This mode is used to check short cantilevers for the action of a lateral force to ensure the strength in a compressed oblique strip between the load and the support in compliance with Sec. 3.34 of SNiP 2.03.01-84*, KMK 2.03.01-96 and Sec. 3.99 of the Guide to SNiP, and Annex G of SP 63.13330.
The check is performed once all the necessary conditions and requirements to the short cantilevers are satisfied. The main condition is S1 ≤ 0,9h0, where h0=h-a1 is the effective height of the support section of the cantilever, S1 is the distance from the inner face of the lower part of the column to the end of the bearing area of the beam. Only single-sided cantilevers of three types are considered: a rectangular cantilever, a cantilever with a slope to support a girder, and a cantilever with a slope to support a crane beam. Click on the respective icon to select the type of the cantilever.
The General tab is used to specify:
(a) a crane beam is supported by the cantilever;
(b) a floor beam (girder) is supported by the cantilever;
the height of the cantilever in the support section, h; the height of the free end of the cantilever, h1; the cantilever overhang length, L1; the actual length of the bearing area of the beam along the cantilever overhang, L2; the distance from the inner face of the column to the side face of the beam, а; the height (of the section) of the upper part of the column, с1; the height (of the section) of the lower part of the column, с2; the width of the column or the cantilever, b; the concrete cover of the longitudinal reinforcement, а1;
weld leg, length of the fillet weld, design strength of welds to shear;
The Concrete tab is generally similar to those described in the previous modes, but you do not have to specify the conditions of hardening here, and a service factor for concrete, γb2, has to be entered.
Cantilevers with haunches with an arbitrary angle of slope are considered. If the height of a cantilever is 100 mm or less, or if its overhang is L1 = 100…150 mm, it can be designed as rectangular.
The dimensions of the cantilevers are specified on the following basis: the height of the cantilever, h, in its support section must not be less than 250 mm; the height of the free edge, h1, of cantilevers bearing precast crane beams is taken depending on the design capacity of the crane, Q, according to the following rules:
Q ≤ 5 tons — h1 ≥ 300
mm,
5 tons < Q < 15 tons — h1 ≥ 400 mm,
Q ≥ 15 tons — h1 ≥ 500 mm;
and the condition h1 ≥ (1/3)h must hold.
The strength in the oblique compressed strip between the load and the support is checked irrespective of whether there is or there is no transverse reinforcement.
If a girder is supported by the cantilever, the Qс force is applied to the center of gravity of the bearing triangle, i.e. at the distance of 1/3 L2 from the edge of the cantilever. When the Fixed bearing area checkbox is checked, the Qс force is applied at a given distance, Lq, from the inner face of the upper part of the column. Moreover, in this case the user has to specify the length of the load transfer area, Lsup. This area is assumed to be symmetric with respect to the application point of the Qс load.
The width of the cantilever, b, is set equal to the width of the column. The width of the girder, b1, is set to be less than or equal to the width of the cantilever.
Two types of connections between the beam and the column are considered: a hinge connection, and a rigid one with joint grouting and welding of the lower reinforcement of the girder to the cantilever reinforcement through inserts. If, in the rigid connection, the М1 moment puts the lower face of the girder in tension, then it should be used with the "minus" sign.
Transverse reinforcement for the cantilevers consists of:
where C is the distance from the inner face of the lower part of the column to the application point of force Qc.
The spacing of stirrups must (in all cases) be not greater than h/4 and not greater than 150 mm.
By default, the transverse reinforcement of the cantilever is implemented as two-leg stirrups (thus the design formulas will include the double area of the transverse rebar specified in the dialog box).
In case when the transverse reinforcement consists of four-leg stirrups (when the respective checkbox is checked), the design formulas will include the quadruple area of the transverse reinforcement.
In all cases if the cantilever overhang, L1, is less than the length of the bearing area, L2, the analysis takes into account only the load on the cantilever located within the cantilever overhang.
Concrete of the cantilever under the bearing area is checked; the bearing stresses in the areas where the load is transferred onto the cantilever must not exceed Rb, loc (Sec. 3.39 of SNiP II-23-81*), otherwise it is necessary to increase the class of concrete or the load transfer area. In the check for local compression, the bearing area is taken equal to its design value.
In the check of the longitudinal reinforcement, if the girder and the column are connected rigidly, one of the limitations of the horizontal force, Ns, depends on the height and length of the fillet weld connecting inserts of the girder and those of the cantilever. The minimum weld leg, Kf, is assigned in compliance with Table 38* of SNiP II-23-81*, depending on the type of weld, the yield point of steel, the thickness of the thicker of the welded members, and varies between 3 and 12 mm. The design strength of the fillet welds for shear in the metal, Rwf, is taken from Table 56 of SNiP II-23-81* depending on the electrode type (for E42, E42A it is 180 MPa; for E46, E46A it is 200 MPa; for E50, E50A it is 215 MPa; for E60 it is 240 MPa; for E70 it is 280 MPa; for E85 it is 240 MPa). The length of the fillet weld, lw, connecting the inserts of the girder and those of the column is determined by the sizes of the inserts, but must not exceed the double length of the load transfer area along the cantilever overhang, 2L2, and must be not less than 4Kf.
Limitations related to the design arrangement of the joint are terminal: once they are violated, the respective analysis cannot be performed.
Since the application operates only with the class and diameter of longitudinal and transverse reinforcement, it is the user who is fully responsible for the design arrangement of reinforcement in the cantilever, installation of the proper anchorage (Sec. 5.14 of SNiP 2.03.01-84* and Sec. 5.45 of the Manual [7]) for the longitudinal (primary) reinforcement, and the type of transverse reinforcement (see recommendations above).
The application of rigid reinforcement to reinforce a cantilever of a limited height is not considered.
Limitations related to the structural requirements are not terminal: the analysis can be performed, but the user gets a warning 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 minimum weld leg, the reinforcement class etc.
The longitudinal reinforcement and bent rebars of the cantilevers should be of class A-III; class A-II is also acceptable.
The stirrups and transverse rebars should be of class A-I.