A3 - Finding Protrusions in the Plan: When its status is marked in the program by the user
In buildings with A3 type irregularities, floor slabs are automatically modeled with two-dimensional plate (membrane) or shell finite elements to show that they can safely transfer earthquake forces between vertical bearing system elements in their own planes (See 184.108.40.206 ).
A3 type irregularity situation occurs when both the dimensions of the protruding parts of the building floor plan in perpendicular directions to each other are greater than 20% of the total boat in the same direction as indicated in TBDY Table 3.6 . This situation is shown in TBDY Figure 3.3 .
In the above figure, if L x is the floor plan length in the x direction, a x is the length of the projecting section in this direction. Similarly, if L y is the length of the floor plan in the y direction, a y is the length of the projecting section in this direction. if
ax > Lx
a y > L y
If the conditions occur at the same time, A3 type irregularity occurs in the building .
According to Article 220.127.116.11 and 18.104.22.168 of TBDY , floors in buildings with A2 and A3 type irregularities are modeled with two-dimensional finite elements. The following picture shows the analysis model of an example whose tiles are modeled with two-dimensional finite elements (shell).
As a result of three-dimensional analysis of shell finite elements (slabs, curtains and polygonal walls), they generate stresses and forces per unit length. The directions of these stresses and forces per unit length are determined according to the local axes of the shell finite element.
Shell finite element forces are obtained as a result of stresses formed by shell finite elements in three dimensional analysis.
M11, M22: Bending moments per unit length (tfm / m or kNm / m) formed around axes 1 and 2. They are also called out-of-plane bending moments.
M12: Means unit length planar torsion moment (tfm / m or kNm / m). It is also called the in-plane torsion moment.
V13, V23: Shell is the unit length shear forces (tf / m or kN / m) on the surface of the finite element and perpendicular to the plane of the finite element. It is also called the out-of-plane shear force.
F11, F22: Tensile and compressive forces per unit length (tf / m or kN / m) parallel to the plane of the acceptance finite element in the respective direction. It is also called in-plane pressure-pull forces.
F12: Unit length shear forces (tf / m or kN / m) parallel to the shell finite element plane. It is also called in-plane shear forces.
Shell finite element results can be viewed from the "Shell Results" tab in the Analysis Model.
Floor discontinuities cause accumulation in floor stresses caused by vertical loads and earthquake loads. The plan view and stress distribution of a system solved with semi-rigid diaphragm acceptance for A3 type irregularity is shown in the picture below. As can be seen, in the structure containing A3 type irregularities, F11, which is the in-plane axial stress value, increased in certain regions.
A3 type irregularity occurs due to floor gaps. For this reason, slab in-plane deformations were neglected. Rigid diaphragm solution is not applied in this type of irregularity. In buildings with A3 type irregularities, a semi-rigid diaphragm solution should be made where the floors are modeled with shell finite elements .
Floor stress controls specified in Article 7.11.3 of TBDY are applied in buildings with A3 type irregularities due to floor gaps . In slab stress controls, in-plane compressive stress, in-plane tensile stress and in-plane shear stress are controlled in the floors of buildings. In order to make these controls, floors should be modeled with shell finite elements. Detailed explanation of slab stress controls is available at Slab Stress Controls . Slab Stress Controls
According to Article 7.11.5 of TBDY , earthquake loads must be safely transferred from floors to vertical bearing elements. In the definition of A3 type irregularity, a floor plan in which "the presence of local floor gaps that make it difficult to transfer earthquake loads to vertical bearing system elements" is shown in the above picture. The shear stresses accumulated in these spacesare also controlled by article 7.11.5 . When such gaps are opened in the critical areas of the vertical bearing elements, both 7.11.3 slab stress checks and 7.11.5 seismic loads are safely transferred from the floors to the vertical bearing elements.