INTERNATIONAL JOURNAL OF ADVANCED STRUCTURAL ENGINEERING
Year:2017 | Volume:9 | Issue:1|Papers Count:7

The present study aims at performing a mechanical analysis of 2D viscoelastic cracked structural materials using the Boundary Element Method (BEM). The mesh dimensionality reduction provided by the BEM and its accuracy in representing high gradient fields make this numerical method robust to solve fracture mechanics problems. Viscoelastic models address phenomena that provide changes on the mechanical material properties along time. Well-established viscoelastic models such as Maxwell, Kelvin–Voigt and Boltzmann are used in this study. The numerical viscoelastic scheme, which is based on algebraic BEM equations, utilizes the Euler method for time derivative evaluation. Therefore, the unknown variables at the structural boundary and its variations along time are determined through an ordinary linear system of equations. Moreover, time-dependent boundary conditions may be considered, which represent loading phases. The dual BEM formulation is adopted for modelling the mechanical structural behaviour of cracks bodies. Three examples are considered to illustrate the robustness of the adopted formulation. The results achieved by the BEM are in good agreement with reported data and numerical stability is observed.

Near-field ground motions are significantly severely affected on seismic response of structure compared with far-field ground motions, and the reason is that the nearsource forward directivity ground motions contain pulselong periods. Therefore, the cumulative effects of far-fault records are minor. The damage and collapse of engineering structures observed in the last decades’ earthquakes show the potential of damage in existing structures under near-field ground motions. One important subject studied by earthquake engineers as part of a performance-based approach is the determination of demand and collapse capacity under near-field earthquake. Different methods for evaluating seismic structural performance have been suggested along with and as part of the development of performance-based earthquake engineering. This study investigated the results of illustrious characteristics of near-fault ground motions on the seismic response of reinforced concrete (RC) structures, by the use of Incremental Nonlinear Dynamic Analysis (IDA) method. Due to the fact that various ground motions result in different intensity-versus-response plots, this analysis is done again under various ground motions in order to achieve significant statistical averages. The OpenSees software was used to conduct nonlinear structural evaluations.Numerical modelling showed that near-source outcomes cause most of the seismic energy from the rupture to arrive in a single coherent long-period pulse of motion and permanent ground displacements. Finally, a vulnerability of RC building can be evaluated against pulse-like near-fault ground motions effects.

In this paper, the performance of multiple tuned liquid damper (MTLD) has been investigated in mitigating the response of a structure under dynamic loading, i.e., harmonic excitation. For comparative study, the responses of single-tuned liquid damper (STLD) have also been considered. A set of experiments are conducted on a scaled model of steel-structure-STLD and MTLD systems to evaluate the performance of the respective TLD models under harmonic excitation. Several excitation frequency ratios (0.5–2.0) and depth ratios (0.05–0.30) are considered for this study. The effect of resonance as well as tuned condition (wd/ws=1) on the structural response has also been noticed. The effectiveness of the STLD and MTLDs is evaluated based on the response reduction of the structure.It has been found that the structural responses of displacement and acceleration are reduced significantly due to the installation of STLD and MTLD to the structure, respectively. Therefore, from this experimental study, it can be concluded that a TLD can successfully mitigate the response of the structure, but MTLD is not significantly more effective than an STLD when the liquid sloshing in the TLD is large.

A generic procedure is formulated for the determination of the moment capacity of composite beams having a complex cross-section. The key feature is the use of Fourier series to convert the piecewise functions of the cross-sectional stress distribution into a single-rule function.This eliminates the need for several capacity expressions to cover different stress stages, since the procedure permits the use of the general moment capacity expression.It also eliminates any iteration process when determining the location of the neutral axis since equilibrium of the cross-section can be satisfied explicitly. Numerical examples are given to demonstrate the validation and the applications of the formulation.

A 2D model of two adjacent buildings with different heights (6 and 12 floors) and foundation levels without separation distance under seismic load and considering SSI is investigated. A special arrangement of contact elements (gap elements) each 1 m of the low height building in the contact zone is taken into consideration to fulfill all possible deformation contact modes which take place under seismic load (earthquake). Soil is modeled by 2D shell elements in contact with foundations of the two adjacent buildings. This paper focuses on the study of double pounding that takes place between the two adjacent buildings in some upper points at superstructure in the contact zone and also at foundation level. The forces of double pounding between the two adjacent buildings, which increase by softening of the soil, give a valuable assessment of straining actions of the two adjacent buildings and change the behavior of soil under the foundations and around basement floor.

Performance-based seismic engineering is focused on the definition of limit states to represent different levels of damage, which can be described by material strains, drifts, displacements or even changes in dissipating properties and stiffness of the structure. This study presents a research plan to evaluate the behavior of reinforced concrete (RC) moment resistant frames at different performance levels established by the ASCE 41-06 seismic rehabilitation code. Sixteen RC plane moment frames with different span-to-depth ratios and three 3D RC frames were analyzed to evaluate their seismic behavior at different damage levels established by the ASCE 41-06.For each span-to-depth ratio, four different beam longitudinal reinforcement steel ratios were used that varied from 0.85 to 2.5% for the 2D frames. Nonlinear time history analyses of the frames were performed using scaled ground motions. The impact of different span-to-depth and reinforcement ratios on the damage levels was evaluated.Material strains, rotations and seismic hysteretic energy changes at different damage levels were studied.

Finite element (FE) analyses were performed to explore the prying influence on moment–rotation behaviour and to locate yielding zones of top- and seat-angle connections in author’s past research studies. The results of those FE analyses with experimental failure strategies of the connections were used to develop failure mechanisms of top- and seat-angle connections in the present study.Then a formulation was developed based on three simple failure mechanisms considering bending and shear deformations, effects of prying action on the top angle and stiffness of the tension bolts to estimate rationally the ultimate moment Mu of the connection, which is a vital parameter of the proposed four-parameter power model.Applicability of the proposed formulation is assessed by comparing moment-rotation (M- qr) curves and ultimate moment capacities with those measured by experiments and estimated by FE analyses and three-parameter power model. This study shows that proposed formulation and Kishi–Chen’s method both achieved close approximation driving M-qr curves of all given connections except a few cases of Kishi–Chen model, and Mu estimated by the proposed formulation is more rational than that predicted by Kishi–Chen’s method.