Steel Buildings in Europe

Part 4: Detailed Design of Portal Frames 4 - 72 w c : precamber in the unloaded structural member w 1 : Initial part of the deflection under permanent loads of the relevant combination of actions w 2 : Long-term part of the deflection under permanent loads, not to be considered for single-storey steel buildings, w 3 : Additional part of the deflection due to the variable actions of the relevant combination of actions w tot = w 1 + w 2 + w 3 w max : Remaining total deflection taking into account the precamber Figure A.3 Definition of vertical deflections Table A.3 Recommended limiting values for vertical deflections Deflection limits Country Structure W max W a Comments France Roofs in general L /200 L /250 Roofs frequently carrying personnel other than for maintenance L /200 L /300 Roofs supporting plaster or other brittle toppings or non-flexible parts L /250 L /350 Values are given in the National Annex to EN 1993-1-1 and should be used if nothing else is agreed with the client. The values of the deflections calculated from the characteristic combinations should be compared to these limits. Germany There are no national deflection limits. The limits should be taken from manufacturers’ instructions (technical approvals) or should be agreed with the client. Roofs in general L /300(*) - Roofs with access only for maintenance L /250(*) Spain Values are given in the national technical document for steel structures and in the Technical Building Code and should be used if nothing else is agreed with the client. (*) This values refers to w 2 + w 3 but w 2 = 0 for steel structures. Ultimate limit state: Ponding Where the roof slope is less than 5%, additional calculations should be made to check that collapse cannot occur due to the weight of water:  either collected in pools which may be formed due to the deflection of structural members or roofing material  or retained by snow. These additional checks should be based on the combinations at the Ultimate Limit States. Precambering of beams may reduce the likelihood of rainwater collecting in pools, provided that rainwater outlets are appropriately located. w c w max w 1 w 2 w 3 w tot