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Supplemental Structural Correction Sheet Steel Braced Frame Design

( 2002 LABC )

Plan Check Checked

PLAN DETAILS A. GENERAL 9 1. Column splices shall not be located within 4 feet nor one-half the column clear height of beam-to-column connections, whichever is less. AISC I-8.3a ~ 9 2. Beveled transitions are not required when changes in thickness and width of flanges and webs occur in column splices. AISC I-8.3b. ~ B. ORDINARY & SPECIAL CONCENTRICALLY BRACED FRAMES (OCBF/SCBF) 9 1. Bolted stitches in the built-up braces of SCBF shall not be located in the middle onefourth of the clear brace length. AISC I-13.2e ~ 9 2. In a V-type and inverted V-type brace frame, a beam that is intersected by braces shall be continuous between columns. AISC I-13.4a C. ECCENTRICALLY BRACED FRAME (EBF) 9 1. Web shall be single thickness without doubler-plate reinforcement & without penetration. 9 2. Provide full-depth web stiffeners on both sides of the link web at the diagonal brace ends and at intermediate locations of the link, as per AISC-15.3a & 15.3b.~ 9 3. The intersection of the centerline of the diagonal brace and the beam outside the Link shall be at the ends of the Link or in the Link. AISC-15.6c.~ 9 4. Beam-to-column connections away from Links are permitted to be designed as pinned in the plane of the web. AISC-15.7 ~

CALCULATIONS A. GENERAL 9 9 1. The total static design base shear in a given direction shall be determined per 91.1630.2.~ 2. In addition to the load combinations listed in 91.1612, the amplified horizontal earthquake load shall also be used if required by 91.1630.3.1. In addition to the load combination specifies in 91.1612, load combinations using the amplified horizontal earthquake load shall be evaluated per AISC I-4.1 as follows:~

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9 a) 1.2D + 0.5L + 0.2S + SoQE, where the load factor on L in this load combination shall equal to 1.0 for garages, areas occupied as places of public assembly and all areas where the live load is greater than 100 psf.~ 9 b) 0.9D - SoQE~ 9 3. The drift or horizontal displacements of the structure shall be computed as required in 91.1630.9.1 and shall be amplified as required in 1630.9.2. Story drift limits shall be determined as specified in 91.1630.10.~

9 4. Orthogonal earthquake effects shall be included in the analysis as required in 91.1633.1.~ 9 5. Required strength of a connection or related member by using LRFD shall be determined from the Expected Yield Strength Fye of the connected member. AISC I-6.2 The design strength of structural steel members and connections by using ASD shall be determined per AISC III-4.3.~ 9 6. When Pu/Pn for columns is greater than 0.4, the requirements in AISC I-8.2 must be satisfied.~ 9 9 7. The R value used to determine the base shear shall not be greater than the least R value of the different structural systems as specified in 91.1630.4.4.~ 8. Foundation of the steel frame shall be designed to resist applicable sliding shear, uplift force, and/or moment.~

B. SPECIAL CONCENTRICALLY BRACED FRAMES (SCBF) 9 1. Bracing members shall have Kl/r < 1000//Fy . AISC I-13.2a ~ 9 2. The required strength of a bracing member in axial compression shall not exceed kcPn. AISC I-13.2b ~ 9 3. Along any line of bracing, braces shall be deployed in alternate directions such that, for either direction of force parallel to the bracing, at least 30% but no more than 70% of the total horizontal force is resisted by tension braces. AISC I-13.2c ~ 9 4. Width-thickness ratios of stiffened and unstiffened compression elements of braces shall meet the compactness requirements on LRFD Specification Table B5.1 (i.e. < p ) and the requirements in AISC I-13.2d. ~ 9 5. Design the stitches of a built up member for a minimum shear strength equals to the design tensile strength of the each element. The spacing of the stitches shall be uniform and not less than two stitches shall be used. Bolted stitches are not permitted within one-fourth of the clear brace length. AISC I-13.2e ~ 9 6. Distribute stitches uniformly over the length of a built-up brace member such that the slenderness ratio l/r of individual elements between the stitches does not exceed 0.4 times the governing slenderness ratio of the entire member. AISC I-13.2e ~ 9 7. Design the bracing connection (including beam-to-column connection if part of the bracing system) for the least of the following: 9 a) minimum nominal axial tensile strength of the bracing member, RyFyAg; 9 b) the maximum force, indicated by analysis, that can be transferred to the brace by the system. (AISC I-13.3a ~)

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9 8. Verify that the minimum tensile strength of the bracing member, ktPn, is the least value obtained according to the limit states of yielding as follows: 9 a) for gross section yielding: 0.9FyAg 9 b) for fracture in the net section: 0.75FuAe. (AISC I-13.3b ~) 9 9. Address the design flexural strength of the bracing connection in the direction the brace will buckle. The minimum desired strength shall be equal to or greater than the expected nominal flexural strength of the brace 1.1RyMp about critical buckling axis of the brace (see exceptions). AISC I-13.3c ~ 9 10. The design of gusset plate of the bracing connection shall include consideration of buckling. AISC I-13.3d ~ 9 11. In a V-type and inverted V-type bracing, a beam that is intersected by braces shall be designed to meet the following: 9 a) support the effects of all tributary dead and live loads from LRFD Load Combinations A4-1, A4-2 and A4-3 assuming that the bracing is not present; 9 b) resist the effects of LRFD Load Combinations A4-5 and A4-6 except that load Qb shall be substituted for the term E. 9 c) the top and bottom flanges at the point of intersection of braces are able to support a lateral force that is equal to 0.2Fybftbf. AISC I-13.4a ~ 9 12. Design column splices to develop at least the nominal shear strength of the smaller connected member and 50% of the nominal flexural strength of the connected section. AISC I-13.5b ~ 9 13. Use R value of 6.4 for the base shear determination. Table 16-N ~

C. ORDINARY CONCENTRICALLY BRACED FRAMES (OCBF) 9 1. Braces with Kl/r > 720//Fy shall not be used in V or inverted V configuration. AISC I14.2 ~ 9 2. Width-thickness ratios of stiffened and unstiffened compression elements in braces shall meet the requirements in LRFD Specification Table B5.1 9 3. OCBF is not permitted to be uased as part of a dual system. Table 16-N ~ 4. Design the brace connections for the minimum nominal axial tensile strength of the bracing member, determined A5 RyFyAg.

~ 5. Use R value of 5.0 for the base shear determination. Table 16-N ~ ~ 6. Design members and connections, other than brace connections, based on load combinations 4-1 and 4-2. ~ 7. Comply with maximum height of OCBF as per Table 16-N, footnote #6.

D. ECCENTRICALLY BRACED FRAMES (EBF)

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~ 1. Link members shall comply with the width to thickness ratio per AISC Table I-9-1 ~ ~ 2. The minimum yield strength of the Link member shall not exceed 50 ksi. AISC I-15.2b ~ ~ 3. The required shear strength of Link members Vu shall not exceed kVn. AISC I-15.2d ~ ~ 4. If the required axial strength Pu in a Link member exceeds 0.15Py (0.15Fy Ag), the following shall be met: 9 a) the design shear strength of the link shall be the lesser of kVpa or 2 kMpa/e. AISC I15.2f.1 ~ 9 b) the length of the link shall be limited per AISC I-15.2f.2 ~ ~ 5. Limit the link rotation angle to the following, when the total story drift is equal to the design story drift ª: 9 a) 0.08 radians for link length #1.6Mp/Vp, 9 b) 0.02 radians for link length $2.6Mp/Vp, 9 c) shall be determined by linear interpolation for link length between 1.6Mp/Vp and 2.6Mp/Vp. AISC I-15.2g ~ ~ 6. Use R value of 7 for the base shear determination. Table 16-N ~ ~ 7. Design the beam-to-column connection away from the link. The connection shall have the strength to resist two equal and opposite forces of at least 2% of the beam flange nominal strength (0.02Fybf tf). AISC I-15.2g ~ ~ 8. Design column per LRFD load combination A4-5 & A4-6. ~ ~ 9. Provide intermediate web stiffeners at the Link. Web stiffeners shall meet the design requirements as per AISC I-15.3b ~ ~ 10. Design the weld connection between the Link stiffener and the Link web as per AISC I15.3c ~ ~ 11. Design the link-to-column connection based upon cyclic test results as per AISC 9.2a & 9.2b, with an inelastic rotation angle as per AISC I-15.2g. AISC I-15.4a ~ ~ 12. Provide lateral support at top and bottom flanges of the Link ends. End lateral support shall have a design strength of 6% of the nominal Link flange strength (0.06RyFybf tf). AISC I-15.5 ~ ~ 13. Design the diagonal brace outside of the Link for the minimum axial and flexural forces generated by the 125% of the shear strength of the Link (1.25RyVn) but not less than the design strengths as per LRFD Specs Chapter H (including Appndx. H3). AISC I-15.6a ~ ~ 14. Design the beam outside the Link for minimum strength of 110% of the shear strength of the Link (1.1RyVn). AISC I-15.6b1 ~ ~ 15. Provide and design lateral support at top and bottom flanges of the beam outside the Link for a minimum strength of 0.02Fybf tf. Lateral support may be eliminated if analysis demonstrate that the beam is stable. AISC I-15.6b2 ~ ~ 16. Design the diagonal brace-to-beam connection at the Link end for a minimum required strength equivalent to the strength of the brace. AISC I-15.6d ~

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~ 17. Show width-thickness ratio of the brace that satisfies p in LRFD specification Table B5.1. AISC I-15.6e ~ ~ 18. Design the beam-column connection away from the Link to resist rotation about the longitudinal axis of the beam. Rotation shall be based on a force couple of at least 0.02Fybf tf acting laterally on the beam flanges. AISC I-15.7 ~ NOTES ON PLANS A. General 9 1. The seismic design, fabrication, and erection of structural steel shall be in accordance with Part I (LRFD) and Part III (ASD) of the Seismic Provisions for Structural Steel Buildings, April 15, 1997, published by the American Institute of Steel Construction (AISC). These provisions shall be applied in conjunction with Chapter 22, Division II. 91.2210.~ 9 2. Welding shall be performed in accordance with a Welding Procedure Specification (WPS) as required in AWS D1.1 and approved by the Engineer of Record. Specify the required "Welding Procedure Specification" on plans.~ 9 3. All complete-joint-penetration groove welds used in the Seismic Force Resisting System shall be made with a filler metal that has a minimum CVN toughness of 20 ft-lbs at minus 20E F.~ 9 4. Discontinuities in weld created by errors or by fabrication or erection operations, such as tack welds, erection aids, air-arc gouging and flame cutting, shall be repaired as required by the Engineer of Record.~ 9 5. All bolts used as a part of the seismic force resisting system shall be fully tensioned high strength bolts.~ 9 6. The specification and Fabrication for steel frames shall comply with attached Welding and Fabrication procedures. B. SPECIAL CONCENTRICALLY BRACED FRAMES (SCBF) 9 1. Splices shall be located in the middle 1/3 of the column clear height. AISC I-13.5b ~ C. ECCENTRICALLY BRACED FRAMES (EBF) 9 1. No part of the brace-to-beam connection shall extend over the Link length. If the brace resists a portion of the Link end moment, the connection shall be designed as an FR moment connection. AISC I-15.6d ~

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