For samples with 1% fiber content, the sample with coarse aggregates showed slightly better properties than the one without coarse aggregates, which means that the use of 1% fiber content did not ensure the strain hardening behavior even when coarse aggregates were excluded. . nominal strength Pn; the calculated lateral load corresponding to the event when the extreme concrete compression fibers reach the maximum allowable deformation.
INTRODUCTION
Background and motivation
Also, HPFRCCs can significantly increase the shear strength of structural members (Cheng and Parra-Montesinos 2010, Lequesne et al. 2011, Naaman et al. 2007).
Objectivity
Thesis
LITERATURE REVIEW OF FRCC
- Fiber reinforced cement composite
- History of FRCC
- Characteristics of HPFRCC
- Mechanics of HPFRCC
- Impact of HPFRCC on structures
- Application of HPFRCC
- Code for HPFRCC
Tensile stress of fiber reinforced cement composites (FRCC) is added as a component of tensile stress leading to the assumption in stress and strain distribution in the section of an R/FRCC member (Figure 8). Crack width, controlled by fiber-reinforced cement composites (FRCC), prevents corrosion of steel reinforcement, while crack shapes, in reinforced concrete members, allow corrosive mass transport (Figure 12).
LITERATURE REVIEW OF HOLLOW COLUMNS
- Hollow columns
- Differences between solid and hollow columns
- Properties of hollow columns
- Preview for previous hollow column tests
Hollow columns resist higher moments and shear demands by reducing seismic mass (Lignola et al. 2008). Based on previous studies of hollow columns (Table 2 and Table 3), most studies have focused on examining various details of confinement reinforcement in order to develop appropriate methods to ensure satisfactory ductility and stress relief of reinforcement (Cheng et al. 2005, Mo et al. 2003 , Mo et al. 2004, Yeh et al. 2002).
MATERIAL TEST OF HPFRCC
Test methods
- Compressive tests
- Splitting tensile tests
- Direct tensile tests
The load is applied diametrically and uniformly along the length of the cylinder until failure of the cylinder along the vertical diameter. Two linear variable differential transformers (LVDTs) with a gauge length of 178 mm were attached along the sides of the sample in the loading direction.
Test results
- Compressive test results
- Splitting tensile test results
- Direct tensile tests
The average of three LVDT measurements (placed along the circumference of the cylindrical specimen) was used to estimate the compressive strain at a given step. The average of two LVDT measurements was used to estimate the tensile strain at each step.
EXPERIMENTAL PROGRAM FOR HPFRCC HOLLOW COLUMNS
Specimens
Sample SA2F1 contained 1% steel fibers and no coarse aggregates in the lower portion, and had a column width ratio of 2. Compared with SA2F1, sample SA2F2 had the same design details except that it had a fiber ratio of 2%, and GA2F1 had coarse aggregates in the lower part.
Material properties
- Steel fiber
- Steel reinforcing bar
- Concrete and HPFRCC
Test setup
The extent of shear crack damage was quantified by inspecting the increase in shear deformation in the specimen relative to the applied drift. Thus, it is believed that the failure of the specimens was largely attributed to the shear crack damage. The shear deformations were estimated using test data from the two LVDTs installed on the right (R) and left (L) sides of the sample, respectively.
The development of the bending mechanism was quantified by inspecting the rotational behavior of the specimen. In the previous sections, the behavior of the specimen was qualitatively described in relation to the shear strain and the bending rotation. Here it is assumed that the shear strain (g) given by Eq. 1) was uniform throughout the length (l) of the sample.
Furthermore, in the specimens with 1% steel ratio, was estimated to be more than 70% of the total displacement at the final stage of the test (although this would be somewhat overestimated due to excessive openings of the oblique shear cracks). This is supporting evidence that the failures of the FRCC specimens were strongly influenced by the shear crack damage. However, the tested FRCCs were not very effective in reducing the shear cracking damage of the hollow columns.
However, the exclusion of coarse aggregates in FRCC containing 1% fiber content did not further improve the ductility of the hollow columns. Using a higher proportion of fibers generally improved the energy dissipation capacity of the hollow columns.
HOLLOW COLUMNS TEST RESULTS
Cracking and fiailure mode
Overall load-displacement response
Note that Py and Pn were estimated without considering the effects of steel fibers on the stress-strain relationship. Successive yielding of the column bars around the column resulted in a further reduction in stiffness; the first loot occurred at about 0.75 or 1%. the drift ratio, which was estimated from data measured by strain gauges at the column-leg interface. The yield strength of GA2F0 was lower than that of FRCC specimens, mainly due to the lower yield strength of steel, but the maximum load divided by ′ was similar to that of FRCC specimens with an aspect ratio of 2; see the fourth row of Table 15.).
Therefore, the strengths of the FRCC specimens were governed by a combination of flexural hinges and shear cracking, and they eventually collapsed due to shear bond failure combined with column bar bending. From the results, it can be said that the steel strands were quite effective in holding the wide openings of inclined cracks. This suggests that the exclusion of coarse aggregates in FRCC of 1% steel fiber ratio, which generally increases the material cost, did not further improve the ductility of the hollow columns.
In summary, the use of a higher fiber ratio generally improved the displacement ductility of the hollow columns as well as the load capacity.
Energy dissipation behavior
For example, sample GA2F1 with 1% fiber ratio achieved significantly higher ductility than GA2F0 of normal concrete: 3.5 vs. The samples with 2% fiber ratio showed more stable load-displacement behavior than those with 1% fiber ratio. Among the three FRCC specimens with aspect ratio 2, SA2F2 with 2% fiber ratio reached more than 10% higher peak load than the specimens with 1% fiber ratio.
Specimens with 0% or 1% fiber ratio showed large compression in load and displacement responses, resulting in relatively small amounts of energy dissipation. In contrast, the 2% fiber samples showed greater energy dissipation with much less compression (see Fig. 28), especially during the inelastic response cycles before the critical strength drops. Therefore, it can be said that the use of 2% fiber ratio for the selected type of fiber improved the energy dissipation capacity of the hollow columns.
Equivalent viscous damping was used as a normalized measure for comparing the energy dissipation capacity of the test samples.
Shear distortion
The dissipated energy in GA2F0 for a cycle was much smaller than that in GA2F1, due to the smaller displacement intervals between adjacent cycles. However, the accumulated energy up to a given drift in GA2F0 was similar to the others.). This is supporting evidence that using a 1% volume ratio for the selected fiber type, even without coarse aggregates, was not sufficient to ensure satisfactory fiber bridging performance across multiple microcracks, which is considered the main source of energy dissipation. (Li2003).
The shear deformation remained small at the initial stage, but increased abruptly from about 3% drift in GA2F1, SA2F1, and SA3F2, and from 4% drift in SA2F2. For all four samples, it is noted that a significant force drop occurred just after the indicated drift level; the load-drift response was stable until the first cycle to the indicated drift. Comparing SA2F1 and SA2F2, where fiber volume only varied, SA2F2 at 2% fiber ratio showed much smaller shear deformations than SA2F1 at similar drift ratios.
This shows that the exclusion of coarse aggregates, with a volume ratio of 1% of the selected fiber type, had no positive effect on controlling adverse shear crack damage.
Flexural and fixed-end rotations
For example, both specimens were subjected to similar lateral loads at 3% drift, but SA2F1 suffered shear distortions greater than 0.02, while those in SA2F2 were only of the order of 0.005. This shows that the exclusion of coarse aggregates, with 1% volume ratio of the chosen fiber type, did not have a positive effect in controlling adverse shear cracking damage. 21 . reinforcement performance beyond the section of h/2 was not significant.). In general, the sample that had the smaller shear distortion (Figure 36) showed the larger rotation.
This was reasonable because the two deformations were the main sources for the lateral displacement in the specimens. Therefore, it can be said that the higher fiber ratio better limited the growth of shear (diagonal tension) cracks to reduce the shear deformation and correspondingly improve the development of flexural hinges at the bottom of the column. This happened when some large oblique cracks (Figure 27) opened excessively, leading to a sudden increase in the shear strain.
This was because the column had slipped about 5mm relative to the footing in the direction of the load, so the extensometer wires caught the bottom of the column.
Displacement components
21. The reinforcement yielding beyond the section h/2 was not significant.) In general, the sample with the smaller shear deformation (Figure 36) showed the larger rotation. The rotation in SA2F1 was measured inaccurately as if it increased during the 4% and 5% drift cycles. On the other hand, it is noteworthy that the load-drift responses remained stable (see Figure 28), even though the shear deformation component was already substantial (30 to 45% of the applied displacement) before the occurrence of the critical strength drop.
This was probably due to the beneficial effect of the steel fibers, which well resisted the excessive openings (i.e. widths) of the inclined shear cracks.
SUMMARY AND CONCLUSIONS
Summary of tests
Conclusions
It was concluded that the FRCCs were quite effective in maintaining wide openings of the oblique shear cracks. The specimens with the higher fiber ratio inhibited the growth of shear cracks better to reduce the shear distortion and consequently improved the development of flexural hinges at the base of the column. 3% (2nd cycle) Failure Mode Bend-Shear Bend-Shear Bend-Shear Bend-Shear Bend-Shear Pn = calculated lateral load corresponding to the event of the extreme concrete compression fiber reaching the maximum allowable strain (taken as 0.003).
Evaluation of steel fiber reinforcement for punch shear resistance in plate column connections-part 1: monotonically increased load. Evaluation of steel fiber reinforcement for punch shear resistance in plate-column connections-part 2: lateral displacement reversals. Recommendation for Design and Construction of High Performance Fiber Reinforced Cement Composites with Multiple Fine Cracks.
Seismic details and behavior of coupling beams with high-performance fiber-reinforced concrete (ACI SP-272). Numerical study of confinement performance in solid and hollow reinforced concrete bridge piers: analysis results and discussion. 2010).Shear strength of pseudo deformation cementitious composite joint beam. - high-performance fiber-reinforced cement composites;. alternative for seismic design of structures. 2005). Highly damage-resistant beam-to-column joints using high-performance fiber-reinforced cementitious composites.
