![]() ![]() Here temperature of the boiler feed water is around the saturation temperature corresponding to its pressure. Water circulation in boiler can be classified in three different types of systems.īoiler feed water which is pumped with high pressure boiler feed water pumps first reaches at economizer. A limiting drift ratio of 0.03 is indirectly used in Clause 18.7.5.4 of ACI 318-19 when specifying the transverse confining reinforcement for SMF.Ībdulqader Al-sheikh, "ASCE 7-16 Provisions for Lateral Drift Determination-Parts 1 & 2", STRUCTURE Magazine, July 2019 and Dec.2019, pp.Types of water circulation in industrial steam water tube boilers: Advertisements The allowable drift limit for certain seismic systems is about 10 times the drift allowed under wind loading.ĭRLim, the limiting drift ratio, may be taken as 0.015 for moderate seismicity and 0.025 for high seismicity. The allowable drift limits of seismic force-resisting systems are much higher than those permitted for wind force resisting systems. ACI 318-19, instead, states in its Commentary that, for wind design, effective stiffnesses representative of pre-yield behavior may be appropriate because the philosophy of wind design does not allow the nonlinear response.Īllowable drift limits for structures under wind and seismic forces are, to a great extent, different because of the different design philosophies. Yet, they do not state the same for wind drift. 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).ĪSCE 7-16 and ACI 318-19 have explicitly stated that the effect of reinforced concrete cracking shall be considered for obtaining realistic estimates of seismic drift. The seismic drift of structures is determined at the strength-load level (Strength Limit). This can be clearly seen from the strict allowable drift limits under wind loads as compared with the relaxed allowable seismic drift. The nonlinear response of the wind force resisting system is not permitted. On the other hand, wind drift is considered an elastic drift because the wind force resisting system interacts linearly with the design wind forces. Thus, a deflection amplification factor, Cd, is used to account for an inelastic drift. Seismic drift is recognized as inelastic drift because of the inelastic behavior of the seismic force-resisting system. The main differences are summarized as follows: 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.īoth 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 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). 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 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.
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