Curso de Manejo de águas pluviais<<strong>br</strong> />Capítulo 5-<strong>Microdrenagem</strong><<strong>br</strong> />Engenheiro Plínio Tomaz 3 de agosto de 2012 pliniotomaz@uol.<strong>com</strong>.<strong>br</strong><<strong>br</strong> />Figura 5.44- Coeficientes para o calculo do raio hidráulico para a velocidade critica da NBR 9649/86.<<strong>br</strong> />Fonte: Crespo, 1997<<strong>br</strong> />Exemplo 5.41<<strong>br</strong> />Calcular o ângulo central crítico e a velocidade crítica para vazão de 0,010m 3 /s, diâmetro D=0,15m<<strong>br</strong> />tubo de PVC n=0,010.<<strong>br</strong> />c= sen c + 8 ( Q 2 /g) 1/3 [sen(c/2)] 1/3 x D -5/3<<strong>br</strong> />c= sen c + 8 ( 0,010 2 /9,81) 0,33 [sen(c/2)] 0,33 x 0,15 -1,67<<strong>br</strong> />c= sen c +4,29 [sen(c/2)] 0,33<<strong>br</strong> />5-92
Curso de Manejo de águas pluviais<<strong>br</strong> />Capítulo 5-<strong>Microdrenagem</strong><<strong>br</strong> />Engenheiro Plínio Tomaz 3 de agosto de 2012 pliniotomaz@uol.<strong>com</strong>.<strong>br</strong><<strong>br</strong> />Tabela 5.32- Cálculo para o ângulo central por tentativas<<strong>br</strong> />c c= sen c +4,29 [sen(c/2)] 0,33<<strong>br</strong> /><<strong>br</strong> />4 3,40<<strong>br</strong> />3,40 4,02<<strong>br</strong> />4,02 3,38<<strong>br</strong> />3,38 4,04<<strong>br</strong> />4,04 3,36<<strong>br</strong> />3,36 4,07<<strong>br</strong> />4,07 3,34<<strong>br</strong> />3,34 4,09<<strong>br</strong> />4,09 3,32<<strong>br</strong> />3,32 4,11<<strong>br</strong> />4,11 3,30<<strong>br</strong> />3,30 4,13<<strong>br</strong> />4,13 3,28<<strong>br</strong> />Tomamos o valor médio c= (4,13+3,28)/2= 3,67 rad<<strong>br</strong> />yc/D= (1/2) x (1 – cos c/2)<<strong>br</strong> />yc/0,15=(1/2)x (1 – cos 3,67/2)=0,63 < 0,75D<<strong>br</strong> />yc=0,095m<<strong>br</strong> />Verificação<<strong>br</strong> />Conforme Metcalf&Eddy, 1981 o valor de yc pode ser estimado por:<<strong>br</strong> />yc= 0,483 x (Q/D) 2/3 + 0,083D<<strong>br</strong> />yc= 0,483 x (0,01/0,15) 2/3 + 0,083x0,15=0,0933m<<strong>br</strong> />y/D= 0,63<<strong>br</strong> />R= (D/4) ( 1 – sen θ/ θ )<<strong>br</strong> />R= (0,15/4) [ 1 – (sen 3,67)/ 3,67 ] =0,043m<<strong>br</strong> />Vc= {[g xD/ (8 sen(c /2))] x (c - sen (c)} 0,5<<strong>br</strong> />Vc= {[9,81 x0,15/ (8 sen(3,67 /2))] x (3,67 - sen (3,67))} 0,5<<strong>br</strong> />Vc= {[0,19 x (3,67 +0,50} 0,5<<strong>br</strong> />Vc=0,89m/s<<strong>br</strong> />Declividade crítica<<strong>br</strong> />Ic= =[n 2 x g/ (sen(c/2))] x [c 4 / (2,0 D (c – sen c))] (1/3)<<strong>br</strong> />Ic= =[0,010 2 x 9,81/ (sen(3,67/2] x [3,67 4 / (2,0x0,15(3,67-sen 3,67] (1/3)<<strong>br</strong> />Ic= =[0,00101 x 5,17] 1/3<<strong>br</strong> />Ic=0,0052m/m<<strong>br</strong> />5-93