Journal of Structural Engineering

An efficient approximate method that uses the multi-degrees-of-freedom (MDOF) modal equations of motion for the seismic response history analysis of asymmetric elastic buildings with soil–structure interaction (SSI) is presented in this paper. The systems considered are two-way asymmetric shear buildings resting on the surface of an elastic half-space, which are excited by two-directional seismic ground motions. The SSI forces were simulated using frequency-independent soil springs and dashpots. First, the MDOF modal equations of motion for the SSI systems were derived. The modal response histories were obtained by solving the MDOF modal equations of motion using the step-by-step integration method. Subsequently, the seismic response histories of the whole SSI system were determined from the arithmetic summation of the modal response histories. The MDOF modal equations of motion retain the property of nonproportional damping of the original SSI system. The proposed method has the advantages of the conventional modal response history analysis, which requires only the first few vibration modes to obtain accurate analytical results. Finally, the efficiency of the proposed method was validated using numerical examples of a two-way asymmetric four-story building with large and small SSI effects.

The objective of this paper is to present a seismic evaluation procedure based on an energy balance concept. The method is based on a framework that utilizes energy demand and capacity diagrams. The skeleton force–displacement (capacity) curve of the structure is converted into an energy capacity plot that is superimposed over the corresponding energy demand plot for a given hazard level to determine the expected peak displacement demand. First, the energy balance concept as applied in the seismic design of structures is discussed. Next, the underlying theory and framework for carrying out seismic evaluation are presented. The analysis procedure is then applied to an example three-story moment frame structure to estimate the displacement demands. The results obtained from the proposed procedure are then evaluated and compared with the results from nonlinear dynamic analysis as well as those from other well-established nonlinear static procedures. Observations regarding the accuracy of different nonlinear static procedures are discussed. The results show that the proposed method can be used effectively to estimate the response under a given ground motion.

Tests were performed on full-size prefabricated steel stair assemblies to assess seismic interstory drift response combined with factored gravity loads. The stair assemblies were production-run units of a standard system and were designed for a typical steel frame building. Two different stair assembly units were tested: one with checker plate and one with concrete-filled pans. A loading system and testing protocol were developed to evaluate the seismic performance using seismic and gravity load combinations. Lateral drifts were imposed in both orthogonal stair directions followed by factored live and dead gravity loads. Imposed lateral drift placed high deformation demands on the stair-to-landing connections and overall performance is dependent on the deformability and endurance of these connections. Careful detailing, fabrication, and inspection of the stair-to-landing connections are required to ensure desired system performance.

Structural engineers have long recognized the importance of member ductility, that is member rotation, in the design of reinforced concrete structures in order to redistribute moment and absorb energy due to dynamic, seismic, and blast loads. Understanding the rotation mechanism has been a difficult task due to the complex and variable behavior of reinforced concrete members and this is reflected in the slow but steady research progress. In this paper, the three components of the rotational mechanism of reinforced concrete beams are described. The rotation due to yield penetration of the reinforcing bars is then mathematically quantified using partial-interaction theory, which depends on the bond characteristics. The results are compared with published empirical approaches and shown to be in good agreement. Finally, a variable hinge length that is specific to the rotation limit due to fracture of the reinforcing bar, that is yield penetration, is mathematically developed.

Recent strong earthquakes have shown that column failure is the primary cause of collapse in many existing older buildings and bridges. The main objective of this paper is to develop a macromodel to simulate the cyclic lateral load–deformation response of reinforced concrete columns with limited computational effort. Flexural, longitudinal bar slip, and shear deformations are predicted under monotonic lateral loads, including the effects of strength decay and stiffness degradation. Using these monotonic responses as envelopes or primary curves, cyclic responses corresponding to these three deformation components are calculated. The column under consideration is classified into one of five categories considering the potential for flexural, shear, or axial load failure. Individual cyclic responses then are combined to obtain the total lateral response of the column based on its identified failure mode. Comparison of predicted cyclic response and experimental data showed that the proposed model is sufficiently accurate.

Analytical and experimental studies were undertaken to assess and improve modeling techniques for capturing the nonlinear behavior of flat-plate systems using results from shake table tests of two, approximately one-third scale, two-story reinforced concrete and posttensioned concrete slab–column frames. The modeling approach selected accounts for slab flexural yielding, slab flexural yielding due to unbalanced moment transfer, and loss of slab-to-column moment transfer capacity due to punching shear failure. For punching shear failure, a limit state model based on gravity shear ratio and lateral interstory drift was implemented into a computational platform (OpenSees). Comparisons of measured and predicted responses indicate that the proposed model was capable of reproducing the experimental results well for an isolated connection test, as well as the two shake table test specimens.

Wood-frame residential construction represents a major investment in the United States, which, when exposed to hurricanes, earthquakes, and other natural hazards, may sustain substantial damage. Although in many parts of the country one natural hazard dominates, in certain areas multiple hazards may pose a significant threat to buildings. Building design and construction practices should address the overall risk to residential construction from multiple hazards to achieve design strategies and risk levels that are consistent with occupant expectations and social objectives. This paper presents a framework for multihazard risk assessment using hurricane and earthquake hazards as an example. Structural reliability-based methods that describe natural hazard and structural system response probabilistically are essential for quantifying expected losses from natural disasters and for developing appropriate strategies to manage risk. The framework permits the main sources of uncertainty that affect building performance to be identified, and provides insight on strategies for effective multihazard mitigation efforts.

The majority of buildings and the vast majority of residential structures in North America are constructed using light-frame wood. Many of these structures are subjected to high winds along the eastern seaboard and gulf coast, and as a result routinely suffer damage resulting in financial losses. A relatively new paradigm in the field of earthquake engineering is performance-based design. This paper presents the concept of performance-based wind engineering for wood-frame buildings through the development and application of fragilities to form different owner/user performance expectations, namely, occupant comfort, continued occupancy, life safety, and structural integrity. The approach includes the development and application of fragility curves. An example analysis and design for a simple light-frame wood building for all four performance expectations is presented. The final design of the building needed to achieve the specified levels of structural performance are discussed for each performance expectation level.

The lateral performance of structurally nonsymmetric diagonal-braced wood shear walls used in post-and-beam timber buildings was investigated with laboratory testing and computer modeling. Monotonic and reversed cyclic tests were performed to study the capacities of a total of eight full-scale shear walls, with and without gypsum wallboard sheathing. Significant increases of strength, stiffness, and energy dissipation were observed in the shear walls with the additional gypsum wallboard sheathing. An efficient mechanics-based wood shear wall model was then introduced to represent the hysteretic load–drift behavior of these diagonal-braced walls. The predicted seismic response of the model agreed very well with the shake table test results of a simple one-story post-and-beam structure, making it possible to develop, in future research, structural models for more-complicated post-and-beam buildings with good computational efficiency and accuracy.

This paper reports a full-scale experimental program consisting of six pipe specimens made of X65 material (specified minimum yield $\text{strength}=448\mathrm{MPa}$ ) with $508\mathrm{mm}$ outer diameter, and a diameter-to-thickness ratio $(D∕t)$ of 81.2 subjected to combinations of bending, axial tension, and internal pressure. The study is aimed at determining whether the pipes are able to attain their modified plastic moment as predicted by analytically derived plastic interaction relations. The moment versus curvature relations, peak moment values, and local buckling behavior of the specimens as obtained from the experiments are documented. The peak moments obtained are compared to the analytically predicted moments. A nonlinear shell finite-element model is also developed using the finite-element analysis (FEA) simulator ABAQUS in order to predict the moment capacity and the local buckling behavior. Test results compare well with FEA results. It is observed that under certain combinations of axial tension and internal pressure, pipes with $D∕t=81.2$ are able to attain their plastic moment resistances.

The finite-strip method (FSM) is one of the most efficient methods for structural analysis of bridges, reducing the time required for analysis without affecting the degree of accuracy. FSM is therefore an ideal platform for traditional time-consuming fracture analysis. This paper presents a new bending crack strip (BCS) that combines the shape functions of the spline finite strip with the eigenfunction solutions of the differential equations that govern the deflection around a crack. When this new BCS is implemented in FSM, complex three-dimensional plate structures with embedded cracks that are perpendicular to the longitudinal axis of the strips can be analyzed efficiently. The stress intensity factors of such structures can be directly computed with BCS. Extra nodal points are used around the cracked area to increase the precision of the numerical method. A substructuring technique is employed to determine the corresponding degrees of freedom of the boundary nodes, resulting in efficient analyses of cracked plates and plate-girder structures. This paper presents two examples to illustrate the accuracy and convergence rate of BCS as well as to demonstrate applications of the proposed model in the analysis of plates and plate girder bridges.