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Research on the effect of bolt end plate connection and its calculation
In order to minimize excessive force, reduce the thickness difference between the column edge and the end plate, and limit the elongation of the end plate, it is essential to incorporate stiffeners at the joints for improved performance. Additionally, using multiple smaller diameter bolts has proven more effective than relying on fewer larger bolts, as it distributes the load more evenly and reduces localized stress. For lightweight portal steel frame structures without stiffeners or with thin end plates, the influence of applied forces must be carefully considered. From the actual stress analysis of the joint, it is evident that the node is not solely subjected to axial force. In this simulation, a concentrated force was applied at the beam end of a group of nodes, revealing that the maximum stress occurs in the depth direction of the end plate, while the width direction shows minimal stress. However, some nodes exhibited longitudinal stress exceeding 50% of the depth direction stress, particularly between the bolt positions, which is attributed to component deformation and bolt compression.
From the simulation results, it is clear that the maximum end force is not uniformly distributed along the edge of the end plate as conventionally assumed. Instead, the highest concentration of force appears between the bolts, with the distribution area located near the edges of both the bolts and the end plate. This effect becomes more pronounced when the end plate is thin or experiences significant elongation. Among all tested specimens, two (C and E) ultimately failed due to excessive deformation of the end plate, resulting in overextension. Thin end plates and large elongation were identified as the primary causes of stress concentration. The failure modes observed in other specimens included bolt yielding, damage at the beam and column edges, web yielding, excessive node rotation, and joint failure.
Under the same loading conditions, the end plates in test pieces C and E experienced the highest forces, whereas those in test piece H showed the least pulling force. The simulation analysis also revealed that as the concentrated load at the beam end increased, the force grew linearly, but the rate of increase slowed at higher loads. This behavior is attributed to the deformation of the end plate and column edge under high actual loads. The material properties in the simulation followed a multi-linear stress-strain relationship, and as the load increased, the material entered the plastic stage. To simplify calculations, the simulated data was fitted using the least squares method. This result suggests that current Chinese standards may not fully capture the non-uniform plastic development in planar end plates, making them somewhat conservative in certain scenarios.
Due to the long length of the prestressed beam (slm), the mid-span loss of prestress is significant—approximately 5 meters. To address this, the design requires tensioning at both ends, along with super-tensioning and compensation methods. A key challenge in prestressed beams is the reverse arch caused by the absence of roof loads (excluding the self-weight of the structure and slab) during construction. Therefore, construction planning includes checking and calculating the arching and mid-span loading for each span.
Special attention must be given to potential interference between prestressed and non-prestressed tendons at the anchorage points, as well as the selection of appropriate anchors. Prestress design should be tailored to specific conditions, such as the relationship between the support width and the anti-bending point of the prestressed beam, and the alignment of the support centerline with the bending moment at the support. Accurately calculating the prestressed tendons is crucial for the design process, ensuring that the structure meets the basic requirements for ultimate load capacity, deflection control, and crack resistance under normal service conditions. It is also important to optimize the design to reduce the number of prestressed tendons used. Prestressed beams offer good ductility, and the reverse arch generated from prestressing remains manageable, leading to cost savings and efficient use of resources.