Click for next page ( 37

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement

Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 36
36 length of penetration of epoxy seal Figure 3.42. Very limited penetration of the epoxy repair. The web sections were cut into 16-in. strips, as shown in Figure 3.43. One strip was extracted from each of the four ends of the two girders. Each specimen was turned on its side and subjected to a bending test, as shown in Figure 3.43. The struc- tural testing was performed to find the cracking moment and tensile capacity of the specimens. The supports were set 18 in. apart. A two-point loading system was used, with the two points 6 in. apart. Table 3.3 provides the description and prop- erties of each specimen. 3.3.4 Test Results Specimen S1L (No End Zone Reinforcement, Repaired) Figure 3.43. The 16-in.-wide strips and test setup. The last recorded load point was 47.8 kips, but the speci- men actually reached a load of 56 kips before failure. While testing, a crack began to form at the bottom center of the Table 3.3. Properties of test specimens. Girder Specimen Specimen #1 Specimen #2 (Without Special End (With Special End Reinforcement) Reinforcement) Test Specimen S1L S1R S1MS S2L S2R Location of the Specimen Left End Right End Midspan Left Right Repaired (R) or R UR UR R UR Unrepaired (UR) No cracks End Reinforcement Design No special end reinforcement LRFD Proposed Reinforcement on Each 4 #4 @ 1.25 in. 7 #5 @ 4 #6 @1.31 in. + Face 1.31 in. 3 #4 @ 1.25 in. Dimensions b (width) = 16 in., h (depth) = 6 in., l (length) = 24 in. Concrete Strength 8,000 psi

OCR for page 36
37 beam due to the bending stress, as shown in Figure 3.44(a). The lack of a bearing surface contributed to premature fail- ure, as shown in Figure 3.44(b). Figure 3.44(c) shows cracks that formed on the bottom on the specimen during testing. Before testing, this specimen had a crack along the length of a vertical bar. It appeared to have formed during prestress release. This preexisting crack was not visible before the saw cutting and was not grouted with epoxy. The final failure cracking was a continuation of this preexisting crack. The fail- ure load resulting in this test may be considered to be unreli- able due to the setup issues (bearing and data acquisition). An important lesson learned, besides refining the setup for future testing, was that the epoxy repair used may not be effective in restoring the tensile capacity, and may not totally fill and seal all cracks. (a) Flexural Cracking Specimen S1R (No End Zone Reinforcement, Unrepaired) The specimen failed at a load of 109 kips with a maximum deflection of 0.236 in. This maximum load was much greater than that of the repaired Specimen S1L. The unrepaired sec- tion had larger bearings, each with a 4 12-in. contact area. This specimen also did not contain a crack along its rebar as observed in Specimen S1L. Figure 3.45 shows the specimen setup before and after failure. Specimen S1MS (No End Zone Reinforcement, Midspan Strip) This specimen had no cracks, and therefore no repair was required. The specimen failed at a load of 103 kips and reached (b) Bearing Failure at the Support a maximum deflection of 0.251 in. Figure 3.46 shows both ends of the specimen after failure. The cracks formed vertically along the rebar. Specimen S2L (LRFD End Zone Reinforcement, Repaired) Similar to Specimen S1L, this specimen contained a crack along the rebar before testing, as shown in Figure 3.47(a). The specimen failed at 103.4 kips and reached a maximum deflection of 0.260 in. Figures 3.47(b) and (c) show both ends of the specimen after failure. This specimen also split along the direction of the rebars at failure. Figure 3.47(d) shows how the splitting occurred through the epoxy injection. Instead of the concrete failing, the epoxy-crack separated. This shows that the epoxy repair of these specimens did not appear to be effective. The rest of the cracking occurred in the same (c) Bottom Surface at Failure planes as the pre-existing crack along the rebar, as shown Figure 3.44. Test specimen S1L after failure. in Figure 3.47(e).