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HomeMy WebLinkAboutX2012-1998 - Alternative Material & Methods (4)CITY OF NEWPORT BEACH o COMMUNITY DEVELOPMENT DEPARTMENT '' „ '•`'_fn - BUILDING DIVISION 3300 Newport Boulevard I P.O. Box 17681 Newport Beach, CA 92658 t�ttruRT�r www.neLA beachca.oav l (949) 644-3275 CASE NO.: Zot 7 .i 1 PAID LIAR 12 2013 CITY OF NEWPORT REACH ® REQUEST FOR MODIFICATION TO PROVISIONS FOR STAFF: USE ONLY . OF TITLE 15 OF THE NEWPORT BEACH MUNICIPAL CODE Plan Check# i B `20IZ #of Stories (See Reverse for Basis for Approval) (Fee $257) ❑ REQUEST FOR ALTERNATE MATERIAL Occupancy Classification , S Use of Buiidin Y i w V: # of Units OR METHOD OF CONSTRUCTION (See Reverse for Basis for Approval) (Fee $257) ❑ REQUEST FOR EXEMPTION FROM DISABLED Project Status : r *-� Nu CoR S Inc Rb✓e Construction Type .T 3 Verified by t=i No. of Items I ACCESS DUE TO PHYSICAL OR LEGAL CONSTRAINT (Fee $6,494) Fee due 42 917 (Ratification by the Board of Appeals will be required.) For above requests, complete Sections t, 2 & 3 below by printing in ink or typing. DISTRIBUTION: ❑ Owner Ian Check Petitioner 2&lnspector Fire 0 Other 1 JOB ADDRESS: PETITIONER ADDRESS: SITE ADDRESS 545 SAN NICOLAS DRIVE Petitioner NABIH YOUSSEF & ASSOCIATES Owner THE IRVINE COMPANY (Petidonerto be architectorengin"d Address 550 NEWPORT CENTER DRIVE Address 800 WILSHIRE BLVD #200 IRVINE, CA Zip 92660 LOSANGELES, CA Zip 90017 Daytime Phone ( 949.-)- 720-2000 Daytime Phone ( 213 ) 362-0707 E. REQUEST: Submit plans if necessary to illustrate request. Additional sheets or data may be attached. Design of shear transfer across horizontal shear p lane see attached 5/SGW6-0 at perimeter of structure per ASCE41-06 and 1997UBC Section 1923 in lieu of prescriptive requirements per AC1318-08 section11.6.4 (adopted code). Flease see attached or calculations per 41- 0 6 and 1997UBC and excerpts from 41-06 an _3jJUSTIFICATIONIFINDINGS OF EQUIVALENCY: CODE SECTIONS: ACI318-08 see 11.6.4 - (1) Proposed detail is standard for parking structure construction industry. ASCE 41-06 sec 6.3.5 (eq 6-2) (2) Proposed structural design is within standard of care of the structural en ineerin desi n communi 3) Demand / - capacity is very low (-0.10) across shear plane. (4) Design per ASCE41-06 for rehabilitation of existing buildings is based on same level of risk or occupants as anDesign per section 1923 Is deemed appropriate for low demand I capacity ratios. is a reference standard In . Petitioner's Position Principal Signature - CA Professional Lie. # 52026 Date 03/17/2013 FOR STAFF USE -ONLY DEPARTMENT ACTION: In accordance with: ❑CBC Appendix 104.11 ,,`,'(BC Appendix 104.10 018C (Alternate materials & methods) Modification) ❑ Concurrence from the Fire Marshal is required. f] Approved ❑ Disapproved 0 Written Comments Attached By: Date ElRequest (DOES) (DOES NOT) lessen any fire protection requirements. ❑ Request (DOES) (DOES NOT) lessen the structural integrity The Request is ranted ElDenied (See reverse for Granted (Ratification required) appeal information) Conditions of Approval: Signatu IL�Positionr—H/Er Qft,ft-17iN6—Date Print Name <Z V©j7F=(C i &d' L APPEAL OF DIVISION ACTION TO THE BUILDING BOARD OF APPEALS (See Reverse) (Signature, statement of owner or applicant, statement of reasons for appeal and filing fees are required.) CASHIER RECEIPT NUMBER: M<-, oloL-2�2 CL1 <� ' 1 Formslregmodif 01119/12 *RQAC E 11 11 59S s au vrc� s — toc s Tf YYJc'� ii0� ��sSUr-9//Y�� 7 'dT Ca�'r✓ r?.C.=%2.J°-YMf�,�ai� a� m Ilk 91nra� 1 54,ell Ar (,4,/ )f �Ze } 5F'AuAJC, of S?iRLKf" » c Z Project: W. Q. No.: ©ate: Caic. By: Checked By: Sheet at Nabih Youssef & Associates Structural Engineers 118" �, 6 Sam 0 1. P(Sr.%'5..1 icw RpChT e� Nokj chic Ara 4 A131-20/ Z2 ®' V I/15 (TYPE A ORC) C or _ _ {2.,5 (,5 oc 1 j(ise't- gg;l 606c) R 14 sa BUYS P ii'ac. M, 7ETMMTr: suss wl sm sa Poac r ays a ssas. SCKM ri / X �u cu: 5�aa 4G kp qE 2 4 's° Lkp. YYP �lraP/ST COW ®:sortwMCOW. 17 Cry TYPICAL MOMENT FRAME BEAM SECi1C>=N sm—rws 4Y 1� 4 �d �44 k �5 t4oIA-�ko _fa� ) � SHE d Q" t C►i sc�.0 1 ASCE STANDARD ASCE/SEB41-06 p�ERiY 0� louc i.t�FtRR American Society of Civil Engineers Seismic Rehabilitation of Existing Buildings This document uses both the International System of Units (SI) and customary units. SEIL ASCESYludurel En9�neetlnpI Style Published by the Aineriean Soelet',y of Civil Engineers M, ,. = expected bending moment strength about x-axis, kip -in.; Mcs,, = expected bending moment strength about y-axis, kip -in.; in, = in -factor for column for bending about x-axis in accordance with Table 6-12; and m, = in -factor for column for bending about y-axis in accordance with Table 6-12, Alternative approaches based on principles of mechanics shall be permitted. C6.3.3 Flexure and Axial Loads Laboratory tests indicate that flexural deformabil- ity may be reduced as coexisting shear forces increase. As flexural ductility demands increase, shear capacity decreases, which may result in a shear failure before theoretical flexural deformation capacities are reached. Caution should be exercised where flexural deforma- tion capacities are determined by calculation. FEMA 306 (FEMA 1998) is a resource for guidance regard- ing the interaction between shear and flexure. 6.3.3.1 Usable Strain Limits Without confining transverse reinforcement, the maximum usable strain at the extreme concrete com- pression fiber shall not exceed 0.002 for components in nearly pure compression and 0.005 for other com- ponents unless larger strains are substantiated by experimental evidence and approved by the authority having jurisdiction. Maximum usable compressive strains for confined concrete shall be based on expen mental evidence and shall consider limitations posed by fracture of transverse reinforcement, buckling of longitudinal reinforcement, and degradation of compo- nent resistance at large deformation levels. Maximum compressive strains in longitudinal reinforcement shall not exceed 0.02, and maximum tensile strains in longi- tudinal reinforcement shall not exceed 0.05. 6.3.4 Shear and Torsion Strengths in shear and torsion shall be calculated according to ACI 318 (ACI 2002) except as modified in this standard. Within yielding regions of components with mod- erate or high ductility demands, shear and torsional strength shall be calculated according to procedures for ductile components, such as the provisions in Chapter 21 of ACI 3IS. Within yielding regions of components with low ductility demands and outside yielding regions for all ductility demands, calculation of design shear strength using procedures for effective ASCE/SEI 41-06 elastic response such as the provisions in Chapter 11 of ACI 318 shall be permitted. Where the longitudinal spacing of transverse rein- forcement exceeds half the component effective depth measured in the direction of shear, transverse rein- forcement shall be assumed not more than 50% effec- tive in resisting shear or torsion. Where the longitudi- nal spacing of transverse reinforcement exceeds the component effective depth measured in the direction of shear, transverse reinforcement shall be assumed ineffective in resisting shear or torsion. For beams and columns in which perimeter hoops are either lap - spliced or have hooks that are not adequately anchored in the concrete core, transverse reinforcement shall be assumed not more than 50% effective in regions of moderate ductility demand and shall be assumed inef- fective in regions of high ductility demand. Shear friction strength shall be calculated accord- ing to ACI 318, taking into consideration the expected axial load due to gravity and earthquake effects. Where rehabilitation involves the addition of concrete requiring overhead work with dry -pack, the shear fric- tion coefficient, p, shall be taken as equal to 70% of the value specified by ACI 319. 6.3.5 Development and Splices of Reinforcement Development of straight bars, hooked bars, and lap -spliced bars shall be calculated according to the provisions of ACI 318 (ACI 2002), with the following modifications: 1. Deformed straight bars, hooked bars, and lap - spliced bars shall meet the development require- ments of Chapter 12 of ACI 318 except require- ments for lap splices shall be the same as those for straight development of bars in tension without consroerauon of bars, and lap -spliced bars do not meet the develop- ment requirements of (1) above, the capacity of existing reinforcement shall be calculated using Eq. 6-2: f = 1 l°f (Eq. 6-2) where f,. = maximum stress that can be developed in the bar for the straight development, hook, or lap splice length 1, provided; f = yield strength of reinforcement; and 1, — ten- th required by Chap- ter 12 of ACI 318 for straight development, hook development, or lap splice length, except required 157 SEISMIC REHABILITATION OF EXISTING BUILDINGS splice lengths may be taken as straight bar develop- ment lengths in tension. Where transverse rein- forcement is distributed along the development length with spacing not exceeding one-third of the effective depth of the component, it shall be per- mitted to assume the reinforcement retains the cal- culated maximum stress to high ductility demands. For larger spacings of transverse reinforcement, the developed stress shall be assumed to degrade from f at a ductility demand or DCR equal to 1.0 to 0.2f at a ductility demand or DCR equal to 2.0; 3. Strength of deformed straight, discontinuous bars embedded in concrete sections or beam —column joints, with clear cover over the embedded bar not less than 3db, shall be calculated according to Eq. 6-3: 4. 5. 158 2500 b where f = maximum stress (in psi) that can be devel- oped in an embedded bar having embedment length 1, (in in.); db = diameter of embedded bar (in in.); and fy = bar yield stress (in psi). Where f is less than f, and the calculated stress in the bar due to design loads equals or exceeds f„ the maximum developed stress shall be assumed to degrade from f to 0.2f at a ductility demand or DCR equal to 2.0. In beams with short bottom bar embedments into beam —column joints, flexural strength shall be calculated considering the stress limitation of Eq. 6-3; For plain straight bars, hooked bars, and lap -spliced bars, development and splice lengths shall be taken as twice the values determined in accordance with ACI 318 unless other lengths are justified by approved tests or calculations considering only the chemical bond between the bar and the concrete; Doweled bars added in seismic rehabilitation shall be assumed to develop yield stress where all the following conditions are satisfied: 5.1, Drilled holes for dowel bars are cleaned with a stiff brush that extends the length of the hole; and 5.2. Embedment length 1, is not less than 10db; and 5.3. Minimum spacing of dowel bars is not less .ban 41, and minimum edge distance is not less than 21e. Design values for dowel bars not satisfying these conditions shall be verified by test data. Field samples shall be obtained to ensure design strengths are developed in accordance with Section 6.3. C6.3.5 Development and Splices of Reinforcement Development requirements in accordance with Chapter 12 of ACI 318 (ACI 2002) will be applicable to development of bars in all components. Chapter 21 of ACI 318 provides development requirements that are only intended for use in yielding components of reinforced concrete moment frames that comply with die cover and confinement provisions of Chapter 21. Chapter 12 permits reductions in lengths if mini- mum cover and confinement exist in an existing component. Experimental tests by Melek and Wallace (2004) and Lynn (2001) have demonstrated that lap splices can achieve a higher flexural capacity than that calcu- lated using the effective steel stress given in Eq. 6-2. The possibility of a shear failure in lap -spliced columns may go undetected if die flexural capacity is underestimated. Cho and Pincheira (2006) suggest an alternative model for the effective steel stress in tap - splice bars which provides a better estimate of the mean flexural strength observed in experimental tests. For buildings constructed prior to 1950, the bond strength developed between reinforcing steel and con- crete may be less than present-day strength. Current equations for development and splices of reinforcement account for mechanical bond due to deformations pres- ent in deformed bars in addition to chemical bond. The length required to develop plain bars will be much greater than that required for deformed bars, and will be more sensitive to cracking in the concrete. Procedures for testing and assessment of tensile lap splices and development length of plain reinforcing steel may be found in Evaluation of Reinforcing Steel Systems in Old Reinforced Concrete Structures (CRSI 1981). 6.3.5.1 Square Reinforcing Bars Square reinforcing bars in a building shall be clas- sified as either twisted or straight. The developed strength of twisted square bars shall be as specified for deformed bars in Section 6.3.5, using an effective diameter calculated based on the gross area of the square bar. Straight square bars shall be considered as plain bars, and the developed strength stall be as specified for plain bars in Section 6.3.5. 6.3.6 Connections to Existing Concrete Connections used to connect two or more compo- nents shall be classified according to their anchoring systems as cast -in -place or as post -installed. 3491.4.3 Bepiacenrent, r eteneaon aabl extension of or igIn, iaata:zuls. [1101)!, i.,acal ordaiartces nr regulatioxs shall permit the repiacemeni, retention card e_xtensiou oj'origfrtal ntcneriaLs, and tare use of original methods of construction, Jim anro buildag or- accessor). Oracnnre, provided such bt i%ling oc stn�ctnre corrtplied is Ith the building code provi- sions br effect at the tine Of original construction and the building or accessory structure does not become at- cora- finite to be a substandard L-uilding. For additional naforrna- tion, see Health and Safety Code Sections 17912, 17920.3, 17922(d), 17922.3, 17958.8 and 17958.9. 34t)I 5 Atloptioir gf ASC'I' 4I.-[0,511PD 2 & 31All additioru, alterations, zepairs arzd seismic retrofit to the existing strac- i rarer or portions thereof may be designed ill accordance t'ith the l;rarisions of ASC'E 41, as modified her ein- 34 1.5.1 ?>roeferen-ceet Standards. All reference standards listed inASCE41 shall be replaced bi,referenced standards bred in CTtaptei35 of this code and shall include all amendnzerns to the reference .standaady in this code. 3 401.5.2 ASCE 41 Section 1.4—Rehabilitation Objectives. i 72nget building perfonncnace level shall be Life Safety (LS) Building PeTorrnance Level (3-C) as dejineel in Section 1.5.3 2 atBaric Safaiy Earthquake I (BSE-1) Seismic Haz- ard Level as defined in section 1.6.1.2 i'br Occupancy Cate- , orn II Stria fares and Basic Safety Objective (BSO) Level as defined in Section 1.4.1 for Oceupan<v Categonr III Strtr(anre's- ! t)ccupauri Categnry IV stator res shall satisfy lnzrrrecti- r ate Oceunancl('IO)R.ufldtngPerformanceLevelof(I-B)as [ deftned in Section 1-5,3.2 at Basic Safety Earthquake 1 I (BS I) SersrnicHasatd Level as defined iii Section 1-6.1.2 and Collapse Pneretatvn (£'P) banking perfornsance level (5E) per Section 1.5 i4 at Bash Safety Earthquake 2 (i13! _2) Seisrau-duzard Lcnrel as 'fined m Sectiau 1.6.1-1. 340153ASCE41 Section 1.6- Seismic Hazard. Response Tec7-a and acceleration time histories shall be constructed bt accordance with sections 1613 and 1803.7. 3401.5.4Analysis procedure. The selection of particular arudvsis procedure from ASCF 41 neat' be sliNect to the approval of the enforcement agent. I ; 3401.5.5 Stractutfif davzgr criteria. Prior to implernertta- tlovt c:f ASCF; 411 rtartliiaear dvnamic procedures—rhe ulael motet rc, naly. c; and design methods, material a.>su„tfrtians arzd accepisrice srtteriaProposed bar the engi- ,:eer shall be rc vie:c•ed by the enjorEeinent agent. . 4 tI.5.6 Saw iarai wiser vateon, te,tYag and inspections, F.>rasfnrc:tiar. tcstcrzh, inaysectiaa crud striwairal obsr-7 az.- tre m<luitern tree shalti,easretlulre 1€r nernc'on cut€rticn. 'Isr �rddtzg<,rrrt;5.,a0cCUPU!ciOe,,F4arfljtbrsmoke aiarcj rcqubell .¢g 7a ctisPing bvcCd ngs see cr 7isr-c 90Z2-11.5. 34 L7 Delngerous easidigi an. jBS j Rcgardle,,�s of the extent n arwcaaal at n mvr,-atf t,rrar damage, the building ('ode elf cisl hatlhavetileatal,onivfo,iequirefieelimirmtionoff'ondl- iions deemed dangercirs. 592 SECTION 3402 DEFINITIONS 34011 Deflnition.s. The following words and terms shall, for The purposes of this chapter and as used elsewhere in the code, have the meanings shown herein. DANGEROUS. Ally building or st tour, or pe tion thereof that meets any of the conditions described below shall be deemed dangerous: 1. he building or structure has collapsed, partially col- lapsed, moved off hs foundation or lacks the support of ground necessary to support it. 2. Tihereexistsasi.mflcantaiskofcollapse,deachmentordis- Iod-Punt of any portion, member, appurtenance or orna- mentation of the building or structure under sei vice loads. EXISTING STRUCTURE. A structure erected prior to the date of adoption of the appropriate code, or one for which a legal building permit has been issued. 'PRIMARY FUNCTION. Aprimaryfunctiou is a major activ- ity for which the facility is intended. Areas that contain a pr i- 'Vern fimction include, but are not linuted to, the customer service lobby of a bank, the dining area ofa cafeteria, the meet- ing rooms in a conference center, as well as offices and other work areas in which the activities of the public accommodation or otherprivate entity using the facility are carried out.Mechani- cal rooms, boiler Moms, supply storage rooms, employee lounges or locker rooms, janitorial closets, entrances, corridors and restrooms are not areas containing a primary. function. SUBSTANTIAL IAL, 3 T RUC'sFURAL DAMAGE. A condition where: 1. In any story, the vertical elements of the lateral force -resisting systern have suffered damage such that the lateral load -carrying capacity of the structure in any horizontal direction has been reduced by more than 20 percent from its pre-dania_ae condition; or 2. The capacity of ally vertical gravity load -carrying tour ponent, or any group of such components, that supports more than 30 percent of the total area of the structure's f loor(s) and roofs} has been reduced n}ore than 20 per - Cent ion he pre fltlmaEc' condition and the rernaining. capacity of such nfieeted elements, with respect to ail dead and live loads, is less that, 75 percent of that cet to col by this code for new buildings of sinnkar str uc- ture, propose and location. TECHNICALLY INFEASIBLE. E. Ali alto rcriox ofa buildurg or a h _nhu that has little Nkciihcod of rcin,p a coniplished because the existi~g strucalm' conthlions require the retroval or alto; motion of a load -bearing member that is an essential part Of the struetuml frame, or because other existing physical or site constraints prohibit modi leaden or addition of elements. spaces r l-ale" -s which are in Full and strr c omphance with then nimutu requirennents fornew construction and which are necessary to provide accessibility. 2010 CALIFORNIA BUILDING CODE �EWPORT CITY OF NEWP®RI" BEACH 'n ADMINISTRATIVE SERVICES 3300 NEWPORT BLVD.. cy�r P.O. BOX 1768, NEWPORT BEACH, CA 92658-8915 RECEIVED BY: SMCCOURT TODAY'S DATE: 03/12/13 29005002 PLAN CHECK FEES RECEIPT NUMBER: 05000002657 PAYOR: LPA INC REGISTER DATE: 03/12/13 TIME: 11:26 MODIFICATION 1481-2012 $257.00 ------------------- TOTAL DUE: $257.00 CHECK $257.00$257.00 $.00 ; REF NUM: 6244 ASCE.41-06 Seismic Rehabilitation of Existing Buildings A New Tool fo; Achieving Seismic Safety By Cbris D. Poland, S.E, F SE40C Earthquakes wreak havoc on our lives, our businesses and our communities. For the last 140 plus Years, scientists and engineers have been working to understand where they can occur and how to best mitigate their efFects. Whir starred as a concern centered along the - West Coast has become known as areal threat that affects the vast majority of states in the United States. Thanks to the work of the United States Geological': Survey, we now have a science-based4o`. understanding of earthquake hazards .;. .PQ nationwide, which has become the source for national earthquake hazard maps. For over 50 years, engineers have focused on protecting lives and the virility of OW q The mid communities by writing buildvtncode� and seismic provisions. Engikgrs ar . all exirti: ous" wZll be ha r personal Un " runlet; chist"p" '` ess achieved fulltence leaves stu Mast 20 v�ars a s4ew�has left us not a probie wrath a�i inventory 0 - mldina nation if din re aamage or we e f(finter of toe aYY4 [voram rsquaze anrtstrates rwt not ompliant building£trre dangerous. One bug " a pa " lly collapsed while others rema;nedurabk. ConrteryrgfLt��u nisp nsible when i oe ow ehis same situation exists in your ability, fears ofip us region, but it remains a tough sell. From Lip, even A( it - si- Memphis to the eastern seaboard, the A ressiop",xrhat there is skepticism runs high among owners and their design professionals and only El this from a practice limited recognition is evident. vvrde w 'Cie more [hair"*80 percent are along the ?ysc'Coast, you recognize Fortunately, the American Society of unable Meet the recognized s'r. sttuanpn and the need. From the Civil Engineers' Standard Number 41, stands ds where they are I to Th.Wasatch Front in Utah, many of you Seismic Rehabilitation ofExzsting Build - seismic rehabilitation of theist- Target Building Performance Levels and Ranges rugs (ASCE 41) provides useful ing building stock is a key- element tools to assist design profession - in the process of achieving seismic Expected Post -Earthquake als in tackling all three of these safety and turning our cities into Damage State higher performance barriers; risk perception, cost of resilient communities. Operetiocxat {t-Aj Tess loss rehabilitation, and professional Unsurprisingly, when owners un- Backup utility services maintain Liability. It provides the next gen- dertand and accept the risk of an functions;very little damage. eration of tools needed to achieve earthquake, they want it brought (S-1 & N-A) seismic safery nationwide. ASCE under control and mitigated to an 41 is the culmination of over 25 appropriate level. Often it takes cupancy O-B) immediate remains welt The building remains safe to years of work that began with a a personal, life -changing earthquake occupy; any repairs are minor. FEMA_ sponsored dream for a li- experience to bring home the reality (S-1 & N-B) baaey of guidelines and standards of an eardhquake's consequences. related to the seismic evaluation For those owners who lack such 'fie Safety (a-CL and rehabilitation of buildings. personal experiences, the conse- quences of earthquakes most he described in intuitive terms in order to appreciate the importance of seismic mitigation. Another barrier to mitigation is cost; man", interest- edownecs hat done nodilng because they think that the investment required to bring older buildings "up to code" is ridiculously high. Finally, we structural engineers are too often reluctant to speak up and declare what is going to happen because we sense that somehow Having successfully completed the balloting process, ASCE 41 is now approved by the American National Standards Institute (ANSI) as a standard that can be refer- enced without amendment by local codes. As a standard, it pro- vides the liability shield that we all need to practice with confidence. lower performance No one aspects perfection; they just more loss expect us to practice at the `stare of ASCE 41 defines rang forperformana lewL--lar structural and the p ictinn" level, and ASCE 41 non str mural elmwm tbatserve "the basis ofa rehabilitation clearly defines what that mearts. objective. This ehan ilitso Les the range from minimum safml to high perfnrrnance. Courtesy afASCE 41, 2005. Structure remains stable and has significant reserve capacity; hazardous nonstructural damage is controlled. (5-3 & N-C) Collapse Prevention (5-E) The building remains standing, but only barely; any other damage or loss is acceptable. (S-5 & N-E) STRUCTUkc ma azine . September 2008 Predicting Performance Buildings respond to earthquakes in a wide 4ariety of ways, but always within the same patterns. As the ground shaking begins, the building moves and develops distortions in proportion to its mass, stiffness, and the frequency of the ground motion. The accelerations that are experienced join with the mass that is present and generate farces that the building needs to resist. If the &aces are within the strength of the building, little distortion develops and only minor damage occurs If the forces that are developed exceed the capacity of the building, then the building starts to break up, the distortions increase, and damage becomes more severe. As the building breaks up, it destroys its lateral strength and the building experiences extensive distortions and, in some cases, par" or complete collapse, The design guidelines for new buildings are set to prevent the breaking up process from starting in moderate earthquakes, and prevent the building from distorting to point of pulling apart in VLq - The rode uses the base evethe mviimum stn reqequires specific cl constrain the brzak ng up p s anddesired required details p 'de the "du fin - d to contras the of darmti, e net+ - has ac ® ed its purpose balance trength and • iptive requirements, Er uiidings may not have the required balance of strength and ductility that new buildings possess. Attempts to apply the prescriptive requirements of the new code will lead engineers to the conclusion that most old buildings need new lateral force resisting systems. That is, unfortunately, the key, driver of the high rehabilitation costs that often resulr. However, earthquake damage pattems illustrate that new lateral systems are not always necessary, and ASCE 41 provides the tools to distinguish when strengthening is actually needed and to what extent. It provides the ability to judge the adequacy of the ductility that is available given the strength that is present. As such, ASCE 41 is a toolbox of procedures that can be applied as appropriate for the derailed evaluation and rehabilitation of existing buildings in order to minimize the cost of sErengthen4 It provides a systematic process that defines target performance levels, considers earthquakes of various sizes, and provides four distinct analysis techniques and a wide variety of modeling tech tuques to guide the evaluating e g nzer into an appropriate conclusion about a building's rehabilitation needs. ASCE 4I makes recommendations for basic safety, enhanced, and limited performance levels, and detailed options can be applied as needed to match the project needs. performance levels are: defined that range from "collapse prevention to `operational" in ASCE 41 that, when combined w-ihazard levels, yield the rehabilitatioobi e. The ASCE 41 process uzs wn h requirements for gather",; tod for carrying out cation. for mationar, ,along values fo e when not availabl erail€d WdtAally, gb ' also includedturc, ill on mzthads are Simplifi and Systematic. The Method is aimed at small, regular, d ��nieerm�nmmuirin®�, ai sr dings and follows a process of 'tlexain Pare bless Ccltfomid tdxtt - correcting the deficiencies identified using N&k e2U aSimmnI trh ASCE 31 e in order to achieve a agedr urinhemuttnmgtba life o level. The Systematic avmod inOl hemodemaekrelol`s b dro ' astep-by-step process that uses up tocttrrred'•eofanal}m-s the to err levels of analysis to accurately predict Po an t 2 ormance of a rehabilitation plan and in the A Q- r Al P Ce5 process m n m ze the cost of rehabilitar on. The process of developing and validating Regardlessofw er S isbeingused a rehabilitation plan using the Systematic kBi��,gq, 'o tool ' njunetion with the Method addresses the deficiencies found n So ety,,ff ,t Engineers' Standard by ASCE 31 by showing they have been Seismic Evaluation of Existing corrected or that they are acceptabte. (ASCE 31) or for a rehabilitation In the process of defining the requirements project, it begins with the seismic hazard and for rehabilitation, Chapter I of ASCE 41 the desired performance levels. Unlike the explains the background and importance prescriptive requirements for new buildings, of each step of the evaluation process, and the LDP, is suitable to demonstwe the syst nu adeq=y since there is only a ringle lateral bard path at the first level Con-rtery of Chris Poland, 2DO3. STRUCTURE magazine 0 September 2008 provides the most definitive statcxnenr on performance based seismic evaluation and design currently available. Within the section on Performance Levels, there are a series of tables that describe the expected damage for each of the four level. This information is particularly useful in describing the expected perfsrrnance of buildings to owners. The four levels of analysis provided by ASCE 41, which are explained below, give 1 progressively detailed information about t the need for, and extent of, strengthening. The first two levels match the model code style of fora -based design, and cannot be used on buildings with long periods or significant irregularities. The second two an based on displacement and serve to directly determine the post yield capability of the buildings. In addition to a set of general analysis requirements, each analysis method is defined in terms of specific modeling requirements and procedures. A common acceptance criterion is provided for linear methods (force based) and e non- linear methods (displacem bat . The or criteria are ex , o: rwe, and b the e four analysis ehods for j in eed for strengrhem or the si to ty a tion plan with d e i ei that the s ceduriqu ould be used show adeq - . Build'ngs deserve a break owners sh d not be required to streatvthe percet eficiencies that are not truly a problem. Buildings should not be considered in need of strengthening until all four techniques are considered, and possibly used, � C& University Library located near Palo Alm, Califm4z hat w•as rehabilitated unng the third keel efanatysis the NSP. By relying an the new eantikveremerete walls boated each comer to armst the deflection ofthe building; the exciting conerrte forme was held to within it- Groin fors" performance Courmy ofCh�ris Pokme4 2003. to minia9p,e extent of edcd and the cost of wriectinoldic deficien rst level alysis is the Lin static are (IS that provides an eq ent force, v distribution o cc$ les for elimg, and accep ce A first ce, it looks like the lateral fo ure from the 1970s and s, except th e much higher and th du ' factors, are clx s t ed to be s bn aiaad ev servative to allow one an two ory buildings of regular s because of their ai e str -h. nfortunately many rst uses of ASCE 41 gravitate to cis section and base their work on it alone because it looks familiar. They never take the time to explore the other processes. Few - existing buildings, except wood frame or light metal construction, can pass this conservative rest. The LSP should only be used to show 1960s Concrete Weather $when in Taiwan eucrw ally rescred over 125 percenrground shaking without maipse because ofibe multiple Lateral land resisting,/s.emt that includes ionerere framer and masonry waltz Only the fourrh level ofanalysis, NDP can come close to predicting web performanee. Courim of Chris Poiuud 1999. that a budding is okay, not to determine the extent of strengthening it might need. If a building is immediately strengthened to meet the LSP requirements, it will miss the beneficial, cost saving opportunities that ASCE 41 provides. The second Level of analysis is the Linear Dynamic Procedure (LDP) thatuses modal analysis and site-sp . ponce spectra to determine the demands. The LDP also includes m big it that coca aeration o uc- ttue in as �, propriate prance It fM ing `ads, and b tint effects of ple es, It a ter out limict- u in t it cannot properly evaluate a b significant redundancy, that is sign strength even after damage begins to occur. The or judging the building to be adeq triggers unacceptable ;perfo - firs, significant donator i the t Test lateral system exceeds its tit . For some buildings, this technique is satisfactory since once significant yielding occurs, there is nothing else to step in and provide resistance. The first of the displacement -based pro- cedures is the Non -linear Static Procedure (NSP), commonly referred to as the push over method. Using analytical techniques, ac- cessible in commercially available advanced computer programs, a model of the building is literally and analytically subjected to increasing defiecaon while the impact on the lateral force resisting elements is monitored. As the yield limits are exceeded, the elements are allowed to yield and the computer program tracks their post }Meld displacement to determine when the building loses its lateral force resisting ability. In the process, first significant yield does not signal a problem; instead, it signifies that other elements need to step up and rake over. Using a series of approximations, a target displacement is calculated based on sue -specific response spectra. If there is a lateral system within the STRUCTEJRB mogozfre September 2008 building that can arrest the movement to within the target displacement, the building is judged adequate. If riot, then there is one more level of analysis, if the building is wordy die cost of running it. This process of analysis matches the wzy buildings behave in earth- quakes since it estimates the building's actual movement and resulting damage - 'Me second displacement based method is a Non -linear Dynamic Procedure (NDP) that uses time history records to represent the possible shaking that the site could experience, Byworking with a hill time series of motion, it is possible to take advantage of the beneficial effects of shaking since the ground motion is applying as much restoring force to the building as it is applying forces that cause damage. The frequency content of the record is used directly to determine the displacement demand and gives a more accurate representation. Also, the number of cycles of non -linear behavior can be monitored and used to more aceuTat predict the extent of damage that will res from the non -linear b dings tha need to rely on a high 1 o n-linear behavior to their to di acement benefit m the ND - ings that ok heavily d ged in but remain standi raight up, t beneficial effeees he time his I record. he NDP can . e dose to predicting sus lore. and Conclusion Having a new state-of—the-art standard to evaluate and rehabilitate buildings is only part of what is needed to achieve seismic safety ASCE 41 allows the use of a variety of earthquake threats and defines three per- formance levels: immediate occupancy, life safety and collapse prevention. The ASCE 41 process assists the engineer in determining the expected performance, but seismic safety is achieved when a proper evaluation is done, the resulting options are understood, and appropriate answers selected and imple- mented. owners need to know what is going to happen in terms of life threatening injuries, what it will cost to repair their buildings, and how long the buildings will not be usable. Fortunately, this information can be deduced from the ASCE 41 analysis. When reporting the results to owners, it is best to focus on the description of expected damage before and after the proposed rehabilitation, as opposed to the minutia of the evaluation itsel£ In that war, ow-neis v '1 be able to relate the impact the performance will have on their use of the buildings and they will have a basis for deter- mining what to do. As structural engineers, we need to advocate seismicsafe yin ourcemmtmities and carry out theroleofearthquakeengineersoneve rprojez Wencedto develop ache irundecstandingofthe difference between designing a new building following the prescriptive requirement,; of the code and design existing buildings following the performance -based evaluation approaches. The nation's inventory of existing buildings that do not meet minimum seismic safety levels is very Iarge, and the cost to replace them is out of the question, not to mention unnecessary. ASCE 41 is the best "tool kith of procedures available that allows for site specific and deliberate performance based etialva STRUCTURE magazine 0 September 2008 for rehabilitation. And, when applied properly, the necessary rehabilitation can be completed at a minimum cost for the awriasi and without liability for the structural engineers.• ;a�ricWR s�rsrsW IN THE SPECS CB THE 10B AT i'A!B SEHhCE"