Editor’s Note

The opening paper “Reliability, Brittleness, Covert Understrength Factors, and Fringe Formulas in Concrete Design Codes” by Bazant and Yu examines the consequences of uncertainties associated with certain empirical design factors embedded in current structural design codes. It is argued that these “fringe formulas” do not account for the scatter and uncertainty associated with different combinations of individual risks. It is suggested that additional statistical measures, such as the coefficient of variation and type of probability distribution, be incorporated into the specification.

A two-part paper by Fragiacomo and Ceccotti deals with numerical modeling and response simulation of the “Long-Term Behavior of Timber-Concrete Composite Beams.” In the first part, a finite element model is developed wherein all relevant phenomena affecting long-term behavior—such as creep, shrinkage, swelling, and temperature variations—are incorporated. The companion paper examines the importance of different rheological phenomena and the influence of inelastic strains produced by temperature-induced shrinkage and swelling on the long-term behavior of timber-concrete composite beams in an outdoor environment. A “Numerical Model for the Analysis of Unbonded Prestressed Members” is developed by Barbieri, Gastal, and Filho. Geometric nonlinearity, composite construction, and time-dependent effects are considered in the formulation. Comparison with experimental results, including tendon stresses and cracking patterns, serves to validate the proposed model. Closed-form analytical solutions are derived by James Croll in “Design Analysis for Buckling of Tanks and Silos.” The solution considers geometric imperfections and predicts either first-surface or full-section plasticity, allowing buckling to be summarized in a form analogous to the Ayrton-Perry formula for column buckling.

Liu, Burns, and Wen consider two objective functions simultaneously in developing a “Genetic Algorithm-Based Construction-Conscious Minimum Weight Design of Seismic Steel Moment-Resisting Frames.” The resulting optimization problem produces a set of alternative designs establishing optimized trade-off between the two merit objectives. The goal of the study is to foster further research efforts that integrate consideration of construction issues into structural optimization so that the resulting designs can be more viable in real-world practice.

A new method for “Determining Equivalent Linear Parameters for Use in a Capacity Spectrum Method of Analysis” is proposed by Guyader and Iwan. The study finds that ATC-40 provisions are significantly unconservative at low ductilities and conservative at higher ductilities, whereas the proposed method offers substantial improvement over the ATC methodology. Hybrid models, comprising appropriately scaled experimental and numerical substructures for evaluating the seismic response of complex structures is presented by Stojadinovic, Mosqueda, and Mahin in “Event-Driven Control System for Geographically Distributed Hybrid Simulation.” The ability of the system to mitigate the adverse effects of random completion times of communication, computation, actuation, and measurement tasks during a hybrid simulation is demonstrated. The third paper in this issue on the theme of seismic effects investigates the “Effects of Connection Fractures on Global Behavior of Steel Moment Frames Subjected to Earthquakes.” Authored by Rodgers and Mahin, the paper reports on a series of shaking table tests on a one-third scale, two-story, single-bay steel moment frame. It is concluded that deleterious consequences of connection fractures depend on a number of complex interrelated factors, including number of fractures, excitation amplitude, excitation characteristics, and spatial distribution and severity of fractures.

“Implementation of a Feasible Control Design Process Incorporating Robustness Criteria for Wind-Excited Highrise Buildings” is experimentally verified by Wu, Lu, and Hsu. An identification scheme that models wind loads and the likely interaction between the control devices and the structure is proposed. The performance of the proposed controllers is shown through experiments to be superior to classical LQG controllers. Adeli and Jiang present a new “Dynamic Fuzzy Wavelet Neural Network Model for Structural System Identification.” In addition to denoising, wavelets are employed to create a new pattern-recognition model that captures the characteristics of the sensor data accurately and efficiently.

An “Unloading and Reloading Stress-Strain Model for Confined Concrete” derived from a series of experimental tests of reinforced concrete columns is presented by Sakai and Kawashima. The model incorporates the effect of repeated loading and unloading cycles, including partial loading excursions. Matthys, Toutanji, and Taerwe propose a model to simulate the “Stress-Strain Behavior of Large-Scale Circular Columns Confined with FRP Composites.” Existing models derived from tests on smaller scale models are shown to be ineffective in reproducing observed stress-strain behavior of large-scale components.

Findings from an experimental study are reported by Zhou and Young in “Cold-Formed Stainless Steel Sections Subjected to Web Crippling.” Test strengths are compared with design strengths specified in various codes and a unified web crippling equation for cold-formed stainless steel sections with a single web.

Mi et al. describe results from full-scale monotonic and cyclic tests of wood walls with various sheathing details in “Racking Performance of Tall Unblocked Shear Walls.” The test results are used to study the influence of different configurations on unblocked shear wall strengths, and the writers recommend that the provisions for 2.44 m walls in the current Canadian code may be conservatively applied to 4.88-m-tall four-wall configurations. The “Performance of Wood Shear Walls Sheathed with FRP-Reinforced OSB Panels” is the subject of the next paper, by Cassidy et al. The panel consists of thin outer sheets of oriented-strand-boards (OSBs) bonded to strips of FRP that are sandwiched between the OSB panels and the edges. On the basis of results of monotonic and cyclic tests, it is concluded that the FRP-reinforced OSB panels have potential to improve the lateral resistance of wood frame structures.

A direct solution that compares favorably with the Uniform Building Code (UBC) is developed by Tam Ha in “Nonconstrained Flagpole Design Formula.” The simplified flagpole design is applicable only for loads applied above the ground bearing surface. Design examples illustrate the application of the proposed formula.

The issue concludes with a discussion by Birkle and Gayed on the paper “Alternative Shear Reinforcement for Reinforced Concrete Flat Slabs,” which appeared in the September 2003 issue of the journal. The discussers contend that the shear bands proposed by the writers are not practical and do not satisfy the anchorage requirements of ACI 318-02. The writers of the original paper attempt to clarify the strain recordings reported in the paper and reaffirm the advantages of the proposed shear band reinforcement.

Kmet, S., and Kokorudova, Z. (2006). “Nonlinear analytical solution for a cable truss.” J. Eng. Mech., 132(1).

Chang, S-Y. (2006). “Accurate representation of external force in time-history analysis.” J. Eng. Mech., 132(1).

Kunde, M. C., and Jangid, R. S. (2006). “Effects of pier and deck flexibility on the seismic response of isolated bridges.” J. Bridge Eng., 11(1).

Wilkinson, S.M., and Knapton, J. (2006). “Analysis and solution to human-induced lateral vibrations on a historic footbridge.” J. Bridge Eng., 11(1).

Maleki, S., and Bisadi, V. (2006). “Orthogonal effects in seismic analysis of skewed bridges.” J. Bridge Eng., 11(1).