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The study which resulted in this report was supported by grants and services from eight private industries organizations and by support through contracts from seven agencies of the Federal Government. Reproduction in whole or in part i s permitted for any purpose of the United States Giovemment. Full-scale l e s ' l i i j i'^' F a i r stiLn.tii'e>« i f J Inquiries concerning this publication should be addressed to: Tbe Executive Director, Building Research Advisory Board, Division of EngineeringâNational Research Council, 2101 Constitution Avenue, N. W., Washington, D. C. 204l8. i i
SPECIAL ADVISORY COMMITTEE on FULL-SCALE TESTING OF NEW YORK WORLD'S FAIR STRUCTURES CHAIRMAN ROBERT B. TAYLOR, Mapleton Development Inc., Minerva, Ohio MEMBERS WILLIAM J. BOBISCH, Engineering Division, Naval F a c i l i t i e s Engineering Command, Washington, D. C. CHARLES D. MORRISSEY, Praeger-Kavanagh-Waterbury, New York, N. Y. RAYMOND C. REESE, Raymond C. Reese Associates, Toledo, Ohio MICHAEL N. SALGO, F a c i l i t i e s Engineering, Col\anbia Broetdcasting System Inc., New York, N. Y. CHESTER P. SIESS, Department of C i v i l Engineering, University of I l l i n o i s , Urbana, I l l i n o i s I . M. VIEST, Bethlehem Steel Corporation, Bethlehem, Pennsylvania TECHNICAL LIAISON DONALD C. TAYLOR, American Society of C i v i l Engineers, New York, N. Y. BRAB STAFF ROBERT W. SPANGLER, Assistant Director-Program Planning (Former) WILLIAM A. COSBY, Staff Engineer JAMES R. SMITH, Assistant Director-Technical Operations i i i
ACKNOWLEDGMENTS The program of f u l l - s c a l e t e s t i n g of selected structures of the Hew York World's Fair was conceived by the American Society of C i v i l Engineers. The f i r m of Wiss^ Janney, Elstner and Associates supeirvised general plan- ning f o r the t e s t i n g program and also the actual f i e l d t e s t i n g . In addi- t i o n t o designing methods of t e s t and tests performed on both the Chimes Tower and Bourbon Street structures; f o r the Chimes Tower, Professor V. J. McDonald of the University of I l l i n o i s was consultant on instrumenta- t i o n . For the Rathskeller structure, Professor M. A. Sozen of the University of I l l i n o i s I n i t i a l l y suggested the t e s t plan and served as a consultant; detailed plans f o r t e s t i n g of t h i s structvire were devel- oped by personnel of the Structural Development Section of the Portland Cement Association. Field t e s t i n g was carried out by personnel of Wiss, Janney, Elstner and Associates, Simms Engineering, the Corbetta Construc- t i o n Company, and the Portland Cement Association. The v i b r a t i o n generator and a u x i l i a r y equipment used In the dynamic t e s t - ing of the Chimes Tower structure were supplied by the Department of Engineering of the University of C a l i f o r n i a , Los Angeles; much i n s t r u - mentation used i n the program was provided by the U. S. Army Engineering Waterways Esqerlment Station at Vicksburg, Mississippi, and by the U. S. Army Aberdeen Proving Grounds at Aberdeen, Maryland. Grateful acknowledgaent i s due the many individuals who gave f r e e l y of assistance and suggestions which contributed s i g n i f i c a n t l y t o the suc- cessful completion of t h i s project. In t h i s regard, p a r t i c u l a r recog- n i t i o n must be given t o the s t a f f of the New York World's Fair 19614-65 Corporation--to Messrs. John T. O'Neill, Joseph Myers, S. A. Potter, Pazel G. Jackson Jr . , and William McCarthy; t o Messrs. Robert G. Mathey
and James R. Bryson of the National Bureau of Standards; Messrs. William Palmertree and Norman G. Hansen of the U. S. Army Corps of Engineers; t o Mr. Albert Peter of the General Services Administration; Mr. Howard Johnson of AAA Photographers; and Mr. Eugene L. Herzman, the structviral designer of the Chimes Tower. ⢠A note of special recognition i s due Mr. Donald C. Taylor, Research Manager, American Society of C i v i l Engineers, whose e f f o r t s were i n s t r u - mental i n making the program a r e a l i t y . Appreciation and acknowledgment also must be escpressed f o r the support provided by a group of sponsors from both industry and government; namely, American Iron and Steel I n s t i t u t e National Aeronautics and Space Administration American Society of C i v i l Engineers (Services) National Bureau of Standards Army Corps of Engineers National Science Foundation Concrete Reinforcing Steel I n s t i t u t e Office of C i v i l Defense Engineering Foundation Portland Cement Association (Services) Ford Foundation General Services Administration Reinforced Concrete Research Council ^li^f^^^^^^ Engineering ^^^^ j ^ . ^ ^ I n s t i t u t e F i n a l l y , the contributions t o the program of the Chairman and members of the Special Advisory Committee are g r a t e f u l l y acknowledged. v l
FOREWORD H i s t o r i c a l l y , b u i l d i n g science has been hampered by the dearth of informa- t i o n on the performance of f u l l - s c a l e structures. For the obvious reason of cost, t o t a l b u i l d i n g structtires t r a d i t i o n a l l y have not been erected f o r the sole purpose of t e s t i n g t o or near to d e s t r u c t i o n â y e t , doing so i s an obvious necessity i f one i s t o be able to t r u l y validate design c r i t e r i a . I n the absence of such t e s t i n g , the research and design communities have had t o r e l y t o a great extent upon assumed ultimate structure performance extrapolated from scale-model and component te s t s . As a consequence there has always been the nagging doubt as t o whether designed structures actu- a l l y perform as predicted; that i s , whether structures are i n some respects overdesigned and i n others, underdesigned. Engineering l i t e r a t u r e throughout the world does contain l i m i t e d references t o t e s t i n g of f x i l l - s c a l e structvires erected f o r normal use. From the few tests reported, much of what was learned has been of value t o researchers and others concerned with b u i l d i n g performance. Perhaps the most s i g n i f i - cant consequence of f t i l l - s c a l e t e s t i n g has been the indication that the ultimate load-carrying c a p a b i l i t y of three-dimensional structures may be considerably I n excess of that which would be predicted from accepted de- sign c r i t e r i a ; that i s , t h a t factors of safety may be f a r greater than needed or intended. Thus, i t has long been f e l t that i f s u f f i c i e n t data could be obtained through t e s t i n g of a series of f u l l - s c a l e buildings, a better understanding of actual performance would be gained, more rea- l i s t i c performance requirements established, and improved design c r i t e r i a and techniques developed--the net r e s u l t being improved b u i l d i n g e f f i - ciency and economy. v i i
The complex of structures b u i l t f o r the 196U-65 New York World's Fair presented an opportunity almost without precedent f o r conducting such f u l l - s c a l e s t r u c t u r a l t e s t i n g . Most of the structures already were scheduled f o r demolition, and, though t h i s obviously imposed a time l i m i t a t i o n on the t e s t i n g program, t h e i r a v a i l a b i l i t y precluded the large f i n a n c i a l commitment which would otherwise have been required t o b u i l d the structures solely f o r t e s t i n g . Also, although r e l a t i v e l y new, the structures had been subjected t o occupancy conditions. Thus, the complex of structures constituted a unique resource. Many of the structures constructed f o r the f a i r represented innovations i n design, but most were representative of contemporary, conventional construction. I t was decided t o select a representative sample of the l a t t e r f o r t e s t i n g i n the b e l i e f that r e s u l t i n g information woiild be of greater universal value since such structures would most l i k e l y r e f l e c t current design c r i t e r i a and construction practices. Obviously, these structiores presented one major l i m i t a t i o n â t h e y were not designed and b u i l t s p e c i f i c a l l y f o r t e s t i n g . As a r e s u l t , one could expect i n - consistencies i n both application of design c r i t e r i a and actual f i e l d performance during construction. A Special Advisory Committee, comprising knowledgeable individuals recognized f o r t h e i r technical expertise i n one or more of the p r i n c i - p al areas of Investigation, was appointed by the Building Research Advisory Board t o conduct the study. Results of the t e s t i n g program, which constitute the culmination of a unique and rewarding research e f f o r t i n the f i e l d of b u i l d i n g science, are reported i n t h i s and two other volumes prepared f o r the Board by the Special Advisory Committee. Each volume has been reviewed, accepted, and approved f o r t r a n s m i t t a l t o the program sponsors by the Executive Committee of the Board, acting on behalf of the" Board. ROBINSON NEWCOMB, Chairman Building Research Advisory Board
CONTENTS Page Foreword v l i Section I . INTRODUCTION 1 Purpose Scope and Limitations Publication of Results I I . REPORT OF THE SPECIAL ADVISORY COMMITTEE 7 I I I . SUBCONTRACTOR REPORT l 3 TEST TO DESTRUCTION OF A MULTIPANEL WAFFLE SLAB STRUCTURE and TECHNIQUES FOR FIELD TESTS OF A MULTIPANEL SLAB by D. D. Magura and W. G. Corley i x
I INTRODUCTION Purpose The fundamental purpose of the program was t o t e s t f u l l - s c a l e structures selected from the complex of buildings erected f o r the 196^-65 New York World's Fair i n order t o ascertain t o the extent possible the degree of corr e l a t i o n between performance of actual s t r u c t u r a l systems and t h a t predicted from laboratory t e s t i n g and design theories. Scope ajid Limitations While the program was coordinated with the New York World's Fair Corpora- t i o n which gave i t s f u l l support, previously established demolition schedules had t o be maintained, necessitating expeditious planning and execution of the t e s t i n g phase of the program. Structural drawings were obtained and studied t o make a determination of which structures were best suited f o r t e s t ; of 15 i n i t i a l l y \mder consideration, three, repre- sentative of contemporary construction, were selected f o r f u l l - s c a l e t e s t i n g : 1. A l l ^ t - f r a m e , open-web steel-Joist and steel-pipe colimm type known as the Bourbon Street structure 2. A one-story multlpanel relnforced-concrete waffle- slab type known as the Rathskeller structure 3« A seven-story tower fabricated with standard s t e e l structxiral members known as the Chimes Tower. The Bourbon Street S t r u c t t t r e â . This was a two-story structure, approxi- mately 750 feet long and 50 feet wide. The ground f l o o r was concrete slab-on-grade; the second f l o o r consisted of open-web stee l Joists with a lightweight concrete deck supported by a corrugated st e e l decking, spot welded t o the top cord of the Joists. The Joists were carried by wide- flange st e e l sections framing i n t o s t e e l pipe columns, or wide-flange
columns which were part of the wind framing provided at in t e r v a l s of approximately 50 feet throughout the length of the structure. The columns were supported by reinforced concrete grade-beam footings. Roof construction was similar t o that of the second f l o o r , except th a t a standard metal deck supported r i g i d insulation and roofing material. The following t e s t s were conducted on t h i s structure: 1. Lateral loading of the frames t o observe and evaluate a. diaphragm action of the roof and second f l o o r b. s t r u c t u r a l behavior of wind frame and pipe colvmins c. mode of f a i l u r e . 2. Uniform loading of the f l o o r and roof t o a. determine mode of f a i l u r e and maximum load capacity of the two s t r u c t u r a l systems ( f l o o r and roof) and compare re s u l t s w i t h what would be predicted b. investigate those conditions, usually not considered i n simple designs, which may have a strength-enhancing or strength-di- minishing e f f e c t on the structvire ( i . e . , unintended composite action, s t i f f e n i n g e f f e c t s of unintentional continuity, fotin- datlon settlements, supporting-beam l a t e r a l rotations and translations due t o unsymmetrlcal loading, and ef f e c t s of attached cvirtaln walls) c. determine the loads (stresses) Induced i n the various struc- t u r a l elements (chord and web members) comprising a stee l j o i s t and compare re s u l t s with values predicted from beam or truss analysis d. determine deflection behavior of the v£u:lous s t r u c t \ i r a l elements under load and compare results with values pre- dicted from t h e o r e t i c a l analysis e. determine, i f possible, areas where additional laboratory research i s required t o obtain a better understanding of s t r u c t u r a l elements connected i n t o a three-dimensional framework f . evaluate loading and Instrvmientatlon techniques used i n t e s t i n g the b u i l d i n g t o f a i l u r e . 3. Concentrated load tests t o evaluate a b i l i t y of second f l o o r t o sustain such loading.
k. v i b r a t i o n loading t o determine a. natural frequencies of several of the open-web Joist f l o o r s b. magnitude of the dynamic deflection and the degree of damp- ing under impact. The Rathskeller S t r u c t u r e â This was a one-story, box-like structure meas\irlng approximately l80 by 120 feet i n plan and 20 feet i n height. A 2-foot-thick waffle slab supported on columns, about 30 feet on cen- t e r s , formed the roof. The f l o o r was a 2.5-foot-thick reinforced slab t h a t formed a r a f t foundation f o r the structure. Outside walls of the b u i l d i n g were 12 inches t h i c k . Uniform loading tests were conducted on t h i s structure t o Investigate: 1. Shear strength of an i n t e r i o r panel. 2. Strength of coltmin-to-slab connections at edg@ panels. 3. Strengthening of a slab due t o arch action when a single panel i s loaded. k. Residual strength a f t e r i n i t i a l f a i l u r e under each of the above patterns of loading. The Chimes Tower S t r u c t u r e â . This was a seven-story structxire construc- ted of r o l l e d steel sections bolted and/or rive t e d together. The struc- ture was 9 f e e t - 3-3/8 inches square and 86 feet-8 inches t a l l . A l l f l o o r s had a uniform height of 12 feet except the top story, which was Ik feet-8 inches high. Dynamic tests were conducted on t h i s structure t o determine: 1. Nattiral frequencies and mode shapes, and t o compare r e s t i l t s with values predicted t h e o r e t i c a l l y . 2. Degree of damping. 3. P a r t i c i p a t i o n of the foundation i n motion of the tower. Static t e s t s were aJ.so conducted on the structure t o : 1. Allow comparisons of f l o o r deflections and foundation motion with those observed during the dynamic te s t s .
Conduct of the Program The concept of f u l l - s c a l e t e s t i n g of selected New York World's Fair struc- tures originated i n 1965 with the American Society of C i v i l Engineers. A f t e r I n i t i a l and favorable discussions with o f f i c i a l s of the New York World's Fair Corporation and following encouraging recommendations from the f i r m of Wlss, Janney, Elstner and Associates regarding f e a s i b i l i t y of conducting the t e s t s , a Special Advisory Committee was appointed by the Building Research Advisory Board at the request of ASCE t o administer the e n t i r e program. Responsibilities assigned to the Advisory Committee Included: 1. Determination of those structvires t h a t would be load tested on the basis of: Analysis of s t r u c t u r a l and construction drawings and on-site inspection; information obtained from designers, contractors, owners, and the World's Fair Authority; and the amount of funds available f o r planning and conducting the t e s t i n g program. 2. Determination of the kinds of data that would be obtained from the t e s t s . 3. Determination of the loading techniques, instrumentation, and procedures f o r recording data. k. Guidance t o the t e s t i n g organization. 5. Review and analysis of data and preparation of reports f o r publication. Under the guidance of the Special Advisory Committee, the engineering f i r m of Wlss, Janney, Elstner and Associates was retained under contract by the National Academy of Sciences, t o supervise general planning f o r the entire t e s t i n g program and t o carry out or supervise a l l f i e l d t e s t i n g ; i n addi- t i o n the f i n n selected and/or designed a l l methods of t e s t and planned the tests performed on both the Chimes Tower and the Bourbon Street structure. For the Rathskeller structvire, detailed plans f o r t e s t i n g were developed \mder guidance of the Committee by personnel of the Structural Development Section of the Portland Cement Association. Subsequently, Wlss, Janney, Elstner and Associates prepared and submitted t o the Advisory Committee highly detailed reports r e l a t i n g t o the actvial t e s t i n g performed on both
the Chimes Tower and Bourbon Street Structure, as wel l as findings, con- clusions and recommendations based on analyses of the collected data; and personnel of the Portland Cement Association prepared and submitted a similetr report on the t e s t i n g of the Rathskeller structure t o the Advisory Committee through Wiss, Janney, Elstner and Associates. Prior t o t h e i r acceptance, a l l reports were c r i t i q u e d by the Advisory Committee meeting repeatedly i n session with the various report authors. Publication of Results Results of the t e s t i n g program are published i n three separate volumes, under the general t i t l e heading FULL-SCALE TESTING OF NEW YORK WORLD'S FAIR STRUCTURES. The three volumes carry the s u b t i t l e s The Bourbon Street Structure (Volvime l ) The Rathskeller Structvire (Volume I I ) The Chimes Tower Structure (Volume I I I ) Each volume i s camprised of three sections: INTRODUCTION; REPORT OP THE SPECIAL ADVISORY COMMITTEE;.and SUBCONTRACTOR REPORT. The INTRODUCTION section i s i d e n t i c a l i n each volume and relates the ov e r a l l purpose of the program, gives a b r i e f description of the three structures tested, and d e t a i l s tbe t e s t s conducted on each of the three structures. The second section, REPORT OF THE SPECIAL ADVISORY COMMITTEE, i s , l i k e the introduction, i d e n t i c a l i n each volume and contains comments from the Committee on salient aspects of the o v e r a l l program and particTilarly s i g n i f i c a n t results of te s t s performed on the ind i v i d u a l structures, the SUBCONTRACTOR REPORT section of each volume i s comprised of the re- port prepared by the t e s t i n g subcontractor on the p a r t i c u l a r structure bearing t h a t volume s u b t i t l e . Presented i n each such SUBCONTRACTOR REPORT section, i s a detailed description of the t e s t i n g program, re- svilts of te s t s and comparative analyses, conclusions and recommendations, and tabulated data.
I I REPORT OF THE SPECIAL ADVISORY COMMITTEE The i n d i v i d u a l subcontractor reports emanating from t h i s investigation, reviewed and accepted by the Advisory Committee, contain d e t a i l s of the actual t e s t i n g performed on the three structures Involved, as w e l l as a l l f i n d i n g s , conclusions, and recommendations. Comments from the Committee, on salient aspects of the o v e r a l l program and p a r t i c u l a r l y s i g n i f i c a n t resvats of tests performed on the in d i v i d u a l structures, follow. Value of the Testing Program and Results The t e s t s performed revealed vinsuspected strengths and weaknesses; however, neither design practices nor build i n g codes reasonably could be revised or modified solely on the basis of these few f u l l - s c a l e t e s t s . Nor should judgments as t o the a p p l i c a b i l i t y of t e s t findings t o other similar structures be made without extreme caution u n t i l s u f f i c i e n t data are collected through other f u l l - s c a l e t e s t i n g pro- grams t o permit establishment of findings and conclusions having s t a t i s t i c a l significance. Results of the t e s t s do h i g h l i g h t specific areas i n which f u r t h e r research and laboratory investigation could probably lead t o considerable Improvement i n e x i s t i n g design c r i t e r i a . I n p a r t i c u l a r , no determination co\ild be made of whether the ultimate strengths of the structures tested t o destruction reflected actual factors of safety associated with design techniques or the synergistic strengthening e f f e c t of three-dimensional interplay. However, the program demonstrated the complete f e a s i b i l i t y of t e s t i n g f u l l - s c a l e structures i n the f i e l d with a degree of precision approximating t h a t attainable i n the laboratory. At t h i s stage of development f u l l - s c a l e t e s t i n g of stxnctvires must be viewed p r i n c i p a l l y as a source f o r devel- oping questions rather than answers; consequently, follow-up
investigations involving both laboratory t e s t i n g and th e o r e t i c a l anal- ysesâwith the aim of obtaining answers t o the questions raisedâmust be pursued i f the p o t e n t i a l benefit of a f u l l - s c a l e t e s t i n g program i s to be realized. Within the time, funds, and resources made available, the Committee could not perform a l l possible analyses of the data collected. Thus, a l l re- corded data have been reduced and are published i n the reports r e s u l t i n g from the program t o allow interested researchers t o investigate areas and aspects of pa r t i c u l a r i n t e r e s t t o them. The Committee encourages t h i s type of follow-up a c t i v i t y and, i n order t o realize the f u l l e s t benefits of the program, urges researchers t o make t h e i r r e sults a v a i l - able through technical journals. (Copies of raw data may be obtained from the National Academy of Sciences by any interested researcher.) Future Programs f o r Testing Full-Scale Structures Much was learned during the course of t h i s investigation regarding con- duct of f u l l - s c a l e structure t e s t i n g which shoiild be of benefit t o the management of any similar program i n the f u t i i r e . Of p a r t i c u l a r import- ance i s the absolute need t o know what i s t o be tested. Thus, provi- sions should be made at the onset f o r investigation of the his t o r y of the structure ( i . e . , when and how i t was b u i l t and how used) as w e l l as f o r : 1. A thorough suirvey t o detennine whether or not the structure has undergone i n t e r n a l stresses due t o unequal settlements, creep, or other influences; and 2. detailed v i s u a l examination of connection, weldments, e c c e n t r i c i t i e s , and the l i k e , t o i d e n t i f y and isolate areas of known weakness. An e f f o r t should then be made t o rate the structure i n l i g h t of t h i s knowledge. As-built drawings ought t o be obtained, and devia- tions from design determined and noted. Perhaps most important, a thorough post-mortem examination of the struc- ture should be performed t o determine deviations from design' specifications (e.g., a s u f f i c i e n t number of material samples sho\ald be taken from
structures and tested In the laboratory t o determine actual strength characteristics; actual dimensions t o which the structure was b u i l t should be obtained; location, type, and q u a l i t y of concrete r e i n - forcement bars determined; number and q u a l i t y of b o l t s used i n previously concealed connections determined; f i x i t y of end connections assessed.) The Bourbon Street Struct\ire This structure, one of the two tested t o destruction, served adeq\iately as designed, providing more than s u f f i c i e n t factor of safety. Under uniform loading, ultimate f a i l u r e of both the roof and second f l o o r occurred at points near the ends of the bar j o i s t s . Mode of f a i l u r e could not be p o s i t i v e l y i d e n t i f i e d ; however, a close examination of the records suggests that f a i l u r e of both the roof and f l o o r systems was I n i t i a t e d by y i e l d i n g of the j o i s t s followed by buckling of diag- onals and top chords i n the area of f a i l u r e . Cause of the f a i l u r e could not be d e f i n i t e l y i d e n t i f i e d e i t h e r , but various hypotheses f o r the cause are given i n the detailed subcontractor report (Volume l ) on the structTire. The spandrel beams experienced torsional d i s t o r t i o n ; t h i s would l i k e l y have contributed s i g n i f i c a n t l y t o i n i t i a t i o n of the f a i l i i r e . The horizontal forces exerted on side walls due t o the vacuum created w i t h i n the structure t o apply the \inlform load also might have had a contributing e f f e c t . Comparison of results from the uniform load tests with those predicted using conventional methods of analysis and design indicated t h a t : 1. Deflections of the s t e e l j o i s t s roof system could be predicted accurately by use of the simple-span beam formula with a m u l t i p l i e r of 1.25, while deflections of the f l o o r j o i s t s ranged between values below those com- puted with the beam formiila without a m u l t i p l i e r and those computed using a m u l t i p l i e r of 1.25; and 2. top and bottom chord a x i a l stress can be closely estimated by beam analysis using only chord area t o determine section properties of the j o i s t .
Of the results obtained from l a t e r a l load t e s t i n g of the Bourbon Street structure, i t was s i g n i f i c a n t that the structure resisted lateraJL loads i n excess of the t h e o r e t i c a l f u l l y p l a s t i c capacity of the whole frame. This, combined with the plate diaphragm action of both the roof and se- cond-floor systems, which permitted f u l l p a r t i c i p a t i o n i n l a t e r a l r e s i s t - ance not only of the wind frames but also of a l l pipe columns, led t o a l a t e r a l load capacity considerably i n excess of that required f o r wind design. I t i s s i g n i f i c a n t also that f o r the types of foundation and column base used, the wind frame column base connections acted as i f neither f u l l y f i x e d nor pinned. Concentrated load t e s t i n g of the structure demonstrated that the 0 . 5 -inch diameter horizontal bridging was f u l l y e f f e c t i v e and eidequate i n providing l a t e r a l s t a b i l i t y t o the st e e l bar j o i s t s ; composite action between the concrete deck and j o i s t s did not e x i s t t o a s i g n i f i c a n t degree. The f l o o r v i b r a t i o n tests developed excellent, usable data on the v i b r a t i o n character- i s t i c s of an open-web j o i s t f l o o r ; the most interesting feature of the t e s t was the high degree of damping reaJ.ized. The Rathskeller Structure This structure served adequately as designed, providing s u f f i c i e n t factor of safety. For example, i f i t i s assumed th a t the t o t a l design load was approximately 567 psf (dead load of k7 psf f o r flagstone, mortar bed, and waterproofing, plus 220 psf f o r concrete slab, f o r a t o t a l of 267; plus a design l i v e load of 300 psf) r a t i o s of oatimate t e s t load t o 567 psf wo\ild be approximately 2 .0 , l.k, and 3 .9 , respectively, f o r the tests with four i n t e r i o r panels loaded, three edge panels loaded, and a single i n t e r i o r panel loEided. Despite the ample safety provided, flexursJ. capacity was not reached i n any of the three t e s t s . Rather, ultimate strength was governed by shear at i n t e r i o r and edge columns before a y i e l d i n g mechanism could be devel- oped completely. Cause of such f a i l u r e i s not known; however, p r i o r t o 10
application of t e s t loads^ damage t o the structure was v i s i b l e , which co\2ld have reduced shear capacity, p a r t i c u l a r l y at the edge columns. This i s an area which c a l l s f o r further research. With f u r t h e r regard t o shear f a i l u r e , i t was noted that the shear strength of the slab a t the I n t e r i o r column loaded from a l l four sides was greater than Implied by ultimate strength design methods of the 1963 ACI Code; and the shear strength of the slab at edge columns and at an i n t e r i o r column supporting a single loaded panel was less than t h a t implied by design methods of the Commentary on the I963 ACI Code. The Chimes Tower Structiire F a r t i c t i l a r l y impressive was the high degree of damping e3q)erienced and the low degree of p a r t i c i p a t i o n of the foundation i n motion of the structure. S i g n i f i c a n t l y , damping did increase with increasing stress l e v e l and with increasing mode frequency, and description of the damping mechanism re- quired I n t e r f l o o r dashpots; a hlgja. degree of correlation was reeilized be- tween actual and t h e o r e t i c a l response. I t i s also s i g n i f i c a n t t h a t : 1. During one dynamic t e s t , response of the structvire induced about 75?^ of the base shear which would l i k e l y have resulted from groiind motion of I n t e n s i t y equal to t h a t of the l^ko E l Centro strong-motion earthquakfij and 2. the foundation slab rotated p r i m a r i l y about one horizontal axis i n the plane of the bottom of the base, perpendicular t o the d i r e c t i o n of the e x c i t i n g force, but there was also r o t a t i o n about a horizontal eucis p a r a l l e l t o the d i r e c t i o n of the e x c i t i n g force, located approximately 2.5 t o 3.0 feet beneath the bottom of the foundation slab. 11 -
I l l SUBCONTRACTORS REPORT TEST TO DESTRUCTION OF A MULTIPANEL WAFFLE SLAB STRUCTURE and TECHNIQUES FOR FIELD TESTS OF A MULTIPANEL SLAB by D. D. Magura and W. G. Corley 13
TEST TO DESTRUCTION OF A MULTIPAWEL WAITLE SLAB STRUCTURE CONTENTS Synopsis 1 Introduction 2 Background 2 Choice of Test Structure 3 Object and Scope k Program Outline h Reports 5 Description of Test Structiore 6 Dimensions and Reinforcing D e t a i l s 6 Materials 7 Design 8 Condition Prior to Testing 11 Structural Tests 1Ì^ Outline of Tests ik Test Preparation ik Loading System 15 Instrumentation l6 Conduct of Tests 19 Test Results 21 Test Data 21 Behavior 21 Test I 21 Test I I 2h Test I I I 26 Analysis of Results 30 Equivalent Frame Analysis 30 Deflections 30 Column Loads 32 Shear Strength of Slab 3^ Comparison of Measured and Computed Shear Strengths ^ Test I kO Tfest I I ho Ttest I I I h2 F l e x u r a l Strength hS
Contents--continued Discussion of Results ^7 Service Load Behavior 47 Strength Under Overload 0Ì Test I 50 Test I I 52 Otest I I I 53 Post-failure Behavior 53 Conclusions 55 Figures 57 References 117 Appendices 119 A. Frame Analysis B. Tables--Detalled Test Data C. Figures--Detailed Test Data
TESTS TO DESTRUCTION OF A MULTIPANEL WAFFLE SLAB STRUCTURE by D. D. Magura and W. G. Corley* SYNOPSIS Three load t e s t s to destruction were made on the waffle slab roof of the Rathskeller Building in the Belgian V i l l a g e exhibit at the 196U-65 New York World's F a i r . Uniform loading was f i r s t applied to four adjacent ' In t e r i o r panels, then to three panels along an edge of the slab, and f i n a l l y to a single i n t e r i o r panel. The behavior of the s t r i c t u r e was in general accord with e x i s t i n g theories, though a shear weakness was observed a t edge columns. How- ever, damage to the structure before t e s t i n g began may have influenced both performance and strength. Performance of the slab under service loads was sa t i s f a c t o r y . Ultimate strength of the slab in a l l three t e s t s \ia.s governed by shear at one or more columns. Ultimate loads were 1.0 dead load plus applied loads ranging from I.9 to 6.h design l i v e load. Only in the single-panel t e s t did f l e x u r a l reinforcement y i e l d before shear punching occurred. The slab possessed some strength a f t e r f i r s t shear f a i l u r e occurred i n each t e s t . Key Words: cracking; deflection; f i e l d t e s t ; f l a t plate; f l e x u r a l strength; reinforced concrete; slab; shear strength; ultimate strength; waffle slab. * Development Engineer and Manager, respectively. Structural Development Section, Portland Cement Association Research and Development Division, Skokie, 111ino1s. 1-1
INTRODUCTION BACKGROUND Field t e s t s of buildings have played an important r o l e i n the development of reinforced concrete f l a t slab and f l a t plate construction. One of the e a r l i e s t tests i n North American was reported by W. A. Slater i n 1913.Ì -'-Ì A few years l a t e r , the results of a number of similar tests were simimar- (2) ized and discussed i n a paper by H. M. Westergaard and W. A. Slater. A l l but one of the tests reported were terminated before f a i l u r e of the structure. Despite the lack of sophisticated equipment now available, these early tests were instrimiental i n the evolution of design procedures f o r f l a t slab and f l a t plate structures. Many of the design c r i t e r i a developed i n t h i s way are s t i l l being used more than years l a t e r . Structural tests conducted i n the f i e l d during the l a s t h a l f century have generally been patterned a f t e r the early tests of f l a t slabs. I t has seldom been possible t o carry the tests t o destruction, e i t h e r be- cause of safety r e s t r i c t i o n s or because the structure was due to be placed i n service a f t e r completion of the t e s t s . Few investigators have made any attempt t o canry lavoratory procedvires i n t o the f i e l d . Where attempts t o do t h i s have been made, they have generally met with l i m i t e d success. In the mid-1950's, A. J. Ockleston tested a bu i l d i n g to destruction i n South A f r i c a , ^ ^ ' ^ ' ^ ^ a reinforced concrete hospital scheduled f o r demoli- t i o n . Measurements were made using modified laboratory proced\ires. 1-2
More recently t e s t s by J . B. Read^^^ successfully made use of laboratory procedures in f i e l d t e s t s . An accurate determination of both applied loads and response of the structure was made i n t e s t s to destruction of two f u l l - s i z e p o r t a l frames. Although some problems with the use of vibrating wire s t r a i n gages were encountered, mechanical s t r a i n gages were successfully employed. In these t e s t s , a l l quantities were inea- svired with an accuracy comparable to that obtained i n the laboratory- Demolition of buildings a f t e r completion of the 1964-1965 New York World's F a i r presented a unique opportunity f or f i e l d t e s t s of struc- tures. The planned demolition of these buildings permitted s t r u c t u r a l t e s t s to be ca r r i e d to destruction. Although the la c k of adequate time to prepare for the t e s t s was a handicap, laboratory procedures were used to carry out the t e s t s and to gather data. I t was found that, with pro- per attention to d e t a i l s , f i e l d t e s t s can be conducted with precision" associated with laboratory work. CHOICE OF TEST STRUCTURE When i t was learned that some buildings at the s i t e of the 1964-1965 New York World's F a i r might be available for te s t i n g , a preliminary sur- vey of a l l potential t e s t structures was made. Several highly unusual structures u t i l i z i n g free-form s h e l l s and other l i t t l e used s t r u c t u r a l forms were b u i l t for the New York F a i r . Although t e s t s of these struc- tures would have been valuable, the a p p l i c a b i l i t y of the r e s u l t s would have been limited. Consequently, buildings of commonly used s t r u c t u r a l forms were chosen. Three structures were selected for the t e s t s . Two of these were common types of s t e e l frame construction. One of the s t e e l frames was a seven (7) story tower fabricated with standard s t r u c t u r a l shapes; i t was tested to determine i t s dynamic response. The other s t e e l structure was of (8) l i g h t frame and open web s t e e l j o i s t construction. Portions of t h i s building were tested to destruction under both v e r t i c a l and l a t e r a l loads. 1-3
This paper reports tests of the t h i r d structure, a multipanel reinforced concrete waffle slab. During the f a i r , t h i s b u i l d i n g was known as the "Rathskeller"; i t was located beneath a portion of the "Belgian V i l l a g e " shown i n Fig. 1. The approximate outline of the roof of the "Rathskeller" i s indicated on t h i s view by the dashed l i n e s . The t e s t structure was a box-like b u i l d i n g measuring approximately l80 f t by 120 f t i n plan and 20 f t i n height. A 2-ft t h i c k waffle slab supported on columns about 30-ft on center formed the roof of the "Rathskeller". The f l o o r was a 2.5-ft t h i c k reinforced slab that formed a r a f t foundation f o r the structure. Outside walls of the b u i l d i n g were 12 i n . t h i c k . The roof plan and t y p i c a l elevations are shown i n Fig. 2 and 3- OBJECT AND SCOPE In recent decades there has been an I n t e n s i f i c a t i o n of s t r u c t u r a l labor- atory investigation. Results from such work, combined with p r a c t i c a l experience, have formed the basis f o r rapid advances i n s t r u c t u r a l design procedures. Although some observations of ax:tual structures have been made, f i e l d t ests have been hampered by high costs and lack of the con- t r o l s available i n the laboratory. The tests reported i n t h i s paper were carried out (a) t o obtain data from t e s t s t o destruction of a f u l l - s i z e structure, (b) t o correlate t h i s i n - formation with the results of laboratory t e s t s , and (c) to adapt labora- t o r y procedures to f i e l d t e s ts. As o r i g i n a l l y planned, the tests on the "Rathskeller" were intended to investigate: ( l ) shear strength of an i n t e r i o r panel, ( l l ) strenght of column-to-slab connections at edge panels, ( i l l ) "strengthening" of a slab due t o "arch action" when a single panel i s loaded. Behavior a f t e r f i r s t f a i l u r e under each pattern of loading was also studied. PROGRAM OUTLINE Preliminary investigations of possible t e s t buildings and i n i t i a l planning was started i n December 1965. By the end of January I966, i t was decided tha t the "Rathskeller" would be tested. Detailed planning, design of 1-h
loading equipment and acquisition of both instruments and equipment was carr i e d out over the next two months. Demolition of the temporary structures on top of the "Rathskeller" and removal of non-structural i n t e r i o r f i x t u r e s was completed in March, 1966 and preparation began for the f i r s t t e s t . Waterproofing was cleaned from the roof to expose the concrete, and holes were d r i l l e d in the roof and floor to accommodate the loading equipment. F i n a l preparations began two weeks before the f i r s t t e s t was scheduled. Load equipment was i n - s t a l l e d , and a l l instrumentation was attached and calibrated. The f i r s t of three t e s t s was conducted l a t e in A p r i l 1966. Each t e s t was carried out over a two-day period. On the f i r s t day service loads and moderate overloads were applied. Since a l l s t r a i n s and deflections measured during t h i s phase of loading were expected to be small, the t e s t s were commenced in the l a t e afternoon and were completed during the night to avoid e f f e c t s on the readings of d i r e c t sunlight. Tests to destruction were completed the second day in each case. The t h i r d and f i n a l t e s t was completed ear l y i n May 1966. After t h i s , one week was used to take samples of s t e e l and concrete and to obtain other informa- tion concerning the physical properties of the stmcture. REPORTS The Building Research Advisory Board, administrator for the project, re- quested that highly detailed reports be prepared on the World's F a i r t e s t s . The report on the waffle slab t e s t s i s divided into two separate papers. This f i r s t paper contains a detailed description of the structure and t e s t procedures. Results are analyzed and compared with laboratory investiga- tions and building code requirements; detailed t e s t data are presented in Appendix B. A second paper describes t e s t techniques m considerable de- t a i l , so that investigators conducting future f i e l d t e s t s can benefit from the experiences gained during t h i s work.^9) 1-5
DESCRIPTION OF TEST STRUCTORE DIMENSIONS AMD REINFORCING DETAILS A plan of the "Rathskeller" roof slab i s shown i n Fig. 2. The waffle slab roof area was bounded by column Lines B, E, 1, and 7- Between column Lines A and B, the roof was an 8-in. deep one-way slab continuous over Line A-B. Overall depth of the waffle slab portion of the structiare was 2k i n . Along Line E there was a 30.375-in. by 45-in. wide edge beam. Beams between columns and s o l i d areas surrounding the columns were obtained by omitting the domes. Within each panel, domes were spaced t o provide a 3-ft center-to- center r i b spacing and a 6-in. stem width at the bottom of the r i b . The domes were l6 i n . deep. This provided a nominal slab thickness of 8 i n . over each dome. Typical sections of the b u i l d i n g are shown i n Fig. 3. Inside the b u i l d i n g , a mezzanine ran along three sides between column Lines 1 and 2, 6 and 7, and A and B. The ex t e r i o r walls of the buil d i n g were 12 i n . t h i c k . I n t e r i o r columns i n the t e s t area were 26 x 26 i n . Several large openings were provided i n the wa l l along the south face of the b u i l d - ing. Line E. Column E3 was 12 x 32 i n . and Colimm Ek was 12 x 24 i n . A view of the south w a l l i s shown i n Fig. k. The "Rathskeller" f l o o r was the top STorface of a r a f t foundation that supported the structure. I t consisted of a s o l i d reinforced concrete f l a t plate having a nominal thickness of 28 i n . A plan view of the founda- t i o n i s presented i n Fig. 5« Typical reinforcement arrangements f o r the roof slab and columns are given i n Fig. 6 and 7, respectively. In the slab, a l l reinforcement l y i n g para- l l e l t o column Lines A through E was placed f i r s t . Temperature reinforce- ment i n the slab was No. h bars on 12 i n . centers i n both directions. The temperature reinforcement p a r a l l e l t o column Lines 1 through 7 was placed k i n . below the top of the slab. Ties f o r the columns were No. 3 bars placed at 12 i n . centers. 1-6
Schedules of the reinforcement and controlling dimensions for the columns, r i b s , beams and column s t r i p s are l i s t e d i n Appendix B, Tables B-1 to B-5. S i m i l a r l y , designations of the r i b s , beams and column s t r i p s are shown i n F i g . C-1 to C-3 of Appendix C. Closed rectangular s t i r r u p s were used i n the beams l i s t e d i n Table B-3. MATERIALS During the post-test investigation to determine the properties of the concrete and the location and properties of the reinforcement, several samples of the s t e e l and concrete were taken. Coupons of the r e i n f o r c i n g bars with lengths of about 40 i n . were taken at locations where no y i e l d - ing was observed during the t e s t s . Cores with a nominal diameter of 4 i n . were taken from sound concrete i n each t e s t area. Locations of these samples are shown in F i g . 8 and 9. A l l specimens were shipped to the PCA Laboratories where t h e i r physical properties were determined. Reinforcement i n the structure was specified as "intermediate grade b i l - l e t s t e e l " with deformations conforming to ASTM Standard A305-56. Samples of reinforcement taken from the slab a f t e r the t e s t s were completed were tested i n tension after having been saw cut to lengths of 30 i n . Resiilts of a l l tension t e s t s are presented m Appendix B, Table B-6; average v a l - ues are summarized in Table I . A t y p i c a l s t r e s s - s t r a i n curve obtained from the No. 11 bars i s shown i n Fig. 10. This s t e e l met the require- ments of ASTM designation A15, intermediate grade, as assianed i n the design. TABLE I AVERAGE PROPERTIES OF REINFORCING BARS Bar Size Average Yiel d Stress, k s i Average Ultimate Stress, k s i 8 46.1 78.6 9 53.3 89.7 10 42.7 79.8 11 41.9 80.2 1-7
Concrete cores 1, 2, and 3 were taken from the slab before t e s t i n g started. The remainder of the cores were obtained a f t e r the tests were completed. The rough ends of the cylinders were trimmed by a diamond saw before t e s t - ing. Diameter, height, and height-to-diameter r a t i o of the cylinders a f t e r they were trimmed are l i s t e d i n Table I I . Diameters were approximately 3.75 i n . while heights of the cores ranged from about 2.5 t o 7'5 i n . Cy- linders with a height-to-diameter r a t i o less than one were used f o r s p l i t cylinder t e s t s . A l l others were tested i n compression. Table I I also gives correction factors f o r the e f f e c t s of the height-to- depth r a t i o (â¢'â¢Ì^ and the presence of horizontal r e i n f o r c i n g s t e e l , The "Equivalent Cylinder Strength, f ^ " l i s t e d i n Table I I I i s the pro- duct of the correction factors and the measured compressive strength of each core sample. Tensile strengths presented i n Table I I I are based on measured load without correction. Specifications f o r concrete i n the slab called f o r 0.75-in. maximum size aggregate and a compressive strength of 3»500 p s i a f t e r 28 days. The con- crete contained normal weight aggregat^. I t s u n i t weight was about 15O pcf at the time of te s t . Ends trimmed from the cores were subjected t o petrographic analysis at the PCA Laboratories. Aggregate appeared to be chemically i n e r t and physically sound. Coarse aggregate was p r i n c i p a l l y quartz and quartzite plus a small proportion of granite and g r a n i t i c gneiss. Fine aggregate was p r i n c i p a l l y subangular t o rovinded quartz and feldspar. The con- crete was not air-entrained. A i r content was 1 to 1.5 percent. HESIGS During the Fair, the i n t e r i o r of the structure was used as a restaurant. Atop the waffle slab roof were temporary timber structures with pedestrian walks between the buildings. The walks were made of flagstone set i n a mortar bed, which, i n addition t o the membrane waterproofing, exerted a load of 47 psf on the waffle slab. A view of the roof area i s shown i n Fig. 1. 1-8
TABLE I I CONCRETE CORE DIMENSIONS AND STRENGTH CORRECTION FACTORS Core No. Height, b, inches Diameter, d, inches ^/d Correction Factor for h/d Correction Factor for Steel Core No. Height, h, inches Diameter, d, inches Correction Factor for h/d Correction Factor for St e e l 1 6.hk 3.73 1.73 0.98 â lU 3.kO h.19 3.73 3.73 0.91 1.12 0.92 â 2 5.00 3.73 1.34 0.95 1.08 15 3.56 3.71 0.96 â â 3 5.62 3.73 1.51 0.97 1.08 16 k.ko 3.73 1.18 0.93 â k k. 50 3.73 1.21 0.93 â 17 2.60 7.67 3.73 3-70 0.70 2.08 â 1.08 5 5.60 3.73 1.50 0.97 â 18 3.39 7.31 3.73 3.73 0.91 1.96 â 1.13 6 3.54 3.74 0.95 â â 19 2.87 k.ok 3-73 3-73 0.77 1.08 0.92 â 7 3,47 3.73 0.93 â â 20 5.83 3.73 1.56 0.97 1.08 8 9 3.74 6.01 7.58 3.73 3.73 3.73 1.00 1.61 2.03 0.97 1.08 1.08 21 22 6.38 2.99 7.64 3.75 3.74 3.74 1.70 0.80 2.04 0.98 â 10 3.80 k.hl 3-72 3.73 1.02 1.18 0.93 â 23 7.62 3.75 2.03 â 1.08 11 k.ok 3.72 1.09 0.92 â 12 3.33 3.68 0.91 â â 13 3.60 3-72 0.97 â â
TABLE I I I PROPERTIES OF CONCRETE Specimen Compressive Equivalent Tesnile Specimen Compressive Equivalent Tensile Location Strength 6 X 1 2 -in. Strength,* Location Strength 6 X 1 2 -in. Strength,* of Core, Cylinder p s i of Core, Cylinder p s i p s i Strength, fi p s i Strength, 1 5360 5250 12 1*00 2 52I4O 5390 - 13 â â 390 3 5170 51Ì 20 - Ih 6U9O 5970 450 1* 5020 1Ì 670 - 15 â â 310 5 1Ì 300 1*170 - 16 5190 1*830 - 6 â â U30 17 5420 5850 1*00 7 â â 3*Ì 5 18 5020 5670 1*80 8 6230 6530 370 19 5800 531*0 hio 9 5200 5620 - 20 51*60 5720 - 10 5800 5390 21 5260 5150 - 11 6760 6220 - 22 3620 3620 1*60 23 3260 3520 - * S p l i t Cylinder t e s t
The e n t i r e roof was designed f o r a l i v e load of 300 psf as required by the New York City Building Code f o r sidewalks; combined dead and l i v e loads from structures atop the roof did not exceed t h i s value. Dead loads f o r each t e s t panel--computed using a u n i t weight f o r concrete of 150 pcf and mea- surements of overall slab depth--are l i s t e d i n Table IV; the average com- puted dead load was about 220 psf. A note on the plans f o r t h i s . b u i l d i n g indicated i t was designed f o r a t o t a l load, l i v e plus dead, of 513 psf. TABLE IV AVERAGE DEAD LOAD OF PAMELS Panel 3,U-B,C U,5-B,C 3,U-C,D U,5-C,D 2,3-D,E 3,i^-I',E U,5-D,E 5,6-C,D Depth of Area of Average Slab, Panel, Dead Load f t f t ^ psf 1.89 923 207 1.92 923 212 1.96 893 227 1.9^ 893 22U 1.95 969 22U 2.02 9^7 233 1.99 9^7 228 1.95 91U 220 The b u i l d i n g was designed t o meet the provisions of the 1956 ACI Building Code.Ì -'-Ì ^ The "Elastic Analysis" outlined i n Chapter 10 of that Code was used to determine design moments and shears. CONDITION PRIOR TO TESTING In preparation f o r tests of the structure, the frame buildings and the f l a g - stone walks were removed from the roof of the "Rathskeller." Heavy con- struction equipment was used f o r these operations. During the removal of debris, material was heaped over r e l a t i v e l y small areas of the structure. Load i n t e n s i t y could not be estimated and could l i k e l y have been m excess of previous superimposed loads. Thus i t was not surprising t o f i n d p r i o r to t e s t i n g that certain areas of the structijre were severely cracked. An overa l l inspection of the "Rathskeller" was made before the tests were started. In p a r t i c u l a r , cracking of the b u i l d i n g was noted and deviations from s t r u c t u r a l plans were investigated. 1-11
Cracks were observed throughout the roof area running, i n general, i n a di r e c t i o n p a r a l l e l to the numbered column l i n e s . A f l a t black paint covered the underside of the waffle slab. Consequently, cracks were re a d i l y v i s i b l e . White stains from leaching through the slab accented some of these cracks and indicated t h a t the cracks penetrated through the 8-in. slab thickness above the pan openings. OveraJl crack patterns i n the t e s t area as w e l l as a close- up view of t y p i c a l cracks are shown i n Fig. 11. Cracking i n the i n d i v i d u a l t e s t areas viewed from the underside of the slab i s shown i n Fig. 12, 13, and 14. Although a portion of the observed cracking could be a t t r i b u t e d t o shrinkage of the concrete, both the extent of cracking and the crack patterns suggested another cause. Flexural cracks caused by loads on top of the waffle slab were discounted as the cause since many of the cracks occvirred where the con- crete would be i n compression from such loading. Further investigation indicated that cracking of the waffle slab probably was caused p r i m a r i l y by settlement of the structure. From l e v e l sightings, con- tours of defle c t i o n were drawn as shown i n Fig. 15. A point at the north- center of Panel 4,5-B,C was taken as the zero reference f o r deflections. Assuming that the roof slab was o r i g i n a l l y l e v e l , i t i s seen th a t settlement may have exceeded seven inches at the southwest comer of the structure. Further consequence of t h i s settlement was observed along the south face of the b u ilding. The wall between column Lines 1 and 2 was severely cracked diagonally as shown i n Fig. l6. Similar diagonal cracks were noted i n the edge beam along column Line E between Lines 2 and k. This cracking probably had considerable influence on the results of Test I I , as w i l l be discussed l a t e r . During construction of the b u i l d i n g , a very soft material was encountered under the southwest portion of the structure. I n addition, p i l e s that were used t o support a structure t h a t had previously occupied the s i t e of the "Rathskeller" were found i n the central portion of the foundation excavation. These p i l e s were cut o f f at about the l e v e l of the bottom of the foundation slab. Such foundation conditions should be expected t o produce a s e t t l e - ment pattern s i m i l a r to that indicated i n Fig. 15. 1- 12
Between column Lines 2 and 3, 3 and h, and U,and 5Ì intermediate reinforced concrete columns were cast t o support the a r c h i t e c t u r a l facing along the south wall. Locations of these columns i s shown i n Fig. k. Although they were not intended t o be part of the s t r u c t u r a l system they were cast mono- l i t h i c a l l y with the edge heani, consequently, these coltimns acted to support the roof slab. Since none of these columns between the p r i n c i p a l supports was considered i n the s t r u c t u r a l design, no negative moment reinforcement was added above them i n the edge beams or i n the slab p a r a l l e l t o the beams and cracks developed i n the slab. Before t e s t i n g , the columns were cut away from the edge beams. 1- 13
STRUCTURAL TESTS OUTLINE OF TESTS Three load t e s t s were conducted on separate areas of the waffle slab roof. Locations of loaded panels f o r each of the three te s t s are i n - dicated i n Fig. 17, 18, and I9. The t e s t numbers indicate the chrono- l o g i c a l order of tes t i n g . I n a l l t e s t s , loads were applied through concentrated reactions evenly d i s t r i b u t e d over the panels t o approximate a uniform load. Test I covered the four panels withi n column Lines 3,5-B,D. This t e s t was intended t o determine the shear strength of the slab at Column Ck. A l l four panels were loaded during the t e s t . I n Test I I , the slab- column connections at ex t e r i o r panels were investigated. The loaded area i n Test I I included the three panels along the south edge of the bui l d i n g between column Lines 2 and 5 and column Lines D and E. A l l three panels were loaded during the f i r s t phase of the t e s t . I n the second phase of Test I I , Panel i^,5-D,E and the adjacent h a l f of Panel 3,if-D,E were loaded. I n Test I I I , only the single Panel 5,6-C,D was loaded. This loading was intended t o show the significance of i n - plane forces on a panel f a i l i n g i n flexure. A f t e r i n i t i a l s t r u c t u r a l f a i l u r e occurred i n each t e s t , loading was continued t o determine reserve strength. I n Tests I and I I , the post- f a i l u r e loading was terminated when i t appeared that f u r t h e r loading would damage the structure i n the area of the next t e s t . TEST PREPARATION The structure was stripped t o the concrete both inside and out. Buildings and the flagstone pedestrian walks were cleared from the top of the slab. V/here possible, the decorative facing was removed from the outside walls. Paneling and a l l f i x t u r e s were removed from the i n t e r i o r of the building. On the roof, the t e s t areas were fur t h e r cleaned to remove what remained 1- Ik
of the waterproofing membrane. Before any tests were conducted, photo- graphs were taken of a l l walls and columns to record t h e i r condition. I n Test I , computed shear strengths of the roof and foundation slabs were about the same. To provide an adequate margin against a shear f a i l u r e of the foundation slab, a reinforced concrete sheaxhead was cast at the base of Coliann Ch. Details of the shearhead are shown i n Fig. 20. Nominal concrete strength was ItOOO psi at seven days. The sequence of work i n preparation f o r each t e s t was similar. Detailed information describing techniques and special equipment i s given else- where . (9) Holes were d r i l l e d i n t o the foundation and through the roof slab at each of the load points. Holes through the roof were 1-in. dia- meter. Next, the slab thickness was measured, instrumentation i n s t a l l e d , and cracks mapped i n the t e s t area. F i n a l l y , the loading equipment was put i n place. After the t e s t was completed, loading equipment was re- moved and cracks were again mapped i n the t e s t area. Photographs were then taken to record the condition of the structure a f t e r the t e s t . LOADING SYSTEM Hydraulic rams were used to apply load to the structure. To approximate uniform load on the t e s t panels the rams were evenly d i s t r i b u t e d over the t e s t panels. Nominal spacing of the loads f o r each t e s t i s given j n Fig. 17, l8, and I9. Individual rams were moved s l i g h t l y o f f these grids so that holes d r i l l e d through the roof slab would not h i t major reinforce- ment or pass through the r i b s . A schematic drawing of the loading equipment i s shown i n Fig. 21; de- t a i l e d information i s provided elsevrhere.^9) On top of the waffle slab, a hydraulic center-hole ram was placed over a steel load d i s t r i b u t i o n plate centered on a hole d r i l l e d through the roof. One end of a 7-wire prestressing strand was coupled to the ram and passed through the roof slab. The other end was coupled to a rock anchor set m the foundation. As hydraulic pressure was applied, the ram reacted against the upper strand g r i p and pushed down on the roof slab. 1-15
Two e l e c t r i c a l l y driven pumps were used to supply hydraulic pressure. (9) Low load i n t e n s i t i e s f o r each t e s t were applied with only about 20 per- cent of the t o t a l ntanber of rams connected. As higher i n t e n s i t i e s of load were required, additional rams were activated. This procedure was used so t h a t , f o r any load i n t e n s i t y , hydraulic pressure was at a l e v e l high enough t o reduce the importance of ram f r i c t i o n . For each arrange- ment, active rams were evenly spaced over the t e s t area as indicated i n Fig. I T , 18, and 19. Table V l i s t s pertinent data concerning the load- ing arrangement. INSTRUMENTATION The condition of the structure before and a f t e r each t e s t was recorded by photographs. Before each t e s t , cracks v i s i b l e i n the t e s t area on the underside of the waffle slab were marked with white chalk. A com- posite photograph of the t e s t area was then made before t e s t loads were applied. Several composite photographs were also taken during the t e s t s ; however, new, unmarked cracks were not easily discernible. A f t e r each t e s t was completed, cracks were again marked with chalk and a f i n a l composite photograph was taken. Both s t i l l and movie cameras were used t o photograph s t r u c t u r a l damage a f t e r the tests. During the t e s t s , 16 mm and 35 mm time-lapse cameras were focused on c r i t i c a l regions. In Test I , two cameras were trained on the underside of the roof slab at Column Ck where punching occurred. In Test I I , cameras were used t o record behavior of the structure i n the areas about Colvmins E3 and El*-. An o v e r a l l view of the loaded panel i n Test I I I was taken from the top of the roof slab. For these detailed observations, cameras were operated during the time load was being increased and f o r a short period a f t e r the higher load stage was reached. Deflections of the roof slab were measiored using precision levels sighting on targets attached t o the slab. A description of these t a r - gets and of the instruments and techniques used t o read them i s given 1- 16
TABLE V ARRANGEMENT OF HYDRAULIC LOADING EQUIFMENT DURING TESTS Test Load Number Panel Area Remarks No. Number of Rams Per Ram, Per Test Ft^ For a l l of Test: 1-T kS 75-68 Ram pressure i n panels 3,4-B,C I 8-19 10k 34.93 and 3,4-C,D controlled by pump 1. 20-28 208 17.49 Ram pressure i n panels 4,5-B,C and 4,5-C,D controlled by pirnip 2. For f i r s t part of t e s t : Ram pressure i n panel 2,3-D,E and one-half panel 3,4-D,E con- t r o l l e d by pump 1. 1-7 36 79-55 Ram pressure i n panel 4,5-D,E I I 8-19 8k 34.09 and one-half panel 3,4-D,E con- t r o l l e d by pump 2. 20-27 k2 34.09 For second part of t e s t : Ram pressure i n panel 4,5-D,E and one-half panel 3,4-D,E con- t r o l l e d by pimp 1. 1-7 Ik 65.27 For a l l of t e s t : I I I 8-20 ko 22.85 Ram pressure i n panel 5Ì 6-C,D 21-38 80 11.42 controlled by p\jmp 1. TABLE V I ACTIVE DEFLECTION LOCATIONS AND STRAIN GAGES Test No. Deflection Location No. Strain Gage No. I 1-6, 9-11, 17-42, 44-47, 59, 60 50-56, 1-13, 20, 21, 30-42, 60-66, 68 I I 8-11, 13-16, 22, 24, 26, 3k-k6, 48-56, 58-60 30-32, 8-11, 14-15, 21, 35-38, 42-45, 61, 62, 64, 66-70 I I I 6, 7, 11, 12, 20, 26-29, 33, 38-43, 46, 47, 54-57, 32, 61 16-19, 46-51, 71-74 1-17
elsewhere.(9*13) uvo levels located on the mezzanine were used t o observe deflections from the underside of the roof. These instruments sighted on targets located at the middle of each panel and at midspan of the column l i n e s . A t h i r d l e v e l was used t o record movement of targets mounted on top of the roof at the centers of columns i n the t e s t areas. A l l levels were referenced t o a standard mounted outside the structure. Designation and location of a l l targets used i n the three t e s t s are given i n Fig. 22. Those read during each t e s t are l i s t e d i n Table V I i Most locations f o r measviring deflections were common to a l l three t e s t s ; how- ever, locations remote from the loaded area of a p a r t i c u l a r t e s t were not monitored. E l e c t r i c a l resistance s t r a i n gages were used t o obtain strains i n r e i n - forcement and i n the concrete at selected locations. ManuaJ-ly operated switch boxes and portable s t r a i n indicators were used t o monitor the gages. Table VI also l i s t s the s t r a i n gages monitored during each t e s t . Designation and location of these gages are shown i n Fig. 23 and 2h. A number of gages i n Test I and Test I I areas were read during both t e s t s . Gages i n the Test I I I area were monitored only during Test I I I . A l l gages were waterproofed t o reduce ef f e c t s of moisture on indicated strains. Typical gage i n s t a l l a t i o n s on top reinforcement of the slab are shown i n Fig. 25. Each active gage was provided with a temperature compensating gage mounted on a separate, unstressed piece of steel or concrete. The compensating gages were placed near t h e i r companion active gage dviring the tests. I n addition t o the gages on the slab, one gage was mounted on the concrete on each face of Column Ch. S i m i l a r l y a gage was placed j u s t below the edge beam on the reinforcement of Coltmin E 3 . Hydraulic pressure was used as the primary means of detexmining applied load. For f u r t h e r control six load c e l l s were placed i n the t e s t system t o measure d i r e c t l y the applied load at selected points. Locations of the load c e l l s i n each t e s t are shown i n Fig. 26. They were read by a portable s t r a i n indicator. Ì -Ì ^Ì Pressure was meas\ired i n three independent 1-18
ways. Each pump had an i n t e g r a l Bourdon type d i a l indicator pressure gage. These gages were used i n c o n t r o l l i n g pressure during the t e s t s . Bourdon-type s t r i p chart recorders were placed i n the hydraulic l i n e s from each pump. These recorders were used p r i m a r i l y t o check pres- sure levels and determine pressure f l u c t u a t i o n during hold periods of loading. A t h i r d check of pressure l e v e l was provided by a pressure c e l l placed i n the hydraulic system. PressTore i n the c e l l was sensed by e l e c t r i c a l resistance s t r a i n gages and a s t r a i n indicator. A l l equipment, the rams, load c e l l s , and pressure indicators, were c a l i - brated at the PCA Laboratories before and a f t e r the t e s t s . Detailed information concerning the equipment and i t s c a l i b r a t i o n i s given elsewhere.(9) Two methods were used t o determine thickness of the t e s t slab. Level sightings above and below the slab were taken at r i b intersections and at i n t e r v a l s along the edge beam on column Line E. These readings were referenced t o sightings taken at a core hole d r i l l e d through the slab. A d i r e c t measurement of slab thickness was made at the hole. I t was then possible t o determine slab thicknesses from the l e v e l readings. At each hole th a t was d r i l l e d through the roof at a load point, a specially constructed caliper was used t o measure slab thickness. This \ i n i t incorporated a 0.001-in. d i a l gage and was capable of mea- suring depths i n the 8 i n . and 2k i n . t h i c k slab regions. Further d e t a i l s of t h i s caliper are given i n Ref. 9- Average thickness of the panels i n the r i b areas and m the s o l i d areas surrounding the columns are shown m Fig. 27; depth of the edge beam along coliamn Line K i s also included. CONDUCT OF TESTS Afte r a l l equipment and instrumentation was i n place and had been checked f o r proper operation, an I n i t i a l set of "zero applied load" readings was taken. Load i n t e n s i t y of l*-7 psf was then applied t o equal the load f o r the flagstone walks and waterproofing that had 1- 19
