Journal of Structural Engineering

Magnel's graphical method for the analysis of a prestressed concrete beam is very useful for the determination of safe prestressing force and eccentricity. The paper presents the characteristics of the original Magnel diagram, reviews the writers' modifications to and extensions of the method, discusses relevant work by others, and offers a further simplification for the plotting of the safe zone, illustrated by a worked example.

The geometric nonlinearities in elastic nonsway frames are examined and used to review the rationale and accuracy of the ACI slender column design method. The use of nonsway effective length factors to account for effects of end restraints, and the assumptions of idealized end restraints in the conventional alinement chart for effective length factors are investigated. The discussion is also applicable to the moment magnifier portion of the AISC column interaction equation.

Based on 69 tests, recommendations are made for immediate revision o design standards and necessary additional research on timber connectors. he mean safety factor for four‐connector joints is alarmingly low at .88 for the first series of 34 specimens and increases to 1.21 for the 20 tests of he second series from a new shipment of billets. The mean safety factor for 5 three‐connector tests is 1.06. Tensile strengths perpendicular to the glueline re reported and compared with tests reported in 1975. The strength of the test aterial is about 1/3 to 1/2 of that expected. The low safety factors are attributed o a combination of the poor distribution of loads among connectors and he low perpendicular to glueline tensile strength. A finite element stress analysis n single connector joints is used to investigate the effect of varying end istances.

The fracture and flow characteristics of ice is dependent upon the state of stress, substructure geometry, temperature and strain rate. Compressive and tensile strength vary greatly due to the variety of ice types and their dependence on these factors. Simplifications of the mechanical behavior and failure criteria of ice are often necessary for engineering applications. Common idealizations of ice mechanics are addressed with emphasis on the suitability of various yield criteria for combined stress states. The failure of ice can be considered to be either yield‐dominant or as fracture‐dominant, while retaining the simplicity of conventional criteria. Their suitability to ice mechanics is enhanced by their capability of being adapted to a wide range of tension‐compression failure envelopes.

An analytical method is proposed and a computer program developed to analyze double chord trusses comprised of rectangular hollow sections. Three types of local yield mechanisms are incorporated: (1) Plastic hinge formation; (2) member yielding due to plastic load limit; and (3) yielding of shear springs that model the connections. The analysis is carried out in an incremental manner. Overall failure of a truss is declared when either an overall mechanism forms or excessive deflection occurs. A bilinear axial force‐moment interaction diagram is used to allow for reduction in the plastic moment capacity due to the presence of axial force. Results from analyses of Warren trusses with three different types of connections are presented and compared with those obtained experimentally from a previous study. Overall, very good agreement is observed thus verifying the validity of the analytical model.

The paper summarizes trends presently being followed in the windtunnel simulation of bridges. Topics treated are scale factors, section, partialand full‐bridge models, testing under laminar and turbulent flow, and the measurement techniques attendant upon the identification of aerodynamic coefficients of various kinds, including those related to aeroelastic effects. Attention is focused on the section model. The primary purpose as well as secondary purposes of the section model are examined. Section model testing under turbulence and the appropriateness of the test turbulence are also reviewed.

A bibliography on the design and performance of diaphragms using lumber, plywood or reconstituted wood panels is presented. Entries are listed in reverse chronological order, the most recent dated 1982 and the earliest dated 1927. References on design loads on building diaphragms and methods for testing diaphragms are included. Annotations are included where practical.

Elastomeric bearings are widely used by structural engineers, but their behavior is not well understood. The paper provides a brief description of the state of knowledge throughout the world with respect to these bearings. It summarizes the material behavior of elastomers and the theoretical and experimental research on bearings. It notes the various modes of failure, and the major design methods are described and compared. There are wide variations in standard practice throughout the world, and the contradictions and reasons behind the variations are noted. The objective of the paper is to help the structural engineer get a better understanding of the design and selection of elastomeric bearings.

This paper documents the structural design and analysis as it evolved in the planning of the new Capital Bank Plaza in Houston, Texas. The 1,375,000 sq ft $\left(127\text{,}900m^2\right)$ office tower consists of 50 levels above grade and 2 levels below grade. Wind resistance for the tower, an irregular shaped octagon in plan, facilitated the “framed tube” concept. Two‐story high prefabricated “tree column” modules were located at 10 ft (3 m) on center at the building perimeter. The structure is supported by a foundation mat with a basic thickness of 8 ft (2.4 m). Shortly after steel erection had commenced on the structure originally planned as a speculative office development, a Houston bank initiated plans to move their banking operations into the tower. To accommodate the bank's space planning requirements, the lower levels were redesigned to accommodate expansive open atrium banking and executive office areas with elevated walkways crossing the atrium spaces at various levels.

The numerical formulas are presented for quick determination of natural frequencies of orthotropic and isotropic continuous uniform plates. A one‐way continuous plate consists of two types of independent vibration modes in both directions. The transverse mode represents the number of half‐waves across the width of a plate. The longitudinal mode possesses more implicit characteristics, nevertheless it may represent shape distribution across all the panels. It has been noted that the frequencies of continuous uniform plates can be grouped in formation of clusters. The frequency clusters analyzed in this paper are based on the transverse modes. Therefore, each cluster consists of the number of longitudinal frequencies equal to the number of panels or spans in a continuous system. An example of twelve‐span continuous plate and 164 natural frequencies is included. Over sixty percent of the frequencies has error percentage less than 0.01. The maximum error is only 0.044%.

The moment‐ratio method developed is a numerical procedure to determine the natural frequencies of continuous orthotropic and isotropic plates. The basic concept employs dynamic flexibility functions at the panel joints. The moment‐ratio function of a panel may be obtained from the transfer of the preceding one. A fixed number of computational steps equal to the number of panels is required for each cycle. One of the natural frequencies will be obtained when the terminal moment‐ratio vanishes. A sufficient number of times with assumed varying frequencies will determine one of the natural frequencies to a degree of desired accuracy. Three numerical examples are included. Some of the numerical solutions are compared with existing data. Four types of boundary conditions of continuous plates—partial constraint, simple‐simple, simple‐clamp, and clamp‐clamp—are developed. An equivalent analysis of continuous orthotropic and isotropic plate systems is presented and their numerical frequencies are compared. Frequency clusters formed in uniform systems are introduced in the moment‐ratio method.

A general solution method of a system of coupled differential equations governing the elastic buckling of thin‐walled curved members is presented. The finite element displacement method is formulated based on a variational principle. The stiffness and stability properties of the finite elements are consistent and are obtained within the bounds of linearized displacement theories. Included are the warping contributions to the buckling loads and the effects of antisymmetry of the cross section which were found to be significant. Examination of a convergence test indicated an extremely fast converging upper bound solutions as expected due to the utilization of the variational procedure. Critical loads were obtained using a computer program (CVSTB) developed for a few combinations of loading and boundary conditions and design charts were prepared. Comparative studies were made with a few existing solutions and possible sources of discrepancies were traced.