OpenBuildings™ Station Designer Help

Place Bar Joist

Used to automate bar joist modeling by utilizing data from SJI (Steel Joist Institute) standards. Place, modify, or manipulate bar joists by establishing a span and selecting a bar joist series.

Accessed from:


  • Ribbon: Building Design > Structural > Place Structural Elements > Trusses split button > Place Bar Joists


Bar joists are manufactured in several standard series. Each is designed for specific spanning and loading characteristics. In engineering drawings or specifications, bar joists are designated by a three part code. Consider an example bar joist specification 18K6. The first number (18) designates the joist depth or the distance from the top surface of the top chord to the bottom surface of the bottom chord. The letter (K) designates the series. The last number (6) identifies the top and bottom chord section number.

The Place Bar Joist tool supports K, LH, DLH and SLH series bar joists. K series are used in common applications typically spanning 8 feet (2.5 m) to 60 feet (18.3 m) with depths between 8 inches (203 mm) to 30 inches (762 mm). LH, DLH and SLH span progressively larger distances with progressively larger depths.

Bar Joist Modeling dialog

Initially, selecting opens a preliminary dialog which governs the main tool settings window.



SettingDescription
Mode Select the placement or modification modes used for designing bar joists. Selections made here determine the prompts that guide you through the tool modes.
Place Single One bar joist assembly is placed as a compound cell along the selected span. Spans are specified using data points between structural members or other elements.
Place Multiple Multiple placement requires the selection of two members establishing a span. Additional settings related to multiples appear in the Properties tab.
Modify Joist Previously placed bar joists are modified by selecting this option and then selecting the bar joist. Modify seat heights, series and section definitions for example.
Manipulate Joist Previously placed bar joist spans are manipulated using this option. Drag the element representing the span to change its length or direction. Once a new end point is selected, the Bar Joist Placement Program dialog reappears where modifications are made to the various settings like series, loads and sections.
Note: Mode is not editable once selected for a given bar joist. It is disabled in the Place Bar Joist and in the Modify Bar Joist dialogs

Construction elements

Temporary construction elements appear during placement and manipulation providing assistance with visualizing bar joist seat height and span attributes.


  1. Bearing Line — Represented by a red line, the bearing line is the line drawn when defining a span in both single and multiple placement modes.
  2. Span — Represented by a cyan line, the span is the actual bar joist span. It is always displayed along the top chord.
  3. Seat Height — Represented with a green line, the seat height is the offset distance from the bearing member to the top chord. Seat height is defined on the end detail tabs.
  4. SJI Minimum Seat Height — Represented with a blue dot, the SJI (Steel Joist Institute) minimum seat height is derived from the SJI data associated with the specific bar joist configuration chosen.

SJI Code Check

The SJI (Steel Joist Institute) publishes standards for bar joists. One portion of the standards describes minimum seat heights. Seat height minimums depend on:

  • Joist series (K, LH, DLH and SLH)
  • Joist slope.
  • Top chord depth.
  • Width of support member (when associated during multiple placement)
  • Top chord extension
  • Chord section definitions
SettingDescription
SJI code check messages If the seat heights are outside the guidelines (Standard Specifications, 42nd Edition, Load Tables and Weigh Tables for Steel Joists and Joist Girders, pages 10-11), the Seat Height parameter is displayed in red, and a flyover hint is displayed showing the recommended SJI seat height.


Warnings are also displayed (in the Message Center) when attributes such as the top chord extension, the top chord section depth, the support members and the joist series, all of which influence the minimum seat heights, are modified.
CAUTION: Recommended seat height values are approximations provided only as an alert to potential problems. They are not a substitute for normal engineering calculations and review by qualified engineers.

Properties tab

SettingDescription
Series panel Lists all of the available series three part codes available for the series that is selected in the Series section of the Properties tab. One must be selected before you can place the bar joist. The tool automatically selects the standard series configuration associated with the selected span length. Other choices are offered at this time in the form of additional spans of slightly longer lengths.


Properties Displays and offers entry fields for properties associated with the selected bar joist.
  • Series - Automatically selected based on span distance, slope and number of bar joists (multiple placement). Series is then changed to suit individual applications.
    • K - Loads the K – Series (common open web joists) list of standard bar joists.
    • LH - Loads the LH – Series (long span) list of standard bar joists.
    • DLH - Loads the DLH – Series (deep long span) list of standard bar joists.
    • SLH - Loads the SLH – Series (super long span) list of standard bar joists.
  • Span (S) — Displays the span length.
    Note: Span length is permanently disabled for bar joists associated with structural members (multiple placement mode).
  • Mark — Displays the identifier used to relate the bar joist to the project where it is to be used. By default, the series three part code is automatically entered, but is also editable.
  • Approx Wt — Displays the approximate weight of the bar joist in pounds per linear foot (plf).
  • Design Load (Plf) — Enter the structure's design load in pounds per linear foot. Enter the design load manually and the Total Load (K) value is calculated automatically.
  • Total Load — Displays the total load of the in pounds per linear foot (plf). The value is taken from the SJI (Steel Joist Institute) data.
  • Total Load (K) — Displays the actual total load based on the design load using the equation:

    Total Load (K) = (Design Load x Span) / 1000

  • Live Load (L/360) — Displays the live load in pounds per linear foot (plf). Live loads are not permanent and tend to move during the life of the structure. Use and occupancy changes are factors determining live load. Live load does not include wind, snow or seismic loads.
  • Place By - Enabled for Place Single mode. Two options for placement points are available from the drop down.
    • Bearing Endpoints — The bar joist placement points are defined by selecting seat points.
    • Top Chord Endpoints — The bar joist placement points are defined by selecting points for the top chord of the assembly.


      The figure illustrates the two place by options: Top - place by bearing endpoints, Bottom - place by option is top chord endpoints. The arrows indicate the locations of the data points used to determine the span. The two End Detail tabs provide an offset option for seat heights.

Preferences
  • Add detailed Members - Turn on this check box to add detailed members to the modeled bar joist. When on, all members (top chord, web members, bottom chord) are placed. When off, only the joist envelope member is placed.
  • SJI Joist File - Displays the SJI bar joist data file (*.xml).
Multiple Copies (enabled for Place Multiple mode) The dialog appears with additional settings when multiple bar joists are placed spanning two structural members.


  • Place By — Select the method of placing the multiple bar joist models. The drop list items work in conjunction with the Spacing value field. Select a placement method and then key in an appropriate value in the Spacing field.
    • Number – The number of joists is equal to the value in the Spacing text field. The supporting member's length is divided by the number of joist.
    • Absolute – The value in the Spacing field represents the actual distance between the bar joists.
    • Maximum – The value in the Spacing text box represents the maximum spacing allowed. The supporting member's length is divided by the maximum spacing value, and rounded down to equalize bar joist spacing.
  • Spacing - Used to enter the spacing between the multiple joists.
  • Perpendicular to — Turn on this check box if the bar joists should be placed perpendicular to the first support member. That is, the order in which support members are picked is relevant to the orientation of the bar joists.
  • End Members — Turn on this check box if the bar joists should be placed at the specified spacing and at the end members. When off, no bar joists placed at the support members' ends.
Sections Sets section definitions used for the individual components that comprise the bar joist assembly.
  • Top Chord — Selects the section definition to be used for the top chord members.
  • Web Members — Selects the section definition to be used for the web members.
  • Bottom Chord — Selects the section definition to be used for the bottom chord members.
Bottom Chord | Joist Envelope | Top Chord | Web Members
  • Catalog Type - Selects the DataGroup catalog type for the joist component member.
  • Catalog instance - Selects the DataGroup catalog item for the joist component member.
Tip: The Joist Envelope defines the approximate outer boundary of the joist. Joist envelope sections are added automatically to the active section file when new joists are placed. The name of the envelope section is set to the name of the joist configuration (for example: 18LH02). The depth of the section matches the depth of the joist.
Place Places the bar joists using the active settings.
End 1 | 2 Detail tabs These tabs contain settings used to complete designing the bar joist:
Key-in: MDL LOAD BENTLEY.BUILDING.STRUCTURAL.BARJOISTTOOL PLACEBARJOIST
End 1 Details tab
End 2 Detail tab
To place a single bar joist
To place multiple bar joists
To modify a bar joist by selecting a new support member
To manipulate a modeled bar joist by increasing the span
Parent topic: Trusses