Analysis of shrinkage deformations in concrete structures

Electronic Journal of Structural Engineering, 2001

This paper addresses the effects of shrinkage on the serviceability of concrete structures. It outlines why shrinkage is important, its major influence on the final extent of cracking and the magnitude of deflection in structures, and what to do about it in design. A model is presented for predicting the shrinkage strain in normal and high strength concrete and the time-dependent behaviour of plain concrete and reinforced concrete, with and without external restraints, is explained. Analytical procedures are described for estimating the final width and spacing of both flexural cracks and direct tension cracks and a simplified procedure is presented for including the effects of shrinkage when calculating long-term deflection. The paper also contains an overview of the considerations currently being made by the working group established by Standards Australia to revise the serviceability provisions of AS3600-1994, particularly those clauses related to shrinkage.

Advances in Structural Engineering, 2013

INTRODUCTION Concrete shrinkage along with cracking provides one of the major concerns to the structural designer because of the inaccuracies and unknowns that surround them. Serviceability behavior of reinforced concrete (RC) structures (crack width and deformations) is greatly influenced by cracking and shrinkage, and their interaction. It is well known that shrinkage might significantly affect cracking resistance and deformations of RC members. The necessity to assess shrinkage influence on deformation behavior of cracked RC members has been recognized since the beginning

Journal of Civil Engineering and Management, 2008

This paper introduces the recent state of research on shrinkage of concrete. It reviews prediction models of shrinkage strain and curvature analysis methods of reinforced concrete members. New test data on concrete shrinkage has been presented. Various factors that influence shrinkage have been discussed. A calculation technique on short-term deformations of cracked reinforced concrete members including shrinkage has been introduced. The technique is based on layer model and smeared crack approach. Shrinkage influence on behaviour of reinforced concrete beams was investigated numerically and compared with test data reported in the literature. It has been shown that shrinkage has significantly reduced the cracking resistance and leads to larger deflections.

2013

Traditionally, concrete shrinkage along with cracking provides one of the major concerns to the designers because of the inaccuracies and unknowns that surround them. Although shrinkage is mainly associated with long-term effects, even at first loading, restrained shrinkage may cause cracking of concrete. The essential point of present study is to specify the cases of short-term deformation analysis of reinforced concrete (RC) structures when the shrinkage effect should not be neglected. The study combines the knowledge on material and structural aspects of shrinkage phenomenon. The manuscript considers physical nature of shrinkage pointing out the major means of reducing shrinkage deformations. The article also discusses peculiarities of constitutive modeling of shrunk reinforced concrete members and gives recommendations for improving adequacy of the design. Furthermore, the paper discusses application of steel fibers as an efficient additive to reduce adverse effects of restrained shrinkage.

Engineering Structures, 2018

Shrinkage induced curvatures in reinforced concrete elements are thought to be affected only by section geometry and distribution/ratio of reinforcement. The variation in the level of internal restraint caused by the non-uniform distribution of concrete constituents within the section, however, can also lead to additional shrinkage induced deformations, and potentially to larger than expected deformations in critical structural elements, even under service conditions. This study examines experimentally the development of non-uniform shrinkage strains in unreinforced as well as symmetrically and asymmetrically reinforced concrete elements. Results confirm that shrinkage is non-uniform due to the variations in internal restrains (coarse aggregates and reinforcement). The addition of steel fibres mitigates this effect and reduces overall shrinkage curvature. A prediction model for shrinkage induced curvature of plain and reinforced concrete is proposed, taking into account the non-uniform distribution of concrete constituents. The proposed model yields results in good agreement with experimentally observed values of shrinkage curvature and can be used to improve the predictions of design guidelines.

Materials

The contribution of concrete to the tensile stiffness (tension stiffening) of a reinforced concrete (RC) member is a key governing factor for structural serviceability analyses. However, among the current tension stiffening models, few consider the effect brought forth by concrete shrinkage, and none studies take account of the effect for very long-term shrinkage. The present work intends to tackle this exact issue by testing multiple RC tensile elements (with different bar diameters and reinforcement ratios) after a five-year shrinking time period. The experimental deformative and tension stiffening responses were subjected to a mathematical process of shrinkage removal aimed at assessing its effect on the former. The results showed shrinkage distinctly lowered the cracking load of the RC members and caused an apparent tension stiffening reduction. Furthermore, both of these effects were exacerbated in the members with higher reinforcement ratios. The experimental and shrinkage-fre...

2012

Shrinkage of concrete is a natural phenomenon, with several well known mechanisms. However, restrained shrinkage is the challenging problem both to design and construction practice. External and/or internal restraint to shrinkage generates tensile stresses that may easily result in time-dependent excessive cracking states, compromising the durability of the structures. After a brief introduction, the paper presents aspects concerning cracking states induced by restrained shrinkage of concrete, met in the last decade in Romania. Consequently, a new design guide was released, as part of the Romanian technical regulations system. Next, the paper presents a synthetic critical review of the guide. Résumé Le retrait du béton est un phénomène naturel, issu de plusieurs mécanismes bien connus. Pourtant, le retrait gêné reste un défi à la fois pour la conception et les méthodes constructives. Les entraves au retrait, d’origine externe ou interne, génèrent des contraintes de traction qui prod...

2014

Results obtained by testing shrinkage deformation on ten groups of concrete, using the total of thirty one mixtures, are presented in the paper. Concrete groups differed according to the quantity of water and mineral and chemical admixtures. In this way, a wide range of concrete compressive strength values, from normal concrete to high strength concrete, was obtained, in addition to different consistency values. The shrinkage of concrete specimens after a two-day cure in water was monitored over a period of more than one year. An another series of twenty-nine concrete mixtures was also prepared to monitor the autogenous shrinkage of concrete. The total shrinkage of concrete was defined as the sum of the autogenous shrinkage of concrete at one day of age, and the shrinkage of concrete after the end of curing. In this paper, the model was developed and used in order to predict concrete shrinkage values after initial curing, and total shrinkage values, as related to compressive strengt...

Concrete Solutions 2011, 2011

ABSTRACT Stresses due to restrained shrinkage have long been recognized as the main causes of cracking and debonding of repaired concrete members especially in hot weather environments. Although several studies have been conducted to investigate this effect, there is no widely accepted method for calculating restrained shrinkage stresses in the repair system. In this paper, a rational numerical method is proposed to determine the tensile stress in repaired concrete members by measuring the free shrinkage values in the laboratory. The effects of repair dimensions, interface surface roughness, and creep relaxation have been considered in the proposed method.

ACI Materials Journal, 2016

Imperial College, London, UK. He is a member of fib task group 9.3 (Composites for construction) and the leader of several EU funded multi-partner projects including '' Anagennisi''. His research interests include structural concrete behaviour, earthquake engineering, composites for construction and construction innovation.