Published online on September 2018
S.S. Roy, S.R. Dash
Abstract:Bridges are one of the most important lifeline facilities, which are expected to be functional even after a catastrophic event like an earthquake. Prominent failure of bridges due to the complete collapse of piers has been observed in every major seismic event. In this paper, the dynamic behavior of a pre-stressed, continuous girder bridge is studied. Modal and nonlinear modal time history analysis is carried out for both non-isolated and seismically isolated bridge with lead rubber bearing (LRB). Simple elastic model is applied to model the various components of the bridge. Both abutments and pile caps are modeled as rigid members. First five mode shapes, modal characteristics, shifting of time periods, base shear, super structure and pier head displacement and deck acceleration are observed in this study. Changes in base shear are also investigated due to shifting of time period as per available codes of practice. The benefit that can be derived by the use of isolation bearing in the dynamic response of the bridge has been quantified in this paper with the incorporation of soil softening effect that may happen during earthquakes.
International Journal of Bridge Engineering, Vol. 6, No. 2, 2018: pp. 1-23
Osama Mohammed Elmardi Suleiman Khayal, Tagelsir Hassan
Abstract:The following assumptions were made in developing the mathematical formulations of laminated deck plates: 1. All layers behave elastically; 2. Displacements are small compared with the plate thickness; 3. Perfect bonding exists between layers; 4. The laminate is equivalent to a single anisotropic layer; 5. The plate is flat and has a constant thickness; 6. The plate buckles in a vacuum and all kinds of damping are neglected. Unlike homogeneous plates, where the coordinates are chosen solely based on the plate shape, coordinates for laminated plates should be chosen carefully. There are two main factors for the choice of the coordinate system. The first factor is the shape of the plate. Where rectangular plates will be best represented by the choice of rectangular (i.e. Cartesian) coordinates. It will be relatively easy to represent the boundaries of such plates with coordinates. The second factor is the fiber orientation or orthotropy. If the fibers are set straight within each lamina, then rectangular orthotropy would result. It is possible to set the fibers in a radial and circular fashion, which would result in circular orthotropy. Indeed, the fibers can also be set in elliptical directions, which would result in elliptical orthotropy.
International Journal of Bridge Engineering, Vol. 6, No. 2, 2018: pp. 25-39
Domenico Bruno, Paolo Lonetti, Arturo Pascuzzo
Abstract:A numerical study is proposed to investigate the structural behavior of network arch bridges subjected to the cable loss accidental event. The main aim of the paper is to analyze the effects produced by potential cable loss scenarios on the main stress and kinematic design variables of the structure. To this end, a parametric study in terms of the main structural and geometric parameters is developed with the purpose to identify the key factors that contribute to reduce hazards produced by the cable loss event. The structural analyses are performed by using a refined FE nonlinear geometric formulation, in which the influence of large displacements and local vibrations of cable elements are taken into account. The loss of the cable is reproduced by means of a proper damage law, developed in the framework of Continuum Damage Mechanics theory. Cable loss analyses are performed by means of both nonlinear dynamic analyses and simplified methodologies proposed by existing codes on cable supported bridges. In this framework, the applicability of such simplified methodologies in the case of the network arch bridges are discussed.
International Journal of Bridge Engineering, Vol. 6, No. 2, 2018: pp. 41-59
J. Kent Hsiao, Alexander Y. Jiang
Abstract:Deflection control is an important design criterion for the serviceability of pretensioned concrete bridges. Upward cambers due to prestressing forces can be utilized to offset downward deflections due to gravity loads in order to control cracks and/or to produce desired cambers. The traditional hand-calculated approach simplifies the computation of pretensioned concrete girders by: (1) assuming that the prestressing force acting at the midspan of a girder remains constant along the entire span of the girder, (2) neglecting the p-δ effect on the girder due to the axial compression force in the girder, and (3) using the gross concrete section of the girder to compute the moment of inertia of the girder. The purpose of this work is to investigate the accuracy of the hand-calculated approach for the computation of cambers due to prestressing forces. The type of prestressed concrete girder investigated in this work is a pretensioned I-girder with a combination of straight strands and harped strands. The major findings derived from this work are: (1) the variation (non-uniformity) among prestressing forces acting along the tendons has no significant effect on the deflection of the girder, (2) the traditional hand-calculated approach neglecting the P-δ effect may result in considerably smaller girder deflections, and (3) the traditional hand-calculated approach using the moment of inertia of the gross concrete section (neglecting the additional stiffness contributed by tendons) may result in considerably larger girder deflections.
International Journal of Bridge Engineering, Vol. 6, No. 2, 2018: pp. 61-84
Atef Gendy, Magdy Rashed
Abstract:Step-by-step solution strategy for segmental prestressed concrete bridge calls for: (i) time dependent effects of creep and shrinkage of concrete, and relaxation of prestressed steel; (ii) losses due to friction and anchor setting of prestressing tendons; (iii) sequence of construction, and change of geometry and support conditions; (iv) tension stiffening effect of concrete after cracking; (v) effects of nonprestressed steel on the redistribution of stresses. These significant parameters have been accounted for to obtain the time dependent serviceability analysis of several segmental prestressed concrete bridges over the Nile River utilizing Eurocode specifications. Redistribution of stresses in concrete, prestressed as well as nonprestressed steels due to time-dependent effects during construction and after a long time of operation is one of our objectives. Such redistribution of stresses/moments produced by time dependent analysis is to be place in an intermediate state between the analyses obtained from two different cases: (a) adding all partial stresses for each construction step using corresponding statical system; (b) assuming all loads and prestress forces to be applied on the final statical system. This paper is to report on estimated contributions of each of the two time-independent cases in order to minimize the difference with results obtained from the time-dependent analysis. To this end, a number of robust, and computationally efficient, algorithms are presented and integrated through software ESTMATOR, which casts the optimum parameters as a minimum-error nonlinear optimization problem with constraints and solves it with the sequential quadratic nonlinear programming technique.
International Journal of Bridge Engineering, Vol. 6, No. 2, 2018: pp. 85-107