10-F.1       Scope

Steel structures checking according to the Chinese Steel Design Code GB50017 in CivilFEM includes the checking of structures composed of welded or rolled shapes subjected to axial forces, shear forces and bending moments in 3D.

The calculations made by CivilFEM correspond to the provisions of GB50017 from the following sections:

 

Section 4	Bending element calculations
Section 5	Axially loaded structures and calculation of compression and bending

 

10-F.2       Checking Types

For checks within CivilFEM according to GB50017, it is possible to accomplish the following checking and analysis types:

·         Checking of sections subjected to: 

- Bending force	GB50017 Art. 4.1.1
- Shear force	GB50017 Art. 4.1.2
- Bending and shear force	GB50017 Art. 4.1.4
- Axial force	GB50017 Art. 5.1.1
- Bending and axial force	GB50017 Art. 5.2.1
- Compression buckling	GB50017 Art. 5.1.2

 

10-F.3       Valid Element Types

The valid element types supported by CivilFEM are the following 2D and 3D ANSYS link and beam elements:

2D Link	LINK1
3D Link	LINK8
3D Link	LINK10
2D Beam	BEAM3
3D Beam	BEAM4
3D Tapered Unsymmetrical Beam	BEAM44
2D Tapered Elastic Unsymmetrical Beam	BEAM54
2D Plastic Beam	BEAM23
3D Thin-walled Beam	BEAM24
3D Elastic Straight Pipe	PIPE16
3D Plastic Straight Pipe	PIPE20
3D Finite Linear Strain Beam	BEAM188
3D Quadratic Linear Strain Beam	BEAM189

 

Moreover, it is possible to check solid sections captured from 2D or 3D models with a transverse cross section classified as “structural steel”.

 

 

10-F.4       Valid Cross-Section Types

Valid cross-sections supported by CivilFEM for checking according to LRFD are the following:

• All the rolled shapes included in the program libraries (see the hot rolled shapes library and ~SSECLIB command)
• The following welded beams: I shapes, U or channel shapes, T shapes, box, equal and unequal legs angles and pipes. (~SSECDMS commands).
• Structural steel sections defined by plates (command ~SSECPLT).
• Shapes from solid sections captured from 2D or 3D models with transverse cross sections classified as “structural steel” (command ~SLDSEC).

10-F.5       Calculation Basis

10-F.5.1           Section Data

The section data of the element must be included in the CivilFEM database. All geometrical and mechanical properties are automatically obtained defining the cross section or capturing the solid section. Below, the section data necessary for checking according to GB50017 are listed:

 

Table 10-F.5‑1 Section Data

 

From net section, only the area is considered. This area is calculated by subtracting the holes for screws, rivets and other holes from the gross section area. The user should be aware that LRFD indicates the diameter from which to calculate the parameter AHOLES is greater than the real diameter (the total calculated area is introduced in the parameter AHOLES with the command ~SECMDF).

 

10-F.5.2           Member Properties

For LRFD, the checked data set used at member level is shown in the following table. All data is stored with the section data in user units and in CivilFEM reference axis. (Parameters GAMMAy, GAMMAz, TSECy, TSECz, L, KY, KZ, of ~MEMBPRO command).

 

 

 

Table 10-F.5‑2 Member Properties

 

10-F.5.3           Cross Section Type Classification

The cross section type is defined by values introduced in TSECY and TSECZ  member properties (see ~MEMBPRO command). Otherwise they will be computed from the following table 10-F.5‑3:

 

 

Table 10-F.5‑3 The cross-section classification (plate thickness t < 40 mm)

CROSS SECTION TYPE			Y	Z
I Section	Rolled Section	If	b	a
		If	b	b
	Welded Section		b	b
Channel	Rolled or Welded		b	b
Pipe	Rolled		a	a
	By dimensions		b	b
L angle	Rolled		b	b
Square Tubing or Box	Rolled or Welded if		c	c
Standard T	Rolled or Welded		b	b

 

 

Table 10-F.5‑4 The cross-section classification (plate thickness t  40 mm)

CROSS SECTION TYPE			Y	Z
I Section	Rolled	If	c	b
		If	d	c
	Welded (default)			b
Square Tubing or Box	Rolled or Welded if			b
	Rolled or Welded if			c

 

10-F.5.4           Material Properties

In GB50017 checking, the following material properties are used:

 

Table 10-F.5‑5 Material properties

*th = plate thickness

 

 

10-F.5.5           Forces and Moments

Forces and moments for element’s ends are obtained from CivilFEM’s results file (file. RCV) for the selected load step and substep.

 

Table 10-F.5‑6 Forces and Moments

 

10-F.6       Checking Process

Required steps to conduct the different checks in CivilFEM are as follows:

a)    Obtain the cross-section data corresponding to the element.

b)    Specific section checking according to the type of external load.

c)    Results. Checking results are available in CivilFEM for each element end, grouping them into alternatives in the results file .RCV, in such way that the user may access them by indicating the number of the alternative using the CivilFEM command ~CFSET.

In sections corresponding to the different types of checking, the necessary data corresponding to the each type of solicitation is described.

 

10-F.6.1           Bending Checking

In CivilFEM the checking of elements under bending according to GB50017 code is done for each element end of those selected elements or solid sections of the model with a cross section type of structural steel. For this check, the program follows the steps below:

 

10-F.6.1.1         Calculation of the Maximum Normal Stress

The maximum normal stress is calculated with the general equation for sections subjected to bending moments according to axes, not necessarily principal of inertia:

Where:

	Bending moment in Y direction
	Bending moment in Z direction
	Moment of inertia in Y direction
	Moment of inertia in Z direction
	Product of inertia about YZ

Plastic development coefficients  are obtained from the associated member properties (see ~MEMBPRO command). Otherwise they should be defined according to Table 10-F.6.1.

 

 

Table10-F.6.1 Plastic development coefficients

CROSS SECTION TYPE
	1.20	1.05
		1.05
	1.15	1.15
	1.05	1.05
	1.20
Otherwise	1.00	1.00

 

 

10-F.6.1.2         Calculation of GB50017 Criterion

The equivalent stress previously obtained is then divided by the steel design strength s_u in order to obtain a value that is stored as the CRT_TOT parameter in the active alternative in CivilFEM’s results file for each element end. This value shall be between 0.0 and 1.0 so that the element will be valid according to the GB50017 code; therefore, the equivalent stress must be lower than the steel design stress.

 

10-F.6.2           Shear Checking

In CivilFEM, the checking of elements under shear force according to the GB50017 code is performed for each element end of those selected elements or solid sections of the model with a cross section type of structural steel.

 

10-F.6.2.1         Calculation of the Maximum Tangential Stress

The maximum tangential shear and torsion stresses for each element end are calculated from shear forces and section mechanical properties in the following equation:

 

Where:

 

	Shear Force in Y direction
	Shear Force in Z direction
	Shear area about Y axis.
	Shear area about Z axis.

 

10-F.6.2.2         Calculation of GB50017 Criterion

The equivalent stress obtained is divided by the steel design strength s_u in order to obtain a value that is stored as the CRT_TOT parameter in the active alternative in CivilFEM’s results file for each element end. This value shall be between 0.0 and 1.0 so that the element will be valid according to the GB50017 code; consequently, the equivalent stress must be lower than the steel design stress.

 

10-F.6.3           Bending & Shear Checking

In CivilFEM the checking of elements under bending and shear forces according to GB50017 code is done for each element end of those selected elements or solid sections of the model with a cross section type of structural steel. The following steps:

 

10-F.6.3.1         Calculation of the Maximum Normal Stress

The maximum normal stress is calculated with the general equation for sections subjected to bending moments according to axes, not necessarily the principal axes of inertia:

Where:

 

	Bending moment in Y direction
	Bending moment in Z direction
	Moment of inertia in Y direction
	Moment of inertia in Z direction
	Product of inertia about YZ

 

10-F.6.3.2         Calculation of the Maximum Tangential Stress

The maximum tangential shear and torsion stresses for each element end are calculated from shear forces and section mechanical properties in the following equation:

 

Where:

 

	Shear Force in Y direction
	Shear Force in Z direction
	Shear area about Y axis.
	Shear area about Z axis.

 

10-F.6.3.3         Calculation of the Maximum Equivalent Stress

The maximum equivalent stress in the section s^* is calculated by using:

The maximum equivalent stress for each element end is stored in the active alternative in CivilFEM’s results file with the parameter named SCEQV.

 

10-F.6.3.4         Calculation of GB50017 Criterion

The equivalent stress obtained is divided by the steel design strength s_u in order to obtain a value that is stored as the CRT_TOT parameter in the active alternative in CivilFEM’s results file for each element end. This value shall be between 0.0 and 1.0 so that the element will be valid according to the GB50017 code; thus, the equivalent stress must be lower than the steel design stress.

 

Where  is the amplifying factor for the combined design strength. If  and  have different sign = 1.2, otherwise = 1.1.

 

10-F.6.4           Axial Force Checking

In CivilFEM, the checking of elements under axial forces (without considering buckling) according to the GB50017 code is done for each element end of those selected elements or solid sections of the model with a cross section type of structural steel.

 

10-F.6.4.1         Calculation of the Maximum Axial Stress

The maximum tangential shear and torsion stresses for each element end are calculated from shear forces and section mechanical properties in the following equation:

Where:

 

	Axial force
	Net area of the cross section
	Number of high-strength frictional bolts
	Number of bolts at the calculated section

 

In CivilFEM   coefficient is given by RTB factor which can be modified with ~SECMDF command.

 

10-F.6.4.2         Calculation of GB50017 Criterion

The equivalent stress obtained is then divided by the steel design strength s_u in order to obtain a value that is stored as the CRT_TOT parameter in the active alternative in the CivilFEM’s results file for each element end. This value shall be between 0.0 and 1.0 so that the element will be valid according to the GB50017 code; therefore, the equivalent stress must be lower than the steel design stress.

 

10-F.6.5           Bending & Axial Checking

In CivilFEM, checking elements subjected to bending and axial forces according to GB50017 code is conducted for each element end of those selected elements or solid sections of the model with a cross section type of structural steel.

 

10-F.6.5.1         Calculation of the Maximum Equivalent Stress

The maximum equivalent stress in the section s^* is calculated by using:

 

Where:

 

	Bending moment in Y direction
	Bending moment in Z direction
	Moment of inertia in Y direction
	Moment of inertia in Z direction
	Product of inertia about YZ

 

Plastic development coefficients  are obtained from the associated member properties (see ~MEMBPRO command). Otherwise they should be defined according to Table 10-F.6.1.

 

10-F.6.5.2         Calculation of GB50017 Criterion

The equivalent stress obtained is then divided by the steel design strength s_u in order to obtain a value that is stored as the CRT_TOT parameter in the active alternative in CivilFEM’s results file for each element end. This value shall be between 0.0 and 1.0 so that the element will be valid according to the GB50017 code; therefore, the equivalent stress must be lower than the steel design stress.

10-F.6.6           Compression Buckling Checking

In CivilFEM the checking of elements considering buckling according to GB50017 code is done for each element end of those selected elements or solid sections of the model with a cross section type of structural steel and subjected to a compressive force.

10-F.6.6.1         Calculation of the Maximum Equivalent Stress

The maximum equivalent stress in the section s^* is calculated by using:

 

Where   is the stability coefficient for axially compressed members. The stability coefficient  is calculated from the slenderness ratio:

Where:

 

L	Unbraced length of member (see ~MEMBPRO command)
	Buckling length factors in Y axis (see ~MEMBPRO command)
	Buckling length factors in Z axis (see ~MEMBPRO command)
	Rotational radius to Y axis
	Rotational radius to Z axis

 

In non symmetric sections, the axes are defined as the directions of principal inertia.

To compute:

a)    If  then 

 

b)    Otherwise:

 

Where  are chosen according to the following table:

 

Table  10-F.6.2   Coefficients

CROSS SECTION
a		0.410	0.986	0.152
b		0.650	0.965	0.300
c		0.730	0.906	0.595
			1.216	0.302
d		1.350	0.868	0.915
			1.375	0.432

 

The cross section type is determined from tables of chapter 10-F.5.3

 

10-F.6.6.2         Calculation of GB50017 Criterion

The equivalent stress obtained is then divided by the steel design strength s_u in order to obtain a value that is stored as the CRT_TOT parameter in the active alternative in CivilFEM’s results file for each element end. This value shall be between 0.0 and 1.0 so that the element will be valid according to the GB50017 code; consequently, the equivalent stress must be lower than the steel design stress.