Beam web openings to SCI P355

Tekla Structural Designer
2021
Tekla Structural Designer

Beam web openings to SCI P355

Note: When the Head Code has been set to Eurocode, Tekla Structural Designer adopts the following approach to web openings which is specific to the UK National Annex.

As each web opening is added it is checked against certain geometric and proximity recommendations taken from Table 2.1 of SCI Publication P355 (see below).

Guidance on size and positioning of openings

The following general guidance on size and positioning of openings is taken from Table 2.1 Section 2.6 of the SCI Publication P355

Note: These geometric limits should normally be observed when providing openings in the webs of beams. It should be noted that these limits relate specifically to composite beams and caution should be used in applying these limits to non-composite beams.
Parameter Limit
Circular Opening Rectangular Opening
Max. depth of opening: <= 0.8h <= 0.7h
Min. depth of Tee, >= tf +30 mm >= 0.1h
Min. depth of Top Tee: As above

As above and >= 0.1 lo

if unstiffened

Max. ratio of depth of Tees: hb/ht

hb/ht

<= 3

> = 0.5

<=2

>= 1

Max. unstiffened opening length, lo

Max. stiffened opening length, lo

-

-

-

-

<= 1.5 ho high shear*

<= 2.5 ho low shear

<= 2.5 ho high shear*

<= 4 ho low shear

Min. width of web post:

- Low shear regions

-High shear regions

>= 0.3h o

>= 0.4h o

>= 0.5 lo

>= lo

Corner radius of rectangular openings: -

ro >= 2 tw

but ro >= 15 mm

Min. width of end post, se: >= 0.5 ho

>= lo

and >= h

Min. horizontal distance to point load:

- no stiffeners

- with stiffeners

>= 0.5 h

>= 0.25 ho

>= h

>= 0.5 ho

* A high shear region is where the design shear force is greater than half the maximum value of design shear force acting on the beam.

Symbols used in the above table:

h = overall depth of steel section

ho = depth of opening [diameter for circular openings]

ht = overall depth of upper Tee [including flange]

hb = overall depth of lower Tee [including flange]

lo = (clear) length of opening [diameter for circular openings]

se = width of end post [minimum clear distance between opening and support]

tf = thickness of flange

tw = thickness of web

ro = corner radius of opening

In addition, the following fundamental geometric requirements must be satisfied.

do <= 0.8*h for circular openings

do <= 0.7*h for rectangular openings

do < 2 * (doc - tt - rt)

do < 2 * (h - doc - tb - rb)

d2 < doc - do/2 - tt- ts/2

d2 < h - tb- doc - do - ts/2

lo < 2 * Lc

lo < 2 * (L - Lc)

Ls < 2 * Lc

Ls < 2 * (L - Lc)

where

dt= the depth of the web of the upper tee section measured from the underside of the top flange

doc = the distance to the centre line of the opening from the top of the steel section

d2 = the distance from the edge of the opening to the centre line of the stiffener

ts = thickness of stiffener [constrained to be the same top and bottom]

tt = the thickness of the top flange of the steel section

tb = the thickness of the bottom flange of the steel section

rt = root radius at the top of the steel section

rb = root radius at the bottom of the steel section

Lc = the distance to the centre line of the opening from the left hand support

L = the span of the beam

Note: Dimensional checks - The program does not check that openings are positioned in the best position (between 1/5 and 1/3 length for udls and in a low shear zone for point loads). This is because for anything other than simple loading the best position becomes a question of engineering judgment or is pre-defined by the service runs.
Note: Adjustment to deflections - The calculated deflections are adjusted to allow for the web openings
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