Tall Buildings and Urban Habitat RECOMMENDATIONS OF AISC TALL BUILDING STUDY COMMITTEE Compiled by Le-Wu Lu Randall M. Haist Tzu-Chieh Lin Lynn S. Beedle Department of Civil Engineering Fritz Engineering Laboratory Lehigh University Bethlehem, Pa. 18015 August 1980 Fritz Engineering Laboratory Report No. 440.6 440.6 ABSTRACT KEY WORDS: AISC, Implementation, Specification, Tall Steel Buildings This report is part of an implementation effort by the Council on Tall Buildings and Urban Habitat. The AISC Tall Building Study Committee was formed with the purpose of determining revisions to the AISC Specification based on Monograph Volume SB. The report identifies suggestions in three categories: specific Specification changes, specific Commentary changes, and general recommendations to both the Specification and the Commentary. A total of 51 recommend ations are included in the report. A ballot is provided for committee members to record their opinion. Recommendations approved by the committee will be sent to the AISC Specification Committee for its consideration. 440.6 TABLE OF CONTENTS Page 1. INTRODUCTION 1 2. RECOMMENDATIONS WITH REGARD TO THE SPECIFICATION 3 3. RECOMMENDATIONS WITH REGARD TO THE COMMENTARY 9 4. OTHER SUGGESTIONS COVERING THE SPECIFICATION AND COMMENTARY 20 5. APPENDIX 48 6. REFERENCES 51 440.6 1 1. INTRODUCTION This report is part of an overall implementation effort by the Council on Tall Buildings and Urban Habitat, in which the latest information and research findings are collected, incorporated into the Council's Monograph, and provided to code and specification jurisdictions under which tall buildings are planned and designed. Fritz Engineering Laboratory Report No. 440.2 gives an overview of the purpose and progress of the implementation program (Beedle, 1978). The 1978 Specification of the American Institute of Steel Construct ion was chosen as the first major subject of this implementation effort. In 1978, discussion between F. R. Khan, W. A. Milek, and L. S. Beedle led eventually to the formation of the AISC Tall Building Study Committee. The role of the committee is to provide recommendations to the AISC Specification Committee regarding changes in both the AISC Specification and Commentary. The members of the committee had been active in the preparation of Monograph Volume SB (Council on Tall Buildings, 1979), with most of them serving as editors of individual chapters. Members of the committee are as follows: F. R. Khan (Chairman), L. S. Beedle, W. F. Chen, G. C. Driscoll, M. Foreman, T.V. Galambos, E. H. Gaylord, T. R. Higgins, J. S. B. Iffland, S. H. Iyengar, L. W. Lu, W. McGuire, W. A. Milek, W. H. Munse, E. P. Popov, and I. M. Viest. With the publicatLon of the Monograph Volume SB in June 1979, the committee was ready to begin its work. The AISC Tall Building Study Committee held its first meeting on August 29, 1979 in Chicago. It was 440.6 2 agreed that the Monograph should be the primary source for suggestions, but that the committee should not necessarily restrict itself to this material. This report is the result of the meeting and of the subsequent written suggestions (AISC Tall Building Study Committee, 1979). Its purpose is to compile the recommendations of the committee members. Recommendations approved by the committee would then be forwarded to the AISC Specification Committee. The body of the report is divided into three sections: Specification recommendations, Commentary recommendations, and other suggestions to. the Specification and Commentary. The first and second sections contain recommendations for specific changes, while the third section deals with suggestions which are general in nature or require additional investi gation. Each section is arranged according to AISC Specification sequence, with topics not covered in the Specification appearing at the end of the third section. The suggested revisions to the Specification proper and to the Commentary are arranged with the present provision appearing at the top of the page, and the suggested revision below it. The material is presented the way it was received from the committee members, modified only to provide clarity as to the precise suggestions being made. The appendix contains the ballot that is provided to the committee members to record their opinion. 440.6 3 2. RECOMMENDATIONS WITH REGARD TO THE SPECIFICATION 1.3.5 Wind Proper provision shall be made for stresses caused by wind, both during erection and after completion of the building. · Suggested Specification Change (Foreman 16Aug79} Add a second paragrapli to Specification Section 1.3.5: The deflection of the structure due to wind should be considered, and the effect of cladding on the stiffness and strength of tall buildings should also be taken into account. 440.6 4 SECTION 1.7 MEMBERS AND CONNECTIONS SUBJECT TO REPEATED VARIATION OF STRESS (FATIGUE) 1.7.1 General Fatigue, as used in this Specification, is defined as the damage that may result in fracture after a sufficient number of fluctuations of stress. Stress range is defined as the magnitude of these fluctuations. In the case of a stress reversal, stress range shall be computed as the numerical sum of maximum repeated tensile and compressive stresses or the sum of maximum shearing stresses of opposite direction at a given point, resulting from differing arrangements of live load. Few members or connections in conventional buildings need to be designed for fatigue, since most load changes in such structures occur onl a small number imes or roduce onl minor stress fluctuations. The occurrence of full design wind or earth uake loads is too infr uent to warrant consideration in fati e desi However, crane runways and supporting structures for machinery and equipment are often subject to fatigue loading conditions. Suggested Specification Change (.Munse 12Sep79} Replace Specification Section 1.7.1- Paragraph 2- Line 3 with the following: The occurrences of full design wind, thermal or earthquake loadings are rare and generally need not be considered in fatigue design. 5 440.6 SECTION 1.11 COMPOSITE CONSTRUCTION 1.11.1 Deimition Composite construction shall consist of steel beams or girders supporting a reinforced concrete slab • so interconnected that the beam and slab act together to resist bending. When the slab extends on both sides of the beam, e e ectwe w t o e concrete flange shall be taken as not more than lf the span of the 4 beam, and its effective projection beyond the edge of the beam shall not be taken as more than %the clear distance.to the adjacent beam. nor more than 8 times the slab thickness. When the slab is present on only one side of the beam, the effective projection shall be taken as not more than lft of the beam span, nor 6 2 · · hickn s nor the clear distance to the ad·a cent beam. Beams totally encased 2 inches or more on their sides and soffit in concrete cast integrally with the slab may be assumed to be interconnected to the concrete by natural bond, without additional anchorage, provided the top of the beam is at least llf2 inches below the top and 2 inches above the bottom of the slab, and further provided that the encasement has adequate mesh or other reinforcing steel throughout the whole depth and across the soffit of the beam to prevent spalling of the concrete. When shear connectors are provided in accordance with Sect. 1.11.4, encasement of the beam to achieve composite. action is not required. ~uggested Specification Change (Viest 29Aug79) EFFECTIVE WIDTH Replace Specification Section 1.11.1 -Paragraph 1 - Lines 3-9 with the following: The effective width of the concrete slab on each side of the beam centerline shall be taken as the least of (1} one-eighth of the beam span, center-to-center of supports, (2) one-half the distance to the centerline of the adjacent beam and (3) the distance to the edge of the slab. 6 440.6 SECTION 2.4 COLUMNS Members subject to combined axial load and bending moment shall b~ pro portioned to satisfy the following interaction formulas: (2.4-2) p + MM S 1.0; M S Mp (2.4-3) Py 1.18 p Suggested Specification Change (Driscoll 14Sep79) A) Replace Equations (2.4-2) and (2.4-3) with the following: (Council on Tall Buildings, 1979, pp. 255-256) (2 .4-2) At a braced location e = 1.6 - (2.4-3) (2.4-4a) M = 1.19 M [1 - (-pp (] (2.4-4b) uy PY yJ 440.6 7 To check stability between braced points use [ cm xM x JB + [cm yM y JB < 1.0 (2.4-Sa) M M ux uy B = 0.4 +! + DB 2:, 1.0 when DB 2 :, 0.3 (2.4-Sb) p y B B = 1.0 when - < 0.3 (2.4-Sc) D [:J] [p:J] Mux - Mml1- [1- (2.4-6a) l t:J rp:J Muy = MPA1 - 1[1 (2.4-6b) ~ P = - Ct/r)jF A (2.4-7) u 2C ~ y c ~.rhere /2; E 2 c = c y when l/r exceeds C c = (2.4-8) p u in which p = applied_ axial load·, lcips p = axial load at full yield condition y p = ultimate load of axially loaded column u p = Euler buckling load about x axis of bending ex p = Euler buckling load about y axis of bending ey