K5Welds of plates and branches to HSS

The available strength of branch connections shall be determined considering the nonuniformity of load transfer along the line of weld, due to differences in relative stiffness of HSS walls in HSS-to-HSS connections and between elements in transverse plate-to-HSS connections, as follows:

Interaction shall be considered.

• (a) For fillet welds

$\phi=0.75$ (LRFD) $\quad \Omega=2.00$ (ASD)

• (b) For partial-joint-penetration groove welds

= 0.80 (LRFD) Ω = 1.88 (ASD)

Figure description:

where

$F_{n w}=$ nominal stress of weld metal in accordance with Chapter J, ksi (MPa)

• $S_{i p}=$ effective elastic section modulus of welds for in-plane bending (Table K5.1), in. ${ }^{3}\left(\mathrm{~mm}^{3}\right)$
• $S_{o p}=$ effective elastic section modulus of welds for out-of-plane bending (Table K5.1), in. ${ }^{3}\left(\mathrm{~mm}^{3}\right)$
• $\begin{aligned} l_{e} & =\text { total effective weld length of groove and fillet welds to HSS for weld } \\ & \text { strength calculations, in. (mm) }\end{aligned}$
• $\begin{aligned} t_{w} & =\text { smallest effective weld throat thickness around the perimeter of branch or } \\ & \text { plate, in. (mm) }\end{aligned}$

User Note: Where flexure results in tension in any load case in the weld the directional strength increase factor cannot exceed 1.0 in fillet welds to the end of rectangular HSS.

When a rectangular overlapped K-connection has been designed in accordance with Table K3.2, and the branch member component forces normal to the chord are 80% balanced (in other words, the branch member forces normal to the chord face differ by no more than 20%), the hidden weld under an overlapping branch may be omitted if the remaining welds to the overlapped branch everywhere develop the full capacity of the overlapped branch member walls.

The weld checks in Tables K5.1 and K5.2 are not required if the welds are capable of developing the full strength of the branch member wall along its entire perimeter (or a plate along its entire length).

User Note: The approach used here to allow downsizing of welds assumes a constant weld size around the full perimeter of the HSS branch. Special attention is required for equal width (or near-equal width) connections to rectangular HSS, which combine partial-joint-penetration groove welds along the matched edges of the connection, with fillet welds generally across the chord member face.

TABLE K5.1 (continued)

Effective Weld Properties for Connections to Rectangular HSS

Connection Type Weld Properties

Overlapped K-connections under branch axial load

Figure description:

Key Information: Overlapped K-Connection Diagram

Structural Components and Parameters:

• Main Member (Chord:
  • $H, B, t$: Height, width, and wall thickness of the rectangular chord.
  • $e$: Eccentricity (vertical distance between branch axis intersection and chord centerline.
• Overlapping Branch ($i$:
  • $H_{bi}, B_{bi}, t_b$: Height, width, and wall thickness.
  • $\theta_i$: Angle of inclination to the chord.
  • $P$: Applied axial tensile load.
• Overlapped Branch ($j$:
  • $H_{bj}, B_{bj}, t_b$: Height, width, and wall thickness.
  • $\theta_j$: Angle of inclination to the chord.
  • $P$: Applied axial compressive load.

Connection Details:

• Type: Overlapped K-connection where member $i$ sits partially on member $j$.
• Load State: Branches are subjected to opposing axial loads ($P$.

Overlapping member effective weld properties (all dimensions are for the overlapping branch, i)

Figure description:

• Technical diagram showing effective weld properties for an overlapping branch member.
• Section A-A: Effective weld layout for conditions where $B_{bj} \le 0.85$ and $\theta_j \le 50^\circ$.
• Horizontal Dimension: $\frac{H_{bj}}{\sin \theta_j}$
• Vertical Dimension: $\frac{B_{ej}}{2}$
• Key Entities: Represents the weld configuration on a structural member with dashed and solid lines indicating weld boundaries.

Section A-A: Effectve weld when $\frac{B_{b j}}{B} \leq 0.85$ and $\theta_{j} \leq 50^{\circ}$

Figure description:

Key Information: Section A-A: Effective Weld

• Subject: Structural diagram for calculating effective weld length in a connection.
• Formula: $\frac{H_{bj} - 1.2t_{bj}}{\sin \theta_j}$
• Application Condition: This specific calculation for Section A-A applies when:
  • $\frac{B_{bj}}{B} > 0.85$ OR
  • $\theta_j > 50^\circ$
• Visual Elements: Diagram shows a cross-section of a rectangular or square hollow section with the dimension for the effective weld indicated between two internal points.

Note that the force arrows shown for overlapped K-connections may be reversed; $i$ and $j$ control member identification.

When $25 \% \leq O_{\mathrm{v}}<50 \%$

(K5-10)

When 50% ≤ Ov < 80%

(K5-11)

When $80 \% \leq O_{v}<100 \%$

(K5-12)

(K3-13)

(K3-14)

When $B_{b i} / B>0.85$ or $\theta_{i}>50^{\circ}, B_{e o i} / 2$ shall not exceed $B_{b i} / 4$ and when $B_{b i} / B_{b j}>0.85$ or $\left(180-\theta_{i}-\theta_{j}\right)>50^{\circ}, B_{e o v} / 2$ shall not exceed $B_{b i} / 4$.

Subscript $i$ refers to the overlapping branch. Subscript $j$ refers to the overlapped branch.

Overlapped member effective weld properties (all dimensions are for the overlapped branch, j)

(K5-13)

(K5-14)

When $B_{b j} / B>0.85$ or $\theta_{i}>50^{\circ}$

$l_{e, j}=2\left(H_{b j}-1.2 t_{b j}\right) / \sin \theta_{j}$ (K5-15)

Figure description:

Effective Weld Properties for Connections to Round HSS

TABLE K5.2 Effective Weld Properties for Connections to Round HSS

Annotations

• Not present for T- or Y-connections (text_label - position: Referring to the bottom branch of the cross-connection diagram)
• Section A-A: Effective weld (text_label - position: Label for the bottom-left diagram showing the arc of effective weld)
• l_e/2 (text_label - position: Arc angle label in Section A-A diagram)
• D_b, t_b (text_label - position: Dimensions of the branch cross-section)
• D, t (text_label - position: Dimensions of the chord cross-section)