输电杆塔开挖类基础基于极限状态设计的作用组合选择研究

Research on selection of action combinations based on limit state design for excavated foundations of transmission pole and tower

合理选用由杆塔结构传递而来的作用效应是地基基础设计的重要前提,为了确定输电杆塔开挖类基础基于极限状态设计的作用组合值,分析了输电杆塔对基础的作用特点,并针对上部杆塔对基础作用的3种主要工况,利用静载荷试验结果研究了开挖类基础与地基结构体系的承载特性、破坏特征及其易超越的主要极限状态,并给出了地基基础体系设计时所采用的作用组合,研究表明,上拔和倾覆工况下常规条件开挖类基础承载过大时表现为脆性破坏,按承载能力极限状态设计,采用由可变荷载控制的基本组合;下压工况下开挖类基础的荷载与位移关系曲线一般为非陡降型,按正常使用极限状态设计,主要采用标准组合和准永久组合。

Reasonable selection of action combinations is an important prerequisite for ground and foundation design. To determine action combinations based on limited states design for excavated foundations of transmission pole and tower, force characteristic of foundations was analyzed. According to the main three action conditions on foundations of transmission pole and tower, bearing and failure characteristic and easier exceeding limited states of structural system including excavated foundation and ground were studied, and action design combinations of the ground-foundation system were provided. The failure characteristic of excavated foundations bearing too much load is brittle under uplifting or overturning conditions, and fundamental combination controlled by variable load are adopted as required by ultimate limit state design. The relationship curves between load and displacement of excavated foundations are non-steep-fall under downward force condition, based on serviceability limit state design, characteristic or quasi-permanent combinations should be mainly used.