Under-clearance of bridges is one of the major considerations when planning and designing bridges. Especially for sea-crossing bridges, under-clearance is more important for safe passage of ships. Long span cable bridges with steel orthotropic deck usually show relatively large deflections and excessive deflections may be not only disadvantageous to the clearance plan, but also a problem in bridge serviceability. The clearance of sea-crossing bridge is designed with air draft from the waterline to top of mast, ship’s trim, psychological free space, sea level, height of wave and bridge deflection by live loads. At design stage, bridge engineers need a live load deflection limit to ensure adequate clearance. The limitation of live load deflection is also considered for ensuring the serviceability of vibration of bridges. For vibrational serviceability, the live load deflection limit is expressed as a ratio to the span or the formula by natural frequency. On the other hand, some standards specify vibration serviceability limit by peak or root-mean-square (RMS) acceleration. The purpose of this study is to propose new deflection limit criteria for long span steel cable bridges based on analysis and long-term measurement data. Structural analysis was performed on two steel suspension and three steel cable-stayed bridges with more than 200 m of main span under design live load model of DL24 and new live load model KL510 in limit state design code. Also, the deflection limit criterion was evaluated by probabilistic method using the deflection data measured for 1 year. The results of this study are expected to be useful data for bridge engineers designing long span steel cable bridges.

在规划和设计桥梁时，桥梁的间隙不足是主要考虑因素之一。特别是对于跨海桥梁，通行不足对于船舶的安全通过更为重要。具有正交异性钢甲板的大跨度斜拉桥通常会出现较大的挠度，挠度过大不仅不利于通行方案，而且还会影响桥梁的使用寿命。跨海大桥的净空设计为从吃水线到桅杆顶部的吃水深度，船舶的纵倾，心理自由空间，海平面，波浪高度和桥梁在活荷载作用下的挠度。在设计阶段，桥梁工程师需要有效载荷挠度极限以确保足够的间隙。为了确保桥梁振动的可服务性，还考虑了活载挠度的限制。对于振动使用性，活载荷挠度极限表示为与跨度之比或公式与固有频率之比。另一方面，某些标准通过峰值加速度或均方根（RMS）加速度来指定振动适用性极限。本研究的目的是根据分析和长期测量数据为大跨度钢索桥提出新的挠度极限标准。在极限状态设计规范下，在DL24的设计活荷载模型和新的KL510活荷载模型下，对主跨度超过200 m的两座钢悬索桥和三座主跨度的钢斜拉桥进行了结构分析。同样，使用1年测量的挠度数据通过概率方法评估挠度极限标准。