Long-term shrinkage prediction from theoretical considerations and data analysis

Upon the release of the data from the tragic collapse in 1996 of the record-span segmental box-girder bridge in Palau, it was found that the 18-year deflection was 200 - 400% larger than the predictions based on the American, European and Japanese design codes or recommendations. This finding triggered further studies that led to a collection of deflection histories of 69 large-span segmental bridges, most of which suffered excessive, logarithmically growing, deflections with no sign of an asymptotic bound. It thus became clear that major improvements in design codes and practices are required. Data collection efforts led to a new database of laboratory concrete creep and shrinkage data. With over 3000 test curves, this database more than doubles the size of the previous RILEM database. Unfortunately, the duration of about 94% of the available lab tests is <6 years, 97% ≤12 years, and only 3% attains 30 years, while 100-year lifetimes are generally desired. So it became evident that the only way to develop a realistic multi-decade prediction model was by joint statistical optimization of the fit of the laboratory data and the multi-decade bridge data. Regrettably, most of the bridge data are insufficient for inverse FE analysis. The relative increases of multi-decade deflection after about 1,500 days could be used for calibration. The combination of incomplete multi-decade bridge data with the short-time laboratory database posed a challenge for statistical optimization of the model parameters. Nonlinear least-square regression was used to inform the information of obtained from the database with the bridge deflection measurements. The database of laboratory tests has further been extended to include high-strength concretes (up to 167 MPa strength at 28 days), as well as modern concretes with various admixtures, classified into six classes, some of which decrease and others increase the creep and shrinkage. Through correlation analyses and the incorporation of previously studied trends, new formulas for estimating the model parameters from concrete strength and composition (with admixtures) have been identified

Development and validation of the model B4 for concrete creep and shrinkage

An analysis of 69 recorded bridge deflection histories reveals that the existing formulations for the creep and shrinkage of concrete structures greatly underestimate the multi-decade creep deflections of structures, often designed for lifetimes >100 years. Despite having the correct form, the existing model B3 (a 1995 RILEM Recommendation) markedly underestimates the multi-decade deflections. So does the new fib Model Code 2010. Presented is a new model, labeled B4, which overcomes two main shortcomings of the ACI, CEB, JSCE and GL models. First, the new model is calibrated using the collected bridge deflection data to ensure the proper terminal slope of the compliance function in logarithmic time. Second, model B4 extends the scope of prediction to modern concretes with various types of admixtures and high strengths

Developing alternative SCDDP implementations for hydro-thermal scheduling in New Zealand.

In a hydro-dominated system, such as New Zealand, the continual improvement and development of effective optimization and simulation software to inform decision making is necessary for effective resource management. Stochastic Constructive Dual Dynamic Programming (SCDDP) is a technique which has been effectively applied to the New Zealand system for optimization and simulation. This variant of Dynamic Programming (DP) allows optimization to occur in the dual space reducing the computational complexity and allows solutions from a single run to be formed as price signal surfaces and trajectories. However, any application of this method suffers from issues with computational tractability for higher reservoir numbers. Furthermore, New Zealand specific applications currently provide limited information on the system as they all use the same two-reservoir approximation of the New Zealand system. This limitation is of increasing importance with the decentralization of the New Zealand electricity sector. In this thesis we develop this theory with respect to two key goals: • To advance the theory surrounding SCDDP to be generalizable to higher reservoir numbers through the application of the point-wise algorithm explored in R. A. Read, Dye, S. & Read, E.G. (2012) to the stochastic case. • To develop at least two new and distinct two-reservoir SCDDP representations of the New Zealand system to provide a theoretical basis for greater flexibility in simulation and optimization of hydro-thermal scheduling in the New Zealand context

Stress state influence on nonlocal interactions in damage modelling

This paper presents a modification of an integral nonlocal damage model used to describe concrete behaviour. It aims at providing a better treatment of areas close to a boundary and a fracture process zone where the interactions between points should vanish. Modifications on the original integral nonlocal model are introduced by considering the stress state of points in the weight function used to compute the nonlocal variables. Computations show that local information such as strain or damage profiles are significantly different, leading to a narrower region where damage equal to 1 in the case of the modified nonlocal model. It allows to better approach a discontinuity of the displacement field upon failure and thus, improves the estimation of the crack opening that has been developed in post-processing for this type of calculation

Non local damage model Boundary and evolving boundary effects

International audienceThe present contribution aims at providing a closer insight on boundary effects in non local damage modelling. From micromechanics, we show that on a boundary interaction stress components normal to the surface should vanish. These interaction stresses are at the origin of non locality and therefore the material response of points located on the boundary should be partially local. Then, we discuss a tentative modification of the classical non local damage model aimed at accounting for this effect due to existing boundaries and also boundaries that arise from crack propagation. One-dimensional computations show that the profiles of damage are quite different compared to those obtained with the original formulation. The region in which damage is equal to 1 is small. The modified model performs better at complete failure, with a consistent description of discontinuity of the displacement field after failure

The Political Economy of Unfairness in U.S. Health Policy

Oberlander discusses the political economy of unfairness in US health policy by first highlighting the moral issues raised by the US\u27s system of financing medical care and then by analyzing the political dynamics that sustain that system