A numerical investigation into stripping failure of bolt assemblies at elevated temperatures

Abstract

A detailed finite element (FE) study is presented investigating the factors affecting the failure modes of high strength and stainless steel bolt assemblies under tensile force at ambient and elevated temperatures. Axisymmetric FE models incorporating key behavioural aspects including surface interaction and damage modelling of steel at elevated temperatures were developed. In practice, stripping failure is generally undesired because it results in premature failure of the bolt which can deteriorate rotational capacity of connections and hence compromise the robustness of steel frames. Yet, stripping failure has not been previously investigated in the open literature. In this study, the examined stainless steel bolt assemblies displayed an outstanding ductile response even when stripping failure was observed. Parameters that can govern the failure modes of bolt assemblies at elevated temperatures include the thread length in the grip (L t ), and the relative strength and friction between the mating threads. At ambient temperature, stripping was observed at certain L t lengths depending on the nut dimension deviation from the basic profile. The L t stripping failure threshold reduces with temperature for high strength bolt assemblies while the value fluctuates without a discernible pattern for stainless steel types. Increasing the relative strength and friction coefficient can reduce the L t length threshold, with the former having the greatest influence.

Experimental investigation and numerical analysis of precast reinforced concrete shear walls with shoe bolt connections

“…The test data in Table 1 were used to determine the key point of the curve. For the high strength steel bolt that had no yielding stage, due to a lack of tested stress–strain curve in the present work, its uniaxial stress–strain relationship in the FE model was defined as a multilinear form (Figure 14(c)) based on the test data in (Shaheen et al, 2020).…”

New Technique to Improve the Ductility of Steel Beam to Column Bolted Connections: A Numerical Investigation

“…The stress-strain curve for the plate material and the high strength bolt are shown in Figure 4. The damage parameters of material are defined following Pavlovic et al [24] and Shaheen et al [16], with the lowest damage evolution variable value considered during the analysis being 0.9 to avoid a sudden drop in stress at the material point, which can cause dynamic instability and convergence problems. Tables 1 and 2 illustrate the damage variable (D) and the plastic displacement (u pl ) for bolt and plate, respectively.…”

“…Tables 1 and 2 illustrate the damage variable (D) and the plastic displacement (u pl ) for bolt and plate, respectively. A detailed description of the material modelling approach can be found at Shaheen et al [16]. The FE model is validated against the connection specimens tested by Yu et al [23] at ambient temperature.…”

“…Consequently, high elongation of the bolt is required to achieve high rotational capacity of the connection [15]. In common practice, the most frequently used bolts tend to be from high-strength steel grades of 8.8 and 10.9 which reach their ultimate strength at a strain of ~0.05 [16], followed by a sudden fracture, while mild steel can achieve a strain of 0.2 [17] without failure. In addition to this, the relatively small length of the bolt leads to a reduced contribution to the connection's rotational capacity in comparison to the end plate.…”

A novel device to improve robustness of end plate beam-column connections

“…In the absence of coupon tests, the damage evolution variable D is defined by trial and error, varying the plastic displacement u pl until the post-peak behaviour is captured [10]. The damage parameters are defined following Pavlovic et al [11] and Shaheen et al [12], with the lowest D value considered during the analysis being 0.9 to avoid sudden drop in stress at the material point, which can cause dynamic instability and convergence problems.…”