next to
the icon indicating the selected design codes which invokes a special
dialog box for specifying additional calculation parameters. In many modes there is a button next to
the icon indicating the selected design codes which invokes a special
dialog box for specifying additional calculation parameters.
The program performs the analysis of plate elements based on the theory of N.I. Karpenko, since SP 63.13330 provides recommendations for calculating flat elements only for particular cases (slabs and deep beams). The codes do not provide any clear guidelines for the calculation of shell elements with simultaneously acting membrane and bending groups of forces. SCAD determines the crack opening width by the formulas recommended by N.I. Karpenko of the type (εx+εy)l, where l is the distance between cracks, εx,εy are strains in the respective directions.
To determine the crack opening width in flat elements SP 63.13330 refers to Section 8.2 (requiring to neglect the torque), which considers the formation of cracks in bar elements and contains the following limitation on the distance between cracks: “not less than 10ds and 10 cm and not more than 40ds and 40 cm”. The authors of the program do not know whether this limitation is reasonable with respect to plate elements, therefore it is not used by default. However, you can activate it using this additional setting.
The default algorithm for calculating reinforced concrete flat elements is based on two separate calculations — for the action of Qx and Qy. SP 63.13330 contains the following recommendation for the calculation for shear forces — formula (8.106)
\[ \frac{Q_{x} }{Q_{x,ult} }+\frac{Q_{y} }{Q_{y,ult} }\le 1. \]
This formula sums the stresses at various sites and can hardly seem reasonable. Based on the vector addition rules, it would be more logical to consider the shear force \(Q=\sqrt{Q_x^2 +Q_y^2} \). The following paper S.N. Karpenko, Modern design techniques of high buildings made of monolith reinforced concrete, High Buildings, 2007, No. 3, 34-39, for example, contains a similar recommendation on the analysis of flat elements.
Section 8.1.34 which has appeared in SP 63.13330 regulates the consideration of a longitudinal force in the analysis of the behavior of a bar element under shear forces. This section is obviously taken from EN 1992-1-1 (see Sec. 6.3.2). However, unlike the Eurocode, where the coefficient jn is used only for prestressed structures, SP 63.13330 requires to use it even when there is no prestress.
When the longitudinal forces are relatively large, there are two methods for selecting transverse reinforcement. If the first (default) one is used, the transverse reinforcement is selected after the longitudinal one. The previously selected longitudinal reinforcement is taken into account when calculating the coefficient φn, but the area of longitudinal reinforcement does not change when selecting transverse reinforcement. In the second case having established that the value φn is too small, you can try (it is not always possible) to increase the area of longitudinal reinforcement and select the transverse reinforcement. The second method in most cases leads to an unreasonably high reinforcement ratio (it is much more effective to increase the formwork sizes of the section) and is not used by default. However, this additional setting enables to activate it.
This option can be used when the analysis is performed according to EN 1992-1-1. It has been added due to the fact that Sec. 6.3.1(2) EN 1992-1-1 mentions a rather wide range of cases when torsion can be ignored. Moreover, using this option enables to avoid one inconsistency of EN 1992-1-1. The thing is that if a member is subjected to shear, both the resistance of concrete and the resistance of reinforcement are taken into account in the analysis (see Sec. 6.2.3). If a member is simultaneously subjected to both torsion and shear, then Sec. 6.3.2(4) limits its resistance by the capacity of the concrete struts.
The new Sec. 8.1.34 of SP 63.13330 regulates the shear analysis during eccentric compression/tension. It should be noted that the rules for calculating the coefficient φn in this section are almost literally taken from EN 1992-1-1, but in EN 1992-1-1 these rules apply only to prestressed elements. In addition, Sec. 8.1.34 of SP 63.13330 does not provide any rules for calculating the coefficient φn in the case when the average stress from the tensile force σt exceeds Rbt. The default value is φn=10-6, but it is also possible (and quite logical) to set the following value φn=0.5 (which corresponds to σt = Rbt). In order to avoid the above problems, the software allows to set the lower limit of the coefficient φn for tension, as well as the upper and lower limits of φn for compression. In particular, by setting all limit values to 1.0, you can perform the analysis corresponding to the recommendations of EN 1992-1-1, and by setting the lower limit jn equal to 0.5, you can determine φn for σt > Rbt.
Change No. 2 to SP 63.13330.2018 changes the rules for calculating the coefficient φn. When choosing SP 63.13330.2018 as the design code, this change will be taken into account, but a special option allows you to refuse to use this change.
In the case of the seismic analysis of ductile reinforced concrete walls Sec. 5.4.3.4.1(2) of EN 1998-1 requires that the value of the normalized axial load should not exceed 0.4. You can use this checkbox to perform an additional calculation of the factor equal to N/(0.4×A×fcd) during the check in order to control the fulfillment of this requirement.
You can use this checkbox to increase the values of shear forces by 50% for the seismic analysis and thereby satisfy the requirement of Sec. 5.4.2.4(7) of EN 1998-1.
A bilinear stress-strain diagram of concrete is used in the ultimate limit state analyses by default according to the requirements of Sec. 6.1.16 of SP 311.1325800 and Sec. 8.26 of STO 36554501-006-2006.
At the same time, SP 63.13330 allows to use both bilinear and trilinear diagrams. This parameter enables to switch to the trilinear diagram mode.
Most standards require not to take into account the behaviour of tensile concrete in the ultimate limit state analyses. However, in the case of the strength analysis of normal sections based on a nonlinear deformation model, some standards say that “the resistance of concrete in the tension area may not be taken into account” (see Sec. 6.1.2 of DBN V.2.6-98:2009 or Sec. 8.1.20 of SP 63.13330). This parameter enables to perform the analyses taking into account the resistance of tensile concrete.
The design codes provide clear rules for taking into account buckling (second order effects) for bar elements, while the rules for plates are not so clear. Therefore, allowing for these effects in the program is optional. If the user has specified the effective length for the X1 axis (similarly for Y1), then if there is a compressive force Nx, the moment Mx will be increased by the buckling coefficient η.
The design codes provide clear rules for taking into account geometric imperfections (random eccentricity) for bar elements, while the rules for plates are not so clear. Therefore, allowing for these effects in the program is optional. When the analysis is performed according to EN 1992 and there is a compressive force Nx (similarly for Ny), a minimum eccentricity is used equal to e0=max(h/30; 20 mm), where h is the plate thickness. When the analysis is performed according to SNiP, DBN, SP – e0=max(L/600;h/30; 10 mm), where L is the respective effective length specified by the user (see above). If the effective lengths are not specified during the analyses according to these codes, then the value of the minimum eccentricity will be calculated without taking into account the L/600 term.
When performing the serviceability limit state analysis according to EN 1992-1-1 (Sec. 7.2) or DBN B.2.6-98:2009 (Sec. 5.2 of DSTU B B.2.6-156-2010) the stress shall be limited in some cases in order to avoid longitudinal micro-cracks. This option enables to calculate the respective factors during the design of reinforced concrete structures.
When calculating for the action of accidental loads, by default characteristic properties of materials are used instead of the design ones (see Sec. 5.6 of SP 296.1325800.2017). Since this section was excluded by Change No. 2 to SP 296.1325800.2017, the user can (using the appropriate checkbox) choose which material properties (characteristic or design) to use.