Time-Dependent Strains in Axially Loaded Reinforced Concrete Columns
01 Aug 2020-Journal of Engineering Mechanics-asce (American Society of Civil Engineers (ASCE))-Vol. 146, Iss: 8, pp 04020076
Abstract: Time-dependent strains in reinforced concrete (RC) members are usually estimated using approximate algebraic methods. This paper presents an exact method for estimating the time-dependent s...
01 May 2000-
01 Sep 2020-
15 Sep 2021-Engineering Structures
Abstract: Steel tube confined reinforced concrete (STCRC) columns have a promising future in high-rise buildings owing to their ease in connection, high bearing capacity, and excellent seismic behaviour. To date, no investigation is available for the time-dependent behaviour of STCRC columns despite of the numerous researches conducted on the short-term and seismic behaviour. This paper intends to experimentally study the time-dependent behaviour of STCRC columns. Seventeen pairs of circular STCRC stub columns were under sustained loading for 490 days. The experimental parameters include the concrete loading age, the concrete compressive strength, the steel ratio (i.e. the ratio of the steel tube area over the core concrete area), the longitudinal reinforcement ratio (i.e. the ratio of the longitudinal reinforcement area over the concrete area) and the bond condition of the steel–concrete interface. Special attention was given to study how, if any, the confinement effects and the vertical load resistance offered by the steel tube influence the time-dependent behaviour of the composite column. Key factors influencing the time effects of the STCRC columns were determined, and the difference between the long-term deformation of STCRC columns and that of traditional concrete-filled steel tubular (CFST) columns with the same steel consumption were compared. A numerical model was then proposed for calculating the long-term deformation of STCRC stub columns based on the cross-sectional analysis method and the step-by-step method, and was benchmarked against the available test results. Experimental results indicated that the static responses of STCRC were significantly influenced by time effects, which is much more pronounced than that of companion CFST columns. Within the parameter range considered in this investigation, both the confinement effects and the bond properties of the steel–concrete interface rarely influence the long-term behaviour of STCRC stub columns. The proposed numerical analysis method in this paper achieved reasonable accuracy for calculating the long-term deformation of STCRC stub columns, with the slope of regression line and the correlation coefficient of 1.013 and 0.916, respectively. It is worth highlighting that all the conclusions in this paper are only applicable within the parameter range in this paper, and further study is still required for more comprehensive insight in the long-term behaviour of STCRC columns.
01 Jul 1995-
Abstract: A model for the characterization of concrete creep and shrinkage in the design of concrete structures is recommended. It is simplier, agrees better with the experimental data and is justified better theoretically than the previous models. The model complies with the general guidelines recently formulated by RILEM TC 107. Justification of the model and various refinements are to be published shortly in two parts.
01 Nov 2011-Aci Structural Journal
Abstract: An obsolete standard recommendation for creep design led to significant underestimation of the observed 18-year deflections of the Koror-Babeldaob (KB) Bridge in the island nation of Palau. A search for data on similar bridges revealed that 56 other large-span, prestressed concrete, segmentally erected box girders (66 by the time of proof) have been found to exhibit excessive long-time deflections. There are probably many more in existence. The observed deflections give no sign of approaching a finite bound, as implied in the empirical ACI Committee 209, CEB-fib, and GL models for creep. They were found to evolve approximately logarithmically beginning at about 1000 days after span closing. While sufficient data for the finite element creep analysis of these deflections were not obtainable, comparisons with accurate deflection solutions for the KB Bridge showed that the terminal logarithmic deflection trend can be predicted well by a simple extrapolation of the measured 1000-day deflection under the hypothesis of proportionality to the compliance function increment since the time of span closing. Comparisons of the extrapolations according to various creep models show that the underestimation of long-time deflections is much less severe for the theoretically based Model B3 than it is for the three other models, and that the terminal trend is logarithmic. A simple update of this model that gives the same mean terminal trend as the 56 bridges is devised that should allow for improving the durability of segmental bridges.
30 Jan 2018-
31 Mar 2008-Journal of Civil Engineering and Management
01 Dec 1969-
Abstract: BASED ON THE PRESENT STATE OF THE ART, A PRACTICAL DESIGN PROCEDURE IS PRESENTED TO PREDICT THE CREEP AND SHRINKAGE STRAINS IN COLUMNS OF MULTISTORY BUILDINGS, CONSIDERING THE EFFECTS OF LOADING HISTORY, MEMBER SIZE AND PERCENTAGE OF REINFORCEMENT. ALTHOUGH THE MAGNITUDE OF CREEP AND SHRINKAGE OF PLAIN CONCRETE SPECIMENS MAY VARY CONSIDERABLY, THE FINAL INELASTIC STRAINS IN REINFORCED CONCRETE COLUMNS AND WALLS HAVE MUCH LESS VARIATION DUE TO THE RESTRAINING EFFECT OF THE REINFORCEMENT. ELEMENTS WHICH RECEIVE A SUBSTANTIAL LOADING AT EARLY AGES, SUCH AS PRESTRESSED ELEMENTS AND COLUMNS IN THE UPPER STORIES OF TALL STRUCTURES OR COLUMNS OF LOW-RISE STRUCTURES, ARE PRONE TO HIGHER SHRINKAGE AND CREEP STRAINS. LOWER STORY COLUMNS OF TALL STRUCTURES HAVE CONSIDERABLY SMALLER CREEP AND SHRINKAGE STRAINS THAN COMMONLY ASSUMED AS A RESULT OF: (1) INCREMENTAL LOADING OVER A LONGER PERIOD OF TIME WHICH REDUCES CREEP; (2) A SUBSTANTIAL VOLUME-TO-SURFACE RATIO WHICH REDUCES SHRINKAGE; AND (3) A SUBSTANTIAL PERCENTAGE OF REINFORCEMENT WHICH REDUCES BOTH SHRINKAGE AND CREEP. IN A TALL STRUCTURE THE RELATIVE VERTICAL MOVEMENT BETWEEN COLUMNS AND ADJACENT WALLS CAN CAUSE STRUCTURAL AND ARCHITECTURAL DISTRESS UNLESS PROPER DESIGN AND DETAILS ARE PROVIDED. /AUTHOR/
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