The reinforced concrete wall structure is found in most high -rise civil buildings, playing an important role in the hardness of the building to bear the horizontal load (wind, earthquake) increasing with the scale of the house height. In the actual construction design, there are many methods of calculating reinforced design for walls. Like columns, the design results are designed according to foreign standards often for higher value when calculating according to Vietnamese standards. So set the task for Structural engineer TCVN must be applied to ensure the economy for the structural design problem. This article would like to introduce some practical ways to apply TCVN 5574: 2012 to calculate reinforcement in wall structure design.
The internal force of the flat wall consists of vertical force N, shear force q, the moment of bending in the plane of the M wall (the bending moment in the perpendicular direction of the small wall plane can be ignored in calculation). There are 3 methods to calculate vertical reinforcement layout for the walls from internal force pairs (n, m) as follows:
Assumption:
– Steel reinforcement is located on the border area of the two walls to bear the entire moment (safe)
– Traction pressure due to reinforcement
– Compressive pressure due to concrete and reinforcement
At that time, the force of traction and compressed into the two border areas:
$$P_{l,r}=\frac{N}{A}A_b\pm\frac{M_x}{L-0,5B_l-0,5B_r}$$
The computational area is like compressed components, properly pulling the mind, calculating the area of reinforced steel $A_ {SL}, A_ {SR} $. The middle area is calculated as the component component of the heart with the compression force equal to $n-P_L-P_R $, out the area of reinforced steel vertical $a_ {SC} $
Assumption:
– Elastic material
– Traction pressure due to reinforced steel, compression pressure due to both concrete and reinforcement
The vertical force is correct about each element calculated:
$$n_i =\frac {n} {n}+\frac {m_x} {\sum {y_i^2}} y_i $$ with i = 1.2 … number from left to right in the picture above. Seal + compression.
Compressed reinforcement area in the right compressive element:
$$A_ {SC} =\frac {\frac {N_I} {\varphi} -R_BA_B} {R_ {SC}}, A_B = A.T_W $$
Compressed reinforcement content should be limited to $2\mu_{min}\leqslant\mu_c\leqslant\mu_{max}$. The container content is tensile should be limited to $\mu_t=0,4\sim6\%$
This method is the most accurate method used for the wall structure design problem: The reinforcement can be arranged for the border and the middle area according to the calculation results of the two methods mentioned above. Theoretical principle is as shown in the topic here. The compatible chart of $ (M^*, N) $ is made according to the flat eccentric compression problem because the moment is mainly in the plane of the wall. Proceed to check by comparing the inner force pairs corresponding to each interior force combination with the interactive chart similar to the column.
Can be calculated according to TCVN 5574: 2012 according to the beam structure, which is sheared in the case of a centralized shear force at the two ends of the water height of the wall. At that time, the dangerous tilted section $C_O $ was equal to the height of the wall of the wall. Calculation principle as presented as follows:
When the beam is subject to concentrated load, it is necessary to calculate with all inclined cross -sections coming from the title (at the floor) but does not exceed the largest torque.
With the problem of designing flat wall structures, only inclined cross -section is projection $ c_1 = c_o $ with shear force Q.
Calculate $q_b =\frac {m_b} {c_1} $, $m_b =\varphi_ {b2} (1+\varphi_f+\varphi_n) r_ {bt} bh_o^2 $
Where:
The coefficient of $\varphi_ {b2} = 2.0 $ corresponding to heavy concrete
The coefficient of $\varphi_f = 0 $ due to only rectangular section review
The coefficient of $\varphi_n $ considering the effect of vertical force N, determined by:
$$\varphi_n=\frac{0,1N}{R_{bt}bh_o}$$
The value of $(1+ \varphi_f+ \varphi_n) $ takes does not exceed 1.5.
Simultaneously controlled $Q_b\geqslant{Q_{bmin}}=\varphi_{b3}(1+\varphi_f+\varphi_n)R_{bt}bh_o$
The coefficient of $\varphi_{b3}=0,6$ with heavy concrete
Next, calculate $\chi_1=\frac{Q-Q_b}{Q_b}$ and then take $c_o = c_1$ but not greater than $2h_o $, calculate:
$$\chi_ {o1} = \frac {q_ {b_min}} {q_b} \frac {c_o} {2h_o} $$
Determine the values $q_ {sw} $ in the following cases:
Case 1: When $\chi_ 1 <\chi_ {O1} $, calculate
$$q_{sw1}=\frac{Q}{C_o}\frac{\chi_{o1}}{\chi_{o1}+1}$$
Case 2: When $\chi_ {O1}\leqslant \chi_1 \leqslant \frac {c_1} {c_o} = 1 $, calculate
$$q_{sw2}=\frac{Q-Q_b}{C_o}$$
Case 3: When $\frac {c_1} {c_o} < \chi_1 \leqslant \frac {c_1} {h_o} $, calculate
$$q_{sw3}=\frac{\left(Q-Q_b\right)^2}{M_b}$$
Case 4: When $\chi_1> \frac {c_1} {h_o} $, calculate
$$q_{sw4}=\frac{Q-Q_b}{h_o}$$
here takes $h_o\leqslant{C_1}$
From $q_ {SW}$ reinforcement is distributed on 1 unit of wall height according to the formula:
$$A_{sw}/s=\frac{q_{sw}}{R_{sw}}$$
With $ R_ {SW} $ is the calculation intensity of the horizontal reinforcement when shear.
At the same time, the horizontal distance S must meet the structural conditions for the shear components: $s \leqslant \left ( \frac {h} {2} and 150mm \right) $ and satisfy the calculation conditions:
$$s_{max}=\frac{\varphi_{b4}\left(1+\varphi_n\right)R_{bt}bh_o^2}{Q}$$
The coefficient of $\varphi_ {b4} = 1.5 $ with heavy concrete.
Usually, flat wall structural situations show that the concrete section is capable of shear, the arrangement of horizontal reinforcement for the wall is mainly according to the structure requirements, resistance to high -rise buildings.
Due to quite a lot of calculation volume, it is best to set up Excel spreadsheets in combination with programming VBA functions to facilitate the application of construction design. Please give 🎁1 spreadsheet here.
Reference:
TCVN 5574: 2012: “Concrete structure and reinforced concrete. Design standards””Some reinforcement methods for reinforced concrete walls” – PhD. Vo Manh Tung, Nguyen Tuan Trung – Department of reinforced concrete works – University of Construction.
“Calculation of reinforced concrete structure practice according to TCXDVN 356: 2005” – GS. Nguyen Dinh Cong – Construction Publishing House
