Lap Connections Research Articles

STensile behaviour of T-stub to hollow section column using elliptical-head one-side bolts

The Elliptical-head one-side bolt (EOB) is a typical representative of the third generation for one-side bolts, relying on its elliptical head and bolt hole to achieve orthogonal anchorage, and the application scenario is mainly the bolted connection of closed-section members. Studies have been reported for the shear performance of EOBs bolted lap connections and the tensile behaviour of concrete-filled steel tubes, but there is still a lack of the tensile performance of EOBs connecting Hollow section columns (HSCs), which is necessary for the application of the component method for the beam-column joints design. Therefore, numerical simulation and theoretical analysis methods were employed in this paper to demonstrate the feasibility of adopting EOBs for this type of connection, including typical failure modes, novel yield line pattern in the HSC wall, comparison with the Conventional high-strength bolt (CHB) connections, analysis of the parameters related to the elliptical bolt head and hole, and the establishment and validation of the methodology for calculating the HSC bearing capacity. The results show that: The novel trapezoidal yield line pattern tended to show in the HSC wall with the smaller bolt pitch distance and larger gauge distance; The yield strength of the EOBs bolted T-stub to HSC connections was reduced by about 15% compared to the CHBs bolted ones; Vertical layout of bolt holes, accuracy of rough assembly, rotation deviation of bolt shank within 20° and avoidance of bolt offsets in bolt hole were recommended for EOB connections; The novel yield line pattern established in this paper predicted the yield strength of the connections, and the accuracy and stability were verified by comparing with finite element modelling (FEM) results.

Experimental Study on the Mechanical Properties of Vertical Corrugated Pipe Grout Anchor Connection Joints

Prefabricated buildings’ quality, safety, and construction efficiency are closely related to the connections between various prefabricated components. This study optimizes the design of corrugated pipe-restrained grout anchor lap connections, further simplifying the construction methodology while ensuring reliable connection performance. The objective is to achieve cost savings and accelerate construction progress. A pull-out test of this new type of joint is conducted, generating two sets of 17 specimens each. The research examines the effects of grouting material strength, grout anchor steel bar anchorage length, and U-shaped stirrup spacing on the connection performance of corrugated pipe grout anchor connections. The results indicated that the specimens primarily experience two types of failure: anchorage failure with steel bar pull-out and steel bar tensile failure without anchorage failure. The strength of the grouting material and the anchorage length of the grout anchor steel bar positively correlate with bond anchorage performance. U-shaped stirrups contribute to restraint and enhance the bonding force between the corrugated pipe, grouting materials, and the grout anchor steel bar to a certain extent.

A computational modeling approach for cold-formed steel bolted connections exhibiting bolt slip and bearing behavior

Cold-formed steel (CFS) is increasingly used for buildings and infrastructures, as it is lightweight and easy to install in the field when a bolted joint method is used to join elements. Unlike “rigid” welded joints, bolted joints allow for movement during load transfer, adding flexibility. Such flexibility is more prominent in thin-walled CFS bolted connections. The structural performance of a CFS structure with bolted joints is considerably governed by the mechanical behavior of the bolted joints. In many existing finite element (FE) simulations, an individual CFS bolted joint was modeled as a simplified linear or bilinear behavior, leading to less accurate results of both local and global behavior of the CFS structure. This study presents a novel FE-based method for modeling a bolted joint for CFS, which enables the simulation of nonlinear behavior of the bolted joint, characterized by the bolt slip and the progressive bearing. This approach utilizes the connector elements in series, defined with the friction and plasticity models, to model this bolt slip-bearing behavior. A well-known torque–friction force relationship is used to estimate the bolt friction slip load needed for the friction model definition. Rex equation is used to predict the bearing load–deformation response, which is inserted as the input into the plasticity model. The suitability and the capability of the approach is first validated using two of the CFS lap connections with a single bolted joint subjected to monotonic/cyclic loading. Then, the proposed approach is validated for the large-scale moment-resisting CFS connection beams with eight different configurations. It is expected that the application of the proposed approach can be extended to any type of thin-walled bolted connections exhibiting the bolt slip and bearing response.

Parametric study on fatigue behavior of steel friction connections in shear

A parametric study on the fatigue behavior of steel friction connections was conducted in this paper. Fatigue failure mechanism of the connections and two periods of fatigue life were discussed in detail. The procedure to predict the fatigue life of steel friction connections was proposed using the finite element method, and was verified by the fatigue test results. A parametric study was then performed based on the prediction procedure. Considering the connection type, bolt related parameters, and plate related parameters, a total of ten cases were included in the parametric study. The results show that the fatigue strength of single lap connections is much lower than that of double lap connections, which is caused by the local bending of bolted plates and contact status change on the interface. Fatigue behavior of the single lap connections is greatly affected by the number of bolts, steel grade, and hole-making process, while the fatigue behavior of the double lap connections is greatly affected by the bolt preload, slip factor, main plate thickness, steel grade, and hole-making process.

Flexural Performance of Splice Connections in Cross-Laminated Timber

This study demonstrates the moment resistance performance of various splice connections of cross-laminated timber (CLT) subjected to flatwise bending. A total of 33 samples in two groups (half-lapped and single-splined) were tested under four-point bending. The influence of fastener types on the half-lapped connections was investigated. Additionally, different lap lengths were considered to understand the influence of lap length on different fastener types. Steel plates with two different thicknesses and plywoods were attached with bolts onto the bottom face only to make the single spline connections. Additionally, plywoods were attached to the CLT members in two ways: (i) with the bolt only and (ii) glue plus bolts. The effect of bolt diameters on the spline connections was also examined, and the connections were tested along both the major and minor axes. To determine the characteristic values of the resistance properties, a statistical analysis was carried out following EN 14358:2016. The results indicate the bolted lap connections experience plastic deformations, whereas the screwed lap connections exhibit relatively linear behaviour until failure. The bolted and screwed lap connection with a lap length of 100 mm showed 39% and 33% higher moment capacity, respectively, than that with a 75 mm lap length. Additionally, the rotational rigidity and ductility of the lap connections increase with the increase in lap length. Irrespective of lap lengths, the bolted lap connections show higher moment capacity, support rotation and ductility, but lower rotational rigidity than screwed lap connections. An increase in bolt diameter increases moment capacity but decreases rotational rigidity. Compared to the plywood spline connections, the steel spline connections showed approximately 24%, 5% and 73% higher moment capacity, rotational rigidity and ductility, respectively. Additionally, the plywood spline connections without glue performed better than glued connections. Overall, compared to the half-lapped connections, the single-spline connections showed better performance.

Preload loss of high-strength bolts in friction connections considering corrosion damage and fatigue loading

The preload loss of high-strength bolts in friction connections was investigated considering the corrosion damage and fatigue loading. Double lap connections were assembled and the ultrasonic measurement method was employed to obtain the real-time preload of the bolts. Accelerated corrosion tests of specimens were used to achieve four corrosion levels and the and the corresponding weight loss ratio of the specimens varied from 0 to 10.1%. Fatigue test was then performed on eight corroded connections. The preload change of bolts after installation, corrosion tests, and certain number of load cycles was measured. It is found that the corrosion effects on the bolt preload loss was significant, and an average value of 41.2% preload loss was observed for specimens of 10% weight loss. The influence of fatigue load on the preload loss after unloading could be ignored, but the combination of tensile loading, fatigue loading, and corrosion damage could lead to an up to 11% preload loss.

Experimental study of precast concrete shear walls with spiral-confined lap connections under cyclic loads

In this paper, full-scaled precast concrete shear walls (PCSWs) with spiral-confined lap connections were tested under low reversed cyclic loading tests with axial compression ratios of 0.12 and 0.24. Both one-row and two-row connections were considered in the test program. The spirals in the connections were used to provide additional confinement and to shorten the lap length (a reduced lap length of 1.0laE was used). Results showed that all PCSWs suffered flexural-shear failure mode, and their load-carrying capacity, hysteretic behavior, energy dissipation and stiffness degradation characteristics were similar to the monolithic reference specimens. The ductility of the PCSWs under the axial compression of 0.12 was 3.86 and 4.00, which was close to that of the monolithic wall (4.19). Under the axial compression of 0.24, the spiral-confined lap splices prevented the earlier failure of the PCSWs, leading to significantly higher ductility (4.08 and 4.07) than the monolithic wall (3.05). The test results also indicated that the reduced lap length of 1.0laE was validated to be acceptable under simulated earthquake actions. In addition, the PCSWs with one-row and two-row connections exhibited comparable structural performance, and they could both be considered as emulative structures.

Power-actuated fasteners in single shear-An experimental investigation and proposed design rules

This paper presents the results of 81 experimental tests on the design strength of power-actuated fasteners (PAFs) in single shear connections for a light gauge steel framing (LGSF), as an alternative to self-drilling screws for selective uses. This type of connection can be employed to install a reinforcing plate on one or both sides of the frame, to connect steel strap cross bracing to framing, as well as for many other applications. These power-actuated fasteners present a very efficient and practical solution which can increase productivity and work quality by replacing time consuming screw connections. In this study, two different steel grades (G300 and G550), along with three different steel sheet configurations were investigated. Modes of failure for both the PAFs and the connected material were examined so to provide an understanding of the structural performance of nailed single lap connections and develop design recommendations and proposed formulae. The investigation covers a wide range of steel gauges (0.75 mm, 0.95 mm and 1.15 mm), commonly used in LGSF residential and commercial applications. Two groups of tests were performed. The first group of tests was conducted to determine the shear strength of connectors with two types being tested. The second tests series were carried out in various steel grade and gauge configurations for assembled connections. The results of this research and the proposed design formula can be used to establish the strength prediction model for power-actuated fasteners (PAFs) embedded into LGSF.

Shear Behavior of Lapped Connections Bolted by thread-fixed one-side bolts at elevated temperatures

The Thread-fixed One-side Bolt (TOB) is the bolt that can be installed from outside of a steel tube column, which is anchored by the threads on the bolt hole wall instead of the nuts. A series of tests were carried out to investigate the shear behavior of the lapped connection bolted by TOBs using both the steady state fire tests and the transient state fire tests. The two observed failure modes of TOB connected lapped connections were the bolt hole bearing failure (failure mode 1) and the bolt shank fracture (failure mode 2). The high temperature might cause the change of failure mode from failure mode 1 to failure mode 2. Lapped connections using Standard High Strength Bolt (SHSB) were also tested. The comparison results showed that the ultimate shear resistance of lapped connections using TOBs at different temperatures was about 90% of that using SHSBs with the same configuration at steady state fire test. Applicability of the design equations provided by Eurocode 3 was validated by the steady state fire test results. A Finite Element Model (FEM) was built and validated by the test results and the FEM was used to further study more derailed parameter studies including the influence of bolt strength, the bolt pretension force and the high temperature to the shear behavior of TOB connected lap connections.

Research on Initial Behavior of Screwed Lap Connections of Thin Plates – Experimental Tests and FEM Analysis

The paper continues the past research on the screwed thin-plate single-lap connections undertaken by the author. This re-search was focused on stressed skin diaphragm action, where it is essential to know values of connections behavior. Until now, initial stiffness is used for common engineering estimations. The main aim of this paper is to compare the experimental results of the shear tests conducted on the connections with the theoretical predictions of their initial behavior obtained from the FEM models. The experiments followed the Eurocode rules for design aided by testing and the European Convention for Constructional Steelwork (ECCS) recommendations. FEM parametric models are introduced as a consideration to use, taking into account screw threads and EPDM washers. In the technical literature, various techniques are described for the modelling of threaded connections. A modification to a known solution is applied in this analysis where a spiral thread is substituted by simple horizontal rings; this simplification allows use of symmetry in a static system, which is particularly desirable for large models such as those prepared in this paper. In contrast to the mentioned known solutions, the thread mod-el presented here has a triangular cross-section related to the geometry used in real screws. The numerical results correspond reasonably well to the test’s early stage measurements from the lab experiments and can be useful for initial stiffness examination (e.g. where no data is provided for a particular connector by a producer) or as a base to further research on the model.

Statistical evaluation of bearing resistance and related strength functions for bolted connections

The paper is concerned with the statistical analysis of strength functions for bolted connections, namely the bearing resistance, the block tearing resistance, the net cross-section resistance and the resistance of angles in tension connected by a single row of bolts in one leg to obtain partial factors. These strength functions are proposed in the second generation of EN 1993-1-8 and EN 1993-1-1. The statistical analysis is performed using 884 test results available in the background documentation to Eurocode 3 and an additional 380 test results of lap connections with different bolt arrangements, which are available in the literature. A suitable sampling criterion of the test results allowed sufficiently large data sets with a small coefficient of variation, which allowed the assumption of partial factor γM2 = 1.25. EN 1993-1-8 provides the design check of the effective net cross-cross section resistance of angles connected by a single row of bolts in one leg (EN 1993-1-8, 3.10.3). It is demonstrated that this design check is superfluous and can be completely replaced by the design block tearing resistance, taking into account the design upper limit of the net cross-section resistance.

Bearing behavior of multi-bolt high strength steel connections

This paper presents an experimental and numerical investigation on the bearing behavior of multi-bolt high strength steel connections in single bolt line. Three grades of high strength steel with nominal yield stress of 550 MPa, 690 MPa and 890 MPa were used to fabricate thirty lap connections with two or three bolts. It is found that the deformation capability of high strength steel plate near bolt hole is sufficient to meet the deformation demand of compatibility in multi-bolt connection even with an intended bolt hole misalignment of 2 mm for M24 high strength bolt. The comparison with Eurocode3 and AISC 360-16 is conducted. When no partial or safety factors are considered, the original formulae of Eurocode3 already has sufficient safety while AISC 360-16 gives unsafe predictions. Numerical models were established and verified by test results. With the obtained results, the full-range distribution of internal load among different bolts can be divided into four stages. Features for each stage are summarized and the effect of bolt hole misalignment on the distribution pattern is evaluated. Numerical analysis results indicate that, behavior of an individual bolt in multi-bolt connection may be influenced by surrounding bolts. The formation of critical yielding band between different bolts may explain this influence. Based on the experimental and numerical analyses, this paper proposed a new ultimate bearing resistance model for multi-bolt connections. The proposed model is capable of describing the nonlinearity in the ultimate bearing resistance of multi-bolt connection and achieves improved predicting accuracy compared to classical models.

Design of Bolted Single Shear Lap Connection with Different Thicknesses of Splice Plates

AbstractA method based on elastic stability analysis to design bolted single shear lap (SSL) connections, which are traditionally used for hollow structural section (HSS) bracing members, is propos...

Assessment of fretting fatigue in high strength steel bolted connections with simplified Fe modelling techniques

Abstract The fretting fatigue (FF) damage on contact surfaces constitutes a major problem in High Strength Steel (HSS) bolted connections when subjected to cyclic loadings, in that it significantly lowers the fatigue life. Moreover, the estimation of damage in the contact areas is challenging and laborious through experiments. The present paper proposes a simplified modelling technique to estimate the fretting fatigue damage in high cycle regime by considering the pretension effect and contact properties of bolted lap connections. To do so, a three-dimensional solid model is developed and validated. Afterwards, simplified FE models are validated using the three-dimensional model and test results to identify the most computationally efficient model for bolt connection in HSS under static and fatigue loading conditions. It was observed that the newly developed FE model could retain all the components on contacting surfaces while saving of up to 97% of the computational time over full solid models. These results successively provided insight into the crack initiation location and the fatigue lifetime of the joint and showed good agreement with experimental and three-dimensional solid model data.

Research on Self-Drilling Screwed Lap Connections in Steel Diaphragms and the Design Models

Abstract In this paper, the results of a research on thin-plate single-lap connections are presented. Such type of connections is popular in steel roofs made of trapezoidal plates and other thin-walled elements. In case of a building safety it is necessary to ensure that materials with proper durability and ductility are used. Connections are one of the most important components in such structures, particularly when in-plane strength of a roof is taken into account. So far, in many existing regulations, only general calculations of such connections are conducted. However recently, discrete and computational methods can be used to build new, expanded mathematical design models, such as those presented here. Such models could be useful in an advanced design where a static analysis is combined with the safety assessment of the connections in a structural system. This is difficult when sheeting is utilized as a structural in-plane shear diaphragm. These require to take into consideration the important interactions of structure with covering and covering with another covering elements. The research is an effect of authors works on practical design approaches. Such methods can be effectively used for structural designs of buildings where the stressed skin diaphragm action is involved. Finally, practical input values about connections can be acquired from the presented data.

Shear behavior of lap connection using one-side bolts

Experimental and numerical investigations on the basic shear behaviors of the lap connections connected by the threaded-fixed one-side bolts were presented. The threaded-fixed one-side bolt in the connection was clamped by internal threads on the wall of a bolt hole, instead of the traditional nut. 36 test specimens with different thicknesses of screwed shear plate and different bolt pre-tension forces were conducted. The failure mode of the shear connection obtained from tests were perfectly consistent with those predicted by EC3-1-8 design equations and the ultimate shear predicted resistance was conservative compared with the test result, both of which differed by 4.6%. A finite element model was built and verified to further investigate effects of the thickness of base plate and the bolt diameter on the shear behavior of the lap connection. The simulated results concluded that the bolt would tilt if the thickness of base plate was smaller than the bolt diameter. The lap connection using the threaded-fixed one-side bolts and the traditional bolts with nut were compared. Difference in the ultimate shear resistance is 0.24% as only the bolt shear fracture failure occurred, however, difference in the ultimate shear resistance is 2.5% as the bolt shear fracture accompanied by the bolt tilting occurred. This paper proved that the screwed shear plate could replace the traditional nut in engineering applications.

Net section fracture assessment of steel bolted joints with shear lag effect

Bolted connections are willingly used in steel structures because of their easiness of fabrication and assembly, but often they are the weakest component in the construction. In case of tensile lap connections, fracture of net cross section usually determines a joint capacity. Additionally, possible eccentricities can affect the distribution of stresses in the cross section and hence its load capacity. Analysis of fracture is a completely different issue compared to well-known and established problems of stability or plastic resistance. Paper relates to steel angle tension members connected by one bolt. It starts from the description of experimental investigations which results were used for hierarchical validation of computational models. Choice between two types of material models (elastic-plastic and Gurson–Tvergaard–Needleman) and building of FE models, representing different degrees of complexity, were described. Paper ends with parametric study taking into account influence of the edge distance from the centre of a fastener hole to the adjacent edge of angle. The paper’s aim is to verify and present the methodology for fracture prediction in steel angle tension members, which can be next extended for bolted joints with larger number of bolts and different geometrical configurations.

Stability analysis and design of double shear lap bolted connections in steel x-bracing systems

In this paper elastic and inelastic buckling analysis of the bolted double shear lap connections (DSL) are investigated, which are commonly used in concentrically braced steel frames comprised of cold-formed hollow structural section (HSS), as brace members. By the lack of any approach to evaluate the compression strength of a DSL connections, their design is usually relied on the tension load demand developed in the brace member. The results of quasi-static cyclic tests performed on six full-scaledX-bracing specimens have shown that the discontinuous brace member with DSL connection, not designed for compression, failed and fractured by the buckling at the connection. In all the specimens, the typical brace buckling only occurred in the continuous members, as expected. In this study. a simplified elastic stability analysis is employed to calculate elastic buckling load and effective length factor usable for the design of DSL connections. Anon-linear static analysis is also performed on a suggested numerical model comprised of beam-column elements to predict the response of the studied X-bracings, exhibiting the connection and member buckling. It is shown that the results of the both suggested design procedure based on the stability analysis and the numerical model agree well with the buckling load of the test specimens. It is also indicated that the slip of connection plates decreases the compression capacity and should be considered in the analysis and design procedures.

PERFORMANCE OF SINGLE LAP JOINTS USING ADHESIVE AND SELF-DRILLING SCREW FOR COLD-FORMED STEEL UNDER TENSILE LOADING

Adhesive and screw connections are usually used in single lap connections for coldformed steel. In this study, the work focuses on the joints strength of connection for both adhesive and self-drilling screw on tensile performance. Experimental investigations were conducted on the single lap joints design. The average failure load (joints strength) of adhesive connections was found to be 50% higher than the screws joints. More often than not, the joint effectiveness of adhesive is based along the area of adhesive meanwhile for screw depends on the number of screws used.

Numerical modelling of lockbolted lap connections for aluminium alloy plates

A numerical modelling method for lockbolted lap connections of aluminium alloy plates is studied based on experimental tests. The mechanical properties and constitutive models of aluminium alloy 6061-T6 and stainless steel 304HC were intensively determined by tensile tests. A tensile test of a single-lockbolted lap connection was conducted to obtain its elongation and strain responses. A basic numerical model that considers the lockbolt preload, interface contact and friction, and gaps between the lockbolt and bolt hole was established to simulate the tensile behaviours of this connection. This model was updated to minimize errors between the numerical and test results, and values for the friction coefficients of different contact surfaces were suggested. To improve the accuracy and efficiency of the numerical analysis, an incompatible mode solid element was adopted in the numerical model. It was determined to be better than refining the mesh or accepting a higher-precision element type. This numerical modelling method was investigated by two types of double-lockbolted connections, and its validity was verified by comparing the displacement and strain responses between the numerical and test models. The modelling method suggested in this paper is applicable for simulating the mechanical behaviours of complicated joints with lockbolted lap connections.