1
11'31'32'3I0?b?h?x??bfx??bf?b??x?hf????ES?1?As?h0?x?333?13?200??1500?543.03?3?13?2000?543.033?13??2000?200???543.03?125?3??5.797?1??11788.4??1357?543.03?2?2.464752656?1011mm4抗裂边缘的弹性惯性矩：
I0?2.464752656?1011W0??2.575579857?108mm3h?x1500?543.03
换算截面重心轴以上部分面积对重心轴的面积矩：
S12bx20???b'f?b?h'f?x?0.5h'f??12?200?543.032??2000?200??125??543.03?0.5?125? ?1.37607408?108mm3换算截面积：
A'0??b'f?b?hf???ES?1?As??2000?200??125??5.797?1??11788.4 ?2.81549?105mm2
B、开裂截面
?b'A?f?b?h'f??ESAsb??2000?200??125?5.797?11788.4200
?1466.6mm 31
1
'B??bf?b??h'f?2?2?ESAsh0b??2000?200??1252?2?5.797?11788.4?1357200
?1.067963?106mm2x?A2?B?A?1466.62?1.067963?106?1466.6 ?327.5mm换算截面惯性矩：
I?13b'313?b''32crfx?f?b??x?hf???ESAs?h0?x??13?2000?327.53?13??2000?200???327.5?125?3 ?5.797?11788.4??1357?327.5?2?9.0864?1010mm4据《公预规》6.5.1条，受弯构件的刚度计算公式：
B?B0?22
?Mcr???M?????1?Mcr??B0s????M??s???Bcr 式中：
B0.95?
0?0.95EcI0??3.45?104???2.464752656?1011??8.07822683?1015(Nmm2) ??2S02?1.37607408?108W?108?1.0686
02.575579857?Mcr??ftkW0 ?1.0686?2.65?2.575579857?108
?7.29350?108Nmm 32
1
Bcr?EcIcr??3.45?104???9.0864?1010? ?3.134808?1015Nmm2代入刚度计算公式得
82???7.29350?10??7.29350?10?8.07822683?1015?2559.7?106????1?2559.7?106???3.134808?1015?????????5.7750?1015Nmm28B?8.07822683?10152?5.7750?106KNm2按短期荷载效应组合，简支梁跨中最大挠度:
5MSl52559.7KNm??24.5m?f?????0.0277m，
6248B485.7750?10KNm据《公预规》6.5.3条，???1.45，考虑挠度长期效应的影响，简支梁最大挠度：
22f?1.45?0.0277?0.0402m
11?l??24.5?0.0408m 60060011l??24.5?0.0153m
1600160011l?f?l，符合《公预规》6.5.3条的要求，据6.5.5条，必须设预即
1600600拱度。
3、预拱度设置
结构自重产生的跨中弯矩为1569KNm，1/2可变荷载频遇值对应的弯矩为
0.5??1.4?1460?0.8?1.4?147??1104KNm2，预拱度的计算：
5Ml25?1569?1104??24.5f????0.0288m。
648B485.79604?10
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