Punching (SNiP 2.03.01-84*)

This mode implements a check of slab structures (without transverse reinforcement) for punching in compliance with the regulations of Sec. 3.42 of SNiP 2.03.01-84*and Sec. 3.98 of the Manual on designing of concrete and reinforced concrete structures made of heavy-weight concrete. Both structures with the additional lateral reinforcement by vertical bars located within the bearing pyramid and structures without any lateral reinforcement can be checked here.

Depending on the presence of lateral reinforcement, one of the following factors is calculated:

strength from conditions of punching without additional reinforcement;
strength from conditions of punching with additional reinforcement.

General

The General tab is used to specify:

the sizes of the slab base;
the sizes of the load application area;
the height of the slab (H), or the effective height of the section (h) where:
h is the distance from the slab top to the center of gravity of the lower reinforcement (it can be selected using the respective radio button). If the slab height parameter H is used, the value of h is taken as 0.9H;
the resultant of the punching load applied to the center of the load application area;
a uniform load (including the zero load) applied to the base of the slab and resisting punching.

When the Additional vertical reinforcement checkbox is checked, the following data have to be specified:

the class and the diameter of vertical rebars that make up the meshes parallel to the sides of the slab;
the number of rows of vertical bars parallel to the sides of the slab;
the location of first rows with respect to the load application area;
the number of rows of vertical rebars along each side of the base;
the spacing (the distance between the rebars in a row);
the number of rebars in rows.

Clicking the button $image\ebx_-1313385743.jpg$ displays the arrangement of rebars according to the parameters of the specified additional vertical reinforcement.

Concrete

Properties of concrete are specified in the Concrete tab in the standard way.

Peculiarities of the implementation

The requirement of Sec. 3.42 of SNiP 2.03.01-84*, KMK 2.03.01-96 that the punching force should act on a "limited area" is implemented in the following way: the area is considered to be "limited" if the inclination of the side faces of the bearing pyramid to the horizon does not exceed 68°. This limitation complies with the fifth paragraph of Sec. 3.42 of SNiP 2.03.01-84*, KMK 2.03.01-96.

The punching is analyzed only for slab structures. Steps in the slabs (such as those of the foundation) are not taken into consideration.

The vertical punching load and the load applied to the base of the slab are assumed to be uniformly distributed over their application areas.

Eccentricities of the application of loads are not taken into account.

The next-to-last paragraph of Sec. 3.42 of SNiP 2.03.01-84*, KMK 2.03.01-96 is not implemented.

Additional lateral reinforcement is implemented only as vertical meshes with the effective vertical rebars. The meshes are arranged parallel to the sides of the slab, symmetrically, and do not fall within the load application area. The location of meshes nearest to the load application area is such that they always fall within the bearing prism.

The requirement of Sec. 5.29 of SNiP 2.03.01-84* concerning the installation of additional reinforcement at the punching analysis is implemented.

When there is no additional reinforcement the application automatically applies the coefficient of 0.9 to the value R_bt on the basis of the requirements of item 9 of table 15 in the case when only a concrete section is considered.

Limitations

The limitations deal with the following circumstances:

whether it is legitimate to perform the check for punching (it depends on the ratio of the lateral sizes of the slab and the sizes of the load application area);
the ratio of the punching load and the pressure under the base of the slab;
structural limitations of the used classes and diameters of rebars, the spacing between rebars in meshes and between the meshes, and other limitations given in documents [7], [15], [16].

Limitations related to the legitimacy of a check and the ratios of loads are terminal: once they are violated, the respective analysis cannot be performed.

Limitations related to the structural requirements are not terminal: the analysis can be performed, but the user gets a warning in the report and on the screen that the limitations have been violated. Some of these limitations are implemented in the following way: you can select certain values only from a limited list, e.g., the number of rebar rows, the reinforcement class etc. You only receive warnings in the reports and on the screen about the violation of other limitations.

The following structural limitations are implemented in the application:

the reinforcement classes are Bp-I, A-I, A-II, A-III according to SNiP 2.03.01-84*, KMK 2.03.01-96, and A400C according to [6];
the diameters of rebars depending on their class are from 3 to 14 mm;
the minimum spacing between the rows of rebars is defined by Sec. 5.29 of SNiP 2.03.01-84*, KMK 2.03.01-96;
the distance from the first row of rebars to the load application area must be not less than 30 mm and not greater than the spacing between the rows;
the total number of rebar rows along each side is from 2 to 10;
the number of rebars in each row must be the same for the rows along each side and must not be less than 2 and not greater than 10.

The check determines the number of rows and the number of rebars in the rows which fall within the bearing prism. If some of the rebar rows or rebars in the rows do not fall within the bearing prism, the respective messages are displayed on the screen and included in the report.