Walter P. Murphy

Bio: Walter P. Murphy is an academic researcher from Northwestern University. The author has contributed to research in topics: Creep & Shrinkage. The author has an hindex of 3, co-authored 3 publications receiving 620 citations.

Creep and shrinkage prediction model for analysis and design of concrete structures - model B3

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.

Probabilistic modeling of quasibrittle fracture and size effect

Abstract: Progres si nstructura ldesig nrequire sprobabilisti cmodelin go fquasibrittle fracture ,whic hi stypica lo fconcrete ,fibe rcomposites ,rocks ,toughene dceramics ,se aic eand man y'hig htech 'materials .Th emos timportan tconsequenc eo fquasibrittl ebehavio ri sa deterministi c(energetic )siz eeffect ,th etheor yo fwhic hevolve dnea rth een do flas tcentury. After a review of the background, the present plenary lecture describes the recent efforts to combin eth eclassica lWeibul ltheor yo fstatistica lsiz eeffec tdu et oloca lstrengt hrandomness with the recently developed energetic theory, and also surveys various related problems, such as the probability tail structure of the stochastic finite element methods, the random scatter in fracture testing, the role of fractal nature of cracks, the reliability provisions of design codes, and the lessons from past structural catastrophes.

Why direct tension specimens flex and break at midlength

Abstract: In a direct tension test, unnotched specimens of quasibrittle materials that exhibit post-peak strain softening do not deform symmetrically. The equilibrium path bifurcates and the thermodynamic criterion of stable path requires the specimen to flex to one side, even if the geometry is perfect and if the straightening effect of the moment of the axial force about the centroid of the deflected cross section is taken into account. In absence of rotational restraints at the ends, the specimen fails right after the peak load. But if the attachments to the loading machine exert a sufficient restraint against rotation, the flexing to the side is retarded and failure occurs at midlength. The phenomenon (which is similar to the recently discovered behavior of notched tensile fracture specimens) is illustrated using a simple model in which the specimen consists of two bars of unequal length, joined by a strain-softening link.

Microprestress-Solidification Theory for Concrete Creep. I: Aging and Drying Effects

Abstract: A new physical theory and constitutive model for the effects of long-term aging and drying on concrete creep are proposed. The previously proposed solidification theory, in which the aging is explained and modeled by the volume growth (into the pores of hardened portland cement paste) of a nonaging viscoelastic constituent (cement gel), cannot explain long-term aging because the volume growth of the hydration products is too short-lived. The paper presents an improvement of the solidification theory in which the viscosity of the flow term of the compliance function is a function of a tensile microprestress carried by the bonds and bridges crossing the micropores (gel pores) in the hardened cement gel. The microprestress is generated by the disjoining pressure of the hindered adsorbed water in the micropores and by very large and highly localized volume changes caused by hydration or drying. The long-term creep, deviatoric as well as volumetric, is assumed to originate from viscous shear slips between the opposite walls of the micropores in which the bonds or bridges that cross the micropores and transmit the microprestress break and reform. The long-term aging exhibited by the flow term in the creep model is caused by relaxation of the tensile microprestress transverse to the slip plane. The Pickett effect (drying creep) is caused by changes of the microprestress balancing the changes in the disjoining pressure, which in turn are engendered by changes of the relative humidity in the capillary pores. Numerical implementation, application and comparison with test data is relegated to a companion paper that follows in this issue.

Nanogranular origin of concrete creep.

Abstract: Concrete, the solid that forms at room temperature from mixing Portland cement with water, sand, and aggregates, suffers from time-dependent deformation under load. This creep occurs at a rate that deteriorates the durability and truncates the lifespan of concrete structures. However, despite decades of research, the origin of concrete creep remains unknown. Here, we measure the in situ creep behavior of calcium–silicate–hydrates (C–S–H), the nano-meter sized particles that form the fundamental building block of Portland cement concrete. We show that C–S–H exhibits a logarithmic creep that depends only on the packing of 3 structurally distinct but compositionally similar C–S–H forms: low density, high density, ultra-high density. We demonstrate that the creep rate (≈1/t) is likely due to the rearrangement of nanoscale particles around limit packing densities following the free-volume dynamics theory of granular physics. These findings could lead to a new basis for nanoengineering concrete materials and structures with minimal creep rates monitored by packing density distributions of nanoscale particles, and predicted by nanoscale creep measurements in some minute time, which are as exact as macroscopic creep tests carried out over years.

The Statistical Analysis, of Experimental Data: A Fresh Approach Employing a Graphical Method for Investigating Non‐Normal Frequency Distributions

Abstract: WHILE the introduction of statistical methods into the analysis of aeronautical experimental data, whether for quality control in production, for the interpretation of the results of structural and aerodynamic laboratory experiments, or for airline operation, has been brought about only in recent years, it may by now be fair to assert that their advantages and even their indispensability are no longer in dispute. Hitherto, investigations on these lines have usually involved, explicitly or implicitly, only the ‘normal curve of error’ and allied considerations; owing, it may be thought, to the controllability of the various manufacturing or laboratory techniques, but also perhaps to the scarcity of data hitherto available. It may well be, however, that with the accumulation of information arising out of investigations planned with particular reference to the statistical analysis of their results the whole range of the apparatus for statistical analysis, usually confined to such fields as those of biology or economics, will be called into full play.

Characterization of Cementitiously Stabilized Layers for Use in Pavement Design and Analysis

Abstract: This report presents information on the characterization of cementitiously stabilized layers and the properties that influence pavement performance. It also contains recommended performance-related procedures for characterizing these layers and performance-prediction models for incorporation into the mechanistic–empirical pavement analysis methods. Individual chapters highlight pavement distresses of hot-mix asphalt pavements and concrete pavements, laboratory tests and model development, and model calibration. The material contained in the report will be of immediate interest to state materials, pavement, and construction engineers and others involved in the different aspects of pavement design and construction.