Kisssoft Bolt Analysis Manual

Chapter 38 IV-750 Bolts

38 Bolts

Chapter 38BoltsKISSsoft calculates bolt joints in accordance with VDI 2230 (2003). The bolt calculation functions help you find your way through the maze of tables and data defined in the standards. In addition to providing tables with standard values, the program also has a range of options that allow you to enter your own definitions for most of the constraint values (such as geometry and material data). Although the VDI 2230 standard does not have iteration functionality, i.e. it can be calculated manually, the flexible input and modification options give you a userfriendly soft-ware solution at your fingertips. However, you must be familiar with VDI 2230 before you can interpret the results and enter the required values correctly in the program.

VDI 2230 compares the permissible assembly preload (FM and also, to some extent, FMzul) with the minimum and maximum assembly preload (FMmax and FMmin). Here the first is a value calculated with 90% of the bolt yield point and the last two are determined by the loads required to guarantee that the joint functions correctly. Assembly preload FMzulis therefore determined from the strength of the bolt, while assembly preloads FMmin and FMmax are determined from the function of the connec-tion. The necessary assembly preload FMmin is calculated from the axial force FA

and the resilience of the parts and the screw , the embedding loss FZ, the thermal forces FV th and the required clamping force FKerf. FMmaxcan be calculated from FMmin while taking into consideration the coefficient of friction and the tightening technique (tightening factor A).

(38.1)

(38.2)

The necessary assembly preload FMmax must now be smaller than the sustainable pretension of the bolt FMzul. Similar to this comparison is the comparison between the minimum required assembly preload FMminand the minimum preload achieved by tightening at, for instance, 90% of the yield point FMzul/ A:

(38.3)


38.1 Inputs for Basic dataThe entries you make in the Basic Data tab form part of the service- and bolt data and include the bolt type, washers, and the tightening technique.

Figure 38.1: Basic data input tab.

38.1.1 Working dataYou enter operating data in the Basic data tab. You can then use it for the following screwing configurations:

1. Bolted joint subject to an axial load

2. Bolted joint subject to an axial and a transverse load

3. Flanged joint with torque and loads

4. Multi-bolted plate joint for any bolt position


An axial loading FAmax,FAmin and a required clamping force FKerf are determined each time, from the operating data.

Figure 38.2: Bolting configurations: 1/2, 3 and 4

3 8. 1 . 1 . 1 B olt e d jo in t su b je ct t o an axi al lo adThe occurring axial forces FAmax and FAmin are entered directly. The necessary clamping force FKerf is defined in accordance with

(38.4)

and the required clamping force for axial load transmission FKQ and the sealing function FKP are calculated. FKA is present to prevent gaping in the required clamping force and is calculated by the program.

3 8. 1 . 1 . 2 B olt jo int u nd e r axi al a n d sh e arin g fo rc eIn the second configuration, the required clamping force for axial load transmission is calculated from the shearing force FQ, the torque MT , the coefficient of friction mT , the diameter da and the number of load transmitting interfaces qT :

(38.5)


(38.6)

FKQ Required clamping force for transferring a shearing force and/or a torque through friction grip (for e.g. for friction grip)

FKP Clamping force required to guarantee a sealing function (required when internal pressure is present)

T Interface coefficient of friction (when shearing force or torques are present), see Figure on page IV-753.

3 8. 1 . 1 . 3 Flan g e d jo int wit h t o rq u e and lo ad sThe forces on the single bolt in the case of flanged joints (with stress from torque and/or shearing force and/or bending moment and/or axial force) are calculated in accordance with [63], and also partially in accordance with [61], Example. 8.4:

d Bolt nominal diameter

n Number of bolts

T Coefficient of friction between the parts, see Figure 38.3

FQ Shearing force on configuration

FAmax Axial force on configuration (maximum)

FAmin Axial force on configuration (minimum) Resultant operating load on the bolt that is subject to the highest stress:

FBo Upper threshold value


FBu Lower threshold value

FKP Configuration sealing load

FKerf? Required clamping force

MB Bending moment on configuration

MT Torque on configuration

FKerf Required clamping force

FKQe Required clamping force (e.g. for friction grip)

FKPe Required clamping force to ensure sealing (for internal pressure)

FKA Required clamping force to prevent gaping under eccentric load

If you select a flanged joint configuration, we strongly recommend that you define the geometry of the stressed parts as individual annulus segments. The program then automatically generates a suggested value for the pitch (tt) and the screw radius (trs).

Experience shows that the results of VDI 2230 are usually very conservative for flanged joints. In order to achieve realistic results, you should increase the coefficient of friction between the parts.

Figure 38.3: Interface friction grip coefficients in accordance with [75]

3 8. 1 . 1 . 4 M ul ti - sc re we d p lat e jo i nt fo r an y sc re w p o sit i o nFor multi-bolted plate joints, you can define bolts in any position subject to shearing force and a bending moment in two directions as well as a torsional mo-ment. The bolts load distribution is calculated assuming that rigid plates are


connected by springs at the bolts positions. By using a rigidity coefficient you can model different bolt diameters (doubled diameter equals fourfold rigidity).

Once you have entered the operating data in the Basic data tab, you can define the screw positions in the Positions of Bolt tab. You can either enter the bolt positions in a table or import them from a file. The resulting axial forces as well as the clamping forces required to transmit shearing force are also displayed in the table.

Figure 38.4: Bolt position tab

Optionally an additional factor for thrust bolts can be defined, in which it is assumed that compression is transmitted directly via the plates. However, you must know what you are doing when you select this coefficient. In [62], under the keyword Multi-bolted Plate Joint, for example, an average pressure point of ¼ plate height is assumed. You use the factor for thrust bolts to set this status.

The program then automatically selects the bolt with the highest axial force for the calculation. As a rule and, to ensure that the calculation results are on the safe side, the maximum required clamping force is used for all bolts. However, you can select a further option to deactivate this function.

When you calculate the necessary clamping force, you can also take the prefix of the shearing force into account. Shear loads caused by torsional and transverse for-ce are then added at specific points and subtracted at other points. You should only include the prefix if you know the direction of the shearing force and if this force is constant.

To save you having to specify the sequence in which the incremental distances between the bolts repeat themselves, for every single bolt, you can define the posi-


tion of particular bolts in the Sizing function. Click the button in the table (above, on the right) in the Bolt position tab to open this window where you can enter different configurations.

You can enter these values here:

line (values for: starting point, end point, number of bolts)

circle (values for: center point, radius, number of bolts)

circle segment (values for: radius, starting angle, end angle, number of bolts)


Figure 38.5: Size position of bolt

Figure 38.6: Position sizing options

You can add positions by transferring existing positions, however, if you only want to use positions shown in the configuration, you must delete all the others.

38.1.2 Screw dataThe type, geometry, surface roughness and strength class of a bolt can all be defined as bolt data.

Bolt type: the following standard bolt data stored in the database can be accessed to help define a particular bolt type:

EN ISO 4762/ Cylindrical screw with socket head bolt

DIN 912 Standard thread M1.6 - M64

EN ISO 4014/ Hexagon headed bolts with shank (formerly DIN 931 T1)

DIN EN 24014 Standard thread M1.6 - M64

EN ISO 4017/ Hexagon headed bolt with thread to head (formerly DIN 933)

DIN EN 24017 Standard thread M1.6 - M64


EN ISO 1207/ Cylinder head stud with slot

DIN 84 Standard thread M1.0 - M10

EN ISO 8765 Hexagon headed bolt with shank

Fine thread M8.0 - M64

EN ISO 8676 Hexagon headed bolt without shank

Fine thread M8.0 - M64

EN 1662 Hexagon headed bolt with flange, light series form F

Standard thread M5.0 - M16

EN 1662 Hexagon headed bolt with flange, light series form U


EN 1665 Hexagon headed bolt with flange, heavy series form F


EN 1665 Hexagon headed bolt with flange, heavy series form U


ASME B18.2.1 Square bolts, UNC thread, 0.25-1.5in

ASME B18.2.1 Hex bolts, UNC thread, 0.25-4in

ASME B18.2.1 Heavy hex bolts, UNC thread, 0.5-3 in

ASME B18.2.1 Hex cap screws, UNC thread, 0.25-3 in

ASME B18.2.1 Heavy hex screws, UNC thread, 0.5-3 in

Reference diameter: you can input any value as the reference diameter or,

after entering the operating data, click a button to input an approximate size. This sizing function usually leads to bolt diameters that are too large. We therefore recommend you input a value that is 1 or 2 standard sizes less than the system's propsed value.

Bolt length: if you are entering your own bolt geometry, you can input any value as the bolt length. Otherwise, after you input the bolt length, the system sets it to the next standard length.

Surface roughness of thread/head support: the surface roughness influences the amount of embedding and consequently the preload loss of the screw connection.

Strength class: behind the input field for standard strength classes, click

the button to define your own strength values.

Own definition of bolt geometry: to define your own bolt geometry, set the Bolt type selection list to Own input. This activates the Define... button and can be used to input your own values for bolt geometry.


Figure 38.7: Dialog with three tabs for defining your own bolt geometry.

Figure 38.8: Bolt geometry

1. General: input the bolt head dimensions and the hole diameter if a bored bolt is being used.

2. Thread: input for the standard value, thread size, pitch and thread length.

3. General: values for the individual bolt cross-sections. button adds a

new cross-section, button removes the selected one. Click the but-ton to delete all the cross-sections.


38.1.3 Type of bolt connectionTo define the bolt joint type, activate either Nut or Blind hole. This corresponds to the difference between Through-bolt and Single-bolt joints as defined in VDI. Click on the appropriate Define... button to open the corresponding input dialog for additional data about the nut or the threaded part.

Figure 38.9: Input dialog for data about thread and nut

For cut threads, the counter bore depth ts describes a threadless milling that is primarily designed to extend the clamping length (see also Figure on page IV-757).


38.1.4 WashersIf this flag is set, a flat washer is inserted between the nut and the part and/or the head and part. Click Define to enter additional data

Figure 38.10: Defining washers.

38.1.5 Tightening techniqueUncertainties such as, for example, the variation of coefficients of friction, differently precise tightening techniques, instrument, operating and reading errors result in the variation of the achievable assembly preload. For this reason, oversizing the bolt is necessary, and is expressed by the tightening factor A = FMmax/FMmin. If the required minimum preload FMminremains constant, then an increasing tightening factor A means that the bolt must be sized for a larger maxi-mum assembly preload FMmax (due to the greater variation). Tightening technique and associated tightening factors:

Tightening fac-

tor A

Tightening technique Adjusting technique

1,0 Yield point-determinedTightening mechanically or manually

1,0 Angle of rotation-controlledtightening mechanically or

Experimental determination ofthe preload moment and angle of


manually rotation

1.2 to 1.6 Hydraulic tightening Adjustment by means of measuring length or pressure

1.4 to 0.25 Torque controlled tightening with a torque wrench, torque indicating wrench or a precision torque wrench with dynamic torque measurement

Experimental determination of the required tightening torques on the original bolting part, e.g. by measuring the length of the bolt

1.6 to 1.8 ditto Defining the nominal tightening torque by estimating the coefficient of friction (surface andlubrication ratios)

1.7 to 0.25 Torque controlled tightening with a torque wrench

Torque wrench adjustment with a tightening torque, set to the nominal tightening moment (for an estimated coefficient of friction) plus a supplement.

2.5 to 0.25 Pulse controlled tightening with a percussion wrench

Torque wrench adjustment with tightening torque as described above


38.2 Data input for clamped partsThe Clamped parts mask displays data about the materials and geometry of the clamped parts, the distances involved for eccentric load/clamping and data about the load introduction factor.

Figure 38.11: Tab: Clamped parts.

38.2.1 Geometry of clamped partsThere are several basic types of clamped parts:

Plates

Cylinder

Prismatic solids

Segments of annulus


Figure 38.12: Clamped parts.

If you select Plates, it is assumed that the clamping cone will be able to expand freely sidewise. For all the other selection options, click the Geometry button to enter the type of clamped part you want to use in the calculation.

Figure 38.13: Geometry inputs for the cylinder, prismatic bodies and annulus segments.


Click the Bore button to define a threadless through-bore in the part. You can also define chamfers at the head and or nut here. These chamfers are then includedwhen the bearing areas are calculated. The chamfering reduces the outside radius of the bearing area therefore increases the surface pressure.

Figure 38.14: Defining through-bores and chamfers under head and nut.

You simply enter the different material situations in the list. The upper values for permissible pressure, e-module and thermal expansion are material values that apply to room temperature and, unless they are values you entered, always shown with a gray background. If the "Calculate temperature dependent material data automatically with estimation formulae" in Calculations/Settings is set, the values for running temperature are calculated empirically and displayed in the lower half of the particular material. You cannot edit these values. If the flag is not

set, you must input your own values. Click the buttons to call the particular

empirical formulae so they can be applied in the calculation. Click the button

to add a material and the button to delete the selected element. Click the button to delete all the elements. The calculated clamping length is displayed in the lk field.


38.2.2 Distances for eccentric clamping/load

Figure 38.15: Possible load cases in the case of eccentric clamping.

As you can see in Figure 38.12, the axis of the center of gravity of the clamp solid -axis. The distance between load

line of action A - A and the center of gravity axis 0 - 0 is always positive. The dis-tance s between bolt axis S - S and center of gravity axis 0 - 0 is set as positive, if the bolt axis S - S and the load line of action A - A lie on the same side as the cen-ter of gravity axis 0 - 0, if not, this value is negative.

The dimension u defines the distance of the center of gravity axis 0 - 0 to the point at which gaping first occurs. In Figure 38.12 this is the distance to the right-hand side in cases 1 and 2, but the distance to the left-hand side in case 3.

38.2.3 Load applicationThe VDI guideline issued in 2003 defines equations for calculating the load appli-cation factor. Here, you must select a configuration in accordance with Figure 38.13. The parting line must lie within the range shown in gray. The length of the clamped parts h, the distance to the connection piece akand the length of the connected solid lA as shown in Figure 38.14 define the position of the application of load point and therefore also the load application factor.

In single bolt connections, only configurations SV1, SV2 and SV4 are available. You must use the height hESV up to the parting line as the height h.


Figure 38.16: Configurations for defining the load application factor as shown in VDI 36 (16 edition).

Figure 38.17: Inputs for defining the load application factor as shown in VDI 36 (17 edition).


38.3 Input the Constraints dataIn this calculation, you can define the yield point, the maximum assembly preload or both tightening torques as constraints. If you define the maximum and minimum tightening torque as constraints, the tightening factor is then calculated from this torque variation and the friction coefficient variation. You can also enter values for the number of load cycles, embedding amount, preload loss and temperatures for the screw connection in this window.

Figure 38.18: Preset values, ready for input.

Use of the yield point In usual bolt layouts, the bolt is tightened to 90% of its yield point to calculate the pretension force. However, if you use yield point or angle-of-rotation controlled tightening, you can increase this value up to 100%.

Assembly and working temperatureThe extension to KISSsoft's bolt calculation function allows it to be used in the calculation standard specified in VDI 2230, which also calculates bolt connections for working temperatures between -200 and +1000 degrees Celsius. You can specify different temperatures for the bolt and the clamped parts. You can also take into account the temperature-dependent changes in the Young's modulus, in the thermal expansion coefficients, in the yield point and in the pressures permitted for the materials. You can either use empirical formulae to calculate these temperature-dependent values or specify your own values. Since the empirical formulae for steel have already been determined, you should check the values for hightemperature changes or, even better, enter your own values here.


All the criteria for the bolt connection are checked for assembly status at ambient temperature as well as for stationary or non-stationary status at working temperature (in accordance with VDI 2230: preload, bolt load, endurance limit and surface pressure).

KISSsoft automatically performs the calculation for assembly and working temperatures at the same time. This calculation should also be performed for a hig-her temperature difference between the bolt and the parts. The minimum temperature difference between the parts or the bolt and the assembly temperaturemust, at least, equal to 30 °C, so that results appear in the report.

38.3.1 Coefficient of fricti onKISSsoft allows you to specify an interval for coefficients of friction. The mini-mum value is used for calculation with FM, FMmax and the maximum value is used for calculation with FMmin and FM/ A. The maximum value therefore affects the variation of the tightening torques.

Figure 38.19: Coefficients of friction in the thread.


Figure 38.20: Coefficients of friction in head bearing area and nut bearing area.

38.3.2 Angle of rotation -controlled tighteningFor the angle of rotation-controlled tightening, the report displays a preload torque and an angle of rotation split into a number of steps. Here you can enter the value for this preload torque and the number of steps. The angle of rotation is then calculated with the medium assembly preload (FM + FM/ A)/2. If you use a yield point of 100%, this force is applied up to the yield point. To calculate the tightening angle of rotation you can also enter the required plastic elongation of the weakest cross section.


38.4 Stripping strengthSelect Reports/Stripping strength to check the stripping strength of the thread in accordance with VDI 2230 Chapter 5.

Figure 38.21: Input for calculating the stripping strength

This is where you enter values for the length of engagement, tensile strength of bolt/nut and the ratio of shearing strength bolt/nut. When you open this window it already contains default values for the bolt calculation. You can still change these values.

A report then shows the stresses, the minimum length of engagement and the safety against stripping under a load with maximum pretension force for this joint.


38.5 SettingsSelect Calculations > Settings to enter additional values:

Figure 38.22: Coefficients of friction in the thread.

Continue calculation if error messages appear If you set this flag, the calculation will continue even if error messages appear, for example to warn you that the yield point or the permitted pressure has been exceeded.

Operating force only at operating temperature Normally, KISSsoft calculates the minimum preload based on the required clamping load and loading at ambient and working temperatures. This flag can be set when the working load only occurs at working temperatures. In this case, the minimum preload is then only calculated at working temperature.

Calculate minimum preload achieved FM/ A .If this flag is set, the load FM/ A is also calculated. The preload force FM/ A is the minimum preload force that must be present, if the entered FM is included in the preload force. a is the tightening factor; it describes the variation in pre-load. If this option is set, the results overview in the main screen mask shows the results of the calculation with FM, otherwise the results with FMmax appear.

Do not increase required clamping force for eccentric clamping KISSsoft increases the required clamping force to prevent gaping for eccentric clamping. You can switch off this function here. You can then specify your own required clamping force. Take care when using this option. The calculati-on assumes that gaping does not happen!

Automatically define temperature- dependent materials data KISSsoft uses empirical formulae to automatically calculate materials data at


working temperature. These empirical formulae do not take into account the material data you entered, they use a average dependency for "commonly-used steels"! Delete this flag if you want to enter your own materials data at working temperature.

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