Editor’s Note

This issue of the Journal consists of 16 technical papers and a discussion of a paper that appeared in May 2005. The primary themes of the papers assembled for this issue are Metal Structures, Seismic Effects, and Structural Monitoring and System Identification.

A “Testing Protocol for Short Links in Eccentrically Braced Frames” is developed by Richards and Uang. The writers show that the AISC link loading protocol is overly conservative, having 1.5 times the cumulative rotation demand and more large-amplitude cycles than necessary. A rational protocol based on cumulative and maximum link rotation demands obtained from comprehensive time history analyses is proposed. “Ductile Web Fracture Initiation in Steel Shear Links” by Chao, Khandelwal and El-Tawil investigates the observed ductile fractures in recent tests of prevailing A992 rolled shapes. The reasons for the web fractures in the new steel beams as opposed to older links are discussed following detailed finite-element analyses of shear links with different types of details. An alternative stiffener configuration that mitigates ductile fracture is proposed. The cyclic loading behavior of 12 large-scale specimens is reported by Okazaki et al. in “Experimental Performance of Link-to-Column Connections in Eccentrically Braced Frames.” Specimens representing pre-Northridge practice failed after developing only half the inelastic link rotation required in AISC seismic provisions. Specimens with weld filler material with specified notch toughness and modifications in welding details provided only marginal improvement over pre-Northridge connections. The writers consequently recommend that EBF arrangements with links attached to columns be avoided.

Analytical equations are formulated by Kim and Yoo to determine “Brace Forces in Steel Box Girders with Single Diagonal Lateral Bracing Systems.” The analysis and design of bracing systems installed at the top flange level in trapezoidal box girders is critical, so that the noncomposite steel section can support both the concrete and construction load during construction. Member forces caused by bending and torsion computed using the new equations were found to match results obtained with three-dimensional finite-element analyses. Results from a series of experiments on semirigid and inelastic joints are described by Dundu and Kemp in “Plastic and Lateral-Torsional Buckling Behavior of Single Cold-Formed Channels Connected Back-to-Back.” The tests demonstrate the considerable ductility achieved by back-to-back bolted connections. An innovative method is also proposed for connecting each purlin to the web of the column or rafter through a cold-formed angle to restrain the frames from failing due to lateral-torsional buckling.

Results from full-scale laboratory tests and detailed finite-element simulations are summarized by Tutuncu and O’Rourke in “Compression Behavior of Nonslender Cylindrical Steel Members with Small and Large-Scale Geometric Imperfections.” Recommendations are made with respect to the effects of imperfections on compression load capacity and with methods of modeling the imperfections and their implication in design, inspection, and serviceability decisions in the field.

The performance of a high-precision global positioning system (GPS) in terms of its background noise and dynamic tracking ability is investigated by Kijewski-Correa, Kareem, and Kochly in “Experimental Verification and Full-Scale Deployment of Global Positioning Systems to Monitor the Dynamic Response of Tall Buildings.” The writers contend that GPS offers promise as a highly reliable sensor for monitoring total structural movement, not only under the action of wind but also deformations associated with settlement, thermal expansion, and permanent offsets resulting from structural damage.

A two-part paper by Shenton III and Hu introduces a new method for “Damage Identification Based on Dead Load Redistribution” that uses static strain measurements due to dead loads only. Utilizing an analytical model of a fixed-fixed beam, a forward analysis of the beam is first presented to illustrate the redistribution of dead load for different damage scenarios, followed by the definition of the inverse problem as a constrained optimization problem that is solved using a genetic algorithm. The proposed procedure is shown to correctly identify damage for a wide range of locations and damage severities. In the second paper, Hu and Shenton III examine the effect of measurement error in their proposed procedure. The damage identification parameters are determined using a genetic algorithm, and the effect of measurement error is investigated using Monte Carlo simulation. Based on results from false-positive testing, the writers conclude that the procedure will not incorrectly identify damage when it does not exist, even if the measurement error is significant.

A method for estimating the conditional dependence of decision variables in the seismic design process is presented by Mackie and Stojadinovic in “Fourway: Graphical Tool for Perform-ance-Based Earthquake Engineering.” The proposed first-pass assessment tool, which is formulated for use with the Pacific Earthquake Engineering Research Center’s performance-based framework, simplifies the development of decision fragilities by exact determination of first moments and approximate determination of the variance of corresponding probability distributions without a need for numerical integration of intermediate probabilistic models. Jarenprasert, Bazan, and Bielak propose an “Inelastic Spectrum-Based Approach for Seismic Design Spectra.” An expression for the dimensionless yield strength is estimated to have the following form: $C_y=C\left(T\right){\overline{\mu }}^{-n\left(T\right)}$ , where $\overline{\mu }$ is the mean ductility ratio, and both $C$ and $n$ depend only on the elastic natural period of the structure. Explicit formulas for both $C$ and $n$ are obtained for a set of 87 accelerograms recorded in California. It is concluded that $C_y$ can also be expressed approximately in terms of a highly damped mean elastic spectrum divided by a reduction factor that depends only on $\overline{\mu }$ and $T$ .

A two-part paper by Lin et al. presents the implementation of a smart structure using “Active Control with Optical Fiber Sensors and Neural Networks.” Theoretical analysis of the proposed neural network-based Fiber Bragg Grating (FBG) sensor system is described in the first part. Comparison of structural responses using the proposed system with uncontrolled and traditional optimal linear quadratic gain demonstrates the validity and advantages of the novel approach. Experimental verification of a full-scale steel frame structure is described in the second part of the paper by Lin, Chang, and Lin. Signals from the FBG sensors were found to be superior to conventional strain gauges. The writers conclude that the proposed system can be readily applied in seismic protection of buildings.

The results of an experimental study to examine the “Reversed-Cyclic Behavior of a Novel Heavy Timber Tube Connection” are reported by Leijten et al. The connection comprises steel tubes that fit into over-sized holes for ease of assembly and construction. The energy dissipation capacity of the connection was found to be significantly better than other timber connections, with the potential for enhanced seismic performance of timber frame structures equipped with these connections.

A consistent basis for statistically reducing material property test data for load and resistance factor design is developed by Zureick, Bennett, and Ellingwood in “Statistical Characterization of Fiber-Reinforced Polymer Composite Material Properties for Structural Design.” A two-parameter Weibull probability distribution is recommended for modeling both strength and stiffness properties. The procedure also provides a basis for establishing limits for qualification and acceptance criteria for FRP composite structural products.

This issue also includes a discussion of the paper “Reevaluation of Deflection Prediction for Concrete Beams Reinforced with Steel and Fiber-Reinforced Polymer Bars” by P. H. Bischoff that appeared in May 2005. The discusser compares predictions using the equation proposed by Bischoff with measured deflections of simply-supported one-way slabs tested by the discusser. It is shown that Bischoff’s equation more accurately models the instantaneous tension stiffening phenomenon than the Branson equation used in ACI 318-02 and CSA A23.3-04. In providing closure to the topic, Bischoff points to the importance of realizing that tension stiffening is independent of both bar type and reinforcing ratio when the effect is measured relative to the concrete contribution at first cracking.

Abbas, H. H., Sause, R., and Driver, R. G. (2006). “Behavior of corrugated web I-girders under in-plane loads.” J. Eng. Mech., 132(8).

Shan, B., Xiao, Y., and Guo, Y. (2006). “Residual performance of FRP-retrofitted RC columns after being subjected to cyclic loading damage.” J. Compos. Constr., 10(4).

Filiatrault, A., Higgins, P. S., and Wanitkorkul, A. (2006). “Experimental stiffness and seismic response of pallet-type steel storage rack connectors.” Pract. Period. Struct. Des. Constr., 11(3).

Hamad, B. S., and Rteil, A. A. (2006). “Comparison of roles of FRP sheets, stirrups, and steel fibers in confining bond critical regions.” J. Compos. Constr., 10(4).

McLaskey, G., and Sansalone, M. (2006). “Nondestructive dynamic evaluation of a concrete reaction wall—Numerical and experimental studies.” J. Perform. Constr. Facil., 20(3).

Reynolds, P., and Pavic, A. (2006). “Vibration performance of a large cantilever grandstand during an international football match.” J. Perform. Constr. Facil., 20(3).

Salim, H. A., Barker, M., and Davalos, J. F. (2006). “Approximate series solution for analysis of FRP composite highway bridges.” J. Compos. Constr., 10(4).

Sasani, M., Makris, N., and Bolt, B. A. (2006). “Damping in shear beam structures and estimation of drift response.” J. Eng. Mech., 132(8).

Sivaselvan, M. V., and Reinhorn, A. M. (2006). “Lagrangian approach to structural collapse simulation.” J. Eng. Mech., 132(8).

Zoghi, M., and Farhey, D. N. (2006). “Performance assessment of a precast-concrete, buried, small arch bridge.” J. Perform. Constr. Facil., 20(3).