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CONTENTS
Volume 1, Number 1, March 2010
 

Abstract
It has been known that one-dimensional rod theory is very effective as a simplified analytical approach to large scale or complicated structures such as high-rise buildings, in preliminary design stages. It replaces an original structure by a one-dimensional rod which has an equivalent stiffness in terms of global properties. If the structure is composed of distinct constituents of different stiffness such as coupled walls with opening, structural behavior is significantly governed by the local variation of stiffness. This paper proposes an extended version of the rod theory which accounts for the two-dimensional local variation of structural stiffness; viz, variation in the transverse direction as well as longitudinal stiffness distribution. The governing equation for the two-dimensional rod theory is formulated from Hamilton

Key Words
simplified analytical method; extended rod theory; two-dimensional stiffness of structures; preliminary design for buildings; dynamic analysis; shear wall with opening.

Address
Hideo Takabatake: Department of Architecture, Kanazawa Institute of Technology, 7-1 Ohgigaoka Nonoichi Ishikawa 921-8501, Japan; Institute of Disaster and Environmental Science, 3-1 Yatsukaho, Hakusan, Ishikawa Prefecture, 924-0838, Japan

Abstract
Multi-span steel-concrete composite (SCC) bridges are very sensitive to earthquake loading. Extensive damage may occur not only in the substructures (piers), which are expected to yield, but also in the other components (e.g., deck, abutments) involved in carrying the seismic loads. Current seismic codes allow the design of regular bridges by means of linear elastic analysis based on inelastic design spectra. In bridges with superstructure transverse motion restrained at the abutments, a dual load path behavior is observed. The sequential yielding of the piers can lead to a substantial change in the stiffness distribution. Thus, force distributions and displacement demand can significantly differ from linear elastic analysis predictions. The objectives of this study are assessing the influence of piers-deck stiffness ratio and of soilstructure interaction effects on the seismic behavior of continuous SCC bridges with dual load path, and evaluating the suitability of linear elastic analysis in predicting the actual seismic behavior of these bridges. Parametric analysis results are presented and discussed for a common bridge typology. The response dependence on the parameters is studied by nonlinear multi-record incremental dynamic analysis (IDA). Comparisons are made with linear time history analysis results. The results presented suggest that simplified linear elastic analysis based on inelastic design spectra could produce very inaccurate estimates of the structural behavior of SCC bridges with dual load path.

Key Words
steel-concrete composite structures; bridges; nonlinear finite element method; soil-structure interaction; seismic behavior; incremental dynamic analysis.

Address
E. Tubaldi: 1DACS, Dipartimento di Architettura Costruzione e Strutture, Universita Politecnica delle Marche, Via Brecce Bianche, 60131, Ancona, Italy
M. Barbato: Department of Civil & Environmental Engineering, Louisiana State University and A&M College,
3531 Patrick F. Taylor Hall, Nicholson Extension, Baton Rouge, Louisiana 70803, USA
A. Dall

Abstract
A gradient-based evolutionary optimization methodology is presented for finding the optimal design of both the added dampers and their supporting members to minimize an objective function of a linear multi-storey structure subjected to the critical ground acceleration. The objective function is taken as the sum of the stochastic interstorey drifts. A frequency-dependent viscoelastic damper and the supporting member are treated as a vibration control device. Due to the added stiffness by the supplemental viscoelastic damper, the variable critical excitation needs to be updated simultaneously within the evolutionary phase of the optimal damper placement. Two different models of the entire damper unit are investigated. The first model is a detailed model referred to as

Key Words
optimal damper placement; evolutionary optimization; viscoelastic damper; critical excitation; stochastic process; supporting stiffness, multi-storey buildings

Address
Kohei Fujita: Department of Urban & Environmental Engineering, Graduate School of Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan
Abbas Moustafa: Department of Urban & Environmental Engineering, Graduate School of Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan
Izuru Takewaki: Department of Urban & Environmental Engineering, Graduate School of Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan

Abstract
Current seismic design codes do not contemplate explicitly some variables that are relevant for the design of structures subjected to ground motions exhibiting large energy content. Particularly, the lack of explicit consideration of the cumulative plastic demands and of the degradation of the hysteretic cycle may result in a significant underestimation of the lateral strength of reinforced concrete structures built on soft soils. This paper introduces and illustrates the use of a numerical performance-based methodology for the predesign of standard-occupation reinforced concrete ductile structures. The methodology takes into account two limit states, the performance of the non-structural system, and in the case of the life safety limit state, the effect of cumulative plastic demands and of the degradation of the hysteretic cycle on the assessment of structural performance.

Key Words
nonlinear analysis; narrow-banded motions; stiffness degradation; ductile reinforced concrete frames; cumulative plastic demands.

Address
Amador Teran-Gilmore: Departamento de Materiales, Universidad Autonoma Metropolitana, Av. San Pablo 180,
Col. Reynosa Tamaulipas, Mexico 02200, D.F.
Marco Espinosa-Johnson: Departamento de Materiales, Universidad Autonoma Metropolitana, Av. San Pablo 180,
Col. Reynosa Tamaulipas, Mexico 02200, D.F.
Alberto Sanchez-Badillo: Alonso y Asociados, Carretera Mexico-Toluca 1725, Despacho C-5, Col. Lomas de Palo Alto,
Mexico 05110, D.F.

Abstract
This paper investigates the seismic performance of existing reinforced concrete frames with wide beams mainly designed for gravity loads, as typically found in the seismic-prone Mediterranean area before the introduction of modern codes. The seismic capacity is evaluated in terms of the overall amount of input energy that the frame can dissipate/absorb up to collapse. This approach provides a quantitative evaluation that can be useful for selecting and designing an appropriate retrofit strategy. Six prototype frames representative of past construction practices in the southern part of Spain are designed, and the corresponding non-linear numerical models are developed and calibrated with purposely conducted tests on wide beamcolumn subassemblages. The models are subjected to sixteen earthquake records until collapse by applying the incremental dynamic analysis method. It is found that the ultimate energy dissipation capacity at the story level is markedly low (about 1.36 times the product of the lateral yield strength and yield displacement of the story), giving values for the maximum amount of energy that the frame can dissipate which are from one fourth to half of that required in moderate-seismicity regions.

Key Words
seismic performance; existing frames; energy dissipation capacity; wide beams.

Address
A. Benavent-Climent: Department of Structural Mechanics, University of Granada, Edificio Politecnico, 18071 Granada, Spain
R. Zahran: Department of Structural Mechanics, University of Granada, Edificio Politecnico, 18071 Granada, Spain

Abstract
This work aims at introducing structural sensitivity analysis capabilities into existing commercial finite element software codes for the purpose of mapping retrofit strategies for a broad group of structures including heritage-type buildings. More specifically, the first stage sensitivity analysis is implemented for the standard deterministic environment, followed by stochastic structural sensitivity analysis defined for the probabilistic environment in a subsequent, second phase. It is believed that this new generation of software that will be released by the industrial partner will address the needs of a rapidly developing specialty within the engineering design profession, namely commercial retrofit and rehabilitation activities. In congested urban areas, these activities are carried out in reference to a certain percentage of the contemporary building stock that can no longer be demolished to give room for new construction because of economical, historical or cultural reasons. Furthermore, such analysis tools are becoming essential in reference to a new generation of national codes that spell out in detail how retrofit strategies ought to be implemented. More specifically, our work focuses on identifying the minimum-cost intervention on a given structure undergoing retrofit. Finally, an additional factor that arises in earthquake-prone regions across the world is the random nature of seismic activity that further complicates the task of determining the dynamic overstress that is being induced in the building stock and the additional demands placed on the supporting structural system.

Key Words
structural sensitivity; structural uncertainty; finite element method; structural dynamics; earthquake engineering; random vibrations; deficiency indices; minimum-cost optimization.

Address
G.D. Manolis: Department of Civil Engineering, Aristotle University, Thessaloniki, GR-54124, Greece
C.G. Panagiotopoulos: Department of Civil Engineering, Aristotle University, Thessaloniki, GR-54124, Greece
E.A. Paraskevopoulos: Department of Mechanical Engineering, Aristotle University, Thessaloniki, GR-54124, Greece
F.E. Karaoulanis: Department of Civil Engineering, Aristotle University, Thessaloniki, GR-54124, Greece
G.N. Vadaloukas: VK-4M Software Company, 9 Mykinon Str., Athens, GR-15223, Greece
A.G. Papachristidis: VK-4M Software Company, 9 Mykinon Str., Athens, GR-15223, Greece

Abstract
This paper proposes an approximate procedure to estimate seismic displacement capacity - defined as yield displacement times the displacement ductility − of piles in marine oil terminals. It is shown that the displacement ductility of piles is relatively insensitive to most of the pile parameters within ranges typically applicable to most piles in marine oil terminals. Based on parametric studies, lower bound values of the displacement ductility of two types of piles commonly used in marine oil terminals − reinforced-concrete and hollow-steel − with either pin connection or full-moment-connection to the deck for two seismic design levels – Level 1 or Level 2 − and for two locations of the hinging in the pile − near the deck or below the ground − are proposed. The lower bound values of the displacement ductility are determined such that the material strain limits specified in the Marine Oil Terminal Engineering and Maintenance Standard (MOTEMS) are satisfied at each design level. The simplified procedure presented in this paper is intended to be used for preliminary design of piles or as a check on the results from the detailed nonlinear static pushover analysis procedure, with material strain control, specified in the MOTEMS.

Key Words
marine structures; seismic displacement capacity; seismic ductility; seismic analysis; seismic design, piles.

Address
Rakesh K. Goel: Department of Civil and Environmental Engineering, California Polytechnic State University,
San Luis Obispo, CA 93407, USA


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