张拉施工方案对预应力混凝土多层框架梁设计的影响

Influence of construction processes upon beam performance of multi-story prestressed concrete frame

多层预应力混凝土框架结构的施工多采用“逐层浇筑,逐层张拉”或“数层浇筑,数层张拉”的施工方案,而现行设计方法是假定“整体浇筑,整体张拉”的施工方案进行设计计算.显然设计的计算模型与实际施工方案不吻合.由于在“逐层浇筑,逐层张拉”时,下层张拉对上层未建结构内力无影响,因此结构内力的设计值与实际值将出现偏离.本文根据结构力学原理分别建立了现行设计法中预应力综合弯矩和次弯矩偏离实际值大小的相对差公式;结合施工的具体情况对预应力混凝土框架梁进行了计算分析.框架梁内力的设计值偏离实际值的大小受张拉施工方案、所在层、所处部位、结构的跨数、梁柱线刚度比、荷载等各种因素的影响.当采用现行设计法以整榀框架为计算模型时,按本文提供的方法对框架梁控制截面处内力进行修正,可以满足抗裂和承载力的要求.

Applying the principle of structural mechanics, the formula for estimating the relative deviation of internal force from the normal design to the reality according to construction processes are provided. Some factors such as floors, spans, sites, loads and the ratio of column to beam having influence upon structural performance are discussed. By calculated MPCF, the resultant and secondary moment taken from varied construction process are compared to that of designing model. Then the relation of the relative moment deviation and the ratio of column to beam are drawn. It is suggested that calculated model should accord with the construction process when designing MPCF. The simple design method is put forward to satisfy the requirement for ultimate cracking capacity during normal service and ultimate bearing capacity of prestressed beams in MPCF.