The maximum pull-out force of the anchor bolt ranges from 22.5 kN to 30 kN, with a total slip amount reaching between 1 mm and 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 further tension. This behavior may repeat or occur only once, depending on the material properties and loading conditions. Eventually, the bolt will fail due to increasing slip, which reduces its load-bearing capacity.
In the new composite shell structure, the pull-out resistance of the bolt directly influences the bending resistance at the joints. Similar to the bond between steel and concrete in reinforced concrete systems, several factors affect the bolt's pull-out resistance. These include the strength of the surrounding concrete, the length of the anchor, and the diameter of the bolt. Understanding these relationships is essential for optimizing joint performance and ensuring structural integrity.
Computational modeling plays a key role in analyzing the bending capacity of composite components. The overall bending resistance is determined by two main elements: the steel-concrete composite section and the bolted connection. For example, in 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 top steel plate,
- $ R_{sb} $ and $ A_b $ are the stress and area of the bottom steel plate,
- $ x $ is the depth of the compressed concrete section,
- $ c $ is the center distance between the side plates,
- $ h_0 $ is the total height of the section,
- $ f_{cm} $ is the compressive strength of the concrete.
For section AA, the analysis assumes that the elements on either side of the bolt joint act as rigid bodies, while other parts of the structure remain unaffected. Under bending moment, if the corner of the node is denoted as $ H $, the relationship can be expressed as:
$$ f_{cm} b x = F \cos H $$
$$ M = F (h_0 - d - \frac{x}{2}) \cos H $$
Here, $ F $ represents the pulling force of the bolt, which consists of two components: the anchoring force of the bolt within the concrete ($ F_b $) and the tensile strength of the side panel ($ F_s $). The total force is given by:
$$ F = F_b + A F_s $$
Where $ A $ is a reduction factor that accounts for the fact that $ F_b $ and $ F_s $ do not typically 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 failure occurs before the full tensile capacity is reached.
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