Get rights and content

Highlights

•
The addition of extra head to the Headed Anchored Blind Bolts (HABBs) improved the behaviour of the blind bolt.
•
Cyclic deterioration of stiffness of Double Headed Anchored Blind Bolts (DHABB) under cyclic load was not significant.
•
The tensile behaviour of DHABBs in concrete with fibre reinforced was not consistent from one test to other.

Abstract

This paper presents the tensile behaviour of individual Double Headed Anchored Blind Bolts (DHABBs) which are anchored within Concrete Filled Square Hollow Section (CFSHS) tubes. The DHABB consists of a conventional Headed Anchored Blind Bolt (HABB) with one additional middle head, between the existing end head in the embedded region and head next to the tube wall. A series of experiments were conducted on the pull-out of single DHABBs under monotonic and cyclic loading using different tube sizes, bolt sizes and concrete types. Detailed results from the experimental work are presented in this paper. A comprehensive three dimensional finite element model was developed and the results were compared with full scale pull-out test results. A good agreement was obtained between the FE and experimental results.

Introduction

Concrete filled steel tubes (CFST) are popular as the structural columns in many countries around the world. They have a large load bearing capacity, favourable ductility and look aesthetically beautiful. However, in many countries, including Australia, CFSTs are not very popular because of the perceived difficulties in connecting beams to the columns. In such places, welding (which is the most common method of achieving the moment resisting connection between beam and CFST) is not preferred at site due to cost and quality issues. Due to the lack of access to the inner side of the column, it is not possible to install ordinary structural bolts.

In the last few decades, research has been conducted to investigate alternative solutions to welded connections, including that on blind bolts, i.e. ones that can be installed from the outside of the tube. In this research, modified Ajax Oneside blind bolts have been used. The Ajax Oneside was originally developed by Ajax Engineered Fasteners [1] and later modified by Goldsworthy & Gardner [2], Yao et al. [3] and Pokharel et al. [4], and the modified bolt is called a double headed anchored blind bolt (DHABB). The modification involves an extension of the bolt beyond the head of the Ajax Oneside that bears on the inside wall of the tube; anchorage into the infill concrete is achieved by providing two heads along this extension (one at the end of the extension and another between the end head and the head next to the tube wall). The extension was embedded into the concrete to increase the stiffness of the connection and also to limit the local deformation of the tube wall.

The ultimate aim of the research is to develop a moment resisting connection for low to moderate seismic regions using DHABBs. The concrete filled square hollow section (CFSHS) has been selected as the column rather than a concrete-filled circular hollow section (CFCHS) as it is relatively easier to connect to the beam because of its simpler geometry, and it has stiffness that is comparable with that of the CFCHSs.

The tensile behaviour of headed anchored blind bolts (HABB) has been investigated recently by Agheshlui et al. [5] and Oktavianus et al. [6] for single blind bolts and by Agheshlui et al. [7] and Pokharel et al. [8] for group behaviour. In those researches, monotonic load regimes were used in investigating the behaviour of the blind bolts. The tensile behaviour of blind bolts under cyclic loading has not been investigated so far. The tensile behaviour of cogged anchored blind bolts has been investigated in references [3], [9]. A similar concept in which a blind bolt has been extended and anchored into the infill concrete has been used by some other researchers using Hollo-bolts [10].

During pull-out of anchored blind bolts, the load from the bolt is transferred to the concrete in two ways; one is through the tangential/frictional force between the threaded rod and surrounding concrete, i.e. bond, and the other is from bearing of the embedded head onto the concrete. The frictional component was found to be very small compared with the bearing component [11]. When the load is first applied, the tensile load from the blind bolt will be transferred to the surrounding concrete due to the bond between the concrete and the blind bolt. The bond will be lost at a low load and then the bearing action will be the main load transfer mechanism. If the applied load is sufficiently high to cause failure, the failure mechanism is expected to be due to either steel failure (of the blind bolt itself) or concrete failure. The concrete related failure is very complex and is affected by several factors. The concrete related failure modes have been studied by several researchers [12], [13], [14]. However, in this study, the load on the blind bolts is limited to 60% of their nominal capacities and thus the concrete related failure is less likely.

This paper presents the tensile behaviour of the modified blind bolt (DHABB) under cyclic loading. The DHABBs are anchored within the concrete filled square hollow sections (CFSHS). Firstly, details are given about the experimental program in which pull-out tests were conducted; the results of these tests are also presented. Then the finite element (FE) analysis of those pull-out tests is presented. Finally, the FE results are compared with the experimental results, and effectiveness of the modification of HABB to DHABB in improving the stiffness and strength of the connection is assessed. The cyclic deterioration caused by the cyclic loading is also investigated in this study.

Section snippets

Experimental program

A series of pull-out tests was conducted to investigate the behaviour of double headed anchored blind bolts (DHABBs) in concrete filled square hollow section (CFSHS) columns. The modification involving transforming headed anchored blind bolts (HABBs) to double headed anchored blind bolts (DHABBs) is presented in reference [4]. Fig. 1 shows the original HABB and the modified blind bolt (DHABB) with one additional head between the existing heads in the embedded region. This head will be called

Test results

Fig. 9 shows the pull-out load vs displacement curve for different specimens. The displacement in each figure is the actual pull-out displacement of DHABB at the outer face of the steel tube. The LDTs were removed when the load was close to the failure load to prevent damage to the LDTs, and hence the load vs. displacement curve is cut off prior to the failure condition being reached.

Fig. 10 shows a comparison of the backbone and full cyclic curves of force vs. pull-out displacement for the

Discussion

The summary of test results is presented in Table 2 which shows the ultimate strength, secant stiffness at 60% of the nominal capacity of bolts and residual displacement at the end of the 5th cycle at 60% of nominal capacity. Each of those values are the average of two tests. The test has different tube sections (SHS 400 × 400 × 10 and SHS 400 × 400 × 12.5), bolt sizes (M20 and M24), concrete (N50 and S50) and loading (monotonic and cyclic).

FE models

A FE package ABAQUS/Explicit [21] was used for modelling the pull-out tests. Taking advantage of symmetric conditions along the transverse direction of the concrete filled hollow section (CFSHS), a half of each test specimen was modelled. The FE model used to simulate the pull-out of M24 DHABBs from a CFSHS 400 × 400 × 10 (C-24-10) is shown in Fig. 21.

Eight-noded brick elements with reduced integration (C3D8R) were used to model all the components. Surface to surface contact was used between

Conclusions

The experimental and numerical behaviour of double headed anchored blind bolts was investigated in this paper. From the experimental result, it was verified that the addition of a middle head to the HABB improved the behaviour of the blind bolt. The behaviour of the DHABB was found to be dependent on the bolt sizes and SHS section sizes. The larger bolt was found to have a higher strength and stiffness as expected.

The deterioration of stiffness in a DHABB under cyclic loads was very small up to

Conflict of interest

None.

Acknowledgement

This study was funded by Australian Research Council (ARC) and collaborating organisations Orrcon Steel and AJAX Engineered Fasteners through Linkage grant LP110200511.

References (26)

W. Tizani et al.
Rotational stiffness of a blind-bolted connection to concrete-filled tubes using modified hollo-bolt
J. Constr. Steel Res.
(2013)
J. Ožbolt et al.
3d fe analysis of anchor bolts with large embedment depths
Eng. Fract. Mech.
(2007)
L. Contrafatto et al.
Behaviour of post-installed adhesive anchors in natural stone
Constr. Build. Mater.
(2014)
J. Cairns et al.
Influence of corrosion on the friction characteristics of the steel/concrete interface
Constr. Build. Mater.
(2007)
A. Hillerborg et al.
Analysis of crack formation and crack growth in concrete by means of fracture mechanics and finite elements
Cem. Concr. Res.
(1976)
Ajax Engineered Fasteners, Ajax fasteners, Ajax...
H. Goldsworthy et al.
Feasibility study for blind-bolted connections to concrete-filled circular steel tubular columns
Struct. Eng. Mech.
(2006)
H. Yao et al.
Experimental and numerical investigation of the tensile behavior of blind-bolted t-stub connections to concrete-filled circular columns
J. Struct. Eng.
(2008)
T. Pokharel, H. Goldsworthy, E. Gad, Improved performance of moment resisting connections to concrete filled square...
H. Agheshlui et al.
Tensile behaviour of anchored blind bolts in concrete filled square hollow sections
Mater. Struct.
(2016)

Y. Oktavianus et al.

Pull-out behaviour of blind bolts from concrete-filled tubes

Proc. Inst. Civil Eng. Struct. Build.

(2015)

H. Agheshlui et al.

Tensile behavior of groups of anchored blind bolts within concrete-filled steel square hollow sections

J. Struct. Eng.

(2015)

T. Pokharel et al.

Numerical and experimental behaviour of moment resisting connections using blind bolts within cfshs columns

Cited by (15)

Experimental and numerical investigations of tensile behavior of slip-critical blind bolts anchored in concrete-filled steel tubes
2023, Structures
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.
Static behavior of TOBs bolted endplate connection to strengthened HSST with fixed thread length
2023, Structures
Five thread-anchored one-side bolts connected endplate connections to Hollow Square Steel Tube (TOBEC-HSSTs) with various strengthening measures were tested to investigate the structural performance under monotonic loads. The thread anchored length was 1.2 times the bolt diameter for all specimens. The connection behaviour were influenced by the endplate thicknesses and the strengthening measures (i.e. the internal polygonal tube, the internal polygonal tube with infilled concrete, and the cross-H section stiffener with infilled concrete). The failure patterns, moment-rotation curves, and strain response of joints were obtained through tests. It was found that (1) 1.2 times the bolt diameter was taken as the safe thread assembled length, which can avoid the premature failure of hole threads not before the fracture of other components under monotonic loads. (2) The presence of the infilled concrete can improve the rigidity and strength of the connection by 84% and 23%, respectively, compared to the reference joint without the infilled concrete, and the thickness of the column wall can be reduced when the concrete was infilled into hollow steel tube. (3) For the connections with thin endplates, the cross-H section stiffener exhibited 8.8% and 3.5% higher preliminary stiffness and yield bending moment than the inner polygonal tube, but the cross-H section stiffener had 14.3% lower rotation capacity. (4) Thickening endplates can change the failure modes of the connections to beam plastic hinge formation, enhance the preliminary stiffness and yield bending moment of joints by 2.4% ∼11%, but decrease the rotation capacity of joints by 54% compared to thin endplates. Based on experimental results, the calculation methods of the bending moment bearing capacity for TOBEC-HSSTs considering the strengthening effect of internal stiffeners and infilled concrete under different failure patterns were proposed with errors no greater than 15%.
Review on blind bolted connections to concrete-filled steel tubes
2023, Thin-Walled Structures
Citation Excerpt :
An optimal embedment length was also suggested in the study to achieve the highest stiffness. Cyclic performance of the double-headed Ajax bolt connected to square CFSTs was studied in Pokharel et al. [40] by pullout test similar as Oktavianus et al. [20] (Fig. 3(a)). The steel tube size was 400 × 12.5 mm and 400 × 10 mm, and the bolt was located at the 1/4 location of the tube face wall.
Development of blind bolting systems offers an alternative solution of jointing steel beams to concrete-filled steel tubular (CFST) columns that only allow one-side access. This paper presents a critical review on recent studies about the blind bolted connections to CFSTs representing the tension zone in a beam-to-column joint. Various types of blind bolts have been proposed to improve their tensile behavior in CFSTs by implementing innovative interlocking mechanisms to tube wall and anchoring techniques in concrete. Experimental and finite element (FE) studies were first reviewed in this paper. Tensile behavior of a single bolt or a group of bolts in CFSTs was investigated by one-side or two-side pullout test. Its performance depended on a wide range of parameters, such as bolt type, bolt size, bolt grade, bolt layout, tube size, tube yield strength, concrete strength and embedment length. In FE simulations, modeling of concrete using concrete damage plasticity model was reviewed in detail to provide insights for an accurate FE analysis. Theoretical models for the tensile behavior of blind bolted connections to CFSTs were then reviewed. Strength and stiffness of a connection are mainly contributed by the tube face wall bearing effect, the anchorage in concrete and the elongation of bolts. Finally, potential research directions for future studies were suggested for blind bolted connections. In general, this jointing technique has a broad prospect to achieve a semi-rigid or even a rigid connection in beam-to-CFST joints.
Experimental study on cyclic behavior of thread-fixed one-side bolts bolted endplate connection to strengthened concrete filled square steel tube with fixed thread length
2022, Journal of Building Engineering
This paper presented the experimental results of the Endplate Connection to Concrete Filled square Steel Tube (ECCFST) with fixed thread length via Thread-fixed One-side Bolts (TOBs) under cyclic loading. Two stiffening strategies, namely the internal polygonal tube stiffener and the cross-H section stiffener, with two stiffener flange thicknesses (18 mm and 14 mm) corresponding to two column wall thicknesses (6 mm and 10 mm), respectively, were proposed to strengthen the panel zone of the connections. Failure modes occurring for the connections were mainly affected by the weakest component of the joint region. Besides, the moment-rotation hysteretic curves and seismic performance of the joints were compared and analyzed. For all cases with fixed thread anchored length, the TOBs performed well and no thread failure occurred under the repeated reversal loading. Test results revealed that the mechanical performance of the joints can be ameliorated by adopting the strengthening components especially the cross-H section stiffener, which effectively limited the tube wall deformation from transferring the force to the opposite tube wall through the web of the stiffener. The rotation capacity and ductility of ECCFSTs were satisfactory and can meet the ductility limitation with regard to FEMA-350, demonstrating a potential for ECCFSTs in practical application.
Seismic response on T-head square-neck one-side bolted endplate connection of beam to square tubular column
2021, Engineering Structures
Totally four T-head square-neck one-side bolted connections (TSOBCs) for H-beam to hollow section steel column (HSSC) and a standard double-sides bolted connection (SDBC) for comparison were tested under cyclic load to evaluate the seismic performance of TSOBC. Two arrangement patterns of the slotted bolt holes and two strengthening measures for the connections were studied in the tests, especially the comparison between the TSOBCs and the SDBC. The test results show that the failure mode of the TSOBCs is the same as that of the SDBC, which is endplate fracture. The TSOBC with Type-V bolt holes has higher rigidity, bending moment capacity, and energy dissipation capacity than the TSOBC with Type-H bolt holes. Overall, the TSOBCs have no less than 85% of the bending moment capacity and more than 130% of the ductility coefficient, and 145% of the energy dissipation capacity of the SDBC in whole cycle life, which indicates that TSOBC can replace SDBC under certain conditions. Moreover, the strengthening measures of endplate stiffener and concrete filled in the HSSC can significantly improve the yield bending moment of TSOBC by 13.2% and 50.8%, respectively, but the latter will weaken the ductility coefficient of the joint by 35.2%. Test results on the bending moment capacity and failure mode of TSOBC under static and cyclic loads agreed well with calculated results by currently available computational models.
Cyclic behavior of T-stub connection to hollow section steel column using TSOBs
2021, Journal of Constructional Steel Research
Citation Excerpt :
Hence, the method of field welding to connect the Hollow Section Steel Column (HSSC) and the open section beam is adopted in many constructions. Field welding is susceptible to the weather and can introduce residual stresses into structures [4]. To overcome the difficulty of connecting the HSSC to the open section beam, the one-side bolts capable of connecting the HSSC members are proposed constantly.
The One-side bolts are widely used in the connection of the closed section members in the prefabricated buildings. As a novel type of one-side bolt, T-head Square-neck One-side Bolt has the advantages of the simple structure, the convenient installation, and no need for special installation tools. In this paper, the sub-model for the tension region of the T-stub bolted beam-column connection was selected as the research object, and the cyclic test was conducted on four T-head Square-neck One-side Bolted Connections (TSOBCs) for T-stub to Hollow Section Steel Column (HSSC) and two Traditional High-strength Bolted Connections (THBCs) for comparison. The results of the test including the failure modes, the applied force-displacement hysteretic curves, the applied force-displacement envelope curves, the deformation capacity and ductility, the strength degradation, the stiffness degradation, the energy dissipation, and the strain evolution are discussed and analyzed in this paper. The experimental results denote that: (1) There are two failure modes in the test, mode i, HSSC wall yielding and mode ii, T-stub flange yielding; (2) The initial stiffness and peak bearing capacity of the TSOBCs decreased by 2.5% ~ 35.6% and 21.7% ~ 39.4%, respectively, compared with those of the THBCs; (3) When the failure mode ii occurred, the ductility and the equivalent damping coefficient of the TSOBC with vertical mounting holes are 42.5% and 5.4% higher than those of the THBC, respectively. Besides, the plastic deformation, rigid displacement, and bolt offset in the TSOBCs are analyzed using finite element models.

View all citing articles on Scopus

View full text

Tensile behaviour of double headed anchored blind bolt in concrete filled square hollow section under cyclic loading

Highlights

Abstract

Introduction

Section snippets

Experimental program

Test results

Discussion

FE models

Conclusions

Conflict of interest

Acknowledgement

J. Constr. Steel Res.

Eng. Fract. Mech.

Constr. Build. Mater.

Constr. Build. Mater.

Cem. Concr. Res.

Feasibility study for blind-bolted connections to concrete-filled circular steel tubular columns

Struct. Eng. Mech.

Experimental and numerical investigation of the tensile behavior of blind-bolted t-stub connections to concrete-filled circular columns

J. Struct. Eng.

Tensile behaviour of anchored blind bolts in concrete filled square hollow sections

Mater. Struct.

Pull-out behaviour of blind bolts from concrete-filled tubes

Proc. Inst. Civil Eng. Struct. Build.

Tensile behavior of groups of anchored blind bolts within concrete-filled steel square hollow sections

J. Struct. Eng.

Numerical and experimental behaviour of moment resisting connections using blind bolts within cfshs columns