The maximum pull-out force of the anchor bolt ranges from 22.5 kN to 30 kN, with a total slip amount reaching 1 mm to 1.2 mm. During each test, the first significant sliding between the bolt and the concrete releases energy. After this initial slip, the system rebalances and continues to resist tension. This behavior may occur again or only once, depending on the conditions, but ultimately, failure occurs as the bolt slip increases. In the new composite shell structure, the pull-out resistance of the bolts plays a critical role in determining the bending capacity of the joints. Similar to the bond between steel and concrete in traditional reinforced concrete systems, the pull-out resistance of the bolts is influenced by multiple factors, such as concrete strength, anchor length, and bolt diameter.
In the computational model analysis for the composite component, the bending moment capacity depends on two main aspects: the steel-concrete composite section and the bolted joint section. For section BB, the bending resistance can be calculated using the following formula:
$$ M = R_{st} A_t \left(h_0 - \frac{x}{2} - c\right) + R_{sb} A_b \left(h_0 - \frac{x}{2}\right) $$
Where:
- $ R_{st} $ and $ A_t $ are the average stress and area of the steel plate on one side,
- $ R_{sb} $ and $ A_b $ are the stress and area of the bottom plate,
- $ c $ and $ x $ represent the center distance of the side plates and the compressed height of the section,
- $ f_{cm} $ is the compressive bending strength of the concrete,
- $ h_0 $ is the overall height of the cross-section.
For section AA, the elements on both sides of the bolt joint are assumed to be rigid bodies, while other parts of the structure do not rotate. When a bending moment is applied, and if the corner of the node is denoted as H, then:
$$ f_{cm} b x = F \cos H $$
$$ M = F (h_0 - d - \frac{x}{2}) \cos H $$
Here, $ F $ represents the tensile force in the bolt, which consists of two components: the pull-out force of the side panels and the anchoring force of the bolt. The total force can be expressed as:
$$ F = F_b + A F_s $$
Where:
- $ F_b $ is the anchoring strength of the bolt in the concrete,
- $ F_s $ is the tensile strength of the side panel,
- $ A $ is a reduction factor that accounts for the fact that $ F_b $ and $ F_s $ typically do not reach their maximum values simultaneously.
Based on experimental results, when the anchor length is sufficient, $ A = 0.3 $; otherwise, $ A = 1 $. It is clear that $ F < f_t $, indicating that the system reaches its limit before full capacity is achieved.
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