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reached, a shear f a i l t i r e occurred at Column Eh. A photograph of the f a i l u r e zone i s shown i n F i g . ko. Load at f a i l i i r e was equal to added dead plus about 2.3 l i v e loads. The load-deflection data i n Appendix B show greatly increased deformation as load i n t e n s i t y increased be- yond 607 psf. A f t e r f a i l u r e , i t was possible to maintain a load i n t e n s i t y of ^66 psf. The slab was deflected f a r t h e r u n t i l a secondary shear f a i l u r e occurred at Column Dl* under an applied load of 59^ psf. To prevent damage i n the Test I I I area. Part B of Test I I was terminated when Column Bk punched through. Deflections at the conclusion of Test I I are shown i n F i g . hi. The r e s i d u a l deflections indicate considerable separa- t i o n of the slab from the columns both along the edge of the building and at Column Dk. Cracking on the underside of the slab a f t e r the t e s t i s shown i n F i g . 42. Test I I I . The f i n a l t e s t i n the s e r i e s c a r r i e d out on the waffle slab consisted of loading Panel 5^6-C,D. This panel was the second bay i n from the nearest edge of the building. From previous t e s t s , the four columns along column Line k from Line B to Line E suffered damage from shear. In Tests I and I I , i t was observed that e f f e c t s of loading were small outside the loaded areas. Consequently, i t was not expected that the condition of the slab along column Line k- would have a major influence on the re- s \ a t s of Test I I I . Deflections at an applied load of 3^5 psf (added dead plus 1.0 l i v e load) are shown i n F i g . 43. At the center of the t e s t panel, deflection was 0.26 i n . Deflection of the slab at midspan of column Lines C and D was about 0.18 i n . , twice that measured at midspan of the boundaries at column Lines 5 and 6. Load deflection relationships for the t e s t panel are shown i n F i g . kh for center of the panel and at midspan of the two column s t r i p s along Lines 5 1-26
and 6. The curves are very nearly l i n e a r for loading up to 6hh psf. Resi- dual deflection measured when applied load was released a f t e r the added dead load plus one, plus 1-3, and plus two l i v e loads were nearly zero. Strains measured by gages on the concrete also showed l i n e a r response to load up to 6kk psf applied load. Load-strain data are presented i n F i g . 45 f o r gages on the bottom of the slab adjacent to Columns C3, D5, and D6. Measured s t r a i n s shown i n F i g . U5 did not exceed 0.0002 at a load of 6hh psf. Load-strain data for gages mounted on reinforce- ment in the loaded panel are given i n Appendix B. Some of the gages on the top la y e r of reinforcement showed e r r a t i c behavior. However, gages on the bottom reinforcement responded as expected. S t r a i n s i n the bot- tom reinforcement at the center of the panel were about O.OOOU for an applied load of 6kh psf. F i r s t s i g n i f i c a n t cracking was observed at an applied load of 10U6 psf. Cracking was seen on the top of the slab at Column D6. Similar cracking was observed at a l l the columns when loading reached 1U89 psf. These cracks were located i n the loaded panel a few inches inside the bound- ary of the colxanns. Negative moment cracking was v i s i b l e i n Panel U,5-C,D at lk89 psf applied load. This cracking was si m i l a r to that observed during Test I . The crack was p a r a l l e l to the edge of the loaded panel and was located where negative moment reinforcement ended. Crack width was about 0.125 m. under an applied load of 1730 psf. Deflections measured at an applied load of 1730 psf (added dead plus about 5.6 l i v e loads) are given m F i g . k6. At the center of the loaded panel, deflection was over 2 i n . There was also a downward deflection at the center of adjacent Panels 5^6-B,C and 5,6-D,E, while the three panels bounded by column Lines U, 5, B, and E, were deflected upward. A punching f a i l u r e occurred a t Column C5 at an applied load of 1972 psf. This load i s equal to added dead plus 6.4 l i v e loads. A view of the f a i l u r e area at the top of the slab i s shown i n Fig. k j . I t i s seen 1-27
that negative moment reinforcement over the column was pulled from the slab. The close view of Colimin C5 i n F i g . kQ shows that some of the reinforcement was spliced d i r e c t l y over the column. This was not observed a t any other location. Load-strain data f o r the f i n a l stage of Test 111 are given i n Appendix B. At most gage locations, reinforcement s t r a i n s were proportional to load u n t i l applied load was about 1000 psf. Beyond t h i s load i n t e n s i t y , s t r a i n s increased more rapidly as load was increased. Yielding of reinforcement i n the positive moment region of the slab was f i r s t detected at Gage No. 71 under an applied load of about 15OO psf. This gage was mounted on the bottom reinforcement of the column s t r i p along column Line 5 as indicated i n F i g . 24. At an applied load of about 1900 psf. Gages 72 and 73 a l s o indicated reinforcement y i e l d . Just before shear f a i l u r e at Column C5, Gage jk indicated that y i e l d i n g was imminent. None of the s t r a i n s measured i n the top layer of reinforcement indicated y i e l d i n g of the negative moment reinforcement. After slab punching occurred at Column C5, load was dropped to zero. Load was again applied a f t e r the slab had been examined. At 14^9 psf applied load (added dead plus 4.6lO l i v e l o a d s ) , the slab f a i l e d i n shear a t Column D5. Applied load immediately dropped to about 6kh psf (added dead plus 2.0 l i v e loads). This was the maximum load that could be maintained a f t e r punching at Columns C5 and D5. F i g . 49 indicates deflections under an applied load of 644 psf Just be- fore load was removed and the t e s t was ended. The pattern of deflections shows the t e s t panel was s t i l l i n t a c t along column Line 6. Although load was applied only to Panel 5,6-C,D, substantial downward deflections were measured i n the previously tested panels adjacent to the axea of Test I I I . These deflections occurred as the r e s u l t of punching a t Columns C5 and D5 and at columns along Line 4. In the aorea along Lines 4 and 5, the slab 1-28
was simply pushed down since the columns offered very l i t t l e support. F i g . 50, taken at the end of Test I I I , shows that the slab was pushed down nearly a foot at Colvmin D5. Major cracks on top of the slah a f t e r Test I I I are shown i n Fig. 51. A l l of the cracks are associated with negative moments induced during the t e s t . Except for the cracks at Columns C6 and D6, crack locations were very near cut off points f or negative moment reinforcement. Crack- ing on the bottom of the slab a f t e r the t e s t i s seen i n the composite photo, Fig. 52. Extensive cracking i s v i s i b l e i n the slab area near Columns C5 and D5. The coliamn s t r i p between Columns C5 and D5 was severely cracked also. These cracks were formed a f t e r the shear f a i l u r e at Columns C5 and D5. 1-29
