Steel Design: Types Of Elements

STEEL DESIGN: TYPES OF ELEMENTS

IS 800:2007 classifies elements in to three types, as per Cl. 3.7.3., as follows.

1. Internal elements

These are elements attached along both longitudinal edges to other elements or to longitudinal stiffeners connected at suitable intervals to transverse stiffeners, for example, web of I-section and flanges and web of box section.

2. Outside elements or outstands

These are elements attached along only one of the longitudinal edges to an adjacent element, the other edge being free to displace out of plane, for example flange overhang of an I-section, stem of T-section and legs of an angle section.

3. Tapered elements

These maybe treated as flat elements having average thickness as defined in SP 6 (Part 1).

MAXIMUM EFFECTIVE SLENDERNESS RATIO

The maximum effective slenderness ratio, as per Cl. 3.8 of IS 800:2007, KL/r values of a beam, strut or tension member shall not exceed those given in Table 3 of IS 800:2007. 'KL' is the effective length of the member and 'r' is appropriate radius of gyration based on the effective section as defined in Cl.

3.6.1 of IS 800:2007. This data is reproduced here in Table 4.

Table 4 Maximum effective slenderness ratio               

Member : Maximum Effective Slenderness Ratio (KL/r)        

A member carrying compressive loads resulting from dead loads and imposed loads  :          180   

A tension member in which a reversal of direct stress occurs due to loads other than wind or seismic forces       : 180 

A member subjected to compression forces resulting only from combination

with wind/earthquake actions, provided the deformation of such member : 250 

does not adversely affect tbe stress in any part of the structure                

Compression flange of a beam against lateral torsional buckling     : 300

A member normally acting m a tie in a roof truss or a bracing system not         

considered effective when subject to possible reversal of stress into : 350 

compression resulting from the action of wind or earthquake forces                  

Members always under tension (other than pre-tensioned members)         : 400