Journal of Structural Engineering

Gluing of fiber reinforced polymer (FRP) strips by a structural adhesive into thin slits cut in the cover of reinforced concrete (RC) beams’ lateral faces is a shear strengthening technique that is gaining increasing attention of the FRP community. Nonetheless, certain aspects related to the failure modes affecting the behavior at ultimate of such near surface mounted (NSM) strips need to be clarified. Recent findings have spotlighted that besides debonding and tensile rupture of the strips, another possible failure mode should be considered, which involves the fracture of concrete in the shape of semicones along the strips. Thus, a comprehensive analytical model accounting for all of those failure modes was recently developed for predicting the NSM contribution to RC beams shear capacity. Despite its consistency with experimental recordings, that model still needs improvement since some aspects related to the interaction between the force transferred by bond to the surrounding concrete and its tensile fracture still need to be clarified. The need to improve that analytical model led us to further address the issues regarding the debonding failure mode affecting the behavior, at ultimate, of a NSM FRP strip. A new local bond stress-slip relationship is proposed and closed-form equations to be implemented in that analytical model are derived and appraised on the basis of some of the most recent experimental results available in the literature.

In recent years, a great deal of research on the carbon fiber-reinforced polymer (CFRP) composite retrofitted systems has been done. The investigation of CFRP retrofit systems, however, has focused on flexural and shear strengthening for slender concrete members. Very limited work has been done on CFRP strengthened deep concrete structures. For analysis of CFRP strengthened deep reinforced concrete (RC) members, the strut-and-tie method (STM) is also a powerful analysis tool since a bonded CFRP element acts as an additional tension tie. In this paper, a practical analysis and design process for CFRP strengthened deep RC members using the STM is presented. In addition, seven effective factor models accounting for reduction of strength in cracked concrete were also investigated. A total of 17 experimental deep beam test results were compared with the proposed STM approach results. It has been shown that the proposed STM approach with an effective factor model depending on the strut angle provides the best agreement with the test results.

In this study, a performance-based model is proposed, capable of simulating seismic behavior of typical confined masonry (CM) walls whose response is governed by shear deformations. This model is developed on the basis of both monotonic and reversed-cyclic experiments assembled in an extensive database, and derived through an iterative linear regression analysis. Owing to the limited data available and inconsistencies in observed behavior in some tests, only specimens with two tie columns, one on either edge of the wall; multiple longitudinal rebar per confining element; no bed joint reinforcement; no openings within the confined panel; and a height-to-length ratio that varies from 0.7 to 1.2, are considered for the purpose of 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. The accuracy of the model is also verified for CM walls with different characteristics. The proposed model simulates reasonably well the seismic behavior of CM walls whose properties conform to the assumptions of the model and that correspond to typical CM walls.

Two series of tests with different depth wood I-joists were conducted to study the effects of circular and square web openings and the placement of steel angle retrofits at openings. Finite-element analysis of all test configurations was used to improve understanding of how web openings and retrofits affect the stiffness, stress distributions around openings, and ultimate failure mechanisms. Test results show failure loads well above prescribed design loads; however, the presence of web openings affected the type of failure modes. Control joists failed at the tension flange, whereas joists with web openings failed in shear through web openings or by means directly attributable to the presence of an opening. Ultimate capacity and stiffness was generally reduced by the presence of a web opening, with openings located closer to high shear areas producing worse results. Square web openings lowered the ultimate capacity approximately 10% more than circular openings when located at the same location. Steel angle retrofits improved capacity if an adequate retrofit length was used to redistribute stress concentrations. Finite-element models accurately predicted decreases in stiffness due to web openings; however, the models predict an improvement in stiffness due to the presence of steel retrofits that was not ascertained in experimental results.

The overall goal of this study is to gain an insight into the load sharing aspect between oriented strand board (OSB) and gypsum wall board (GWB) in shear wall assembly during racking load. Sixteen standard $\mathrm{2,440}\times \mathrm{2,440}\mathrm{mm}$ walls were tested monotonically, in total, out of which 11 (Type A) were sheathed on both sides (OSB on one side and GWB on the other), while five walls were tested without GWB (Type B). Digital image correlation (DIC) was used for data acquisition and analysis which is a full-field, noncontact technique for measurement of displacements and strains. The system returns full-field three-dimensional displacement and strain data measured over the visible specimen surfaces. Overall, these tests suggest that initially during loading of a wall the load is shared between OSB and GWB. However, the proportion of load sharing is not known. As GWB fails first at about 60% of ultimate load capacity of the wall, the load shifts to the OSB panel which resists it until the failure of the wall. The tests also revealed that the load path in wall Types A and B is different and so is the failure pattern. Strains were locally concentrated around the fasteners, while the strains in the field of the panel were below the detection limit of DIC system.

The feasibility of using meshfree methods in nonlinear structural analysis is explored in an attempt to establish a new paradigm in structural engineering computation. 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 two-dimensional domain simulates beam bending, $J2$ plasticity characterizes material behavior, and stabilized nodal integration yields the discrete equations. The particular case of steel frames composed of wide flange sections is investigated, though the concepts introduced can be extended to other structural materials and systems. Results of numerical simulations are compared with analytical solutions, finite-element simulations, and experimental data to validate the methodology. The findings indicate that meshfree methods offer an alternative approach with enhanced capabilities for nonlinear structural analysis. The proposed method can be integrated with finite elements so that a structural system is composed of meshfree regions and finite-element regions to facilitate simulations of large-scale systems.

Throughout recent history, well documented records of building failures may be found, unfortunately accompanied by great human loss and major economic consequences. One of the mechanisms of failure is referred to as “progressive collapse”: one or several structural members suddenly fail, whatever the cause (accident or attack). The building then collapses progressively, every load redistribution in turn causing the failure of other structural elements, until the complete failure of the building or of a major part of it. Various procedures are proposed in the literature in order to simulate the effects of this phenomenon, all of them based on different specific assumptions, such as the independence of the procedure with respect to the cause of the initial failure, or the sequence in which the loads are applied. Since the degree of approximation induced by these assumptions is not discussed in these contributions, the aim of this paper is to assess it. A more complete yet still simplified approach, avoiding some of these assumptions, is devised, based on a finite-element large displacement code, using plastic hinges associated with beam finite elements. Comparisons are established between these results and those obtained with four quasi-static procedures already present in the literature. A discussion based on the results of a large-scale example, provides an assessment of their degree of validity. Discrepancies appear in some cases between the results obtained with the procedures taken form the literature and the reference solutions obtained with the more complete approach. As a result, the better procedures out of those studied can thus be singled out.

Although current code guidelines specify different seismic performance objectives for fixed-base and isolated buildings, the future of performance-based design will allow user-selected performance objectives, motivating the need for a consistent performance comparison of the two systems. Based on response history analysis to a suite of motions, constant ductility spectra are generated for fixed-base and isolated buildings. Both superstructure force (base shear) and deformation demands in base-isolated buildings are lower than in fixed-base buildings responding with identical deformation ductility. To compare the relative performance of many systems or to predict the best system to achieve a given performance objective, a response index is developed and used for rapid prototyping of response as a function of system characteristics. When evaluated for a life safety performance objective, 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. 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.

This paper presents the basis of a procedure to estimate the explosive charge weight and stand-off 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. Test results showed that the procedure was accurate in predicting the explosive charge weight and stand-off distance to impose a given damage level on the tested RC slabs. This main conclusion was derived because a reasonable agreement was observed between the damage levels selected for assessment and the damage levels observed during testing.

In comparison with atmospheric boundary layer winds, which are customarily treated as stationary, winds associated with gust fronts originating from a thunderstorm/downburst exhibit rapid changes during a short time period, which may be accompanied by changes in direction. This introduces nonstationarity both in the mean and the standard deviation of wind fluctuations. In order to realistically capture characteristics of gust-front winds and their attendant load effects, a new analysis framework is presented, which is named here as the gust-front factor approach. This is akin to the gust loading factor format used in codes and standards worldwide for the treatment of conventional boundary layer winds. The gust-front factor expresses a generalized description of the genesis of the overall wind load effects on structures under both gust-front and boundary layer winds and it reduces simply to the gust loading factor for the case of conventional boundary layer winds. This approach encapsulates both the kinematic and dynamic features of gust-front induced wind effects on structures that distinguish themselves from those experienced in conventional boundary layer flows, i.e., variation in the kinematics of the velocity profile and its effects on the associated aerodynamics, dynamic effects induced by the sudden rise in wind speed, nonstationarity of turbulence in gust-front winds, and transient aerodynamics. To facilitate expeditious utilization of this framework in design practice and inclusion in codes and standards, the analysis framework and its workflow is introduced within a web-based portal. This eliminates the need for an in-depth understanding of the background within the framework and the need for associated computational effort. The portal has a user-friendly interface, which is available at http://gff.ce.nd.edu, permitting convenient analysis of several design scenarios with a host of potential loading conditions including the current ASCE 7-05 procedure in boundary layer winds for immediate comparison.

Based on the long-term monitored strain data induced by heavy vehicle traffic on an existing bridge, this paper presents an efficient approach to assessing the bridge system performance through a series-parallel system model consisting of bridge component reliabilities. The correlations among the bridge component safety margins are obtained by using actual traffic and strain data from structural health monitoring (SHM). The prediction of bridge system reliability in the future is dependent on the performance functions of components. Sensitivity studies with respect to system modeling, correlations, extreme value probability distributions, measurement errors, and number of observations are carried out. A case study of the proposed approach is provided on an existing highway bridge in Wisconsin, which was monitored in 2004 by the Advanced Technology for Large Structural Systems Center, a National Engineering Research Center at Lehigh University, Bethlehem, Pa, USA. This study provides a solid basis for integrating SHM data into practical assessment of bridge system performance.

Effective beam width model (EBWM) has been widely used for predicting lateral drifts and slab moments in flat slab structures under lateral loads. As the slab moment due to lateral loads increases, slab stiffness decreases due to crack formation. The accuracy of the EBWM strongly depends on how the reduced slab stiffness is estimated. For this purpose, this study developed equations for calculating slab stiffness reduction factor $\left(\beta \right)$ by conducting nonlinear regression analysis using stiffness reduction factors estimated from collected test results. The slab stiffness reduction factor $\left(\beta \right)$ is defined as a ratio of reduced slab stiffness due to crack formation to the stiffness of the uncracked slab section. For verifying the proposed equation, the lateral stiffness of two slab–column connection specimens tested by the writers was compared with the lateral stiffness calculated using the EBWM with the proposed stiffness reduction factor. Further, two flat plate specimens having two continuous spans were also considered for verifying the proposed equations for $\beta$ .