STRUCTURAL STEEL SHAPESWelcome to a discussion on C & MC shapes

~-~-~ Presented by Viji Anto & Team~-~-~

Based on AISC manual 13th edition.

INTRODUCTION

Structural steel is one of the basic materials commonly used in structures, such as industrial and commercial buildings, bridges, and piers. It is produced in a wide range of shapes and grades, which permits great flexibility in its usage. It is relatively inexpensive to manufacture and is the strongest and most versatile material available to the construction industry.

AISC manual 13th edition classifies the structural steel shapes generally into,

Hollow Structural Sections & Pipe Shapes

I shapes - W, M, S & HP

Channels - C & MC Shapes

Tee sections - WT, MT & ST Shapes

Angles -

Our discussion today focuses on Channels - C & MC Shapes

C SHAPES Introduction

As the name suggests C channels have a shape similar to alphabet “C”. The shape is unsymmetrical with a web, 2 flanges at top and bottom projecting to one of the sides & the other side is flat in the cross section.

Also called American standard channelsCommon, Standard & readily available with most of the manufacturers.Rolled with a constant inner flange surface slope of 2 on 12

C channel is designated as C<nominal depth, in.>X<nominal weight, lbs/ft>Where nominal depth is the overall depth of the member rounded of to a whole number in inches & nominal weight is the weight of the cross section in Lbs/ft.

For dimensions & properties refer next slide

C SHAPES

Dimensions

Properties

Reference: Table 1-5AISC Manual 13th Edition.

Shape

Area Depth Thickness Width Average thickness k T

Work-able gage

rts h0

A d tw tw/2 bf tf

in2 in in in in in in in in in in

C3X3.5 1.09 3.0 3 0.132 1/8 1/16 1.37 1”3/8 0.273 1/4 11/16 1”5/8 - 0.455 2.73

C15X50 14.7 15.0 15 0.716 11/16 3/8 3.72 3”3/4 0.650 5/8 1”7/16 12”1/8 2”1/4 1.17 14.4

Nominal wt

Shear centre Axis X-X Axis Y-Y Torsional properties

e0 I S r Z I S r x Z xp J Cw r0 H

Lb/ft in in4 in3 in in3 in4 in3 in in in3 in in4 In6 in

3.5 0.493 1.57 1.04 1.20 1.24 0.169 0.182 0.394 0.443 0.364 0.296 0.0226 0.276 1.57 0.645

50 0.583 404 53.8 5.24 68.5 11.0 3.77 0.865 0.799 8.14 0.490 2.65 492 5.49 0.937

Dimensions & properties

A – Area of cross section (in2)

d – Overall depth of the member (in)

tw – thickness of web (in)

bf - width of flange (in)

tf – thickness of flange (in)

k – Distance from outer flange of flange to web toe of fillet (in)

T – Distance between web toes of fillets at top and at bottom of web (in)

rts – Effective radius of gyration (in)

e0 – Shear centre (in)

I – Moment Of Inertia (in4)

h0 – distance between the flange centroids (in)

General nomenclature used in Table -5 & Table -6 of AISC manual 13th edn.

r – radius of gyration (in)

Z – Plastic section modulus(in3)

xp – Horizontal distance from the designated edge of member to its plastic neutral axis (in)

x – Horizontal distance from outer edge of a channel web to its centroid (in)

J – Torsional constant (in4)

PNA – Plastic neutral axis

Cw – Warping constant (in6)

r0 – Polar radius of gyration about the shear center (in)

H – Flexural constant

General nomenclature used in Table -5 & Table -6 of AISC manual 13th edn.

S – Elastic section modulus(in3)

MC SHAPES Introduction

MC or Miscellaneous channels (similar to C channel) have a shape similar to alphabet “C”. The shape is unsymmetrical with a web, 2 flanges at top and bottom projecting to one of the sides & the other side is flat in the cross section.

Also called ship / car channelNon standard channels & not readily available with all the manufacturers.the inner-flange slope of MC-shapes will vary from manufacturer to

manufacturer

MC is designated as MC<nominal depth, in.>X<nominal weight, lbs/ft>Where nominal depth is the overall depth of the member rounded of to a whole number in inches & nominal weight is the weight of the cross section in Lbs/ft.

For dimensions & properties refer next slide

Shape

Area Depth Thickness Width Average thickness k T Work-

able gage

rts h0

A d tw tw/2 bf tf

in2 in in in in in in in in in in

MC3X7.1 2.11 3.0 3 0.312 5/16 3/16 1.94 2 0.351 3/8 13/16 1”3/8 - 0.657 2.65-

MC18X58 17.1 18.0 18 0.700 11/16 3/8 4.20 4”1/4 0.625 5/8 1”7/16 15”1/8 2”1/2 1.35 17.4

MC SHAPES

Nominal wt

Shear centre Axis X-X Axis Y-Y Torsional properties

e0 I S r Z I S r x Z xp J Cw r0

Lb/ft in in4 in3 in in3 in4 in3 in in in3 in in4 In6 in

7.1 0.574 2.72 1.81 1.14 2.24 0.666 0.518 0.562 0.653 0.998 0.414 0.0928 0.915 1.76

58 0.695 675 75.0 6.29 95.4 17.6 5.28 1.02 0.862 10.7 0.474 2.81 1070 6.56

Dimensions

Properties

Dimensions & properties

Reference: Table 1-6AISC Manual 13th Edition.

MILL TOLERANCES FOR C & MC SHAPES

a A is measured at centerline of web for beams & at back of web for channelsb T + T’ applies when flanges of channels are toed in or out

MILL TOLERANCES FOR C & MC SHAPES

Indicates that there is no requirement

c The permitted variation under the specified length is 0 in for all lengths. There are no requirements for lengths over 65 ft.

dThe tolerances specified herein are taken from ASTM A6 and apply to the straightness of members received from the rolling mill, measured as illustrated in Figure 1-1. For tolerance on induced camber & sweep, see Code of standard practice section 6.4.4.

APPLICABLE ASTM SPECIFICATIONS FOR C & MC SHAPES

Preferred material specification

Other applicable material specification, the availability of which should be confirmed prior to specification.

Material specification does not apply.

APPLICATIONS OF C & MC SHAPES IN THE STRUCTURAL STEEL CONSTRUCTION INDUSTRY

Neither type of shape is very commonly used in structural steel applications for buildings, but the c-shapes may be a little more common. This is mainly due to the cross sectional asymmetry of the section which makes it a back seater when structural properties are the consideration.

But it can be can be advantageous in various situations:

Channels can be used at floor / roof openings, as stair stringer, door header, door jamb etc by taking advantage of the fact that one of its sides along the major axis is a flat surface.

Channels are also used as Platform beams, landing beams, girts, purlins & other light weight applications.

Channels are widely used in built-up sections resisting transverse or axial load

Relatively lesser resistance to torsion & warping makes the channels less favorable for transverse loading.

Asymmetry, slenderness & buckling makes it less favorable for axial loading

Thank you

Viji Anto & Team