Journal of Structural Engineering

There are significant differences in glass strength information presented by major United States glass manufacturers. These differences have caused considerable confusion among glass designers. The differences are the result of different simplifying assumptions in formulation of the respective glass design procedures. Presented in this paper is a glass failure prediction model which relates the probability of failure of glass to surface flaw characteristics and induced stresses. This is accomplished by combining a statistical failure theory for brittle materials with results of a geometrically nonlinear plate analysis. The model is formulated to include all factors which are known to significantly affect the strength of glass, such as load duration, surface area, etc. As such the model provides a basis for resolving current conflicts in the glass design process.

The coupling action of a slab which is connected by moment‐resisting joints to the core and peripheral frames in a laterally loaded hull‐core structure is investigated by a finite element method. The relative influences of a range of geometrical and stiffness parameters are evaluated. It is found that the column to slab flexural stiffness ratio has a significant effect on the rotational stiffness and effective width of the slab, but practical variations in column axial stiffnesses have negligible effects on the slab stiffness. With a constant column‐slab flexural stiffness ratio, the influences of both column spacing and spandrel beam stiffness are negligible. The effective slab width increases with both relative core width and core depth. Curves are presented to facilitate the evaluation of rotational stiffness and effective width for practical situations. The coupling action reduces the shear lag in the outer framed‐tube.

Failure criteria for the tensile strength of ungrouted and grouted unreinforced concrete masonry are developed. These criteria account for the strength variation due to the anisotropic nature of masonry as a composite material. The tensile strengths normal and parallel to the bed joints are described in terms of the strength and geometric characteristics of the block, mortar, and grout. The diagonal tensile strength is described as a function of the strengths normal and parallel to the bed joints. Tension failure and combined shear‐tension failure are the two possible failure modes that were considered in the development of the failure criteria for tension parallel to the bed joint and for diagonal cracking. The predicted ultimate strengths using the proposed expressions are compared with experimental results for splitting tests of ungrouted and grouted masonry disks. Good agreement is shown, and it is concluded that the proposed criteria can be used to evaluate the influence of the stress orientation and the effect of varying the different strength and geometric properties of the components on the tensile strength of concrete block masonry.

Simple design‐oriented analytical expressions are developed to estimate the reserve‐load carrying capacity of circular tubular beam‐column members with overall bending and local denting damage. The analysis is based on a member with a reduced effective section to account for the effects of such damage. Comparisons show the method to provide close lower bound predictions of available theoretical and experimental results. Finally, the mechanics of damage are examined in a detailed parametric study, the results of which can be useful in direct design applications.

Proof sampling is the proof load testing of a sample of structural components. A probabilistic model of posterior strength is developed for the untested components in a lot that passes a proof sampling test. When strengths in a lot are highly correlated, it is found that the proof sampling test is virtually equivalent to a proof test of all components. On the other hand, if component strengths are uncorrelated, it is found that there is no point to the test unless all components in the lot are proof tested. Load factors are calculated for the inferred distribution of strength assuming a Gaussian distribution of load. The load factors can be used to find a limit load that the untested components can support with target reliability or, conversely, to specify a required test load for safety verification. In an example concerning lot‐produced roof trusses with moderately high correlation, the proof load testing of two trusses, in situ, avoids other costly testing alternatives.

Following an extensive educational program and the provision of the necessary design aids, Canada's national design standard for limit states design of steel structures for buildings, CAN3 S16.1‐M78, is being used to design structures with greater economy and more uniform safety than before. The standard, developed over a period of 5 yr, was first introduced in 1974. Steel designs are now considerably more cost competitive with weight savings of up to 10% or more as compared to working stress design. Students learn the same methodology for steel and reinforced concrete design. The limit states format leads to simplification and greater understanding by users. Designers are made more aware of structural behavior and the need for checking both ultimate (strength) and serviceability limit states. Building structures up to 40 storys high with many types of framing and steel masses up to 40,000 tonnes have been built. In 1985, after 10 yr of parallel use with the working stress design standard, only the limit states design standard will be referenced in the National Building Code of Canada.

A method of analyzing the elastic flexural‐torsional buckling of curved beams is presented. Included in the solution is warping contribution to the bifurcation buckling load. Since the coefficients of the general differential equations describing the buckling behavior of a spatial curved member remain constant under in‐plane bending considered, a closed form solution technique is used in determining the buckling loads with or without in‐plane deformation. Comparative studies are made and possible sources of discrepancies are traced.

Low‐cycle fatigue tests were conducted for X‐type welded tubular joint specimens with three types of stiffeners. The test data are arranged in the form of total plastic work, total strain, and the S‐N curve; and the relationship between type of stiffener and scatter of strength is examined in connection with fatigue resistance.

Stiffening effect on the X‐type welded tubular joint is evaluated by a numerical procedure. Tubular joints with three kinds of stiffeners are analyzed by finite element technique using an elasto‐plastic isoparametric thick shell element. Two parameters are introduced to the evaluation of the stiffening effect; they are a mean equivalent plastic strain increment and a plastic work increment per unit volume. The parameters are calculated in the three cases of the stiffening types, and are compared with the experimental results prepared by the writers. It is concluded both of them are effective, and the former is recommendable. The calculation is stood on a static load condition, nevertheless the results can be applied to a fatigue problem because the fatigue resistance of the stiffened joint is in proportion to its static strength. Finite element analysis is also applied to the estimation of an optimum shape of the st.

Pressures, loads, dynamic responses and adverse pedestrian‐level environments caused by wind action on buildings and structures are commonly determined by physical modeling in wind tunnels. Accurate quantitative evaluation of these effects for wind engineering requires that natural wind characteristics be simulated with reasonable fidelity. Features of boundary‐layer wind tunnels that meet this requirement are presented and reviewed. Two general criteria are proposed as minimum performance requirements of wind tunnels used to test buildings and structures for wind effects.

The eccentrically braced steel frame provides an efficient structural system for resisting lateral loads caused by wind or seismic activity. In some applications, this versatile system can reduce overall material requirements and result in a frame which is still under moderate loads yet ductile at extreme overloads, an essential feature in seismic design. In this paper, some of the fundamental characteristics of the behavior of eccentrically braced frames are examined by studying some simple examples. The results provide a qualitative assessment of the behavior of the framing system for use in seismically active regions.

An experimental investigation was undertaken to determine the effect of two curing environments on the development of relationships between pullout strength, compressive strength and the maturity of concrete. For the one batch of concrete used and the curing environments chosen, the following significant conclusions resulted from the investigation: (1) Maturity can be used to predict the pullout force or compressive strength; (2) pullout testing provides a measurement of concrete strength; (3) pullout testing results obtained by testing a column of concrete were influenced by top‐to‐bottom effects; and (4) the strength of a controlled cylinder most nearly represented the concrete strength in the bottom portion of the column at an age of 28‐days.

Alongwind and acrosswind response of self‐supporting reinforced concrete and latticed steel towers is studied analytically as well as experimentally. The analytical approach utilizes existing methods of analysis with certain modifications, while experimental study is carried out on aeroelastic models placed in uniform as well as shear flow fields generated in a medium size closecircuit wind tunnel. Results obtained are compared with measured prototype data and the comparison is found to be satisfactory. Experimental results further indicate that towers can be modeled adequately with respect to their mass and stiffness distribution without adding discrete masses. For prediction of alongwind response however, the models can not be relied upon unless these are tested in a boundary layer flow with adequate turbulence intensities.

Based on a large number of test results obtained from 747 specimens, an attempt is made to find out simple mathematical expressions that explain the resistances of tube‐to‐tube joints with circular hollow sections under axial brace loading. Multiple regression analysis is performed on a carefully established data base to obtain the best predictive equations. The proposed yield and ultimate strength equations are shown to be in good agreement with the test results, provided that the joints are not controlled by brittle failure. These equations are applicable for wide range of basic variables, which include the geometry and size of the joints, the yield stress and yield ratio of material and the axial stress in the chord. The resistance factors for the design for an ultimate limit state are calculated. It is shown that the standards of tolerance control and material selection and the dimensions of structures must be considered to determine the resistance factor appropriate to the design situations.

Floor vibrations arising from normal human activity may affect the serviceability of modern building structures, which are becoming lighter and more flexible. Existing serviceability criteria for floors are reviewed in the light of research dealing with human perception of structural motion. The dynamic response of floors to realistic pedestrian movement excitation models is analyzed. Tentative serviceability criteria to minimize floor vibrations that are objectionable to building occupants are presented.