Joint Slip Research Articles

2012 William M. Murray Lecture: Some Curious Unresolved Problems, Speculations, and Advances in Mechanical Fastening

Mechanical joining is one of the oldest, most important, and most neglected aspects of engineering design of machines and structures of all types and sizes. Approximately 250 U.S. companies manufacture fasteners worth over $8 billion per year. There are 18,000 fasteners in a common fighter jet airframe, and fasteners account for roughly one-third the cost of a typical airplane. Yet, most failures of structures, including aircraft, originate at fasteners, suggesting that improved understanding of fastener mechanics, better design criteria, and informed applications of fundamental knowledge are required. This issue is exacerbated by increased demands on systems, particularly in the transportation and military sectors, and by the growing use of composites, for which current fastening practice seems to be underdeveloped owing to the complexities of material structure and response. This lecture first traces a brief history of mechanical joining, its importance, and the problems faced by engineers in designing for fastening. Research and development of fasteners through analysis and experiment are complicated by the large array of variables involved, and investigators must have at hand an extensive array of experimental and analytical techniques as well as an appreciation of the practicalities of fastening. Verification and validation of findings are crucial, and extrapolation is fraught with pitfalls. Described subsequently are some examples of experimental results that generate speculation and that might provide points of entry for investigators who are willing to take on difficult challenges where progress would be valuable but is not easily realized. These cases include, among others, odd and perhaps dangerous behaviors resulting from coldworking holes in engines and structures, impact stresses caused by joint slippage in composites, the use of inserts to control stress concentrations, difficulties in applying sufficient clamping force in composites, merits of hole shaping, and unusual configurations of conical washers. Finally, some ideas for hybrid joining and for systems that allow quick field assembly/disassembly are briefly described.

Dynamic response of wall-floor joints of wooden light-frame constructions under forced harmonic vibrations

Shaking table tests of the wall-floor joints of wooden light-frame constructions under forced harmonic vibrations are conducted in this study so as to observe the dynamic responsive characteristics. The principal results are as follows: The responsive characteristics of timber constructions under strong earthquakes cannot be directly correlated with their resonant frequencies under free or forced vibrations with low input accelerations, because they behave as continuous bodies when the input accelerations are less than the apparent frictional limits of structural joints. The apparent frictional limits are reduced by periodic fluctuation of the effective vertical loads as a result of the vertical motion of the specimens. The characteristic dynamic responses of wall-floor joints depend clearly upon the frequency and input accelerations of forced vibrations. These dependencies arise from the nonlinear load-slip relationship of the wall-floor joints. The equivalent stiffness in their successive transient phases decreases as joint slip increases, which gradually changes the resonant frequencies of the wall-floor joints. This indicates that the frequency components dominant to ultimate or safety-limit resistance should be distinguished from those dominant to allowable or serviceability-limit resistance.

Numerical Modelling for Sensitivity Analysis of Wood Joints Made with Double-Sided Punched Metal Plate Fasteners

Single-sided punched metal plate fasteners have been used in construction industry for a few decades. However, its double-sided version is relatively new and is increasingly attracting more users due to its advantages on fire resistance and aesthetics. Owing to complex nature of such fastener, limited research has been undertaken up to date. In this paper, a finite element method-based inverse modelling technique was developed for optimization analyses of a prototype double-sided fastener. The non-unique nature of inverse model solutions makes assessment of model sensitivity to input material properties imperatively. This paper uses validated numerical models for sensitivity analysis of joint modelling output. Joint stiffness is most sensitive to wood elastic moduli. Ultimate strength is significantly influenced by steel yield strength and wood embedding strength and shear strength. The coefficient of friction, steel yield strength, wood shear and embedding strengths have significant effects on joint slip.

Accurate modeling of joint effects in lattice transmission towers

Lattice Transmission towers are vital components of overhead transmission lines which play an important role in the operation of electrical power systems. Accurate prediction of the structural capacity of lattice towers under different failure modes is very important for accurate assessment of the reliability of transmission lines and power grids, and for design of efficient failure containment measures. Traditionally, lattice towers are analyzed as ideal trusses or frame-truss systems without explicitly considering loading eccentricities and slippage effects in bolted joints. Such effects are always observed in full-scale tower tests and introduce great differences in the ultimate bearing capacity and failure modes obtained from classical linear analysis models. In this paper experimental results available from full-scale prototype tests of a single-circuit 110 kV and a single-circuit 220 kV lattice transmission towers subjected to different load cases are presented and compared with those obtained from four series of numerical models that include joint eccentricity effects and different joint slippage models. The numerical simulation results confirm that joint slippage dramatically increases the deformation of the lattice towers, while its influence on load-bearing capacity will vary in different load cases according to the magnitude of vertical loading and the tower failure mode. Results from the pushover nonlinear static analysis of the towers considering both joint slippage and eccentricity are found in agreement with the experimental results. This type of analysis can be used to model joint effects in lattice towers.

Bifurcation analysis for a rate‐sensitive, non‐associative, three‐invariant, isotropic/kinematic hardening cap plasticity model for geomaterials: Part I. Small strain

AbstractLocalized deformations such as shear bands, compaction bands, dilation bands, combined shear/compaction or shear/dilation bands, fractures, and joint slippage are commonly found in geomaterials like soil and rock. Thus, modeling their inception, development, and propagation, and effect on mechanical response of the body or structure is important. The paper will focus on one, now classical, analysis method for modeling the inception of these localized deformations for a rate‐sensitive, non‐associative, three‐invariant, isotropic/kinematic hardening cap plasticity model. Bifurcation analysis, in terms of continuous and discontinuous conditions (Int. J. Solids Struct. 1980; 16:597–605), provides the mathematical conditions under which a localized deformation mode could be admissible, and it should not to be confused with attempting to model the microstructural evolution of the geomaterial as it transitions from a nearly uniform to localized deformation response at a material point. Analysis determines that continuous and discontinuous bifurcation are different for weak discontinuity and the same for strong discontinuity, and such conditions are identified for the plasticity model. Rate sensitivity will preclude bifurcation regardless of viscosity value. Numerical examples demonstrate various plasticity model features that enable detection of localization using bifurcation analysis. All analyses are conducted currently in the small strain regime. Copyright © 2010 John Wiley & Sons, Ltd.

Thermally induced strains and stresses in cast iron water distribution pipes: an experimental investigation

Full-scale tests have been carried out on lengths of unrestrained and restrained plain and jointed distribution pipe sections (similar to 4 '' or similar to 100 mm internal diameter) in order to investigate the strains and loads generated in cast iron water distribution mains as a result of temperature fluctuations. Tests on unrestrained sections enabled the coefficient of thermal expansion of the pipe material to be measured. In a fully restrained situation, which can occur in a pipe section in service when the joints are locked, tensile stresses arise from a decrease in temperature ( in accordance with the predictions of a simple one-dimensional model) and it is shown that these stresses are sufficiently high to fracture a corroded pipe. In situations where the tensile stress leads to joint slippage, leakage through the joint is observed. Water leakage was also observed through the wall of corroded pipes that retained sufficient structural stability to carry load without failure.

Towards an understanding of the loosening characteristics of prevailing torque nuts

Prevailing torque nuts are an extremely popular method of providing resistance to vibration-induced self-loosening of fasteners. Such nuts have a self-contained prevailing torque feature that provides a degree of resistance to rotation. Although such nuts are frequently used, it is not widely realized that they can occasionally come completely detached from bolts. The mechanism by which this can occur has hitherto been unidentified since it has not been possible to replicate detachment under laboratory testing. This article identifies a general condition that can result in the complete loosening and detachment of prevailing torque type nuts. This mechanism involves the application of an axial load when transverse joint slip is occurring. This article describes a modified Junker test machine that allows the application of axial loading to a joint while experiencing transverse displacement. Tests have been completed using an intermittent as well as a constant axial load. Loading in both modes has been demonstrated to result in the complete detachment of this nut type. Based on this investigation, if the magnitude of the axial loading exceeds the residual preload in the bolt retained from sustaining transverse movement alone, the all-metal type of prevailing torque nut can completely detach. Applications that involve shear and axial loading being simultaneously applied to a joint are numerous in engineering.

Experimental Study on the Energy Dissipation Capacity of a Plane Transmission Tower Substructure With Friction-Type Reinforcing Members

Friction-type reinforcing members (FRMs) developed for the purpose of enhancing the wind-resistant performance of transmission towers are tested experimentally. The FRMs, in the middle of which slotted bolted connections (SBCs) are installed, are placed on the outside of tower legs, and provide additional damping and stiffness to the tower structure under bending deformations. First, the SBCs used in the FRMs are tested for various frictional sliding interface conditions. Second, the FRMs are installed on a 1/2 scale plane tower substructure and cyclic loading tests are conducted. Energy dissipation capacity and effects from local deformations of the FRMs and joint slips are investigated. From the test results, remarkable energy dissipation capacity, reaching to the 2.4 times of that before the installation of the FRMs, is observed. However, the local deformation of the SBC and joint slip should be prevented for more reliable design of the FRMs.

Influence of Bolted-Joint Slippage on the Response of Transmission Towers Subjected to Frost-Heave

Slippage of bolted joints is an important factor in the behavior of transmission towers. Field inspections of towers located in the northern regions of Canada show substantial frost-heave induced displacements. The conventional structural analysis software solutions for tower leg axial forces, based on idealized joint behavior under field-observed frost-heave induced displacements, are excessively large, implying tower failure in some cases. However, field inspections show structurally stable towers, and design engineers often consider joint slippage as the main reason for this discrepancy. In this paper, the experimental slippage behavior of transmission-tower bolted joints investigated by Ungkurupanian (2000) is incorporated into a non-linear joint finite element and applied to study the behavior of transmission towers under working loads by using the finite element method. The analysis shows that tower-leg joint slippage has a significant influence on tower behavior by either reducing the load carrying capacity or significantly increasing the deflections under working loads. On the other hand, joint slippage has a positive effect on towers subjected to frost-heave induced displacements, as the resulting member axial forces are much lower than those corresponding to rigid joints.

Load-carrying capacity of steel-to-timber joints with a pretensioned bolt

Previous experimental studies reported that bolt pretensioning greatly increases the initial stiffness and load-carrying capacity of bolted joints. It is also a matter of great importance to structural designers to understand the effect of pretension on the load-carrying capacities of bolted joints, and this study presents an extended yield model that considers the fastener’s pretension force. In the extended yield model, the load-carrying capacity was defined as the load at a slip of 15 mm. The ultimate fastener bending angle at the yielded cross section equivalent to this joint slip, which was affected by the fastener’s axial force, was iteratively evaluated in numerical analyses. The introduction of bolt pretensioning largely increased the joint slip resistance at initial loading, but it decreased the ultimate fastener bending angle. This decrease of fastener bending angle resulted in a relatively low stiffness hardening (or secondary stiffness), which is caused by secondary axial forces associated with embedment of steel plates into the wood member. Prediction was verified by the tests of 36 steel-to-timber joints under three different pretension forces and two loading directions relative to the grain. Some of the observed load-carrying capacities of the joints, particularly in loading perpendicular to the grain, however, were not as high as those expected by the numerical analyses considering the given pretension forces.

Quasi-static mechanical behaviour of a double-shear single dowel wood connection

Results of a double-shear single dowel wood connection tested under monotonic quasi-static loading, according to the EN26891 standard, are discussed in this paper. The Pinus pinaster species, which is one of the most important Portuguese woods, was used in this study. The initial joint slip modulus, the ultimate strength and the ductility are evaluated and compared with values given by the Eurocode 5. Embedding tests are also carried out according to the EN383 standard. The resulting data is used to predict the joint slip modulus, through a proposed analytical model supported by statistical regression analysis data. Finally, a three dimensional finite element model of the wood connection was built and calibrated using available experimental data. This model can be applied to evaluate accurate values for the joint initial slip modulus.

Earthquake Shear Load in Load-Bearing Masonry Buildings

Load-bearing masonry buildings are composed of concrete slabs and supporting masonry walls, and in Australia usually incorporate slip joints in the interfaces between walls and slabs for serviceability reasons. The apparent conflicting requirements of the slip joints, to slip under long-term loads and to transmit short-term loading from wind and earthquake actions, together with the lack of attention to the design of slip joints, make slip in the joints likely to occur when the building is subjected to a lateral loading. Joint slip leads to a redistribution of loading in the building wall system, resulting in wall shear loads different from that determined using the current standard elastic design procedures. Redistribution of loading may be also caused by softening of the masonry. This paper has assessed the realistic response of various load-bearing masonry buildings, including the potential for slip in the joints and softening of the masonry, and evaluated the level of wall shear load deviations resulting from the application of current design procedures. Analyses of the buildings, using non-linear static and dynamic finite element models, have indicated that joint slip may occur in buildings subjected to earthquake loading. The application of current elastic design procedures, which do not account for loading redistribution, resulted in major wall shear load deviations, such as overestimations of up to +75% and underestimations of up to-62%. It was therefore concluded that improvements in the current design procedures are required for a more accurate evaluation of wall shear loads in load-bearing masonry buildings subjected to the lateral loading.

Distribution of slip from 11 Mw > 6 earthquakes in the northern Chile subduction zone

We use interferometric synthetic aperture radar, GPS, and teleseismic data to constrain the relative location of coseismic slip from 11 earthquakes on the subduction interface in northern Chile (23°–25°S) between the years 1993 and 2000. We invert body wave waveforms and geodetic data both jointly and separately for the four largest earthquakes during this time period (1993 Mw 6.8; 1995 Mw 8.1; 1996 Mw 6.7; 1998 Mw 7.1). While the location of slip in the teleseismic‐only, geodetic‐only, and joint slip inversions is similar for the small earthquakes, there are differences for the 1995 Mw 8.1 event, probably related to nonuniqueness of models that fit the teleseismic data. There is a consistent mislocation of the Harvard centroid moment tensor locations of many of the 6 < Mw < 8 earthquakes by 30–50 km toward the trench. For all models, the teleseismic data are better able to resolve fine details of the earthquake slip distribution. The 1995 earthquake did not rupture to the maximum depth of the seismogenic zone (as defined by the other earthquakes). In addition to the above events, we use only teleseismic data to determine the rupture characteristics of four other Mw > 6 earthquakes, as well as three Mw > 7 events from the 1980s. All of these earthquakes appear to rupture different portions of the fault interface and do not rerupture a limited number of asperities.

Detailed modeling of bolted joints with slippage

Bolted connections that allow for slippage are widely used on roadside structures. Due to limitations in existing analysis tools, non-linear finite-element analysis was used to develop detailed modeling techniques for bolted joints that slip in one direction when loaded in shear. Because bolt preload, and thus clamping forces, is very critical in determining joint slippage behavior, two modeling techniques were developed: (1) a discrete-spring based clamping model with several rigid parts, and (2) a stress based clamping model with deformable elements. Both techniques were used to simulate physical testing of a bolted joint undergoing slippage. Simulation results compared fairly well with test results. Very good accuracy was achieved when using finely meshed deformable elements for all parts. Of course, the cost of increased accuracy has significantly increased computational time.

Modelling the influence of boundary conditions on the concentrated load performance of oriented strand board floor decking

Concentrated load performance tests to failure have been carried out on 18-mm thick one-way simply supported, screwed and bolted oriented strand board (OSB) panels with spans of 300 and 450 mm. The screwed and bolted panels simulated the near minimum and maximum edge restraints, respectively, associated with dowel-type fasteners. The mechanical properties of the panels enabled the calculation of the service responses of the simply supported models of the panels that are used in routine design. The measured stiffnesses of the screwed and bolted panels included the effect of joint slip on stiffnesses. Comparison of the test and analytical results reveals that the stiffnesses of the dowel-fastened panels are between 10 and 20 percent greater than the analytically determined stiffnesses of the simply supported models. All the panels exhibited punching shear-type failures. The experimentally determined load capacities support the theoretical prediction that the concentrated load capacity of a one-way panel, loaded at the centre of span, is almost independent of the boundary conditions.

Joint slip in steel electric transmission towers

Joint slip is the relative displacement of a bolted joint under shear. It is greater in transmission towers as bolt diameters are small, members joined are thin, bearing type joints with a lower clamping force are used, and coefficient of friction of galvanized faying surfaces is low. This study on behaviour of such joints, incorporated 36 joint tests, generated joint slip data and developed mathematical expressions to describe slip and load-deformation behaviour. As currently used construction clearance was found satisfactory, joint slip cannot be eliminated. Hence, incorporation of the reported joint slip data or mathematical expressions in tower analysis software will refine their results.

Application of high strength plate bolts in friction grip joints

High Tension Bolts (HTB) are known to exert a significant influence on the strength characteristics of connections and have a significant influence on the ductility and behaviour of the joint. Normally HTB failure occurs in the shape resultant high stress concentration neck and thread areas resulting in relatively low ductility characteristics. Creep and relaxation occur after HTB tightening causing shaft tension loss and further stress redistribution in the connected components. Past research has shown that waisting the HTB shaft diameter reduces stress concentrations, shaft tension loss and increases ductility. With the further modification of making the HTB head plate shape counter sunk, a plate HTB with an aesthetically pleasing flat surface less susceptible to rain corrosion results. In this research, tensile, relaxation and friction grip joint slip experiments were done on waisted shank, counter sunk plate head HTB to ascertain the ductility improvement, the resulting decrease in shaft tension loss and its magnitude, as well as their applicability in friction grip steel connections. Apart from significant shaft tension loss reduction, no detrimental effects are induced in the slip coefficient results when these HTBs are applied in friction grip joints. Within these experimental parameters, the closest to ideal HTB shape is proposed. (Journal of Civil Engineering, JKUAT: 2002 7: 67-80)

Dynamic response of an opening in jointed rock

Abstract A large-scale test was performed on a 0.4 m diameter lined cylindrical opening in a 2 m cube of jointed limestone for the purpose of gathering data to develop and validate computational models for the dynamic response of structures in jointed rock. The limestone cube was assembled from over four thousand 51 mm square×0.6 to 1.2 m long limestone bricks and was then embedded in a concrete test bed and loaded explosively with a 100 MPa, cylindrically diverging stress wave. The material velocity around the boundary of the jointed limestone cube was measured with accelerometers and these data were used to generate a continuous velocity boundary condition that can be used for computational simulations. Additional instrumentation measured stress in the limestone, joint slip and deformation of the opening. After the test, the limestone cube was recovered and carefully disassembled to reveal fracture patterns in the limestone bricks. Vertical fractures emanating from the springlines formed a chimney of bricks that slipped measurably relative to the rest of the rock mass above the opening and to a lesser degree below the opening.

Development of 3D Indirect Boundary Element Methods which Consider Joint Slip and Joint Separation.

The authors have developed 3D analysis computing program for the coupled FS-DD method which considers joint slip and joint separation. In order to confirm the applicability of the developed methods, the model of rectangular prism excavation beneath the horizontal joint and the model of the large underground excavation (Super Kamiokande) was used as a numerical example and a case study, respectively. In this paper, the numerical procedure and the analyzed result of the numerical example and the case study are presented.

Effect of seismic load on a proposed nuclear waste repository at Yucca Mountain

Abstract Long term stability of waste emplacement drifts is of interest in assessing the safety of disposal of high-level nuclear waste (HLW) in the proposed repository at Yucca Mountain (YM). The repository preclosure operation period is about 100 years, and the decision regarding the use of backfill in the emplacement drifts during the postclosure period of about 10,000 years has not been finalized. Two significant factors that can induce drift instability include thermal loads generated by the decay of emplaced waste and repeated seismic loads from earthquakes. One of the failure mechanisms for an excavation in a jointed rock mass subjected to repeated seismic loading is through accumulation of shear displacements along joints. These dynamic ground motions at YM due to earthquakes (and possible nearby weapons testing) will take place in the presence of in situ stresses, excavation induced stresses, and thermal-mechanically induced stresses. This paper presents a discrete element analysis using the code UDEC (Version 3.0) to investigate the effect of repeated seismic loading on cumulative joint slip and failure around a heated, unsupported, emplacement drift in the proposed repository at YM. A 100 MTU/acre thermal loading was used. Computer results indicate that slip along joints and closing of the drift take place with both single and repeated episodes of seismic loading at peak accelerations of 0.4g if yielding has occurred in the rock around the drift during the thermal-mechanical loading stage prior to seismic loading. This cumulative effect of repeated seismic loading confirms the findings of a field investigation (Hsiung et al. 1992) and a laboratory study (Hsiung et al. 1997). However, if the rock remains in the elastic state after the thermal loading is applied, no measurable cumulative slip on joints or drift convergence is evident with repeated episodes of seismic loading up to 0.4g, aside from that which occurs during the first sequence of seismic loading.