Probability density functions (normal, lognormal, and three-parameter Weibull) were used to characterize strength data for three different types of metal-plate-connected wood truss joints (web at the bottom chord, tension splice, and heel). Modulus of elasticity (MOE) of the lumber used to fabricate the joints was also characterized. A probability-plot technique, in conjunction with Kolmogorov-Smirnov and chi-square statistics, was used to determine which distribution best fit the data. Lumber MOE was best described by a lognormal distribution. No single distribution form fit the strength data for all three joint types with equal accuracy. Lumber MOE and joint strength were unrelated. Strength data for the web at the bottom chord and heel joints were best described by normal distributions; however, none of the distributions considered fit the data for the tension splice joints. The probability-plot technique provided a better visual inspection of fit than did a density function superimposed over a histogram. Fitted distributions are easy to work with and can be used in reliability analyses to simulate strength values of joints. The results presented here are for particular joint types and plates and should not be extrapolated to other truss joints.
A series of experiments to determine the effect of roughness spacing on open channel flow is reported. The experiments were conducted in an 8-ft wide by 72-ft-long adjustable-slope flume. Roughness elements consisting of sheet metal baffles were placed on the bed of the flume at various longitudinal and transverse spacings. The data are analyzed in terms of the von Karman-Prandtl concepts of turbulent flow near a rough boundary. Logarithmic flow formulas are developed in which the roughness factor is related to the size and spacing characteristics of the roughness elements. The experimental results are compared with those of some other investigators. In addition, some observations are made on the von Karma n turbulence coefficient and the problem of depth determination in rough channels.
Recent experimental work on brittle cleavage fractures in iron and steel has shown that these failures originate with cleavage microcracks. Microcracks with lengths of one grain diameter and longer have been observed in tensile specimens that have been unloaded just below the fracture stress. It has also been shown that local plastic flow of the order of the yield strain occurs prior to the formation of these microcracks even though the subsequent failure involves very little overall deformation. Some of the current dislocation theories predict the formation of microcracks of this type, and the correlation between theory and experiment is encouraging.
Formulas and graphs for determination of critical elastic buckling loads of uniformly tapered columns having wide flange section, box section, and other cross-sectional shapes are presented; columns with pinned ends, fixed-free ends, fixed-pinned ends, and fixed ends are considered; critical elastic buckling loads may be obtained directly from graphs presented.
Design procedures for minimum weight statically determinate beams are developed using deflection criterion; optimum flange width and web thickness variations are given for I-beams designed with respect to bending and shear deflection; stiffness and strength properties.
By making a slight extension to E. W. Lane's tractive-force theory of stable channel design, and by combining it with Strickler's formula, equations are deduced similar inform to G. Lacey's "regime" equations. In particular it is shown that Lacey's width-discharge relation, P ∞ Q, is true for the narrow channel developed in Lane 's theory. It is pointed out that the similarity is of limited significance because the regime condition implies that the bed is live, whereas the tractive force criterion assumes that the bed is only on the thresh old of motion. The latter criterion requires that the shear stress, and hence RS, is constant at all points along the channel. Lacey 's observations on the other hand were to the effect that R2S is constant along the channel, and it is shown by using the Einstein bed load function that this condition is fulfilled in a stable channel with a live bed. These results are then applied to the consideration of longitudinal profiles of stable rivers and canals. It is pointed out that only two stable channel equations can be obtained from consideration of bed conditions and flow resistance, and that a third equation, such as Lacey 's P∞ can be true only if there is a certain slope-discharge relationship, that is a certain longitudinal profile. The nature of this relationship is determined both for fixed (threshold) and live bed conditions, and the former is found to fit well to some data of L. B. Leopold, F. ASCE, and M. G. Wolman on natural rivers in coarse alluvium. Hence, it is argued that in such rivers the relations obtaining at the threshold of motion substantially determine the processes of natural river formation, both in cross section and in longitudinal profile, and that the results obtained herein may form a basis for a general attack on the problem.
Factors to consider in selection of freeboard allowances for wind generated waves in large inland reservoirs; studies conducted by Corps of Engineers concerning estimating characteristics of wind-waves generated in inland reservoirs; outline of wind-tide relations as associated with inland reservoirs; hydraulic model studies and related analyses examined; sample computations presented to illustrate applications of generalized relationships described.
Basin is device for dissipating excess kinetic energy and has important advantages for some conditions; 2 field installations of manifold stilling basin are described; both were made at outlet ends of pipe drops in canals in which vertical drop of water surface was several tens of feet.
From results of former airport pavement researches it is concluded that use of properly distributed wire reinforcement in concrete airfield pavements controls cracking, reduces maintenance, and increases service life; aspects of design; computation of steel area based on subgrade drag theory; coefficient of subgrade; pavement design of Indianapolis, Ind, municipal airport.
Elasto-plastic analysis for bending and buckling of prismatic structural members by numerical procedures is presented; stress-strain diagram composed of 2 straight line segments is used to approximate actual stress-strain diagram of material; this simplifies computations and gives good accuracy for materials having defined stress-strain diagrams.
Theoretical prediction of diffusion in homogeneous turbulent fields from the Taylor theory of diffusion by continuous movements requires knowledge of the Lagrangian turbulent velocity correlation coefficient. Although a direct theoretical connection between the Lagrangian and Eulerian correlation coefficients has not been found, it is shown that an empirical relation can be established. Eulerian correlation coefficients from hot-wire anemometer measurements are compared with Lagrangian correlation coefficients derived from diffusion measurements in a homogeneous turbulent flow. From this comparison, a relationis found that permits a direct prediction of turbulent diffusion from hotwire (Eulerian) measurements of the turbulent field. Some measurements of a mixed space-time Eulerian correlation coefficient are described, and a possible direction of further research is presented.
