Journal of Structural Engineering

A series of framed unreinforced masonry (URM) infill walls were retrofitted with modern materials to evaluate the abilities of these materials to mitigate blast effects. The walls were constructed from traditional and alternative masonry materials to assess the applicability of using a wood-fiber fly ash material for infill construction. The walls were tested in the laboratory under static conditions and were evaluated using several criteria: energy absorption, out-of-plane load resistance, out-of-plane deformability, and the reduction of masonry debris scatter upon collapse. Due to the presence of the surrounding frame structure, all of the walls in this program experienced some form of an arching mechanism. 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 due to a lack of anchorage between the strengthened walls and surrounding structure. A simplified analytical model to estimate the ultimate out-of-plane capacity for FRP strengthened URM arching walls was developed. The analytical model was empirically calibrated using test data from this work as well as previous studies. The model predictions agree well with the experimental results reported in this paper.

Both maximum displacement and displacement ductility factors should be considered in the design of a blast-resistant structure since both parameters correlate with an expected performance level of a reinforced concrete (RC) structural member during a blast event. The blast-resistant design procedure discussed in this paper takes into account both the maximum displacement and displacement ductility responses of an equivalent single-degree-of-freedom (SDOF) system, while the response of the SDOF system is made equivalent to the corresponding targets of design performance. Some approximate errors are present when comparing the actual responses of the structural member, which has been designed for blast loading, and their corresponding design performance targets. Two indices are defined to quantify the approximation errors, and their expressions are obtained through comprehensive numerical and statistical analyses. By using the error indices, the design procedure is then modified such that the approximate responses of the RC member are equivalent to the targets of the design performance. The modified procedure is implemented in three design examples and numerically evaluated. It is concluded that the modified procedure can be used more effectively in order to ensure that the actual responses of designed members reflect the respective targets of design performance.

The paper deals with the probabilistic modeling of the thermomechanical behavior of cardboard–plaster–cardboard (CPC) multilayer plates submitted to fire load. The proposed model takes into account data and model uncertainties. This work is justified by the fact that fire resistance tests of plasterboard-lined partitions are made impossible when their dimensions exceed those of furnaces. A fundamental key to solve such a problem is the development and experimental validation of a deterministic and probabilistic model of CPC multilayers submitted to fire load. The first step of this work concerns the constitution of an experimental thermomechanical data base for a CPC multilayer and for its components. These experimental tests are carried out by the use of a bench test specially designed for this work. The second step is the development of a homogenization thermomechanical mean model for the CPC multilayer. The third step is the development of a probabilistic model of uncertainties based on the nonparametric probabilistic approach. Numerical results are compared with the experimental ones.

This paper presents the results from an experimental pushover test on a one-third-scale model of a special inverted-V-braced steel frame with zipper struts. Zipper elements are vertical elements added at the intersections of the braces above the first floor and designed to carry upward the unbalanced loads resulting from buckling of the braces. As far as the writers know, this is the first test on such a configuration that has been suggested as an alternate to conventional braced frames in the American Institute of Steel Construction seismic specification for many years. The model was pushed to a target roof drift ratio of $+3.58\%$ , which was achieved without strength degradation and followed a trilinear backbone curve. The load was then reversed until the bottom story brace in tension fractured at a drift of $-0.78\%$ . After this fracture, the frame still carried about 37% of the maximum base shear. The zipper elements demonstrated their ability to activate buckling in all stories except the top one, redistributing the loads in the structure and minimizing strength losses. Two-dimensional and one three-dimensional frame models were analyzed and found to reproduce satisfactorily the experimental results up to the beginning of tearing in the tension brace.

This study examines the experimentally obtained lateral response characteristics of model scale square fiber-reinforced elastomeric isolator (FREI) bearings, which are intended to mitigate seismic induced forces on ordinary low-rise buildings. The bearings consist of an unfilled soft neoprene compound as the elastomer material and bidirectional carbon fiber fabric as the reinforcement. The bearings have been employed in an unbonded application, which means they are not attached to the upper and lower platens of the test machine. 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 comparable to that of conventional high damped steel reinforced bearings. The adequacy of the bearings has been verified in conformance with provisions of ASCE in 2005.

Previous research has shown that weakening of inelastic structures can limit the maximum response accelerations they experience during ground motions, but may lead to an increase in the displacements (or interstory drifts). Added damping by using fluid viscous devices, on the other hand, reduces the interstory drifts and has no significant effect on total accelerations, when structures behave inelastically. The weakening and damping technique, thus, limits the total acceleration due to the weakening, and reduces the interstory drifts by adding damping, and hence addresses the two main causes for both structural and nonstructural damage in buildings. Optimal weakening and damping, which is the subject of this paper, involves the determination of the optimal locations and amount of weakening of the structural components as well as the optimal locations and magnitudes of added dampers. Weakening of the structure might create stability issues in the building that can be automatically considered, if active control theory is used for design. Based on a nonlinear active control procedure, control forces are calculated and implemented using equivalent passive dampers and weakening elements in order to achieve the closest effects. The methodology is applied to a case study of an eight-story nonlinear building tested 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.

Stiffened plates are major structural components in ships and offshore structures. Their structural integrity has direct implications on the safety of human beings and goods on ships. Accurate prediction of the ultimate strength of stiffened plates has been a very important task for ship designers. In this study, an artificial neural network-based response surface method (ANN-RSM) is applied to derive a formula to predict the ultimate strength of stiffened plates under uniaxial compression using the existing experimental data. The key issues in optimizing an ANN model are systematically examined. The developed formula is compared with some existing analytical formulas, such as Faulkner’s formulas, Pu’s formulas, and Carlsen’s formula. It is determined that the formula proposed in this study is much more accurate than existing analytical methods based on the current database. The hyperbolic tangent activation function can produce more accurate results than the sigmoid function in this application. The normalization range of input and output variables also has an effect on the performance of the ANN model, which should be considered. ANN-RSM has fairly good extrapolation capacity.

Beam string pipeline crossing (BSP) is a new type of a self-supporting, large-span pipeline crossing structure. Based on the ANSYS program, the prestressing force of a $100\mathrm{m}$ span BSP was optimized using the first-order method, and the structural stability under three types of boundary conditions were analyzed and compared by nonlinear buckling analysis. In addition, some key geometric parameters, such as the rise-span ratio, rag-span ratio, struts arrangement, and cross section of the beam, string, and struts, were determined by parameter analysis. On this basis, a 1:15 model test was carried out to investigate the behaviors of BSP during the full-range, including the stretching phase, serviceability phase and ultimate load carrying phase. The test and analytical results of finite-element analysis showed that the stability and loading-bearing capacity of the BSP was reliable and the semispan water load case was the controlling load case in the design. Finally, calculation formulas for the deformation and internal force of BSP in the elastic stage and plastic ultimate load were proposed by the Ritz method.

Performance-based design is being developed and implemented in seismic and fire resistant design. The field of structural wind engineering has introduced several techniques that may eventually lead to performance-based wind engineering for buildings such as database assisted design. For wood-frame buildings, one deficiency is the lack of accurate load/response models with the ability to go beyond first failure leaving only force-based approaches which protect life safety but only infer certain levels of performance. This paper introduces a new nonlinear roof sheathing fastener model that is a function of not only the uplift pressure acting on the roof sheathing, but the effective moment arm (not just the moment) acting on the edge nails. 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 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. It is anticipated that this more accurate nail model can aid in the development of performance-based wind engineering for wood-frame buildings.

This technical note introduces a novel model conversion technique for structural dynamic systems that is capable of converting a physically realizable, higher-order model (termed the source model) into a completely different, predefined, physically realizable, lower-order model (termed the target model). Upon the complexion of the conversion, the resulting target model preserves or approximates the dynamic characteristics—the chosen structural frequencies and their mode shapes—of the source model. Mathematically, the procedure to implement the model conversion technique is like a model updating approach, which is fundamentally different from that used in traditional model reduction schemes. A numerical example of converting a five-story two-dimensional frame structure model into a five-story classical/generalized one-dimensional shear-building model is demonstrated.