بررسي قابليت اعتماد برش‌گيرهاي پيچي-اصطكاكي (HSFGB) و رفتار احتمالاتي تيرهاي مركب با اين نوع برش‌گيرها

In recent years, the high-strength friction grip bolt (HSFGB) shear connectors in steel-concrete composite beams as deconstructable connectors are of great research interest since they are aligned with sustainable construction. However, the lack of design guidelines and regulations for this type of composite system has limited their use in design and construction. Therefore, the main objectives of this study are to understand the probabilistic behavior of composite beams with deconstructable high-strength friction grip bolts and to analyze their safety while considering uncertainties. To achieve these objectives, the resistance relationship of the deconstructable high-strength friction grip bolts is presented, and a suitable partial safety factor is eva‎luated. Additionally, probabilistic analysis of the composite beam and the eva‎luation of its flexural strength resistance factor are discussed. In this regard, a three-dimensional finite element model of the push-out test for the high-strength friction grip bolt is developed and validated against experimental results. Sensitivity analysis and the development of Plackett-Burman (PB) design method are then performed to identify the influence of different parameters on the behavior of these friction grip bolts and the factors affecting their ultimate resistance. Furthermore, statistical analyses are employed to provide a predictive equation for the ultimate resistance of deconstructable high-strength friction grip bolt. The implementation of a reliability analysis in compliance with the safety approach led to a partial safety factor of 1.52 for the design of such friction grip bolts, ensuring an acceptable level of safety for the proposed design equation. The next step involved a three-dimensional probabilistic finite element analysis to investigate the effects of material and shear connector uncertainties on the flexural behavior of composite beams. First, the statistical properties of the HSFGBs were eva‎luated. Then, a suitable finite element model was developed that simultaneously offered sufficient accuracy for behavior eva‎luation and computational efficiency for a large number of probabilistic analyses. Three methods were used for the probabilistic analyses: Monte Carlo simulation (MCS), Latin hypercube sampling (LHS), and Rosenblueth point estimate (RS) method. Since design regulations based on the Load and Resistance Factor Design (LRFD) method incorporate the shear connector safety factor as part of the overall beam resistance factor, it is crucial to investigate the influence of the connector type on the flexural performance of these beams. To this end, after developing and validating a three-dimensional finite element model for composite beams, sensitivity analysis, database expansion, and reliability analyses were performed for this type of beam. The results showed that the reduction factor for flexural resistance of composite beams with HSFGBs and full shear connection is close to the value recommended in AISC 360-22 for composite beams with welded shear connectors. However, using the code-specified reduction factor for composite beams with HSFGBs and partial shear connection is non-conservative.

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