Editor’s Note

The primary theme of papers in this issue of the Journal is seismic effects. The remaining papers include the following general areas: health monitoring, metal structures, concrete structures, wood-concrete composite structures, structural control, safety and reliability, and analysis and computation.

A two-part paper evaluating the seismic behavior of buckling-restrained brace frames (BRBF) by Fahnestock, Ricles, and Sause opens this issue of the Journal. In the first paper, the writers describe the “Experimental Evaluation of a Large-Scale Buckling-Restrained Braced Frame.” Tests on a BRBF with improved connection details indicate that connection enhancements led to the test frame sustaining story drifts of $0.05\text{radians}$ with minimal damage and no stiffness or strength deterioration. In the follow-on paper, the “Seismic Response and Performance of Buckling-Restrained Braced Frames” is evaluated through a detailed analytical study. It is shown that the currently accepted deflection amplification factor underestimates mean inelastic lateral displacements under design-level earthquakes, while the system overstrength factor may be unconservative. A more rigorous method for predicting the maximum ductility demands of such frames is proposed.

To investigate the effectiveness of several strengthening techniques, “Testing of a Full-Scale Unreinforced Masonry Building Following Seismic Strengthening” is carried out by Moon et al. The strengthening schemes consisted of the application of FRP overlays, near-surface mounted rods, and vertical posttensioning. Results indicate that all techniques are effective in improving the seismic resistance of unreinforced masonry structures. An experimental study investigating the influence of lateral displacement on the “Vertical Stiffness of Elastomeric and Lead–Rubber Seismic Isolation Bearings” is presented by Warn, Whittaker, and Constantinou. The vertical stiffness data are used to evaluate four formulations for estimation of vertical stiffness as a function of lateral displacement. The Koh-Kelly two-spring model and another model based on a piecewise linear relationship showed good agreement with experimental data for a range of lateral displacements.

An “Assessment of Improved Nonlinear Static Procedures in FEMA-440” is carried out by Akkar and Metin through a detailed study of the seismic response of nondegrading 3 to 9 story reinforced concrete frames. It is reported that the displacement coefficient method tends to overestimate the global deformation demands compared to the capacity spectrum method.

Altunok, Reda Taha, and Ross propose a “Possibilistic Approach for Damage Detection in Structural Health Monitoring” in the context of a nonstatistical damage detection paradigm. The application of possibility theory does not require probabilistic knowledge or assumptions on the damage feature and thus encompass aleatoric and epistemic types of uncertainties. Application to damage detection is demonstrated by means of a case study. A laboratory-based experimental and finite-element analytical study to evaluate “Vibration-Based Detection of Small-Scale Damage on a Bridge Deck” is the subject of the paper by Zhou, Wegner, and Sparling. It is shown that damage can be detected and localized longitudinally within a distance equal to the spacing between measurement points using data for only the fundamental mode shape before and after damage.

Present design standards require that the design parameters for composite slabs using cold-formed profiled steel decks be obtained from full-size bending tests. Since this can be costly and time consuming, Abdullah and Easterling propose the “Determination of Composite Slab Strength Using a New Elemental Test Method.” It is shown that the performance of the elemental test method is in good agreement with the performance of the full-size specimens. Results from a systematic finite-element study are reported by Qian et al. in “Static Strength of Thick-Walled CHS X-Joints Subjected to Brace Moment Loadings.” The significance of the joint geometric parameters and the tensile chord stress effect on the ultimate joint strength is highlighted, and a new chord stress function that incorporates the geometric dependency is proposed.

A “Confinement Model of Concrete with Externally Bonded FRP Jackets or Posttensioned FRP Shells” is developed by Pantelides and Yan. Based on the bilinear four-parameter formulation by Richard and Abbot, the writers adopt the five-parameter bounding surface plasticity model of William and Warnke and a strain-dependent stiffness to derive the constitutive model. Comparisons of the proposed stress-strain expressions show good agreement with available uniaxial experiments. Dimitri Val examines the “Deterioration of Strength of RC Beams due to Corrosion and Its Influence on Beam Reliability.” Probabilities of failure are evaluated using Monte Carlo simulation. Findings from the study suggest that corrosion of stirrups, particularly pitting corrosion, has significant influence on the reliability of reinforced concrete beams.

The “Long-Term Behavior of Wood-Concrete Composite Floor∕Deck Systems with Shear Key Connection Detail” is investigated by Fragiacomo et al. The beam specimens were monitored for an overall period of $133\text{days}$ after application of service loads and then extended to their entire service life using finite-element simulations. It is found that the increase in moisture content due to bleeding of the concrete is not an issue for the durability of the wood deck, while the rheological phenomena experienced by the constituent materials lead to significantly large deflections over the service life.

Zhu, Elwood, and Haukaas develop probabilistic drift capacity models at axial load failure in “Classification and Seismic Safety Evaluation of Existing Reinforced Concrete Columns.” A classification method is proposed to distinguish flexure-dominated and shear-dominated columns followed by the development of a probabilistic shear capacity model through the application of an existing Bayesian methodology to an experimental database. Fragility curves with confidence bounds are generated and used to evaluate the probability of failure implied in current seismic rehabilitation guidelines.

A gradient-based optimization algorithm is used by Attard in “Controlling All Interstory Displacements in Highly Nonlinear Steel Buildings Using Optimal Viscous Damping.” Optimal damping ratios are computed in each mode of vibration such that the sum of the errors between interstory displacements and the “just-yielded” performance objectives is minimized. Numerical examples are used to demonstrate the ability of the proposed algorithm.

“Analytical Sensitivity of Plastic Rotations in Beam-Column Elements” is investigated by Michael Scott for reliability and optimization algorithms in structural engineering. Plastic rotation sensitivity to uncertain design parameters and modeling assumptions are also assessed. The response sensitivity is verified by finite differences and then applied to a first-order reliability analysis of a steel frame subassembly.

The issue concludes with a discussion by Esmaeily, Hart, and Gaitan on a paper by Sakai and Kawashima that appeared in the January 2006 issue of the Journal. The model proposed by the writers was evaluated by the discussers by conducting several tests on concrete cylinders confined by carbon fiber reinforced polymer material. While the model performed satisfactorily for different conditions, the discussers contend that issues still remain on the validity of the model for random loading scenarios, loading rate, and creep history.