Block Shear Failure Research Articles

Behaviour and design of duplex stainless steel bolted connections failing in block shear

Duplex stainless steel (DSS) is an emerging construction material for structural engineering, which is featured with high mechanical strength and superior corrosion resistance. Compared with considerable research on DSS structural members, available research is relatively limited for structural joints/connections between these members. In line with this concern, this paper presents a comprehensive experimental and numerical study of duplex stainless steel bolted connections (DSSBCs), focusing on the behaviour and design related to block shear failure. Eleven specimens are tested to investigate the effect of different bolt arrangements on the block shear behaviour. Furthermore, a detailed numerical study was performed as a supplement to the experimental tests, where the anisotropic mechanical properties of DSS are considered in the finite element modelling. Based on the test and analysis results, it is found that the block shear failure mode of DSSBCs resembles that of carbon steel bolted connections, which can be characterised as necking of the tensile section and yielding of the shear sections. Using the experimental and numerical data obtained in this and previous studies, the applicability of various block shear design methods to stainless steel bolted connections is assessed. An updated design method is proposed for predicting the block shear capacity of duplex and austenitic stainless steel bolted connections. A proper partial safety factor/resistance factor is suggested for the proposed method based on the results of reliability analyses.

Block shear failure of austenitic stainless steel bolted connections

Austenitic stainless steel possesses very high ductility and ultimate-to-yield strength ratio, which could possibly affect the block shear failure mechanism and the corresponding ultimate capacity of bolted connections made of this material. In response to this concern, a comprehensive experimental and numerical study on the block shear behaviour of austenitic stainless steel bolted connections (ASSBCs) is conducted and reported in this paper. Based on the results of 15 experimental tests, it is found that the governing block shear mechanism of ASSBCs (for 14 out of the 15 tests) at the ultimate load corresponds to cracking of the shear sections prior to fracture of the tensile sections. This differs significantly from the conventionally accepted block shear mechanism of mild steel bolted connections, which is net section fracture of the tension area and yielding of the shear area. This observation was further confirmed by a numerical study based on validated finite element models, where three block shear mechanisms were identified for ASSBCs. A thorough parametric study was then carried out to clarify the effects of key design parameters on the block shear behaviour of ASSBCs. Finally, the experimental and numerical results are used to evaluate the applicability of existing design equations to predicting the block shear capacity of ASSBCs. An improved block shear equation is subsequently proposed based on the available data.

Block shear strength of high strength steel staggered bolted connections

AbstractThis paper presents an experimental and numerical study of block shear strength of staggered bolted connections made of high strength steel (HSS). The study aims to examine the effect of low ductility and low tensile‐to‐yield strength ratio of HSS material on the behaviour and block shear strength of staggered bolted connections. Two Q690 HSS staggered bolted connections were tested and failed in block shear failure, which was characterised by tension fracture of the staggered net tension plane and significant shear deformation along the shear plane. The test observations were further interpreted by finite element (FE) analysis. The test results and FE analysis indicate that the block shear failure mechanism of staggered bolted connections is the fracture of the staggered net tension plane combined with the yielding of the effective shear plane. Finally, the design methods in various design codes for evaluating the block shear strength of bolted connections were assessed and the results showed that the existing design methods provided inconsistent predictions of the block shear strength of HSS staggered bolted connections. More experimental and numerical works are currently in progress to further understand the block shear strength of HSS staggered bolted connections.

Experimental study on wire and arc additively manufactured steel double-shear bolted connections

Wire and arc additive manufacturing (WAAM) has emerged as a highly promising technique for manufacturing large-scale steel structural elements. However, the distinct mechanical properties of WAAM steel could potentially lead to different performance of WAAM steel bolted connections compared to the traditional steel bolted connections. This study aims to investigate the material properties of WAAM steel and the structural behaviours of WAAM steel bolted connections, focusing on the effects of print layer orientation and connection plate geometrical dimensions. A total number of 24 WAAM steel coupon specimens with three different print layer orientations and 36 WAAM double-shear bolted connections with two print layer orientations and different geometric dimensions were designed, fabricated and tested under monotonic tension. These specimens were measured using a 3D laser scanner and Digital Image Correlation (DIC) was adopted to measure the structural response during testing. The impact of print layer orientations on WAAM material properties and the effects of WAAM material properties on bolted connections were analysed and discussed. The current design codes for traditional steel bolted connections were evaluated against the test results of WAAM steel bolted connections. The study found that the print layer orientations of WAAM steel plates initiated an anisotropic material property of the coupon specimens, demonstrated by the differences in ultimate tensile strength and strain of specimens with different print layer orientations. Five failure modes, including net section tension, shear-out, bearing, end-splitting, and block shear failure were observed for the bolted connections. The material anisotropy further affects the performance of the bolted connections, though in the same dimensions, 28% of the specimens presented different failure modes due to the different print layer orientations. The effectiveness of current steel design standards was compromised by inaccurate predictions of failure modes due to the distinct end-splitting failure mode and the effects of material anisotropy, though the predictions of the ultimate capacities of the WAAM lap shear specimens were relatively accurate.

Comparison of Self-Tapping Screws and Bamboo Nails in Reinforcing the Zuo-Dou Connections in Traditional Oriental Timber Frames of Asia

This paper is focused on the retrofitting techniques of Zuo-Dou connections in Dieh-Dou timber frames in Far East Asia. The target is to develop appropriate techniques for the reinforcement and maintenance of the wooden cultural heritage. A series of full-scale tests are intended for the evaluation of the rotational and shear characteristics of the various retrofitting techniques for the Zuo-Dou joints. These retrofitting techniques are conceived by this study based on the principles of the conservation of cultural heritage. The reversible materials, invisible layouts, and structurally efficient schemes are taken into account to figure out the reinforcement strategies. Regarding the conservation targets, this study applies the self-tapping screw (STS) and the bamboo nail for reinforcement. Corresponding to the loading circumstances, moment- and shear-constraining schemes are developed. The STS and the bamboo nail are applied by means of moment- or shear-constraining strategies. Then, rotational and shear tests are carried out to estimate the structural efficiency of the conceived retrofitting techniques. With the appropriate schemes, the STS and the bamboo nail contribute to the enhancement of the structural performance of the Zuo-Dou connection. The STS in a moment-constraining profile can ameliorate the Zuo-Dou’s rotational behaviour. As far as post retrofitting and preventing reinforcing are concerned, the STS reveals considerable structural efficiency. The bamboo nail in a shear-constraining scheme can increase the shear capacity of the Zuo-Dou joint. Besides the quantitative outcomes, these retrofitting techniques exhibit ductility and enhance the deformation processes of the connections. With the alternative fasteners, the slump or vibration during the deformation becomes moderate and the severe damages, such as rocking or block shear failure, are alleviated. The techniques and associated materials used in this study exhibit compatibility and feasibility for constraining the rotation, deformation, and crack of the Zuo-Dou connection. These effects are helpful for retaining the joints’ structural behaviour and contribute to the conservation of traditional timber constructions.

Experimental and numerical investigations of block shear failure in gusset plates welded to double angle members

Double angle braces are used extensively in structures to resist lateral loads such as wind, earthquake, and blast loads. A possible failure mode in the gusset plate when all-around weld is used for the angles is the block shear failure. To date, only limited test data on welded gusset plates failing in this mode have been reported in the literature, and all of them only considered concentrically loaded gusset plates. This paper investigates the block shear failure in welded gusset plates experimentally and numerically when connected to double angle members with possible in-plane load eccentricity effects. The test results, including failure loads, fracture sequences, and load-displacement responses are reported in detail. Results showed that tensile fracture was initiated adjacent to the angle heel weld and then propagated along the tension plane. Due to existing in-plane load eccentricity, shear planes did not rupture simultaneously and the shear plane adjacent to the heel weld failed earlier. Following the testing, a numerical investigation using nonlinear finite element analyses with ductile damage capability was performed on the tested specimens. Subsequently, a parametric study was carried out to generate further numerical data over a wide range of gusset and angle dimensions, welding configurations, and connection lengths. Accordingly, the existing design equations for block shear strength as given by AISC specification were evaluated. It was shown that AISC provides excessively conservative and scattered failure loads because of ignoring stress triaxiality and using shear yield instead of shear rupture in its strength equations. In addition, equations specified for welded gusset plates by previous studies were considered and shown to be unsafe for general use. To address these shortcomings, an improved block shear strength equation is proposed in this paper and shown to predict the gusset strength in block shear with improved accuracy.

Investigation of block shear strength of high strength steel bolted connections

This study presents an experimental and numerical investigation of block shear strength of high strength steel (HSS) bolted connections under double shear. A total of 16 HSS (grades Q690 and Q960) and eight mild steel (MS) (grade Q345) bolted connection specimens with various geometric configurations were tested and failed in block shear failure mode. The test and finite element (FE) analysis results confirmed that the block shear failure is a combination of fracture of the net tension plane and yielding of the effective shear plane, which is located between the net and gross shear planes. The effects of material properties (such as ductility and tensile-to-yield strengths ratio (fu/fy)) of steel materials on the block shear strength were comprehensively investigated based on the validated FE models. It was found that the tensile stress across the net tension plane could be fully developed irrespective of the steel grade due to effective stress redistribution along the net tension plane and the beneficial effect of the biaxial tensile stress state. However, the shear stress magnitude along the shear plane is influenced by the ductility and fu/fy ratio of steel materials and the length of the shear plane. The low ductility and fu/fy ratio of HSS materials did not allow for effective stress redistribution along the long shear plane and the shear yielding could only partially develop along the shear plane at the ultimate state. For the HSS specimens with short shear planes, the shear stress could develop up to the shear yield strength in general. Finally, the accuracy of the existing design equations in various design codes (i.e., prEN 1993–1–8: 2021, ANSI/AISC 360–16, and CSA S16–19) and relevant literature for predicting the block shear strength of bolted connections was evaluated and design recommendations were provided.

Failure Modes Of Cold Formed Steel Angle Sections

Tension members consisting of single and double angles, single channels and similar sections are frequently used for lateral bracing and as truss elements. Such members normally have eccentric connections which results in bending of tension member. It is often permitted, by current design specifications, to neglect this eccentricity in the design of the member. The present study is focus on mode of failure on cold formed steel angle. This analysis carries single angles and double angles sections of 2mm under plain (without Lipped) and with Lipped conditions subjected to tension. Analyses were carried out for thirty-six numbers of angle sections under condition such as double angle were connected same side to gusset plate and connected to opposite side. Figure shows connection failure and mode of failure. Local buckling, global buckling, tearing failure, net section failure, and block shear failure.

Advanced Design of Block Shear Failure

This paper presents the behaviour and design procedure of bolted connections which tend to be sensitive to block shear failure. The finite element method is employed to examine the block shear failure. The research-oriented finite element method (RFEM) model is validated with the results of experimental tests. The validated model is used to verify the component-based FEM (CBFEM) model, which combines the analysis of internal forces by the finite element method and design of plates, bolts and welds by the component method (CM). The CBFEM model is verified by an analytical solution based on existing formulas. The method is developed for the design of generally loaded complicated joints, where the distribution of internal forces is complex. The resistance of the steel plates is controlled by limiting the plastic strain of plates and the strength of connectors, e.g., welds, bolts and anchor bolts. The design of plates at a post-critical stage is available to allow local buckling of slender plates. The prediction of the initial stiffness and the deformation capacity is included natively. Finally, a sensitivity study is prepared. The studied parameters include gusset plate thickness and pitch distance.

Conventional I-shape brace member bolted connections under seismic loading: Laboratory study

In many regions of the world, a conventional low-ductility concentrically braced frame (CBF) is commonly chosen as the seismic force resisting system. The energy dissipation is not restricted to yielding and buckling of the braces, as would be required for ductile braced frames; rather, energy dissipation is assumed to occur through localised yielding and friction in connections, as well as limited member yielding. The objective of this study was to characterize by means of laboratory testing the inelastic response of full-scale conventional I-shape braces and their bolted connections under reversed-cyclic seismic loading. Six brace specimens comprising two commonly used bolted connection types, flange plate and flange angle, were designed following the Type CC provisions prescribed by CSA S16. The brace specimens achieved storey drift ratios of 1%–2%, due to inelastic deformations in both the braces and the connections, even though capacity based design provisions were not incorporated in their design. Energy dissipation resulted from overall and local brace buckling, gusset plate buckling, tension yielding of flange plates, angles and gusset plates, block shear failure of brace webs and angles, bolt fracture and fracture of the gusset plates, along with bolt slip. However, the observed performance of these braces and connections in this laboratory based study is not necessarily guaranteed to be replicated for all conventional CBF designs due to the conservative nature and variability in accuracy of the existing CSA S16 design equations that were relied upon to design and detail the test specimens.

Finite Element Analysis on Block Shear Mechanism of Lean Duplex Stainless Steel Welded Connections

The block shear equations specified in the current AISC specification for structural steel buildings and North American cold-formed steel design specifications are based on research results of carbon steel bolted connections. These equations were found to be inapplicable for the welded connections in the literature. This issue is primarily associated with the use of the incorrect assumption on block shear failure mechanism. The present paper examines the accuracy of various block shear equations available in the design specifications and in the literature. The paper also examines the shear hardening capacity and the level of tensile stress over the critical net area with the results of finite element analysis, in which the fracture simulation is considered. It shows that the block shear capacities of lean duplex stainless steel welded connections can be predicted accurately using tensile stress equal to 1.25Fu, as proposed in the literature.

Block shear behaviour and design of cold-formed staggered hole bolted connections

Block shear strength of cold-formed steel bolted connections has been thoroughly investigated in the literature, although the behaviour of block shear with staggered holes has not been studied in detail. It is more complex and apparent that a combination of tension and inclined shear behaviour due to the presence of the staggered holes affects the shear strength and behaviour of the bolted connections. This paper presents an experimental program on the block shear behaviour of staggered hole bolted connections to provide a better understanding on the failure modes. A total of 24 tests using G450 sheets was conducted at the University of Sydney with 1.9 and 2.4 mm thicknesses. Digital Image Correlation (DIC) was employed to capture both the full field of the displacement and the block shear failure mode of the staggered hole bolted connections during testing. A comparison of the experimental strength with existing design equations for block shear with staggered holes in AISI S100:2016 and AS/NZS 4600:2018 is included in the paper. A calibrated Finite Element Model is then developed by the commercial program ABAQUS to validate against the test results and to further provide detailed insights which could not be seen in actual tests (i.e, stress and strain distributions). In the FE simulation, to study the whole range of deformation of the staggered hole bolted connections (i.e., elastic, plastic and fracture stages), a plasticity model and a ductile damage model are applied to the cold-formed steel sheets to represent various stress states in the steel during failure.

Effect of synthesis parameters of cold-setting melamine-urea-formaldehyde resins on the adhesion in wood bonding

This work studied the effect of the synthesis parameters (i.e. synthesis method and melamine content) on the adhesion of cold-setting melamine-urea-formaldehyde (MUF) resins in wood bonding. Two types of cold-setting MUF resins were synthesized: MUF-A resins with three melamine contents (30, 40, and 50 wt%) prepared by the simultaneous reaction of urea, formaldehyde, and melamine, and MUF-B resins with the same melamine levels but synthesized by a sequential reaction process of melamine with formaldehyde and urea. The curing behaviors of both resins were characterized by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), and their adhesion performance in the dry and wet states were compared in block-shear strength (BSS) and wood failure (WF) tests. As the melamine content increased, the viscosity and peak temperature (Tp ) of the resins increased. However, MUF-B resins showed lower activation energy (Ea ) than those of MUF-A resins. Dynamic and isothermal DMA scans also showed that MUF-B resins also had greater maximum storage modulus (E′max) than those of MUF-A resins in their neat resins and resins/wood composites, indicating stronger interphase adhesion and cohesion. Lower Tp , lower Ea , and higher E′max, of MUF-B resins than those of MUF-A resins resulted in higher BSS and WF of MUF-B resins in wood bonding. In particular, MUF-B resins with 40% melamine showed the highest BSS and WF. These results indicate that the MUF resin synthesis method is closely related to the adhesion performance in wood bonding.

Partially restrained beam-column weak-axis moment connections of low-rise steel structures

In this study, partially restrained beam-column moment joints in the weak-axis direction were examined using three large-scale specimens subject to cyclic loading in order to assess the seismic resistance of the joints of low-rise steel structures and to propose joint details based on the test results. The influence of different number of bolts on the moment joints was thoroughly investigated. It was found that the flexural capacity of the joints in the direction of weak axis was highly dependent on the number of high-tension bolts. In addition, even though the flexural connections subjected to cyclic loading was perfectly designed in accordance with current design codes, severe failure mode such as block shear failure could occur at beam flange. Therefore, to prevent excessive deformation at bolt holes under cyclic loading conditions, the holes in beam flange need to have larger bearing capacity than the required tensile force. In particular, if the thickness of the connecting plate is larger than that of the beam flange, the bearing capacity of the flange should be checked for structural safety.

Material ductility and temperature effects on block shear capacity of bolted connections

The block shear equation in the current Australasian and amended North American cold-formed steel design specifications is based on shear yielding without strain hardening, while that in the new Aluminum Design Manual assumes full shear strain hardening. This study investigates the range of applicability for both assumptions through experimental tests involving ultra-high strength steel bolted connections at room (ambient) and elevated temperatures, where the levels of material ductility are vastly different from each other. The experimental program has found that the block shear capacities of the ultra-high strength steel bolted connections at room temperature can be determined accurately by neglecting shear strain hardening, but full hardening can be assumed for high strength and mild steel connections. Surprisingly, at temperatures above 300 °C, even the assumption of full shear strain hardening for single-row bolted connections is too conservative, by up to 50%. Finite element analysis is used to show that the catenary effect increases with increasing temperature, as does the extent of shear strain hardening. Another finding is that a conventional block shear failure may occur by simultaneous tensile and shear ruptures, if the material ductility is low enough (rather than high enough as believed in the literature). Contrary to intuition, the block shear capacity of a bolted connection failing by simultaneous tensile and shear ruptures has to be computed using the shear yield stress rather than the shear ultimate stress.

Experimental Investigation of Block Shear Failure in a Single Angle Tension Member

A limited test data are available for double-bolt line connection in a single angle tension member, which failed in block shear. To address this, twelve single angle tension members with a double bolt-line connection was reported in this paper, considering the block aspect ratio and connection length as the test parameters. All the tested specimens were failed in block shear. For the tested specimens, numerical analysis was performed, which shows good agreement with experimental results. Experimental outcomes were then compared with the current design provisions present in the IS 800, AISC, CSA, AIJ, EC 3, SBC, and with other existing proposed models. These standards and models show some discrepancies with regard to the experimental results. This discrepancy was due to the shear failure plane position as assumed in the design standards. Those shear planes were specified in the standards as net and gross shear planes. However, the experimental and numerical investigation shows that between the gross shear plane and the net shear plane lies the actual shear failure plane. Based on this, the block shear mechanism was modified and proposed a rational equation that provides a more exact prediction of block shear capacity than the current design standards and the other existing models. The proposed block shear equation shows the precise forecast for both single and double-bolt line connections used in a single angle tension member.

Application of Damage Mechanics for Prediction of Failure of Structural Materials and Elements

The article deals with the practical application of damage mechanics for modelling and predicting the failure of materials and structural elements. One of the recently developed and used models of Bai–Wierzbicki material is discussed in more detail. In this model the effect of hydrostatic pressure and the third invariant of the deviatoric stress on the process of the material plastic deformation is taken into account. It allows to model damage processes in the material and predict its total failure with high accuracy. Consequently, this enables the practical application in engineering calculations of structural elements. As an example, several such analyses were presented and discussed. They included the simulations of tensile elements made of C45E+N steel under proportional and non‐ proportional loading conditions in uniaxial and spatial stress state. Another analysis considered numerical simulations of the ductile fracture in Battelle Drop-Weight- Tear (BDWT) specimens used in pipeline sections tests. The problem concerned the phenomenon of block shear failure in bolted steel connections was the subject of the last presented simulations.

Block shear failure in welded gusset plates under combined loading

Block shear failure in the base metal of welded steel connections is a potential failure mode affecting many steel structures. However, there are only a few studies on the block shear failure of welded connections under combined shear and axial loading. Combined loading is defined as a simultaneous loading parallel and perpendicular to the weld lines (or an inclined loading) in the plane of the connecting plate. In this research, a nonlinear finite element model is used to study the effect of connection geometry and weld group configuration on the block shear strength of welded connections under combined loading. In current design standards, the block shear failure planes are assumed to consist of shear and tension planes, parallel and perpendicular to the applied load, respectively. The results obtained indicate that for combined loading, inclined failure planes are possible and the state of stress in such planes is a combination of tensile and shear stresses, the extent of which is proportional to the angle of loading. The results are used to describe the behavior of block shear rupture planes in such cases. Finally, to provide a better estimate of block shear strength in welded connections subjected to combined loading, a new equation is proposed that considers the actual shape of displaced block.

Block shear failure of S275 and S690 steel angles with single-line bolted connections

Block shear is a common failure mode for bolted-steel shear connections. However, limited research has been conducted on the block shear failure of bolted high-strength steel (HSS) angle members. In this study, a test programme was conducted using eight single-line bolted angle specimens made of grade S690 steel and five S275 counterparts, to examine their block shear behaviour. The test parameters included steel grades, bolt arrangements (bolt number, pitch, and edge distance), and connection legs. Eleven of the specimens failed by block shear, and the remaining two by shear-out. Finite element models were developed to study the behaviour of the test specimens and to investigate the effects of connection legs on the block shear resistance. Laboratory tests and numerical analyses indicated that the block shear resistance increased only slightly with increasing lengths of the angle legs, and the relatively lower ductility of HSS did not significantly influence the block shear resistance of the HSS angles. It was also found that the predictions made by AISC 360–16 and Eurocode 3 were conservative, whereas CSA S16–14 provided unconservative predictions. The predictions obtained from design equations proposed in previous studies were also evaluated for their accuracy.

Structural behavior of double-CFT-pile foundations under cyclic loads

This paper presents experimental and analytical studies on the structural behavior of double-pile foundations under cyclic loads. Three large-scale pile foundation specimens with vertical or battered concrete filled steel tube (CFT) piles plainly embedded into concrete caps were tested. The effects of embedment depths, inclination angles and unequal heights of the CFT piles on the failure modes, strength, lateral stiffness, ductility and energy dissipation capacity were evaluated. The experimental and analytical results indicate the pile diameter embedment is adequate for forming the plastic hinge at the ends of both vertical and battered CFT piles. However, block shear failure and pry-out of the concrete caps inhibited the complete development of the plastic hinges at CFT pile ends. The use of battered piles significantly increases the loading capacity, lateral stiffness and energy dissipation capacity of pile foundations, but decays the deformation capacity and ductility of pile foundations. The unequal heights of battered CFT piles increase the shear and axial loads carried by the short pile, resulting in the potential premature failure of the short pile. The total lateral loading capacity of the pile foundation is not significantly affected by the unequal heights; however, the deformation capacity of the foundation decreases with increase of the unequal height ratios.