The Effects on Screw Fasteners Spacing on Flexural Behavior and Strength Capacity of Cold-Formed Steel Built-Up Box Sections

The capacity and behaviour of cold-formed steel built-up sections are affected by the arrangement of the connections. This study aims to determine the effect of the screw spacing to the bending capacity and behaviour of the cold-formed steel built-up box section which made from lipped-channel (1.0 mm thick, 81 mm web height, 8.5 mm lip height, upper and lower wing width 38 mm and 40 mm). A total of 19 beams with a length of 1200 mm each are subjected to pure bending moments by applying two point loads spaced 600 mm in the midspan. The screw spacing variations in the moment span are 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, 328 mm, and 350 mm. The test results show the average of bending capacity of the beam test is increasing with the reduction in screw spacing while the screw configuration also affects the beam capacity. Analysis of the bending capacity using the effective width method and the direct strength method based on AISI S100-16 gives very conservative results. The failure mode of the built-up box sections were observed in the form of local buckling, distortion, and lateral-torsional buckling.

A Method to Estimate Inherent Deformation in Thin-Plate Welded Joint With Buckling Distortion

It has been recognized that the elastic finite element method based on inherent strain theory is an effective tool to estimate the total welding deformation of large and complex welded structures. When this computational approach is employed to predict welding deformation in a welded structure, one prerequisite is that the inherent deformation of each welded joint should be known beforehand. The inverse analysis method based on the combination of measuring technology and finite element method has been proposed to obtain the inherent deformations for various welded joints. However, if buckling distortion occurs in a welded joint, it will be difficult for this method to accurately obtain the inherent deformation especially in thin-plate joints. To overcome this difficulty, an improved inverse analysis method with the help of cutting technique was developed in the current study. The effectiveness of the proposed method was demonstrated through obtaining the inherent deformations in an Al-alloy thin-plate joint with buckling distortion.

Buckling of Stiffened Panels and Its Mitigation

The increased use of thin plates, like in ships for high-speed operation, results in significantly increased distortion. In-process control of welding distortion is more desirable than post welding rectification from the point of manufacturing efficiency. This can be achieved by suitably designing and also implementing one or more of the distortion control measures as is suitable for a particular manufacturing situation. In this study, an investigation on buckling phenomenon in fabrication of stiffened panels was carried out. Analytical formulae were used to calculate the weld-induced compressive stresses. Critical buckling stresses considering appropriate buckling coefficient for typical stiffened panels as used in shipbuilding practice were calculated. The predictions from these analytical tools were compared with experimental observations. The experimental results compared fairly well with those of the calculated ones. In the present study the panel design aspect as well as thermomechanical tensioning scheme were studied with regard to buckling mitigation. It was observed that when choosing suitable stiffener spacing in conjunction with plate thickness, buckling distortion can be significantly reduced. Distortion mitigation through thermomechanical tensioning was also found to an effective yet simple-to-implement method of buckling distortion control. However, further investigation is necessary toward fully establishing the method of thermomechanical tensioning. Once this method is established, this pre-tensioning technique can be applied as an active in-process control method to avoid buckling distortion in stiffened panels.

Characterisation of Residual Stress State and Distortion in Welded Plates Stress Engineered by Local Mechanical Tensioning

Local mechanical tensioning is one of the most efficient and industrially relevant stress engineering techniques to modify weld residual stress field and subsequently reduce buckling distortion. However, application of rolling load and its magnitude need to be optimised for an energy efficient rolling process. In the present study gas metal arc butt welded plates of low carbon mild steel were rolled by a dual roller in different rolling configuration (top and reverse side rolling) and with different magnitude of rolling load. All the plates were rolled post welding. Residual strain profiles of the post weld rolled plates were measured, using the SALSA strain scanner, and the in-plane stress were characterized. Average distortion of the rolled plates was correlated with the residual stress. Reverse rolling was found to be more effective in removing distortion while the stress profiles did not show any significant reduction of the peak stress.