Load Carrying Capacity Of Joints Research Articles

Moment-Rotation Calculation Method and Parameter Analysis for Loose Continuous-Tenon Joint in Column-And-Tie Timber Structure

ABSTRACT To quantitatively calculate the moment-rotation relationship of loose continuous-tenon joints in traditional column-and-tie timber frame, the rotational deformation of loose joints is divided into two stages: free sliding and contact compression. Using constitutive, geometric, and equilibrium equations, a theoretical formula for moment-rotation is derived. The calculated values are then compared with experimental results to validate the accuracy of the theoretical calculation method. A sensitivity analysis is conducted on typical parameters, such as beam height, column diameter, joint clearance, and perpendicular compression modulus of wood, to explore their effects on the moment-rotation relationship of tenon joints. The results show that increasing the perpendicular compression modulus of wood leads to greater bending stiffness and load carrying capacity of tenon joints, with the latter increasing more significantly. In the elastic stage, the rotational stiffness of the joint increases with beam height or column diameter, while after entering the elastoplastic stage, the joint stiffness is less influenced by these factors. The initial rotational stiffness and load carrying capacity of the joint both decrease with joint clearance, and the effect of joint clearance on load carrying capacity decreases as the clearance increases when the joint enters the yielding stage.

Load-carrying capacity of timber joints with multiple glued-in steel rods loaded parallel to grain

The joints with glued-in steel rods are efficient joints in the design of timber structures, due to their high stiffness, strength and fire resistance. The ductile behaviour of joints can be achieved through designing the yielding of steel rods prior to wood failure. In practice, the joints are generally with multiple rods rather than single rod. In the case of multiple glued-in rods, the yielding of single rod is designed as prior failure by using mild steel rod, and the load-carrying capacity of joints is expected to be equal to the yield capacity of single rod multiplied by the number of rods. However, the actual pull-out capacity of single rod in timber joints with multiple glued-in rods can be less than that in timber joints with a single glued-in rod, due to the group effect of glued-in rods. Thus, the brittle failure of pull-out of rods can still occur prior to the yielding of steel rods in timber joints with multiple glued-in rods, though the yielding of single rod is designed as prior failure. The pull-out capacity of multiple rods can generally be considered as the pull-out capacity of single rod multiplied by the effective number of rods instead of the actual number of rods. Therefore, it is necessary to determine the effective number of rods in the case of pull-out of rod.This paper presented an experimental investigation on joints composed of multiple glued-in steel rods (two and four rods with different rod spacing) in glued-laminated timber with the pull-out failure mode. The actual experimental results combined with those from literatures, were used to analyze the influence of main factors, e.g. rod diameter, slenderness ratio of rods, number of rods and rod spacing to diameter, on the effective number of rods. Afterwards, based on these main factors, an empirical expression of the effective number of rods was derived. Finally, a model of load-carrying capacity for timber joints with multiple glued-in rods was proposed. The load-carrying capacity of timber joints with multiple rods should be calculated as the minimal value between yielding capacity of a single rod multiplied by the number of rods and pull-out capacity of a single rod multiplied by the effective number of rods. The proposed model is capable of predicting the failure mode and load-carrying capacity for multiple rods.

Mechanical properties of confirmat screws corner joints made of native wood and wood-based composites

Mechanical Properties of Confirmat Screws Corner Joints Made of Native Wood and Wood-Based Composites. The aim of this investigation was to design and determine the mechanical properties of confirmat screws corner joints made of native wood and wood-based composites. The objective of the study was to ascertain the stiffness and load carrying capacity of joints that differed in the diameter and length of confirmat type screw, as well as in the kind of materials. The results include statistical processing of measured and calculated data, and evaluation of the influence of selected factors on mechanical properties. The results are applied to the calculation of the characteristic values of the properties and to the determination of the equations for their calculation for other values of the selected factors. The characteristic values are used for the evaluation of the joints according to the limit state method.

Effect of humidity on the wooden beams of the composite section

In wooden structures, the change in humidity affects the deformability and load-carrying capacity of joints and structures according to the criteria of the first and second groups of limiting states. In wooden beams of the composite cross-section with mechanical connections, with an increase in the moisture content of the timber, the structural strength of the structures is affected both by the increment in the deformations of the joints and by the change in the physical and mechanical characteristics of the wood, primarily, the modulus of elasticity of the material.

The effect of humidity on the operation of wooden beams of a composite section on compliant couplings without the use of glue

In wooden structures, the change in humidity affects the deformability and load-carrying capacity of joints and structures according to the criteria of the first and second groups of limiting states. In wooden beams of the composite cross-section on mechanical connections, with an increase in the moisture content of the timber, the structural strength of the structures is affected both by the increment in the deformations of the joints and by the change in the physical and mechanical characteristics of the wood, primarily the modulus of elasticity of the material.

Numerical investigation on novel geometrical configuration for adhesively bonded T-joint between aluminum and sandwich panel

One of the applications of adhesive joints in marine structures can be the attaching of superstructure to main hull, which classifies as T-joint. Although previous researches have covered T-joint between similar materials (composite to composite and aluminum to aluminum), joining aluminum and sandwich panels has not been considered yet. In this paper, the common lightweight T-joint with triangle fillets were investigated and based on the FEM results, the geometry was modified in order to increase the load bearing capacity subject to tension load. Results show that change in joint geometry can dramatically enhance the strength, and it was observed that the modifications made by authors caused vertical failure load of the joint to rise by 725%. However, in order to utilize full capacity of the joint strength, materials with high strength features should be used, unless the joint components will fail before debonding. Load carrying capacity of joint was increased while the applied adhesive decreased by 10% compared to the common lightweight T-joint. The results of numerical analyses were in a good agreement with experimental tests and confirm the accuracy of numerical analyses. Adhesion interfaces were modeled with contact elements along with Cohesive Zone Model in ANSYS. Contact stress and contact gap at the instance of collapse are also presented to provide the reader with the better understanding of the joint performance and the behavior of various components of the joint in load bearing and force transition.

Study of Beam-Column Junction based on Variations in Concrete Grade at Junction

Objectives: A beam-column joint has to transfer the shear forces, bending moments and other related structural response parameters efficiently. The present paper aims at studying the behavior of beam-column junction based on variations in concrete grade at junction. Analysis: To increase the load carrying capacity of a joint, a higher grade of concrete is used at a joint and also up to 1.5D in the direction of beam from face of column, to shift or relocate the plastic hinge from the interface towards the beam. The different specimens were prepared in a T-shaped mould by changing the grade of concrete at beam-column joint and these samples were tested after 7 and 28 days. Findings: Study reveals that use of M20 or M25 grade of concrete at joint and up to 1.5D (D is the depth of beam) of length of beam (M15 grade of concrete in rest of mould) increases the load carrying capacity approximately to about 20% when compared with M20 or M25 grade of concrete at junction and M15 grade in the remaining mould. The most important finding is that the use of higher grade of concrete at a joint and up to 1.5D of length of beam, shifts the failure away from the beam-column interface Thus, a beam hinging mechanism is achieved which is a ductile type of failure compared to beam-column brittle interface failure and there is approximately 15-30% increase in load carrying capacity, in comparison with higher concrete grade only at a joint core. This is a simple and efficient method of preventing the beam-column joint failure. Improvement/Applications: Based on the test results there is remarkable increase in the load carrying capacity of beam-column joint which enhances the rigidity of beam column joint in terms of strength and stiffness.

Strength and stiffness of timber joints with very high strength steel dowels

Tests on double-shear timber-to-timber joints and double-shear timber joints with slotted-in steel plates loaded parallel-to-grain were undertaken. The used species were spruce, beech, cumaru and azobé (ekki) with one, three and five dowels in a row. Two different steel qualities were used, high strength steel (hss) and very high strength steel (vhss) dowels. The experimental results have shown that the load carrying capacity of joints with vhss dowels is higher than for joints using hss dowels whilst still providing enough plastic deformation capacity to allow for ductile failure modes. No correlation between load carrying capacity and density within one wood species could be observed. The observed effective number of fasteners is lower for the joints with vhss dowels and depends also on the used wood species and the slenderness of dowels. Also for the stiffness Kser, an effective number of fasteners for the joints with more than one dowel in a row could be observed. The well-established Johansen model can be used to design these types of joints.

Effects of thermal ageing and impact loading on tensile properties of adhesively bonded fibre/epoxy composite joints

Abstract An experimental study has been performed to determine the effects of thermal ageing at three different temperatures on tensile properties of adhesively bonded fibre/epoxy composite single lap joints. Primarily, adhesively bonded composite specimens were subjected to thermal ageing process at temperatures of −18 °C, 25 °C and 70 °C. Afterwards, free-fall drop impacts having different energy levels (5, 10, 15, 20, 25 and 30 J) were applied to adhesively bonded single lap composite joints. In order to determine the effects of thermal ageing and free-fall drop impacts on tensile properties, tensile tests were performed under three different temperatures of −18 °C, 25 °C and 70 °C. It is found from the results that thermal ageing at −18 °C increased the load carrying capacity of joints yet, impacts applied to the joints decreased it. In addition reductions have been observed in the failure load of joints at the tensile testing temperatures of −18 and 70 °C.

Round Timber Joints under Tensile Loading Perpendicular to the Grain

This paper presents the results of static tests of non-reinforced round timber bolted joints with slotted-in steel plates loaded perpendicular to the grain. This type of joints loading is particularly widespread in truss structures. Round timber test samples series were prepared to validate the behavior of a joint loaded in tension perpendicular to the grain. The joints samples were experimentally tested in the laboratory of the Faculty of Civil Engineering VŠB TU Ostrava. The test results were compared with the calculated load-carrying capacity of joints by Johansen’s yielding theory.

Evaluation of Damage to Carbon-fibre Composites Induced by Self-pierce Riveting

The damages to fibre-reinforced plastics induced by the self-pierce riveting process are to be analysed and evaluated in a research project. A method was developed for the preparation of test specimens depicting the solid self-pierce riveting process, which allows the evaluation in X-ray computed tomography of defects such as delamination. Correlations of process influences and material variants are determined with the damage so that they can be minimized. In quasi-static and cyclic tests the extent of damage on laminate strength and load carrying capacity of joints will be investigated.

Load-carrying capacity of combined brazed butt joints

The special features of operation of combined brazed butt joints under loading are investigated. It is shown that to increase the load-carrying capacity of these joints, it is necessary to increase the number of steps in joints. The experimental results show that the thickness of the brazed joint in the butt and lap parts of the joint is an important design parameter which controls the efficiency of the stepped joint. An increase in the number of steps reduces the strength of the effect of natural strength of the brazed joint on the limiting load-carrying capacity of the butt joint.

단면결손에 따른 고장력볼트 체결부의 내하력 변화에 관한 연구

This study conducted a static tensile test in order to prevent the lowering of load carrying capacity caused by critical sections made by over bolt holes in the base plate and the cover plate of steel member joints using high-tension bolts. The change of the load carrying capacity of joints was examined by comparison of the maximum load on joint fracture obtained from the tensile test with critical section rate and design strength. According to the results, the rate of decrease in strength was higher when the critical section rate was high, and in particular, decrease in strength was affected much more by critical sections in the base plate than by those in the cover plate. In high-tension bolt joints using over bolt holes for the base plate and the cover plate, load carrying performance was somewhat lower than that in joints using standard bolt holes, but the maximum tensile strength on facture was over 15% higher than design fracture strength. According to the results of this study, the use of over bolt holes in high-tension bolt joints had an insignificant effect on the lowering of load carrying capacity, so the allowance of over bolt holes in the joints of steel members is expected to enhance to the economy and efficiency of the works.

Analysis of the Load-Carrying Capability of the Casing Plug Joint of Steel Tube Structures Considering the Contact Effect

Nonlinear finite element model analysis of the casing plug joints of steel tubular has been realized by ANSYS software. The law of load-carrying capability and stiffness of joint are separately gained by changing the ratio of length and diameter (R/L) and the ratio of the casing length and the main tube length (l/L). The influence of the casing thickness on the load-carrying capability and stiffness are also discussed. The results indicated that the load-carrying capability and stiffness of the joints both increase with the ratio(R/L) increment and the ratio of the casing length and main tube length (l/L). When the main tube thickness is equal to casing thickness, the load-carrying capacity of joints achieves the most.

Effect of interface gap on load–slip characteristics of timber joints fabricated with multiple nails

An experimental program, exploratory in nature, has been carried out to investigate the effect of interface gap on the load–slip behaviour of joints fabricated with multiple nails. In total, 320 joint specimens have been tested. Modification factors are developed to account for the effects of number of nails and interface gap on the overall load-carrying capacity of joints with multiple nails. The current practice for the design of nailed joints is that a joint fastened together with multiple nails in a row, regardless of the interface characteristics of that joint, carries lateral load equal to the product of the lateral-load capacity of the corresponding joint with a single nail and the number of nails in a row of the joint. The findings of this investigation indicate this practice to be somewhat of an overestimation of the overall capacity of the joint. Key words: design, interface gap, interface friction, joint slip, loads (forces), modification factors, multiple fasteners, nailed joints, stiffness, structural engineering, tests, timber construction.

鋼管接合部の局部変形に関する実験的研究 (その 2)

There are several methods for analysing the local behavior of perpendicularly welded tubular joints whose test results were reported in Part 1, here, the application of theoretical solution of cylindrical shell concerned with similar problem and the approximate method assuming a ring with specific wide are investigated. The results of this study are compared with several present design techniques. As the result of these procedure it is shown that the local strength of chord member in perpendicularly profiled joint is given by below expressions approximately. P_max=(80α/π+2)σ_y・Z/R…(2.29) P_y=(60α/π+2)σ_y・Z/R…(2.30) where, α=sin^-1d/D radian Z=B_s・(T^2)/6, B_s=1.52R√<R/T> Above expressions are applicable to chord members which the ratio D/T, between outside diameter and the wall thickness, is within the limits of 15 to 40. Next, we investigate such a case that axial force of branch tube is tensile. Test results show that the load carrying capacity of joints with tensile branch is one and half of those with compressive branch. Although the maximum load is decided by fracture in the heat affected zone of weld, in this case it is also possible that the strength is expressed with the same parameter in the case of compressive branch. This fact implies that the strength of weld is affected by the stress concentration caused by local deformation of chord member.