Bridge Wizard

Compared to the SAP2000 standard bridge design tools available from the Define menu > Bridge Loads commands, the Bridge Modeler utility provides further advances and is easier to use when designing complex bridge structures. An additional license is required for the Bridge Modeler (see the Options menu > Request License command and its related topic in this Help for more information).

Use the Bridge Wizard form to step through the process for building a bridge model using the Bridge Modeler. The large display area on the right side of the form provides a narrative of how to use the Wizard. This topic duplicates that information as well as provides some additional information, all in a printable format.

Basic Approach

The Bridge Modeler can be used to quickly generate a bridge model. In its simplest form, three steps are involved:

1. Define Layout Lines

2. Define Bridge Deck Sections

3. Define Bridge Objects

With these three steps, SAP2000 can generate a bridge model using default definitions. After the bridge model has been built, the bridge analysis can be performed.

Note: Some of the Define menu > Bridge Loads and Bridge menu commands achieve the same result. Specifically, the following command pairs function identically:  

Define menu > Bridge Loads > Lanes                      and Bridge menu > Lanes
Define menu > Bridge Loads > Vehicle Classes      and Bridge menu > Vehicle Classes
Define menu > Bridge Loads > Vehicles                  and Bridge menu > Vehicles
Define menu > Bridge Loads > Bridge Responses  and Bridge menu > Bridge Responses

Bridge Wizard

Note: Assuming that the Bridge Modeler license has been enabled, the Bridge Wizard can be accessed at anytime (i.e., bridge objects can already have been added to a model file).

The Bridge Wizard provides a step-by-step guide through the modeling process using SAP2000's Bridge Modeler utility. The Currently Defined Items area of the Bridge Wizard form performs two functions. It provides a "tree" of the steps involved in the modeling process, and if the Wizard is accessed after a bridge model has been initiated, the area lists any items already defined (e.g., the names of layout lines, deck sections, abutment definitions and so forth). Use the Expand All and Collapse All buttons to show or hide any previously defined items.

Note:  Material, Frame Section, and Link Properties can be defined when they are added to the Bridge Model (i.e., when the Step is used, such as Step 2 Deck Section), or they can be defined before beginning the step-wise process by clicking the appropriate button that appears on the Bridge Wizard form the first time the Wizard is accessed. Click the Define/Show Material Properties button to access the Define Materials form. Click the Define/Show Frame Sections button to access the Frame Properties form. Click the Define/Show Link Properties button to access the Link/Support Properties form. Use those forms to specify the property definitions. Frame sections are used for bent caps and bent columns. Links may be used for bearings, expansion joints, restrainers, foundation springs, and other supports. Material properties are used in frame section properties and in deck section properties.

The right side of the Bridge Wizard form includes a large display area that provides a written explanation of the various steps. This topic includes that information along with additional information for using the Modeler.

Click the Show Introduction button to display the Introduction to the Bridge Modeler. The SAP2000 Bridge Modeler provides a quick and easy way of defining a bridge model. To create a bridge model, follow the steps in this wizard in order, or quickly define the first bridge model as follows:

     a.  Define a layout line (see step 1).

     b.  Define a deck section (see step 2).

     c.  Create a bridge object (see step 8).

     d.  Create a linked model (see step 9).

Then, if necessary, replace the default abutment, bent diaphragm, and hinge properties that may have been used in the bridge object with user defined new properties. Abutments, bents, diaphragms and hinges are defined in steps 3, 4, 5 and 6 of the Wizard. If desired, add prestressing tendons that are defined as a part of the bridge object definition (see step 8). After the new properties have been defined, update the linked model (see step 9).

To perform vehicle live load analysis, define lanes, vehicles, and appropriate load and analysis cases (see steps 10, 11 and 12).

To navigate through the steps in this Wizard click the Next Step and Previous Step buttons, or click one of the rows in the table, or click one of the items in the tree. Note that, as shown in the task list, some steps must be completed before others can be completed (e.g., layout lines and deck section {Steps 1 and 2} must be created before a bridge object can be generated {Step 8}).

Click the Next Step button on the Bridge Wizard.

Step 1 Layout Line becomes active. Click the Define/Show Layout Line button in the middle of the Bridge Wizard form to access the Define Bridge Layout Line form and begin defining a layout line.

Note:  At least one layout line and one deck section must be defined (Steps 1 and 2) before a bridge object can be defined (Step 8).  

Click the Set Preferences button on the Define Bridge Layout Line form to access the Bridge Layout Preferences form and specify the orientation of the North arrow relative to the X axis of the global coordinate system and the discretization (i.e., smoothness) of any curves used in the bridge model.

Layout lines are used as reference lines for defining the vertical and horizontal layout of bridge objects and lanes. Layout lines are defined in terms of stations, bearings and grades. The lines may be straight, bent or curved, both in the horizontal and the vertical plane. Horizontal curves are circular (with spirals if necessary) and vertical curves are parabolic.

Clicking the Add New Line button, or highlighting a previously defined layout line and clicking the Add Copy of Line or Modify/Show Line button, on the Define Bridge Layout Line form will access the Bridge Layout Line Data form. Use the Quick Start buttons to access the Horizontal Layout Line Data - Quick Start or Vertical Layout Line Data - Quick Start forms and select a template to quickly adjust the horizontal or vertical alignment of the layout line(s). Make a selection on that form, return to the previous form, and if necessary click the Define Horizontal Layout Data and Define Vertical Layout Data buttons to access the Bridge Layout Line - Horizontal Layout Data form and the Bridge Layout Line - Vertical Layout Data form; use those forms to make any necessary additional adjustments to the alignment. Step 7 below explains how to adjust the alignment of deck sections relative to the layout line rather than adjusting the layout line itself.  

Click the OK buttons on the individual forms until the Bridge Wizard form redisplays.

Step 2 Deck Section is active when the Bridge Wizard form redisplays. Click the Define/Show Deck Sections button near the middle of the form to display the Define Bridge Deck Sections form. Various parametric bridge deck sections are available on that form for use in defining a bridge. They include concrete box girders, concrete beam and steel beam sections. After selecting the shape for the bridge deck section, another form will display that can be used to specify the section property, material property, the slab and girder thicknesses, and the left and right overhang for the deck section. After a deck section has been defined, it can be assigned to a span during Step 8 Bridge Object Definition.

If desired the bridge section can be specified to vary parametrically along the length of the bridge. Such variations along the length of the bridge are defined for the base section as described in Step 7 Parametric Variations.  Then both the base section and the specified variation are assigned to a span in the bridge object (see Step 8).

Note:  At least one deck section and one layout line must be defined (Steps 2 and 1, respectively) before a bridge object can be defined (i.e., before a model can be created using the Bridge Modeler utility, as described in Step 8).

Click the OK buttons on the individual forms until the Bridge Wizard form redisplays.

Step 3 Abutment Definition is active when the Bridge Wizard form redisplays. Click the Define/Show Abutments button to access the Define Bridge Abutments form. Abutment definitions specify the support conditions at the ends of the bridge. Click the Add New Abutment button or highlight the name of an existing abutment definition and click the Add Copy of Abutment or Modify/Show Abutment button to access the Bridge Abutment Data form. Use that form to specify the abutment definition.

An abutment definition can be a specified Link/Support property or it can be a user defined support condition.  The user support condition allows each of the six degrees of freedom at the abutment to be specified as fixed, free or partially restrained with a specified spring constant. An abutment definition also allows the horizontal location of the abutment supports to be specified.  A single abutment support can be located at the reference line location or multiple abutment supports can be located at each girder or equally spaced over the bridge width. When multiple locations are indicated, the specified abutment support properties are provided at each support location.

It is also possible to specify that a closure (vertical diaphragm) of some thickness be provided at the abutment.  This closure is only applicable to area object and solid object models; it does not apply to spine models.

After an abutment property has been defined, it can be assigned to the bridge during Step 8 Bridge Object Definition.

Note: It is not necessary to define an abutment before defining a bridge object (see Step 8).  If no abutments are defined when a bridge object is first defined, the program automatically creates a default abutment. If appropriate, skip this step by highlighting another step on the Bridge Wizard.

Click the OK buttons on the individual forms until the Bridge Wizard form redisplays.

Step 4 Bent Definition is active and the Define/Show User Support and the Define/Show Bents buttons display on the Bridge Wizard form. Bent definitions specify the geometry and section properties of the bent cap beam and the bent column(s). They also specify the base support condition of the bent columns. The specified base support condition for a bent column can be fixed, pinned or a user defined column support.  A user defined column support can be a specified Link/Support property or it can be a user defined support condition. The user support condition allows each of the six degrees of freedom at the column base to be specified as fixed, free or partially restrained with a specified spring constant. The user defined column support is defined separately from the bent.

Click the Define/Show User Support  button to access the Define Bridge Foundation Springs form. Click the Add New Foundation Springs button or highlight an existing definition and click the Add Copy of Foundation Spring or Modify/Show Foundation Spring button to access the Bridge Column Support Data form; use that form to define the bridge column(s).

Click the Define/Show Bents button to access the Define Bridge Bents form. Click the Add New Bridge Bent button or highlight an existing definition and click the Add Copy of Bridge Bent or Modify/Show Bridge Bent button to access the Bridge Bent Data form. It is also possible to specify that a closure (vertical diaphragm) of some thickness be provided at the bent location. This closure is only applicable to area object and solid object models; it does not apply to spine models.

After a bent has been defined, it can be assigned to the bridge during Step 8 Bridge Object Definition.

Note:  It is not necessary to define a bent before defining a bridge object (see Step 8).  If no bents are defined when a bent is first added to a bridge object, the program automatically creates a default bent. If appropriate, skip this step by highlighting another step on the Bridge Wizard.

Click the OK buttons on the individual forms until the Bridge Wizard form redisplays.

Step 5 Diaphragm Definition is active when the Bridge Wizard form redisplays. Click the Define/Show Diaphragm button to access the Define Bridge Diaphragm Properties form. Click the Add New Diaphragm button, or highlight an existing definition and click the Add Copy of Diaphragm or Modify/Show Diaphragm button, to access the  Bridge Diaphragm Property form; use the form to specify the type and parameters for a bridge diaphragm. Diaphragm definitions specify properties of vertical diaphragms that span across the bridge. A diaphragm property can be solid concrete; steel X, V or K bracing; or a single steel beam. Solid concrete diaphragm properties are only applicable to concrete bridge sections. Steel diaphragm properties are only applicable to steel bridge sections. Diaphragms in general are only applicable to area object and solid object models; they do not apply to spine models. After a diaphragm definition has been created it can be assigned to one or more spans in the bridge object (see Step 8). It is not necessary to define a diaphragm property before defining a bridge object.  If no diaphragms are defined when a diaphragm is first added to a bridge object, the program automatically creates a default diaphragm property.

Click the OK buttons on the individual forms until the Bridge Wizard form redisplays.

Step 6 Hinge Definitions is active when the Bridge Wizard form redisplays. Click the Define/Show Hinges button to access the Define Bridge Hinges (Expansion Joints) form. Click the Add New Bridge Hinge button or highlight a previously defined hinge definition and click the Add Copy of Bridge Hinge or Modify/Show Bridge Hinge button to access the Bridge Hinge (Expansion Joint) Data form; use the form to define bridge hinges (expansion joints).

Hinge definitions specify properties of hinges (expansion joints) and restrainers. A hinge property can be a specified Link/Support property or it can be a user defined spring. The user spring allows each of the six degrees of freedom at the hinge to be specified as fixed, free or partially restrained with a specified spring constant. A restrainer property can be a specified Link/Support property or it can be a user defined restrainer.  The user restrainer is specified by a length, area and modulus of elasticity.

A hinge definition also allows the horizontal location of the hinge springs and restrainers to be specified.  A single hinge spring (and restrainer) can be located at the reference line location or multiple hinge springs (and restrainers) can be located at each girder or equally spaced over the bridge width. When multiple locations are indicated, the specified spring and restrainer properties are provided at each support location.

It is also possible to specify that a closure (vertical diaphragm) of some thickness be provided at the hinge location. The specified closure is provided on each side of the hinge. This closure is applicable only to area object and solid object models. It does not apply to spine models.

After a hinge definition has been created, it can be assigned to one or more spans in the bridge object (see Step 8).

Note:  It is not necessary to define a hinge before defining a bridge object (see Step 8).  If no hinges are defined when a hinge is first added to a bridge object, the program automatically creates a default hinge. If appropriate, skip this step by highlighting another step on the Bridge Wizard.

Click the OK buttons on the individual forms until the Bridge Wizard form redisplays.

Step 7 Parametric Variations is active when the Bridge Wizard form redisplays. Click the Define/Show Variations button to access the Define Parametric Variations form. Click the Add New Variation button or highlight a previously defined variation and click the Add Copy of Variation or Modify/Show Variation button to access the Variation Definition form. Use that form to specify a variation for all or part of the bridge alignment.

Note:  If no variations apply, skip this step by highlighting Step 8 on the Bridge Wizard form.

Parametric variations define variations in the deck section along the length of the bridge. Any parameter used in the parametric definition of the deck section can be specified to vary.  One or more of the parameters can vary at the same time.  Each varying parameter can have its own unique variation. Example uses of parametric variations include varying the bridge depth and the thickness of girders and slabs along the length of the bridge.  The variations may be linear, parabolic or circular. After a variation has been defined, it can be assigned to spans in the bridge object (see Step 8).  When a variation is defined, it should be defined with the same total length as the bridge span to which it is assigned.

Click the OK buttons on the individual forms until the Bridge Wizard form reappears.

Step 8 Bridge Object Definition is active when the Bridge Wizard form redisplays. Click the Define/Show Bridge Objects button to access the Define Bridge Objects form. Click the Add New Bridge Object button or highlight a previously defined bridge object and click the Add Copy of Bridge Object or Modify/Show Bridge Object button to access the Bridge Object Data form.  

The bridge object is the heart of the bridge modeler. Use the Bridge Object Data form to make the necessary definitions and assignments, as follows:

1. Define the bridge spans.

2. Assign deck section properties to each span.

3. Assign parametric deck section variations to each span. Click the Modify/Show Span button to access the Bridge Object Span Definition form. Use that form to review the deck section (a and b in this list) and any variations (c in this list) defined for each span of the named bridge object.

4. Assign user specified discretization points. Click the Modify/Show User Discretization Points button to access the Bridge Object Discretization Points Definitions form. Use that form to add discretization points to selected bridge spans. Adding/specifying points can be useful when displaying bridge forces.

5. Assign abutment properties and skews. Click the Modify/Show Abutments  button to access the Bridge Object Abutment Definition form. Use that form to review, and if necessary modify, the abutment property and bearing.

6. Assign bent properties and skews. Click the Modify/Show Bents button to access the Bridge Object Bent Definition form. Use that form to review, and if necessary modify, the bent property, bearing, and if applicable horizontal and vertical offsets.

7. Assign hinge locations, properties and skews. Click the Modify/Show Hinges (Exp. Joints)  button to access the Bridge Object Hinge Definition form. Use that form to review, and if necessary modify, the hinge property, distance and bearing.

8. Assign diaphragm properties. Click the Modify/Show Cross Diaphragms button to access the Bridge Object Diaphragm Definition form. Use that form to add diaphragms to the bridge model.

9. Assign superelevations to the bridge model. Click the  Modify/Show SuperElevation button to access the Bridge Object SuperElevation Definition form. Use that form to specify the superelevation for the selected layout line.

10. Define prestressing tendons. Click the Modify/Show Bridge Prestress button to access the Define Prestress Tendons form. Click the Add New Tendon button, or highlight an existing tendon definition and click the Add Copy of Tendon or Modify/Show Tendon button, to access the Bridge Tendon Data form.  Use that form to define the tendon, including the vertical and horizontal layout or click the associated Quick Start buttons to select template alignments.

Any time a bridge object definition is modified, the linked model must be updated (see step 9) for the changes to display in the SAP2000 model. Click the OK buttons on the individual forms until the Bridge Wizard form redisplays.

Step 9 Update Linked Model is active when the Bridge Wizard form redisplays. Click the Update Linked Model button to access the Update Bridge Structural Bridge Model form. The update linked model command creates the SAP2000 object-based model from the bridge object definition. If an object-based model of the bridge object already exists, it will be deleted and a new object-based model will be created that includes all of the latest changes to the bridge object definition. Use the options on the Update Bridge Structural Bridge Model form to specify creation of spine models, area object models or solid object models of the bridge when the linked model is updated. Use the options to switch the type of object-based model created from a bridge object definition at any time.

Click the OK buttons on the individual forms until the Bridge Wizard form redisplays.

Step 10 Lane Definition  is active when the Bridge Wizard form redisplays. Click the Define/Show Lanes button to access the Define Lanes form. Lanes must be defined if you want to analyze your bridge for vehicle live loads. As noted in the Prerequisite column of the task list on the Bridge Wizard, lanes can be defined with reference to layout lines (the 1 in the Prerequisite column means Step 1 Layout Lines) or existing frame objects (Frames in the Prerequisite column).  A single lane is referenced to one or more layout lines or one or more frame objects but not a combination of layout lines and frame objects. Lanes can be defined with width if desired. Lanes are used in the definition of Moving Load type analysis cases and in Moving Load type load cases that can be used in static and dynamic multi-step analysis cases.

Click the OK buttons on the individual forms until the Bridge Wizard form redisplays.

Step 11 Vehicle Definition is active and the Define/Show Vehicles and Define/Show Vehicle Classes buttons display on the Bridge Wizard form. Click the Define/Show Vehicles button to access the Define Vehicles form. Use that form to add, modify, or delete vehicles types. Click the Define/Show Vehicle Classes buttons to access the Define Vehicle Classes form. Use that form to add, modify, or delete vehicle classes.

Vehicles must be defined if you want to analyze your bridge for vehicle live loads. In SAP2000 vehicles loads are applied to the structure through lanes. To use a moving load type analysis case, one or more vehicle classes also must be defined. A vehicle class is simply a group of one or more vehicles for which a moving load analysis is performed (one vehicle at a time). Numerous standard vehicle definitions are built into the program. In addition the General Vehicle feature can be used to create your own vehicle definition.  Each vehicle definition consists of one or more concentrated and uniform loads.

Click the OK buttons on the individual forms until the Bridge Wizard form redisplays.

Step 12 Analysis Cases is active and the Define/Show Loads and Define/Show Analysis Cases buttons display on the Bridge Wizard form. Click the Define/Show Loads button to access the Define Loads form. Click the Define/Show Analysis Cases button to access the Analysis Cases Data form.

Although any analysis case type can be used when analyzing your bridge model, several analysis options are specialized for analysis of vehicle live loads. Moving load analysis cases compute influence lines for various quantities and solve all permutations of lane loading to obtain the maximum and minimum response quantities. Multi-step static and multi-step dynamic (direct integration time history - linear, nonlinear) analysis cases can be used to analyze one or more vehicles moving across the bridge at any speed.  These multi-step analysis cases are defined using special moving load type load cases that define the direction, starting time and speed of vehicles moving along lanes.

Click the OK buttons on the individual forms until the Bridge Wizard form redisplays.

Step 13 Bridge Response is active when the Bridge Wizard form redisplays. Click the Define/Show Response Data button to access the Bridge Response Requests form. Use the options on that form  to selectively control what information is calculated for joints and frame objects in the computationally intensive moving-load analysis.

Solution of moving load analysis cases involves calculations that are computationally intensive and can take a significant amount of time for larger models. The bridge response parameters allow you to explicitly specify the analysis results you require for a moving load analysis case. Only the results specified will be calculated and recovered by the program. Thus the program does not spend time calculating and recovering results that are not needed.

If correspondence is to be considered,  for each maximum or minimum response computed, the corresponding force, moment or stress quantities that occur at the same time as the maximum or minimum value are also reported.  For example, in a frame object, when the maximum M3 moment is calculated, if correspondence is specified, the P, V2, V3, T and M2 values that occur at the same time as the maximum M3 value will be reported.  Including correspondence increases the program calculation time and the quantity of response output.

Click the Close Wizard button to close the form.