Civil MDC

X-BRACING ANALYSIS OF BENTS WITH TENSION ONLY

“XBRACING” — ANALYSIS OF BENTS WITH TENSION-ONLY X-BRACING

Program Description:

“XBRACING” is a spreadsheet program written in MS-Excel for the purpose of analyzing X-braced bents with
tension-only systems. From 1-story up to 10-story bents may be analyzed. Specifically, given the bent width,
the story heights, and the lateral story loads, all the member (segment) forces are determined, as well as the
horizontal and vertical reactions at the supports, and the individual story drifts (horizontal deflections).

This program is a workbook consisting of eleven (11) worksheets, described as follows:

Worksheet Name Description
Doc This documentation sheet
X(1) Analysis of 1-story bent with tension-only X-bracing
X(2) Analysis of 2-story bent with tension-only X-bracing
X(3) Analysis of 3-story bent with tension-only X-bracing
X(4) Analysis of 4-story bent with tension-only X-bracing
X(5) Analysis of 5-story bent with tension-only X-bracing
X(6) Analysis of 6-story bent with tension-only X-bracing
X(7) Analysis of 7-story bent with tension-only X-bracing
X(8) Analysis of 8-story bent with tension-only X-bracing
X(9) Analysis of 9-story bent with tension-only X-bracing
X(10) Analysis of 10-story bent with tension-only X-bracing

Program Assumptions and Limitations:

  1. This program assumes that the vertical bent is fully braced, between every story, utilizing a tension-only
    X-bracing system.
  2. In a tension-only bracing system, one brace is assumed effective in tension while the other brace is
    assumed to buckle (in compression), requiring the tension brace to take all of the load.
  3. This program uses the “Method of Virtual Work” to determine the horizontal deflections at each of the story
    levels. The horizontal deflection at a particular story level is determined by first applying a “dummy” unit load
    at that level. Then, the member forces from the unit load are determined. With the member forces due to
    the applied lateral loads already having been calculated, the horizontal deflection at that story level is:
    Dn = S FuL/(A*E)
    where: Dn = horizontal deflection at particular story level number considered (inches)
    F = force in each member due to all applied lateral story loads (kips)
    u = force in each member due to unit load applied at paricular story, ‘n’
    L = length of each member in bent (inches)
    A = area of each member in bent (in.^2)
    E = modulus of elasticity of members in bent, all assumed equal (ksi)
    The horizontal deflections (story drifts) determined are for the joints at the left side of the bent, with all
    members (segments) assumed pinned at both ends.
  4. This program contains “comment boxes” which contain information including explanations of input or output
    items, equations used, etc. (Note: presence of a “comment box” is denoted by a “red triangle” in the upper
    right-hand corner of a cell. Merely move the mouse pointer to the desired cell to view the contents of that
    particular “comment box”.)

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