F13Proportions of beams and girders

F13.1 Strength Reductions for Members with Bolt Holes in the Tension Flange

This section applies to rolled or built-up shapes and cover-plated beams with standard and oversized bolt holes or short- and long-slotted bolt holes parallel to the direction of load, proportioned on the basis of flexural strength of the gross section.

In addition to the limit states specified in other sections of this chapter, the nominal flexural strength, $M_{n}$, shall be limited according to the limit state of tensile rupture of the tension flange.

(a) When $F_{u} A_{f n} \geq Y_{t} F_{y} A_{f g}$, the limit state of tensile rupture does not apply.

• (b) When $F_{u} A_{f n}<Y_{t} F_{y} A_{f g}$, the nominal flexural strength, $M_{n}$, at the location of the holes in the tension flange shall not be taken as greater than

(F13-1)

where

$\begin{aligned} A_{f g} & =\text { gross area of tension flange, calculated in accordance with Section B4.3a, } \\ & \text { in. }^{2}\left(\mathrm{~mm}^{2}\right)\end{aligned}$

$\begin{aligned} A_{f n} & =\text { net area of tension flange, calculated in accordance with Section B4.3b, in. }^{2} \\ & \left(\mathrm{mm}^{2}\right)\end{aligned}$

$F_{u}=$ specified minimum tensile strength, ksi (MPa)

$S_{x}=$ minimum elastic section modulus taken about the x-axis, in. ${ }^{3}\left(\mathrm{~mm}^{3}\right)$

$\begin{aligned} Y_{t} & =1.0 \text { for } F_{y} / F_{u} \leq 0.8 \\ & =1.1 \text { otherwise }\end{aligned}$

F13.2 Proportioning Limits for I-Shaped Members

Singly symmetric I-shaped members shall satisfy the following limit:

(F13-2)

Singly and doubly symmetric I-shaped members with slender webs shall satisfy the following limits:

(a) When $\frac{a}{h} \leq 1.5$

(b) When $\frac{a}{h}>1.5$

(F13-4)

where

$a=$ clear distance between transverse stiffeners, in. (mm)

In unstiffened girders, $h / t_{w}$ shall not exceed 260 . The ratio of 2 times the web area in compression to the compression flange area, $a_{w}$, as defined by Equation F4-12, shall not exceed 10.

F13.3 Cover Plates

• (a) For members with cover plates, the following provisions apply: Flanges of welded beams or girders are permitted to be varied in thickness or width by splicing a series of plates or by the use of cover plates.
• (b) High-strength bolts or welds connecting flange to web, or cover plate to flange, shall be proportioned to resist the total horizontal shear resulting from the bending forces on the girder. The longitudinal distribution of these bolts or intermittent welds shall be in proportion to the intensity of the shear.
• (c) However, the longitudinal spacing shall not exceed the maximum specified for compression or tension members in Section E6 or D4, respectively. Bolts or welds connecting flange to web shall also be proportioned to transmit to the web any loads applied directly to the flange, unless provision is made to transmit such loads by direct bearing.
• (d) Partial-length cover plates shall be extended beyond the theoretical cutoff point and the extended portion shall be attached to the beam or girder by high-strength

bolts in a slip-critical connection or fillet welds. The attachment shall, at the applicable strength given in Section J2.2, J3.9, or B3.11, develop the cover plate’s portion of the flexural strength in the beam or girder at the theoretical cutoff point.

• (e) For welded cover plates, the welds connecting the cover plate termination to the beam or girder shall be continuous welds along both edges of the cover plate in the length $a^{\prime}$, defined in the following, and shall develop the cover plate's portion of the available strength of the beam or girder at the distance $a^{\prime}$ from the end of the cover plate.
• (1) When there is a continuous weld equal to or larger than three-fourths of the plate thickness across the end of the plate

$a^{\prime}=w$

(F13-5)

where

$w=$ width of cover plate, in. (mm)

• (2) When there is a continuous weld smaller than three-fourths of the plate thickness across the end of the plate

$a^{\prime}=1.5 w$ (F13-6)

(3) When there is no weld across the end of the plate

(F13-7)

F13.4 Built-Up Beams

Where two or more beams or channels are used side by side to form a flexural member, they shall be connected together in compliance with Section E6.2. When concentrated loads are carried from one beam to another or distributed between the beams, diaphragms having sufficient stiffness to distribute the load shall be welded or bolted between the beams.