Editor’s Note

A new comprehensive “Bond Model of NSM-FRP Strips in the Context of the Shear Strengthening of RC Beams” is presented by Bianco et al. to account for all potential failure modes, including one that involves the fracture of concrete in the shape of semicones along the strips. The model also addresses issues regarding the debonding failure mode affecting the behavior, at ultimate, of a near-surface mounted (NSM) FRP strip. A new local bond stress-slip relationship is proposed, and closed-form equations to be implemented in the analytical model are derived and appraised on the basis of some of the most recent experimental results available in the literature.

Park and Aboutaha present a practical analysis and design procedure using the “Strut-and-Tie Method for CFRP Strengthened Deep RC Members.” Seven effective factor models accounting for reduction of strength in cracked concrete are investigated. A total of 17 experimental deep-beam test results are compared with the proposed strut-and-tie method (STM) results. It is shown that the proposed STM approach combined with an effective factor model depending on the strut angle provides the best agreement with the test results.

A “Backbone Model for Confined Masonry Walls for Performance-Based Seismic Design” is proposed by Riahi et al. to simulate the seismic behavior of typical confined masonry (CM) walls whose response is governed by shear deformations. The model was developed from an extensive database of both monotonic and reversed-cyclic experiments through an iterative linear regression analysis. Owing to the limited data available and inconsistencies in observed behavior in some tests, only specimens with one column on either edge of the wall, no bed joint reinforcement, and a height-to-length ratio that varies from 0.7 to 1.2, are considered in the model development. The effect of openings on strength characteristics, the capability of existing models to predict seismic behavior of CM walls, and the limitations of the proposed equations are discussed in detail.

Findings from two series of tests with different-depth wood I-joists to study the effects of circular and square web openings and the placement of steel angle retrofits at openings are reported by Morrissey et al. in “Wood I-Joists with Excessive Web Openings: An Experimental and Analytical Investigation.” Finite-element analyses were carried out on all test configurations to gain an understanding of how web openings and retrofits affect stiffness, stress distributions around openings, and ultimate failure mechanisms. Test results show failure loads well above prescribed design loads, though the presence of web openings affected the type of failure modes. Steel angle retrofits are shown to improve capacity if an adequate retrofit length is used to redistribute stress concentrations. The authors also report that the finite-element simulations predicted an improvement in stiffness due to the presence of steel retrofits that was not ascertained in experimental results.

In “Strain Distribution in OSB and GWB in Wood-Frame Shear Walls,” Sinha and Gupta investigate the load sharing between oriented strand board (OSB) and gypsum wall board (GWB) in a shear wall assembly subjected to racking load. Sixteen standard $\mathrm{2,440}\times \mathrm{2,440}\mathrm{mm}$ walls were tested monotonically, of which 11 walls were sheathed on both sides (OSB on one side and GWB on the other side), while 5 were tested without GWB. The authors state that during initial loading of the wall, the load is shared between OSB and GWB, though the proportion of load sharing is not known. The GWB fails first at about 60% of the ultimate load capacity of the wall, following which the load shifts to the OSB panel until the failure of the wall. The tests also revealed that the load path and failure patterns are different for the two wall types.

Yaw et al. examine the feasibility of applying the “Meshfree Method for Inelastic Frame Analysis.” A blended finite-element and meshfree Galerkin approximation scheme is adopted to solve the inelastic response of plane frames. In the proposed method, moving least-squares shape functions represent the displacement field, a plane stress approximation of the 2D domain simulates beam bending, J2 plasticity characterizes material behavior, and stabilized nodal integration yields the discrete equations. Results of numerical simulations are compared with analytical solutions, finite-element simulations, and experimental data to validate the methodology.

In “Comparison and Study of Different Progressive Collapse Simulation Techniques for RC Structures,” Menchel et al. attempt to assess the implications of assumptions that are implied in existing simplified methods to evaluate progressive collapse. Beam-column elements with zero-length plastic hinges to account for inelastic rotations were used to assess four progressive collapse simulation procedures: the linear static procedure prescribed by the General Services Administration (GSA), the linear and the nonlinear static procedures described in the Department of Defense provisions, and the load-history dependent (LHD) procedure. The advanced LHD procedure is assessed to be the most accurate. It is also concluded that the demand-to-capacity limit value of 1.5 for atypical structural configurations, as specified by the GSA linear static procedure, does not always provide a good assessment of the moment redistribution potential by the structure.

Sayani and Ryan carry out a “Comparative Evaluation of Base-Isolated and Fixed-Base Buildings Using a Comprehensive Response Index” to predict the best system to achieve a given performance objective, thereby enabling rapid prototyping of response as a function of system characteristics. When evaluated for a life-safety performance objective, it is shown that the superstructure design base shear of an isolated building is competitive with that of a fixed-base building with identical ductility, and the isolated building generally has improved response. Additionally, isolated buildings can meet a moderate ductility immediate-occupancy objective at low design strengths, whereas comparable ductility fixed-base buildings fail to meet the objective.

In “Blast Resistance Capacity of Reinforced Concrete Slabs,” Silva and Lu present a procedure to estimate the explosive charge weight and standoff distance to impose certain levels of damage on reinforced concrete (RC) structures. A series of experiments were also conducted to confirm its applicability for assessing the blast resistance capacity of RC slabs. However, the procedure is not applicable when punching shear failure is the governing failure mode.

To realistically capture characteristics of gust-front winds and their attendant load effects, a new analysis methodology is proposed by Kwon and Kareem in “Gust-Front Factor: New Framework for Wind Load Effects on Structures.” The procedure is similar to the gust loading factor format used in codes and standards worldwide for the treatment of conventional boundary layer winds. To facilitate expeditious utilization of this framework in design practice and inclusion in codes and standards, the authors provide access to the analysis framework and its workflow in a Web-based portal: http://gff.ce.nd.edu.

Results from long-term monitored strain data induced by heavy vehicle traffic on an existing bridge are presented by Liu et al. in “Bridge System Performance Assessment from Structural Health Monitoring.” A series-parallel system model consisting of bridge component reliabilities forms the basis of the bridge system performance assessment. Sensitivity studies with respect to system modeling, correlations, extreme value probability distributions, measurement errors, and number of observations are also reported. An illustration of the proposed approach is provided on an existing highway bridge in Wisconsin.

Han et al. propose a new “Stiffness Reduction Factor for Flat Slab Structures under Lateral Loads.” The proposed factor is developed by conducting nonlinear regression analysis using stiffness reduction factors estimated from available test data. In the validation study, results from experiments carried out by the authors on slab column connection specimens were compared with predictions by the proposed equation and with the lateral stiffness calculated using the effective beam width model (EBWM). It is concluded that the stiffness reduction factor is significantly affected by the level of applied moments but does not vary with respect to the amount of reinforcement until the slab reinforcement yields. Additionally, the lateral stiffness reduction factor is not always the same as the slab stiffness reduction factor.