#Asce 7 10 Vs Asce 7 16 Cracked Is Likely

In this article, the effect of soil flexibility and cracking of reinforced concrete elements on seismic drift computation of structural systems is addressed. The first article (STRUCTURE, July 2019) discussed main points influencing seismic drift computation. External pressure coefficient GCpf (from Figure 28.4.1 of ASCE 7-16)This article is the second of a two-part article on ASCE 7-16, Minimum Design Loads for Buildings and Other Structures, and its provisions for lateral drift determination. Wind pressure at each zone needs to be calculated separately. Note: For wind pressures at edges and corners of walls and roof are higher than interior zone. GCpi is the internal pressure coefficient from Table 26.11-1 of ASCE 7-10.

Find booksThe citation of ASCE 7-16 in Chapter 35 of the 2018 IBC does not specifically indicate that Supplement 1 is adopted. Effect of Soil Flexibility ModellingASCE 7-16 Minimum Design Loads and Associated Criteria for Buildings and Other Structures American Society of Civil Engineers download Z-Library. A brief comparison between seismic drift and wind drift, in connection to their nature, and a determination procedure is covered.

Column base restraint conditions.Higher п¬‚exibility (pinned base) lengthens the period of the building, resulting in a smaller calculated base shear but larger calculated story drifts.One drawback to the pinned-base condition is that the story drift of the frame, especially the story drift in the lowest story, is difficult to keep within allowable code limits. The FigureВ illustrates four types of base restraint conditions that may be considered. Alternatively, where foundation п¬‚exibility is considered, it shall be in accordance with Section 12.13.3 or Chapter 19.вЂќ Therefore, structural engineers must decide the most appropriate analytical assumptions for the structure considering its construction details.

Asce 7 10 Vs Asce 7 16 Cracked Is Likely

ACI 318-14, Building Code Requirements for Structural Concrete, also states in its CommentaryВ R18.2.2 that, for lateral displacement calculations, assuming all structural elements to be fully cracked is likely to lead to a better estimate of the possible drift than using uncracked stiffness for all members. ASCE 7-16 Section 12.7.3 states that, for reinforced concrete structures, stiffness properties of concrete and masonry elements shall consider the effects of cracked sections. It is, therefore, necessary to consider the reduced stiffness of seismic system elements due to cracking. Effect of Structural Elements CrackingSeismic design is based on consideration of nonlinear response.

Special moment frames, for example, may have higher stiffness reduction factors among a group of seismic force-resisting systems because this system is designed to permit a high level of nonlinear deformation.Selecting reduction factors for different seismic systems in association with their behavior under seismic forces is not clearly stated in ACI 318-14 however, engineering judgment may be employed to select the best value for stiffness reduction based on the type of seismic lateral force resisting system and the intended level of nonlinear deformation. The reduced stiffness of these various systems also varies based on the permitted degree of nonlinear deformation. It should be noted that various seismic force-resisting systems have different levels of nonlinear response, and these levels are represented by the values of response reduction factors R.

CC.2-1 through CC.2-4 of ASCE 7-16). Wind Speed MapsThe Appendix C CommentaryВ presents maps of peak gust wind speeds at 33 feet (10 m) above ground in Exposure C conditions for return periods of 10, 25, 50, and 100 years (Figs. The strength load level is used for checking strength design requirements while service load level is used for complying with serviceability requirements such as drift and vibration. Since 2010, ASCE 7 has considered two wind load levels, which are the strength load level (high mean recurrence interval, MRI) maps with MRI 300, 700, 1700, and 3000 years and the service load level (low mean recurrence interval, MRI) maps with MRI 10, 25, 75, and 100 years. Unlike seismic drift, which is determined at the strength load level, wind drift is still a serviceability concern and thus calculated at the service load level (low mean recurrence interval, MRI). As a result, many changes have been incorporated in comparison to older versions.

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 interstory drift, depending on building type and the type of cladding or partition materials used. Wind Drift LimitThe 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 CCВ (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. The height of the structure, type of cladding materials, and type of cladding detailing are among the most important reasons that may encourage using wind speed maps with high return periods. MRI of 10 and 50 years is recommended but, under certain circumstances, the design engineer can use a higher MRI wind speed in consultation with the client.

Seismic and Wind DriftBoth 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. Table of moment inertia permitted for elastic analysis at service load level.The factors shown in the TableВ are calculated by multiplying the moment of inertia factor for strength load level stipulated in Table 6.6.3.1.1 by 1.4 as stated in R.6.6.3.2.2 of ACI 318-14. According to ACI 318-14 Commentary, the factors shown in the TableВ shall be used to consider cracking effects. This lesser effect stems from the nonlinear response of a structure, which is not considered in wind analysis. Effect of Cracking of Structural ElementsFor wind analysis, the cracking of structural elements has less effect on the structural response of the wind force resisting system.

The allowable drift limit for certain seismic systems is about 10 times the drift allowed under wind loading.One of the inherent provisions in most codes and standards is the consideration of building drift under seismic and wind loading. The allowable drift limits of seismic force-resisting systems are much higher than those permitted for wind force resisting systems. Allowable drift limits for structures under wind and seismic forces are, to a great extent, different because of the different design philosophies. ACI 318-14, 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. Yet, they do not state the same for wind drift. ASCE 7-16 and ACI 318-14 have explicitly stated that the effect of reinforced concrete cracking shall be considered for obtaining realistic estimates of seismic drift.

1, produced by the Applied Technology Council and the Consortium of Universities for Research in Earthquake Engineering for the National Institute of Standards and Technology, Gaithersburg, MD. Chapter 12.Seismic design of reinforced concrete special moment frames: A guide for practicing engineers, Second Edition, GCR 16-917-40, NEHRP Seismic Design Technical Brief No. Reston, Virginia: American Society of Civil Engineers. There are many reasons that necessitate limiting drift the most significant is to address the structural importance of member inelastic strain in the case of seismic design and system stability and to limit damage to non-structural components, which can be a threat to safety, health, and welfare of the public.в– ReferencesASCE/SEI 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures.