Journal of Structural Engineering

Design charts are presented for the design of a stiffened coupled structural wall with a strong beam located somewhere along the building height. The analysis is based on a continuous medium approach with the deflection at the top. The couple due to the axial force in the walls and the shear force in the laminae are presented in the form of graphs. The variations of the couple due to the axial force in the walls and the laminar shear along the structural height are also presented to permit the curtailment of reinforcements where appropriate for achieving economy. The results are given in terms of two dimensionless structural parameters: one is the relative flexural rigidity of the strong beam, and the other is a measure of the effectiveness of the lintel beams. The application of the design charts is illustrated by determining the deflections and the internal forces of a typical 20‐story building.

A general approach is presented for the estimation of expected failure rates of structures per unit time, which accounts for uncertainties about mechanical and geometrical properties, as well as about live load and seismic excitation. Such an approach is applied to one‐, three‐, and nine‐story frames with nonlinear behavior, subjected to random sequences of simulated accelerograms corresponding to soft and hard types of ground. Conclusions are reached concerning the influence of several concepts on the probability of failure of the structures analyzed, including: (1) The influence of the spatial statistical correlation among the mechanical properties of the structural members is relatively small as compared to that of other variables; (2) the number of degrees of freedom has a great influence on the probability of failure; (3) for small coefficients of variation of the available ductility, the probabilities of structural failure for a given intensity are higher than those corresponding to greater coefficients of variation (this is a consequence of the assumed relation between expected and nominal values of this variable); and (4) the structural failure rate decreases when the design ductility factors increase. It is pointed out that these conclusions are not valid if the safety factors with respect to local brittle failure modes are small as compared with those associated with ductile modes.

A viscoelastic model accounting for the stability effect is proposed for high‐damping elastomeric bearings used in aseismic base isolation. This model is consistent with Haringx's theory, which takes into consideration the significant shear deformation of the elastomer. The method of mode superposition is used to obtain an alternative solution to the “Haringx column,” and this solution is readily generalized to include viscoelasticity. Each mode is an eigensolution of the corresponding stability problem. The rapid fourth‐order convergence permits the use of only the first mode to give a very good approximation. The dynamic shear stiffness, damping characteristics, and height reduction of bearings are obtained by the first‐mode consistent model. In particular, the phenomenon of increasing energy dissipation due to the axial load is explained by the model in a consistent way. The applicability of the model is then verified by experiments conducted on multilayer elastomeric isolation bearings with and without lead plugs.

Historical information, research results, and codes/standards provide the basis for a profile of snow load design practices in North America. Canada prescribes 30‐year mean recurrence interval (mri) ground snow using a Gumbel distribution, whereas the United States is adopting 50‐year mri ground snow modeled with a lognormal distribution. Ground‐to‐roof conversion factors are described with reference to the Canadian studies (1956–1967) and the nation‐wide measurements used in writing the 1982 standard for American National Standards Institute. Various field investigations revealed the effects on roof snow accumulations of roof exposure to wind and sun, roof geometry, roof cladding, and building thermal losses. We describe similarities in the three major model building codes, plus standards, in the United States, and the code of Canadian. Critical research needs on snow loads are also explained.

The performance of moment‐resisting connections between precast columns and precast partially prestressed beams was investigated. The specimens represented exterior beam‐column joints. The only variable among the specimens was the type of connection used. The four connection types considered were: posttensioned (BMA); threaded rebar (BMB); composite‐post‐tensioned in the bottom of the beam with a cast‐in‐place top (BMC); and welded (BMD). The structures were designed to develop a primary plastic hinge in the beams outside of the connection region (at 35 in. from the column face) where the prestressing strands were considered fully developed. All of the structures were subjected to identical cyclic lateral load histories. The connections were evaluated based on their performance in terms of strength, ductility and energy dissipation characteristics, as well as, their fabrication feasibility. Of the connection types tested, the most promising details were the threaded rebar and composite connections.

The longitudinal shear flow in composite steel and concrete beams is transferred across the steel‐flange/concrete‐slab interface at a discrete number of points by the dowel action of individual connectors. The dispersal of these concentrated loads into the concrete slab induces lateral tensile forces in the slab, which may cause the slab to split and lead to a loss of interaction and of shear strength. An analysis of 50 reinforced and unreinforced push‐out tests that failed by splitting, and finite element model studies of the shear flow in composite beams, have led to a method of predicting the occurrence of splitting due to the local action of individual connectors and the global action of groups of connectors. It has been found that transverse reinforcement does not prevent splitting but limits the extent of the split and hence limits the loss of interaction and shear connection.

The static and dynamic behavior of a cable dome was studied by testing a 1/50 scale model. Three different pretension levels were considered. The static response of the model under a symmetric and an antisymmetric loading was investigated. The cable dome's behavior changes from a compressive to a tensile membrane with increasing applied central load. The cable model exhibits a hardening response, especially in the antisymmetric mode. The nonlinearity becomes more pronounced with decreasing pretension. The stiffness in the antisymmetric mode is dominated by the geometric stiffness from pretensioning. In the vertical acceleration (symmetric) test at the intermediate pretension the first dominant mode was antisymmetric. A small exciter was also used to apply a single asymmetric controlled force. Up and down harmonic excitation sweeps showed a dynamic instability. The frequency range over which the response is unstable decreases with increasing pretension. The dynamic to static strain ratio decreased from 20% to 2.3% as pretension increased from the lowest to the highest value.

For the calculation of the ultimate strain of compressed concrete elements, a procedure is proposed that is based on the limit stability condition of longitudinal reinforcing bars. The analysis model is the one proposed in Papia et al. (1988), which provides the critical load of the bar with reasonable accuracy. Analogous precision in the values of the critical strain of the longitudinal reinforcement, assumed to coincide with the ultimate strain of the concrete element, is obtained here by not assuming a constant elastic modulus in the strain hardening region of the steel, and by adopting for the latter the constitutive link given in Park and Paulay (1975). The problem is reduced to the solution of an equation in the unknown strain, which depends on the slendemess of the bar of length equal to the spacing of hoops, and on the hoop stiffness. The most widely used steels are then considered with the variations in the parameters indicated above. On the basis of the results obtained, an approximate analytical expression is given of the ultimate strain to be used in practical ductility calculations. A comparison to the experimental results obtained by other authors confirms the validity of the theoretical approach proposed.

The cyclic behavior of reinforced concrete columns subjected to biaxial bending was determined using a hysteretic element consisting of five axial springs. Four composite springs and one concrete spring are used. Their basic properties are controlled by the calculated balanced moment and axial force. A new simple hysteresis model was used for the composite springs and an existing model was used for the concrete spring. The five‐spring element (FSE) was evaluated based on its performance in simulating the response of several reinforced concrete test specimens. The element appeared to be successful in reproducing the response as long as the peak axial force did not exceed the balanced axial force. The FSE was also used to determine the response histories for several bridges. The results indicate that the response histories found based on FSE can be considerably different from those based on an elastoplastic yield surface model.

In the design of composite bridges, the North American practice either ignores or minimizes the contribution of transverse disphragms to the transverse load distribution; this results, among other disadvantages, in heavier longitudinal steel girders than necessary as well as in the loss of headroom. Recent tests have shown that when transverse steel I‐diaphragms are rigidly joined in a welded connection to the longitudinal steel girders, the wheel loads on the bridge become distributed in an orthotropic manner. The influence of bolted and welded transverse I‐diaphragms (to the longitudinal girders) on the response of composite bridges are investigated. Several composite bridge models were tested; repeated load tests were also conducted to examine the fatigue resistance of the longitudinal steel girders as influenced by the welding attachments. The experimental results are compared to theoretical ones based on the finite element method. It is concluded that the response of welded‐diaphragm composite bridges is superior to that of bolted‐diaphragm bridges and that this construction technique be used to rehabilitate existing composite bridges and/or improve their load rating.

A possible candidate for replacement of tension laminations in glulam beams is examined. The replacement is a composite of concrete‐reinforcing steel embedded in oriented flakeboard. Pullout tests were used to select the best of three possible furnishes for the composite. After this selection, $2\mathrm{in}\text{.}6\mathrm{in}\text{.}\times 9\mathrm{ft}(50.8\mathrm{mm}\times 152.4\mathrm{mm}\times 2.74m)$ beams were fabricated. Control beams with no reinforcing and beams with one lamina replaced with the steel‐wood composite were tested. The beams were tested both dry (50% RH) and wet (90% RH). The dry beams exhibited increases in stiffness of 24% and 32% and increases in ultimate moment capacity of 29% and 30% for one number 3 or number 4 bar, respectively, in the beam. The wet beams also showed increases in stiffness on the order of 30% but showed no significant increases in strength. This lack of reinforcing effect is likely to be a combination of increased steel stress due to reduced wood modulus of elasticity with increased moisture content and decreased flakeboard internal bond strength due to increased moisture content.

The theoretical derivations and numerical procedures used in the computer program ODSEWS‐2D‐II for the analysis and optimum design of two‐dimensional regular and irregular steel frames subjected to static, earthquake, and wind forces are presented. The seismic input can be interacting ground motions of actual earthquake records, various response spectra, and different building provisions of the Uniform Building Code (UBC), ATC‐03 in the United States, and TJ‐11 in China. Included are the mathematical formulation based on the consistent mass and the displacement method with consideration of geometric nonlinearity, three levels of recursive optimization procedures, the objective function of minimum construction and damage costs, and the constraints of stresses, displacements, frequencies as well as the upper and lower bounds of the design variables. Several design examples are provided to show the efficiency of the proposed algorithms, the versatility of the computer program, and the effect of the various code requirements on the optimum solutions.

Members carrying both axial force and bending moment are subjected to an interaction between these effects. The analysis of a beam‐column using stability functions as an alternative to the stress stiffness matrix is discussed. Explicit expressions for stability functions for three‐dimensional beam‐columns, in terms of member length, cross‐sectional properties, axial force, and the end moments, are derived. The effect of flexure on axial stiffness and the effect of axial force on flexural stiffness and stiffness against translation are considered in the derivation of stability functions. The effect of axial force on torsional stiffness and the effect of torsional moment on axial stiffness are neglected. The nonlinear stiffness matrix of a three‐dimensional beam‐column using the stability functions is presented by modifying the linear elastic stiffness matrix for a beam‐column (which includes the effect of shear deformations) available in the literature. A numerical example showing the calculation of stability functions for a given beam‐column is also presented.

Composite flexural members with vertical laminations are sometimes loaded in such a manner that individual components of the composite member tend to deflect unevenly. A simple procedure is presented for determining the longitudinal spacing of shear connectors that ensures uniform deflection of vertically laminated composite flexural members. The so-called ``deflection compatibility shear connectors'' are designed to provide a uniform load that opposes uneven deflection assuming the conservative case where total design loads are placed on the most flexible component of the composite member.