Time-dependent Concrete Properties Research Articles

Verification of deflections and cracking of RC flat slabs with numerical and analytical approaches

The Serviceability Limit States (SLS) of reinforced concrete structures, where cracking and deflection limits are verified in the design process, are directly related to time-dependent properties of concrete. In this study, the effects of creep and shrinkage of concrete, implemented in a Finite Element Model for Non-Linear Analysis, are in-deeply investigated for reinforced concrete flat slabs at SLS and used as basis for the development of an analytical framework. In particular, the paper focuses on: (i) the description of the FE model, (ii) the comparison between the numerical and experimental results of some reinforced concrete (RC) flat slab tests from literature characterized by different mechanical properties, span-to-depth ratios, boundary conditions and loading histories and (iii) the development of an analytical framework for the evaluation of long term-term deflections and crack openings in hogging regions of flat slabs near columns. Based on the findings, useful insights for the evaluation of the long term-term deflections and crack opening in the context of Serviceability Limit States are provided for practical purposes.

Noncontact Ultrasonic and Computer Vision Assessment for Sawcut Initiation Time

AbstractSawcut timing of contraction joints in concrete pavements is affected by interactions between the time-dependent concrete properties, notch depth, base friction, climate, and type of saw. E...

Creep and drying shrinkage performance of concrete composite comprising waste polypropylene carpet fibres and palm oil fuel ash

Creep and drying shrinkage are two critical time-dependent properties of concrete. This study presents the outcomes of an investigational work that addresses one-year creep and drying shrinkage performance in addition to the strength development of concrete comprising waste polypropylene carpet fibre and palm oil fuel ash (POFA). In this study, six fibre volume fractions of 0–1.25% with the fibres of 20 mm in length were used for ordinary Portland cement (OPC) concrete mixes. Another six mixes were cast, whereby 20% of POFA replaced OPC. The experimental results revealed that the combination of carpet fibres and POFA enhanced the long-term compressive strength of concrete. At 365 days, the compressive strength was in the range of 43–54 MPa. The combination of waste carpet fibre and POFA, therefore, reduced the creep strain and drying shrinkage of concrete mixtures by approximately 15% and 27%, respectively. The effects of POFA on the strength gain of concrete were to be more noticeable at the ultimate curing ages. The outcomes of this study showed that there is a promising future for the consumption of industrial waste carpet fibres together with POFA in the production of green concrete as structural components.

The Thermal Response of Concrete Frame Buildings in Arabic Area Considering Time-Dependent Properties of Concrete

The Arabic area is known for its significant changes in climate temperatures within different seasons. Riyadh, Cairo, Abu Dhabi, Ras Al-Khaimah, Kuwait, and Baghdad are subjected to the maximum variance in daily temperatures and presents the mean values of daily temperatures considering the data collected by the Hong Kong observatory in China for the last 30 years. The maximum mean value of daily temperature, which is 44.6 ℃ in Kuwait, and the minimum mean value of the daily temperature in Baghdad is 3.8 ℃. The maximum difference values of daily temperatures are observed in the Arabic Gulf area countries, such as Abu Dhabi, Kuwait, and Riyadh. Hence, these values will be considered in this analysis. This study results fit the thermal requirements of Arabic area and regions with similar temperature variation, accounting for various design aspects considering both methodologies of time-dependent properties of concrete as per CEB FIP 90 code and non-time dependent properties as per ACI 224.3R. For those targets a finite element method is utilized by generating 272 single- storey concrete ETABS models. The models are categorized according to column support conditions and development of concrete properties over time. The study findings are utilized to develop a clear understanding of mentioned variable's effects at thermal deformations and column reactions to aid structural engineers in the thermal design of super-long buildings with similar conditions of this study within time. The thermal displacement grows in proportion to the height of the column and the length of the slab. The findings of the analysis also show that employing thick slabs slightly decreases thermal displacements for models with hinged column supports and a 6 m column height. The thermal reactions increase in proportion to the length of the slab and the fixity conditions. Meanwhile, these reactions are inversely proportional to the height of the column. The ratios of time-dependent deformation and reaction to those of non-time-dependent properties are within the range [159%-163%] and [168%-171%] respectively. Ignoring this difference imposes defects, additional cracks, and damages at the structures and related serviceability conditions for 70 years period.

Early Age Deflections in Newly Rehabilitated Steel Girder Bridges Made Composite with Concrete Slabs

This paper focuses on deflections and deformations that occur at early ages in newly rehabilitated bridges made from steel girders and composite concrete deck slabs. The research program responds to problems with elevation control and subsequent ride quality problems exhibited in newly constructed or newly rehabilitated steel girder bridges built composite with concrete decks. A full-scale prototype bridge was built and instrumented at the Bert Cooper Engineering Laboratory on the campus of Oklahoma State University in Stillwater, Oklahoma, USA. Early age deflections of the bridge were measured, as were concrete temperatures, concrete strains, steel girder strains and inclinations of the steel girders at ends. Data were analyzed and their relationship to time-dependent concrete properties is established. Results indicate that the concrete strains associated with volume change, including both temperature-related strains and shrinkage strains, are large enough to be considered as one possible cause for adverse ride quality and unwanted deformations in steel girder bridge. The purpose of the research program is to identify causes for undesirable elevation profiles, and to recommend design and construction practices to help mitigate problems created for the highway users and extend the life span of bridges.

Monitoring, Modeling, and Assessment of a Self-Sensing Railway Bridge during Construction

This study shows how integrating fiber optic sensor (FOS) networks into bridges during the construction stage can be used to quantify preservice performance. Details of the installation of a large FOS network on a new steel-concrete composite railway bridge in the United Kingdom are presented. An overview of the FOS technology, installation techniques, and monitoring program is also presented, and the monitoring results from several construction stages are discussed. A finite-element (FE) model was developed and a phased analysis was carried out to simulate strain development in the bridge during consecutive construction stages. The response of the self-sensing bridge to the time-dependent properties of the concrete deck was evaluated by comparing FOS measurements to predicted results according to several model code formulations implemented in the FE model. The preservice strain distribution due to dead loading is typically assumed to act uniformly along the bridge length; however, the monitoring results revealed that the distribution was highly variable as a result of the complex interactions between gravity loading, bridge geometry, time-dependent concrete properties, and temperature effects. Moment utilization of the main girders and composite beams, during preservice conditions, was assessed and found to be between 19.3 and 24.9% of the respective design cross-section capacities. Quantifying preservice performance via integrated sensing also provided a critical baseline for the bridge, which enables future data-driven condition assessments.

Monitoring of concrete shrinkage and creep using Fiber Bragg Grating sensors

The research work reported in this paper is related to a Structural Health Monitoring (SHM) Project on a bridge in Ontario, Canada. It was recommended to use Fiber Bragg Grating (FBG) sensors to measure the dynamic response of the bridge and to measure creep and shrinkage in the piers of the bridge. The random decrement method is used to determine the deterioration through the dynamic parameters of the bridge as reported by Elshafey et al. [2] and Morsy et al. [15]. The measurements of creep and shrinkage strains are based on the FBG sensors reading that presented in the current paper. This investigation was necessary to ensure the creep and shrinkage strains are accurate based on a portable lab-top windows system integration system for the FBG readings. Normally, the lab FBG integration systems are very bulky and very expensive and fixed at lab location. However, due to the recent development in the electronic industry, it was possible to use a laptop portable computer system in this investigation. The system has been found accurate compared to the lab fixed equipment and it costs fraction of the expense. The test results of the measured creep and shrinkage showed an excellent correlation of the published data on Normal Strength Concrete (NSC), High Performance Concrete (HPC) and Ultra-High Performance Concrete (UHPC) using Fiber Bragg Grating (FBG) sensors. Results show that the FBG is a valid method for studying the time-dependent properties of concrete.

Review of Properties of Concrete , 5th Ed., by A. M. NevillePrentice Hall, Pearson, San Francisco, CA; 2012; ISBN 0273755803 and 978-0273755807; 846 pp.; $160 (paperback).

Review of <i>Properties of Concrete</i> , 5th Ed., by A. M. NevillePrentice Hall, Pearson, San Francisco, CA; 2012; ISBN 0273755803 and 978-0273755807; 846 pp.; $160 (paperback).

Thermal–mechanical analysis of a newly cast concrete wall of a subway structure

Abstract This paper presents a thermal–mechanical analysis of a newly cast concrete wall in the construction of a subway station structure, in an attempt to provide a theoretical basis for establishing early age concrete cracking prediction and prevention measures. Thermal and mechanical simulation procedures are formulated by considering time-dependent concrete properties, and numerical analyses conducted for varied constraint conditions. The key model parameters are determined through laboratory tests and inverse solution of in situ measurements. Suggestions are provided for prediction and control of early age concrete cracking in subway constructions.

Two-year deflections of the Confederation Bridge

A comprehensive research program is currently in progress to monitor and study the behavior and performance of the Confederation Bridge. Part of this program is on monitoring short- and long-term deflections to evaluate the deflection prediction techniques employed in the design of concrete structures in general and this bridge in particular. The investigation comprises measurements of parameters related to the materials used in the bridge. This paper presents some field measurements of vertical deflection as well as the results of computer analysis. Short-term deflections are measured at the time of installation of precast units and also in truck-loading tests. After completion of construction, the deflections are measured at specified intervals. The last readings reported in this paper have been taken 27 months after completion of construction. The computer program CPF (Cracked Plane Frames in prestressed concrete) is employed for analysis of the monitored part of the Confederation Bridge. The bridge is modeled as a plane frame in which the nonprestressed and prestressed steels are considered. Several analyses are performed employing the actual time-dependent concrete properties measured in the field and those calculated from the ACI Committee 209 equations and CEB-FIP Model Code. Comparisons are made between the measured and the predicted deflections. The predicted deflections are found to be in close agreement with the measured values, which indicates that the deflection prediction techniques used in design of this bridge are adequate.Key words: computer analysis, concrete bridges, Confederation Bridge, creep, deflections, field measurements, long-term, prestressed steel, segmental construction, short-term, shrinkage, time-dependent.

Long-Term Behavior of Continuous Precast Concrete Girder Bridge Model

Continuous concrete box girder bridges composed of precast reinforced and prestressed concrete beams with a U cross section and a cast-in-place top slab are frequently used for medium spans due to their competitiveness. The service behavior of such bridges is very much influenced by their segmental construction, due to time-dependent materials behavior that makes it difficult to accurately predict the stresses, strains, and deflections at long term. A 1:2 scale model of a two-span continuous bridge was tested in order to study its behavior during the construction process and under permanent loads. Time-dependent concrete properties, as well as support reactions, deflections, and strains in concrete and steel, were measured for 500 days. Important time-dependent redistributions of stresses and internal forces throughout the bridge were also measured. The test results were compared with analytical predictions obtained by means of a numerical model developed for the nonlinear and time-dependent analysis of segmentally erected, reinforced and prestressed concrete structures. Generally good agreement was obtained, showing the adequacy of the model to reproduce the structural effects of complex interactive time-dependent phenomena.

Effects of time-dependent concrete properties on prestress losses

Prestress losses were calculated for a segmental concrete box-girder bridge. Results were based on the time-dependent investigation of the Kishwaukee River Bridge constructed by the balanced cantilever method. Instruments were installed in the bridge during construction to measure the time-dependent deformations. Short- and long-term properties of concrete used in the instrumented segments were measured. With the actual construction schedule and the measured concrete properties, time-dependent nonlinear analyses were performed. Prestress losses were calculated for each construction step. Time-dependent variations of prestress losses during and after construction are presented. Comparisons between design concrete properties and measured values and between analytical prestress losses and design values were made. Key words: mechanical properties, creep properties, shrinkage, prestressing, losses, prestressed concrete bridges, measurement, analysis.