Editor’s Note

A two-part paper by Helwig and Yura on “Shear Diaphragm Bracing of Beams” opens this issue of the journal. The first part deals with stiffness and strength behavior of the metal decking in building floors that behaves as a shear diaphragm. The diaphragms were connected along two edges to the top flanges of adjacent girders. The parameters considered in the study were diaphragm stiffness, load type, and load position. Findings from this phase of the study provided the basis for developing the design methodology that forms the focus of the second paper. The proposed design requirements consider both stiffness and strength requirements for beam stability. Also proposed is a model that can be used to estimate the forces in the fasteners that connect the diaphragms to the top flanges of the beams.

A two-phase experimental program to investigate the replaceability of infill panels following an earthquake is reported in “Testing of Full-Scale Two-Story Steel Plate Shear Wall with Reduced Beam Section Connections and Composite Floors” by Qu et al. It is shown that the repaired specimen can survive and dissipate significant amounts of hysteretic energy in a new earthquake without severe damages to the boundary frame or overall strength degradation. Experimental results are compared with seismic performance predictions obtained from a dual strip model using tension-only strips and from a monotonic pushover analysis using a 3D finite-element model, and good agreements are observed. “Cast Steel Connectors for Circular Hollow Section Braces under Inelastic Cyclic Loading,” by de Oliveira et al., concerns the use of special connectors that fit between a tubular brace and a gusset plate as an alternative to the reinforced, fabricated connections that are commonly used in seismic load-resisting braced frames. Laboratory results from static and pseudodynamic testing of concentrically loaded brace-connector assemblies showed that the use of a cast steel connector is a viable means of connecting to tubular brace members for seismic (or even static) applications. Further, since the connector was crafted to fit a range of tubular members and can be mass-produced, the proposed solution is an economical alternative to conventional tube-to-gusset connections under seismic loading.

The behavior of I-shaped steel girders with flanges made from concrete-filled tubes is investigated by Sause et al. in “Experimental Study of Tubular Flange Girders.” The investigation included concrete-filled tubular flange girders (CFTFGs) that are either composite or noncomposite with a concrete deck. For the composite CFTFGs, girders with rectangular tubes and either a flat web or a corrugated web are studied, and for the noncomposite CFTFGs, girders with round tubes and flat webs are studied. The experimental results demonstrate the improved lateral torsional buckling (LTB) capacity of CFTFGs, as well as their capability to carry factored design loads under construction and service conditions. Comparison between experimental and analytical results shows the adequacy of simple analytical models for CFTFGs.

Gho and Yang present a “Parametric Equation for Static Strength of Tubular Circular Hollow Section Joints with Complete Overlap of Braces” that is based on both numerical and experimental studies. A detailed parametric study using a calibrated finite-element model is carried out to investigate the ultimate capacity of the joint under various geometrical parameters. A comparison with the existing T/Y-joint’s formulas showed that the ultimate capacity of the tubular CHS joint with complete overlap of braces is close to that of the T/Y-joint at a gap size greater than the through brace diameter.

A new approach to deal with local buckling is described by Ashraf et al. in “Structural Stainless Steel Design: Resistance Based on Deformation Capacity.” The method is based on the deformation capacities of cross sections and applies to stainless steel members subjected to flexural buckling and combined axial loading and bending. The proposed method is verified by using test results and its performance is compared against existing ASCE and Eurocode designs. “Parametric Equations to Predict SCF of Axially Loaded Completely Overlapped Tubular Circular Hollow Section Joints” derived from 5,184 finite-element (FE) models covering all aspects of geometrical parameters of the joint are presented by Gao and Gho. Comparison of strain concentration factors between an experimentally tested specimen and the 8-node thick shell FE model showed that the average difference is 7.9%, whereas the difference is 8.8% for the 20-node solid FE model. The 8-node thick shell FE model is adopted to derive the parametric equations for predicting the SCF of the joint.

Albrecht et al. describe results from finite-element analysis of “Stress Intensity Factors for Structural Steel I-Beams.” The correction factors (the normalized SIF) were found to depend on the crack parameters (size and eccentricity) and the flange-to-web area ratio of the W-shape. In case of the three-tip crack, the interaction forces along the web-to-flange junction line depend on the relative length between the web and flange cracks. Also, good agreement between the SIF values from the 3D and 2D analysis suggests that the interaction between the cracked web and flange is controlled mostly by the compatibility of displacements in the $y$ -direction (direction of the remote applied stress) along the junction line.

The “Influences of Repeated and Sustained Loading on the Performance of Layered Wood–Concrete Composite Beams” is investigated by Balogh et al. Composite beams that were conditioned in a climate chamber to raise the wood moisture content to about 12% were subjected to $\mathrm{21,600}\text{cycles}$ of loading and unloading to simulate the typical live-load frequency experienced by the floor of a commercial building over a $30\text{-}\text{year}$ service life. The beams were then ramp-loaded to failure to determine the ultimate load-carrying capacity and composite efficiency. Additional beams were subjected to sustained load for $133\text{days}$ in an unconditioned environment and then tested to failure. The study finds that relatively high beam stiffness and strength were achieved despite the use of few connectors. The primary failure mechanisms were either shear in the wood between the exterior notch and the beam end or wood bending failure at midspan. The reduction in stiffness and in load capacity because of sustained loading was greater than that attributable to the cyclic loading. Fernández-Cabo et al. address issues related to the design and analysis of mixed beams in “Wood-Concrete and Wood-Wood Mixed Beams: Rational Basis for Selecting the Connections.” In their approach, the problems of strength and stiffness are separated. Nondimensional variables are introduced, and their exact relationships in simple supported beams are presented. The proposed approach provides a rational basis for selecting the connection.

In “Enhancing the Performance of Slab-Column Connections,” Lee et al. investigate the influence of concentrated reinforcement in the immediate column region, the use of high-strength concrete (HSC) slabs, as well as using puddled fiber-reinforced HSC in the slab in a region close to the column. The American, Canadian, British, and European code predictions are compared with the experimental results obtained from the slab-column connections tested in this study and those tested in other studies. The beneficial effects of using concentrated flexural reinforcement, high-strength concrete, and puddled fiber-reinforced HSC are demonstrated.

The “Concept of Equivalent Load for Stiffness and Its Application” is proposed by Kim et al. and applied to a variety of structural problems. In equivalent load for stiffness, a set of additional forces is applied to an original structure to produce the same response as that of a modified structure. The novelty of the proposed algorithm is that it requires fewer computational operations than a complete analysis. The proposed approach is particularly efficient for situations in which a limited number of members are modified. Additionally, the algorithm provides a clear physical concept that is based on static condensation and is applicable to a variety of problems, including sensitivity analyses.

The results of linear elastic and nonlinear elastic analytical investigations are reported by Weggel and Zapata in “Laminated Glass Curtain Walls and Laminated Glass Lites Subjected to Low-Level Blast Loading.” Responses of rectangular glass lites within the curtain wall are compared with those of identical glass lites that are either simply supported or supported on structural silicone sealant beads along all four edges. The comparisons indicate a reduction of principal stresses of the glass lites attributable to the flexibility of the structural silicone bead and, more significantly, the global flexibility of the curtain wall system. Findings also show that the dynamic behavior of a given glass lite varies dramatically with support conditions and that geometric nonlinearities typically reduce dynamic responses only slightly when compared with linear geometry for the low amplitude loads.

The “Progressive Collapse Resistance of Hotel San Diego” initiated by the simultaneous explosion of two adjacent exterior columns is reported by Sasani and Sagiroglu. The mechanism of load redistribution and change in column axial forces (strains) is discussed. The development of bidirectional Vierendeel (frame) action is identified as a major mechanism in redistribution of loads. Recorded data also show the change in the direction of beam bending moments in the vicinity of the removed columns. It is concluded that if the change in the direction of bending moment results in high tensile stresses in the bottom beam reinforcement at the face of a column, brittle local failure in the absence of proper anchorage can occur. The structure, which was almost a century old, without satisfying integrity requirements, resisted progressive collapse with a recorded maximum vertical displacement of only $6.4\mathrm{mm}$ .

“Wind Uplift Behavior of Mechanically Attached Single-Ply Roofing Systems: The Need for Correction Factors in Static Standardized Tests,” by Prevatt et al., investigates three test methods to examine the relationship between failure capacities among these methods. Full-scale wind uplift pressure tests on six specimen sizes and three membrane materials were performed in three phases. A significant difference in the failure loads occurs among different specimen sizes for the same membrane materials. These results suggest that correction factors are necessary for comparing tests on different test beds and that the performance of membranes in the test chamber may not produce the same results on full-scale structures.

A tool to quantify structural safety is proposed by Avinash Nafday in “System Safety Performance Metrics for Skeletal Structures.” The writer explores and clarifies the connection between system safety and structural redundancy concepts, provides an alternative interpretation of structural system redundancy, and proposes two objective system safety performance metrics for skeletal structures with stability as the performance objective. Approaches for identifying critical structural members and quantifying failure path importance are also addressed.