Use of overstrength factor in seismic design pdf

Apr 02, 2015 ive been searching the web for a sort of comprehensive list of what elements get designed for the overstrength factor. Seismic system factors and system overstrength free download as powerpoint presentation. An evaluation of overstrength factor of seismic designed. Deflections are multiplied by the deflection amplification factor, c d, to obtain the expected inelastic deflections. Relying on such overstrength, many seismic codes permit a reduction in design loads. Several factors contribute to this overstrength factor. Frequently misunderstood seismic provisions of asce 710 skgassociates. Ductility and overstrength in seismic design of reinforced concrete structures article pdf available in canadian journal of civil engineering 216. Assessment of redundancy factors for the seismic design of special moment resisting reinforced concrete frames 1 introduction. Aci 31811 seismic anchoring provisions are given in part d.

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. Significant changes from asce 705 to asce 710, part 1. Please also note the exception to 2018 ibc section 1810. Seismic load effects including overstrength factor 6. The ibcreferenced design standard covers dimension lumber, glulam, structural composite lumber and clt as well as fasteners, connections and fire design. Overstrength and ductility factors for steel frames. Accounting for overstrength in seismic design of steel. 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. Topics will also include limitations on the use of wood in seismic design. I am venturing more deeply into higher seismic zones and i could not get printed clarification on when a strucure, or member is exempt from having to use the overstrength factor. 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. Chapter 6 seismic design 61 seismic design responsibility and policy 61. Seismic codes rely on reserve strength and ductility, which improves the. 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.

Seismic design for petrochemical facilities as per nbcc 2005. Structure magazine the most common errors in seismic. 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. A direct relationship between the force reduction factor used in design and the. 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. Seismic overstrength of shear walls in parking structures 89 studied 6 and 12story framewall structures designed in accordance with canadian codes. The nz steel structure design standard nzs3404, uses both a material overstrength factor. As a first step in this direction, however, the factor. Structures assigned to seismic design category c, d, e, and f with type 1a and type 1b horizontal structural irregularity. Recently, a study was conducted to investigate the overstrength factor of. The national design specification nds for wood construction is also helpful when designing woodframe structures to withstand seismic events. For building column or industrial structure such as piperack column anchorage, the structural overstrength factor obtained from asce 710 table 12. Special inspection criteria were moved from this ufc to ufc 330101. Pdf use of overstrength and inelastic response in seismic design.

Seismic stability properties of wood building materials. Which of the following will be required to be increased by a factor of 1. Collector connections using the overstrength factor d. Redundancy and overstrength of structures are two distinct notions the synergy of which affects the overall behavior of frame structures. Seismic design of buildings analysisanddesignofearthquakeresistantbuildings robertotomasi 11. Chapter 12 seismic design requirements for building. Moment redistribution and connection analysis os to an applied overstrength of 1.

Structure magazine the most common errors in seismic design. Accounting for ductility and overstrength in seismic. Some concepts in earthquake behaviour of buildings c. 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. Buildings for use in dod building design and renovation. Seismic design specification for buildings, structures, equipment, and systems. R factor, the system overstrength factor, and deflection amplification factor cd, of new seismic forceresisting systems proposed for inclusion in model building codes. 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. Seismic design for petrochemical facilities as per nbcc 2005 dongxiao wu p. Use of overstrength and inelastic response in seismic design. The r factor is represented graphically in figure 2 along with the remaining two seismic design factors.

Aisc lrfd load and resistance factor design specification for structural steel buildings, american institute of steel construction, 1993. By using the n2 method, the seismic performance of the steel frames are investigated when they are subjected to the design earthquake for singapore. 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. Where can i find this seismic design overstrength factor. Mandatory retrofit program for wood frame buildings with. Application of overstrength factor how deep does it go. 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.

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. Seismic system factors and system overstrength strength of. As an alternative, the seismic analysis and design procedures of alternative simplified chapter 4 shall be permitted to be used in lieu of the. When to and when not to use the overstrength factor. Structures in new zealand a perspective on the seismic. Accounting for ductility and overstrength in seismic design of. You will use your overstrength factors when you have some sort of irregularity or when called for in the materials seismic provisions. The way in which structural overstrength affects structural response and the factors influencing overstrength are.

The manner in which structural overstrength can be accounted for in the design of reinforced concrete structures is presented. Evaluation of overstrength factor of steel moment resisting frames. Pdf seismic design of building structures mansour al. Design of collector elements, splices and connections when using the overstrength factor. 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. Pdf evaluation of overstrength factor of steel moment. The relationship between the lateral capacity, the design force reduction factor, the ductility level and the overstrength factor are investigated. Pdf use of overstrength and inelastic response in seismic. 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.

These include structural redundancy, story drift limits, material overstrength, member oversize, non seismic load combinations, and so on. Pdf ductility and overstrength in seismic design of reinforced. The way in which structural overstrength affects structural response and the factors influencing overstrength are discussed. Overstrength factor in anchor design for seismic loading vertical process vessel sandman21 structural 17 jul 18 18. Structure magazine changes in the aci 318 anchoring to. Quantification of building seismic performance factors. I was hoping i could get some input as to what items to pay atten. The ductility factor increases as the inherent overstrength factor increases. Frequently misunderstood seismic provisions of asce 710. Seismic design forces for foundations, other than pile bents and retaining walls, shall be determined by dividing elastic seismic forces, obtained from article 3. In these structures, reserve strength is almost independent of both the height of the structure and the effect of building sway. You would also need to use the overstrength factor when designing drag struts with non light framed shear wall systems. An apartment building of reinforced concrete construction was built in 1930.

An evaluation of overstrength factor of seismic designed low. Assessment of redundancy factors for the seismic design of. 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. 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. Canada abstract the seismic behaviour factor, r, is a critical parameter in contemporary seismic design. Overstrength factor in anchor design for seismic loading. Overstrength factors for the seismic design of aac structures. 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. I understand how to apply it, just not particularly to which items. Ductility and overstrength in seismic design of reinforced concrete. Pdf overstrength and force reduction factors of multistorey.

Overstrength and force reduction factors of multistorey. Seismic overstrength of shear walls in parking structures. The purpose of this methodology is to provide a rational basis for determining building seismic performance factors that, when properly. Keywords structural redundancy, redundancy factor, seismic codes, reinforced concrete moment frames, ductility, overstrength. Increases in the construction of multistorey buildings. 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. The most common errors in seismic design and how to properly avoid them thomas f. This presentation will summarize and scrutinize the use of seismic response modification coefficient, r, equal to 1, 1. Ive been searching the web for a sort of comprehensive list of what elements get designed for the overstrength factor. I have to take overstrength factor value from ubc97 code. Pdf ductility and overstrength in seismic design of. Higher r factors represent more ductile systems and, therefore, yield a lower seismic design force. Seismic design specification for buildings, structures.

The results show that mrf, cbf, and semirigid steel frame would be subjected to a base shear up to 4. Ductility and overstrength in seismic design of reinforced. 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. Overstrength factors for seismic design of steel structures. The appropriate response modification coefficient, r, system overstrength factor. This paper addresses the issue of horizontal overstrength in modern code. 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. Seismic design category sdc and height of the building on overstrength factors of steel moment resisting frames mrf are. Aci 31808 appendix d seismic design criteria can be summarized as follows. Sitespecific seismic ground motion parameters were removed from this ufc and are now invoked by reference to ufc 330101. 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. These studies have shown in their globality that the overstrength depends on different factors which the most important of them is member ductility factor. When in seismic design category a, you should not use any of the provisions of chapter 12. When using allowable stress design, factor of safety for soil bearing values shall not be less than the overstrength factor of the structures supported.

What are the basic concept to decide structural system. Accounting for ductility and overstrength in seismic design. Overstrength factor, qo, is prescribed to assure sufficient design strength to allow selected members to yield. 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 structural system used shall be in accordance with the seismic design category. Components in seismic design category a are exempt from seismic design requirements, as stated in section 11.

In the topic, the manner in which ground accelerations impart design loads into the structure are described from a code perspective. 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. This revision contains more provisions for the seismic design of structures in corporating precast concrete than its. Seismic design of wood structures in the context of. The above modification is applicable to schools and hospitals in california only.

A new revision of the new zealand concrete design standard, nzs 3101. Changes to the seismic hazard maps are presented, along with explanations as to why they were necessary and how they will affect seismic design. Observed and inherent overstrength factor and ductility factor frame i rec2 0. 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. Egyptian code seismic load design provisions for moment. Use asce 7 basic load combinations but substitute the following for the. 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. 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. Foundation and other elements used to provide overturning resistance at the base of cantilever column elements shall be designed to resist the seismic load effects, including overstrength of section 12. For these projects, the structural design must use the importance factors for risk category iv.