Seismic design of steel special concentrically braced. Seismic design manual illustrates how the provisions of the code are used. Accounting for ductility and overstrength in seismic design. This finding is similar with result obtained by elnashai and mwafy 1 for 8. Horizontal seismic load effect with overstrength factor, emh. These risk levels are considered in structural design to produce buildings with compatible seismic performance levels. Seismic design specification for buildings, structures. Chapter 4 nominal design value wind nominal unit shear capacity vw legacy ibc allowable stress design value x 2. Jan 27, 2010 the overstrength factor should be used when certain vertical or horizontal irregularities apply and is dependent on sdc.
Code application examples, provides stepbystep examples for using individual code provisions, such as computing base shear or building period. Building design examples, furnish examples of seismic design ofcommontypes of buildings. Canada abstract the seismic behaviour factor, r, is a critical parameter in contemporary seismic design. A lower bound is typically imposed in comparison to.
The r factor is represented graphically in figure 2 along with the remaining two seismic design factors. Use of the ed material apart from this ufc must have the permission of the holder. An evaluation of overstrength factor of seismic designed. Part 1 also covers the symbols and terminology found in ascesei 7 that are pertinent to steel seismic design. The ibcreferenced design standard covers dimension lumber, glulam, structural composite lumber and clt as well as fasteners, connections and fire design. Components in seismic design category a are exempt from seismic design requirements, as stated in section 11. Accounting for overstrength in seismic design of steel. The design force levels currently specified by most seismic codes are calculated by dividing the base shear for elastic response by the response modification factor r. The answer to the question depends on the expected system performance of the structure. Chapter 4 seismic design and retrofit page 42 wsdot bridge design manual m 2350. The effect of reinforcement strength on the overstrength. Seismic provisions for structural steel buildings aisc. When in seismic design category sdc a, it is not necessary to use. Asce 716 seismic provisions overview john hooper, p.
Seismic design of steel buckling restrained braced. 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. System overstrength factor g a apparent diaphragm shear stiffness. The overstrength factor increases the required seismic forces and is applied in specific cases or in the design of certain parts of the structure. Strength reduction factors for foundations and earthquake load combinations including overstrength 6. In general the system overstrength factor, qo, is prescribed to assure sufficient design strength to allow selected members to yield. It is required where it is explicitly stated in the code.
Instructional material complementing fema 451, design examples seismic load analysis 9 31 diaphragm flexibility. Seismic provisions for structural steel buildings included in the aisc seismic design manual. The national design specification nds for wood construction is also helpful when designing woodframe structures to withstand seismic events. Brbfs r 8 by ascesei 7, referred to in this guide as asce 7 asce 2010, as. Redundancy factor applied to load combinations for members which do not. Horizontal seismic load effect, including the overstrength factor. The design seismic action for structures of ordinary importance over rock is termed reference seismic action.
Seismic design forces are determined on the basis of earthquake risk levels associated with different regions. Seismic design of reinforced concrete special moment frames. Column design including overstrength plastic moment capacity 500 and. When to and when not to use the overstrength factor. The gravity load framing system consists of woodframe bearing walls for the upper stories and concrete bearing walls for the lower story. Bridge approach embankments and fills through which cutandcover tunnels are constructed should be designed to remain stable during the design seismic event because. Asce 7 says, where specifically required so you simply have to keep your eyes open for references to section 12. Task committee 9 seismic provisions, aisc seismic design manual. Pdf use of overstrength and inelastic response in seismic design. Scribd is the worlds largest social reading and publishing site. The effect of seismic load, e, shall be defined by eq. Moment redistribution and connection analysis os to an applied overstrength of 1.
A wall designed to resist lateral forces parallel to the plane of the wall. Building structures generally comprise a threedimensional framework of structural elements configured to support gravity and. Moc15, 2015, an overstrength reduction factor r is used to compute the inelastic design spectra. A floor, roof, or wall component sheathed to act as a shear wall or diaphragm. Seismic design specification for buildings, structures, equipment, and systems. Pdf ductility and overstrength in seismic design of. An evaluation of overstrength factor of seismic designed low. Where can i find this seismic design overstrength factor. Current diaphragm seismic design force level current seismic design forces for diaphragms in asce 710, to be retained in asce 716, are a function of the design forces acting on the vertical elements and are, therefore, reduced by the r factor that applies to the vertical elements. A guide for practicing engineers applied technology council. 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. The following features of seismic design of steel buildings are illustrated. A summary of the seismic design parameters follows.
The overstrength factor increases when the ductility of the frame increases. Seismic design, earthquake engineering, strength reduction factor, capacity design abstract. Relying on such overstrength, many seismic codes permit a reduction in design loads. Supplement special design provisions for wind and seismic 0602 20m. 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 loads. Allowable stress design load and resistance factor design seismic 2001 cover.
The appropriate response modification coefficient, r, system overstrength factor. Seismic system factors and system overstrength strength of. Mandatory retrofit program for wood frame buildings with. Seismic design of wood structures in the context of. Building structures generally comprise a threedimensional framework of structural elements configured to support gravity and lateral loads. A brief guide to seismic design factors structure magazine. The design code en 19981 3 has introduced three levels of structural ductility class connections with design concepts and range of reference values. Seismic system factors and system overstrength free download as powerpoint presentation. The decrease in strength of the structure results in an decrease in overstrength.
Other input factors and coefficientsthe overstrength factor, r, and the force factor, are direction dependent. Overstrength factors for seismic design of steel structures. Seismic design of steel special concentrically braced frame systems. For building column or industrial structure such as piperack column anchorage, the structural overstrength factor obtained from asce 710 table 12. The nz steel structure design standard nzs3404, uses both a material overstrength factor. Seismic design of castinplace concrete diaphragms, chords, and collectors. The structural system used shall be in accordance with the seismic design category. Seismic stability properties of wood building materials. It has to do with the fact that materials concrete and steel specifically have more capacity than specified. Limited service bridge is open for emergency vehicle traffic. Sdis diaphragm design manual is used for guidance in assessing the stiffness. Current diaphragm seismic design force level current seismic design forces for diaphragms in asce 710, to be retained in asce 716, are a function of the design forces acting on the vertical elements and are, therefore, reduced by the rfactor that applies to the vertical elements. This finding is similar with result obtained by elnashai and mwafy 1 for 8storey irregular frame with transfer beam.
Analysis domain deflection amplification factor c d. A reduced number of lanes for normal traffic is available within three months of the earthquake. Proposed approach for refining the design using overstrength. A 10% in 10 years serviceability action for damage limitation mean return period. Seismic system factors and system overstrength strength. Summary and combination of orthogonal column forces used for design 7. With the simplified procedure of asce 7, section 12. To control drift or to check deformation capacity in some. Paultre, ductility and overstrength in seismic design. Seismic design of steel special concentrically braced frame. Chapter 6 seismic design page 62 geotechnical design manual m 4603.
The inherent overstrength factor of regular gravity load designed and seismic designed building frames are 75% and 125%, respectively, higher than irregular frames with setback. Seismic risk levels have been traditionally characterized as low, moderate and high. Structures assigned to seismic design category c, d, e, and f with type 1a and type 1b horizontal structural irregularity. Pdf evaluation of overstrength factor of steel moment.
In design procedures established in current mexican seismic codes ntcs04, 2004. Answer reprinted from april 2002 steel interchange. The importance factor is based upon the risk category and the. A structural system composed of interconnected members, other than bearing. Strength reduction factors for foundations and earthquake. System for inelastic analysis of structures user manual.
You will use your overstrength factors when you have some sort of irregularity or when called for in the materials seismic provisions. Accounting for ductility and overstrength in seismic. The structures with vertical geometric irregularity have lower demands than regular structures. The seismic load effects including overstrength factor in accordance with sections 2. You would also need to use the overstrength factor when designing drag struts with non light framed shear wall systems. The seismic coefficients ca and cv can either be determined per the code or they can be userdefined. 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. Mandatory retrofit program for wood frame buildings with soft. A guide for practicing engineers concentrically braced frames cbfs are a class of structures resisting lateral loads through a vertical concentric truss system, the axes of the members aligning concentrically at the joints. In the topic, the manner in which ground accelerations impart design loads into the structure are described from a code perspective.
The most common errors in seismic design structure magazine. 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. When a building code requires design of a connection in accor. Applying these low factors of safety has been normal practice. Kevin mcmanus in his report for the canterbury earthquake royal commission foundation design reliability issues, october 2011 has highlighted that this practice may not be appropriate.
Design of collector elements, splices and connections when using the overstrength factor. 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. Seismic design forces for multiple column bent including rfactor, p. Seismic performance factors such as the seismic modification coefficient, r, deflection amplification factor, c d, overstrength factor. Seismic design forces for foundations, other than pile bents and retaining walls, shall be determined by dividing elastic seismic forces, obtained from article 3. The overstrength factor takes this into account, as. This design example illustrates the seismic and wind design of a hotel that includes five stories of woodframe construction over a onestory concrete podium slab and is assigned to seismic design category d. Special reinforced masonry shear wall response modification factor, r.
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