Focal adhesion (FA) assembly, mediated by integrin activation, responds to matrix stiffness; however, the underlying mechanisms are unclear. Here, we showed that β1 integrin and caveolin-1 (Cav1) levels were decreased with declining matrix stiffness. Soft matrix selectively downregulated β1 integrin by endocytosis and subsequent lysosomal degradation. Disruption of lipid rafts with methyl-β-cyclodextrin or nystatin, or knockdown of Cav1 by siRNA decreased cell spreading, FA assembly, and β1 integrin protein levels in cells cultured on stiff matrix. Overexpression of Cav1, particularly the phospho-mimetic mutant Cav1-Y14D, averted soft matrix-induced decreases in β1 integrin protein levels, cell spreading, and FA assembly in NMuMG cells. Interestingly, overexpression of an auto-clustering β1 integrin hindered soft matrix-induced reduction of Cav1 and cell spreading, which suggests a reciprocal regulation between β1 integrin and Cav1. Finally, co-expression of this auto-clustering β1 integrin and Cav1-Y14D synergistically enhanced cell spreading, and FA assembly in HEK293T cells cultured on either stiff ( > G Pa) or soft (0.2 kPa) matrices. Collectively, these results suggest that matrix stiffness governs the expression of β1 integrin and Cav1, which reciprocally control each other, and subsequently determine FA assembly and turnover.

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Many structural members, for example, cold-formed steel members, hot-rolled steel members, and composite beams were extensively used in steel construction due to economic development in cities building design. This was to allow flexible installation of ductwork, piping and other systems. Substantial research has been performed on Channel and Zee cold-formed steel sections, but the papers on Hat section steel purlins turned out to be few only, especially Hat-purlin with perforations. Hence, numerical study on cold-formed Hat section steel purlin with perforation was carried out to investigate the effect of perforation to bending behaviour of such sections. Finite element method using LUSAS software was chosen to carry out the research study. Five different perforation shapes were selected, which were circle, diamond, C-hexagon, square and elongated circle. Perforation depth was fixed at 0.5D2, where D2 is the inclined web depth of the section. The results showed that perforated section had lower bending moment than that of the section without perforation, with a percentage difference of not more than 4%. Most of the perforated sections had similar bending characteristic despite of the difference in perforation shapes, where the yield moment difference was less than 2%. Critical opening length played a crucial role in affecting the bending behaviour of section. Furthermore, the location of perforation also influenced the bending behaviour of Hat-purlin. Regardless of perforation spacing, the perforated sections with equal number of perforations behaved similar elastic characteristic before yielding. Section with diamond perforation had higher bending moment than other perforated section whereas section with elongated circle perforation had the lowest bending moment. The presence of perforations gives minor effect on the bending behaviour of cold-formed steel Hat-purlin.

This paper presents a numerical investigation on the effect of perforation to the steel purlin on bending behaviour. In order to reduce the weight of steel sections, web profile with openings has been introduced in the construction industry, so does the purlin. However, there is no research done on the C-purlin with perforation. Hence, 33 nonlinear analyses were carried out to investigate effect of perforations to the steel purlin on bending behaviour. Yield moment of the steel purlin with and without perforation will be determined. And, effect of various perforation shapes and size on bending behaviour is investigated. Finite element model was developed using software LUSAS. C-channel steel section without opening is used as a control specimen. The results are expressed in term of yield moment. The results show that the edge distance from the opening to the support plays an important role in affecting the moment capacity of C-purlin. Increasing the opening spacing would increase the moment capacity. Number of openings also affects the moment capacity of the section. Octagonal shape with 0.40H and e= 350 mm shows the highest yield moment value with 16.318% higher than that of section without opening. In conclusion, perforation increases the moment capacity of the C-steel purlin.