我structure research到呢到la，做個TO唔駛呢D野。。。
呢條formula 嘅用途可能係，可以直接入數落計數機，用member size 同reinforcement area 計返moment同shear. 打破傳統要寫成條式去計。
With a formula to calculate the moment and shear after entering the member size and reinforcement area. So that we would calculate moment and shear capacity just by the calculator.
3年前，
For double reinforcement
計算R.C. 的逆公式
M=Asc*0.87*fy*(d-d')+k'fcu*b*d^2
k'=0.156 when fcu = 30
depend on fcu, k'=lower with higher grade of concrete
(divided both sides with b*d^2
M/bd^2=Asc/bd*0.87*fy*(1-d'/d)+0.156fcu
呢條應該就係房署個chart嘅formula la~
當知道compassion steel 的area 時，就可以知道beam的moment。
而tension steel 的formula 是:
Ast=k'*fcu*b*d^2/(0.87fy*z)+Asc
我覺得應該用reinforcement 去計番個moment，
因為moment 可以係任何數字，而b,d 同R.C. 個組合係有限ga。
咁就可以generate 一張張紙，用reinforcement 個數，對住張紙來揾moment 係幾多，
但變數太多了...
例如考慮睇housing 呢個圖，直接知moment 就對表，揾R.C. ratio 係乜野，咁就唔駛計。 就算roughtly, 都可以估到個member size 要幾多% Reinforcement或者如果想2% reinforcement ，咁咩member size 先okay.
Shear force 都可以比完鐵之後再睇max shear force 夠唔夠，唔駛design 到一半又重頭計過。
當beam 本身嘅shear stress load 大過vc
vc=0.79(100As/(bd))^1/3*((400/d)^(1/4))*((fcu/25)^(1/3))/1.25
(100As/(bd))^1/3
{should be <3}
((400/d)^(1/4))
>0.67(when no shear reinforcement)
>1 (when has shear reinforcement)
咁就要
入shear reinforcement area, bv同Sv, 計返maximum shear capacity
0.87Asv*fyv/(bv*sv)+vc
跟番manul of design and detailing of reinforced concrete 3.7.1
第2條moment 嘅formula 唔知有冇用:
z/d=0.5+(0.25-k/0.9)^0.5 ...(1)
Ast=M/(0.87fy*z) ...(2)
Combined (1) & (2)
0.87fy*Ast*d-(0.87fy*Ast)^2/(0.9b*fcu)
我structure research到呢到la，做個TO唔駛呢D野。。。
