A full scale mixed structure model with 2 test floor slabs was built in real environment to study the influ-ence of temperature and humidity fluctuation on non-service-load cracks in cast-in-situ RC floor slab. Outdoor and in-door temperature, humidity and the strain of slabs concrete before and after cracking without service load were measured for five months. The test results indicate that fluctuation of outdoor temperature has obvious influence on the strain of the floor slab, which leads to stress fatigue in slab concrete, and the slab can crack easier, but the humidity fluctuation has lit-tle influence on slab cracking; comparing with the temperature and humidity fluctuation in outdoor, the temperature and humidity fluctuation in indoor show the regularity of decrement and delay;in addition, the beams and walls on the edges of floor slab has a certain of shrink, so the boundary restraint to the shrinkage of floor slab is limited and the tensile stress in slab is smaller; It is helpful to reduce cracking in floor slabs by taking better thermal insulation measures to external surface of a building.%为了研究室内外温度、湿度波动对现浇钢筋混凝土楼板非使用荷载裂缝产生的影响，在实际环境中设计建造了足尺的砖混结构模型，对室内、室外的温度和湿度及无使用荷载作用楼板开裂前后板面混凝土的应变进行了5个月的测量。实测数据分析表明，室外温度波动对楼板混凝土应变有明显影响，可以使楼板发生应力疲劳而提前开裂，但湿度波动对裂缝影响较小；室内的温度和湿度波动与室外相比，呈现明显的衰减和滞后规律；楼板边界的梁和墙体也存在收缩应变，其对楼板收缩变形的约束有限，由此而产生的楼板拉应力较小；做好建筑物外表面隔热处理对减少楼板开裂是有益的。
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