Bridge Wizard

The Bridge Wizard provides a step-by-step guide through the modeling process using CSiBridge's Bridge Information Modeler.  It can be used in conjunction with the Blank or Quick Bridge templates to start a model.

The Currently Defined Items area on the left-hand side 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). Click the + (plus symbol) to expand and the (minus symbol) to collapse a listing of any previously defined items.

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.

Note:  The Form Layout slide bar along the bottom middle of the form can be used to change the proportional area devoted to the narrative display area and the Summary Table list of steps and items.

In its most basic approach, the Wizard can quickly generate a bridge model In three steps

  1. Define Layout Lines

  2. Define Bridge Deck Sections

  3. Define Bridge Objects

Using these steps, CSiBridge will generate a bridge model using default definitions. After the bridge model has been built, the bridge analysis can be performed.

The additional steps, and thus the explanation that follows, can be used to refine the model.

Step 1 Introduction

The Bridge Wizard is a step-by-step design tool for modeling bridge structures in CSiBridge. The Summary Table  portion of this form (lower right-hand corner of the Wizard) lists the various steps involved in the process, including:

Note: The Wizard is designed to allow you to exist the process at any point. That is, it is not necessary to complete all steps in the process required to create your bridge model in a single continuous/uninterrupted session.

Click on any row in the Summary Table to jump to that step in the process. Within the Summary Table, use the up and down arrow keys to move from one step to another in the list.

The Step control located below the summary table can be used to move to the first step (<<), previous step (<), next step (>), or last step (>>). Or, type a step number in the Step control and press the Enter key to jump directly to that step.

The tree view (i.e., Currently Defined Items) lists the items that have been defined in the model. Clicking on an item in the tree view displays the step associated with that item. Note that when starting a model for the first time, some items will be listed in advance of those items actually being created or assigned.

For each step in the Bridge Wizard (except Step 1, the Introduction), a button appears on the right-hand side between the informational text box and the Summary Table. Clicking the button opens the form associated with the step. In a few cases, the button may be disabled. This occurs when prerequisite steps have not been completed, such as:

During Step 7, a bridge object drop-down list displays between the informational text box and the Summary Table. That list is used to select the bridge object to which bridge object assignments are made during completion of Step 7.

Step 2 Layout Line. The first process in creating a bridge object is to define the layout line. At least one layout line and one deck section must be defined before a bridge object can be defined. Also, a layout line (or frame objects) must exist in the model before lanes can be defined. Layout lines are reference lines used for defining the horizontal and vertical alignment of the bridge and the vehicle lanes. Layout lines are defined using stations for distance, bearings for horizontal alignment, and grades for vertical alignment. Layout lines may be straight, bent or curved, both horizontally and vertically. Horizontal curves are circular with spirals, if necessary. Vertical curves are parabolic or circular.

Click the Define/Show Layout Line button to access the Define Bridge Layout Line form and begin defining a layout line.

Step 3 Basic Properties.

3.1 Materials -  In CSiBridge material properties can be defined as they are needed, or they can be predefined here. Several default material properties are automatically defined when a model is first created. Material properties are used in frame section property definitions (see Step 3) and in deck section property definitions (see Step 4).

3.2 Frame Sections - Frame section properties are used in some of the property definitions included in Step 4, such as:

3.3 Links - Link properties are an optional advanced item in the Bridge. Link properties may be used in the following property definitions (see Step 4):

In each of those property definitions, a user method of specifying the desired property, without reference to a link property, is available. In general, we recommend that you use the user method rather than specifying your own link properties. If you do use link properties, take special care to make sure the local axes are defined correctly.

In CSiBridge, link properties can be defined at the time they are needed, or, if you prefer, they can be predefined here.

Step 4 Bridge Component Properties.

Step 4.1 Deck Section. At least one deck section property and one layout line must be defined before a bridge object can be defined. Deck sections are used to define the bridge superstructure. Various parametric deck sections are available. They include concrete box girder, concrete flat slab, precast concrete girder and steel girder deck sections. After a deck section has been defined, it can be assigned to a bridge object (see Step 7). As necessary, the bridge superstructure can be specified to vary parametrically along its length. Use the following method to define and assign the variation:

Click the Define/Show Deck Sections button to display the Define Bridge Deck Sections form.

Step 4.2 Diaphragm Definition. Diaphragm properties specify data for 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 diaphragms are applicable only at locations where concrete superstructure deck sections exist. Steel diaphragms are applicable only at locations where steel girder superstructure deck sections exist. In area object and solid object bridge models, the diaphragms are modeled using area and solid objects, respectively. In spine models an automatically generated link object is added at each diaphragm location to represent the diaphragm mass and weight. After a diaphragm property has been defined, it can be assigned to a bridge object (see Step 5 or Step 7).

Click the Define/Show Diaphragm button to access the Define Bridge Diaphragm Properties form.

Step 4.3 Splices. Splice properties specify data for steel I-girder splices. Splices currently do not affect the bridge object model, but are used during superstructure design checks to consider the net area of the top and bottom I-girder flanges.

Click the Define/Show Splice button to access the Define Bridge Splice Properties form.

Step 4.4 Restrainers. Restrainer properties specify data for restrainer cables. Restrainer cables are used as tension ties across superstructure discontinuities. Restrainers may be assigned at abutments and hinges and at bents where the superstructure is discontinuous over the bent (see Step 5 or Step 7). When specified, the program assumes that a restrainer cable exists at each girder location. A restrainer property can be specified as a Link/Support property or it can be user defined. The user defined restrainer is recommended. The user defined restrainer is specified by a length, area and modulus of elasticity.

Click the Define/Show Restrainers button to access the Define Bridge Restrainers form. Use the from to define a new restrainer property or view/revise a previously defined property definition.

Step 4.5 Bearings. Bearing properties specify data for bridge bearings. Bearing properties are used in abutment, bent and hinge assignments to the bridge object (see Step 5 or Step 7). At abutments, bearings are used in the connection between the girders and the substructure. At bents, bearings are used in the connection between the girders and the bent cap beam. At hinges, bearings are used in the connection between the girders on the two sides of the hinge. A bearing property can be specified as a Link/Support property or it can be user defined. The user defined bearing is recommended. The user defined bearing allows each of the six degrees of freedom to be specified as fixed, free or partially restrained with a specified spring constant.

Click the Define/Show Bearings button to access the Define Bridge Bearings form.

Step 4.6 Foundation Springs. Foundation spring properties specify data for the connection of the substructure to the ground. Foundation spring properties are used in abutment and bent property definitions (see Step 4). At bents, foundation springs may be used at the base of each column. In this case the foundation springs are used as point springs. At abutments, foundation springs are used as point springs for a foundation spring-type substructure, and they are used as spring properties per unit length for a continuous beam-type substructure. A foundation spring property can be specified as a Link/Support property or it can be user defined. The user defined spring is recommended. The user defined foundation spring allows each of the six degrees of freedom to be specified as fixed, free or partially restrained with a specified spring constant. For cases where the spring property is used for a continuous beam support, a factor is specified indicating the length over which the specified properties apply.

Click the Define/Show Foundation Springs button to access the Define Bridge Foundation Springs form.

Step 4.7 Abutment Definition.  Abutment definitions specify the support conditions at the ends of the bridge. Abutment properties are used in abutment assignments to the bridge object (see Step 5 or Step 7). The abutment property allows specification of the connection between the abutment and the girders as either integral or connected to the bottom of the girder only. The abutment property also allows the abutment substructure to be specified as a series of point springs (one for each girder) or a continuously supported beam.

Click the Define/Show Abutments button to access the Define Bridge Abutments form.  

Step 4.8 Bent Definition.   Bent properties specify the geometry and section properties of the bent cap and the bent columns. They also specify the base support condition of the bent columns. Bent properties are used in abutment assignments to the bridge object (see Step 5 or Step 7). The bent property allows specification of the connection between the abutment and the girders as integral or connected to the bottom of the girders only. The bent property also allows specification of a single bearing line (continuous superstructure) or a double bearing line (discontinuous superstructure). When double bearing lines are used, the distance from the bent location (that is specified in the bridge object definition, Step 5) to each bearing line is included in the bent property.

Click the Define/Show Bents button to access the Define Bridge Bents form.  

Step 4.9 Point Load Definitions. Point load definitions define concentrated loads that can be applied to the bridge superstructure using bridge object point load assignments. Click the Define/Show Point Loads button to display the Bridge Point Load Definitions form.

Step 4.10 Line Load Definitions. Line load definitions define line loads that can be applied to the bridge superstructure using bridge object line load assignments. Click the Define/Show Line Loads button to display the Bridge Line Load Definitions form.

Step 4.11 Area Load Definitions. Area load definitions define area  loads that can be applied to the bridge superstructure using bridge object area load assignments. Click the Define/Show Area Loads button to display the Bridge Area Load Definitions form.

Step 4.12 Temperature Gradients.  Temperature gradient in accordance with AASHTO or JTG D60 design codes, or user specification, can be defined. Gradient patterns can be positive and negative. Patterns automatically adjust for superstructure material and geometry.

Click the Define/Show Temp Gradients button, to display the Define Bridge Temperature Gradient form.

Step 5 Bridge Object Definition. The bridge object definition is the main component of the CSiBridge Bridge modeler.

Click the Define/Show Bridge Objects button to access the Define Bridge Objects form.

The following are included in a bridge object definition.

In the Modify/Show Assignments display area of the Bridge Object Data form, highlight the a listed item (e.g., Spans, User Discretization Points, Abutments, Bents, and so on) to display the form needed to complete the assignment. All of the assignments (i.e., everything except the first bullet item) can be addressed in Step 7 of this Wizard.

Anytime the bridge object definition is modified, the linked model must be updated (see Step 8) for the changes to appear in the CSiBridge object-based model.

Step 6 Parametric Variations. Parametric variations define variations in the deck section along the length of the bridge. Almost all parameters used in the parametric definition of a deck section can be specified to vary. More than one parameter can vary at the same time, if necessary. 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 bridge. The variations may be linear, parabolic or circular. After a variation has been defined, it can be assigned as part of the deck section assignment to bridge objects (see Step 7).

Click the Define/Show Variations button to access the Define Parametric Variations form.

Note:  If no variations apply, skip this step.

Step 7 Bridge Object Assignments.

Step 7.1 Deck Sections. Deck section assignments allow a deck section property (Step 4) to be specified for each span. Also, parametric variations (Step 6) of the superstructure (deck section) along the length of the span maybe assigned.

Step 7.2 Discretization Points. User discretization points allow you to specify points along the span where the bridge object will be discretized. You also can specify a skew associated with the discretization point. The user discretization points supplement the discretization specified when the linked model is updated (see Step 8). In most models it is not necessary to create user discretization points. The discretization specified when the linked model is updated is sufficient.

Step 7.3 Abutments. Abutments allow specification of the following at each end of the bridge:  end skews; end diaphragm properties, if any; substructure assignment for the abutment, which may be None, an abutment property or a bent property; vertical elevation and horizontal location of the substructure; and the bearing property, elevation and rotation angle from the bridge default. Note that the elevations specified for the substructure and the bearings are Global Z coordinates.

Step 7.4 Bents. Bent assignments allow specification of the following at each bent:  bent property and bent orientation; vertical elevation and horizontal location of the bent; bearing property, elevation and rotation angle from the bridge default; superstructure assignments, including a diaphragm property. For bents at superstructure discontinuities, bearings are separately specified on each side of the discontinuity. For bents at superstructure discontinuities, a diaphragm property of can be specified on each side of the discontinuity, along with a restrainer property, restrainer vertical elevation, and initial gap openings at the top and bottom of the superstructure.

Step 7.5 Hinge Assignment. Hinge assignments allow specification of the following items for each hinge:  location and orientation; the bearing property, elevation and rotation angle from the bridge default; the restrainer property and elevation; diaphragm properties before and after the hinge; initial gap openings at the top and bottom of the superstructure. Note that the elevations specified for the bearing and restrainer are Global Z coordinates. Typically there is one bearing and one restrainer for each girder.

Step 7.6 Diaphragms.  A diaphragm assignment includes a diaphragm location property and orientation. The diaphragms assigned here are in-span diaphragms. Diaphragms that occur at abutments, bents, and hinges are assigned as part of the bridge object abutment, bent, and hinge assignments, respectively. Although any diaphragm property can be assigned within a span, a concrete diaphragm will be used by the program only if it occurs within a span with a concrete deck section, and similarly, a steel diaphragm will be used by the program only if it occurs within a span with a steel deck section.

Step 7.7 Splices. A splice assignment includes a splice location, property, and orientation. Although any splice property can be assigned within a span, they will be used by the program only if it occurs within a span with a steel I-girder deck section.

Step 7.8 Superelevation. A superelevation assignment for a bridge object is referenced to the layout line. The superelevation is specified in percentage and it indicates the rotation of the superstructure about the longitudinal axis. The superelevation may be constant or it may be along the bridge. In most bridge models including superelevation is probably an unnecessary refinement.

Step 7.9 Prestress Tendons. Tendon assignments include the following data:  location of the start and end of the tendon; the vertical and horizontal layout of the tendon; tendon section properties, loss parameters and jacking options; the tendon load specified as either a force or a stress; the tendon modeling option that is either to model the tendon as a load or as elements. Several quick start options are available to assist in defining the tendon geometry. A parabolic calculator is provided to assist in the layout of parabolic tendons.

Step 7.10 Concrete Girder Rebar. Concrete girder rebar assignments allows rebar to be specified in the girders of concrete deck sections. The rebar is used by the program when designing the superstructure. Highlight the Concrete Girder Rebar item and click the Assign/Show Girder Rebar button to display the Bridge Girders Reinforcement Layout form. Both transverse (shear) and longitudinal rebar can be specified.

Step 7.11 Staged Construction Groups. Stage construction group assignments allow specification of data so that the program can automatically create groups that can be used in staged construction load cases. In this assignment, a group is specified to contain certain elements of the bridge structure, for example, girders between two stations along the bridge. When the linked bridge object is updated (Step 8), the program automatically fills the group with the appropriate objects.

Step 7.12 Point Loads. The point loads defined in a previous step are assigned to the bridge superstructure. Select the Bridge Object to which a point load is being assigned using the Bridge Object drop-down list. Then highlight the Point Loads item and click the Assign/Show Point Loads button to display Point Load Assignments form. The defined point load is assigned to a defined load pattern, with the location of the load being specified using a Start Station and then the spacing and the specified number of point loads. The load can also be specified with a transverse variation.

Step 7.13 Line Loads. The line loads defined in a previous step are assigned to the bridge superstructure. Select the Bridge Object to which a line load is being assigned using the Bridge Object drop-down list. Highlight the Line Loads item and click the Assign/Show Line Loads button to display Line Load Assignments form. The defined line load is assigned to a defined load pattern, with the location of the load being specified using a Start and End Stations. The load can also be specified with a transverse variation.

Step 7.14 Area Loads. The area loads defined in a previous step are assigned to the bridge superstructure. Select the Bridge Object to which a area load is being assigned using the Bridge Object drop-down list. Highlight the Area Loads item and click the Assign/Show Area Loads button to display Area Load Assignments form. The defined area load is assigned to a defined load pattern, with the location of the load being specified using a Start and End Stations. The load can also be specified with a transverse variation on the left and right edges of the area load.

Step 7.15 Temperature Loads. Uniform temperature loads and defined temperature-gradient load patterns can be applied to bridge objects. Appropriate thermal loads are developed for the linked model (spine [frame], shell, or solid models). Those loads also can be automatically included in Load Combinations generated for AASHTO or JTG design codes.

Step 8 Update Linked Model. The update linked model command creates the CSiBridge object-based model from the bridge object definition. If an object based model of the bridge object already exists, it is deleted when the new object-based model is created. The new object based model includes all of the latest changes to the bridge object definition. Spine models, area object models, and solid object models can be created when the model is updated. The type of object based model created from the bridge object definition can be switched at any time. Note that the Bridge > Update > Auto Update command is a toggle that allows the bridge model to be automatically updated by the program every time a change is made. The update linked model command allows specification of the discretization of the object based model. In some cases, assignment of user-defined discretization points to the bridge object (Step 7) may be warranted to control the discretization of the object based model.

Step 9 Lane and Vehicle Definitions.

Step 9.1 Lane Definition. Lanes must be defined if you want to analyze your bridge for vehicle live loads. Lanes are used in the definition of bridge live type load patterns that are used in static and dynamic multi-step load cases (Step 12). Lanes can be defined with reference to layout lines or existing frame objects. Typically, when using the bridge modeler, lanes should be defined from layout lines. Lanes can be defined with width, as necessary.

Step 9.2 Vehicle Definition. Vehicles must be defined to analyze a bridge model for vehicle loads. In CSiBridge, vehicle loads are applied to the structure through lanes (Step 9). Numerous standard vehicle types are built into the program. In addition, the General Vehicle feature  allows creation of customized vehicle definitions. Each vehicle definition consists of one or more concentrated or uniform loads.

Step 9.3 Vehicle Classes. Vehicles classes must be defined to analyze a bridge model for vehicle live loads using a moving load load case. 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).

Step 10 Function Definitions

Step 10.1 Response Spectrum Functions. Response spectrum function definitions are required for creating response spectrum load cases. If a response spectrum analysis is to be performed for a bridge model, use this step to define the function. Many standard response spectrum functions are built into CSiBridge. In addition, the user function feature creates user defined functions, and the function from file feature obtains a function definition from an external file.

Step 10.2 Time History Functions. Time history function definitions are required for creating time history load cases. If a time history analysis is to be performed on a bridge model, use this step to define the required function. Some generic time history functions are built into CSiBridge. In addition, user defined function can be created, or a function definition can be imported from an external file.

Step 11 Load Pattern Definitions. A load pattern is a specified spatial distribution of forces, displacements, temperatures, and other effects that act upon the structure. A load pattern by itself does not cause any response in the structure. Load patterns must be applied in load cases in order to produce results. One special type of load pattern available in CSiBridge is the Bridge Live Load pattern. In that type of load pattern, one or move vehicles that move across the bridge can be specified. For each vehicle, the following can be specified:  a time that the vehicle starts loading the bridge, the initial vehicle location, and the direction of travel and the speed of the vehicle. When used in a multi-step static or multi-step dynamic (direct integration time history) load case (Step 12), this type of load pattern is useful in evaluating special vehicle loads.

Step 12 Load Cases.

Step 12.1 Load Cases. A load case defines how loads are to be applied to the structure (e.g., statically or dynamically), how the structure responds (e.g., linearly or nonlinearly), and how the analysis is to be performed (e.g., modally or by direct-integration). Any load case type can be used when analyzing a bridge model. For seismic analysis, static, response spectrum and time history load case types are useful. Pushover analysis can be performed using a nonlinear static load case. Staged construction analysis is also performed using nonlinear static load cases. There are several analysis options that are specialized for analysis of vehicle live loads. Moving load load 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) load cases can be used to analyze one or more vehicles moving across the bridge at a specified speed. These multi-step load cases are defined using special bridge live load patterns that define the direction, starting time and speed of vehicles moving along lanes (see Step 11).

Step 12.2 Construction Scheduler. The construction scheduler is a useful tool if you are performing staged construction analysis for a bridge model. The scheduler uses a spreadsheet for input and a Gantt chart to display the resulting schedule. The scheduler automatically creates the required staged construction load cases to analyze the bridge based on the specified schedule. Staged construction load cases typically use groups to refer to collections of structural objects in the model. The Bridge modeler allows those groups to be defined easily as part of the bridge object definition (Step 7).

Step 13 Moving Load Case Results Saved. Analysis of moving load cases involves calculations that are computationally intensive and can take a significant amount of time for larger models. The moving load case results saved parameters allow you to explicitly specify the analysis results you require for a moving load load case. Only the results specified will be calculated and saved by the program. 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 also are 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. Use the commands on the Analysis tab to complete the analysis and the Design/Ratings tab to design and rate the bridge model.