International Concrete Abstracts Portal

The effects of creep and shrinkage on the time-dependent behavior of reinforced concrete flexural members are discussed and a procedure for the prediction of the long-term deflection of reinforced concrete beams and slabs is presented. The time-dependent deformations caused by creep and shrinkage are modeled using tractable formulations developed using the age-adjusted effective modulus method of analysis. The procedure includes the time varying nature of tension stiffening and the effects of time-dependent shrinkage-induce cracking. Sample calculations are provided. The method is validated against a wide range of test data and is shown to provide reliable estimates of in-service deformations.

Due to the low elastic modulus of fiber reinforced polymer (FRP) materials, concrete members reinforced with FRP bars show greater deflections than members reinforced with steel reinforcement. Deflection is an important factor to consider in the serviceability of floor members. In this study, flexural tests of both AFRP and CFRP reinforced concrete beams were performed with the reinforcement ratio and concrete compressive strength as the main parameters. The test results indicate that the flexural capacity and stiffness increase in proportion to the reinforcement ratio and compressive strength of concrete as expected. In addition, the test results are compared with deflection calculations based on existing proposed equations for the effective moment of inertia. This comparison demonstrates that the ACI 440.1R-06 (ACI Committee 440 2006) approach for FRP reinforcement underestimates deflection of AFRP reinforced concrete, while a more rational approach proposed by Bischoff (2005) is able to predict deflections reasonably well for concrete reinforced with both types of FRP reinforcement investigated (AFRP and CFRP) and for steel reinforcement.

Continual functioning of Liquid Containing Structures “LCS” is necessary for the well being of a society during and after an earthquake. While the seismic design criteria for buildings are primarily based on life safety and prevention of collapse, concrete storage tanks should be designed to meet the serviceability limits such as leakage. This study was aimed at evaluation of the leakage behavior of ground supported open top rectangular RC tanks under the effects of cyclic loading. Full-scale specimens representing a cantilever wall were designed and built to simulate leakage through the most critical region of the tank wall. A steel water pressure chamber was installed at the wall foundation connection region to simulate the effect of the water pressure on the induced cracks at the critical location of the tank wall. Cyclic loading was applied at top of the wall while the critical region of the wall was subjected to pressurized water. This study is limited to rectangular tanks in which the wall dimensions promote one-way behavior. It is concluded that in order for leakage to occur, the strain in the reinforcement at both faces of the wall need to be close to the yield level.

Integral abutment bridges (IABs) have performed successfully for decades and have demonstrated advantages over traditional, jointed bridges with respect to first cost, maintenance costs and service life. However, accurate prediction of IAB response to loading is complex and challenging; behavior is typically nonlinear due to the combined influence of thermal and long-term, time-dependent effects. Summarized herein are measured and computational results from examination of four interstate highway IABs located in central Pennsylvania. The collected data indicates that current AASHTO prediction methods are very conservative with respect to displacements. New computational models are used to perform a parametric study that considers the effects of seasonal thermal loading, thermal gradient, time-dependent material effects, abutment-backfill interaction and pile-soil interaction on deformations that occur over a 75-year bridge life. The measured and parametric study results provide a basis to establish an approximate method for predicting (1) maximum abutment displacement, (2) maximum bridge bending moments and (3) maximum pile moments over the bridge life.

This paper discusses the importance of deflection control in reinforced concrete structures and highlights a number of problems which can complicate accurate deflection calculations. The tension stiffening phenomenon is then described in some detail followed by descriptions of the approaches used to accommodate it in major design codes. Recent experimental work which has resulted in new recommendations for the treatment of long term tension stiffening effects is summarised and areas of current research are indicated. Finally, the paper comments that the tension stiffening phenomenon, in view of its important influence on deflection control, is likely to remain a topic of considerable interest for the foreseeable future.