Journal of Materials in Civil Engineering

Finite element simulations are used to investigate the mechanical behavior, including the detailed sequence of failure, of single‐and multilayer, fabric‐reinforced membrane systems under in‐plane load. In situ, such membranes are frequently loaded by opening of cracks in the substrates to which they are adhered. Simulations of a “joint‐bridge test,” which produces this type of loading, are carried out. For multi‐ply membranes, characteristic of roofing systems, normal and “inverted” systems are examined. Mechanically, these systems behave quite differently from each other and from their component plies. Simulation of a standard tension test shows that in‐jaw displacements can be significant, and that the mechanisms of load carrying and failure can be quite different from joint‐bridge or in situ behavior. The possible mechanical benefits of an initially debonded strip centered on a substrate joint or crack are also evaluated. The analyses provide an important complement to physical testing.

Testing of thermal resistance of masonry walls is very expensive and can be accomplished only on fabricated blocks. Manufacturers and designers thus need a reliable tool for the prediction of the r‐values before producing forms. The paper compares results obtained by the two common simplified computation methods with those derived from a more‐accurate three‐dimensional (30) finite‐difference thermal analysis. The paper shows that the method of combined parallel heat‐flow paths yields a better approximation to the accurate analysis than the method of series of layers perpendicular to the main heat flow. Theoretical results are also compared to data from test measurements of 18 hollow‐core blocks with side indentations and two other blocks. Computations overestimate the measured values by up to 20%. Since measurements have their own inaccuracies and uncertainties, it is concluded that a reliable conservative value can be obtained by reducing the values estimated with the 3D method by 20%.

Construction of shoulders using untreated reclaimed asphalt pavement (UNRAP) represents a new construction technique for Florida Department of Transportation (FDOT) and other DOTs throughout the country. The objective of this study was to provide practical guidelines that can be used in constructing shoulder base courses with UNRAP material. Field and laboratory tests were performed to determine the physical and mechanical properties of UNRAP material. The results suggest the UNRAP material is well graded and its maximum dry density is comparable to those of other conventional granular materials. However, the optimum moisture content for UNRAP is much lower than that for conventional granular materials. The in‐place strength of UNRAP base, as postulated from the Dynaflect test results, is on the order of 70–85% of the strength of the limerock base. The use of UNRAP base in constructing paved shoulders was found to be an economically and technically feasible alternative to traditional limerock. Additional theoretical and experimental studies as well as new test procedures to assess strength characteristics of UNRAP are warranted.

Fiber‐reinforced plastic (FRP) structural members with open or closed thin‐walled sections are being used as beams and columns for structural applications where buckling is the main consideration in the design. Analytical models for several local buckling modes under axial and shear loading, taking the flange‐web interaction into account, are developed. Experimental data correlating predicted and observed behavior are presented for some commercially available structural shapes. Failure envelopes are developed for box‐ and I‐shape FRP columns and beams. The analytical models presented can be used to predict the behavior of any new pultruted material. The Rayleigh‐Ritz method is used in this work to analyze anisotropic flanges of box and I‐beams. The anisotropy of the material is introduced by ±45° angle‐ply layers introduced recently by pultruted manufacturers to improve the buckling strength of columns as suggested by this investigation.

Using a technique for accelerated corrosion monitoring, corrosion‐resisting characteristics of reinforcement of four plain and 36 fly ash blended cement concretes have been evaluated. Three fly ashes of bituminous, sub‐bituminous and lignite origins have been used, in conjunction with four plain cements having $C_{3}A$ contents of 2%, 9%, 11%, and 14%. The 36 blended cements were formulated such that each of the four $C_{3}A$ cements had 10%, 20%, and 30% cement replacements by each of the three fly ashes. Results of corrosion monitoring tests show that fly ash blending of plain cements by 30% partial replacement improved the corrosion‐resistance performance twofold to threefold over plain type I and type V cement concretes, respectively, in terms of corrosion‐initiation time. Fly ash of lignite origin exhibited better impermeability and corrosion‐resisting characteristics than bituminous and sub‐bituminous fly ashes. Level of replacement is a significant performance parameter, with the best performance observed for 30% replacement. The time to initiation of corrosion and weight loss were significantly influenced by the $C_{3}A$ content of the cement; 9%, 11%, and 14% $C_{3}A$ cements performed 1.75, 1.93, and 2.45 times better than the 2% $C_{3}A$ cement in terms of corrosion‐initiation time. The beneficial $C_{3}A$ effect was also operative in fly ash blended cement concretes, although on a reduced level.

The nonlocal microplane model for concrete is improved to describe unloading, reloading, cyclic loading, and the rate effect. The differences compared to the previous formulation are: (1) Normal strain component on the microplane is not split into its volumetric and deviatoric parts—rather the normal component is made dependent on the lateral normal strains on the microplane; and (2) instead of considering on each microplane only one shear strain vector parallel to the shear stress vector, the shear strain is represented by two independent components on the microplane. To introduce rate effect, the stress‐strain law for each microplane component is described by a generalized Maxwell model—a series coupling of a linear viscous element and an elastoplastic‐fracturing element. Nonlinear unloading‐reloading hysteresis rules with back‐ and objective‐stresses are developed to introduce hysteresis. The model is then combined with nonlocal theory to enable describing localization phenomena and avoid spurious mesh sensitivity due to strain softening. The numerical implementation in finite‐element programs is described. The study consists of two parts; part I deals with the general formulation (part II deals with experimental verification).

This second part of the study deals with experimental verification of an improved and generalized nonlocal microplane model whose general formulation was given in the first part. First the stress‐strain relations for a material point are simulated with a local version of the model, and then the representation of some basic tests is studied in finite‐element analyses with the nonlocal calculation.

A series of early‐age creep tests was conducted on mass‐concrete mixtures to be used in the construction of locks and dams. Tests were conducted to determine creep at ages of loading from 18 h through several days. While there is a significant data base for the material properties of mass concrete at later ages, there are very few data for the early‐age creep properties of mass concrete. A discussion of the test procedures and the findings of this investigation are reported. The creep response of mass concretes with different mixture proportions or constituents can be vastly different. Since no universally applicable constituent‐based model of early‐age mass‐concrete creep response is known to exist, early‐age creep tests should be conducted for any concrete mixture or application for which it is an important parameter. The development of models capable of accurately predicting early‐age creep response from constituent properties should be a high‐priority research item in concrete technology.