Journal of Structural Engineering

Flexural collapse loads of eccentrically loaded, individual column footings were investigated using Yield Line Theory. It was found that the cantilever failure mechanism recommended by the AC! Building Code does not give the lowest upper bound on the loads. Governing equations were derived for mechanisms that led to flexural collapse loads as low as one‐half those predicted by the cantilever mechanism for some column/footing combinations. Suggestions are given for a reasonably simple design procedure that should ameliorate the problem.

An overview of the major concepts and methods used in reliabilitybased structural optimization is presented. New formulations related to multicriteria optimization are developed. Comparative results are presented when different criteria are used for the optimum design of a structure under service and ultimate reliability constraints. It is concluded that reliability‐based optimization is now practicable for structural engineers. The writing of appropriate reliability‐based optimum design software is a vital element at present receiving too little attention.

This paper presents a theoretical analysis of thermally induced noise in sheet metal roofs. A quasi‐static model of the roof behavior is developed based on roof support batten frictional forces constraining the thermal expansion and contraction of the sheeting. As a result, in‐plane stresses, set up in the sheeting, build up until the static frictional force limit is exceeded at one of the fasteners. At this point the sheeting slips over the batten at that fastener, the local frictional force is reduced to the dynamic frictional force limit, and a redistribution of in‐plane stresses and fastener forces occurs. The redistribution can cause an overload of an adjacent fastener frictional force to exceed its limit, thereby inducing another slip. The sequence will continue until all frictional forces are below the static frictional force limit. The change in deflection pattern of the roof accompanying each slip is used to estimate the noise generated. With the assumptions that the curvature strain is small relative to the thermal strain, the coefficients of friction at each batten are identical and the batten spacing is uniform, the theory may be used to derive considerable detail of the slip cascade pattern and to determine expressions for the rate of noise bursts, for the necessary temperature change to cause a roof to change from “heating” to “cooling” cycling, and for the impulsive noise level.

Full‐scale wind velocity and structural response data from a tall guyed tower have been analyzed to obtain information concerning wind characteristics and dynamic response. Anemometers and accelerometers were installed at five stations along the height of the tower, and orthogonal components of wind velocities and tower accelerations were recorded. Design guidelines specify 1/7 as the power‐law exponent for wind profiles in coastal regions. However, data from this project, though limited in number of samples and conditions, indicate a mean exponent of 0.287. Digital correlation and spectral analysis are applied to the tower acceleration data to obtain estimates of resonant frequencies and critical damping ratios.

Simple design approximations are presented for determining the transverse moments in single‐span, single‐cell concrete box girder bridges. Five representative loading cases are considered which can be used in combination to model a range of vertical dead and live loading and wind loading. The design approximations are based on the analysis of the cross section as an isolated framework. In the case of twisting loads, the longitudinal distributions are expressed in terms of a dimensionless panel length. The design approximations are derived from a finite element parameter study and give moments that are accurate to about 5%.

Effects of geometrical configurations of welds on stress and strain distributions are investigated experimentally and theoretically. Three types of weld configurations are analyzed under axial and bending loads. Analyses by using a three‐dimensional finite element method are performed, and the results are compared with the experimental ones with good accuracy. Stress and strain concentration factors are also investigated, and the applicability of Neuber's equation is examined.

In several problems of engineering and sciences, the domain of analysis extends to large distances in one or more directions. Such problems can be analyzed efficiently by the method of finite elements by using a combination of finite and infinite elements to discretize the domain of analysis. The existing approaches to formulating infinite elements have not been exploited to their full extent. In this research, these formulations are used to derive some advanced infinite elements with various forms of decay. The implementation of these elements and general formulation are verified by solving an elastic halfspace problem in axisymmetric as well as in plane strain formulations. Also, this method has been applied to the problem of a shallow underground opening in horizontal tensile stress field. The numerical and analytical results are found to be in satisfactory agreement. These infinite elements overcome the difficulties of parametric formulation and numerical integration, but are suitable for the problems of elastostatics only.

This paper deals with the bending moments and shear forces that are induced in the members of the frame by the differential column shortening, taking into account the construction sequence and the sequential application of dead weight in the analysis. Utilizing the substructuring techniques, the entire frame is analyzed by “one substructure at a time” approach in the reverse order of construction. Numerical examples of two high‐rise buildings clearly show the significance of the differential column shortening effects and the effectiveness of the proposed frame analysis technique in coping with the problem.

The stability of steel radial gates used in reservoirs, hydroelectric power stations, etc. is studied by modeling them as rectangular, trapezoidal or triangular frames. The elastic resistance of the rubber seals for preventing leakage is incorporated in the formulation. Results are expressed in terms of the effective length factors of the compression members in the gates.

The integral collocation method (ICM) is used to analyze large deflected circular plates with clamped (radially held and not held) outer edge under uniform pressure. The ICM has been completely computerized with automatic precision control and exhibits excellent results for the aforementioned plates. Convenient formulas have been derived using the least squares method, following an evaluation of many solutions of Von Karman's equations. Critical values of fiber stresses and deflections are presented in numerical and graphical form. For confirming the validity and usefulness of the proposed formulation, comparisons are made with existing formulas. The comparative study shows a significant discrepancy in stresses; however, a good agreement is shown in deflections. The proposed computational technique presents lower stresses in the midplate and higher stresses at the edge of the plate than the existing formulas. However, results show that the edge stresses are always higher than the midplate stresses in both methods. Further confirmations are made by comparison with the finite element results. Results of the comparison indicate that the proposed formulas produce more exact results than the existing formulas.

von Karman equations are used for the analysis of rectangular window glass plates subjected to lateral pressures. A previously reported model that used a finite difference method solved the glass plate problem with simply supported boundary conditions. Here, this model is modified to include conditions where the plate is elastically supported on the boundary. Both linear and nonlinear elastic supports are considered. An efficient iterative procedure is used to solve the nonlinear equations.

Cold‐formed sections allow for very high efficiency since the shape and the size can be fitted to the specific working conditions. The use of these shapes in lieu of hot‐rolled angles in latticed transmission towers favorably affects the overall cost. Recommendations for the design of cold‐formed members for latticed transmission towers are presented, based upon the AISI “Specification for the Design of Cold‐Formed Steel Structural Members” and on significant specific testing experience. These recommendations cover all the shapes except plain angles. Experimental results are presented reflecting the correlation between test results and design recommendations. The fabrication technology calls for special care in the selection of steels which exhibit adequate ductility. Recommendations regarding galvanizing, shape tolerances, and connection are also included to provide guidance for proper design.

An approach is presented for the generation of seismic floor response spectra for structures which cannot be modeled as classically damped. Although the nonclassically damped structures do not possess classical modes, the proposed approach can still employ prescribed ground response spectra directly as input for the generation of floor spectra. The approach requires the solution of a complex eigenvalue problem which provides the information about the equivalent modal frequencies and damping ratios of the structure. The floor response spectrum value is expressed in terms of these equivalent modal parameters. The seismic input is required to be defined in terms of psuedo acceleration and relative velocity ground spectra for the equivalent modal frequencies and damping ratios of the structure and also at the oscillator frequency and its damping ratio. To verify the applicability of the proposed approach in view of simplifying assumptions made in this development, a numerical simulation study has been conducted. The results obtained by the proposed direct approach and the time history approach for an ensemble of acceleration time histories as inputs compare very well with each other, thus validating the applicability of the proposed approach.

An integer programming formulation for the minimum cost design of precast, prestressed concrete simply supported beams is developed. The cross section and gridwork within which strands must be placed are assumed given, and the design problem is to determine the concrete strength and the number, location, and draping of strands that minimizes the total cost of the beam. Constraints limit release and service load stresses, ultimate moment capacity, cracking moment capacity, and release camber. A box girder for a multibeam highway bridge is designed to demonstrate the computer program written to implement the methodology.

The lateral‐torsional motion of tall buildings is investigated. For a square cross‐section building, expressions for the alongwind, acrosswind and torsional loading are developed through the use of spatio‐temporal fluctuations in the pressure field around the building. A simplified formulation is used to represent the dynamic behavior of torsionally coupled buildings by considering a class of buildings in which all floors have the same geometry in plan, the eccentricities between the elastic and mass centers are the same for all stories, and the ratio of the story stiffness in lateral directions is about the same for all stories. Methods of random vibration theory are used to estimate the rms and peak values of various components of response. The results indicate that the torsional response contributes significantly towards the overall dynamic response of a symmetric building. Inclusion of coupling between the lateral and torsional degrees‐of‐freedom further increases the building response. The procedure presented here provides a convenient checking procedure, from a structural reliability viewpoint, for serviceability and survivability limit states, thus ensuring serviceability under normal conditions as well as safety under extreme loads.

A series of 13 wood floors was tested under uniformly distributed load. The floors were manufactured with 12 (nominal) $28\mathrm{hemlock}$ joists, “No. 2 and better” grade, 5/8 in. (15.8 mm) Douglas‐fir plywood, and 8d common nails at 6 in. (152 mm) o.c. In two floors the nail spacing was increased to 12 in. (305 mm), and in one floor, 5/8 in. (15.8 mm) waferboard replaced plywood as the sheathing. Experimental results are presented for floor deflections, first joist failure load, and subsequent failure loads. Test results were compared with theoretical predictions using the computer program FAP. It is concluded that, although first joist failure should be used in reliability analysis, the load carrying capacity of the floor assembly is normally higher and several more joist failures usually occur before total collapse. The variability in floor strength is substantially lower than the variability in bending strength of individual joists. The tests showed that floor behavior was nearly linear, and the results compared well with FAP predictions. In particular, the required nail stiffness may be obtained from a simple nailed joint test in compression. It was also concluded that the weakest joists are not generally the ones that fail first in a floor, and that reliability predictions of floor strength can only be obtained when the bending strength is known for the weaker as well as the stronger joists in the population.