Journal of Structural Engineering

To complement the computer simulations, component testing, and small-scale shake table tests done by other researchers, a full-scale one-story unreinforced brick masonry specimen having a wood diaphragm was subjected to earthquake excitations using pseudo-dynamic testing. The specimen was designed to better understand the flexible-floor/rigid-wall interaction, the impact of wall continuity at the building corners and the effect of a relatively weak diaphragm on the expected seismic behavior. This paper reports on the characteristics of the specimen and the analyses of the dynamic response of the shear walls with piers having a rocking and/or a sliding behavior. These results are compared with predictions from existing seismic evaluation methodologies. It is found that the overall building was relatively resilient to earthquake excitation, even though cracking was extensive, and that some (but not all) of the existing seismic evaluation methodologies accurately capture the rocking/sliding behavior that developed in the shear walls under large displacement.

Models to estimate crack spacings and tension stiffening effects in reinforced concrete (RC) members with externally bonded fiber-reinforced polymer (FRP) sheets are presented. Due to the lack of experimental evidence on the tension stiffening effect of FRP sheeting, a theoretical approach based on the concept of tension chords is introduced. Crack formation and the tension stiffening of tension chords with FRP sheets are subjected to parametric analyses using bond stress-slip relations. The analytical results are then reduced into simple model equations. In addition to the FRP sheet, the bond characteristics between steel bars and concrete is also modeled according to a concept of average bond. These models are incorporated into the distributed stress field model, enabling reasonable estimations of the crack widths and the tension stiffening effects in RC members with the FRP sheets.

This paper introduces an improved steel jacketing method to retrofit reinforced concrete columns with a square or rectangular section for enhanced strength and improved ductility. To retrofit an existing column, relatively thin steel plates were welded to form a rectilinear jacket for shear strength enhancement, and then additional confinement elements (stiffeners) with various types of desired configurations were welded to the potential plastic hinge regions to ensure a ductile behavior. A rational retrofit design procedure was suggested and evaluated through an experimental program. Five 1/3 scale model columns were tested under constant axial load of $0.3A_g{f}_c^{\prime }$ and cyclic lateral force in a double-curvature condition. Test results validated the efficiency of the partially stiffened rectilinear steel jacketing, which not only prevented brittle shear failure but also greatly improved the ductility of the column with achieving an ultimate drift ratio of more than 8%. Besides the structural merits, the partially stiffened rectilinear steel jackets also have appealing architectural features.

This paper presents the experimental results obtained from the testing of nine 1:3 scale square-shaped column specimens. Characteristics of the specimens are low-lateral confinement, low-to-moderate shear span, and high-axial load. Detailing of the transverse reinforcement includes both 90° and 135° hooks. Specimens with low-shear span failed under shear in a brittle manner. Flexural failures were observed in specimens with moderate shear span and having a lateral confinement ratio of 0.003. Lateral confinement has significant influence on the ultimate drift, of which an increase from 0.001 to 0.003 could increase the ultimate drift capacity by up to 100%. Seismic performance of columns with low-to-moderate shear span may not be accurately reflected by the ductility factor. Better representation is provided by the ultimate drift ratio, and can be estimated by an empirical equation. The use of 90° hooks in detailing the transverse reinforcement leads to a 40% reduction on the ultimate drift capacity. Guidelines are also given to estimate the corresponding reduction on the ductility factor.

This paper reports on an experimental research project concerning the poststrengthening of concrete slabs with externally bonded carbon fiber reinforced polymers (CFRP). The two problems studied were strengthening in order to double the load-bearing capacity of slabs and restoration of the original load-bearing capacity of rebars that had been accidentally cut. To this end, the load conditions and the geometrical conditions of steel rebars as well as the length and distribution of CFRP strips were varied. Design, test setup, and selected results of the tests are presented and discussed. On the basis of these tests, design recommendations are given for strengthening and repair. These design recommendations are consistent with the steps typically used for the design and dimensioning of slabs and beams in structural concrete. These steps include calculation of the bending resistance, the shear resistance and the anchoring length of the reinforcement.

Although research in reinforcement corrosion in concrete has been intensive for the past three decades, studies of the most recently published literature reveal that the current state of research in corrosion propagation and its effects on structural resistance deterioration remains unsatisfactory. The intention of this paper is to develop models of structural resistance deterioration used in whole life performance assessment of corrosion-affected concrete structures. An assessment criterion is established to define the structural performance in terms of strength and serviceability limit states. A comparison of the experimental results on strength deterioration as determined from destructive load test and nondestructive measurement of corrosion current density is undertaken. From the developed models, life cycles of corrosion-affected concrete structures are determined in the paper. Together with previous results, a complete picture of whole life performance assessment of corrosion-affected reinforced concrete structures is depicted. The methodology presented in the paper can be used as a tool for structural engineers and asset managers in assessing concrete infrastructure and making decisions with regard to its maintenance and rehabilitation.

A genetic algorithm is used to perform the discrete optimization of reinforced concrete plane frames subject to combinations of gravity loads and lateral loads. Difficulties in finding optimum sections from a semi-infinite set of member sizes and reinforcement arrangements are alleviated by constructing data sets, which contain a finite number of sectional properties of beams and columns in a practical range. Construction practice is also implemented by linking columns and beams by group and by considering “connectivity” between columns located in the same column line. It is shown that the developed genetic algorithm obtained an optimal design for reinforced concrete plane frames.

Artificial neural networks have attracted considerable attention and have shown promise for modeling complex nonlinear relationships. This paper explores the use of artificial neural networks in predicting the confinement efficiency of concentrically loaded reinforced concrete (RC) columns with rectilinear transverse steel. Fifty-five experimental test results were collected from the literature of square columns tested under concentric loading. A multilayer-functional-link neural network was used for training and testing the experimental data. A comparison study between the neural network model and four parametric models is also carried out. It was found that the neural network model could reasonably capture the underlying behavior of confined RC columns. Moreover, compared with parametric models, the neural network approach provides better results. The close correlation between experimental and calculated values shows that neural network-based modeling is a practical method for predicting the confinement efficiency of RC columns with transverse steel because it provided instantaneous result once it is properly trained and tested.

The design of unbraced steel angle section beams against biaxial bending and torsion requires the ability to predict their lateral buckling strengths when bent about the major principal axis. Present design code formulations of lateral buckling strength are based on research on doubly symmetric I-section beams, and may be inappropriate for monosymmetric and asymmetric angle section beams. This paper presents close approximations for the elastic lateral buckling moments of equal and unequal angle section beams loaded by uniformly distributed loads which act at or away from the shear center. Small and large twist rotation elastic analyses of angle section beams with initial twist rotations are used with interaction equations for the biaxial bending section moment capacities to investigate present design code formulations for lateral buckling strength. It is found that these code formulations are unnecessarily conservative, especially at high slendernesses, where the moment capacities predicted by them may be less than the minor axis section capacity instead of greater. An improved formulation is proposed which is simpler and more economic than the present formulations. The use of the elastic lateral buckling approximations in the improved design moment capacity formulation is demonstrated in a worked example.

One of the fundamental components of the moment-rotation behavior of a steel or composite partially restrained (PR) connection is the load-deformation behavior associated with high-strength bolts bearing on steel plates. For many PR connections, the writers believe that this bearing behavior can be approximated by the behavior of a single bolt lap plate connection. One of the primary components of the lap plate connection behavior is the local load-deformation behavior associated with a single bolt bearing on a single plate. This paper presents an experimental and analytical study of the single bolt single plate behavior. The results of the paper include specific methods for predicting the initial stiffness, strength, and overall load-deformation behavior of the single bolt single plate connection.

Tests were conducted on two prototype steel shear links for the main tower of the new San Francisco-Oakland Bay self-anchored suspension bridge to evaluate the link force and deformation capacities. The links were built-up wide-flange sections, designed to yield in shear. A quasi-static loading protocol was used to test the links in reverse curvature, simulating the expected seismic demand. The link capacities exceeded the predicted demands from the Safety Evaluation Earthquake. The specimens behaved in a ductile manner until small cracks initiated at the end of the vertical fillet welds connecting the intermediate stiffeners to the link web. As the cracks propagated further, brittle fracture of the web ensued. The maximum shear strength was nearly twice the expected yield shear strength, a significantly higher overstrength than current codes recognize. Alleviating the stress concentration on the vertical fillet welds of the intermediate web stiffeners is necessary to avoid brittle fracture and to increase the link deformation capacity. Analysis showed that offsetting the fillet welds from the web-flange-stiffener intersection reduced the demand at the end of the weld.

A series of tests is performed on composite beams with web openings. The beams have ribbed slabs with the ribs oriented transversely. The effects of slab width and moment-shear ratio on failure mode and strength are studied. Failure mode of concrete slabs depends on the slab width. Pullout failure around the shear connectors at the high-moment end occurs in the beams with wide slab width, while diagonal tension-type failure occurs in a beam with narrow slab width. Based on the test results, a strength model is developed. The maximum shear capacity is approximated as the sum of the individual shear capacity of the steel beam and the concrete slab. The shear contribution of the concrete slab is taken as the lesser of the shear strength of the slab and the pullout capacity of the studs. Strength predictions of the proposed model are compared with test results and predictions of other strength models. The proposed model is easy to use and gives satisfactory predictions.

The assessment of the current state and the prediction of the future condition of deteriorating structures are crucial processes in the management of civil infrastructure systems. Not only time-varying loads and resistances but also a series of maintenance interventions that are applied to keep structural systems safe and serviceable make the prediction process very difficult. In order to perform a realistic life-cycle analysis of deteriorating structures under different maintenance scenarios the uncertainties involved in this process have to be considered. This paper considers these uncertainties by providing a reliability-based framework and shows that the identification of the optimum maintenance scenario is a straightforward process. This is achieved by using a computer program for Life-Cycle Analysis of Deteriorating Structures (LCADS). This program can consider the effects of various types of actions on the reliability index profile of a group of deteriorating structures. Only the effect of maintenance interventions is considered in this study. However, any environmental or mechanical action affecting the reliability index profile can be considered in LCADS. Most input data are represented by random variables. In this manner, the uncertainties included in maintenance interventions, reliability index profiles, and cost evaluations are all taken into account. The present value of the expected cumulative cost associated with maintenance interventions can be evaluated for both an individual structure and a group of similar structures. Optimization and parametric analysis modules help the identification of the maintenance strategy that best balance cost and reliability index profile over a specified time horizon. Numerical examples of deteriorating bridges are presented to illustrate the capability of the proposed approach. Further development and implementation of this approach are recommended for future research.

A new methodology is developed that can identify the optimal testing procedure to be used in generating S-N curves for predicting damage accumulation under variable-amplitude service loads. This is a significant extension of existing knowledge, which includes a solution to this problem only for situations in which the service loads are constant amplitude. The methodology has the potential to improve significantly the predictions of fatigue damage and reliability under realistic service loads. In general, finding the truly optimal solution involves solving a quartic equation, but it is often possible to use a simplified form that involves only a quadratic equation. The new results are identical to the previously developed formulation for the special situation of a constant-amplitude service load. The information needed to use the general procedure is the distribution of stress amplitudes in the service load and the variability of the service life among identical load/specimen combinations. The procedure is illustrated here by its application to the special case of bilevel service loads, for which numerical results are presented. This includes information on both the optimal S-N testing procedure, and the sensitivity of the mean-squared error to changes in the testing procedure.