Structures assigned to seismic design category c, d, e, and f with type 1a and type 1b horizontal structural irregularity. Evaluation of overstrength factor of steel moment resisting frames. Moment redistribution and connection analysis os to an applied overstrength of 1. Seismic design forces for foundations, other than pile bents and retaining walls, shall be determined by dividing elastic seismic forces, obtained from article 3. Seismic design of wood structures in the context of. The nz steel structure design standard nzs3404, uses both a material overstrength factor. For these projects, the structural design must use the importance factors for risk category iv. Relying on such overstrength, many seismic codes permit a reduction in design loads. Assessment of redundancy factors for the seismic design of.
Accounting for ductility and overstrength in seismic. Seismic design for petrochemical facilities as per nbcc 2005. Fema 451b topic 9 notes seismic load analysis 9 1 instructional material complementing fema 451, design examples seismic load analysis 9 1 seismic load analysis this topic focuses on seismic load analysis. Structure magazine changes in the aci 318 anchoring to.
Topics will also include limitations on the use of wood in seismic design. Seismic design for petrochemical facilities as per nbcc 2005 dongxiao wu p. R factor, the system overstrength factor, and deflection amplification factor cd, of new seismic forceresisting systems proposed for inclusion in model building codes. Seismic overstrength of shear walls in parking structures.
Which of the following will be required to be increased by a factor of 1. Seismic system factors and system overstrength strength of. You will use your overstrength factors when you have some sort of irregularity or when called for in the materials seismic provisions. Pdf ductility and overstrength in seismic design of. Use asce 7 basic load combinations but substitute the following for the. When in seismic design category a, you should not use any of the provisions of chapter 12. Components in seismic design category a are exempt from seismic design requirements, as stated in section 11. Seismic design of buildings analysisanddesignofearthquakeresistantbuildings robertotomasi 11. In these structures, reserve strength is almost independent of both the height of the structure and the effect of building sway. Structure magazine the most common errors in seismic. Accounting for ductility and overstrength in seismic design. In this paper, the effects of various parameters such as the type of the moment frame, seismic design category sdc and height of the building on overstrength factors of steel moment resisting. Quantification of building seismic performance factors.
Assessment of redundancy factors for the seismic design of special moment resisting reinforced concrete frames 1 introduction. These studies have shown in their globality that the overstrength depends on different factors which the most important of them is member ductility factor. The relationship between the lateral capacity, the design force reduction factor, the ductility level and the overstrength factor are investigated. Ductility and overstrength in seismic design of reinforced. I was advised that it comes into account on structures with lateral irregularities, but still no direction, that i could dig up, in the code asce705.
Seismic system factors and system overstrength free download as powerpoint presentation. Seismic stability properties of wood building materials. This presentation will summarize and scrutinize the use of seismic response modification coefficient, r, equal to 1, 1. Pdf ductility and overstrength in seismic design of reinforced. Table i41 in the 2002 seismic provisions applies only in the absence of a specific definition of overstrength factor in the applicable building code section 4. Frequently misunderstood seismic provisions of asce 710 skgassociates. This paper addresses the issue of horizontal overstrength in modern code.
Apr 02, 2015 ive been searching the web for a sort of comprehensive list of what elements get designed for the overstrength factor. Aisc lrfd load and resistance factor design specification for structural steel buildings, american institute of steel construction, 1993. And i am not sure if overstrength factor can be used as a load factor for earthquake load in structure as a whole as you have mentioned that overstrength factor is an force amplification factor applied only to certain elements in load path. Pdf overstrength and force reduction factors of multistorey. Pdf use of overstrength and inelastic response in seismic design.
Significant changes from asce 705 to asce 710, part 1. Instructional material complementing fema 451, design examples seismic load analysis 9 17 1a, 1b stiffness soft story irregularity vertical structural irregularities irregularity 1a exists if stiffness of any story is less than 70% of the stiffness of the story above or less than 80% of the average stiffness of the three stories above. Accounting for overstrength in seismic design of steel. The behaviour factor q is an approximation of the ratio of the seismic forces that the structure would experience if its response was completely elastic with 5% viscous damping, to the seismic forces that may be used in the design, with a conventional. As an alternative, the seismic analysis and design procedures of alternative simplified chapter 4 shall be permitted to be used in lieu of the. Seismic design category sdc and height of the building on overstrength factors of steel moment resisting frames mrf are. The possible sources of reserve strength are outlined in this paper, and it is reasoned that a more rational basis for design would be to account for such sources in assessing the capacity rather than in reducing the design. Mandatory retrofit program for wood frame buildings with. Overstrength factors for the seismic design of aac structures. By using the n2 method, the seismic performance of the steel frames are investigated when they are subjected to the design earthquake for singapore. Increases in the construction of multistorey buildings. Chapter 12 seismic design requirements for building. Application of overstrength factor how deep does it go.
Memo to designers mtd 201 outlines the bridge category and classification, seismic performance criteria, seismic design philosophy and approach, seismic demands and capacities on structural and geotechnical components and seismic design practices that collectively make up caltrans seismic design methodology. It is easy to see that the r factor serves as a basic measure of a systems ability to resist seismic loads and that it is the single most important parameter in seismic design. The purpose of this methodology is to provide a rational basis for determining building seismic performance factors that, when properly. Ductility and overstrength in seismic design of reinforced concrete. Some concepts in earthquake behaviour of buildings c. In the topic, the manner in which ground accelerations impart design loads into the structure are described from a code perspective.
Ive been searching the web for a sort of comprehensive list of what elements get designed for the overstrength factor. I understand how to apply it, just not particularly to which items. The ductility factor increases as the inherent overstrength factor increases. I was hoping i could get some input as to what items to pay atten. Collector connections using the overstrength factor d. This revision contains more provisions for the seismic design of structures in corporating precast concrete than its. When a building code requires design of a connection in accor dance with special load combinations that include the system overstrength factor, the intent is to assure that the connection is strong enough and stiff enough to allow. The ibcreferenced design standard covers dimension lumber, glulam, structural composite lumber and clt as well as fasteners, connections and fire design. Where can i find this seismic design overstrength factor. Overstrength factor in anchor design for seismic loading vertical process vessel sandman21 structural 17 jul 18 18. You would also need to use the overstrength factor when designing drag struts with non light framed shear wall systems. Seismic overstrength of shear walls in parking structures 89 studied 6 and 12story framewall structures designed in accordance with canadian codes. Overstrength and ductility factors for steel frames. Overstrength factor, qo, is prescribed to assure sufficient design strength to allow selected members to yield.
It clearly shows that the inherent overstrength factor of the gravity load designed buildings is lower than seismic design frame, indicates that the seismic resistant building has more reserved strength and also reflects the conservatism of the code. The manner in which structural overstrength can be accounted for in the design of reinforced concrete structures is presented. Seismic design specification for buildings, structures. Design of collector elements, splices and connections when using the overstrength factor.
Egyptian code seismic load design provisions for moment. The national design specification nds for wood construction is also helpful when designing woodframe structures to withstand seismic events. The structural design criteria to be used in the design of buildings and other structures and their components shall be as prescribed in this chapter. Redundancy and overstrength of structures are two distinct notions the synergy of which affects the overall behavior of frame structures. Please also note the exception to 2018 ibc section 1810. And i am not sure if overstrength factor can be used as a load factor for earthquake load in structure as a whole as you. An evaluation of overstrength factor of seismic designed. When using allowable stress design, factor of safety for soil bearing values shall not be less than the overstrength factor of the structures supported. Seismic load effects including overstrength factor 6. This is related to the use of commercial steel bar diameters and the possibility that the minimum amount of steel reinforcement prescribed in codes controls the. The appropriate response modification coefficient, r, system overstrength factor. Accounting for ductility and overstrength in seismic design of. Several factors contribute to this overstrength factor.
Structure magazine the most common errors in seismic design. Aci 31811 seismic anchoring provisions are given in part d. As a first step in this direction, however, the factor. Canada abstract the seismic behaviour factor, r, is a critical parameter in contemporary seismic design. Pdf seismic design of building structures mansour al.
Aci 31808 appendix d seismic design criteria can be summarized as follows. The above modification is applicable to schools and hospitals in california only. Jul 20, 2017 seismic design forces for foundations, other than pile bents and retaining walls, shall be determined by dividing elastic seismic forces, obtained from article 3. Deflections are multiplied by the deflection amplification factor, c d, to obtain the expected inelastic deflections. A new revision of the new zealand concrete design standard, nzs 3101. Structures in new zealand a perspective on the seismic. Pdf evaluation of overstrength factor of steel moment. Observed and inherent overstrength factor and ductility factor frame i rec2 0. The quantification of both redundancy and overstrength during a seismic excitation is a decisive factor that together with ductility contributes to the assessment of structural seismic response and. Keywords structural redundancy, redundancy factor, seismic codes, reinforced concrete moment frames, ductility, overstrength. Use of overstrength and inelastic response in seismic design. These include structural redundancy, story drift limits, material overstrength, member oversize, non seismic load combinations, and so on.
Seismic codes rely on reserve strength and ductility, which improves the. The most common errors in seismic design and how to properly avoid them thomas f. When to and when not to use the overstrength factor. The results show that mrf, cbf, and semirigid steel frame would be subjected to a base shear up to 4. Special inspection criteria were moved from this ufc to ufc 330101. The quantification of both redundancy and overstrength during a seismic excitation is a decisive factor that together with ductility contributes to the assessment of structural seismic response and constitutes the basis of an efficient structural design. An apartment building of reinforced concrete construction was built in 1930. They addressed that structures designed with higher levels of ductility lower design force levels have higher overstrength factors than those for lower levels of ductility. A direct relationship between the force reduction factor used in design and the. Higher r factors represent more ductile systems and, therefore, yield a lower seismic design force. These systems are listed in table 1, along with the ductility and overstrength related seismic force modification factors, rd and ro, respectively, and system restrictions that are prescribed in the upcoming 2010 1 professor, dept. Instructional material complementing fema 451, design examples seismic load analysis 9 31 diaphragm flexibility untopped steel decking and untopped wood structural panels are considered flexible if the vertical seismic. Seismic design specification for buildings, structures, equipment, and systems. I have to take overstrength factor value from ubc97 code.
Pdf use of overstrength and inelastic response in seismic. The four site coefficients s1 to s4 of the ubc 1994, which are independent of the level of ground shaking, were expanded to six soil profile types, which are dependent on the seismic zone factors. Sitespecific seismic ground motion parameters were removed from this ufc and are now invoked by reference to ufc 330101. What are the basic concept to decide structural system. The way in which structural overstrength affects structural response and the factors influencing overstrength are. Jan 27, 2010 you will use your overstrength factors when you have some sort of irregularity or when called for in the materials seismic provisions. Overstrength and force reduction factors of multistorey. Buildings for use in dod building design and renovation.
An evaluation of overstrength factor of seismic designed low. I am doing a research on comparison of response reduction factor considering overstrength and ductility with response reduction factor considering ductility and load combination with overstrength factor in seismic design. Changes to the seismic hazard maps are presented, along with explanations as to why they were necessary and how they will affect seismic design. Code considerations related to woodframe shear walls and diaphragms are discussed, including failure modes of wood shear walls and the detailing required to provide ductile behavior. The way in which structural overstrength affects structural response and the factors influencing overstrength are discussed. Chapter 6 seismic design 61 seismic design responsibility and policy 61. Overstrength factors for seismic design of steel structures. Ductility and overstrength in seismic design of reinforced concrete structures article pdf available in canadian journal of civil engineering 216.
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