后张无粘结预应力楼板开洞改造与加固

Strengthening and opening retrofitting of post-tensioned plates prestressed with unbonded tendons

为满足某7层办公楼改造为公寓式宾馆所需增设两部电梯的要求,需在该房屋的宽11.7m、长13.2m的无粘结预应力混凝土板角部开设2.28m×4.25m洞口。改造需要解决两个关键问题。一是构建电梯井道结构,拟开洞口边后置了混凝土框架,待后置框架结构形成后,采用＂先锚后断＂技术,实现拟开洞口区域的板内双向预应力筋在后置梁上的永久锚固,并保证开洞后板内无粘结筋的有效预应力水平,最后,逐步剔除各层拟开洞区域混凝土及非预应力筋,完成洞口开设;二是针对开洞后的预应力板由四边支承矩形板转变为角部缺失的异形板,分析了开洞后预应力板弯矩分布,介绍了CFRP加固的思路和实施方案。

Two elevators will be arranged in an apartment hotel,which was retrofitted by a 7-story office building. Thus the rectangular opening（ 2. 28 m × 4. 25 m） for elevators shaft needs to be post-built in the corner of the post-tensioned concrete plate,which is a rectangular plate having 11. 7 m-width and 13. 2 m-length. There are two essential issues required to be solved. One is to construct elevator shaft. Reinforced concrete frames were applied to strengthen the plate with opening.After the frame was built,＂cut off after anchoring＂method was used,to achieve the unbonded tendon in two directions succeed to anchor to post-built beams,and to ensure the effective prestress level of the unbonded tendon in the opening plate. Finally,the concrete and steel bars in the openings were progressively demolished; The other one is to concentrate on post-tensioned plates whose supporting conditon was converted from four-edges simple support to six-edges support after opening. The moment distribution of the post-tensioned plate without a corner was complicated compared to the plate originally simply supported in the brick walls. The scheme and details for CFRP strengthening of the opening plate were described.