根据 ACI 进行挡土墙设计检查 318-19
在混凝土悬臂挡土墙设计过程中, 第一步是定义 初步尺寸 并检查 稳定 这个初步几何反对 倾覆, 滑行, 和轴承. 完成这些稳定性检查涉及计算作用在挡土结构上的所有力. 那些负载, 考虑因素时, 是对混凝土挡土墙进行设计检查并确保尺寸和提供的钢筋所需的输入, 将能够承受极限状态载荷. Using our Retaining Wall Design Software, it is possible to perform the stability checks required during the process of a concrete retaining wall design.
综上所述, 对混凝土挡土墙不同组件的设计检查包括:
- 干
- 临界区: 位于茎基部, 在挡土墙底座的表面. For shear strength check, ACI 318 allows using the section at a distance d from the base as the critical one.
- 作用力: 滞留土壤主动压力和来自超载载荷的附加压力.
- 检查效果: Flexure and shear at the critical section cantilever retaining wall’s stem.
- 脚跟
- 临界区: 位于立柱与墙基的交界处. For shear strength check, ACI 318 allows using the section at a distance d from the interface as the critical one.
- 作用力: 保留土壤重量, heel self-weight, 和垂直附加费. Soil pressure below the base could be included, but is usually neglected for being conservative.
- 检查效果: Shear and flexure at the critical section cantilever retaining wall’s heel.
- 脚趾
- 临界区: Located at the face of the stem. For shear strength check, ACI 318 allows using the section at a distance d from the face of the stem as the critical one.
- 作用力: 承受脚趾下方的压力. 作用于脚趾以上的被动土自重通常被忽略, 因为它可能会腐蚀或被移除.
- 检查效果: Shear and flexure at the critical section cantilever retaining wall’s toe.
- 剪切键 (如果包括)
- 临界区: 位于剪力键与墙基的交界处.
- 作用力: 被动土压力.
- 检查效果: Shear at the critical section cantilever retaining wall’s key.
Load Factors as per ACI-318
When performing a design check on a concrete cantilever retaining wall as per the requirements of ACI-318, all the external forces that act on the structure and generate an internal force at the critical section, are factored in according to their nature, 如下:
- For lateral earth pressures, due to the soil’s weight and additional loads, the factor for calculating ultimate state loads is \(1.6\)
- For the structure’s self-weight, the factor for calculating ultimate state loads is \(1.2\)
Those factors reflect the probability of exceeding the calculated “exact” 值, for the case of the structure’s self-weight, the probability of being exceeded is quite low, and therefore the factor is close to 1.0, 然而, external forces such as the weight and lateral pressure of the retained soil and the surcharges are more likely to take a higher value, and that’s why the load factor is closer to 2 than to 1.
Resistance reduction factors as per ACI-318
Apart from increasing the forces acting on the structure, its resistance is also reduced by applying some factors, following the LRFD (负载和阻力系数设计) approach. Each resistance value is reduced as follows:
- For flexure resistance, assuming the member is tension controlled, the reduction factor is \(0.9\)
- For shear resistance, the reduction factor is \(0.75\)
Design requirements as per ACI-318
Comparing the ultimate state internal forces to the reduced member resistance to that internal force, it is possible to determine whether the provided concrete section and embedded reinforcement are strong enough or not. This can be expressed in the following two equations:
- For nominal moment resistance \(M_n\) and ultimate state moment \(M_u\)
\(\φ \; M_n \geq M_u\)
- For nominal shear resistance \(V_n\) and ultimate state shear force\(V_u\)
\(\φ \; V_n \geq V_u\)
Additional requirements as per ACI-318
Apart from fulfilling the requirements mentioned above, ACI-318 presents some additional requirements for successfully completing a Concrete Retaining Wall Design:
- The reinforcement calculated for flexure on any component of the structure is checked against the beam minimum required flexural reinforcement. According to ACI-318, the beam formula is used instead of the one-way slab formula because of the lack of redundancy:
\(一个_{s, \; 分} = frac{3 \sqrt{f'_c}}{f_y} b_w d\)
- Once the required steel area for flexure is calculated, the section is checked to ensure it is tension controlled, in other words making sure that the reinforcement steel yields before concrete cracks:
\(\varepsilon_t = \frac{\varepsilon_c}{C}(d-c) > 0.005\)
在哪里 \(c = \frac{一个}{\测试版_1}\), \(a = 1.31 A_s\), \(\varepsilon_c = 0.003\) (assuming concrete cracks at that strain level), 和 \(d\) is the distance from the compression edge to the center of the reinforcement in tension.
- Some minimum transverse reinforcement area is calculated for each component of the Cantilever Concrete Retaining Wall, using the ratios given in Table 11.6.1 of ACI-318
- Development and splice lengths are also calculated for each component of the Cantilever Concrete Retaining Wall, using the criteria given in 25.4.2 of ACI-318
SkyCiv Retaining Wall Calculator
SkyCiv 提供免费的挡土墙计算器，它将检查挡土墙的滑动并对挡土墙进行稳定性分析. 付费版本还显示完整的计算, 所以你可以一步一步看到, 如何计算挡土墙抗倾覆的稳定性, 滑动轴承! With the paid account, it is also possible to perform design checks as per ACI on the retaining wall.
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