In construction, a bracing is a structural member — usually a diagonal — added to a frame to resist lateral loads (wind and seismic) by carrying them as axial force back to the foundation. Without bracing, a moment-resisting frame must rely on rigid beam-to-column joints; with bracing, simpler pinned joints become acceptable because the diagonal handles the lateral load. Bracing converts what would otherwise be bending in the frame into pure tension or compression along the brace.

What are the types of bracing?

Five common types in modern steel and timber construction. (1) X-bracing — two diagonals form a cross; the most common because at any direction of lateral load one brace works in tension. (2) K-bracing — diagonals meet at the mid-height of a column; seismic-prohibited because column failure is non-redundant. (3) V or inverted-V (chevron) — both diagonals frame into the same beam; common in SCBF. (4) Eccentrically braced (EBF) — diagonals offset from the beam-column joint, with a "link" beam segment that yields in shear. (5) Buckling-restrained (BRBF) — steel core sleeved in mortar/concrete that prevents compression buckling, allowing the brace to yield symmetrically in tension and compression.

What is bracing in construction?

Bracing in construction is any added member (steel rod, angle, channel, HSS tube, timber strut, cable) that prevents lateral movement, racking, or buckling of a frame. It can be permanent (designed into the structure for wind/seismic loads) or temporary (erected during construction to stabilise members until the permanent diaphragm is in place). Wood-framed houses use let-in or metal T-bracing in walls; steel buildings use diagonal HSS members in dedicated braced bays; bridges use cross-bracing between adjacent girders.

What is the purpose of bracing?

Three purposes. (1) Resist lateral loads — wind and seismic forces are transferred from diaphragms through bracing to the foundation. (2) Prevent buckling — a slender beam compression flange is restrained by lateral bracing to allow it to develop its full plastic moment per AISC F2. (3) Control deformation — bracing makes a frame stiff enough to keep drift below the IBC limit (typically H/400 for wind, H/100 to H/40 for seismic depending on system).

What is the difference between bracing and a moment frame?

A braced frame uses diagonal members carrying axial load to resist lateral forces; a moment frame uses rigid beam-to-column joints carrying bending. Braced frames are stiffer and cheaper but block windows and doors at the brace bay. Moment frames are open and architecturally flexible but more expensive (heavier members, complex welded joints) and less stiff. Hybrid "dual systems" combine both to balance stiffness, ductility, and architectural openings.

Reference · Structural · AISC 360 · AISC 341 · ASCE 7

Types of Bracing — Cross, K, V, Lateral & Truss Bracing

Bracing is the structural shorthand for any diagonal or stiffener that carries lateral loads (wind, seismic, vibration) and prevents buckling of compression members. This page covers the five common bracing systems used in modern steel and timber framing — cross, K, V/chevron, eccentric (EBF), and buckling-restrained — plus lateral bracing of beams, truss bracing, and the AISC stiffness and strength rules that size them. Reviewed by a licensed PE.

Figure 1 — Six common bracing systems with the lateral-load path indicated. AISC 341 governs seismic SCBF / EBF / BRBF.

Bracing tools and recommendations

For bracing-system layout decisions, the truss solver (method of joints) computes the axial forces in every brace and chord member of any 2-D braced frame or truss; the AISC HSS section table inside the moment-of-inertia tools gives the radii of gyration needed for KL/r checks. For lateral-torsional buckling of beams, AISC F2 / F3 governs and the embedded steel-section data lets you check Lp / Lr without leaving the page.

→ Truss solver (method of joints) · → Moment of inertia & radius of gyration · → HSS steel material reference

Bracing design formulas

Eq. 01 — Brace axial force from story shear (X-brace) SI

P_{brace} = \frac{V_{story}}{n \cdot \cos \theta}

·: V_story = total lateral force at the level
·: n = number of braces resisting V (one per direction in tension-only X)
·: θ = angle of the brace from horizontal (45–60° typical)

Eq. 02 — Slenderness limit (compression brace) SI

\frac{K \, L}{r} \leq 200 \text{ (general)} \quad \text{or} \quad \leq 4 \sqrt{\frac{E}{F_y}} \text{ (SCBF)}

·: K = effective length factor (1.0 for pinned-pinned brace)
·: L = unbraced length of the brace
·: r = least radius of gyration
·: For A992 steel SCBF: KL/r ≤ 4·√(29 000/50) = 96

Eq. 03 — Required brace stiffness (AISC App 6) SI

\beta_{br} = \frac{1}{\phi} \cdot \frac{4 \, M_r}{L_b \, h_o \, C_d}

·: M_r = required flexural strength at the braced point
·: L_b = unbraced length
·: h_o = distance between flange centroids
·: C_d = 1.0 for single curvature, 2.0 for reverse curvature

Eq. 04 — Required brace strength (AISC App 6) SI

P_{br} = 0.02 \, M_r \, C_d \, / \, h_o

·: 2 % rule — minimum bracing strength for nodal lateral bracing of beams
·: Independent of bracing-element strength check (KL/r, etc.)
·: For columns: P_br = 0.01 P_r

Standards governing bracing design

Document	Scope
ASCE 7-22	Wind (Chapters 26–30) and seismic (Chapters 11–13) loads — sets the lateral demand bracing must resist
AISC 360-22 — Appendix 6	Stability bracing — stiffness and strength requirements for both relative and nodal bracing
AISC 341-22	Seismic Provisions — SCBF (special concentrically braced frame), OCBF, EBF, BRBF, SMF design
AISC 360 §F2.2	Lateral-torsional buckling of doubly-symmetric beams — Lp / Lr / Mn equations
ANSI/AWC NDS-2018	Wood-frame bracing — let-in 1× braces, metal T-braces, diagonal lumber
IBC 2021 §2308	Conventional light-frame wood construction bracing requirements (braced wall lines)
AWC SDPWS-2021	Special Design Provisions for Wind and Seismic — wood diaphragms and shear walls

Reference: bracing system selection by application

Bracing type	Best for	Stiffness	Ductility	Architectural impact
X-bracing (cross)	Wind frames; low-seismic	High	Low (tension-only)	Blocks both directions of bay
K-bracing	Wind only — prohibited for seismic SCBF	High	Very low (column hinge)	Allows door at mid-bay
V / inverted-V (chevron)	Seismic SCBF	High	Medium	Allows door under chevron point
Eccentrically braced (EBF)	High-seismic, ductile	Medium-high	Very high (link beam yields)	Open at link, framed elsewhere
Buckling-restrained (BRBF)	High-seismic, performance-based	High	Highest (symmetric T/C yield)	Same as X but with mortar sleeve
Lateral bracing (beam)	Compression-flange restraint	n/a (member-level)	n/a	Concealed in slab/deck
Truss bracing	Top-chord compression	High (in-plane)	Low	Concealed in roof framing

Identify the lateral loads Quantify wind (ASCE 7 Chapter 26–30) and seismic (ASCE 7 Chapter 11–13) base shears. Bracing is sized for the larger of the two factored cases. Note location, occupancy category, and site class — they cascade through to bracing demand.
Pick a bracing system X-braced (most common, two diagonals form a cross), K-braced (mid-height connection — prohibited for SCBF in seismic), V or inverted-V (chevron, common in seismic SCBF), eccentrically braced (EBF — diagonals connect at a "link" beam segment that yields in shear), or buckling-restrained (BRBF — sleeved braces that yield in tension and compression).
Compute brace axial force For an X-brace at angle θ to horizontal: P_brace = V_story / (n · cos θ), where V is the story shear and n is the number of braces resisting it. A 60° brace is more efficient than a 45° (smaller force) but takes a longer member.
Size the brace member KL/r ≤ 200 for tension-only or 4·√(E/Fy) for SCBF compression members (AISC 341 §F2.5b — about KL/r ≤ 100 for A992 steel). HSS round or square tubes give the best radius of gyration per pound; use AISC Manual Part 4 to pick.
Detail the connections Gusset plates per AISC Manual Part 13: weld or bolt the brace ends with capacity ≥ 1.1·R_y·F_y·A_g for SCBF (capacity-design rule). For tension-only X-braces in wind frames, a simpler bolted gusset designed for the factored brace force suffices.