Soon Huat Tan

Channel frames with semi-rigid joints

Abstract The analysis and tests of cold-formed thin-walled channel frames including nonlinear flexible or semi-rigid connection behaviour is presented. The semi-rigid connection behaviour is modelled using a mathematical approximation of the connection flexibility or moment–rotation relationship. Local instability in the form of local buckling of members is included in the analysis. The full response of the frame, up to the collapse load, can be predicted. Experimental investigation was carried out on a series of simple double storey symmetrical frames with the purpose of verifying the accuracy and validity of the analysis. Agreement between the theoretical and experimental results is acceptable. The investigation also shows that effect connection thickness on the strength of thin-walled frames is less significant compared to that of the members thickness and lip size. The findings also provide further insight into the study of structures, where interaction between flexible connections and phenomenon associated with thin-walled members are present.

Connections in cold-formed thin-walled structures

The nonlinear behaviour of connections employed in cold-formed thin-walled structures are determined experimentally and a mathematical model is developed to represent the connection behaviour. The generalized mathematical model gives a close representation of the experimentally obtained moment-rotation relationships for the connections investigated. The moment-rotation relationships of all the connections investigated were found to be nonlinear.

Subassemblage with semi-rigid joint

The finite element technique is employed to analyse and perform a parametric study on cold-formed thin-walled column subassemblage with a semi-rigid joint. Besides large displacement, the analysis also considers the area of contact between the fastener, connector and the member in the vicinity of the joint. Results obtained from a series of preliminary experimental tests are used to verify and validate the accuracy of the analysis.

Semi-rigid connection in cold-formed thin-walled structures

Abstract The nonlinear behaviour of connections used in cold-formed thin-walled structures is determined experimentally and represented in a mathematical form. Local effects due to the thinness of the connected members affecting the connection moment-rotation behaviour are also studied and discussed. The mathematical model developed gives a close representation of the experimentally obtained moment-rotation relationships for the connections investigated. The moment-rotation relationships for all the connections investigated were found to be nonlinear.

CROSS-SECTIONAL AREA MEASUREMENT OF SOFT TISSUES IN VITRO: A NON-CONTACT LASER SCAN METHOD

Measurements of cross-sectional areas (CSAs) of soft tissues such as tendons and ligaments allow for the evaluation of the biomechanical properties of the tissue. Underlying in vitro techniques are data reduction approaches for determining the average thickness of the tissue and the assumption of the geometry of the cross-section, i.e. circular or elliptical. However, tissue distortions, sagging, and concavities could affect the reliability of these techniques, since these features may not be accounted for adequately. To address some of the concerns faced by these techniques, a non-contact (non-destructive) laser scan technique has been developed. In this technique, a laser scans along the axis of the tissue, a coordinate measuring machine simultaneously locates the corresponding point on the tissue based on the detection of reflected (attenuated) intensity, and, finally, computerized image analysis reconstructs the morphology of the tissue. This technique was applied to patellar tendons (PTs) from New Zealand rabbits. The scanning time for each PT was less than 2 minutes. Reconstructed three-dimensional surface plots revealed microconcavities consistent with images seen under optical microscopy. CSAs of these PTs were determined for repeatability and precision; results from a conventional approach which estimated the corresponding CSAs based on the average thickness and the assumption of ellipsoidal cross-sectional geometry were also determined for the purpose of comparison. Based on the standard cuboid model, the error between the laser technique and the conventional approach was within 0.4%; the reproducibility of the laser technique was within 2%.

Plastic behaviour of two-dimensional regular hexagonal structures with bilinear and uniaxial strength asymmetry in cellular materials

An elasto-plastic micromechanical model of the two-dimensional regular hexagonal structure was developed. General analytical expressions for the incremental constitutive relations were derived in terms of parameters defining the architecture and material of an internal beam. Non-linearity of the structure was introduced by considering the elastic—linear strain hardening behaviour of each internal beam, in which uniaxial strength asymmetry of the cellular material was accounted for. The plastic stress—strain relationship of the structure under any loading conditions can therefore be analysed by localized beam deformation. The results show that the bending deformation of the internal beam dominates under uniaxial stress loading conditions, however, the axial displacement dominates under the uniaxial strain conditions. The structure will present different behaviours under different loading conditions. The corresponding stresses under the uniaxial strain condition are greater than those under the uniaxial stress condition. The analyses also show that the volume fraction is highly correlated with the elastic constants and yield stresses of the structure. The denser the structure, the higher the moduli and yield stresses.

Flexibly-connected thin-walled framework

Abstract The overall behaviour of a structure depends not only on the member behaviour in isolation, but also on how the members interact. For a structure composed of cold-formed thin-walled members, the occurrence of various buckling phenomena, for example, local and torsional flexural buckling, is possible. Coupled with the non-linear characteristic of the connections, the overall behaviour of the structure cannot be accurately predicted or analysed by conventional design and analysis. In this paper, the analytical approach employed to deal with flexibly-connected cold-formed thin-walled framework systems is outlined. Local and torsional flexural buckling of members, connection strength and stiffness, shortening due to flexure and plasticity of the members are considered in the analysis. Experimental tests were carried out on symmetrical single and double storey frameworks fabricated from cold-formed thin-walled plain channel members and connections of varying strength and stiffness. The experimental results are compared with the analytical predictions.

A normative anatomic study of the glenohumeral joint and rotator cuff tendons

Introduction: The purpose of this study is to determine normative values relating to the glenohumeral joint and rotator cuff tendons namely length, width, thickness and footprint of supraspinatus (SS), infraspinatus (IS), teres minor ™ and subscapularis (SC) from 19 specimens. Methods: Rotator cuff tendons and humerus dimensions were measured directly using a digital vernier calliper. In addition, moduli values of rotator cuff tendons were obtained from tensile tests on twelve cadaveric shoulders. The tendon footprints were delineated onto a tracing paper and their dimensions were calculated using digitiser software. The glenoid dimensions were obtained from marking its outline onto a tracing paper and the cavity dimensions from wax moulds. The results were tabulated and statistical analyses, including Students t-test and ANOVA, were performed. Conclusion: The normative anatomic values obtained can be used in finite element modeling, computer simulation, design of implants and surgery.

Effects of Tears and Repairs on Supraspinatus Strain Measurements

Aim: This study aims to simultaneously measure the bursal and articular strains on the supraspinatus and demonstrate the effect of tears and repairs with an intact glenohumeral joint.

Simultaneous Strain Measurements of Rotator Cuff Tendons at Varying Arm Positions and The Effect of Supraspinatus Tear: A Cadaveric Study

Aim: This study aims to measure strains on the different rotator cuff tendons simultaneously and demonstrate the effect of supraspinatus tear on other cuff tendons with an intact glenohumeral joint.