不同持荷水平下预应力混凝土空心板耐火极限试验研究

通过15块预应力混凝土空心板底面受火耐火极限的对比试验，研究了不同持荷水平、板底是否涂抹水泥砂浆粉刷层的底面受火预应力混凝土空心板的耐火极限。结果表明，未受火对比试件和持荷受火试件均发生源于纯弯区受拉裂缝引起的弯曲破坏，持荷受火空心板的跨中挠度显著增大。有粉刷层持荷（8%~72%）p_u （p_u 为未受火对比试件极限荷载的平均值）的试件耐火极限为35~154 min；持荷小于50% p_u 有粉刷层预制空心板的耐火极限均大于43 min。无粉刷层持荷（16%~48%）p_u 的试件耐火极限为31~47 min。随着持荷水平增加，底面受火预制空心板耐火极限逐渐降低；板底涂抹粉刷层后，耐火极限明显提高。无粉刷层预制空心板在受火过程中，孔洞内温度和板顶温度均明显高于有粉刷层的预制空心板。持荷水平对孔洞内和板顶温升梯度无明显影响，但板底涂抹粉刷层对预制空心板温度场变化影响明显。

Experimental research on fire endurance of PC hollow-core slab exposed to fire under different load levels

To investigate the influences of the load level and mortar cover on the fire endurance, 15 specimens were experimentally studied. It shows that the control specimen and the exposed specimens all collapse with the flexural failure mode. The mid-span displacement obviously increases after being exposed to fire. The fire endurances of specimens with mortar cover are 35~154 min when the load levels are 8%~72% of the ultimate load. The fire endurances of specimens with mortar cover are longer than 43 min when the load levels are smaller than 50% of the ultimate load. The fire endurances of specimens without mortar cover are 31~47 min when the load levels are 16%~48% of the ultimate load. It is found that the fire endurance of prestressed concrete hollow-core slabs exposed to fire decreases gradually when the load level increases. The fire endurance increases remarkably when the mortar cover is painted. During the exposing process, the temperatures in the hollow core and on the top surface of specimens without mortar cover are obviously higher than specimens with mortar cover. The load level has little effect on the temperature field of concrete and the hollow core, while the mortar cover has obvious effect.