BUILDING HORIZONTAL DEFLECTION

[jdbpe]

I AM CURRENTLY DESIGNING A NEW FOUR STORY RETAIL MALL STRUCTURE AND WOULD LIKE TO GET A CONSENSUS ON THE LIMIT OF HORIZONTAL DEFELCTION AT THE TOP OF THE BUILDING, i.e. H/200, H/400 etc. THE STRUCTURE WILL CONTAIN LARGE GLASS WINDOWS.

 

[ishvaaag]

I would think at wind service level 1/400 or 0.0025 radians distortion should be the maximum distortion allowed in any interstory height, and 1/600 is considered in highrise to skyscraper the maximum taht economy permits. Always include P-delta.

1/750 in the whole height on brute section 28 days Ec allow for Jackson and Moreland chart sway design of columns in reinforced concrete in Spain's EHE code, otherwise the requirements are those general and undefined in the code but taking into account material and geometrical nonlinearity, so this limit -not too strict in for RC concrete midrise- is near mandatory in Spain for buildings with RC structure if you want to enjoy some protection from the code.

In any case, depending on the particular infills to use, an analysis can be made for the maximum distortion permissible. You can determine for nonattached panels (glass, gypsum) for example, the required gaps, both vertically and horizontally.

Vertical mullions should glide one unto other so no shortening is usually passed; contrarily the drift distortion inmediately is, and the fixed points settling with the vertical loads also will have its influence. It is just a geometrical problem to get the gaps for a void or very low modulus sealant.

For attached masonries I wouldn't go under 1/400 typically. Even so for stores and public buildings the modern trend is to create panels even for brick to diminish or near nullify the posssibility of uncontrolled cracks formation. Think that a fragile masonry can show cracks from 1/2000 to 1/1500 distortion. However I have not seen any code going so strict.

If you have problems in meeting the limit, use box action with some rigid roof, and shearwalls etc.

 

[phuduhudu]

The British Steel code BS5950 limits it to H/300. However you should make sure that your glazing fixing detail can take this amount of movement without compromising the weatherproofing. Carl Bauer

http://www.bauerconsultbotswana.com

 

[Riz]

Inorder for u to be able to set deflection limits, it is important to know whether a tall building is a tall one. Normally the tallest ladder of a fire brigade marks the limit (Schaefer). Australia - 25m; France - 28m; Netherlands - 13m; UK - 28 to 30m; USA - 23 - 30m; Germany -22m. (Ciria Report 102)

Depending on how u r teating your 4 storey mall is equally important.

Ciria (Construction Industry Research & Information Assoc.) recommends a maximum displacement of height/500 for avoiding visible distress.