Single-Span Steel Beam STT User Manual for Frilo design applications Friedrich + Lochner GmbH 2011 Frilo on the web www.frilo.com E-Mail: info@frilo.de STT manual 2a/2011 STT Single-Span Steel Beam 1
Frilo-Application: STT - Single-Span Steel Beam This manual describes the work with the STT application. Inhaltsverzeichnis Application options... 3 Basics of calculation... 4 Design values oft he internal forces... 4 Load cases fort he calculation oft he internal forces... 4 Load case combinations fort he calculation oft he internal forces... 5 Concurrent and alternative groups... 6 Types of analyses... 7 Analyses in the ultimate limit states... 7 Analysis in the limit states of serviceability... 7 Load transfer... 7 Basic parameters... 8 Standard and safety concept... 8 Structural safety... 8 Serviceability... 8 System... 9 Material... 9 Single-span beam... 9 Supporting conditions... 11 Remarks... 11 Loads... 12 Standard loads... 12 Vertical load... 12 Horizontal loads... 13 Node loads... 14 Bar Loads... 16 Calculation and analysis... 19 Analysis in the ultimate limit state... 19 Analysis in the serviceability state... 19 Comments... 19 Output... 20 Function key bar... 20 General... 20 System... 20 Loads... 21 Results... 21 Result graphs... 21 Load transfer... 22 System transfer to the BTII application... 22 Transfer of bearing forces... 22 Frequently asked questions... 23 System... 23 Loads... 23 Calculation... 23 2 Frilo Structural analysis and design
Application options Design standards The STT application performs structural safety analyses in accordance with the Equivalent Bar Method for beams of steel profile s as per EC 3 (EN 1993-1-1) under planned (ec-)centric loading. The regulations of National Appendices are taken into consideration - DIN EN 1993-1-1/NA - ÖNORM B 1993-1-1 - NA to BS EN 1993-1-1 - NEN EN 1993-1-1/NB - NBN EN 1993-1-1 ANB - CSN EN 1993-1-1/NA System The single-span beam system is supported. Loads You can expose the beam system to vertical and horizontal loading and moments on left and right edges. But you cannot define loading that produces planned torsion. Calculation STT generates automatically the appropriate load cases and load case combinations depending on the defined actions and performs the necessary analyses, whereby the decisive load case combination is determined for each limit state. Interfaces to other applications You can transfer the characteristic bearing forces to the applications - STS Steel Column - B5 Reinforced Concrete Column - BTII Lateral Torsional Buckling according second order theory. STT Single-Span Steel Beam 3
Basics of calculation The basis of calculation of the STT application is the standard series Eurocode 3. The National Appendices for Austria, Great Britain, the Netherlands, Belgium and the Czech Republic are implemented in the current version of the application. Design values oft he internal forces Load cases fort he calculation oft he internal forces The load cases are generated from the loads entered by the user independent of the selected design standard. The load cases for permanent and transient actions are always generated separately. The classification scheme is illustrated in detail in the table below. Code G inf G sup-inf Q sup Comprises the self-weight of the beam and all permanent portions of standard, node and bar loads that are included in the calculation with the lower partial safety factor for permanent actions ( G = G,inf ). Under normal conditions, the following applies: G = G,inf = 1.00. Comprises the permanent portion either of the beam self-weight or of standard, node and bar loads, which are multiplied with the difference between the upper and the lower partial safety factor for permanent actions ( G = G,sup - G,inf ). Under normal conditions, the following applies: G = G,sup - G,inf = 1.35-1.00 = 0.35 comprises in each case the variable portion of standard, node and bar loads that are included in the calculation with the upper partial safety factor for variable actions ( Q = Q,sup ). Under normal conditions, the following applies: Q = Q,sup = 1.50. Permanent actions In contrast to variable actions, permanent actions must be taken into account even if they have favourable effects. Consequently, the permanent actions must be included partially with their lower and partially with their upper partial safety factor. Therefore a load case (G inf ) is generated that comprises all permanent actions. This load case is taken into account with the lower partial safety factor for permanent actions. Subsequently, a separate load case is generated for each permanent action. The load cases (G sup-inf ) generated this way are treated like variable load cases. This ensures that they are cancelled if they have a favourable effect and that permanent loads with favourable effects are only taken into account with their lower partial safety factor. Variable actions A separate load case (Q sup ) is generated for each variable action. However, you can mark variable actions with so-called concurrent groups. Loads that are assigned to the same concurrent group always act together and therefore, must correspond to one and the same action. For each defined concurrent group, only a single load case is generated and marked with the action it is based on. All independent actions are marked with a separate load case. Apart from imposed and service loads, variable actions can also result from accidental loading due to impact, earthquake or fire. 4 Frilo Structural analysis and design
Load case combinations fort he calculation oft he internal forces Limit state and design situation To verify fully the structural safety and serviceability of a single-span-beam system you must analyse various limit states in different design situations. The ultimate limit states that can be considered in STT are as follows: - Ultimate elastic or plastic resistance of the cross (CSR) - Lateral buckling (LB) - Lateral torsional buckling (LTB) The available serviceability limit states refer to - maximum displacement in direction of the 1 st main axis (dy) - maximum displacement in direction of the 2 nd main axis (dz) - maximum resulting displacement (dyz) If the design is performed in accordance with the partial safety concept, the following design situations can be distinguished: - the permanent and transient design situation - the accidental design situation - the characteristic (infrequent) situation - the frequent situation and - the quasi-permanent situation The accidental design situation is the decisive design situation as a result of either an accident (impact loads) or seismic loading or fire. For each of these analyses, only a single decisive load case combination exists and must comply with the combination rules as per EN 1990. Load combinations in STT The table below gives an overview of the assignment of load case combinations to the corresponding analyses. Code P/T : CSR P/T : LTB A : CSR A : LTB SERV: dy SERV: dz SERV: dyz Analysis of the elastic or plastic ultimate resistance of the cross in the permanent and transient design situation Analysis of torsional buckling or lateral torsional buckling in the permanent and transient design situation Analysis of the ultimate elastic or plastic resistance of the cross in the accidental design situation Analysis of torsional buckling or lateral torsional buckling in the accidental design situation Analysis of the maximum displacement in direction of the first main axis Analysis of the maximum displacement in direction of the second main axis Analysis of the maximum resulting displacement The user must specify the design situation the serviceability analyses should be based on. The calculation results are represented in the form of a summary in STT. STT Single-Span Steel Beam 5
Concurrent and alternative groups In most cases, the user defines loads in STT that do not comply with the load cases required for combination. He can control the application-internal generation of these load cases via the assignment of loads to concurrent and alternative groups. Loads that are assigned to the same concurrent group always apply simultaneously. The variable portions of those concurrent loads are included in one and the same load case. This means that loads of the same concurrent group must never represent different actions because the border condition that these loads must always occur simultaneously would not be fulfilled in this case. Different partial safety factors and combination coefficients could neither be taken into consideration within the same load case. Loads that are assigned to the same alternative group never apply simultaneously. Combinations of actions including load cases of the same alternative group are excluded from the analysis. Load groups that have been assigned to the same concurrent group and therefore are marked as concurrent loads can be assigned to different alternative group. As a consequence, the load cases generated from several variable loads may exclude each other. Due to this effect, the combination of concurrent and alternative groups allows you to define complex loading situations. This option is particularly suitable for the examination of wind loads from different directions or loads resulting from one and the same action, for instance. Example fort he effects of concurrent and alternative groups The following example is intended to demonstrate the effects of concurrent and alternative groups: Action 1 Load 1 Load 3 Action 2 Load 2 Load 4 Concurrent group 1 Concurrent group 2 Alternative group 1 Illustration 1: Effects produced by concurrent and alternative groups Load 1 acts in the positive y direction, load 2 acts in the negative y direction, i.e. inversely to load 1. The loads 3 and 4 produce the same situation but in the z-direction. The loads in both directions should apply simultaneously. The wind loads in opposite directions must not be defined as acting simultaneously. Therefore, the loads 1 and 3 are assigned to a concurrent group and the loads 2 and 4 to another concurrent group. All loads are assigned to the same alternative group. As a consequence, the loads 1 and 3 form a common load case and so do the loads 2 and 4 whereby both load cases exclude each other. Note: Loads that the user has erroneously assigned to the same concurrent group and the same alternative group are treated as concurrent loads. Concurrent groups have priority in practice. 6 Frilo Structural analysis and design
Types of analyses Analyses in the ultimate limit states According to EN 1990, you may apply the combination rules that produce the design values of the internal forces either to the actions or their effects. Beams are components with a critical stability. Therefore, the combination rules should be applied to the actions independently of whether the structural safety analyses are performed according to the equivalent bar system method or as 2nd order analyses. This approach is implemented in the STT application. For the analysis of the ultimate limit state of the cross, STT uses first order internal forces. The analyses of lateral buckling and lateral torsional buckling are performed on the basis of the equivalent bar system method. These analyses are preceded by a numerical calculation of the respective bifurcation load factors. Analysis in the limit states of serviceability The serviceability analysis refers exclusively to the calculation of the displacements separately for the different main axis and of the shifts resulting from this. Deformations are also calculated in a first order analysis. You should note that, in particular cases, second order deformations can be considerably larger than first order deformations. If the deformations are of particular importance, you should perform an advanced second order analysis. If you have a valid licence for BTII you can use this application for this task. Load transfer The reaction forces of the single-span-beam system can be transferred to the applications - Steel column (STS) - Reinforced Concrete Column (B5) - Girder Support (ST4) - Welding Seam (ST5) You should note in this connection that the reaction forces are calculated as characteristic values in first order analyses for each load case. If the real load conditions do not correspond to the defined standard or the loading situation leads to planned torsion, you cannot use STS for the calculation. The BTII application is available for this purpose. If you have a valid licence for BTII (2nd Order Buckling Torsion Analyses) you can transfer the structural system from STT to BTII via the data export function. The BTII application also performs second order buckling torsion analyses for more complex systems. STT Single-Span Steel Beam 7
Basic parameters Standard and safety concept Design standard Allows you to select the design standard that constitutes the basis of the structural safety analysis. When you select a national version of EN 1993-1-1 also the corresponding National Appendix is used. Consequence classes Allows you to define the consequence class the safety concept should be the based on: CC1, CC2 or CC3. (Only in combination with the analysis as per NEN EN 1993-1-1 and NBN EN 1993-1-1) Equation Allows you to specify the equation which should be used for permanent and transient design situation. Serviceability analysis This option defines the design situation as per EN 1990 which forms the basis of the serviceability analysis. Structural safety Cross- resistances Allows you to specify whether the cross- resistances should be calculated on the basis of the elastic or plastic cross al values. Self-weight Allows you to include the self-weight of the beam automatically into the calculation. Serviceability Limiting deformation A value referring to the system length that represents the limiting deformation in the respective main axes. In y-direction Specifies the permissible maximum displacement in y-direction. In z-direction Specifies the permissible maximum displacement in z-direction. Resulting Specifies the permissible maximum resulting displacement. 8 Frilo Structural analysis and design
System Material Steel grade Allows you to select the steel grade. The following steel grades are currently implemented: - Hot-rolled, non alloy structural steel - Hot-rolled structural steel, normalized - Hot-rolled structural steel, thermomechanically rolled - Hot-rolled, weatherproof structural steel - High-temperature steel - Hot-finished hollow s - User-defined steels Steel quality Allows you to select the steel quality depending on the selected steel grade. User-defined If you have selected user-defined steel among the steel grade options, a dialog for the definition of the user-defined parameters is displayed. Single-span beam Length Koordinate system System sketch l 0 x y z STT Single-Span Steel Beam 9
Cross This options displays a dialog for the selection of a steel profile. See also: Select - edit cross _eng.pdf Stress points on the cross : Double-symmetrical and single-symmetrical I- Double-T with top flange angles Square hollow Round hollow 10 Frilo Structural analysis and design
Supporting conditions Lateral support In addition to the supporting conditions which correspond to the Euler buckling modes, you can define lateral supports. This allows you to simulate applying bracing (discrete supports) or plate-type stiffening structures (continuous supports). The following supports against lateral displacement are available: - unsupported - continuously supported - supported in the middle of the span - supported in the third points - supported in the quarter points - supported at x0 height. Note: The supports are generated with a very high default spring value that produces a quasi rigid support. If you like to define more refined springs you should use the BTII application. (See interface to BTII). Location It is of essential importance for the examination of the stability to define where the lateral supports apply to the cross. The selection list allows you to specify the point of application of the lateral support. Upper chord, bottom chord and shear center are available options. Location Shear center System sketch Upper chord Upper chord y Shear center Bottom chord Bottom chord z Remarks... concerning the system The option displays a dialog for the input of text. You can describe and explain system inputs in this text. STT Single-Span Steel Beam 11
Loads Standard loads Vertical load Load definition Value System sketch gz,k Permanent part of the characteristic vertical load. by qz,k Variable part of the characteristic vertical load. gz,k qz,k by Affected width oft the vertical load. y z Action group The vertical loads are always classified as "imposed loads of class A" (action group 1). Concurrent group The vertical loads do not include any concurrent groups. Alternative group The vertical loads do not include any alternative groups. 12 Frilo Structural analysis and design
Horizontal loads Load definition Value System sketch gy,k Permanent part of the characteristic horizontal load. qy,k Variable part of the characteristic horizontal load. y gy,k qy,k bz bz Affected width oft the horizontal load. z Action group The loads are always classified as "imposed loads of class A" (action group 1). Concurrent group The vertical loads do not include any concurrent groups. Alternative group The vertical loads do not include any alternative groups. STT Single-Span Steel Beam 13
Node loads Nodes Option Abort left right The option displays the insert row for node loads. If you have already defined a node load in this row, it is deleted when you select this option. Node load affect to left support Node load affect to right support Type Option System sketch Axial force (compression positiv) in y Vertikal load in z Bending moment around y This option adds a new axial force to the list. This option adds a horizontal load in y- direction to the list. This option adds a vertical load in z- direction to the list. This option adds a new moment around the y-axis to the list. y z V z M z H y H x M y x Bending moment around z This option adds a new moment around the z-axis to the list. l 0 Load values with axial force (Compression positive) Value System sketch Gh,k Permanent part of the characteristic value of the node load. e z Qh,k Variable part of the characteristic value of the node load ey ez Eccentricity of the load application point in y-direction Eccentricity of the load application point in z-direction y z Qh,k Gh,k e y Load values with horizontal loads in y-direction Value Gk Qk ey Permanent part of the characteristic value of the node load Variable part of the characteristic value of the node load Eccentricity in the y-direction of the load referenced to the 0-point of the cross 14 Frilo Structural analysis and design
Load values with horizontal loads in z-direction Value Gk Qk ez Permanent part of the characteristic value of the node load Variable part of the characteristic value of the node load Eccentricity in the z-direction of the load referenced to the 0-point of the cross Lateral moment around y Value My,g,k My,q,k Permanent part of the characteristic moment around the y-axis. Variable part of the characteristic moment around the y-axis. Lateral moment around z Value Mz,g,k Mz,q,k Permanent part of the characteristic moment around the z-axis. Variable part of the characteristic moment around the z-axis. Action group Category and/or kind of action of the variable load part. The permanent load part is always assigned to the permanent action. Concurrent group Loads that are assigned to the same concurrent group always apply simultaneously. The variable parts of those concurrent loads are included in one and the same load case. This means that loads of the same concurrent group must never represent different actions because the border condition that these loads must always apply simultaneously would not be fulfilled in this case. Different partial safety factors and combination coefficients could neither be taken into consideration within the same load case. Alternative group Loads that are assigned to the same alternative group exclude each other. Combinations of actions including load cases of the same alternative group are excluded from the analysis. Text You can optionally enter a short note or item description that appears in the output. STT Single-Span Steel Beam 15
Bar Loads Type Option System sketch Abort Uniformly distributed load The option displays the insert row for bar loads. If you have already defined a bar load in this row, it is deleted when you select this option. A line load uniformly distributed over the total length of the Beam. gli, qli Concentrated load A concentrated load applying at the distance from the left support. Gli, Qli a Concentrated moment A moment applying at a distance, measured from the left support. Mz My a Trapezoidal load A line load linearly variable over the beam length applying at a distance from the left support. gli, qli gre, qre a l Triangular load over length A triangular load variable over the total length of the beam. gli, qli a Trapezoidal load over length A trapezoidal load variable over the total length of the beam. gli, qli gre, qre a l Load direction Option In or around the y-axis In or around the z-axis The bar loads or moments act in the global y-direction. The bar loads or moments act in the global z-direction. 16 Frilo Structural analysis and design
Load values with uniformly distributed loads Value gkle qkle ey ez Permanent part of the characteristic load. Variable part of the characteristic load. Eccentricity in the y-direction of the load referenced to the 0-point of the cross Eccentricity in the z-direction of the load referenced to the 0-point of the cross Load values with concentrated loads Value Gk Qk a ey ez Permanent part of the characteristic concentrated load. Variable part of the characteristic concentrated load. Distance of the load ordinate from the left support. Eccentricity in the y-direction of the load referenced to the 0-point of the cross Eccentricity in the z-direction of the load referenced to the 0-point of the cross Load values with concentrated moments Value Mg,k Mq,k a ey ez Permanent part of the characteristic concentrated moment. Variable part of the characteristic concentrated moment. Distance of the load ordinate from the left support. Eccentricity in the y-direction of the load referenced to the 0-point of the cross Eccentricity in the z-direction of the load referenced to the 0-point of the cross Load values with trapezoidal loads Value gkle qkle gkri qkri a l ey ez Permanent part of the characteristic load on the left. Variable part of the characteristic load on the left. Permanent part of the characteristic load on the right. Variable part of the characteristic load on the right. Distance of the load ordinate from the left support. Length of the trapezoidal load Eccentricity in the y-direction of the load referenced to the 0-point of the cross Eccentricity in the z-direction of the load referenced to the 0-point of the cross STT Single-Span Steel Beam 17
Load values with triangular loads over length Value gkle Permanent part of the characteristic load on the left. qkle Variable part of the characteristic load on the left. a Distance of the load ordinate from the left support. ey Eccentricity in the y-direction of the load referenced to the 0-point of the cross ez Eccentricity in the z-direction of the load referenced to the 0-point of the cross Load values with trapezoidal loads over length Value gkle qkle gkri qkri a l ey ez Permanent part of the characteristic load on the left. Variable part of the characteristic load on the left. Permanent part of the characteristic load on the right. Variable part of the characteristic load on the right. Distance of the load ordinate from the left support. Length of the trapezoidal load Eccentricity in the y-direction of the load referenced to the 0-point of the cross Eccentricity in the z-direction of the load referenced to the 0-point of the cross Action group Category and/or kind of action of the variable load part. The permanent load part is always assigned to the permanent action. Concurrent group Loads that are assigned to the same concurrent group always apply simultaneously. The variable parts of those concurrent loads are included in one and the same load case. This means that loads of the same concurrent group must never represent different actions because the border condition that these loads must always apply simultaneously would not be fulfilled in this case. Different partial safety factors and combination coefficients could neither be taken into consideration within the same load case. Alternative group Loads that are assigned to the same alternative group exclude each other. Combinations of actions including load cases of the same alternative group are excluded from the analysis. Text You can optionally enter a short note or item description that appears in the output. 18 Frilo Structural analysis and design
Calculation and analysis Analysis in the ultimate limit state The analyses in the ultimate limit state include the following individual verifications: - Analysis of the carrying capacity of the cross giving consideration to the local buckling failure (verification of the c/t-limiting values and assignment to cross classes). - Analysis of lateral buckling. This analysis is only performed if normal forces are applied to the beam. - Analysis of torsional and lateral torsional buckling. This analysis is only performed if the beam has an open cross and is, therefore, susceptible to torsion, and if loads apply that produce this failure mode. The stability analyses of lateral buckling and lateral torsional buckling are based on the socalled equivalent bar system method. This method requires the calculation of the bifurcation loads belonging to the respective failure mode. On the basis of these bifurcation loads, the reduction factors for lateral buckling and lateral torsional buckling can be calculated. When applying the simplified analysis, an eigenvalue calculation is performed using the subspace method. The eigenvalue determination for the FE problem requires the solution of the general matrix eigenvalue problem for the smallest eigenvalue Ki. This task is handled in STS via the calculation module of the BTII application The examination is performed for each load case combination in combination with each applicable design situation. This method ensures that the actually decisive failure situation in accordance with the safety concept can be determined. Analysis in the serviceability state The displacements in direction of the different main axis and the resulting displacement are calculated in a first order analysis. The results are compared to the parameters defined by the user. Evidence is considered to be established if the calculated displacements are smaller or equal to the user-defined values. Comments... concerning the results The option displays a dialog for the input of text. You can describe and explain calculation results in this text. STT Single-Span Steel Beam 19
Output The main menu item "Output" allows you to specify in detail the scope of data to be printed. The individual options are briefly described below. Function key bar As with all other FRILO applications, the available output media include the monitor display, MS Word and the printer. You can launch the output on the display or the printer via the corresponding menu items in the main tree. Options Word Screen Print General Selects all output items. Deselects all output items. Output directly in Microsoft Word (the editor must be installed on the local computer) Displays the values in a text window on the screen The result graphics are not shown, you can access them via the tool bar below the menu bar. The option starts the output on the printer The currently selected output profile is stored in the registry. The output profile stored in the registry is loaded. Option Summary print Legends This option allows you to reduce the output to the necessary results. When you select this option, all tables are described in detail via legends in the output. System Option System graph Scale Comments Material parameters Cross al values Supporting conditions Allows you to specify whether the system graph should be included in the output. Allows you to select the desired scale for the system graph. Allows you to specify whether the comments to the system should be included in the output. Allows you to specify whether the material parameters should be included in the output. Allows you to specify whether the cross al values should be included in the output. Allows you to specify whether the supporting conditions should be included in the output. 20 Frilo Structural analysis and design
Loads Option Remarks Actions Node and bar loads Allows you to specify whether the comments to the system should be included in the output. Allows you to specify whether the actions should be included in the output. Allows you to specify whether the node and bar loads should be included in the output. Results Option Remarks Characteristic bearing forces Load case combinations Internal forces Deformations Bearing forces Analysis of the cross Equivalent bar system method Serviceability analysis Descripition Allows you to specify whether the comments to the calculation results should be included in the output. Allows you to specify whether the characteristic bearing forces per load case should be included in the output. Allows you to specify whether the load case combinations that form the basis of the structural safety analysis should be included in the output. Allows you to specify whether the design values that form the basis of the structural safety analyses should be included in the output. Allows you to specify whether the design values that form the basis of the serviceability analyses should be included in the output. Allows you to specify whether the design values of the bearing forces belonging to the different analyses should be included in the output. Allows you to specify whether the structural safety analysis for the cross should be included in the output. Allows you to specify whether the structural safety analysis for the Equivalent bar system method should be included in the output. Allows you to specify whether the serviceability analysis should be included in the output. Result graphs Option Internal forces diagrams Scale Deformation diagrams Scale Allows you to specify whether the internal forces diagrams that form the basis of the structural safety analyses should be included in the output. Allows you to select the desired scale for the internal forces diagrams. Allows you to specify whether the deformation diagrams that form the basis of the serviceability analyses should be included in the output. Allows you to select the desired scale for the deformation diagrams. STT Single-Span Steel Beam 21
Load transfer The term load transfer refers basically to two advanced functions, the system transfer to BTII and the transfer of bearing forces for the calculation of connected structures. System transfer to the BTII application General The first advanced function is used for the export of the beam system to the BTII application for the calculation of more complex systems or to perform comparative calculations. Higher requirements on the calculation of beam systems, which cannot be fulfilled by an application such as STT, become relevant if the bearing conditions do not comply with the prescribed standard or if loads have to be included that produce either planned torsion or inconstant behaviour of the axial forces. Such systems cannot be verified using the equivalent bar system method. They require second order analyses with consideration to warping torsion. The BTII application offers the necessary performance parameters for this task. Exporting the system The beam system is represented as a system in the BTII application. The bearing conditions correspond to the structural system of the beam including the lateral supports. Exporting loads The BTII application does not use characteristic loads but load cases and load case combinations. They are generated by the STS application only after the calculation has been performed successfully. If no system calculation was performed, only the system is exported. In this case, no loads are transferred to BTII. Transfer of bearing forces STT offers a load transfer feature to other applications for the calculation of connected structures and foundations. The interfaces to STS, B5 allow the transfer of the characteristic bearing forces for the calculation of beam support. 22 Frilo Structural analysis and design
Frequently asked questions System Can I also calculate multi-span systems in STT? No. STT provides for the calculation of single-span beam only. However, you can define lateral supports in the form of discrete and continuous supports. The application point relevant for the stability analyses can be defined either on the top chord, the bottom cord or in the shear center. Loads Can I specify loads that lead to planned torsion? No. Loads that produce planned torsion are not considered in STT. The most important reason for this restriction is that the simplified equivalent bar system analysis must not be used in a comparable load situation. In such a case, a second order analysis of torsional warping is required. We like to point out in this connection that our BTII module is able to perform this task. Calculation Can I perform a second order analysis in addition to the verification on the basis of the equivalent bar system method? No. Systems requiring second order analyses can be calculated with our BTII module. STT Single-Span Steel Beam 23