Design Shear Forces for Walls

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Last updated: Oct 19, 2022 by Zeynep Aladağ
7 min read

  • For walls meeting the H w / l w > 2.0 condition, the design shear force, V e , which will be taken as basis in calculating the transverse reinforcement in any section considered , is automatically calculated with Equation (7.16) .

  • Design Shear Force , V e for each point of the walls is calculated automatically according to the shear force diagram given in Figure 7.12 (c) .

  • The shear force dynamic magnification coefficient in Equation (7.16) is determined automatically. β v = 1.5 is taken as β v = 1.0 in buildings where all of the earthquake load is carried by reinforced concrete walls .

ICONS

D = Strength Excess Coefficient
f ck = Characteristic cylinder compressive strength of concrete
f yk = Characteristic yield strength of longitudinal reinforcement
H w = Total curtain height measured from the top of the foundation or the ground floor slab
H cr = Curtain critical height
l w = Curtain or tie-beam curtain part length in plan
( M p ) t = f ck at the base section of the curtain, f ykand the moment capacity calculated by considering the strength increase of the steel
( M d ) t = The moment calculated under the combined effect of the vertical loads and earthquake loads multiplied by the load coefficients at the base section of the wall
R = The load-bearing system behavior coefficient
V d = The vertical loads and earthquake loads multiplied by the load coefficients Shear force calculated under the joint effect
V e = Shear force based on transverse reinforcement calculation at column, beam, junction area and curtain
β v = Shear force dynamic magnification coefficient in curtain

Design Shear Forces under H w / l w > 2 and H w / l w <= 2

Curtains are modeled with shell finite elements. The curtain section is defined in the center of gravity so as to provide the three-dimensional rigid body movement condition of the curtain finite elements, and the internal forces of the curtain are obtained by summing the values ​​obtained from the curtain finite element results of the relevant loading combination at this center of gravity. TBDY Article 7.6.6.3 and TBDY Figure 7.12 (c) , there are various increments to calculate shear forces of walls.

The design shear force, V e , to be taken as basis in calculating the transverse reinforcement of walls , is explained in Article 7.6.6.3 of TBDY . In addition to this item, the shear force plot of the shear design is shown in TBDY Figure 7.12 (c) . The design shear force calculated for the walls is found from the shear force diagram in TBDY Figure 7.12 (c) .

The shear forces in the graph shown in TBDY Figure 7.12 (c) are explained below.

"The shear force diagram found from the solution" is the shear force diagram calculated under the combined effect of vertical loads and earthquake loads.

The diagram shown with the "increased shear diagram" is the shear force diagram resulting from the increment mentioned in the TBDY Article 7.6.6.3 . In this shear diagram, Equation. The shear force and vertical loads calculated by (7.16) are compared with the shear force value obtained by increasing the shear force calculated from the earthquake according to Section 4 by 1.2D (gapless walls) or 1.4D (bond beam walls) and the smaller shear force is taken into account. taken. These shear forces are calculated at the center of gravity of the curtain. This check is done for all loading combinations and the most unfavorable condition is taken into account.

The diagram shown with "Design shear force V Ed " is the same diagram as the "Increased shear diagram" in the region of H w / 3. H w / 3 In the region above the H w / 3 points in enhanced shear-shear force is taken as half the wall base at the highest point of the screen is the shear force generated in combination with a linear line. This check is done for all loading combinations and the most unfavorable condition is taken into account.

In TBDY Figure 7.12 (c) , H w is the total curtain height measured from the top of the foundation or from the ground floor slab. l w is the plan length of one arm of the polygon curtain. Since the length (l w ) of each arm of polygon curtains may be different from each other, H w / l w values ​​are calculated on the basis of arm.

Considering TBDY Article 7.6.6.3 and TBDY Figure 7.12 (c) , three situations arise when the bulkheads have the design shear force.

 

  • Curtains in the Lower Zone of H w / l w  > 2.0 and H w / 3

Design shear force of walls according to Article 7.6.6.3 of TBDY for walls meeting the condition H w / l w > 2.0, the design shear force, V e , to be taken as basis in the transverse reinforcement calculation, shall be calculated by TBDY Equation 7.16 .

In this equation (M p ) t means the moment capacity calculated by considering the strength increase of f ck , f yk and steel in the base section of the wall . This value is also the moment of power consumption of the curtain cross section. (M d ) t , vertical loads in load multiplied by the base section and earthquake loads curtain means under the influence of torque calculated partners. Here, the results of the finite elements of the wall are summed at the center of gravity of the wall section to provide the three-dimensional rigid body motion condition and (M d ) t value is obtained. V d value is the shear force value calculated under the combined effect of vertical loads and earthquake loads multiplied by the load coefficients. The shear force in this equation dynamic magnification factor  β v = 1/5 is taken. In buildings with reinforced concrete carried the entire burden Earthquake  β v = 1.0 is taken.

However, with the vertical loads, the shear force obtained by increasing the shear force found in the earthquake calculation by 1.2D (gapless walls) and 1.4D (bond beam walls) creates an upper limit. Therefore, if the shear force considered with 1.2D or 1.4D is smaller than the shear force value found by TBDY Equation 7.16 , this shear force is used as the Design Shear Force. This check is done for all loading combinations and the most unfavorable condition is taken into account.

  • Curtains in the upper region of H w / l w  > 2.0 and H w / 3

For  shear  walls meeting the condition H w / l w  > 2.0 and located in the upper region of the height  H w / 3 in the shear force diagram   ,  the linearized design shear force value shown in TBDY Figure 7.11c is used in addition to the control performed using  TBDY Equation 7.16 . In this graph, the shear force value to be used in the upper section of the wall is taken as half of the design shear force at the base of the curtain. H w / 3 The design shear force at the height of the curtain section and the shear force value at the top point of the curtain are combined with a linear line and the design shear forces in other sections are found. This check is done for all loading combinations and the most unfavorable condition is taken into account.

The design shear force V e value of the walls in the upper region of H w / 3 is found with the linearized graph described above. The shear force of the curtains to the center of gravity is found with this graph and Design Shear Force, V e , is obtained. Design Shear Force in all sections of the wall is the shear force to be used in calculating V e transverse reinforcement. This check is done for all loading combinations and the most unfavorable condition is taken into account.

  • Curtains with H w / l w ≤ 2.0

According to TBDY 7.6.6.3 , design shear forces in all sections of walls with H w / l w  ≤ 2.0 should be taken equal to the shear force calculated in accordance with Section 4 . In this case , the Strength Excess Coefficient D specified in Section 4.3.5 should be applied. In addition, in Article 4.3.4.9 , "Except for basement perimeter walls , the internal forces calculated according to the R coefficients given in Table 4.1 for walls with Hw / lw ≤ 2.0 shall be increased by multiplying by the coefficient [3 / (1+ Hw / lw)]. However, this coefficient will not be taken higher than 2. " A condition is specified.

While basement walls with H w / l w  ≤ 2.0 have a design shear force, earthquake results calculated according to the R coefficient are increased by the Resistance Excess Coefficient D. In addition , the internal forces conditions based on the design are taken into consideration in buildings with basements given in Article 4.10.1 of TBDY . As the primary shear force, the shear force under the combined effect of the earthquake loads calculated by taking into account the Resistance Excess Coefficient D and the basement floor increases together with the vertical loads is used.

H w / l w  ≤ 2.0 with and basement environment would hang in the remaining curtain outside curtains shear earthquake calculated by the found R factor with Resistance Redundancy Factor D, and Item 4.3.4.9 'as specified in [3 / (1+ H w / L w ) ] is enlarged by multiplying by the coefficient. As the design shear force, the shear force under the combined effect of the earthquake loads calculated by considering the Resistance Excess Coefficient D and the coefficient [3 / (1+ H w / l w )] together with the vertical loads is used.