Journal of Structural Engineering

An accelerated Newton algorithm based on Krylov subspaces is applied to solving nonlinear equations of structural equilibrium. The algorithm uses a low-rank least-squares analysis to advance the search for equilibrium at the degrees of freedom (DOFs) where the largest changes in structural state occur; then it corrects for smaller changes at the remaining DOFs using a modified Newton computation. The algorithm is suited to simulating the dynamic progressive collapse analysis of frames where yielding and local collapse mechanisms form at a small number of DOFs while the state of the remaining structural components is relatively linear. In addition, the algorithm is able to resolve erroneous search directions that arise from approximation errors in the tangent stiffness matrix. Numerical examples indicate that the Krylov subspace algorithm has a larger radius of convergence and requires fewer matrix factorizations than Newton-Raphson in the dynamic progressive collapse simulation of reinforced concrete and steel frames.

The main objective of this paper is to investigate the tracking (signal reproduction) capability of the UCSD-NEES shake table system through a series of broadband and harmonic experiments with different tuning and test amplitudes. The second objective is to obtain quantitative relations between different measures of the signal reproduction error and the amplitude of the reference excitation used to tune the shake table controller. These relations can be used as guidelines in planning of future seismic tests on the UCSD-NEES shake table or on large shake tables with similar controllers. The third objective is to evaluate the effectiveness of the existing iterative correction/tuning procedure for the UCSD-NEES shake table. The final objective of the paper is to propose some improvements to the current shake table tuning practice.

Lead-rubber bearings are seismic isolators that have been used extensively to protect buildings, bridges, and mission-critical infrastructure from the damaging effects of earthquake shaking. In bridges, lead-rubber bearings are subjected to continuous movement due to service (traffic) and temperature effects. This paper presents data on the effects of cumulative travel on the mechanical properties of lead-rubber bearings based on an experimental investigation of both medium- and small-sized bearings. A theoretical interpretation of the test results is presented.

A new roller seismic isolation bearing is developed for use in highway bridges. This new bearing uses rolling of cylindrical rollers on V-shaped sloping surfaces to achieve seismic isolation. The bearing is characterized by a constant spectral acceleration under horizontal ground motions and by a self-centering capability, which are two desirable properties for seismic applications. The former makes resonance less likely to occur between the bearing and horizontal earthquakes, while the latter guarantees that the bridge superstructure can self-center to its original position after earthquakes. To provide supplemental energy dissipation to reduce the seismic responses, the bearing is designed with a built-in sliding friction mechanism. This paper presents the seismic behavior of the bearing through analytical and experimental studies. First, the acceleration responses of and forces acting on the bearing under base excitation are presented. Next, the governing equation of horizontal motion, the base shear-horizontal displacement relationship, and conditions for self-centering, for the rollers to maintain contact with the bearing plates, and for rolling without sliding are discussed. An experimental study on a prototype bearing was carried out to verify and calibrate its characteristics and the results are discussed.

In this paper, an improved version of a simplified method to assess lateral shear forces attracted by shear walls of regular, low-rise masonry structures is presented. This simplified method for seismic analysis (SMSA) is allowed by Mexican building codes since the 1970s. The impact of shear deformations in the three-dimensional distribution of the forces absorbed by these walls is assessed for different wall aspect ratios $\left(H/L\right)$ . Based on extensive parametric studies, effective shear area factors $\left(F_{AE}\right)$ originally proposed in the SMSA are modified to improve the estimates of shear forces using this method. New $F_{AE}$ are proposed for three different performance levels for the structure: (1) elastic response; (2) completely nonlinear (cracked) response of all walls along the building height; and (3) partially nonlinear (cracked) response along the height.

This paper presents development of a simplified procedure for seismic evaluation of piles with partial-moment connection typically used in marine oil terminals. The current seismic evaluation procedure of the piles in marine oil terminals includes monitoring material strains specified in the Marine Oil Terminal Engineering and Maintenance Standard (MOTEMS) during the nonlinear static pushover analysis to estimate the displacement capacity of piles. This investigation developed closed-form formulas for estimating the displacement capacity of piles by using a simple pile-deck connection system. The displacement capacity estimated from these formulas ensures that the material stain limits specified in the MOTEMS is not exceeded. These formulas are demonstrated to be “accurate” by comparing results from these formulas against those from the nonlinear finite-element analysis. The formulas developed in this investigation utilize the curvature ductility capacity of the pile section and rotation ductility capacity of the connection at the selected seismic design level, along with the parameter $\beta$ which depends on the relative stiffness of the pile and the connection and the parameter $\eta$ which depends on the relative strength of the connection and the pile.

In simple inelastic structures subjected to severe base motions, the maximum acceleration response is bound by the yield strength and is inversely proportional to its mass. It can be demonstrated that a similar effect is approximately produced in structures with multidegrees of freedom. In strong structures, the maximum acceleration response is dependent on the intensity of the earthquake. However, if the strength of the structure is reduced, the maximum acceleration response and associated forces in its structural and nonstructural components can be substantially reduced. If some of the structural columns (carrying gravity loads) are allowed to rock, providing very small resistance to lateral loads, it is possible to reduce the strength of the global structural system and limit the global accelerations in seismic events. However, before overturning such columns may have substantial resistance which may void the effectiveness of weakening. The objective of this study is to (1) develop a simplified analytical model for rocking columns from fixity to overturning; (2) build the computational tools to simulate the behavior of structures including such rocking columns; and (3) examine the global nonlinear static response of a weakened structure. An analytical model is developed using an equivalent flexibility approach, which considers rigid body rotations and flexural deformations. Physical experiments of rocking columns were performed, and the results are used for the calibration and validation of analytical models. An analytical model of a 1:3 scaled structure is developed using IDARC2D modified in this study to evaluate several alternatives of weakening using rocking columns.

Eccentrically braced frames (EBFs) are desirable seismic load resisting systems as they combine the high elastic stiffness of concentrically braced frames with the ductility and stable energy dissipation of moment resisting frames. EBFs with links attached to the columns are particularly appealing for architectural flexibility as they provide multiple locations for placement of doors and hallways. However, previous research has shown that link-to-column connections are prone to failure at low drift levels, due to their susceptibility to fracture at the link flange-to-column welds. This paper investigates the application of the reduced beam section concept for links in eccentrically braced frames to enhance the ductility of link-to-column connections. A design procedure for link section reduction is proposed and preliminary finite-element analyses are conducted on a shear link with various reduced section geometries. A parametric study performed on an array of links having various cross sections and lengths suggests that the reduced link section may substantially reduce the plastic flange strains at the link ends, which can improve the fracture life. The reduction in plastic flange strains is found to be significant for all links, with larger reductions for intermediate and flexural links. Furthermore, the detrimental kinking deformation of the flanges, caused by the large rotation demands in shear links, is moved away from the column face when reduced sections were used. While the analysis results show promise, experimental verification is recommended before the proposed design procedure can be implemented in practice.

Fiber-reinforced polymer (FRP) pultruded profiles are produced by a number of manufacturers worldwide in similar, but nonstandard, wide-flange, I, angle, and tubular profiles. At present there is no American National Standards Institute approved design code in the United States for structural design with pultruded FRP profiles. Manufacturers of pultruded profiles each provide their own design equations, design methods, material properties, and safety factors for their pultruded products. There is a need for standardization of production and design of pultruded profiles to enable mainstream use of these profiles in structural engineering practice. The purpose of this paper is twofold: (1) to provide appropriate resistance factors ( $\varphi$ factors) for wide-flange pultruded columns that are compatible with ASCE 7 load factors and (2) to provide a unified analytical equation for local and global buckling of concentrically loaded axial members, which may be appropriate for a future design code. The resistance factors are provided for different target levels of structural reliability, $\beta$ , and for different nominal design properties of the pultruded materials. The resistance factors were determined using Monte Carlo simulation based on the results of 75 tests of full-scale pultruded columns that have been reported in the literature. In addition, resistance factors and structural reliabilities were calculated for the design equations provided by the manufactures in their design codes. The paper demonstrates that a unified design equation for pultruded columns can be developed for LRFD with reliability indices that are similar to those used for conventional materials. The paper also shows that markedly different reliability indices are obtained for the different manufacturer-provided equations even though identical allowable stress design safety factors are recommended by all manufacturers.

This paper describes a numerical program to analyze the behavior of the concrete-filled steel tubular (CFT) stub columns, and predict various modes of lateral interactions between steel tube and filled-in-concrete under axial compression. The behavior of the CFT columns is controlled by both the strength and the confinement effect of steel tube and filled-in-concrete in the columns. Various lateral interactions between steel tube and filled-in-concrete in CFT columns are classified into eight different cases by the contact between steel tube and filled-in concrete at different stress stages. The paper examines the analytical models with various experimental results in literature. The comparisons showed that the numerical program is reasonable to capture mechanical behavior of concrete-filled circular steel tubes.

The monolithic structural action of various types of walls of flanged cross section and walls with engaged stiffeners or returns (nonrectangular sections) is critically dependent on the shear capacity of the interface between the components making up the section. An assessment of the shear capacity of the interface may also be required as part of the elastic or inelastic analysis of structural elements. Observation of past earthquake events has confirmed that effectively connected flanges also directly influence the seismic performance of nonrectangular sections by providing a more robust and seismically resistant structural element. To analyze the significance of the parameters that influence the vertical shear resistance of interfaces of flanged sections of masonry obtained using different types of bonding and bonding patterns (header units, shear connectors, and wire ties), a series of specimens with “H-shaped” cross sections was tested. The vertical shear capacity of the interface at the flange-web intersection was assessed in each case and compared to predicted code capacities. Considerable strength reserves and shear ductility were observed in almost all cases. Following the experimental study, a numerical investigation was carried out using a simplified micromodeling finite element approach. It showed that both the size of the specimen as well as the boundary and applied loading conditions on the flanges can significantly influence the observed vertical shear resistance of the interfaces of specimens with the same bonding pattern. Using the results of the numerical investigation, the critical parameters for a test to determine the vertical shear capacity of brick masonry nonrectangular cross sections are assessed and the governing parameters for a suitable shear test suggested.

This paper continues a line of research aimed at the development of a dynamically based health condition monitoring of bridge structures in the area of Friuli Venezia Giulia, Italy. One subject of this research program has been a two-span highway bridge with a concrete slab supported by closely spaced precast beams, a constructive typology which is quite diffuse in the regional highway network. Forced-vibration tests and experimental modal analysis were used to determine the vibration properties of the structure. An identification procedure based on dynamic data allowed to define an accurate orthotropic plate model of the deck and to improve the description of some constructional details in the finite-element model of the bridge such as the boundary conditions on abutments and the connection between the deck and pier. The usefulness of the combined experimental and analytical process in the identification of structural properties has been proven and the procedure can be applied to other structures of the same typology.

Decoupling of soil-structure interaction is applied to analyze buried structure damage due to external blast load. The structural element under analysis is assumed to deform as a simply supported rigid-plastic beam. Shear failure, bending failure, and combined failure modes are considered based on five transverse velocity profiles. With proper failure criteria, the critical equations for structural shear and bending failures are derived respectively. Pressure-impulse diagrams are then developed to assess damage of the buried structures. Comparison has been made to show the influences of the soil-structure interaction and the shear-to-bending strength ratio of the buried structure. A case study has been conducted to a buried reinforced concrete box-type structure which shows that the proposed analysis method can be effectively applied.

This paper presents an overview of the approach employed in the development of the wind speed maps for use in ASCE 7-10. The reason for a reduction in the wind speeds in the new standard as compared to those given in the ASCE 7-98 through 7-05 standards is presented, as well as the reason for the reintroduction of Exposure D along the hurricane coastline. The most significant change in the wind speed maps from the previous version is the shift from a single map for an importance factor for buildings and other structures of 1.0 to three separate maps, one for each category of occupancy, thus eliminating the need for importance factors that vary between hurricane and nonhurricane regions.