Cusson试验过程1994(ASCE)
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783
[
~
~
L c:::;:to--.
(b)
1~_~_235 mm
Effectively confinedconcrete
w
)
il
(a)
FIG. 1. and Spacing on Confined Concrete Core: (a) Poor Tie Configuration with Large Tie Spacing; (b) Good Tie Configuration with Small Tie Spacing
INTRODUCTION
The technology of high-strength concrete (HSC) has greatly improved over the last decade. Higher compressive strength, greater modulus of elasticity, and substantial savings resulting from the section reduction are all properties of high-strength concrete that appeal to designers. Unfortunately, present code provisions are often used without any additional precautions for safety in construction projects involving high-strength concrete. Moreover, the parameters defining the requirements for lateral confining reinforcement in current codes are the results of tests done on reinforced concrete members with concrete compressive strengths lower than 40 MPa ( A C I Committee 318, 1989). Therefore, current code requirements may not be adequate nor safe for H S C members. Confinement of normal-strength concrete by rectangular ties has been extensively studied in recent years (Vallenas et al. 1977; Sheikh and Uzumeri 1980; Mander et al. 1988). It has been observed that columns with a good distribution of longitudinal and lateral reinforcement provided in sufficient quantity, as shown in Fig. l(b), possess great ductility and present significant strength gain. Refined stress-strain models for confined concrete have also been proposed. These models, based on test results from normal-strength concrete columns, may not be adequate for concrete of much higher strength. Published data on the performance of large scale (smallest dimension larger than 200 ram) H S C tied columns are scarce (Bjerkeli 1992; Itakura et al. 1992; Nagashima et aL 1992). It has been observed that ductility of HSC columns can be improved by lateral confinement, although in a lesser degree than normal-strength concrete columns. A C I Committee 363 (1987) concluded that more data on the confinement of H S C tied columns are needed. 1Ph.D. Candidate, Dept. of Civ. Engrg., Univ. of Sherbrooke, Sherbrooke, Quebec, Canada, JIK 2R1. 2prof., Dept. of Civ. Engrg., Univ. of Sherbrooke, Sherbrooke, Quebec, Canada. Note. Discussion open until August 1, 1994. To extend the closing date one month, a written request must be filed with the ASCE Manager of Journals. The manuscript for this paper was submitted for review and possible publication on December 23, 1992. ~This paper, is part of the Journal of Structural Engineering, Vol. 120, No. 3, March, 1994. 9 ISSN 0733-9445/94/0003-0783/$2.00 + $.25 per page. Paper No. 5189.
385 mra
\
~1~1
[ 1~zaSmm
Strain gage ~
FIG. 2. Overall Dimensions of Test Specimens and Instrumentation TEST PROGRAM
This paper presents an experimental study of the behavior of large-scale HSC columns confined by rectangular ties tested under concentric loading. Twenty-seven large-scale columns (235 x 235 • 1400 mm) were tested under compressive concentric loading. Fig. 2 shows details of the test specimens and the four tie configurations used. Test variables studied in this 784
HIGH-STRENGTH
C O N C R E T E C O L U M N S C O N F I N E D BY
RECTANGULARTIES
By Daniel Cusson I and Patrick Paultre, 2 Member, ASCE
ABSTRACT: This paper presents an experimental study of the behavior of large-
scale high-strengthconcrete columns confined by rectangular ties under concentric loading. Effects of key variables such as the concrete compressivestrength, the tie yield strength, the tie configuration, the transverse reinforcement ratio, the tie spacing, the longitudinal reinforcementratio, and the spalling of the concrete cover are studied in this research program. The behavior of high-strength concrete columns is characterized by the sudden separation of the concrete cover, leading to a loss of axial capacity before the lateral confinementbecomes effective. After the concrete is completelyspalled, important gains in strength, toughness, and ductility are recorded for the concrete core of well-confined columns.
research program are: (1) The concrete compressive strength, f'; (2) the tie yield strength,fyh; (3) the tie configuration, cfg; (4) the lateral reinforcement ratio, Ph; (5) the tie spacing, s; (6) the longitudinal reinforcement ratio, pg; and (7) the influence of concrete cover, coy. Test specimens are identified with the number of the series and a letter corresponding to the tie configuration used. Specimens in Series 1-5 are made of concrete with a specified strength of 100 MPa. Each series contains four specimens of tie configurations A, B, C, and D. Series 1 includes a fifth specimen, 1D1, identical to specimen 1D, but without concrete cover. Specimens in series 6, 7, and 8 are made of concrete with specified strengths of 120, 80, and 60 MPa, respectively. Each of these series contains two specimens with tie configurations B and D. Table 1 shows the reinforcing steel properties and the unconfined concrete strength for each specimen. Confinement efficiency can be evaluated by making comparisons within 38 matched pairs of specimens with respect to a particular variable, while all other test variables are equal or reasonably so. The comparisons are listed in the last column of Table 1: the first symbol represents the comparison specimen and the second, the test variable whose efficiency is being studied. Ratios of the amount of lateral reinforcement in the specimens to the amol~nt of lateral reinforcement required by the ACI Code (Building 1989) for seismic design ranged from 25% for the lowest confined specimen to 250% for the highest. The tie spacing and diameter requirements for lateral support of the longitudinal reinforcement specified in the ACI Code for seismic design are respected for all specimens except for those in series 3. However, for the four specimens in series 3, a tie spacing of 100 mm is adequate when seismic design is not a concern. Column specimens were cast vertically. After 24 hours, the form was removed and the specimens were submerged in a water tank in order to obtain the 28-day specified concrete strength. The water-curing period lasted two weeks, after which the specimens were left in the laboratory at ambient temperature for two more weeks before testing.
[
~
~
L c:::;:to--.
(b)
1~_~_235 mm
Effectively confinedconcrete
w
)
il
(a)
FIG. 1. and Spacing on Confined Concrete Core: (a) Poor Tie Configuration with Large Tie Spacing; (b) Good Tie Configuration with Small Tie Spacing
INTRODUCTION
The technology of high-strength concrete (HSC) has greatly improved over the last decade. Higher compressive strength, greater modulus of elasticity, and substantial savings resulting from the section reduction are all properties of high-strength concrete that appeal to designers. Unfortunately, present code provisions are often used without any additional precautions for safety in construction projects involving high-strength concrete. Moreover, the parameters defining the requirements for lateral confining reinforcement in current codes are the results of tests done on reinforced concrete members with concrete compressive strengths lower than 40 MPa ( A C I Committee 318, 1989). Therefore, current code requirements may not be adequate nor safe for H S C members. Confinement of normal-strength concrete by rectangular ties has been extensively studied in recent years (Vallenas et al. 1977; Sheikh and Uzumeri 1980; Mander et al. 1988). It has been observed that columns with a good distribution of longitudinal and lateral reinforcement provided in sufficient quantity, as shown in Fig. l(b), possess great ductility and present significant strength gain. Refined stress-strain models for confined concrete have also been proposed. These models, based on test results from normal-strength concrete columns, may not be adequate for concrete of much higher strength. Published data on the performance of large scale (smallest dimension larger than 200 ram) H S C tied columns are scarce (Bjerkeli 1992; Itakura et al. 1992; Nagashima et aL 1992). It has been observed that ductility of HSC columns can be improved by lateral confinement, although in a lesser degree than normal-strength concrete columns. A C I Committee 363 (1987) concluded that more data on the confinement of H S C tied columns are needed. 1Ph.D. Candidate, Dept. of Civ. Engrg., Univ. of Sherbrooke, Sherbrooke, Quebec, Canada, JIK 2R1. 2prof., Dept. of Civ. Engrg., Univ. of Sherbrooke, Sherbrooke, Quebec, Canada. Note. Discussion open until August 1, 1994. To extend the closing date one month, a written request must be filed with the ASCE Manager of Journals. The manuscript for this paper was submitted for review and possible publication on December 23, 1992. ~This paper, is part of the Journal of Structural Engineering, Vol. 120, No. 3, March, 1994. 9 ISSN 0733-9445/94/0003-0783/$2.00 + $.25 per page. Paper No. 5189.
385 mra
\
~1~1
[ 1~zaSmm
Strain gage ~
FIG. 2. Overall Dimensions of Test Specimens and Instrumentation TEST PROGRAM
This paper presents an experimental study of the behavior of large-scale HSC columns confined by rectangular ties tested under concentric loading. Twenty-seven large-scale columns (235 x 235 • 1400 mm) were tested under compressive concentric loading. Fig. 2 shows details of the test specimens and the four tie configurations used. Test variables studied in this 784
HIGH-STRENGTH
C O N C R E T E C O L U M N S C O N F I N E D BY
RECTANGULARTIES
By Daniel Cusson I and Patrick Paultre, 2 Member, ASCE
ABSTRACT: This paper presents an experimental study of the behavior of large-
scale high-strengthconcrete columns confined by rectangular ties under concentric loading. Effects of key variables such as the concrete compressivestrength, the tie yield strength, the tie configuration, the transverse reinforcement ratio, the tie spacing, the longitudinal reinforcementratio, and the spalling of the concrete cover are studied in this research program. The behavior of high-strength concrete columns is characterized by the sudden separation of the concrete cover, leading to a loss of axial capacity before the lateral confinementbecomes effective. After the concrete is completelyspalled, important gains in strength, toughness, and ductility are recorded for the concrete core of well-confined columns.
research program are: (1) The concrete compressive strength, f'; (2) the tie yield strength,fyh; (3) the tie configuration, cfg; (4) the lateral reinforcement ratio, Ph; (5) the tie spacing, s; (6) the longitudinal reinforcement ratio, pg; and (7) the influence of concrete cover, coy. Test specimens are identified with the number of the series and a letter corresponding to the tie configuration used. Specimens in Series 1-5 are made of concrete with a specified strength of 100 MPa. Each series contains four specimens of tie configurations A, B, C, and D. Series 1 includes a fifth specimen, 1D1, identical to specimen 1D, but without concrete cover. Specimens in series 6, 7, and 8 are made of concrete with specified strengths of 120, 80, and 60 MPa, respectively. Each of these series contains two specimens with tie configurations B and D. Table 1 shows the reinforcing steel properties and the unconfined concrete strength for each specimen. Confinement efficiency can be evaluated by making comparisons within 38 matched pairs of specimens with respect to a particular variable, while all other test variables are equal or reasonably so. The comparisons are listed in the last column of Table 1: the first symbol represents the comparison specimen and the second, the test variable whose efficiency is being studied. Ratios of the amount of lateral reinforcement in the specimens to the amol~nt of lateral reinforcement required by the ACI Code (Building 1989) for seismic design ranged from 25% for the lowest confined specimen to 250% for the highest. The tie spacing and diameter requirements for lateral support of the longitudinal reinforcement specified in the ACI Code for seismic design are respected for all specimens except for those in series 3. However, for the four specimens in series 3, a tie spacing of 100 mm is adequate when seismic design is not a concern. Column specimens were cast vertically. After 24 hours, the form was removed and the specimens were submerged in a water tank in order to obtain the 28-day specified concrete strength. The water-curing period lasted two weeks, after which the specimens were left in the laboratory at ambient temperature for two more weeks before testing.