X-Braced Bent Analysis

"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










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 F*u*L/(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".)

"XBRACING.xls" Program

Version 1.0

X-Braced Bent Analysis for Lateral LoadsFor 1-Story Bent

Assuming Fully Braced, Tension-Only System

Job Name: Subject:

Job Number: Originator: Checker:

Forces and Reactions: L = 20.00 ft.

Lateral Story Loads (Bent Width)

P1 = 4.75 k 4.75 k

Story Height -6.55 k

h1 = 19.00 ft. Brace Angle1=43.53 L1=27.59 ft. Ht = 19.00 ft.

(Total Bent Height)

P(bot) = 4.75 k 9.50 k = VL

Member Force Sign Convention:

+ = Compression 20.00 ft.

- = Tension

Vertical Reaction Sign Convention:

Upward = Compression RL = 4.51 k RR =

Downward = Tension (Uplift) Bent Elevation

Input Data for Drift Analysis:

Member Data Nomenclature:

Designation Length Area LC = Left Column Segment

(ft.) (in.^2) RC = Right Column Segment

Left Col. LC1 19.00 7.08 HB = Horizontal Beam

Right Col. RC1 19.00 7.08 DB = Diagonal Brace

Beam HB1 20.00 5.62

Brace DB1 27.59 1.44 Note: Column segments, beams,

and braces are numbered from

Mod. of Elasticity, E = 29000 ksi bottom to top, same as stories.

Results: Note: Results are for joints at left side of bent, with all members (segments) assumed pinned at both ends.

Drift Analysis

Story Total Drift Drift Ratio

Number Dt (in.) (Total)

Story 1 0.0834 Ht / 2734

0.0

0 k

4.5

1 k

4.51 k

2 of 2 2/4/2014 11:01 AM

Documents

X-Braced Bent Analysis