18/02/2024
Wind Drift
The ASCE 7-16 standard does not suggest an allowable drift limit for wind design as it does with a seismic design but, according to the non-mandatory Appendix CC (Serviceability Considerations) of ASCE 7-16, common usage for building design is on the order of 1/600 to 1/400 of the building or story height without more details. Typical wind drift limits in common usage vary from H/100 to H/600 for total building drift and h/200 to h/600 for inter-story drift, depending on building type and the type of cladding or partition materials used. The most widely used values are H (or h)/400 to H (or h)/500 (ASCE Task Committee on Drift Control of Steel Building Structures, 1988). An absolute limit on the inter-story drift is sometimes imposed by designers in light of evidence that damage to nonstructural partitions, cladding, and glazing may occur if the inter-story drift exceeds about 10 mm.
Seismic and Wind Drift
Both seismic and wind drift are lateral deflections that take place because of applied lateral design forces, but they have many differences, such as allowable drift limits, nature of drift, and determination procedures. The main differences are summarized as follows:
Seismic drift is recognized as inelastic drift because of the inelastic behavior of the seismic force-resisting system. Thus, a deflection amplification factor, Cd, is used to account for an inelastic drift. On the other hand, wind drift is considered an elastic drift because the wind force resisting system interacts linearly with the design wind forces.
The nonlinear response of the wind force resisting system is not permitted. This can be clearly seen from the strict allowable drift limits under wind loads as compared with the relaxed allowable seismic drift.
The seismic drift of structures is determined at the strength-load level (Strength Limit). However, wind drift is still regarded as a serviceability limit and is obtained at service load level (service wind speed with a return period of 10, 25, 50, 100 years).
Allowable drift limits for structures under wind and seismic forces are, to a great extent, different because of the different design philosophies. The allowable drift limits of seismic force-resisting systems are much higher than those permitted for wind force resisting systems. The allowable drift limit for certain seismic systems is about 10 times the drift allowed under wind loading.
يختلف حساب قيمة DRIFT في WIND LOADS AND Seismic LOADS
Seismic LOADS تكون القيم محدده في الكود بدقة و تعتمد علي Strength Limit وتكون القيم المسموح بها allowable drift limits أكبرمن القيم المسموح بها في حالة Wind Loads ويتم حسابها عن طريق ultimate load cases نتيجة أن سلوك المنشأ في حالة أحمال الزلازل يكون سلوك غير مرن inelastic behavior
بينما في Wind Loads لا توجد قيم محددة في الكود لحساب قيمة allowable drift limits وتعتمد علي common practices and commentary علي حسب المنشأ و ductility of cladding material and finishes ويتم حسابها عن طريق service load combinationsكما هو موضح لاحقا
لو حابب تتعمق اكثر في مواضيع وتصميم ال WIND LOAD دلوقتي فية عرض مميز علي كورس Advanced Wind Load Analysis Course According ASCE
https://ragabelmasry.com/course/advanced-wind-course/
