Editor’s Note

Foley, Pezeshk, and Alimoradi formulate a multiobjective optimization problem and then apply it in a design context in their two-part paper “Probabilistic Performance-Based Optimal Design of Steel Moment-Resisting Frames.” The first part deals with formulation, which includes a methodology for applying an evolutionary genetic algorithm. The companion paper outlines the application of the automated algorithm to design steel frames with fully restrained and a variety of partially restrained connections. The constraints on the design variables of a permanent structural health monitoring sensor network are used to formulate an optimization problem by Marsh and Frangopol in “Lifetime Multiobjective Optimization of Cost and Spacing of Corrosion Rate Sensors Embedded in a Deteriorating Reinforced Concrete Bridge Deck.” A set of optimal combinations of sensor spacing and cost are established, given specific sensor performance criteria and spatial variability of corrosion current density.

Ranzi and Bradford present “Analytical Solutions for Elevated-Temperature Behavior of Composite Beams with Partial Interaction.” Linear material behavior is assumed but their elastic moduli are modified to account for degradation that the materials exhibit at elevated temperatures. The accuracy of the proposed solutions is validated with results obtained from finite element simulations. A nonlinear finite element model to investigate the “Behavior of Steel Beam to Concrete-Filled Steel Tubular Column Connections after Exposure to Fire” is validated by Han, Huo, and Wang through comparison with experimental results. Among numerous other findings, it is shown that the column stiffness and hence its lateral load-carrying capacity reduce, though connection ductility and energy dissipation increase. Vimonsatit, Tan, and Qian report findings from an experimental program on “Testing of Plate Girder Web Panel Loaded in Shear at Elevated Temperature” that the shear strength of plate girder sections reduces significantly with increasing temperature. While more stocky sections possess higher shear capacity at a certain temperature, shear buckling failure becomes less apparent due to the highly nonlinear mechanical properties of steel at elevated temperatures.

A series of single lap connection tests of single screw fasteners is carried out by Bambach and Rasmussen to examine the “Behavior of Self-Drilling Screws in Light-Gauge Steel Construction.” A variety of in situ conditions are considered and a design equation is proposed to modify the nominal shear strength to account for these conditions.

A constitutive model for circular concrete columns is developed by Saenz and Pantelides in “Strain-Based Confinement Model for FRP-Confined Concrete.” A distinguishing feature of the model is that it includes the effects of FRP confinement on the concrete microstructure by evaluating the internal concrete damage using axial, radial and volumetric strains. Approaches to account for “Tensioning Stiffening in Lightly Reinforced Concrete Slabs” in the American Concrete Institute (ACI), European and British codes are compared with experimental observations by Ian Gilbert. The Eurocode method is found to be more reliable than ACI in modeling the load-deformation response of lightly reinforced members. “Effect of Reinforcement Type on the Ductility of Suspended Reinforced Concrete Slabs” by Gilbert and Sakka describes the observed failure mode and ductility of reinforced concrete slabs with both normal and low-ductility reinforcement. Findings from an experimental program show that slabs with low-ductility welded wire fabric fail in a brittle manner with very limited plastic deformation. Experiments to evaluate flexural, web shear and sliding shear mechanisms are carried out by Salonikios to support model development for the “Analytical Prediction of the Inelastic Response of RC Walls with Low Aspect Ratio.” The methodology proposed takes into account the observed behavior which indicates that the strength envelope is initially defined by the strength of web shear and flexure followed by the strength of the sliding shear mechanism along the flexural crack.

An approach to modeling the vertical flexure of mechanically-fastened “Wooden Ship Hulls as Box Girders with Multiple Interlayer Slip” is proposed by Milner and Peczkis. The writers suggest that typical limitations can be overcome by factoring the incomplete composite action of timber components through a reduced shear modulus, an increased shear lag and a reduced sectional area in tension. Sample computations demonstrate that hull deflections can be limited to about twice that of a complete composite hull if stiff fasteners are used at a much greater density than in traditional construction.

The effect of the unique flag-shaped hysteresis and recentering behavior of superelastic shape memory alloy (SMA) braces is evaluated by McCormick et al. in “Seismic Assessment of Concentrically Braced Steel Frames with Shape Memory Alloy Braces.” Results suggest that SMA braces are effective in limiting both inter-story and residual drifts.

Findings from full-scale tests conducted using simulated wind loads on a portion of a standing seam metal roof are compared with model-scale wind tunnel tests by Surry et al. to assess “Structurally Effective Static Wind Loads for Roof Panels.” The results were found to be remarkably consistent despite the vastly different methods and indicate that influence surface approaches together with experimentally-measured distributions provide an excellent way of determining effective loads on various components.

Schnabl et al. propose a mathematics model and derive an “Analytical Solution of Two-Layer Beam Taking into account Interlayer Slip and Shear Deformation.” It is shown that shear deformations are more important for high slip modulus for short beams with small length-to-depth ratios and for beams with high flexural-to-shear modulus ratios. It is concluded that models which consider partial interaction between the layers should be employed if the beams have very flexible connections.