Editor’s Note

Results from a series of experimental tests are described by Hrynyk and Myers in “Out-of-Plane Behavior of URM Arching Walls with Modern Blast Retrofits: Experimental Results and Analytical Model.” The walls were constructed from traditional and alternative masonry materials to assess the applicability of the use of a wood-fiber fly ash (WFFA) material for infill construction. The walls were tested in the laboratory under static conditions and were evaluated on the basis of their ability to absorb energy, resist out-of-plane load, undergo out-of-plane deformation, and reduce or prevent the occurrence of masonry debris scatter upon collapse. The use of a spray-on polyurea material was found to be highly effective in improving URM energy absorption and reducing masonry fragmentation. Infill walls retrofitted with a combination of fiber-reinforced polymer (FRP) grids and polyurea material were found to fail prematurely because of a lack of anchorage between the strengthened URM walls and the surrounding structure.

Rong and Li develop two indexes to quantify the approximation errors between actual response of a structural member and the corresponding design target in their paper, “Deformation-Controlled Design of Reinforced Concrete Flexural Members Subjected to Blast Loadings.” The error indexes are used to modify the design procedure so that the approximate response of the reinforced concrete member is equal to the design target performance. The modified procedure is implemented in three design examples and the method is shown to be effective in ensuring that the actual response reflects the respective design target.

In “Probabilistic Uncertainty Modeling for Thermomechanical Analysis of Plasterboard Submitted to Fire Load,” Sakji et al. present a combined experimental and analytical study to overcome issues related to fire resistance tests of plasterboard-lined partitions when their dimensions exceed those of furnaces. Specially designed experimental tests are carried out, followed by the development of a thermo-mechanical mean model for the plasterboard multilayer. A probabilistic model of system uncertainties that is based on a nonparametric probabilistic approach is also elaborated. Numerical results are compared with experimental observations to validate the model.

Yang et al. summarize results from an experimental program on the behavior of a $1∕3$ -scale model of special inverted-V-braced steel frames in “Pushover Response of a Braced Frame with Suspended Zipper Struts.” The model was pushed to a target roof drift ratio of approximately 3.6%. The load was then reversed and the bottom story brace fractured at a drift of $-0.78\%$ . The frame still carried about 37% of its maximum load after fracture. The zipper elements demonstrated their ability to activate buckling in all stories except the top one, redistributing the loads in the structure to minimize strength losses. Comparisons of performance indicate that the suspended zipper frame provides more stable and better hysteretic behavior than the typical zipper frames.

The experimentally obtained lateral response characteristics of model scale square fiber reinforced elastomeric isolator (FREI) bearings are presented by Toopchi-Nezhad et al. in “Lateral Response Evaluation of Fiber-Reinforced Neoprene Seismic Isolators Utilized in an Unbonded Application.” This unbonded application results in a stable rollover deformation, which decreases the effective lateral stiffness of the bearings and maximizes their efficiency as a seismic isolator device. Lateral load-displacement hysteresis loops of the FREI bearings with unbonded application are generally found to be similar to that of conventional high-damped steel reinforced bearings. The adequacy of the bearings is verified in conformance with provisions of ASCE-7. The determination of optimal locations and amount of weakening of structural components, as well as the optimal locations and magnitudes of added dampers, is the subject of the paper by Lavan et al. titled “Noniterative Optimization Procedure for Seismic Weakening and Damping of Inelastic Structures.” Weakening of the structure can lead to stability issues in the building that can be automatically considered, if active control theory is used for design. On the basis of a nonlinear active control procedure, control forces are calculated and implemented by using equivalent passive dampers and weakening elements to achieve the closest effects. The methodology is applied to a case study of an eight-story nonlinear building tested by using a set of ground motions corresponding to different hazard levels. Results show that the optimal design leads to a reduction of both peak interstory drifts and peak total accelerations.

“Application of ANN-Based Response Surface Method to Prediction of Ultimate Strength of Stiffened Panels” by Mesbahi and Pu presents an artificial neural network (ANN) based approach to derive a formula to predict the strength of stiffened plates under uniaxial compression using available experimental data. The developed formula is compared with some existing analytical formulas and is shown to be more accurate on basis of the database of selected data. The normalization range of input and output variables is found to have an effect on the performance of the ANN model, which must be taken into consideration when using the proposed approach.

Xue and Liu discuss a methodology to optimize the prestressing force of a $100\mathrm{m}$ span structure in “Studies on a Large-Span Beam String Pipeline Crossing” followed by structural stability analyses under three types of boundary conditions. Additionally, key geometric parameters—such as the rise-span ratio, rag-span ratio, struts arrangement, cross section of the beam, string, and struts—are determined by parameter analysis. A 1:15 model test is carried out to investigate the behavior of beam string pipeline (BSP) crossing for the complete range of loading scenarios. Test and finite-element analytical results show that the stability and loading-bearing capacity of the BSP is reliable and the semispan water load case controlled the design.

A “New Nonlinear Roof Sheathing Fastener Model for Use in Finite-Element Wind Load Applications” that is a function of not only the uplift pressure acting on the roof sheathing but also the effective moment arm acting on the edge nails is proposed by Dao and van de Lindt. A targeted set of experimental tests was conducted to determine the effect of the load eccentricity, a new stiffness matrix for a nail element formulated, and illustrative examples presented for a roof sheathing assembly analyzed by using the finite-element procedure. The model is shown to result in a significantly reduced capacity from current state-of-the-art finite-element analyses, which assume only nail withdrawal.

A novel “Model Conversion Technique for Structural Dynamic Systems” is introduced by Hu and Li. It is capable of converting a physically realizable, higher-order source model into a completely different, predefined, physically realizable, lower-order target model. On completion of the conversion, the resulting target model preserves or approximates the dynamic characteristics (such as the chosen structural frequencies and their mode shapes) of the source model. A numerical example of converting a 5-story two-dimensional (2D) frame structure model into a 5-story classical/generalized one-dimensional (1D) shear-building model is demonstrated.

Yi and Zhou discuss issues related to the work presented by Unger et al. in “System Identification and Damage Detection of a Prestressed Concrete Beam” in the November 2006 issue of the journal. The discussers express concern that damage data such as crack distribution and failure mode of the tested beams are not provided. Questions are also raised on the weighting factors used on the different residuals. Finally the discussers point out that several factors, such as shear deformation and prestressing effects, are ignored in the analysis; and since different models cause different errors, the effects of these factors in the observed difference between measured and calculated quantities should be considered. The authors of the paper indicate that their finite-element model did incorporate the effects of shear deformation and prestressing. although they do not respond to the lack of physical damage data in the paper, they do clarify the other primary issues raised by the discussers.

The second discussion, by Sabouri-Ghomi and Gholhaki, on a paper by Park et al. that appeared in March 2007 seeks to clarify the sequence and location of the plastic moments developed in the frame members, since they depend on numerous parameters. The discussers are particularly concerned with the conclusion of the paper, which suggests that the failure of well-designed steel plate walls occurs at the column base or at the beam-column connection instead of highlighting the need to allow the steel plate to absorb all the energy until failure prior to damage occurring in the primary structural elements. The writers agree that the plastic moment development is a function of numerous parameters but that the results presented are for the particular case discussed in the paper. Further, the conclusion on the failure of the plate walls was based primarily on the fact that local fracture of the plates did not significantly influence the overall strength and deformation capacity of the system.