Portal frame assumptions

The following is a list of assumptions made in the current version of the portal frame builder.

 

AS/NZS1170.2 Assumptions

  • Wind loads are assumed to be uniform over the height of the building (ie. z=h throughout).

  • Torsion due to eccentricities on tall buildings with h > 70m (AS/NZS 1170.2 section 2.5.4) is not considered.

  • Fatigue (AS/NZS 1170.2 sections 2.5.5 and 2.5.6) is not considered.

  • The dynamic response factor Cdyn (AS/NZS 1170.2 section 2.5.7) is taken as 1.0.

  • No allowance is made for impact loading due to windborne debris (AS/NZS 1170.2 section 2.5.8).

  • The building is assumed to be not elevated (AS/NZS 1170.2 section 5.4.1).

  • The permeable cladding reduction factor Kp (AS/NZS 1170.2 section 5.4.5) is taken as 1.0.

  • The distributed live load is applied to the entire area of the roof, even if the roof area is greater than 200m2.

  • The 1.4kN concentrated live load specified in AS/NZS 1170.1 (but not in conjunction with the distributed live load - AS/NZS 1170.1 section 3.1) is not applied.

 

IS:875 Assumptions

  • Wind loads are assumed to be uniform over the height of the building (ie. z=h throughout).

  • In IS875 (Part 3) table 6 for a longitudinal wind direction (ie. q=90deg), areas E and G are assumed to extend a distance of W/2 from the windward edge of the roof, with areas F and H extending for a further distance of W/2.

  • In IS875 (Part 3) table 7 for a longitudinal wind direction (ie. q=90deg), areas H and L are assumed to extend for half of the roof length from the windward edge of the roof.

  • IS875 (Part 3) table 7 is used for all monoslope roofs, even if h/w >= 2.

  • The Kc factor from clause 7.3.3.13 is assumed to be 1.0 in all cases due to the problem of complying with pd >= 0.70pz in clause 7.2. The problem occurs because pd must be calculated for the primary load cases and Kc is unknown at that stage.

  • Interference effects from upwind obstructions are not considered (IS875 (Part 3) section 8).

  • Dynamic effects due to wind are not considered (IS875 (Part 3) sections 9 and 10).

  • Live loads are calculated in accordance with IS875 (Part 2) table 2 and do not include any extra allowance for rain, dust or the 0.90kN incidental concentrated load specified in IS875 (Part 2) section 4.5.