Effect of vehicle flexibility on the vibratory response of bridge R. Lalthlamuana and Sudip Talukdar
Abstract; Full Text (1986K) .	pages 147-170.	DOI: 10.12989/csm.2014.3.2.147

Abstract
In the recent times, dimensions of heavy load carrying vehicle have changed significantly incorporating structural flexibility in vehicle body. The present paper outlines a procedure for the estimation of bridge response statistics considering structural bending modes of the vehicle. Bridge deck roughness has been considered to be non homogeneous random process in space. Influence of pre cambering of bridge surface and settlement of approach slab on the dynamic behavior of the bridge has been studied. A parametric study considering vehicle axle spacing, mass, speed, vehicle flexibility, deck unevenness and eccentricity of vehicle path have been conducted. Dynamic amplification factor (DAF) of the bridge response has been obtained for several of combination of bridge-vehicle parameters. The present study reveals that flexible modes of vehicle can reduce dynamic response of the bridge to the extent of 30-37% of that caused by rigid vehicle model. However, sudden change in the bridge surface profile leads to significant amount of increment in the bridge dynamic response even if flexible bending modes remain active. The eccentricity of vehicle path and flexural/torsional rigidity ratios plays a significant role in dynamic amplification of bridge response.

Key Words
flexibility; deck roughness; non homogeneous; dynamic amplification factor; flexural/torsional rigidity

Address
R. Lalthlamuana and Sudip Talukdar: Department of Civil Engineering, Indian Institute of Technology Guwahati, Guwahati-781039, India

Analytical and numerical algorithm for exploring dynamic response of non-classically damped hybrid structures Shehata E. Abdel Raheem
Abstract; Full Text (2326K) .	pages 171-193.	DOI: 10.12989/csm.2014.3.2.171

Abstract
The dynamic characterization is important in making accurate predictions of the seismic response of the hybrid structures dominated by different damping mechanisms. Different damping characteristics arise from the construction of hybrid structure with different materials: steel for the upper part; reinforced concrete for the lower main part and interaction with supporting soil. The process of modeling damping matrices and experimental verification is challenging because damping cannot be determined via static tests as can mass and stiffness. The assumption of classical damping is not appropriate if the system to be analyzed consists of two or more parts with significantly different levels of damping. The dynamic response of structures is critically determined by the damping mechanisms, and its value is very important for the design and analysis of vibrating structures. A numerical algorithm capable of evaluating the equivalent modal damping ratio from structural components is desirable for improving seismic design. Two approaches are considered to explore the dynamic response of hybrid tower of cable-stayed bridges: The first approach makes use of a simplified model of 2 coupled lumped masses to investigate the effects of subsystems different damping, mass ratio, frequency ratio on dynamic characteristics and equivalent modal damping; the second approach employs a detailed numerical step-by step integration procedure.

Key Words
numerical algorithm; non-classical damping; hybrid structure; modal damping; coupling index

Address
Shehata E. Abdel Raheem:Faculty of Engineering, Taibah University, Madinah 41411, P.O. 344, Saudia Arabia;
Civil Engineering Department, Faculty of Engineering, Assiut University, Assiut 71516, Egypt

Coupling of nonlinear models for steel-concrete interaction in structural RC joints Norberto Domínguez and Jesús Pérez-Mota
Abstract; Full Text (2041K) .	pages 195-211.	DOI: 10.12989/csm.2014.3.2.195

Abstract
When strong seismic forces act on reinforced concrete structures, their beam-column connections are very susceptible to damage during the earthquake event. The aim of this numerical work is to evaluate the influence of the internal steel reinforcement array on the nonlinear response of a RC beam-column connection when it is subjected to strong cyclic loading –as a seismic load. For this, two specimens (extracted from an experimental test of 12 RC beam-column connections reported in literature) were modeled in the Finite Element code FEAP considering different stirrup\' s arrays. In order to evaluate the nonlinear response of the RC beam-column connection, the 2D model takes into account the nonlinear thermodynamic behavior of each component: for concrete, a damage model is used; for steel reinforcement, it is adopted a classical plasticity model; in the case of the steel-concrete bonding, this one is considered perfect without degradation. At the end, we show a comparison between the experimental test

Key Words
beam-column connection; reinforced concrete; non-linear material behavior; finite element

Address
Norberto Domínguez and Jesús Pérez-Mota:Department of Postgraduate and Research Studies (SEPI) ESIA UZ National Polytechnic Institute of Mexico, Edificio de Posgrado e Investigación, Av. Miguel Bernard s/n 07300 Mexico D.F., Mexico

Effect of soil flexibility on bridges subjected to spatially varying excitations Bo Li and Nawawi Chouw
Abstract; Full Text (1689K) .	pages 213-232.	DOI: 10.12989/csm.2014.3.2.213

Abstract
Pounding is a major cause of bridge damage during earthquakes. In an extreme situation, it can even contribute to the unseating of bridge girders. Long-span bridges will inevitably experience spatially varying ground motions. Soil-structure interaction (SSI) may play a significant role in the structural response of these structures. The objective of this research is to experimentally investigate the effect of spatially varying ground motions on the response of a three-segment bridge considering SSI and pounding. To incorporate SSI, the model was placed on sand contained in sandboxes. The sandboxes were fabricated using soft rubber in order to minimise the rigid wall effect. The spatially varying ground motion inputs were simulated based on the New Zealand design spectra for soft soil, shallow soil and strong rock conditions, using an empirical coherency loss function. The results show that with pounding, SSI can amplify the pier bending moments and the relative opening displacements.

Key Words
ground motion spatial variation; plastic hinge development; pounding; relative displacement; shake table experiment

Address
Bo Li:GHD Pty Ltd, New Zealand
Nawawi Chouw: Department of Civil and Environmental Engineering, Faculty of Engineering, the University of Auckland, New Zealand

Parametric study on flexible footing resting on partially saturated soil Mandeep Singh and V.A. Sawant
Abstract; Full Text (1454K) .	pages 233-245.	DOI: 10.12989/csm.2014.3.2.233

Abstract
Coupled finite element analysis is carried out to study the effect of degree of saturation on the vertical displacements and pore water pressures simultaneously by developing a FORTRAN90 code. The finite element formulation adopted in the present study is based upon Biot\'s consolidation theory to include partially saturated soils. Numerical methods are applied to a two-dimensional plane strain strip footing (flexible) problem and the effect of variable degree of saturation on the response of excess pore water pressure dissipation and settlement of the footing is studied. The immediate settlement in the case of partly saturated soils is larger than that of a fully saturated soil, the reason being the presence of pore air in partially saturated soils. On the other hand, the excess pore water pressure for partially saturated soil are smaller than those for fully saturated soil.

Key Words
partially saturated soils; suction; coupled analysis; degree of saturation

Address
Mandeep Singh and V.A. Sawant:Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India