Block Shear Fracture Research Articles

Recommendation on block shear strength equation of double shear four-bolted connection in cold-formed mild carbon steel

In this study, experimental research was performed to investigate the structural behaviors such as the ultimate strength and fracture mode of double shear four-bolted connection fabricated with cold-formed mild carbon steel. It shows that bolted connections failed by either block shear fracture or net-section fracture at test end. Finite element (FE) analysis model was developed to replicate experimental response. After successful verification, it was employed for further analysis such as stress and strain distributions that could not be seen through the physical testing. Three paths on the plate model of bolted connection were established to investigate the critical shear plane and the shear stress distribution on the critical shear plane at ultimate state. A modified block shear fracture strength equation of the bolted connection was proposed considering the shear stress factor (average of ultimate shear stress and yield shear stress) at the critical shear failure plane (midway of gross shear section and net shear section; effective shear plane), and block shear fracture strengths by test and analysis results were compared with those by the suggested equation. It is concluded that the proposed equation is able to provide more accurate prediction in determining block shear strength of double shear four-bolted connection with mild carbon steel.

탄소강 용착금속 블록전단파단 용접접합부의 최대내력에 관한 실험적 연구

탄소강 용착금속 블록전단파단 용접접합부의 최대내력에 관한 실험적 연구

Complete Block Shear Fracture Failure Finite Element Analysis

The experimental and finite element (FE) analyses of the block shear fracture failure in the published literature are limited to the analysis of the fracture on the surface of the gusset plates and connected members without the analysis of the through-thickness fracture in block shear fracture failure. This paper presents the FE analysis of the complete block shear fracture failure covering the analyses of the block shear surface and through-thickness fracture failure. This study reveals the following: The block shear fracture initiation occurs at the tensile plane mid-thickness and not on the tensile plane surface reported in the published literature. The tension plane through-thickness fracture propagation involves mid-thickness-to-surface fracture propagation and not the surface-to-mid-thickness fracture propagation reported in the published literature. The pure shear fracture that is parallel to the tensile loading direction exhibits a surface-to-mid-thickness fracture sequence while the shear lip fracture that is inclined to the tensile loading direction exhibits a mid-thickness-to-surface fracture propagation. This paper thus identifies the accurate fracture initiation location and through-thickness fracture propagation sequence in block shear fracture essential for the accurate and complete analysis of the block shear fracture not hitherto presented in any published literature.

Examination of the block shear fracture test method to measure the Mode-II critical stress intensity factor

Block shear fracture tests were conducted using specimens of western hemlock to determine the properties of the fracture mechanics under the Mode-II condition. In the test, a fixture standardised as the block shear test of solid wood in the Japanese Industrial Association (JIS Z2101-2009) was used. The specimen configuration, location of the crack, and initial crack length were varied, and the effects of these conditions were examined. The Mode-II critical stress intensity factor was effectively obtained when the initial crack was introduced at the opposite location to that where the shear load was applied using a specimen with a cubic configuration. Additionally, the introduction of the additional crack length due to the fracture process zone ahead of the crack tip was also effective in the block shear fracture test and other Mode-II fracture tests.

Development on ultimate strength equation of ferritic stainless steel (STS430) two-bolted connection

This article presents the experimental and numerical results of cold-formed ferritic stainless steel (STS430) bolted connection with two bolts. Single-shear bolted connections with varying end distance were planned and tested. Block shear fracture and curling (out-of-plane deformation) were observed in specimens. Finite element analysis was performed to investigate the conditions for curling occurrence and the curling effect on the ultimate strength of ferritic stainless steel bolted connections with extended end distances and edge distances varying from 24 to 60 mm. Curling occurred for bolted connections with end distances exceeding 39 mm and edge distances exceeding 30 mm. Ultimate strength of curled specimens was reduced up to 33% compared to the ultimate strength of uncurled connection. Since current design equations do not consider the curling effect and the difference in material properties, they did not provide accurate ultimate strength predictions of specimens with typical block shear fracture and curling occurrence. Therefore, a modified block shear equation was suggested for ferritic stainless steel bolted connection with typical block shear fracture mode, considering the actual fracture path and shear stress factor. A revised equation was also proposed for specimens with strength reduction by curling influence, considering the concepts of bearing action against connected plate by bolt (bearing factor, C = 1.6) and net-section tensile fracture between two bolts perpendicular to the direction of the applied force. Moreover, additional experiments for six specimens were performed and the reliability of the two suggested equations in this study was verified.

An Investigation on Base Metal Block Shear Strength of Ferritic Stainless Steel Welded Connection

This study develops a finite element analysis model to predict the ultimate strength of the base metal block shear fracture based on previous experimental results and compares the experimental results with the analysis results to verify the effectiveness of the analysis model. This study also analyzed additional variables of the welding direction and weld length on the applied load to investigate the structural behaviors and fracture conditions. In addition, predicted strength according to the analysis results were compared with those by the current design equations, and the equations proposed by previous researchers. As a result, the design formula by the current design equations, such as Korea Building Code (KBC)/American Institute of Steel Construction (AISC) and European Code (EC3), and the equations proposed by Oosterhof and Driver underestimated the base metal block shear strength of ferritic stainless steel by up to 42%. Equations suggested by Topkaya and Lee et al. for carbon steel and austenitic stainless steel welded connections provided more accurate strength predictions, while they did not reflect the difference of material properties. Therefore, this study proposed a modified strength equation for ferritic stainless steel welded connection with base metal block shear fracture considering the stress triaxiality effect of the welded connection and the material properties of ferritic stainless steel.

Block shear strength of cold-formed austenitic stainless steel (304 type) welded connection with base metal fracture

In this paper, the block shear fracture behavior of base metal in austenitic stainless steel (STS304, corresponds to ASTM 304 type) fillet-welded connection has been investigated through experimental and numerical methods. Even though the block shear fracture strength of welded connection thanks to stress triaxiality effect differs from those of bolted connection under monotonic tension, block shear strength equations of welded connection with base metal fracture in the design codes are identical to those of bolted connection. Main variables are weld method (TIG and Arc welding) and weld length (transverse and longitudinal to the direction of loading). It is found from study results that welding method did not affect the strength of welded connection. Block shear strengths by current codes (KBC2016, AISC2016 and EC3 1–3) and other researchers’ proposed equations were compared with those of experimental results and finite element analysis results. Finite element analysis (FEA) model was developed based on previously test data. Also, parametric study for investigating the weld length effect on strength has been performed with the developed finite element analysis procedures. Consequently, condition of weld length and end distance perpendicular to the direction of applied force for fracture mode transition boundary from tensile fracture to block shear fracture in welded connection was investigated. In addition, block shear strength equation with modified tensile stress and shear stress factors of base metal fracture in austenitic stainless steel (STS304) welded connection is suggested considering stress triaxiality.

Investigation on Ultimate Strength of STS304L Stainless Steel Welded Connection with Base Metal Fracture Using Finite Element Analysis

Many studies on the application of stainless steels as structural materials in buildings and infra-structures have been performed thanks to superior characteristics of corrosion resistance, fire resistance and aesthetic appeal. Experimental investigation to estimate the ultimate strength and fracture mode of the fillet-welded connections of cold-formed austenitic stainless steel (STS304L) with better intergranular corrosion resistance than that of austenitic stainless steel, STS304 commonly used has carried out by authors. Specimens were fabricated to fail by base metal fracture not weld metal fracture with main variables of weld lengths according to loading direction. All specimens showed a block shear fracture mode. In this paper, finite element analysis model was developed to predict the ultimate behaviors of welded connection and its validity was verified through the comparison with test results. Since the block shear behavior of welded connection due to stress triaxiality and shear-lag effects is different from that of bolted connection, stress and strain distributions in the critical path of tensile and shear fracture section were investigated. Test and analysis strengths were compared with those by current design specifications such as AISC, EC3 and existing researcher’s proposed equations. In addition, through parametric analysis with extended variables, the conditions of end distance and longitudinal weld length for block shear fracture and tensile fracture were suggested.

Parametric Study on Ultimate Strength of Four-bolted Connections with Cold-formed Carbon Steel

The curling(out-of-plane deformation in the plate thickness direction) influence on the ultimate strength of cold-formed stainless steel bolted connection has been investigated and modified equations for predicting the ultimate strength considering strength reduction caused by curling through finite element analysis have been suggested by previous researchers. In this paper, single shear four-bolted connections fabricated with thin-walled carbon steel commonly utilized in the light-weight structural members of building were tested under static shear in order to investigate block shear fracture behavior and curling influence on the ultimate strength and fracture mode. Main variables of specimens are plate thickness and end distance parallel to the direction of loading. Curling in the perpendicular direction of applied force also occurred for bolted connections with a relatively long end distance and thin plate. The curling occurrence caused a sudden strength drop and reduced the ultimate strength of bolted connections. Current design specifications such as AISC, AIJ and AISI for block shear strength were summarized and it is known that design equations did not provide the accurate prediction of ultimate strength and fracture mode for thin-walled carbon steel bolted connections. Strength reduction by curling and the condition of curling occurrence were investigated through an additional parametric finite element analysis. As a result, revised strength equations for block shear fracture and bearing fracture were suggested considering fracture path and curling effect and their validity was also verified.

Experimental and numerical study of frictional effects on block shear fracture of steel gusset plates with bolted connections

In this paper, an experimental and a numerical study has been conducted to get information about the effects of slip-critical connections in gusset plates of bolted steel tensile members. To this end, a total of 28 double gusset plates were subjected to tensile loading in seven groups, while the parameters such as the properties of specimen materials, number of bolts, amount of frictional coefficient and the type of connections were selected as experimental variables. A 3D non-linear finite element analysis was done to determine the distribution of tension and shear stresses at different times of tensile loading, showing good agreements with the results of the experiment. The results of the experimental tests and the finite element analysis showed that frictional force due to a pre-tightening force of slip-critical connections could have a significant effect on the capacity response and fracture behaviour of gusset plates under tensile loading with block shear fracture. Therefore, increasing frictional coefficient, reduction of thickness, and the resistance of specimen materials, increased the effect of frictional force on them. On the other hand, in order to evaluate the proposed equations of AISC 2016 and CSA2009 standards, as well as the proposed equations of Topkaya, C. (2004) [13] and Teh and Uz (2015) [14], for predicting the strength of block shear fracture, a comparison was done between the strengths obtained from the predictions of their equations and the strength obtained from laboratory tests. With this comparison, it was found that AISC 2016 and CSA2009 standards have the most conservative and non-conservative forecasts in the proposed equations. In addition, by changing the effective shear stress in the proposed equation of Teh and Uz (2015), from the value of 0.6Fu to Fu3, more precise predictions are provided in comparison to other equations studied in this paper, in which the main reason for its precision is better observation of the shear contribution, because this equation uses active shear planes instead of net or gross shear planes.

Ultimate strength of austenitic stainless steel fillet-welded connections with weld metal fracture

This study investigates ultimate behaviors such as ultimate strength and weld metal fracture mechanism of austenitic stainless steel (304 type) fillet-welded connections with TIG (tungsten inert gas) welding through experimental method. Main variables of test specimens are weld length and welding direction against applied force. Specimens are fabricated with transverse fillet weld (TFW series), longitudinal fillet weld (LFW series) and full fillet weld FW series against loading direction. Specimens of TFW series, LFW series and FW series failed by tensile fracture, shear fracture and block shear fracture in the weld metal of connections. Test ultimate strengths were compared with predictions based on the design specifications, AISC (American institute of steel construction) and ASCE (American Society of Civil Engineers) and existing researcher's equations. Current design equations underestimated excessively the strength of welded connections with weld metal fracture. Consequently, modified design formula is suggested considering actual fracture path and the effect of stress triaxiality on welded connections and its validation was verified in this paper.

Simulation of block shear fracture in bolted connections

Block shear failure in bolted connections is a complex failure mode in steel connections. The complexity of this failure is due to the varying stress-state conditions along the failure path. Failure under this mechanism is distinctively characterized by ductile fracture, particularly on the shear plane, which has recently been identified to not only be dependent on stress triaxiality but also on Lode parameters. Existing numerical models provide extensive knowledge on important performance parameters in the connection; however, further improvements of current simulation approaches can yield significant dividends in characterizing fracture initiation and progression until failure. The aim of this paper is to develop a new numerical simulation technique for capturing block shear failures in bolted connections and to utilize the developed models for further understanding the failure. Specifically, numerical models of gusset plate and coped beam connections are created and loaded up to and including total fracture. This is realized through the application of a newly developed ductile fracture criterion that accounts for the dependency of the fracture path on stress triaxiality and Lode angle parameter. Laboratory test results on large-scale bolted connections serve for validation of the analysis technique. Comparison between the numerical and experimental results include load versus displacement, fracture sequence, and fracture profile and an overall excellent correlation is shown. Through the numerical simulations, the intrinsic mechanisms of block shear in gusset plate and coped beam connections are discussed and the effect of various levels of beam end/rotations, for coped beam connections, on block shear failure is explored. The modeling approach presented in this study can be an alternative mean for modeling block shear failure and can be extended to other types of connections. The analysis results provide insight on block shear failure mechanism and the factors dominating the behavior of this type of connection.

페라이트계 스테인리스강 용접접합부의 모재 블록전단파단에 관한 실험적 연구

페라이트계 스테인리스강 용접접합부의 모재 블록전단파단에 관한 실험적 연구

Estimation of ultimate strength in single shear bolted connections with aluminum alloys (6061-T6)

An experimental investigation for the structural behavior of single shear bolted connection fabricated with aluminum alloys (6061-T6) has been carried out by Kim et al. It is found that ultimate strengths caused by curling (out-of-plane deformation in the direction of plate thickness) were reduced for some specimens with long end distances parallel to the direction of loading. In this paper, finite element analysis model has been developed on the basis of existing experimental results and analysis results were compared with the test results in order to verify the validity of finite element analysis method for predicting the ultimate behaviors of bolted connections. Additional analyses with extended variables such as end distance and edge distance were performed. Strength reduction ratio by curling and the condition of curling occurrence were investigated. Moreover, ultimate strength of analysis result was compared with design strength by American Aluminum Association (AAA) and American Iron Steel Institute (AISI) design standards. Modified strength equations were suggested considering effective shear stress in block shear fracture and curling effect by bolt bearing action.

Experimental investigation on strength and curling influence of bolted connections in thin-walled carbon steel

Experimental studies regarding the influence of curling on the ultimate strength of cold-formed stainless steel bolted connections have been carried out by Kim et al. Basic data and modified equations for predicting the structural behaviors considering strength reduction due to curling through the finite element analysis method have also been suggested by previous researchers.In this paper, single shear bolted connections fabricated with four bolts and thin-walled carbon steel commonly utilized in light-weight structural members were tested to investigate the fracture mechanism and curling influence on the ultimate strength. Main variables for test specimen are plate thicknesses and end distances parallel to the direction of loading. Curling (out-of-plane deformation in the direction of plate thickness) also occurred in thin-walled carbon steel bolted connections with a large end distance and thinner plate like previous cold-formed stainless steel connections. The curling occurrence reduced suddenly the ultimate strength of single shear carbon steel bolted connections and the influence pattern of curling on strength was affected according to the plate thickness and end distance. Current design specifications for block shear strength with the combination of tensile fracture and shear fracture are summarized and the ultimate strengths of test results are compared to the predicted design strengths. AISI (American Iron and Steel Institute) and EC3 (Eurocode 3) made conservative estimates of ultimate strength for thin-walled carbon steel bolted connections with no curling, whereas AIJ (Architectural Institute of Japan) and SSBA(Stainless Steel Building Association) manuals provided a good prediction for ultimate strength and fracture mode. Modified strength equations were recommended respectively for bolted connections with typical block shear fracture considering shear stress factor and severe curling accompanied by strength reduction.

Mechanical behaviours and design strengths of single shear bolted connections fabricated with aluminium alloy 7075-T6

In the study, experimental study has been performed to investigate the mechanical behaviours such as ultimate strength and fracture mode of single shear bolted connections with aluminium alloy 7075-T6. Main variables are bolt arrangement and end distance. As a result, the specimens failed by shear-out fracture and block shear fracture. Some specimens with a long end distance were accompanied by curling (out of plane deformation). The curling led to a sudden ultimate strength reduction. Moreover, the change of strain distribution was investigated according to curling occurrence. The reliability of design rules for single shear bolted connection in AAA, AISI and AIJ specification is evaluated through comparison between test results and predictions by each current design standard. Lastly, the strength equations considering curling effect and bolt arrangement were proposed and compared with test results.

탄소강 2행 1열 일면전단 볼트접합부의 최대내력과 면외변형 영향에 관한 실험적 연구

The purpose of this experimental study is to investigate the ultimate strength and curling influence on structural behaviors of single shear bolted connection of thin-walled carbon steel fabricated with two bolts. The end distance parallel to the loading direction and plate thickness are considered as main variables. Curling also occurred in these carbon steel connections with a long end distance and thinner plate. It is known that all specimens failed by block shear fracture and the curling occurrence led to the ultimate strength reduction of thin-walled carbon steel bolted connections. The ultimate strength and fracture mechanism of test results were compared with those of current design standards such as AIK(KBC2009), AISC, AIJ, AISI NAS and EC3. The design standards provided a poor prediction for the ultimate strength and fracture mechanism. Therefore, modified equations considering curling influence are proposed in this paper.

Investigation on ultimate strength and failure mechanism of bolted joints in two different aluminum alloys

Aluminum alloys have been utilized in various industrial fields and building structures due to high strength-to-weight ratio, increased durability, formability and enhanced service life. They can be classified into seven groups from 1000 to 7000 series according to alloyed chemical compositions except main pure aluminum component. Experiments of single-lap joints with 6061 type alloys were performed by Kim et al. and the results show that curling (out-of-plane deformation toward plate thickness direction) occurred in bolted joints with a long end distance and it is found that the curling influenced mechanical strength. In this paper, ultimate strength and failure mechanism of single shear sheet bolted joints fabricated with two different aluminum alloys; 6061-T6 (aluminum–magnesium–silicon series) and 7075-T6 (aluminum–zinc–magnesium–copper series), which are the most widely used materials due to the need of high strength were compared. Alloy type, plate thickness, end distance and bolt arrangement were considered as main variables. Monotonic tensile tests have been conducted for specimens and two fracture modes such as shear fracture and block shear fracture were observed. Some bolted joints with relatively thinner plate and longer end distance were accompanied by curling and the curling led to sudden strength reduction. The difference of material properties and plate thickness affected failure mechanism and curling occurrence. Moreover, strain distribution and curling deformation pattern against enforced displacement were investigated to grasp the curling effect on the behaviors of joints.

Block Shear Strength of Single Shear Four-Bolted Connections with Aluminum Alloys – Experiment and Design Strength Comparison

Experiments have been carried out to investigate the ultimate behaviors of single shear bolted connections assembled with four bolts (2 rows×2 columns bolt arrangement) under shear and aluminum alloy plate. End distance parallel to the direction of applied load is considered as main variables. All specimens failed in block shear fracture and curling (out of plane deformation) in the direction parallel to plate thickness was also observed for some bolted connections with a long end distance. The curling led to sudden ultimate strength reduction and test strength was compared with the block shear strength predicted by current design specifications.

Block Shear Behaviours of Stainless Steel Channel Bolted Joints with Four Bolts

The introduction of thin-walled stainless steel in buildings has been increased gradually for ensuring the sustainability thanks to excellent corrosion resistance and durability. Many studies on structural behaviors of stainless steel bolted connection fabricated with plane plate have been carried out. This paper is aimed at investigating the ultimate behaviors such as ultimate strength, fracture mode and out of plane deformation(i.e. curling) of channel bolted connection of cold-formed austenitic stainless steel with four bolts (2×2 bolt arrangement). End distance parallel to the direction of applied force is adopted as main variables. Specimens are planned with block shear fracture in ultimate state. In case of bolted connections with a long end distance, curling has also been observed. Ultimate strengths by test results are compared with those of current ASCE design specification and the influence of curling on ultimate strength is discussed.